Acoustic study of the elastic and inelastic properties of high-pressure polyethylene samples with different irradiation histories

The influence of vibrational deformation amplitude $\varepsilon$ on the dynamic elasticity modulus (Young’s modulus $E$) and internal friction (logarithmic decrement $\delta$) of high-pressure polyethylene samples with different histories is studied. Acoustic measurements are made by a resonance method using the longitudinal vibrations of a composite piezoelectric vibrator at a frequency of $\approx$ 100 kHz. The dependences $E(\varepsilon)$ and $\delta(\varepsilon)$ are taken at room temperature. From the acoustic data, the elasticity and microplasticity of the samples are estimated. It is found that the microplasticity remains almost unaffected upon irradiation and aging, while the elasticity modulus and breaking elongation per unit length considerably depend on the history and clearly correlated with each other. The observed effects are explained by the fact that atom-atom interaction and defects inside polymer macromolecules substantially influence the elastic modulus and breaking strength, while the inelastic microplastic strain is most likely associated with molecule-molecule interaction, which is affected by irradiation insignificantly.