Orientation and Shrinkability in Polymers

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Abstract
This work deals with uniaxial orientation and shrinkage of two grades of well-characterized low-density polyethylene (LDPE), and a general-purpose polystyrene (PS). The LDPE grades differed in molecular-weight distribution and degree of long chain branching. The polymer samples were stretched to different levels of deformation over a range of temperature, quenched, and subsequently annealed. The shrinkage and thermoelastic force during recovery were measured upon annealing. Molecular orientation resulting from the stretching process was characterized by birefringence measurements in the amorphous polymer and by X-ray diffraction in the semicrystalline polymer. Morphology changes in the latter were characterized by polarized optical and electron microscopy. The relationship between the amount, rate and temperature of stretching, to the resulting orientation and morphology, and the shrinkage behavior were investigated.

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