Crystal Modulus of Poly(glycolic acid) and Its Temperature Dependence

Abstract

Elastic modulus of the crystalline regions (crystal modulus) of poly(glycolic acid) (PGA) in the directions parallel (El) and perpendicular (Et) to the chain axis was measured by X-ray diffraction. The El value of PGA was 104 GPa at room temperature. This relatively low El value suggests that the PGA skeleton is not fully extended as reported before but contracted. The Et value of PGA was obtained as 7 GPa, which resembles that (7 GPa) of poly(vinyl alcohol) based on intermolecular hydrogen bonds. This reveals strong intermolecular interactions act between PGA molecules in the crystal lattice. Both low El value and high Et value are considered to contribute to the extraordinarily high melting point (223 °C) of PGA among aliphatic polyesters. Temperature dependence (13–400 K) of both El and Et of PGA was also investigated. Abrupt changes around 200 K for both directions were considered to be caused by molecular motion in the crystalline regions of PGA.