Melting parameters of poly(glycolic acid)

Abstract

Equilibrium melting temperature T m 0, heat of fusion Δ H f, and entropy of fusion Δ S f of poly(glycolic acid) (PGA) was determined by using Clapeyron–Clausius equation. Equilibrium melting temperature T m 0 was 504.6 K which was determined by Hoffman–Weeks plots. The pressure dependence of T m 0 was determined by high pressure DTA up to 150 MPa. Volume change Δ V f at melting was determined by using dilatometer. Heat of fusion in PGA was 183.2 (J g −1), which is very close to the value reported by Chujo et al. who determined it by using T m depression in copolymer with poly(lactic acid). Δ S f of PGA was 0.363 (J g −1 K −1), which is about twice that of PLA, and the reason was discussed on the basis of the elastic modulus below T m.