Degree

Doctor of Philosophy (PhD)

Department

School of Renewable Natural Resources

Document Type

Dissertation

Abstract

Cellulose nanofibers isolated from renewable lignocellulosic biomass are considered highly promising fillers in preparing sustainable composite materials. Although previous technologies on the production of cellulose nanofibers were encouraging, drawbacks such as chemical reagent, high energy consumption, time-consumption, and equipment degradation have limited these techniques for practical applications. In this work, bamboo particles were subjected to microwave liquefaction process and the liquefied bamboo residues were characterized to have a better understanding of the liquefaction behaviors of bamboo. Then, the microwave liquefaction process was optimized for the production of cellulose raw materials and the isolation of cellulose nanofibers. The lignin fraction fractionated from the microwave liquefaction process was also characterized for use in bio-based materials.

The overall results revealed that high conversion yield of bamboo to liquid could be archived in mild microwave liquefaction reaction conditions. Lignin and hemicellulose in bamboo could easily undergo decomposition during liquefaction, while cellulose was the main resistance to the liquefaction process. The chemical and morphology analysis results revealed that the liquefied bamboo residues retained fiber structure and cellulose. Bleaching and acid hydrolysis were proved to be effective in purifying the residues for pure white cellulose fibers by removing carboxyl groups and lignin fragments. Long nanofibrils were generated by subjecting the pure cellulose fibers to high-intensity ultrasonic treatment. Good quality fibers with high holocellulose content were successfully produced by removing lignin and extractives from bamboo when the microwave liquefaction temperature was below 120oC. The relative lignin and extractives contents of the liquefied residues from the reaction at 120 oC, 9min were as low as 0.65 and 0.49 %, respectively. Cellulose nanofibers with diameters in the range of 2-30 nm were successfully extracted from the cellulose materials with a subsequent chemical treatment as a purification process and ultrasonication as a nanofibrillation process. The main functionality of the microwave liquefaction process on the nanofiber preparation process was efficiently converting bamboo bundles into micro-sized fibers by almost completely removing lignins and extractives. The isolated cellulose nanofibers have potential application for the fabrication of thermally stable composites because of their high thermal stability. Lignins recovered from the microwave liquefaction system showed high purity and retained their natural structures. The lignin samples were completely soluble in ethanol/water, DMSO, THF, 1, 4-dioxane, and 1mol/L NaOH solution. Polylactic acid (PLA)-lignin composites were successfully fabricated, and the lignin component in the PLA-lignin blends significantly improved the UV light barrier properties of the composites. The utilization of the lignin fraction should enhance the economic value of the microwave liquefaction system on the integrated utilization of bamboo.

Date

12-11-2018

Committee Chair

de Hoop, Cornelis F

Available for download on Tuesday, December 10, 2019

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