X-ray Studies on the Mechanical Behavior of Polymer Crystals

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Elastic moduli of the crystalline regions of various kinds of polymers and their temperature dependence (from low to high temperature) were investigated by x-ray diffraction. Comparison were made between the crystal modulus with the macroscopic deformation and molecular motions of the chains in the crystalline regions. The investigated polymers were as follows : cellulose, cellulose triesters, chitin, chitosan, poly (hydroxybenzoic acid) /poly (ethylene terephthalate) copolymer, poly (ethylene naphthalate) , poly (butylene naphthalate) , poly (p-phenylene benzobisthiazole) , poly (p-phenylene benzobisoxazole) , thermoplastic polyimide, biphenyl type polyimide, Kapton type polyimide, triphenyl type polyimide, ridid rod-like polyimide, syndiotactic polypropylene, ethylene-vinyl alcohol copolymer, isotactic polyvinyl alcohol, polyethylene.The crystal modulus gives the informaton on the extensivity of the chain molecule, the deformation mechanism in the crystal lattice, the maximum attainable modulus. The crystal modulus decreased at a certain temperature for most of polymers, where the molecular motion of the chain molecules in the crystal lattice enhanced. The thermal expansion coefficient changed abruptly around that temperature, which also coincided with the temperature range where the mechanical dispesion, so-called crystal dispersion, was observed.