Lignin samples fractionated from microwave liquefied switchgrass were applied in the preparation of semirigid polyurethane (PU) foams without purification. The objective of this study was to elucidate the influence of lignin in the PU matrix on the morphological, chemical, mechanical, and thermal properties of the PU foams. The scanning electron microscopy (SEM) images revealed that lignin with 5 and 10% content in the PU foams did not influence the cell shape and size. The foam cell size became larger by increasing the lignin content to 15%. Fourier transform infrared spectroscopy (FTIR) indicated that chemical interactions occurred between the lignin hydroxyl and isocyanate revealing that lignin was well dispersed in the matrix materials. The apparent density of the foam with 10% lignin increased by 14.2% compared to the control, while the foam with 15% lignin had a decreased apparent density. The effect of lignin content on the mechanical properties was similar to that on apparent density. The lignin containing foams were much more thermally stable than the control foam as evidenced by having higher initial decomposition temperature and maximum decomposition rate temperature from the thermogravimetric analysis (TGA) profiles.
Bamboo residues were subjected to a microwave-assisted liquefaction process for the production of crude bio-polyols (CBP). The fractionated bio-polyols (FBP) were obtained by the removal of lignin derivatives from the crude bio-polyols (CBP) using a simple method. Polyurethane (PU) foams were successfully prepared from both CBP and FBP. The object of this study was to evaluate the effect of lignin derivatives in bio-polyols on the physical properties, thermal stability, and microstructure of PU foams. The results revealed that the PU foam made from CBP had a higher density and superior thermal stability compared to that made from FBP; however, they were also much more fragile. Scanning electron microscope (SEM) images indicated that the lignin compounds in the CBP had impact on the structure of the PU foam.
Liquefaction of bamboo was performed in glycerol-methanol as co-solvent using microwave energy and was evaluated by characterizing the liquefied residues. High efficiency conversion of bamboo was achieved under mild reaction conditions. Liquefaction temperature and time interacted to affect the liquefaction reaction. Fourier transform infrared analyzes of the residues indicated that hemicellulose and lignin could easily undergo recondensation. Thermogravimetric analysis results showed that residues obtained at higher temperature/longer reaction time displayed a superior thermal stability as compared to those obtained from mild conditions. Moreover, significant differences were observed in the morphology and structures of residues from different liquefaction conditions according to scanning electron microscopy images.
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