Comparing Waste Gypsum with CaCO3 as Filler Towards Developing Low-cost PBAT Composites

Abstract

Melt-mixed composites of poly(butylene adipate-co-terephthalate) (PBAT) with the waste gypsum and calcium carbonate were prepared and their properties were compared. Calcium carbonate and gypsum contain the same cation (Ca2+) but different anions i.e., smaller CO32- and larger SO42- respectively. According to the Fajans' rule, CaCO3 is more ionic whereas gypsum is more polarizable. Because of the abundant polarizability, gypsum was well dispersed in the PBAT matrix through the filler-matrix electrostatic interaction. The gypsum/PBAT showed lower tensile strength but higher elongation at break at a filler to matrix ratio of 20: 80 than those of CaCO3/PBAT. Further, the addition of polylactic acid (PLA) enhanced both the tensile strength and elongation at break of the gypsum/PLA/PBAT while no such effective changes were observed for CaCO3/PLA/PBAT maybe due to the possibility of depolymerization of polymers in the presence CaCO3. Thermal, morphological, and crystallography studies well corroborate with the mechanical behavior of the composites.