The morphology of nascent and moulded ultra-high molecular weight polyethylene. Insights from solid-state NMR, nitric acid etching, GPC and DSC

The differences in morphology between nascent ultra-high molecular weight polyethylene (UHMWPE) GUR415 grade powder and a ram-extruded moulded form have been studied by a variety of techniques. While it would be thought from DSC results that the powder has much thicker crystallites than the moulded material, it is shown quite clearly by nitric acid etching techniques followed by GPC that the crystal lamellae in both forms of the material have similar dimensions, close to 20 nm on average. The GPC also shows, however, that in addition to the lamellar material, there exists a proportion of extended chain crystals in the powder, which may reside within fibrillar structures which have been observed by SEM. NMR measurements show that the amorphous phase in the powder is more constrained than that of the moulded material, and that the powder also has a fraction of monoclinic crystalline material associated with internal stress. Further NMR experiments on the highly crystalline residues from the nitric acid degradation experiments lead to an estimation of the spin-lattice relaxation time in a 100% crystalline PE of 2.5 +/- 0.1 a in an external field of 4.7 T. (C) 2000 Elsevier Science Ltd. All rights reserved.