Accelerated weathering of sustainable and micro-filler Basalt reinforced polymer biocomposites: Physical, mechanical, thermal, wettability, and water absorption studies

Abstract

This study intends to evaluate and comprehend the accelerated weathering behavior of various thermoset and thermoplastic composites loaded with an eco-friendly basalt micro-filler. Basalt incorporation into various polymer matrices is, in fact, a very innovative idea that might present some very exciting, as yet unexplored, perspectives. The four kinds of thermoset polymers (synthetic epoxy, bio-epoxy, polyester, vinyl ester) were reinforced with constant basalt reinforcement (30 wt %) and fabricated via the casting process. Whereas the three kinds of thermoplastic (polylactic acid, polypropylene, high-density polyethylene) polymers were also loaded with a constant basalt ratio and manufactured through an internal mixing process followed by a compression molding technique. The fabricated samples were employed inside the xenon arc light accelerated weathering equipment under ultraviolet (UV) rays, temperature, and humid conditions for 555.55 h as per ASTM G155-13 cycle 1. There is a significant improvement in the density of polymer composites due to highly dense basalt particle incorporation and maximum void percentage was observed in thermosets due to casting defects than in the thermoplastic samples. After weathering, the tensile, flexural, and impact properties of composites were significantly reduced due to the thermo-oxidative reaction and degradation under UV and moisture exposure. As a result of UV-induced chain scission, small fractures may develop. These spaces provide the ideal environment for moisture to infiltrate into the primary composite structures, weakening the links between the reinforcement and matrix. Scanning electron microscopy was used to analyze the significant changes in the surface morphology of weathered and unweathered tensile fractured samples. The hardness was considerably improved due to the presence of highly stiffen and hard basalt particles. The idea that accelerated weathering destruction creates hydrophobic surface characteristics in most of the composites due to a variety of factors, like physical and chemical transformations, is supported by the increased contact angle value and a decrease in surface free energy, particularly the polar section. The thermogravimetric analysis revealed that there is not much significant impact of weathering on composites, however, variations were observed in the thermomechanical analysis due to compatibility issues. It is observed that the onset and endset degradation temperatures got decreased with the reinforcement of 30 wt% basalts after the internal mixing process. This could be brought on by the molecular weight decreasing while mixing. The behavior of polymer composites in water absorption study is found to be unique depending on their hydrophilicity and defects raised during the fabrication.