Empirical determination of the three-dimensional isentropic equation of state of polyethylene

ABSTRACT

An isentropic equation of state (Isen-Eos) in a high-density polyethylene (HDPE) consists of four variables of P_S, V_S, T_S and entropy S where the V_S, P_S and T_S are variables satisfying the isentropic condition that S is constant. The typical values of isentropic derivatives at constant S = 21.35 [J/molK] and T = 313.15 [K] are α_S = −1.66 × 10⁻³ [K⁻¹] and γ_S = 13.8 [10⁻³GPa] where α_S and γ_S are isentropic thermal expansion coefficient and thermal pressure coefficient, respectively, which can compare with isobaric thermal expansion coefficient α_P = 0.368 × 10⁻³ (K⁻¹) and γ_v = 2.4 [10⁻³GPa] at T = 313.15 (K). The P_Hug − V_Hug data of the Hugoniot in the shock wave compression in HDPE can be predicted by the P_S − V_S with S = 24.5 (J/molK) in the isentropic equation of state approximately. The temperature T_Hug and entropy S_Hug in the Hugoniot in the HDPE have also been estimated by the isentropic equations of state and it has been found T_Hug increases with pressure and reaches to about 700 K at 50 (GPa), while S_Hug increases with pressure in low pressure range and then reaches to constant S_Hug = 24.5 (J/molK) over 30∼50 GPa. The Grüneisen parameters ${\gamma }_G$ in HDPE evaluated by S_Hug = 24.5(J/molK) and the isentropic equation of state are in the range of 1.0–1.5 over 0.93 < V (cm³/g) < 1.04.

KEYWORDS:

• Isentropic equation of state
• high-density polyethylene
• low-density polyethylene
• Grüneisen parameter/Hugoniot

Disclosure statement

No potential conflict of interest was reported by the author(s).