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The development of molecular orientation and morphological texture in thermotropic copolyesters (1985)

Viola, G. G. ; Baird, D. G. ; Wilkes, G. L.

Stamford, Conn. [u.a.] : Wiley-Blackwell

Polymer Engineering and Science 25 (1985), S. 888-895

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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: Liquid crystalline polymers can be processed to form high strength/modulus materials. In processing these materials, it is apparent that molecular orientation is an important factor in determining the physical strength of the processed materials. In this study a systematic investigation was carried out to determine how a thermotropic copolyester of parahydroxybenzoic acid (PHB) and polyethylene terephthalate (PET) responds to two basic types of flows: shear and extensional flow. This was accomplished by preparing sheared and extended samples under controlled conditions of temperature and flow history. Sheared disks were prepared using a disk and plate geometry of a Rheometrics Mechanical Spectrometer (RMS model 605), while extended ribbons were prepared using a slit die attached to an Instron capillary rheometer. Two copolymerer compositions of 60 mole percent and 80 mol percent PHB were investigated. The sheared disks and extended ribbons were investigated for molecular orientation and morphological textures using wide angle x-ray scattering (WAXS) and scanning electron microscopy (SEM) analysis, respectively. It was found that extensional flow has a greater capacity for orienting such materials than shear flow. Samples annealed at their softening points for 1 minute (240°C for the 60 mole percent PHB/PET copolymer and 300°C for the 80 mole percent PHB/PET copolymer) showed no significant loss of orientation, indicating that once orientation is produced it may remain in the melt for a long period of time. Sheared samples prepared by shearing the sample while cooling showed significantly higher degrees of orientation than those not cooled while being sheared. This may indicate that a minimum stress level exists for the production of orientation in shear flow.

Additional Material: 16 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/pen.760251405

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Isocyanate trimerization kinetics and heat transfer in structural reaction injection moldingBased on work presented at the Advanced Composites Conference, Detroit, October 1991. (1994)

Viola, G. G. ; Schmeal, W. R.

Stamford, Conn. [u.a.] : Wiley-Blackwell

Polymer Engineering and Science 34 (1994), S. 1173-1186

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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: Guidelines are developed for molding large composite parts via structural reaction injection molding using glass preforms and polyisocyanurate resins. These are based on numerical simulations of the simultaneous heat transfer and reaction kinetics of a commercial system during and after mold filling. Premised requirements are that resin does not gel before the mold is filled, yet, reactions are sufficiently vigorous to approach completion. An existing mechanistic kinetic model is used and material parameters found from a chemical kinetics study employing an insulated cup. It is found desirable to use a high mold temperature and a low preform temperature in molding. Nondimensionalization of the governing equations reveals the existence of a Nusselt number (Nu), which describes the relative importance of heat transfer between resin and glass relative to thermal diffusion to the mold wall. With a Nusselt number of about 50 or higher it is possible to use the cooling capacity of the preform to extend gel time. The magnitude of Nu is influenced by part thickness, glass fraction, strand diameter, and flow velocity. Thus, the effect of the preform on extending resin gel time is within control of the molder.

Additional Material: 14 Ill.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1002/pen.760341503

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