Pressure–volume–temperature behavior of high density polyethylene

Equilibrium pressure‐volume‐temperature behavior in both the solid and molten regtions was determined for a high density (ρ = 0.958 g./cm. 3 ) polyethylene. Data were measured with a recently developed compressibility device capable of obtaining precise and accurate data. Residual curve treatment showed that the data were true equilibrium data. Compressibilities calculated from the data of this Work compared favorably to existing data which were limited to 205°C. The presented work extended the compressibility behavior to 250°C. It was also found that differences in compressibility of low and high density polyethylenes were not eliminated. in the molten region, indicating that the effect of differences in morphology was not eliminated. The Spencer‐Gilmore equation was fitted to the data of the present work. The internal pressure (π) term of the equation showed a definite relation to polymer morphology.