Date of Award

2022

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Forest Science (PhD)

Administrative Home Department

College of Forest Resources and Environmental Science

Advisor 1

Xinfeng Xie

Committee Member 1

Mark Rudnicki

Committee Member 2

David Shonnard

Committee Member 3

Alper Kiziltas

Abstract

Electrically conductive composites are polymer composites filled with electrically conductive filler. Electrically conductive composites can be implemented in the development of lightweight electrically conductive components for the automotive industry. Traditional electrically conductive composites incorporate synthetic carbon-based fillers that have good properties but are very expensive and highly energy intensive, creating the need for a sustainable and cost-effective replacement. This study explores the effectiveness of biocarbon fibers developed from Douglas fir pulp fibers as a potential electrically conductive filler in recycled polyamide (PA) 12 composites.

Biocarbon fibers were developed from pulp by carbonization of the feedstock at 1000° C in an inert nitrogen environment. These biocarbon fibers were incorporated in a recycled polyamide 12 matrix in varying concentrations and characterized for electrical, thermal, and mechanical properties. The results indicate that the incorporation of biocarbon fibers can improve the electrical properties drastically, as the electrical properties of composites filled with 35 wt.% biocarbon were – 0.33 S/cm, which is several orders higher compared to pure polymer conductivity of -14 S.cm. The thermal properties of composites also showed an improvement with an increase in maximum thermal degradation temperature from 407.26 °C to 442.74 °C at 35 wt.% filler concentration indicating improved thermal properties. The storage modulus values of the composites also increased from 1500 MPa to 3500 MPa on the incorporation of 35 wt.% biocarbon fibers. The modeling study of the biocarbon fiber-filled composites was built upon updating a previous carbon fiber-filled composites modeling study and improved the fit between the experimental and theoretical electrical conductivity curves yet leaving room for improvement. Upon comparing biocarbon fiber fillers with biocarbon powder fillers, it was observed that the former has better electrical properties as biocarbon fiber-filled composites reported an electrical conductivity value of -0.33 S/cm while biocarbon powder-filled composites reported electrical conductivity values -2. 541 S/cm. This shows that biocarbon fibers with a higher aspect ratio have better electrical properties in composites.

Finally, the lifecycle analysis of the recycled PA 12-biocarbon composites was carried out to determine the environmental impacts of the composites throughout their lifecycle. The emissions and environmental impacts were estimated using IPCC GWP 100 and TRACI USA 2008 method. The cumulative energy demand was estimated for the composites as well. The total emissions generated in the lifecycle of the composites were estimated to be 124 kg CO2 equivalents with the highest contributor being the use phase of the composites.

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