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  • Polymer and Materials Science  (40)
  • Atomic, Molecular, and Optical Physics  (1)
  • Instable interface  (1)
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  • 1
    ISSN: 1573-4897
    Keywords: MMC ; Nickel coated graphite ; Squeeze casting ; Instable interface ; Electroplating
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Metal Matrix Composites (MMC's) reinforced with continuous fibers were generally fabricated by a foil-sandwich technique or by liquid metal infiltration. Liquid metal infiltration may be used to cast final shapes in molds containing fiber preforms. It is also used to make composite wire from which may be fabricated panels and shapes by hot-press diffusion bonding or pultrusion. The major drawback of this method is that the molten matrix must wet the fiber for successful infiltration to occur, requiring special fiber surface treatments or matrix additives, and that, molten metals generally dissolve or degrade the fibers, necessitating a barrier coating on the fibers. All these problems can be solved using carbon fibers coated with metallic layers, e.g. nickel. This work analyses an easy method to produce modified carbon fibers by electroplating and the process of its recristallization. The topography of the growth front of the deposit has been studied. At temperatures higher than about 300° C an annealing under vacuum is required, because of the high reactivity of metal coating, nevertheless the heat treatment of metal deposit produces always an embrittled material.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Model synthetic tendons consisting of 20 vol % of texturized poly(ethylene terephthalate) fibers and of the water-swollen poly(2-hydroxyethyl methacrylate) matrix have the tensile modulus E = 1.5 ± 0.1 GPa, strength and strain-at-break σb = 85 ± 10 MPa and ∊b = 0.08 ± 0.02. The force required for breaking tendons with the diameters 2, 3, 4 mm is, respectively, 300, 500, and 960 N. By these properties model synthetic tendons closely imitate the properties of natural tendons. Long-term (100 min) and repeated short-term (30 times 1 min) creep shows that on loading model tendons lose some 10% of their stiffness, but that the whole deformation is reversible. The shape of the compliance vs. time dependence of synthetic tendons closely resembles the dependence determined for the parent fiber. The stiffness and strength of a tendon are given by those of the fiber bundle used; by varying fiber volume fraction, it is possible to adjust the required mechanical properties of tendons.
    Additional Material: 6 Ill.
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  • 3
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Poly(2-hydroxyethyl methacrylate)-(PHEMA) has been prepared by polymerizing in presence of different types of water-soluble additives, at various amounts, which were removed by swelling in water. Mechanical properties of swollen samples have been measured and analyzed by using the classical theory of rubber elasticity. Water permeability measurements were also performed to detect the presence of micropores and to determine the type of water transport. It has been shown that it's possible, using different types and amounts of additives, to obtain a wide range of physical properties of swollen PHEMA as required for various biomedical applications.
    Additional Material: 9 Ill.
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  • 4
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Because of its chemical versatility and demonstrated biocompatibility, poly(2-hydroxyethyl methacrylate) (pHEMA) has been widely used as a polymer for biomedical applications. Since this hydrophilic material shows a poor interface with cells, blendings with other polymers were done to improve cytocompatibility. In our polymer, the presence of hydrophobic dominions on the material surface, due to the interpenetrating polymerization of pHEMA with poly(caprolactone) (PCL), seems to ameliorate the cytocompatibility in terms of cell adhesion and metabolism. For our experiments, we used IMR-90 human fibroblasts, as these cells strongly regulate DNA, RNA, and protein synthesis as anchorage-dependent variables. Cell attachment on a pHEMA/PCL interpenetrating polymer network was optimal, suggesting a strong adhesion between the cells and the polymer surface. Cell adhesion was weaker on pHEMA, as a significant fraction of the fibroblasts revealed a lack of spreading, with most cells remaining spherical. Moreover, only fibroblasts seeded on pHEMA significantly decreased mRNA synthesis; collagen production and cell shapes ranged from fully flat and proliferating, to minimally spread and nonproliferating. Finally, DNA synthesis, as a measure of cell proliferation, was markedly inhibited in cells cultured on pHEMA but not on pHEMA/PCL. In conclusion, our results suggest that control of cell growth and metabolism by biomedical polymers is based on physicochemical mechanism(s) in which the hydrophilicity/hydrophobicity ratio of the material surfaces may play an important role. © 1997 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
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  • 5
    ISSN: 0021-9304
    Keywords: composite ; ligaments ; viscoelasticity ; mechanical properties ; hydrogels ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: Despite the compelling need for artificial connective tissue replacements for orthopedic applications, to date, there is no material which can adequately reproduce the mechanical behavior of natural tissue with necessary long-term endurance. In this work, we introduce a novel soft composite material as a more suitable candidate for connective tissue replacement. The material proposed is based on a hydrogel-polymer matrix reinforced with poly(ethylene terephthalate) fibers wound helically to mimic the architecture of the collagen fibers in natural tissue. Macroscopic behaviors such as static stress-strain, stress relaxation, and dynamic frequency responses can be modulated with choice of the components and design of the composite structure. In doing so, the mechanical characteristics of natural ligaments can be qualitatively reproduced and sustained over time. © 1998 John Wiley & Sons, Inc. J. Biomed Mater Res, 42, 6-12, 1998.
    Additional Material: 8 Ill.
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 15 (1971), S. 469-476 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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: Relaxation and stress-strain behavior of SAN-glass bead composites are studied above the glass transition temperature. The strain imposed on the polymeric matrix of the composite is defined as ∊p = ∊c/(1 - φ⅓). Stress relaxation data for the filled polymer which is independent of strain can be calculated by multiplying the relaxation modulus (at a certain strain) by (1 + ∊p). Stress-strain curves at constant strain rate and for different concentrations of the filler can be shifted to form a master curve independent of filler content if the tensile stress is plotted versus ∊p. The relaxation modulus increases with increasing the filler concentration and can be predicted by a modified Kerner equation at 110°C.
    Additional Material: 4 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 15 (1971), S. 1585-1598 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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 theory for predicting the stress-strain characteristics of polymeric solids is developed in terms of a description of microdefect formation. The process of irreversible change in these solids is assumed to be a combination of nucleation of submicroscopic defects at stress inhomogeneities and their subsequent growth to macroscopic dimensions. Straining results in the generation of crazes and cracks which can lead to catastrophic failure through either a general yielding of the material or by brittle fracture. It is assumed that nucleation of submicroscopic defects is an activated process and that defect growth is one-dimensional and linear. The total strain is expressed as the sum of an elastic recoverable strain and a nonlinear, nonrecoverable strain, and expressions are obtained for the stress as a function of time, temperature, and loading history. The criterion for yielding is defined in terms of a gross volume change associated with cavitation within crazes. The sum of the normal Poisson expansion plus this additional volume change leads to a deflection of the stress-strain curve. The criterion for brittle failure is defined in terms of a critical defect size. If the defects grow to their critical size before the stress-strain curve reaches a maximum, brittle failure occurs. The parameters of the resulting model are calculated for polyphenylene oxide polymer based on constant rate of loading experiments, and then the general creep behavior, including the time required under constant load for cold flow, is predicted. Experimental data are shown to agree with these predictions.
    Additional Material: 8 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 20 (1976), S. 561-563 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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
    Additional Material: 1 Ill.
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  • 9
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 22 (1978), S. 2391-2394 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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
    Additional Material: 3 Ill.
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  • 10
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    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 main role of the amino hydrogen bonding in the plasticization of water-penetrated epoxy resins has been tested on a diglycidyl ether of bisphenol-A (DGEBA) epoxy cured with different amounts of triethylenetetramine (TETA). Samples were characterized both by calorimetric and moisture diffusion techniques. The increased water solubilities and glass transition temperature depressions observed for the samples cured with an increased content of amino hardener were attributed to the high hydrophilic character of the amine. Theoretical models, based on the analysis of the free volume and entropy of the water saturated polymer, have been used to test the nature of the polymer-diluent interactions. The comparison between the experimentally determined and theoretical values of the wet glass transition temperatures indicates how the free volume better describes the behavior of the low amino content resins while the entropy model become effective at increasing amino contents. Moreover, the actual water solubilities have been determined by thermal cycling of water-saturated samples of different composition and used in the cited models.
    Additional Material: 4 Ill.
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