Abstract
This thesis explored the valorization of two underutilized industrial/agricultural residues, kraft lignin and hemp stalks, for the development of fully biobased polybutylene succinate (PBS) - based composites. In the first study, lignin was incorporated into PBS via melt blending, and crosslinked with dicumyl peroxide (DCP) to examine the influence of filler loading on the thermal and mechanical performance of the resulting composites. The results showed that lignin addition improved PBS stiffness and thermal stability but reduced the flexural strength, with an optimal loading ranging from 10-20 wt%. DCP crosslinking improved the polymer-filler interaction which was shown by the increased gel fraction, improved melt viscosity and more uniform filler dispersion as seen in SEM micrographs. In the second study, a hybrid system was developed by co-reinforcing PBS-lignin composites with milled hemp stalk, which is composed of both bast fiber and hurd. Hybrid composites were prepared in both blended and DCP-crosslinked formulations using twin screw extrusion. Rheological testing showed that hemp improved the viscosity and shear thinning behavior of the composites, while DCP crosslinking promoted better flow resistance and structural integrity. The mechanical properties were significantly improved in the DCP-treated hybrids, particularly flexural strength and modulus. Thermal analysis showed a decrease in mass loss rate and increased char formation in the lignin-hemp composites, which suggests better heat resistance. However, water absorption and accelerated weathering tests showed that the addition of the lignocellulosic materials caused an increase in moisture uptake and UV sensitivity, especially in DCP-treated formulations. Despite these limitations, all the composite types demonstrated excellent resistance to fungal decay, showing <2% mass loss after 16 weeks of decay exposure.