STUDY OF THE DISTRIBUTION OF THE MOLECULAR-ORIENTATION IN THICK POLYETHYLENE SAMPLES BY X-RAY-DIFFRACTION, INFRARED DICHROISM AND RAMAN-SPECTROSCOPY

The molecular orientation in thick polyethylene samples has been studi ed by wide-angle X-ray diffraction, i.r. dichroism and Raman spectrosc opy. The original specimens, with dimensions of the order of a centime tre, were cut to obtain 1 mm thick platelets on which the measurements were made. The mean coefficient of the second-order Legendre polynomi al, [P2], was calculated from X-ray diffraction and from the 1894 cm-1 i.r. band for the crystalline phase, from the 909 cm-1 i.r. band for the vinyl end groups and from the 1130 and 1060 cm-1 Raman bands for t he all-trans C-C conformers. The fourth-order coefficient, [P4], was a lso determined from X-ray diffraction and Raman spectroscopy for a ser ies of cylindrical rods of draw ratios (lambda) ranging from 6 to 20. An excellent correlation is observed between the [P2] coefficients mea sured from different X-ray reflections and from the 1894 cm-1 i.r. ban d. The Raman spectroscopy results show that the all-trans bonds locate d in the amorphous phase are aligned perpendicular to the extrusion di rection for the lambda = 6 rod, and gradually reorient towards the fib re axis for lambda values up to 20, while the [P2] and [P4] coefficien ts calculated for the crystalline phase remain constant at lambda grea ter-than-or-equal-to 12. The variation of the orientation through the thickness of the samples was investigated for the cylindrical rods and for an H-shaped moulding produced by extrusion and rolling. Minor dif ferences in the degree of molecular orientation were detected between the centre and the surface of the rods, whereas important variations w ere measured for the H-shaped sample.