No abstract

There is considerable literature on the behavior of polyethylene below 200°C and above 400°C. This paper presents results on both high and low density polyethylene between 2000 and 400°C, a range of practical import for various fabrication and processing steps. Practical exposure times may be short and the experimental procedures were designed to give meaningful results for times as low as 1 min. The principal effects are chain‐session and oxidation. Session was isolated by applying an atmosphere of pure nitrogen and proved uite shlow at 300°C but rapid at 400°C. The course of scission and produces discoloration, odor, and rising carbonyl content. A brief discussion is given of the role of diffusion in oxidation.

SynopsisThe connection between intrinsic viscosity and number-average and weight-average molecular weight has been revealed by calculations from distribution curves. Log-normal distributions, and moderate variations thereon, were chosen as typical for polystyrene and other thermoplastics. Intrinsic viscosity and number-average molecular weight are unlikely to be related because of the highly disturbing effect of small variations in molecular .weight distribution. Conversely, intrinsic viscosity is a good practical measure of weight-average molecular weight up to a ratio of 10 for weight-tonumber average.

oxygen partial pressures below 0.1 atmosphere. The rate of carbon oxidation was found to be directly proportional to the oxygen partial pressure and to the amount of carbon in the reactor.These results may be of interest to those concerned with problems such as the decoking of catalysts, and may be applicable to processes such as the fluidized coking of petroleum residues.

synopsisAlthough usually derived from measurements at several concentrations, intrinsic viscosity (IV) can be determined with good precision from a single measurement. IV tends to be a regular and distinct function of melt index (MI) for each family of high-density polyethylenes. The tendency to regularity suggests a use in routine control, uniform production being marked by a small scatter about the IV-MI line. The distinctiveness marks one family of medium high and high-density resins from another, and becomes a rapid means of identifying the production method of a resin. Further, IV a t a given M I correlates roughly with properties, and can be used to characterize a resin. These a& tributes of the IV-MI relationship arise from the correlation of IV a t a given M I with width of molecular weight distribution. Such width varies considerably among commercial high-density polyethylenes, causing a commensurate variation in IV. Among low-density polyethylenes the IV-MI relationships is less useful, being confused by long-chain branching.