Polylactic acid biocomposites with high loadings of melt-flowable organosolv lignin

Abstract

Polylactic acid (PLA) was blended with a new type of organosolv lignin, called Bioleum (BL) using a melt extrusion method to obtain biocomposites with BL loadings as high as 40 wt%. Two plasticizers, namely polyethylene glycol (PEG) and triethyl citrate (TEC) were also introduced to the material system. Gel permeation chromatography, rheological analysis, thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy and tensile testing were performed to characterize the biocomposites. The results revealed that BL exhibits a melt-flowable characteristic. The biocomposites' tensile strength was found to be higher than most of the previously reported cases. Overall, the BL domain size increased as the BL content was increased, causing a drop in the strength and ductility. Even though the addition of both PEG and TEC improved the ductility, PEG proved to significantly outperform TEC. With the introduction of 5 wt% PEG, the elongation at break of PLA_BL20 was increased >9 times, even exceeding that of the neat PLA by several folds. Consequently, PLA_BL20_PEG5 produced a toughness that is twice as the of the neat PLA. The findings suggest a great promise of BL to develop scalable and melt processable composites.