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Chemical and Mechanical Characterization of Pyrolysis in Wood

Author(s):

Year:

2020

Publication type:

Dissertations

Primary Station(s):

Forest Products Laboratory

Source:

Ph.D. dissertation

Description

Pyrolysis of wood is a series of chemical and physical changes that occur simultaneously. Previous investigations of pyrolysis have often simplified the process. For wood building materials, the pyrolysis process is typically simplified to the formation of “char” at 300°C. Pyrolysis models are often simplified by using the thermal degradation of isolates reference polymers in an inert atmosphere. This approach assumes that the structure of bulk wood performs similarly to that of the isolated polymers being used and ignores reactions with oxygen. This dissertation explores the molecular-scale changes in wood and lignocellulosic polymers using innovative techniques to obtain a deeper understanding of the materials as they undergo pyrolysis. Thermogravimetric analysis (TGA) was used on isolated lignocellulosic polymers and solid Douglas-fir latewood to obtain a baseline of the thermal degradation of the specific materials that can be used to compare against the current literature. It was found that the thermal degradation of the Douglas-fir latewood was not completely represented by a weighted average of the individual polymers as the in situ interactions between the polymers are not considered and, instead, a ratelimiting model is necessary. X-ray photoelectron spectroscopy (XPS) was used to evaluate the chemical changes as a function of temperature in lignocellulosic polymers and Douglas-fir latewood. The chemical changes that occur through charred Douglas-fir latewood using XPS showed the thermal degradation of the holocellulose in the Douglas-fir occurred at lower temperature ranges than those observed in the isolated cellulose and is likely due to the in situ hemicellulose. Additionally, the bond scission observed using XPS on the charred Douglas-fir correlated well with the mass loss results obtained using TGA. iv Nanoindentation was used to study the effect of polymer degradation on the mechanical response of wood cell wall. Ultimately, under dry conditions, the mechanical changes observed occur in a narrow, 2 mm / 100°C region. The experiments conducted and the findings presented in this dissertation on the charred Douglas-fir latewood provide the first chemical and mechanical changes caused by pyrolysis in thermally thick wood, increasing the understanding of pyrolysis for model verification and creating new avenues for research directions.

Citation

Hasburgh, L.E. 2020. Chemical and Mechanical Characterization of Pyrolysis in Wood. Madison, WI: University of Wisconsin-Madison. 119 p +appendix. Ph.D. dissertation.

Publication Notes

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https://www.fs.usda.gov/treesearch/pubs/62971