Date of Award

2020

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Chemical Engineering (PhD)

Administrative Home Department

Department of Chemical Engineering

Advisor 1

Rebecca G. Ong

Committee Member 1

Caryn Heldt

Committee Member 2

Tara L. Bal

Committee Member 3

Xinfeng Xie

Abstract

In the modern forest industry, the need for bio-based, renewable, and environmentally-benign wood preservatives is increasing. Preservatives are used to prevent or limit decay and there has been an increasing interest in developing wood preservatives from renewable materials. To support the need for bio-based, environmentally-friendly preservatives, this work employed kraft lignin as a raw material to produce a novel bio-based wood preservative.

For the first project, a statistical design of experiments approach in Minitab® was used to study how fractionation process variables during acid precipitation of lignin influence the lignin mass yield and characteristics. After precipitating lignin from black liquor, we found a positive correlation between temperature, mass yield, molecular weight and dark coloration. For pH < 4, condensation of molecular fragments and sorption onto larger chains seem to drive the precipitation process. The optimum precipitation conditions were found to be pH 1.7, 85 °C, 2.5 hours.

In the second study, the recovered kraft lignin was dissolved without further modification in tetrahydrofuran and inserted dropwise into a water/ethanol solution containing sacrificial surfactant templates, to produce innovative, monodispersed, hollow, double-shell nanocapsules via two-step self-assembly. The nanocapsules were loaded with propiconazole and preserved in water to investigate the release mechanism of the system. The nanocapsules had an average hydrodynamic diameter of 242 ± 33 nm, and encapsulated propiconazole at an efficiency of 56 ± 2 %.

In the third project, the water-dispersible, biologically-activated preservative system, which consisted of the double-shelled nanocapsule encapsulating propiconazole, was tested for its synergistic biocidal efficacy at combating Gleophyllum trabeum decay in southern yellow pine wood. Following three months of soil-jar incubation, only 20.1 ± 2.1 % weight loss was observed from vacuum-pressure impregnation compared to 42.1 ± 9.5 % from control blocks with no preservative, 43.8 ± 7.1 % from blocks vacuum-pressure treated with propiconazole, and 16.4 ± 3.8 % from blocks vacuum-pressure treated with a standard inorganic preservative, chromated copper arsenate (CCA).

In conclusion, the novel preservative system is a viable bio-based fungicide. The double-shell nanocapsule could replace non-biodegradable actives in preservatives employing propiconazole as a co-biocide. Furthermore, this novel synthetic methodology will support designing lignin nanoparticles for different uses.

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