Automatic measurement of the absolute CTE of thin polymer samples. II. Effect of chain orientation on thermal expansion of drawn polymer films



More details about the coefficient of thermal expansion (CTE) and thermal expansion anisotropy, Δα, of drawn films from polypropylene (PP) and high density polyethylene (HDPE) are discussed. CTE of the selected polymers are measured along different directions relative to the drawing direction (MD). The coefficient of thermal expansion parallel to drawing direction (α) was less than that in the transverse direction for both of the used polycrystalline polymers. Also α for PP and HDPE for different draw ratios are measured. The morphology of measured samples is investigated by using an optical polarizing microscope and from the 2D-plot of the angular distribution of the absorption coefficient of light through a polymer sample between two crossed polarizers. An agreement between obtained figures was found. Birefringence of samples was measured photometrically. The orientation of drawn polymer chains is estimated from the birefringence measurement. The set up of the used optical system is explained. The CTE variations of drawn polycrystalline polymer are explained on bases of the associated morphological variations. A recommendation was given to produce an all-PP-composite with satisfactory dimension stability at elevated temperature. Construction and operation of a simple drawing machine is given too. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4452–4460, 2006