Nan Nan

Date of Graduation

2016

Document Type

Dissertation

Degree Type

PhD

College

Davis College of Agriculture, Natural Resources and Design

Department

Forest Resource Management

Committee Chair

David B DeVallance

Committee Co-Chair

Ben Dawson-Andoh

Committee Member

Robin S Hissam

Committee Member

Jingxin Wang

Committee Member

Xinfeng Xie

Committee Member

John Zondlo

Abstract

The first goal of this research was to explore the potential value of hardwood-derived carbon materials as fillers for reinforcing polymer materials, and investigate the effect of filler content on various properties of reinforced composites. Three loading levels of biochar particles, 2wt%, 6wt%, and 10wt% (by weight) were added to a 10wt% polyvinyl alcohol (PVA) solution (by weight) and composites were formed via the film-casting method. The morphological, tensile, thermal, and dynamic mechanical properties of PVA/biochar composite films were tested and analyzed. Tensile tests indicated that the addition of biochar reduced the tensile strength and elongation at break of the films. The tensile modulus, however, was improved through the addition of biochar. Dynamic mechanical analyses (DMA) indicated when the temperature was above 83°C (melting point of PVA) the storage modulus of the composite films was higher than the PVA films. Also, the addition of biochar particles increased the thermal stability of the PVA films. Results of this study indicated that the combination of PVA with biochar has a potential to produce film materials with improved thermal and tensile properties.;Further evaluation was conducted to investigate the electrical conductivity and piezoresistive behaviors of the developed PVA/biochar films for the use of piezoresistive pressure sensor. The PVA/biochar films exhibited a similar electrical conductivity as most carbon nanotube and graphene reinforced PVA composites. Additionally, with increased pressure from 0 to 358kPa, the average electrical resistance of PVA/biochar composite films with 8wt%, 10wt%, and 12wt% biochar content decreased by 92%, 98%, and 99%, respectively. Additionally, the effect of film thickness (0.40mm to 0.60mm) and temperature (-20°C to 70°C) were investigated. Results indicated that the effect of thickness was most influential in the PVA/biochar films with 8wt% biochar. Higher temperature (40°C to 70°C) enhanced the piezoresistive effect, while lower temperature (-5°C to -20°C) reduced the piezoresistive effect.;To further develop conductive bio-based carbon material, research was conducted on biochar preparation. The biochar was made from red oak, yellow-poplar, and willow by pyrolysis at different heating temperatures (HTTs). The electrical conductivity of these biochar particles was measured under compression. Additionally, scanning electron microscope, Brunauer-Emmett-Teller (BET) test, fourier transform infrared spectroscopy, X-ray diffraction, and raman spectroscopy analysis were performed to investigate the physicochemical properties of carbonized biochar. Results showed that the electrical conductivity of wood-derived carbons was markedly influenced by the applied pressure, feedstock, and HTT. Specifically, the biochar obtained at 1000°C HTT exhibited the highest electrical conductivity among all HTTs tested under pressure. The results of the physicochemical tests show that the increase of HTT significantly increased carbon content, decreased chemical groups, increased both of D-band and G-band of the carbon structure, and increased the surface area of biochar. These results may indicate that via changing the physical and chemical properties of biochar, the HTT and feedstock impacted the electrical conductivity of biochar.;Finally, to investigate the effect of feedstock and particle size distribution of the biochar filler on the conductivity and piezoresistive behavior of PVA/biochar composites, biochar was prepared from red oak, yellow-poplar, and willow feedstock at 1000°C HTT with two particle size distributions. Results indicated that the percolation threshold of the composites was between 16wt% and 18wt%. The impact of particle size on conductivity and piezoresistive behavior depended on the biochar content and feedstock. Additionally, applied temperature increased the conductivity of all the specimens, specifically at lower biochar contents (6wt% and 8wt%). These results indicated that the electrical conductivity and piezoresistive behavior of PVA/biochar composite films strongly depended on the feedstock, particle size, and temperature.

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