Wood Cellulose-Based New Materials: Functionalization and Applications

• Author / Creator

  Gong, Xiaoyu

• Canada has great forest area with tremendous wood-based cellulose resource. However, the research effort for wood fibers to develop wood cellulose-based advanced materials is still limited. The overall objective of this research is to provide some feasible and efficient approaches for the functionalization and application of wood-based cellulose materials. First, spruce cellulose was hydrolyzed by diluted sulfuric acid of various concentrations and hydrolysis times. The dissolution of these hydrolyzed samples was investigated in a NaOH/urea aqueous solution system considered environmentally "green". The effects of acid hydrolysis on the structure and properties of subsequent thermally induced gels were examined using scanning electron microscopy, swelling and reswelling experiments, and mechanical test. The molecular weight of spruce cellulose was significantly reduced by acid hydrolysis, whereas its crystallinity slightly increased because of the removal of amorphous regions. Hydrolyzed cellulose samples with lower molecular weight exhibited higher solubility. Rheological experiments showed these cellulose suspensions could form gels easily upon heating. A porous network structure was observed in which dissolved cellulose was physically crosslinked upon heating and then regenerated to form a 3D network, where the dispersed swollen cellulose fibers filled spaces to reinforce the structure. The swelling behavior and mechanical properties of these "matrix-filler" gels could be controlled by varying the mild acid hydrolysis conditions, which adjusts their degree of solubility. Second, wood cellulose was consecutively oxidized to prepare oxidized cellulose nanocrystals followed with modification by phenyltrimethylammonium chloride to create hydrophobic domains comprised of phenyl groups. These modified oxidized cellulose nanocrystals were homogeneous/electrostatically stable in water and they can stabilize O/W Pickering emulsions. The dispersed phase volume fraction (DPVF) of the Pickering emulsion was 0.7 at around 1.5 g/L, whereas the tween-20 control needed a 13-fold greater concentration to have a similar DPVR. In addition, these modified oxidized cellulose nanocrystal stabilized Pickering emulsions also showed good mechanical and thermal stability against centrifugation and heat, as well as size controllability. Next, hydrocolloidally stable cellulose nanocrystals (CNCs) with zeta potentials lower than -30 mV at low electrolyte concentrations were prepared from wood-based cellulose. The cellulose nanocrystals were then homogeneously distributed in aqueous Poly(vinyl alcohol)(PVA) solutions and embedded evenly in the PVA matrix after crosslinking and freeze-drying. The morphology observations revealed the crosslinked CNCs/PVA aerogels had a strong, dense, and porous structure with cellulose nanocrystals percolated in the networks and supported by the crosslinked PVA matrix. The mechanical study showed small amount of cellulose nanocrystals (0.5-2.0 w/w%) can significantly increase the compressive modulus of the aerogels from 49.9±5.2 KPa to 200.9±8.0 KPa. Further compressibility studies graphically demonstrated the excellent shape recovery of the crosslinked CNCs/PVA aerogels and the aerogels could be cyclically compressed for ten times without significant variation in mechanical performance. Molecular interaction study by FTIR and crystallinity study by wide-angle x-ray diffraction indicated cellulose nanocrystals firstly formed the percolated network with each other by hydrogen bonding, and then strongly interacted with PVA matrix by hydrogen bonding. Meanwhile, the PVA matrix was further crosslinked by epichlorohydrin to form the strong, dense, and porous microstructures. Finally, compressive aerogels were prepared from cross-linked poly(vinyl alcohol)/cellulose nanocrystals, followed by modification through thermal chemical vapor deposition of methyltrichlorosilane. With the 3D interconnected microstructure, the aerogels were highly porous (porosity > 97.69%) and ultralight with density ranging from 22.50 to 36.13 mg/cm3, and floatable on water surface. The wettability test revealed that the aerogel surfaces were highly hydrophobic with contact angles to water droplet up to 144.5°. In addition, the aerogels could be compressible up to 50 cycles without significant decrease in mechanical strength, thus demonstrated excellent robustness. The aerogels were capable of absorbing various oils and nonpolar solvents and efficiently separating them from water, with the absorption capacity up to 32.70 times of its original weight. Two simple approaches, including squeezing and rinsing, were applied to recycle the aerogels, demonstrating the aerogels could be cyclically used without obvious decrease of absorption capacity up to 10 times. In summary, this research has developed several feasible approaches for the functionalization and application of wood-based cellulose materials. The hydrogels, Pickering emulsions, compressive aerogels, and oil absorbents fabricated from wood-based cellulose materials are potential for a wide range of applications.

• Subjects / Keywords

  • Pickering emulsions
  • cellulose nanocrystals
  • cellulose

• Graduation date

  Spring 2019

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-b6jb-8x40

• License

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