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 p olyethylene (UHMWPE) GUR415 grade powder and a ram-extruded moulded form ha ve 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 follo wed by GPC that the crystal lamellae in both forms of the material have sim ilar dimensions, close to 20 nm on average. The GPC also shows, however, th at in addition to the lamellar material, there exists a proportion of exten ded chain crystals in the powder, which may reside within fibrillar structu res which have been observed by SEM. NMR measurements show that the amorpho us phase in the powder is more constrained than that of the moulded materia l, and that the powder also has a fraction of monoclinic crystalline materi al associated with internal stress. Further NMR experiments on the highly c rystalline 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.