Doctor of Philosophy (PhD)


The School of Renewable Natural Resources

Document Type



Polyurethane (PU) foam is one of the most versatile construction insulations due to its low density, low thermal conductivity, and high mechanical performance. However, it is still highly dependent on petro-based chemicals, i.e. polyol and isocyanate. In this work, biomass, such as rape straw, switchgrass, and yaupon holly (Ilex vomitoria) were liquefied using microwave energy to produce bio-based polyol in order to substitute petro-based polyol in the production of PU foam. Cellulose nanocrystals (CNCs) were also extracted from liquefaction solid residue. They were then applied to reinforce high bio-content PU foam. Moreover, lignin was fractionated from bio-polyol by adding distilled water, and then it was used as filler to reinforce PU foam. In addition, the microwave liquefaction conditions of woody underbrush were optimized to obtain the maximum conversion yield.

The overall results indicated that higher liquefaction temperature was beneficial to obtaining higher energy consumption efficiency as heated by microwave irradiation. Moderate liquefaction conditions could result in a high content of hydroxyl group products, while severe reaction conditions could produce a high yield of levulinic ester products. The rapid decomposition of hemicellulose and lignin during liquefaction process contributed to the decrease of activation energy (Eα), whereas the recondensation/repolymerization reaction could remarkably increase Eα. Most of lignin and hemicelluloses in the solid residues from 180oC/7.5 min were removed by liquefaction. The retained hemicelluloses and impurities were then eliminated by 2% NaOH and 5% H2O2 treatments. With high-intensity ultrasonic nanofibrillation treatment, CNCs with an average diameter of 12.59 nm were obtained from chemical purified samples. PU foam with 40% bio-polyol could be remarkably reinforced by 4% CNCs because the hydroxyl-rich structure in CNCs increased the crosslinking density. As compared with PU foam without CNCs, the Young’s modulus and compressive stress in the 4% CNCs reinforced bio-foam increased by 590% and 150%, respectively. The foam with 10% lignin fractionated from bio-polyol had the highest apparent density of 0.061g/cm3, best mechanical strength, and superior thermal stability. The optimized parameters of the microwave liquefaction of underbrush can be summarized as follows: 1) particle size was controlled in the range of 16- to 40-mesh; 2) both the glycerol to EG ratio and liquid to solid ratio were set at 3:1; and 3) the liquefaction process was conducted at 160 °C for 10 min and catalyzed by 1.5% H2SO4. The optimal liquefaction conversion yield was 94.9%.



Committee Chair

De Hoop, Cornelis F

Available for download on Friday, August 30, 2019