Wood Flour-Reinforced Green Composites: Parameter Optimization via Multi-criteria Decision-Making Methods

Abstract

The aim of this study was to investigate the physical, mechanical, morphological, structural, and thermal properties of polylactic acid (PLA) and polyhydroxybutyrate (PHB) biopolymer composites reinforced with thermally treated wood flour and to determine the formulations having optimum properties by using multi-criteria decision-making (MCDM) methods. As a filler, Scots pine wood flour (untreated and thermally treated at 212 degrees C) was used at the loading rates of 10% and 30%. The samples were prepared using a twin-screw extruder and then by compression molding. The results showed that the addition of both thermally treated and untreated wood flour slightly increased the density of the composites. According to the color measurement, the thermally treated wood composites were slightly darkened in appearance. In the composites, with both wood fillers, the water absorption and thickness swelling ratios had increased during the 20-250 days of water exposure. Lower water absorption and thickness swelling rates were found for the composites with thermally treated wood filler compared to the other composites. The wood fillers generally lowered the mechanical properties of the PLA and PLA/PHB composites, with the PHB composites as the exception. However, the tensile modulus and Izod impact strength of the composites generally increased with the addition of wood fillers. Morphological examination performed by scanning electron microscopy (SEM) indicated that the wood flour was mostly homogeneously distributed in the matrix, which improved the mechanical properties of the composites. Thermogravimetric analysis (TGA) showed that the addition of wood filler to the neat biopolymers as a rule did not provide significant improvement in the thermal stability; however, the fillers increased the thermal stability of neat PHB. The Fourier-transform infrared (FTIR) spectroscopy detected no differences in the chemical structure of the composites. The X-ray diffraction (XRD) results indicated a general increase in the crystallinity with the addition of wood fillers to the neat biopolymers and the blends. All the findings were subjected to MCDM analysis to determine the formulation having the optimum properties and the results showed this to be the neat PLA sample.