Heat of fusion and lamellar structure of polyethylene single crystal mats

Recently published results for solution crystallized PE single crystals have shown, that the experimental heat of fusionH^* is higher, if the solvent is exchanged to silicon oil (oil suspension samples) as compared with dried mats. This has been interpreted by the collapse of the original hollow pyramids during drying, inducing lateral defects within the lamellae. The present investigation does not confirm this unexpected result.H^* of dried mats (T_c 66 to 91 °C) and of the corresponding oil suspension samples agree within the rather small limits of experimental error. The crystallinities as derived fromH^*, density or WAXS are in excellent agreement.SEM micrographs of cold fractured dried mats show their spongy macromorphology, but TEM micrographs of stained ultra-thin sections reveal the lamellar morphology of the walls, consisting of curved lamellae and stacked hollow pyramides. If a dried mat is sintered at room temperature, a dense transparent film is obtained with a rather regular stacked morphology of large flat lamellae.H^* of these films agrees with that of the original mat.Dedicated to Professor Dr. F. H. Müller.