| Liquefaction of bamboo was carried out in glycerol-methanol as co-solvent using microwave energy and was evaluated by characterizing the liquefied residues. The effects of liquefaction conditions, including glycerol/methanol ratio, liquefaction temperature, and reaction time on the conversion yield were investigated. The fractionated bio-polyols (FBP) were obtained by the removal of lignin derivatives from the crude bio-polyols (CBP) using a simple method. Results of this investigation were as following:The bamboo branches had the highest Klason lignin and ash content, about 26% and 2.75%, respectively. The epidermis layer sample had a relatively higher carbohydrate content, while the wax layer sample had the highest hot water and ethanol-toluene extractives and starch content. The results indicated that the bamboo processing residues showed potential for different chemical feedstocks. No significant differences were found in the infrared spectroscopy (FTIR) spectra of the different samples, indicating that the chemical functional groups were the same, despite variation in chemical components between samples. Klason lignin isolated from the residues showed a higher maximum degradation rate temperature (501℃) and wider degradation temperature range (200 to 550℃) than the carbohydrates.The optimal liquefaction conditions were estimated as:the temperature of 120℃, the reaction time of 7min, the glycerol-methanol-bamboo ratio of 8/0/2 (W/W), and microwave power of 300W with the maximum conversion yield of 96.7%. Liquefaction temperature and time interacted to affect the liquefaction reaction.Fourier transform-infrared (FT-IR) analyses of the residues indicated that hemicellulose and lignin could easily undergo recondensation. Thermogravimetric analysis (TGA) 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 (SEM) images.Higher vessel and parenchyma percentages and lower cellulose and lignin contents in ILW contributed to lower residue content, while higher fiber percentage and cellulose or lignin contents in ELW resulted in higher residue content. Recondensation took place during the liquefaction of ELW, which was indicated by small granules appearing on the liquefied residue surface according to SEM images. The intense bands corresponding to hemicellulose and lignin in the FT-IR spectrum of the liquefied ELW residue gave further evidence that the liquefaction of ELW is a complex solvolysis process involving simultaneous reactions of chemical degradation and recondensation.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. |
PDF Full Text Request