Rates of dehydration under vacuum, and a t a series of controlled water vapor pressures, have been carried out for powdered samples of magnesium sulphate heptahydrate and of cobaltous chloride hexahydrate. I t has been found for the magnesium salt that as the pressures are increased, the rate a t first drops rapidly, this decrease being followed by a period of acceleration which is followed in turn by a decline. The curves are similar to those previously reported for copper sulphate pentahydrate, but the changes occur over a much wider range of water vapor pressures. In the dehydration of cobaltous chloride hexahydrate the initial drop in rate with increase in water vapor pressure is not observed. The results are interpreted in terms of the crystallization of intermediate products in the presence of adsorbed water.

not available

SynopsisChanges in flow properties of poIyethylene resins have often been observed during processing operations. Studies in this laboratory show that melt viscosity of polyethylene normally increases when the resin is heated in a compression mold at temperatures below 300°C. At the same time, the solution viscosity actually decreases in some cases. During extrusion, on the other hand, both melt viscosity and solution viscosity are shown to decrease. In addition, the logarithm of melt flow rate is seen to deviate markedly from the expected linear dependence on reciprocal of absolute temperature. The results suggest that both crosslinking and chain-scission reactions occur during processing, the former predominating at low or zero shear, the latter at high shear.

No abstract

synopsisVarious physical properties of 43 experimental ethylene-l-olefin copolymers and ethylene homopolymers produced by the Ziegler route were subjected to a statistical analysis. Correlations obtained indicate that the density of these polymers is a function almost solely of the number of branches introduced by the comonomer, regardless of their length. Similarly, tensile modulus and yield strength are shown to depend primarily on density, and to be independent of branch length. Physical properties of commercial resins produced by both low-and high-pressure processes are shown to follow the same relationships. Examination of homopolymers of widely Merent melt indexes indicates that vinyl unsaturation is not a reliable measure of numberaverage molecular weight.