A solvent‐etching technique, reported by Reding and Walter, is used to reveal the spherulitic structure of molded polyethylene surfaces. This technique was found to be limited in application to some polyethylenes because the etched surfaces were obscured by reprecipitated polymer. When precautions were taken to prevent reprecipitation the characteristic spherulitic structure of molded polyethylene was exposed. The polymer dissolved by the etchant often reprecipitated on polyethylene surfaces in the form of long, fibrous, crystalline ribbons about 200 A. thick. On carbon surfaces, the same polymers precipitated as diamond‐shaped crystals, sometimes with dendritic outgrowths. Thus the nature of the substrate influences the crystal form of the precipitate. The polymer which was studied in the original work of Reding and Walter precipitates on itself in a formless mass with few fibers. This explains the fiber‐free appearance of the surfaces etched by the former method.

This study proposes a modelling strategy to simulate the heating stage during the production of thermoplastic composite tapes. Impregnation using a slurry powder technique with carbon fibres and PEKK (PolyEther-Ketone-Ketone) requires a heating step, achieved with an infrared (IR) oven, to evaporate the water and melt the polymer powder. These phenomenon are highly temperature dependant justifying the need to characterise heat transfer within the infrared oven. In the literature, most of the models refer to clear lamps with Lambertian emission. The case of tubular lamps with coating on the backside (i.e. integrated reflectors) then needed to be investigated. The reflector greatly modifies the lamps spatial emission, so a single emissivity and temperature assumption is no longer sufficient. Here we propose an adaption of the radiosity method to predict spatial emission accounting for a ceramic coated reflector in terms of radiative exchange. Inverse analysis was used to characterise the emission of these lamps. An IR camera (FLIR SC325, [7.5-13] µm) was used to perform measurements on the back surface of a heated ABS (Acrylonitrile Butadiene Styrene) plate for which radiative as well as thermophysical properties are known form previous in-lab research works [1]. Temperature distribution results were transferred into the commercial software COMSOL Multiphysics® to estimate model parameters: filament temperature and an emissivity distribution function.

SynopsisRabesiaka and Kovacs have reported experiments in which the shapes of crystallization isotherms of several polyethylenes depended on the sample history as well as the intrinsic properties of the polymers. The suggestion was made that, in general, molten polyethylene is not in a true thermodynamic equilibrium and includes some quasiindestructible clusters, which act as heterogeneous nuclei in the crystallization process. This paper reports anomalous brittleness temperature experiments on polyethylenes, the results of which are explainable in terms of quasi-indestructible clusters. The data are consistent with the supposition that the crystalline embryos responsible for the observed behavior result from strong entanglements or cross-linking in natural polyethylene and from binding to carbon black surfaces in black compounds. At the low, nonuniform shear rates in compression molding these clusters may survive relatively intact. If subsequent remelting is performed in the absence of shear, any ordered structure between entanglement points will expand but not break. Such configurations can contract to form crystalline embryos as the polymer is cooled.