Deciphering gypsum reuse through green composites development and the effect of three different bioplasticizers on their properties

Abstract

Starting from post-consumer gypsum, green composites have been produced by melt-blending polylactic acid (PLA), anhydrous calcium sulfate (CaSO₄) filler, and bioplasticizers (coconut oil, cardanol, and epoxidized soybean oil) to solve the actual problem of poor performance and low production efficiency of biocomposites—such as poor properties and tendency to agglomerate. The dehydration of gypsum residues was studied by grinding and calcining them at 500 °C for 1 h and 3 h, and it was observed that only the sample calcined for 3 h (GR3) was completely dehydrated. The composites were characterized by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and mechanical tests of tensile, flexural, and impact strength. The results showed that the gypsum fillers increased PLA’s toughness, and the compositions with coconut oil (PLA–RG3–COC) and epoxidized soybean oil (PLA–RG3–ESO) obtained increases in stiffness and toughness, observed by changes in Young’s modulus (from 2 up to 2.5 GPa) and strain at break (from 3 up to 40%), respectively. Gypsum fillers promoted the shift of degradation temperature for higher temperatures (~ 360 °C), and the addition of the bioplasticizers slightly influenced the thermal stability of the composites. A plasticizing effect on the decreasing glass transition temperature of the composites was observed with the addition of coconut oil, cardanol, and epoxidized soybean oil. The developed composites cover new advanced materials to revolutionize conventional PLA-residue composites, bolster sustainability, and enhance their applicability.

Graphical Abstract