الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
The molecular composites model is utilized to predict and to analyze the thermal expansion behavior of oriented polypropylene sheets. Polypropylene is known to have a cross-hatched morphology, generated by crystallographic twining mechanisms. Accordingly, the model has been refined to account for the dual population of the crystalline phase axes. New empirical equations, describing the variation of the orthogonal in-plane crystalline phase mechanical and expansion properties with drawing, have been developed. A parametric mapping analysis of the thermal expansion bchavior of oriented polypropylene has been carried out using the refined molecular composites model. Theresults are expressed as three-dimension structure-property maps. Such maps illustrate the variation of the orthogonal in-plane thermal expansion coefficients of polypropylene as functions of selective pairs of model variables at a time . The input model parameters were experimentally measured using pycnornctry, differential thermal analysis, scanning electron microscopy and wide angle X-ray diffraction. Polypropylene samples have been prepared by compression molding using three different thermal histories and uniaxially oriented by hot drawing. The orthogonal linear thermal expansion coefficients for polypropylene samples of different draw ratios (I to 5) were measured, between room temperature and 115°C. The overall pattern of the thermal expansion behavior of anisotropic polypropylene has been correctly predicted through the• refined model Apart from temperature the major parameters affecting such a behavior are the crystalline phase orientation distribution and the volume fraction crystallinity of the polymer. On the other hand, the effect of the longitudinal and the transverse aspect ratios is found to be trivial. Above the glass transition temperature, it is only sufficient to align 85% of the crystallitc with their c-axis at ± 15° to the draw direction to attain the ultimate degree of anisotropy in the thermal expansion bchavior of oriented polypropylene. It was found that the longitudinal thermal expansion coefficient was almost negative for all drawn samples and decreases with both drawing and temperature: The transverse thermal expansion coefficient was always positive and increased with drawing and temperature.