CHARACTERIZATION OF THE MOLECULAR-ORIENTATION IN HIGHLY ORIENTED ROLLED POLYPROPYLENE SHEETS BY X-RAY-DIFFRACTION

Isotactic polypropylene sheets deformed by rolling to draw ratios betw een 6.6 and 15.8 were studied by wide-angle X-ray diffraction. Even or der [P-n(cos chi)], coefficients of the Legendre polynomial series des cribing the orientation distribution of the molecular chains were dete rmined from measurements made on nine hkO and hkl crystal planes, for n up to 100. The correlation between the results obtained from these d ifferent X-ray reflections is excellent. All the coefficients were use d to calculate the orientation distribution of the molecular chains, w hich cannot be measured directly since there are no reflections parall el to the c-axis for the monoclinic unit cell of isotactic polypropyle ne. The [P-2(cos chi)](c) and [P-4(cos chi)](c) values are close to un ity for the sheets rolled to lambda greater than or equal to 7.6, indi cating that the polymer chains are already well oriented in the deform ation direction at these draw ratios. However, the evolution of the cr ystal phase orientation beyond lambda=8 can be characterized using the high-order [P-n(cos chi)](c) coefficients, which still increase up to the highest rolling ratio measured in this work.