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  • General Chemistry  (9,374)
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  • 1
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-03-03
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 2
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-04-14
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
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  • 3
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-04-14
    Description: The allotropes formed by carbon reflect differences in its bonding: single bonds in diamond, double bonds in graphite and graphene, and triple bonds in polyynes. Fashioning graphene sheets into bowls, monkey saddles, balls, and tubes has led to a number of molecular allotropes of carbon or carbon-rich quasi-allotropes with novel topologies and shapes. A simple ring of carbon can be reduced to practice in various forms (1): a cyclic array of carbon atoms, a “pearl necklace” of benzene rings, or a cylindrical hoop of flank-fused benzenes, just to name a few. On page 172 of this issue, Povie et al. (2) report on the synthesis of an angular-fused hoop structure, which has been a long-standing target. Author: Jay S. Siegel
    Keywords: Organic Chemistry
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  • 4
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-04-14
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 5
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-03-03
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 6
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-04-01
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
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  • 7
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2017-01-13
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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  • 8
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-07-08
    Description: Author: Phil Szuromi
    Keywords: Organic Chemistry
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    Electronic ISSN: 1095-9203
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  • 9
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-07-08
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 10
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-05-27
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 11
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-07-15
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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    Electronic ISSN: 1095-9203
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  • 12
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-07-22
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
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  • 13
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-06-24
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 14
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-07-01
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 15
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-06-10
    Description: Transition metal–catalyzed arylation of C–H bonds has been intensively studied for forming C–C bonds in complex-molecule synthesis (1). An acidic C–H bond (for example, one near a double bond or an O atom) is cleaved to form a carbon–metal bond, which then couples to arene. Many of these organometallic species can be generated catalytically. Much less research has dealt with unreactive nonacidic sp3 C–H bond functionalization (3). On page 1304 of this issue, Shaw et al. (3) report an efficient and general method that focuses on arylation of sp3 C–H bonds at carbon atoms adjacent to amines and to cyclic ethers by combining nickel, visible-light photoredox, and hydrogen-atom transfer (HAT) catalysis. Author: Corinne Fruit
    Keywords: Organic Chemistry
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  • 16
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-06-10
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 17
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-09-09
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 18
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-09-07
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 19
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-05-20
    Description: Antibiotics have been taking it on the chin lately. Not only has resistance to the anti-infective medications been growing, but drug companies have been dropping antibiotic research programs, because the drugs are difficult and expensive to make. Now, new help is on the way. Researchers report this week that they've found a way to churn out new members of one of the most widely used classes of antibiotics. These drugs, called macrolides, were first developed in the 1950s and now represent a major bulwark against infections. A bevy of possible new drugs in this class could lead to new weapons against antibiotic-resistant infections, and possibly save millions of lives. Author: Robert F. Service
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
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    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 20
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-04-22
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 21
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-04-29
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 22
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-05-13
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 23
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-04-01
    Description: The SN2 nucleophilic substitution reaction, X− + RY → XR + Y−, is a paradigm reaction in organic chemistry (1). The modern understanding of the SN2 reaction mechanism is based on work of Hughes and Ingold (2), who proposed that the nucleophile (X−) approaches the carbon atom that bears the leaving group (Y−). As a result, the bond between the carbon atom and the leaving group becomes weakened. As this bond breaks and a new bond forms between the nucleophile and the carbon atom, the configuration of the carbon atom is inverted. Analyses of gas-phase reaction rates led to the suggestion of a potential energy surface (PES) with two wells connected by a central barrier transition state (3). Electronic structure calculations have confirmed this picture for some SN2 reactions (4), but recent studies have shown that the actual reaction dynamics may be considerably more complex (see the figure) (5–8). Authors: Jing Xie, William L. Hase
    Keywords: Organic Chemistry
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  • 24
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-04-01
    Description: Author: Julia Fahrenkamp-Uppenbrink
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
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  • 25
    Publication Date: 2016-03-19
    Description: Exploiting binding affinities between molecules is an established practice in many fields, including biochemical separations, diagnostics, and drug development; however, using these affinities to control biomolecule release is a more recent strategy. Affinity-controlled release takes advantage of the reversible nature of noncovalent interactions between a therapeutic protein and a binding partner to slow the diffusive release of the protein from a vehicle. This process, in contrast to degradation-controlled sustained-release formulations such as poly(lactic-co-glycolic acid) microspheres, is controlled through the strength of the binding interaction, the binding kinetics, and the concentration of binding partners. In the context of affinity-controlled release--and specifically the discovery or design of binding partners--we review advances in in vitro selection and directed evolution of proteins, peptides, and oligonucleotides (aptamers), aided by computational design.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pakulska, Malgosia M -- Miersch, Shane -- Shoichet, Molly S -- Canadian Institutes of Health Research/Canada -- New York, N.Y. -- Science. 2016 Mar 18;351(6279):aac4750. doi: 10.1126/science.aac4750.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Department of Chemical Engineering and Applied Chemistry, Institute of Biomaterials and Biomedical Engineering, and Donnelly Centre, University of Toronto, Toronto, Ontario, Canada. ; Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada. ; Department of Chemical Engineering and Applied Chemistry, Institute of Biomaterials and Biomedical Engineering, and Donnelly Centre, University of Toronto, Toronto, Ontario, Canada. Department of Chemistry, University of Toronto, Toronto, Ontario, Canada.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/26989257" target="_blank"〉PubMed〈/a〉
    Keywords: Chemical Engineering ; Combinatorial Chemistry Techniques ; Delayed-Action Preparations/*chemistry ; Directed Molecular Evolution ; *Drug Design ; Humans ; Lactic Acid/*chemistry ; Microspheres ; Polyglycolic Acid/*chemistry ; Proteins/*administration & dosage
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    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 26
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-11-18
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 27
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-11-18
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 28
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-12-09
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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    Electronic ISSN: 1095-9203
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  • 29
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    American Association for the Advancement of Science (AAAS)
    In: Science
    Publication Date: 2016-10-21
    Description: Author: Jake Yeston
    Keywords: Organic Chemistry
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    Electronic ISSN: 1095-9203
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  • 30
    Publication Date: 2007-11-17
    Description: Artificial biochemical circuits are likely to play as large a role in biological engineering as electrical circuits have played in the engineering of electromechanical devices. Toward that end, nucleic acids provide a designable substrate for the regulation of biochemical reactions. However, it has been difficult to incorporate signal amplification components. We introduce a design strategy that allows a specified input oligonucleotide to catalyze the release of a specified output oligonucleotide, which in turn can serve as a catalyst for other reactions. This reaction, which is driven forward by the configurational entropy of the released molecule, provides an amplifying circuit element that is simple, fast, modular, composable, and robust. We have constructed and characterized several circuits that amplify nucleic acid signals, including a feedforward cascade with quadratic kinetics and a positive feedback circuit with exponential growth kinetics.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Zhang, David Yu -- Turberfield, Andrew J -- Yurke, Bernard -- Winfree, Erik -- New York, N.Y. -- Science. 2007 Nov 16;318(5853):1121-5.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Computation and Neural Systems, California Institute of Technology, MC 136-93, 1200 East California Boulevard, Pasadena, CA91125, USA. dzhang@dna.caltech.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18006742" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Catalysis ; Chemical Engineering ; *Computers, Molecular ; DNA/*chemistry ; Entropy ; Equipment Design ; Feedback, Physiological ; Mice ; Nanotechnology ; Nucleic Acid Hybridization ; Rabbits
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    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
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  • 31
    Keywords: Biomass conversion ; Biotechnology ; Chemical Engineering ; Chemistry industry ; Industrial Chemistry ; Kent ; Riegel ; biochemical engineering
    Description / Table of Contents: Substantially revising and updating the classic reference in the field, this handbook offers a valuable overview and myriad details on current chemical processes, products, and practices. No other source offers as much data on the chemistry, engineering, economics, and infrastructure of the industry. The Handbook serves a spectrum of individuals, from those who are directly involved in the chemical industry to others in related industries and activities. It provides not only the underlying science and technology for important industry sectors, but also broad coverage of critical supporting topics. Industrial processes and products can be much enhanced through observing the tenets and applying the methodologies found in chapters on Green Engineering and Chemistry (specifically, biomass conversion), Practical Catalysis, and Environmental Measurements; as well as expanded treatment of Safety, chemistry plant security, and Emergency Preparedness. Understanding these factors allows them to be part of the total process and helps achieve optimum results in, for example, process development, review, and modification. Important topics in the energy field, namely nuclear, coal, natural gas, and petroleum, are covered in individual chapters. Other new chapters include energy conversion, energy storage, emerging nanoscience and technology. Updated sections include more material on biomass conversion, as well as three chapters covering biotechnology topics, namely, Industrial Biotechnology, Industrial Enzymes, and Industrial Production of Therapeutic Proteins.
    Pages: Online-Ressource (XIV, 1562 pages)
    ISBN: 9780387278438
    Language: English
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  • 32
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 169-174 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Water-ground Phlogopite micas were classified into narrow particle-size distributions containing flakes with well-defined diameters and thicknesses in order to evaluate the influence of particle size and flake aspect ratio on the mechanical properties of mica-filled polypropylenes, For the purposes of comparison, most of the injection-molded specimens contained 40 percent (by weight) mica. As expected, the flexural and tensile modulus values increased in proportion to the aspect ratio over the range from 30 to 60 to a maximum of 8 GPa. The measured tensile strengths of the mica-filled polypropylenes increased substantially as the flake diameter became smaller, but did not correlate with the flake aspect ratio. The attainable properties were frequently dependent upon the method of mixing, and considerable care was necessary to ensure proper dispersion and adequate coupling. Intensive mixing, as in a Gelimat Mixer, may cause in situ delamination and particle-size reduction of the mica filler particles, leading to a marked increase in tensile strength of the resulting composite. The mica-filled compounds could be reprocessed many times without significant loss of properties, particularly compounds having mica particles less than 40 μm in diameter. The fracture energies (notched Izod) and the heat-distortion temperatures were not appreciably influenced by the size or aspect ratios of the mica within this range. Increased fracture toughness could be achieved by reducing the mica concentration or employing a polypropylene copolymer. Guidelines are presented to indicate the preferred characteristics of mica fillers and the influence of mixing conditions on performance.
    Additional Material: 7 Ill.
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  • 33
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 30-41 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A mathematical model has been developed to compute the molecular weight distribution (MWD) in the polyethylene terephthalate (PET) manufacturing process. Unlike the previous efforts, this model takes into account the influence of side reactions and various interchange reactions on MWD. The process of blending of molten polyester chips has also been simulated with a view to calculate the equilibrium MWD as well as the time required to reach the equilibrium MWD. The1 significance of the results has been discussed in terms of industrial operations involving PET polymerization and PET blending.
    Additional Material: 10 Ill.
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  • 34
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 541-543 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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  • 35
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 555-562 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Methods of preparation and of determining miscibility limits for partially miscible binary polymer blends are described. An equation-of-state, theoretical description of this behavior is introduced and the terms describing interactions within the system discussed, Values of these interaction terms are obtained by fitting the models to measured cloud point curves, heats of mixing data, etc. The use of neutron scattering experiments to obtain molecular conformation and interaction parameters is described and a comparison made with values extracted from the thermodynamic measurements.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 36
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 163-168 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Dextran-g-poly(acrylamide-co-sodium acrylates) were prepared by partial hydrolysis of dextran-g-poly(acrylamides) with controlled numbers and lengths of grafted chains. This hydrolysis route proved to be more effective than Ce(IV)-induced cografting of acrylamide and sodium acrylate comonomers onto dextran in producing the desired graft-copolymer structures. The resulting copolymers were characterized and the effects of composition, temperature, ionic strength, and shear rate on dilute solution rheological properties were studied.
    Additional Material: 6 Ill.
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  • 37
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 194-204 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The formation of polyethylene terephthalate (PET) has been modeled to have reactions with monofunctional compounds, redistribution, and cyclization reactions in addition to the usual polycondensation step. In the final stages, the overall polymerization is mass-transfer controlled and solution of the reactor performance equations have been determined through the orthogonal collocation technique. This technique is found to be considerably more efficient for PET reactors compared to the finite difference method; the use of ten collocation points gives results which are close to the exact solution.
    Additional Material: 11 Ill.
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  • 38
    Electronic Resource
    Electronic Resource
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 218-225 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This review focuses on a new type of para-catenated aromatic polymer being used in the preparation of high-performance films and fibers of exceptional strength, thermal stability, and environmental resistance, including inertness to essentially all common solvents. Polymers of this type include cis and transpoly(p-phenylene benzobisoxazole) (PBO), and the cis and trans forms of the corresponding poly(p-phenylene benzobis-thiazole)(PBT). The purpose of this paper is to summarize the authors' theoretical work on the structures, conformational energies, intermolecular interactions, and electronic properties of PBO and PBT chains, including the protonated forms known to exist in strong acids. The emphasis is on how such studies provide a molecular understanding of the unusual properties and processing characteristics of this new class of materials.
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  • 39
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Poly(p-phenylene terephthalamide) (PPD-T) films have been prepared by continuous extrusion of liquid crystalline 17 percent PPD-T/sulphuric acid solutions through an annular die followed by coagulation, Films extruded without drawdown exhibit some polymer chain orientation in the machine direction. This is increased by uniaxially drawing down films. Films produced with a lubricated conical mandrel sitting between the die and the coagulation bath exhibit an equal biaxial orientation. The uniaxially oriented films exhibit highly anisotropic mechanical properties, while the mandrel-produced film exhibits balanced properties. Heat treatment at 350°C results in significant enhancement of the tensile strength of the mandrel film. Void structures in the films have been investigated by mass density, scanning electron microscopy (SEM), and small-angle X-ray scattering (SAXS). Density measurement indicate a void content decreasing with decreasing film thickness and heat treatment. SEM locates micron-size voids in the thickest films, apparently caused by rapid coagulation. SAXS indicates much smaller void sixes which are roughly prolate ellipsoids (long axis in machine direction) for uniaxial films and oblate ellipsoids (short axis in thickness direction) for the mandrel produced films. Various techniques are used to estimate mean void size.
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  • 40
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    Polymer Engineering and Science 24 (1984), S. 278-286 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Poly(vinyl chloride) (PVC) and its blends with polybutadiene-acrylonitrile (NBR) (containing 21.7 weight-percent acrylonitrile (AN), a heterogeneous two-phase system; and containing 41.6 weight-percent of AN, a homogeneous one-phase system) and with polyethylene-vinyl acetate (EVA) (containing 45 weight-percent of vinyl acetate (VA), a heterogenous two-phase system; and containing 65 weight-percent VA, a homogeneous one-phase system) were UV-irradiated (at 3500 Å UV-light (solar spectrum)). After UV irradiation the kinetics measurements were made of the formation of hydroperoxy (OOH) and carbonyl (CO) groups and the changes of mechanical properties: tensile strength, elongation to break, and impact energy. As a result of the photooxidative degradation of PVC blends, decreases of mechanical properties were observed. The effects are more severe in PVC/NBR blends, which contain unsaturated bonds (polybutadiene segments) than in the case of PVC/EVA. The phase structure plays an evident role on the UV degradation only of PVC/NBR blends. The photostability of PVC blends can be slightly improved by introducing Tinuvin P or Ni-chelates photostabilizers.
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  • 41
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    Polymer Engineering and Science 24 (1984), S. 292-292 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 42
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    Polymer Engineering and Science 24 (1984), S. 319-327 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An investigation was carried out in order to study the effect of prestrain on the subsequent crystallization of a specific copolyester based on lactic and glycolic acid. This polymer, which can be easily quenched into an amorphous glass, has a Tg of 43°C and when in crystalline form has a melting point of 210°C. Using amorphous films, samples were prestrained to various levels at temperatures not far above Tg. In some cases films were immediately quenched at the prestrain level so as to retain the elongation while others were allowed to immediately retract whereby they showed a relatively small degree of permanent Set. Utilizing birefringence, quenched samples whose initial elongation was maintained showed linear behavior with prestrain while those that retracted showed essentially zero birefringence until a prestrain of about 150 percent after which a small degree of positive birefringence resulted. Wide angle x-ray diffraction (WAXS) showed no signs of crystallinity in all cases. These same films were then quickly taken to 150°C and rapidly crystallized. Again, one series of the prestrained samples were in the elongated state during crystallization whereas the second series was unrestrained during crystallization. Using microscopy and small angle light scattering (SALS), the morphological textures of these crystallized films were investigated. In all cases, spherulitic textures were observed of equivalent size up to a value of about 200 percent elongation the spherulite size systematically decreased with the prestrain an increase in clearly showing that prestrain had a pronounced effect upon the nucleation density. Increasing draw rate displayed a similar effect on nucleation density. Since spherulite size was noted to be the same in either series, it indicated that nucleation was induced as a result of the prestrain and remained irrelevant of whether the sample was allowed to relax or not. The morphology above the transitional state was similar to row structure common to polymers crystallized in the oriented state. WAXS and birefringence was applied to the crystallized materials and it was found that up until the transitional zone, no crystal orientation was observed in either series indicating that although nucleation density was strongly affected up until that point, no orientation was retained within the sample upon crystallization. A simplified model is used to explain the observed results.
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  • 43
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    Polymer Engineering and Science 24 (1984), S. 965-973 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A method based on network theory is developed for characterizing molecular orientation in amorphous polymers. The proposed procedure gives not only the orientation distribution function for the chain segments in the polymer network (and hence the average orientation) but also a quantitative measure of how this orientation is distributed among the various types of entanglement junctions. The orientation of chain segments can be characterized by two parameters, one which gives the average orientation and another which reflects how much orientation is concentrated in long time entanglement junctions. The new method of characterizing orientation is used to interpret tensile strength data for both brittle and ductile failures.
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    Polymer Engineering and Science 24 (1984) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 45
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    Polymer Engineering and Science 24 (1984), S. 1025-1025 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 46
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    Polymer Engineering and Science 24 (1984), S. 1035-1042 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A study of the crystalline orientation, light transmission, and surface roughness of polyethylene tubular film prepared in our laboratories is presented. The present studies were primarily carried out on low-density (LDPE) and linear-low-density (LLDPE) polyethylene films. The optical properties of a few films of high-density polyethylene (HDPE) prepared for a previous study of morphology were characterized for comparison to the LDPE and LLDPE films. Wide angle X-ray diffraction and birefringence were used to characterize orientation. Both the LDPE and LLDPE films exhibited crystalline texture in which the b-axes tended to be perpendicular to the film surface and the a-axes had some tendency to align with the machine direction. The c-axes tended to be concentrated in the plane of the film with nearly equal biaxial orientation with respect to the machine and transverse directions. Little variation in the crystalline orientation was found with changes of process conditions in the range studied. Birefringence results indicate that the amorphous regions developed an orientation in which the chains tend to be normal to the film surface. The majority of light scattering from these films and a series of HDPE films was from the surface and not from the film interior. The transmission coefficient for the surface contribution was found to be a monotonic decreasing function of the standard deviation of the surface height obtained from surface profiles measured by profilometer. The surface asperites were largest for the HDPE and smallest for the LDPE samples. The intensity of both the surface and interior contributions to the scattering increased with increasing frostline height, i.e., a slower cooling rate. As draw-down ratio and blow-up ratio increase the scattering contribution from the film interior decreases but the contribution from the surface increases somewhat. These effects are discussed in terms of the changes in crystalline morphology and surface roughness produced by flow defects generated during extrusion.
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  • 47
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    Polymer Engineering and Science 24 (1984), S. 1064-1070 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Stress-corrosion data for poly(ethylene terephthalate) reinforced with short glass fibers are provided under various environments and the microscopic observations are compared with the lifetime data. It is concluded that the lifetime behavior coincides with the microstructural features; this aspect is quantified by the statistical analysis.
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  • 48
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    Polymer Engineering and Science 24 (1984), S. 442-454 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The two major problems encountered in industrial liquid-phase addition polymerization are: the heat released by highly exothermic reactions and the great increase in viscosity with conversion. The high rate or heat generation, coupled with the low thermal diffusivity of the reacting system, often lead to thermal runaway. Even with the process kept under marginal control, large temperature variations broaden the product molecular-weight distribution. Temperature control is particularly difficult in the Trommsdorff region, where reaction rate rapidly increases as temperature rises and viscosity builds up. A two-stage process is developed in this work to attack these problems and to achieve continuous operation of poly(methyl methacrylate) bulk polymerization. This process utilizes a continuous stirred-tank reactor (CSTR) as a first-stage prepolymerizer and a spray tower as the second-stage finishing reactor. Use of a CSTR offers good temperature control and product uniformity during the early stages of reaction and eases delivery of the reacting system to the second stage at the desired conversion and molecular-weight level. Spraying the partially polymerized mixture into the tower as fine droplets prior to the onset of gel effect eliminates the problems of transporting, agitating, and mixing a reacting system with a rapidly increasing viscosity. Heat of reaction is efficiently removed by a countercurrent stream of nitrogen in the tower, in direct contact with the falling droplets. The high surface-to-volume ratio of these small droplets facilitates heat transfer, and the problem of heat buildup can be efficiently controlled. Products from the bottom of the tower can then be melt-processed by conventional methods, such as extrusion. Experiments performed in the laboratory have demonstrated the feasibility of this proposed concept. Process optimization was in no way achieved due to serious space and equipment limitations. The process was thus further examined by computer simulation and model parameter sensitivity study. A practical design was recommended based on the model predictions.
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  • 49
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    Polymer Engineering and Science 24 (1984), S. 473-481 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An experimental study was conducted on the injection molding of a thermosetting polyester resin. For the study, a general-purpose unsaturated polyester resin was used, with benzoyl peroxide as initiator. A differential scanning calorimeter (DSC) was used for studying the curing kinetics, under isothermal curing conditions. A plunger-type injection-molding apparatus was constructed, and a rectangular mold cavity with glass windows on both sides was constructed, which permitted us to record on a film the changes in stress birefringence patterns in the mold cavity during the molding operation (i.e., during the isothermal cure, post cure, and subsequent cooling), using a crossed circular polariscope. The injection-molded specimens were used to determine the distribution of the degree of cure at various positions in the flow direction, and to relate the degree of cure to the dynamic mechanical properties.
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  • 50
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    Polymer Engineering and Science 24 (1984), S. 1240-1244 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Standard test specimens of mortar were cured under water for 15 days to achieve satisfactory strength. They were dried without allowing dehydration reactions to occur, evacuated to 40 millimeters (mm) Hg, and impregnated with a styreneacrylonitrile comonomer, which gives the highest strength after polymerization. Positive pressure of 0.6 N/mm2 was applied and thermal catalytic polymerization was carried out. Optimum initiator concentration was found to be 2 percent. Strength (compressive and tensile) increases with polymerization temperature up to 120°C, above which rapid deterioration occurs due to monomer loss, production of short chains with high polymerization rates, and the possibility of polymer degradation at high temperature. Optimum polymerization period of' 10 hours was selected. Inexpensive methods for field polymerization were tried at 95°C. Hot water yields a strength more than double that obtained with a, flow of hot air and about 80 percent of that obtained radiolytically. While hot air accelerates evaporation, hot water forms a hydraulic head above the capillaries and decreases the monomer losses tremendously.
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  • 51
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The absorption of water vapor by propellants based on hydroxy-terminated polybutadiene and an isocyanate from atmospheres of increasing relative humidities, and the swelling index of the propellant which had absorbed various proportions of water, were measured in an attempt to establish the extent of hydrolytic damage. The method was found incapable of assessing such damage, but it was shown that there was no measurable absorption of vapor below 92 percent relative humidity (RH). The MEK/polymer and toluene/polymer interaction parameters were determined.
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  • 52
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    Polymer Engineering and Science 24 (1984), S. 673-685 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The hierarchy of mathematical models of injection molding is reviewed. Compatibility of the models of the hierarchy, usefulness of simultaneous applications of models formulated on several different levels of the hierarchy and compatability between physical approximations leading to the formulation of a model, and mathematical approximations used to solve numerically the governing equations of the model are discussed. This review is intended to facilitate the search for a model that is best suited to a given need and to indicate future research.
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    Polymer Engineering and Science 24 (1984), S. 716-721 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 54
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    Polymer Engineering and Science 24 (1984), S. 737-749 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper discusses some new mechanical and small angle neutron scattering (SANS) data on glassy polymers, both thermoplastics and thermoset resins, from the point of view of dislocation-like defects introduced in the molecular chain arrangement by deformation. In the pre-yield stage, a new parameter, the work-hardening rate K is introduced and its measurement is defined. Experiments are reported which show that K can be used as a very sensitive probe for microstructural changes during physical aging or curing. In one hand, the theory of yielding is revisited to make clear how dislocations and their propagation in polymers depend on specific features like entanglements and chain stiffness. On this basis, experimental internal stresses and activation volumes at yield (i.e., the temperature slope of yield stress) are accounted for. On the other hand, SANS data provide us with experimental evidence at the scale of 10 to 20 Å of the dislocation nature of the molecular “shear defects” introduced in the polymer by deformation. Finally, temperature is known to have a pronounced influence on yield processes. It is shown that two distinct deformation modes exist below and above a critical temperature Tc. Above Tc, a dislocation climb, which probably involves β-processes, gives rise to a “diffusional” deformation mode where chains within a (diffuse) shear band are no longer oriented. A tentative formalization of this behavior, and its relation to the small strain creep of polymers, are then presented.
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  • 55
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    Polymer Engineering and Science 24 (1984), S. 724-736 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The deformation behavior of three polymers, polyethylene terephthalate (PET), polymethylmethacrylate (PMMA), and linear polyethylene (LPE) is considered in terms of two key factors, the stretching of a molecular network and the influence of thermally activated processes. In PET the observation of a natural draw ratio leads to studies of shrinkage, shrinkage force, and optical birefringence to define the nature of the network. The network is further exemplified by measurements of the molecular reorientation in deformation bands, spectroscopic studies of molecular orientation in drawing, and the concept of a true stress-strain curve. Yield and plastic deformation are also to be considered as thermally activated processes, but it appears that a major part of the flow stress is associated with the stretching of the molecular network. In PMMA the concept of a true stress strain curve also appears to be valuable, but the possibility of network breakdown during deformation has to be admitted as an extra complexity. In LPE the concept of a molecular network embracing both crystalline and non-crystalline material is helpful in understanding the drawing behavior. There is also direct evidence for the existence of a network from measurements of shrinkage and shrinkage force, and the existence of a true-stress strain curve. However, the dominant contribution to the flow stress now appears to come from thermally activated processes, with a key contribution from a small activation volume process which is tentatively associated with slip in the crystalline regions.
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  • 56
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    Polymer Engineering and Science 24 (1984), S. 886-894 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Internal friction has been measured by torsion at 1 Hz during tensile tests performed on glassy polycarbonate at room-temperature. Steady-state flow and transient effects have been studied during continuous tensile tests and strain-rate changes. During steady-state, internal friction and flow-stress vary in a similar way with strain-rate. But during transients, internal friction varies continuously while flow-stress passes through a maximum (or a minimum). These results are interpreted assuming that non-elastic deformation of glassy polymers requires some microscopic discontinuous processes such as motion of defects. Two parameters are considered: the velocity v and the density ρ of mobile defects. Assuming that the former is directly related to the flow stress, it has been shown that internal friction is related to the density of mobile defects ρ. This feature is used to interpret the different stages of a tensile test curve. Activation volumes for both velocity and density of mobile defects are calculated from experimental data.
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  • 57
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    Polymer Engineering and Science 24 (1984), S. 915-920 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The molecular kinetic theory near the glass transition, bused on the existence of free volume distribution, is extended to incorporate the effects of stress and stress rate. The fundamental equations for the volume relaxation and recovery in stressed amorphous polymers are derived in accordance with the balance of nonequilibrium statistical entropy. Using these kinetic equations, an earlier nonequilibrium criterion for the glass transition temperature, Tg, is generalized to include the effects of stress and stress rate. In contrast to the prevalent thinking toward free volume theories, an explicit expression between Tg and stress is developed and reveals that Tg does not continue to increase at all pressures but levels off to a “universal” asymptote at very high pressure (〉10 K bars). The expression is applicable to any tension and compression stress conditions. A comparison between theory and experiment under constant stresses determines the activation volume tensor which reveals the molecular mechanism relating Tg and the plastic yield of glassy polymers.
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  • 58
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: Paper properties of the thermochemical pulp modified by ozonation and grafting with styrene, acrylamide or their mixtures have been studied. Paper sheets, prepared by hot pressing from ozonated and grafted pulps showed improvement in: wet breaking length; dry breaking length; burst and dimensional stability.
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  • 59
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    Polymer Engineering and Science 24 (1984), S. 608-611 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A commercial polyarylate (PAr), a copolyester of Bisphenol-A with 50 percent terephthalate-50 percent isophthalate, has been characterized by means of a combination of gel permeation chromatography and viscometry. It has been studied as first component of a series of polymer blends. The presence of either one glass transition temperature (Tg) or two has been used as a criterion to determine the miscibility of each blend. In some cases, the possible incidence of transesterification reactions has been considered.
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    Polymer Engineering and Science 24 (1984), S. 624-625 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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    Polymer Engineering and Science 24 (1984), S. 645-651 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The residence time distribution (RTD) in a fully intermeshing, corotating twin screw extruder was determined with a stimulus-response technique. In addition to varying three process parameters (i.e. throughput, screw rotational speed, and barrel temperature), two screw configurations were also studied: one containing four kneading block mixing sections, and the other consisting only of regular screw bushings. Although screw configuration was an important variable, it was found that for both configurations the throughput had the largest effect on RTD. The screw rotational speed was second in importance, and the barrel temperature change produced no effect.A fluid mechanical model based on the fluid flow in a partially-filled rectangular channel was used to explain the experimentally observed dependence of RTD on the process parameters. Reaction engineering approaches were adopted to compare the RTD results of two screw configurations with two idealized flows.
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    Polymer Engineering and Science 24 (1984), S. 686-691 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Some aspects of injection-molding dynamics were studied using a laboratory injection-molding machine operated under the control of a microprocessor-based servocontrol system. Two types of experiments were performed: deterministic tests which introduced step changes in the servovalve opening and stochastic tests using pseudo-random binary sequence (PRBS) perturbations of the servovalve. Deterministic models were written for the hydraulic and nozzle pressures which were in good agreement with the experimental data. A stochastic transfer function-noise model was obtained for the nozzle pressure, but an adequate model was not found for the hydraulic pressure. The agreement between the nozzle pressure stochastic model and the corresponding step test model was satisfactory.
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    Polymer Engineering and Science 24 (1984), S. 707-715 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A general-purpose finite element program has been used to simulate the flow of Newtonian, power-law, and viscoelastic fluids in the entry and exit regions of a slit die. It was found that shear-thinning increases the entrance correction while it decreases the exit correction. Shear-thinning reduces the size of the small corner vortex that forms in the entry flow of a Newtonian fluid. The swelling ratio had a value of 1.196 for Newtonian fluids and decreased as the value of the power-law index decreased. Viscoelastic calculations were performed using the Criminale-Ericksen-Filbey (CEF) constitutive equation. Convergence of the iterative scheme was unattainable for Deborah numbers above 1.0. The results showed a decrease of the entrance correction and an increase of the exit correction with elasticity. Extrudate swell first decreased slightly and further increased with the Deborah number.
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    Polymer Engineering and Science 24 (1984), S. 761-769 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: As crazes grow in areal extent they also increase in width. The areal growth involves craze tip advance which has been shown to occur by the Taylor meniscus instability. Craze widening, at least for air crazes, occurs by drawing more fibrillar material from the craze-bulk polymer interfaces at essentially constant extension ratio. Simple arguments will be given to predict the scale of the fibrillation in terms of the stress S at the craze tip and interfaces and an effective polymer surface energy (Γ) where:\documentclass{article}\pagestyle{empty}\begin{document}$$ {\Gamma = \gamma + {\raise0.5ex\hbox{$\scriptstyle 1$}\kern-0.1em/\kern-0.15em\lower0.25ex\hbox{$\scriptstyle 4$}}d \cdot v_E U_b} $$\end{document} which assumes that all entangled chain crossing the surface are broken [γ represents the van-der-Waals (intermolecular) surface energy, d is the entanglement mesh size, vE is the entanglement density, and Ub is the energy required to break a single backbone bond]. These arguments also give the rate of fibrillation as a function of S, a nominal plastic resistance σy and Γ and can explain the fact that the stress for crazing increases relative to that for shear deformation as the entanglement density of the polymer is increased. The geometrically necessary entanglement loss (either by scission as assumed above or by disentanglement- at temperatures just below Tg) that accompanies fibril formation has important consequences for fibril stability. The probability p that a given entangled chain is lost can be computed from simple geometrical considerations knowing the fibril diameter D, its extension ratio λ and the mesh size d; p increases rapidly as Dλ½ becomes comparable to or less than d. These concepts can be tested in blends of high molecular weight polymer with chains of the same polymer that are too short to entangle.
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  • 65
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    Polymer Engineering and Science 24 (1984), S. 1174-1179 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Critical strains causing environmental stress cracking of injection-molded poly(acrylonitrile-butadiene-styrene) (ABS) and poly(styrene-acrylonitrile) (SAN) plaques were determined upon exposure to methanol. Measurements were obtained for samples strained either parallel or perpendicular to the melt flow direction and for samples located at various distances from the mold gate. Critical strains were significantly higher in the direction parallel to the melt flow compared to the transverse direction. The degree of anisotropy increased with increasing rubber content. For ABS containing 46 percent rubber, the critical strain at one point was determined to be 2.99 percent in the direction of melt flow, but only 0.47 percent in the orthogonal direction. For this material, critical strains determined parallel to the melt flow decreased with distance from the gate; whereas, critical strains for SAN and ABS containing 30 percent rubber remained essentially constant. Orientation of the plaques was assessed using shrinkage determinations and a thermal conductivity technique. Though a straightforward correlation of orientation with critical strain is observed for ABS, a similar relationship is not observed for SAN. These results suggest that although stress cracking occurs in the glassy matrix of ABS, it is the dispersed rubbery phase which controls the magnitude of strain required to initiate cracking.
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  • 66
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    Polymer Engineering and Science 24 (1984), S. 1185-1201 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A basic study of the kinematics, dynamics, and heat transfer occuring during tubular film extrusion of polyethylene is outlined. Three rheologically characterized polyethylenes, a low-density polyethylene (LDPE), a linear-low-density polyethylene (L-LDPE), and a high-density polyethylene (HDPE) were used in this study. The kinematics and stability of the tubular film process were investigated over a wide range of blow-up ratios, drawdown ratios, and frost-line heights. Local deformation rates along the bubble have been determined. Regions of stability and instability are described. Tensions and inflation pressures have been measured and expressed in terms of locol elongational viscosities. Temperature profiles along the bubble were determined and interpreted in terms of local heat transfer coefficients. Positions of crystallization and temperature profiles have been noted and used to estimate rates of crystallization. The characteristics of the LDPE, LLDPE, and HDPE are contrasted.
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    Polymer Engineering and Science 24 (1984) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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    Polymer Engineering and Science 24 (1984), S. 1020-1020 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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    Polymer Engineering and Science 24 (1984), S. 1026-1034 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A mathematical analysis of bubble growth in an expanding foam is presented. The analysis is based on a cell model whereby the foam is divided into spherical microscopic unit cells of equal and constant mass, each consisting of a liquid envelope (or shell) and a concentric spherical gas bubble. Expansion occurs by diffusion of a dissolved gas from the supersaturated envelope into the bubble. This cell model is capable of describing important qualitative features of a real system of numerous bubbles growing in close proximity to one another, and is intended as the building block of a global analysis of macroscopic foam expansion. The coupled algebraic and differential equations governing the growth of a cell are derived and solved numerically. Five dimensionless parameters are identified for the case of constant temperature and pressure outside the cell, and their effects are demonstrated through computer simulations of the system. Of these parameters, surface tension and initial radius prove to be of relatively little importance in the practical cases considered. The other parameters are the thermodynamic driving force, the cell mass (inversely proportional to the number density of bubbles), and the ratio of characteristic times for mass and momentum transport.
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    Polymer Engineering and Science 24 (1984), S. 1277-1282 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper outlines the development of an acoustical technique for measuring the dispersion of an additive in a polymer melt. It included a justification of the use of sound over other interrogating methods and an analysis of the acoustical system's operation. Results for dispersions of liquid or solid additives were shown. It was demonstrated that this system could detect the presence or absence of large particles in melts filled with small particles.
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    Polymer Engineering and Science 24 (1984) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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    Polymer Engineering and Science 24 (1984), S. 1284-1290 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: We discuss the free-energy expressions for homogeneous melts and their blends, based on our hole theory. Equation of state (PVT) and free energy of mixing (ΔGm) are considered from a common point of view without the introduction of additional parameters to pass from the first to the second set of properties. Practical problems arise from the fact that ΔGm represents a difference between large quantities. As illustrations we analyze two typical systems. One is the n - C6 + n - C16 pair where PVT and ΔGm, the latter at atmospheric pressure only, have been studied experimentally. The other is n - C6 with a low and high molecular weight respectively of polyethylene as solute. Here the PVT relations of the components only are known. The effects of intercomponent attractions, temperature, pressure, and molecular weight on phase behavior are investigated. Critical coordinates, lower critical-solution temperatures (LCST) and their pressure dependence are computed. An iso-free volume condition obtains for this dependence where free volume is defined by the hole fraction inherent in the theory. Comparisons with experimental observations and other theoretical computations for different molecular weights are limited by the effect of polydispersity. Moreover, cloud point curves are shown. We finally compute the composition and pressure dependence of the χ-parameter which is implicit in the theory. We conclude with some comments regarding polymer blends.
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    Polymer Engineering and Science 24 (1984), S. 1312-1318 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Blends of polycarbonate/polystyrene (PC/PS), polycarbonate/polypropylene (PC/PP) and ternary blends of the three components (PC/PS/PP) were studied. Extrudate swell of the molten blends increased with increasing concentrations of the minor components and leveled off at characteristic blend compositions. These compositions corresponded to the limits of compatibility as judged by the onset of brittleness in tensile tests. Both PS and PP appear to have some limited practical compatibility with PC. The change in extrudate swell behavior with concentration may be a rapid and convenient test for the effective concentration limits of partially miscible polymers.
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  • 74
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    Notes: An experimental study of the development of phase morphology in incompatible polymer melt blends of polyethylene/polystyrene (PE/PS), polyethylene/polycarbonate (PE/PC), and polyethylene/nylon-6 (PE/N6) is presented. Different temperatures (180°C, 240°C) of mixing and polyethylene molecular- weight levels were used in the PE/PS studies. Little variation in the cross-sectional phase morphology of the PE/PS extrudates was observed with these variables, though the morphology became finer with increased shear rate/stress in capillary die flow. Variations in the longitudinal morphology are observed with continuous filaments of dispersed phase only arising when the dispersed phase has an equal or lower viscosity than the continuous phase. The PE/N6 and PE/PC, especially the former, give coarser morphologies when the N6 and PC are the continuous phases. This was attributed to larger inter-facial tensions. The effect of viscoelasticity was also discussed.
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    Polymer Engineering and Science 24 (1984) 
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    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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    Polymer Engineering and Science 24 (1984), S. 42-47 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Kevlar 29 fiber has been widely considered for the manufacture of very-long high-performance cables. Due to low transverse strength fiber-on-fiber rubbing leads to rapid deterioration. The usefulness of impregnating Kevlar 29 braids with resin to overcome this drawback has been evaluated by performing reverse bending fatigue tests. Braids of identical construction, one of them being impregnated with a polyurethane resin by a patented process, were fatigued to failure on a purpose-built rig under varying applied loads. Fatigue tests were also carried out to 30 percent and 50 percent of total braid life and residual strength values measured. It was found that high applied loads (∼50 percent of ultimate) lead to premature braid failure dominated by a creep mechanism. Both braids showed similar behavior, although the impregnated braid was superior. At low applied loads, however, where the failure mechanisms was dominated by wear or internal abrasion, it was seen that resin impregnation could increase braid life by a factor of four. Resin impregnation coupled with bending fatigue significantly stiffens braids, as was demonstrated by tensile testing up to braid failure.
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    Polymer Engineering and Science 24 (1984), S. 22-29 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In this article the kinetics of chemical-controlled radical-chain copolymerization have been reduced to pseudohomopolymerization kinetics by introducing the apparent rate constants, The methods for the determinations of the values of the apparent rate constants, mode of termination, and the methods for the calculation of molecular weights and distributions are proposed. The data required for these determinations and calculations are simply obtained by the usual steady-state method. According to the traditional kinetics along with the definitions of the apparent rate constants, these apparent rate constants as functions of traditional rate constants, monomer compositions, and copolymer compositions are derived. Further utilizing the theoretical expressions obtained, we show that the apparent rate constants are the general rate constants for both radical chain homo- and copolymerizations. The bulk radical copolymerizations of methyl methacrylate and styrene at various monomer feed compositions at 60°C are used to test the proposed model. The empirical apparent rate constants obtained are described well, by the following expressions, \documentclass{article}\pagestyle{empty}\begin{document}$$ \beta = 0.997{\rm }F_1 + 0.398{\rm }F_2 + 0.039\left({F_1 F_2 } \right)^{\frac{1}{2}} $$\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$$ {{k_t^a } \mathord{\left/ {\vphantom {{k_t^a} {\left({k_p^a} \right)}}} \right. \kern-\nulldelimiterspace} {\left({k_p^a } \right)}}^2 = - 0.138 \times 10^4 \left({{{F_1 } \mathord{\left/ {\vphantom {{F_1 } {f_1 }}} \right. \kern-\nulldelimiterspace} {f_1 }}} \right)^2 + 0.354 \times 10^4 \left({{{F_1 F_2 } \mathord{\left/ {\vphantom {{F_1 F_2 } {f_1 f_2 }}} \right. \kern-\nulldelimiterspace} {f_1 f_2 }}} \right) - 0.114 \times 10^4 \left({{{F_2 } \mathord{\left/ {\vphantom {{F_2 } {f_2 }}} \right. \kern-\nulldelimiterspace} {f_2 }}} \right)^2 $$\end{document} and the mode of termination on the combination termination is \documentclass{article}\pagestyle{empty}\begin{document}$$ {1 \mathord{\left/ {\vphantom {1 {{\rm k}_p^a = - 0.132}}} \right. \kern-\nulldelimiterspace} {{\rm k}_p^a = - 0.132}} \times 10^{ - 2} \left({{{F_1 } \mathord{\left/ {\vphantom {{F_1 } {f_1 }}} \right. \kern-\nulldelimiterspace} {f_1 }}} \right) + 0.428 \times 10^{ - 2} \left({{{F_2 } \mathord{\left/ {\vphantom {{F_2 } {f_2 }}} \right. \kern-\nulldelimiterspace} {f_2 }}} \right) $$\end{document} where Kaa and Kta denote the apparent rate constants of propagation and termination, respectively. The term f1(= 1 - f2) stands for the mole fraction of styrene in the monomer solution fed. F1 is the copolymer composition produced at f1. β is the mode of termination.
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  • 78
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    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The modification of an amorphous random ethylene-propylene rubbery copolymer (EPM) has been accomplished by solution grafting of maleic anhydride molecules promoted by radical initiators, The resulting EPM-g-succinic anhydride (EPM-g-SA) and EPM have been used to obtain binary polyamide 6/EPM or polyamide 6/EPM-g-SA and ternary polyamide 6/EPM/EPM-g-SA blends by melt mixing. The formation of an EPM-g-PA6 graft copolymer during the blend preparation has been assumed. Different blend morphologies were observed by scanning electron microscopy (SEM) according to the nature and content of the rubber used. The tensile mechanical properties and the impact behavior of the prepared blends were investigated and correlated with the SEM analysis of the fracture surfaces. Binary and ternary blends containing 20 percent by weight of total rubber show a significant improvement of the impact properties at low temperature (-20°C) when the rubber is partly or entirely EPM-g-SA. In the case of PA6/EPM-g-SA (80/20) blend these results are related to the presence of rubbery domains of very small size strongly adherent to the PA6 matrix. In the case of 80/10/10 ternary blends, a much more complicated overall morphology is observed. Such morphology is characterized by the presence of large EPM domains, likely containing some EPM-g-PA6 graft molecules acting as an interfacial agent, and domains of EPM-g-PA6 of smaller size strongly adherent to the matrix as in the previous case.
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  • 79
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    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The Lower Critical Solution Temperature (LCST) of polyethylene (PE), polypropylene (PP), and ethylene-propylene block and random copolymers have been measured in heptanes. A thermogram related to the variation of the turbidity of the solution is obtained between 100 and 210°C. The temperature of the onset of the turbidity peak is defined as the LCST of the system. The width and the area of the turbidity peaks are tentatively associated with the polymer polydispersity and the amount of polymer involved in the phase separation. The thermograms of solutions containing both homopolymers show two distinct turbidity peaks situated at a 70°C interval. Correlations of molecular orientations in the concentrated phase, possible in PE systems but not in PP solutions, are at the origin of the lower LCST values for PE solutions. The LCST of copolymers are situated between those of the homopolymers but the dependence of the LCST on the copolymer ethylene content is different for block and random copolymers. Examples of thermograms are also given for mixtures of copolymers with PE and PP. By analysis of their thermograms, some commercial block EP copolymers were also found to contain PK and PP. This method seems well suited for characterizing polymer mixtures.
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    Polymer Engineering and Science 24 (1984), S. 144-152 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The dielectric properties of miscible blends of poly(vinyl chloride) (PVC) and poly(α-methyl-α-n-propy-β-propiolae-tone) (PMPPL) have been investigated at different temperatures above and below Tg. The results were analyzed using the Cole-Cole representation and lead to the conclusion that this mixture does not exhibit micro-scale heterogeneities. Dielectric constant and dielectric loss master curves were constructed using the stress relaxation shift factors determined previously; the same shift factors could be used for the homopolymers and their blends. Similarities between the dielectric master curves and the stress relaxation master curves of PVC, PMPPL, and their blends, are also discussed.
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    Polymer Engineering and Science 24 (1984), S. 175-184 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An experimental study was carried out to investigate the isothermal and non-isothermal curing kinetics of unsaturated polyester and vinyl ester resins, using differential scanning calorimetry (DSC). Emphasis was put on investigating the effect of low-profile additives on the curing kinetics of the thermo-setting resins. For the study, a general-purpose polyester resin and a vinyl ester resin were used, together with polyvinyl acetate (PVAc) as low-profile additive, benzoyl peroxide as initiator, and N,N-dimethyl aniline as promoter. It has been found that (1) the addition of the low-profile thermoplastic-additive decreases the rate of cure and, also, the final degree of cure of the resins, (2) the total heat of cure generated by isothermal cure is lower than that generated by non-isothermal cure, and (3) the resin/initiator mixture with promoter exhibits two major exotherm peaks during non-isothermal cure, but only a single exotherm peak during isothermal cure.
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    Polymer Engineering and Science 24 (1984), S. 205-210 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A phenomenological model of entanglement networks is developed and applied to deformed glassy polymers. Thermal expansivities and birefringence are analyzed. The model assumes a stable network of entanglements up to draw ratios of about 5. Beyond that range the entanglement structure breaks down to maintain a nearly constant drawing stress. The results are used to determine the ultimate linear expansivities of atactic polystyrene.
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    Polymer Engineering and Science 24 (1984), S. 227-241 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Distortion of bars injection-molded from polystyrene, polypropylene, and glass-fiber-filled polypropylene and subsequently placed in a temperature gradient has been examined. Residual stress distributions have been measured both for the as-molded state and after annealing in a temperature gradient. In the as-molded state all moldings showed the usual residual stress distribution with compressive stresses near the surface and tensile stresses in the interior. In all three materials it was found that tensile stresses could be developed near to the warmer surface on gradient annealing and that tensile stresses still remained at this surface when the bar was cooled and permitted to bend to restore internal equilibrium. It is shown therefore that in addition to the dimensional changes which occur and which may render the molding unserviceable after temperature gradient annealing, another undesirable change takes place, leaving the molding much more susceptible to fracture from a surface flaw. Uniform annealing is found to be much less likely to cause stress reversal and the stresses remain balanced so that distortion is minimal.
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    Polymer Engineering and Science 24 (1984), S. 519-519 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Notes: The mechanical properties of a variety of immiscible binary blends, with and without third component polymeric compatibilizers, are reviewed and qualitatively related to the degree of adhesion between blend components as determined by lap shear testing. Generally, blends comprised of components which adhere well, one to the other, show improved ductility relative to blends of components which do not adhere, Similarly, polymeric compatibilizers are found to be more effective for improving the properties of a binary blend system if they adhere well to both primary components of the immiscible mixture. These results suggest that adhesion between phases in the mixture strongly influences the ultimate properties of the blend. Some evidence is presented which suggests that components which adhere well are partially miscible.
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    Polymer Engineering and Science 24 (1984), S. 598-600 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This paper presents an overview of the subject of phase separation in polymer blends with an emphasis on the thermodynamic stability criteria for phase stability and the classical thermodynamic and microscopic description of polymer interfaces.
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    Polymer Engineering and Science 24 (1984) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 88
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 421-427 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The extent of molecular degradation of amorphous polystyrene when subjected to mechanical grinding at cryogenic temperature has been investigated using electron spin resonance, infrared spectroscopy, and viscometry. Essentially identical concentrations of chain ruptures in the degraded samples were found from infrared spectroscopic determinations of molecular end group concentrations and by the changes in the viscosity-average molecular weights. The chain-scission concentration was from two to four times the free-radical concentrations, indicating that free-radical-propagation reactions play a much less dominant role in the degree of molecular damage associated with mechanically induced chain scission in glassy polymers. In addition, experiments were carried out as a function of molecular weight and these indicated a virtual independent behavior with molecular weight.
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  • 89
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    Polymer Engineering and Science 24 (1984), S. 79-86 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An abbreviated review of the current state of knowledge of polymer interfacial phenomena is given. Classical thermodynamics treats the interfacial zone (the interphase) as a “black box” and yields rigorous relationships among interfacial quantities. A recent reformulation of interphase thermodynamics, which eliminates the use of a Gibbs dividing surface, is shown to be an invaluable tool for investigating interfacial properties. Microscopic theories, such as the gradient theory, yield more details about what is in the black box, but the information is only approximate. The gradient theory has been used to: (1) relate the surface tension of a polymer liquid to its isothermal compressibility, (2) develop a quantitative theory of polymer liquid surface tension, and (3) determine the interfacial tension between two immiscible polymer liquids. The gradient theory will be shown to be in harmony with the microscopic theory of Helfand and co-workers although the latter treats polymer interfaces from a completely different point of view.
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  • 90
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    Polymer Engineering and Science 24 (1984), S. 698-706 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Thermosetting materials have found widespread use over a broad spectrum of engineering applications due to their intrinsic mechanical strength, thermal and dimensional stability, and other unique properties. Consideration is given to those aspects of reaction kinetics, rheology, fluid mechanics, and heat transfer which are of relevance for the mathematical modeling of reactive polymer processing. Particular emphasis is given to the characterization of reaction kinetics under non-isothermal conditions, the effect of fillers or reinforcing agents on the heat transfer and kinetic behavior, and the complex nature of the interactions brought about by the reactivity of these systems. In addition, the current status of the mathematical simulation of reactive polymer processing is briefly reviewed.
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  • 91
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 843-843 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 92
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 921-929 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The evolution of poly(methyl methacrylate) (PMMA) during physical aging at 90°C is followed by torsional microcreep tests. On the aged specimen a longitudinal stress is applied which induces a strain of 5 percent after 30 days of creep. The torsional microcreep tests are performed during the longitudinal creep in order to compare the structure evolution of PMMA caused by straining with its evolution measured during aging. The microcreep, for the first 800s, follows a reversible logarithmic law. In this stage the mobile defects achieve their activated form which is perfectly reversible when unloaded. The physical aging reduces this logarithmic part of microcreep. This is due to the decrease of either the number or the volume of the mobile defects. Beyond a critical elongation ∊ = 1 percent, the longitudinal straining has just the opposite influence, i.e., the logarithmic part of microcreep increases. This critical elongation ∊ = 1 percent corresponds to the beginning of the steady state longitudinal creep. The transient that precedes this steady state has no detectable influence on the structure of the specimen.
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  • 93
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 94
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 345-349 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Small angle X-ray scattering (SAXS) has been used to evaluate the size and concentration of voids in poly(N,N′-bis-(phenoxyphenyl)pyromellitimide), PMDA-ODA. Analysis of the angular dependence of the scattering indicates the presence of voids ranging from 50 to 150 Å in radius. Integrated SAXS demonstrated that the volume fraction of voids was 7 × 10-4. These results were supported by measurements of the attenuation factor as a function of the sample thickness.
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  • 95
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984) 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
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  • 96
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 1087-1103 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The response of glass-forming systems to isobaric three-step thermal cycles involving cooling, isothermal annealing, and subsequent reheating has been investigated comprehensively using numerous combinations of the experimental and material parameters. The latter include the retardation spectrum or response function and the parameter x which determines the relative contributions of temperature and structure to the retardation times. The results show that, on heating, multiparameter systems can display three kinds of peak in the expansion coefficient α or the heat capacity Cp originating from the interactions of the elementary retardation processes with the thermal history of the glass. The conditions under which these peaks occur, their shifts with x, and the experimental variables have been investigated in detail. In particular, it has been shown that for a thoroughly stabilized glass reheated rapidly, the temperature at which the main peak occurs is strongly dependent on the experimental variables and on x, and that this dependence can lead to an estimate of the value of x. For poorly stabilized glasses reheated slowly, on the other hand, the main peak apparently vanishes and allows an upper peak to appear, which is small and insensitive to x and the experimental variables. Intermediate situations in which the main and the upper peaks occur separately give rise to a range of effects which may become quite complicated as the two peaks approach each other. The occurrence of such multiple peaks, which has usually been overlooked or misinterpreted in the past, is discussed and explained in detail and is compared with some experimental observations reported in the literature.
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  • 97
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    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 24 (1984), S. 1130-1137 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The relationship of valence-coordinate deformation to the temperature dependence of some infrared peak-absorption frequencies in Poly(vinyl chloride) (PVC) and polystyrene (PS) is stated. A skeletal band and a CH2 rocking band in PVC and a ring-mode band in PS were studied in two kinds of experiments: steady heating and cooling of a quenched (nonequilibrium, glassy) sample through its glass-transition temperature, Tg, and long-term annealing of quenched samples below Tg, followed by steady heating and cooling. The results, a slope discontinuity, ΔM, in the v(T) relation at Tg and a frequency shift, Δviso, during isothermal annealing below Tg, are analyzed in two theoretical approaches. Interchain and intrachain contributions to the observed frequency shifts are expected to occur with a differing relative significance in different kinds of molecular vibrations, leading to one possible method of distinguishing valence-coordinate deformation (chain strain) from other effects.
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  • 98
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    Polymer Engineering and Science 24 (1984), S. 117-126 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An attempt was made to melt incorporate ultra high molecular weight polyethylene, UHMWPE, into medium density polyethylene, MDPE. The behavior of the mixtures, containing up to 6 wt percent of UHMWPE, was examined using mechanical and rheological testing. The mechanical test results were found to contain large experimental errors, which makes interpretation very difficult. On the other hand, melt rheology studies, using dynamic and extensional deformations, gave direct insight into the extent and effect of blending. Degradation during the processing was evaluated by size exclusion chromatography. The degree of dispersion of the UHMWPE was examined under the optical microscope.
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  • 99
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    Polymer Engineering and Science 24 (1984), S. 112-116 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: This note describes the application of infrared spectroscopy to determine the proportion of ester groups of poly(∊-caprolac-tone) which are involved in specific interactions with the hydroxyl groups of the poly(2-hydroxypropyl ether of bisphenol A) (Phenoxy, Union Carbide) in a series of miscible blends of the two polymers, Even with a fifteen-fold excess of hydroxyl groups, only about 50 percent of the ester groups of poly(∊-caprolactone) are hydrogen-bonded, presumably reflecting steric restrictions to the ester-hydroxyl interactions. Partially miscible blends of these two polymers may also be prepared by a suitable choice of casting solvent, and infrared spectroscopy may then be used to follow the kinetics of miscibility when the partially miscible blend is heated.
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  • 100
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    Polymer Engineering and Science 24 (1984), S. 153-162 
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The transport of small molecules (gases) in incompatible polymer blends, semi-crystalline polymers, and filled polymer systems is usually examined in terms of transient sorption and permeation experiments which yield effective values of diffusivity and permeability. From a modeling standpoint these complex systems can be regarded as composites with complex morphology whereas the gas can be considered as a molecular probe of the morphology and especially its connectedness. In this paper we present a brief review of transport descriptions in prototype ordered and disordered systems with special emphasis on simulation of transient measurements. The simulations presented are selected in such a way as to aid in the interpretation of experimental results obtained by sorption and permeation and in the construction and evaluation of morphologies with desired effective transport properties.
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