Sound velocity, young's modulus and transition temperature in polythenes with different degrees of crystallinity

Mechanical dynamic properties of some polythenes with different degrees of crystalinity have been measured over a temperature range from −70°C. to above room temperature, at frequencies in the range 5–30 kcps. At room temperature Young's modulus and resonance coefficient increase with increasing crystallinity. A transition temperature, independent of the degree of crystallinity, at about −24°C. is found in partially amorphous polythenes. The transition region is sharper for more amorphous samples. The modulus increases with increasing degree of crystallinity at temperatures above the transition point but appears to decrease somewhat with increasing degree of crystallinity below the transition point.