Electronic Thesis and Dissertation Repository

Degree

Master of Engineering Science

Program

Chemical and Biochemical Engineering

Supervisor

Dr. Chunbao (Charles) Xu

2nd Supervisor

Dr. Takashi Kuboki

Joint Supervisor

Abstract

Lignin, a major component of biomass, is an attractive alternative to hindered phenol-based antioxidants for polymers due to its renewable nature and naturally occurring hindered phenolic structure. In this study, for the first time, lignin de-polymerization was explored as a promising approach to improve the reactivity of the lignin-based antioxidants for polymers (polyethylene, PE and polypropylene, PP). A proprietary hydrolytic de-polymerization process was utilized to increase the antioxidant activity of two types of technical lignin: kraft lignin, KL (a by-product from the pulp and paper industry) and hydrolysis lignin, HL (a by-product from the pre-treatment processes in cellulosic ethanol plants). The de-polymerized lignins had up to five times more antioxidant activity compared to the crude lignins, a result of their higher phenolic content, improved hydrophobicity, and lower molecular weight. The results also revealed that the addition of 2.5 wt% DKL or 5 wt% DHL attained the same level of antioxidant activity as the addition of 0.5 wt% commercial antioxidant. Owing to the lower price of DKL or DHL compared with that of the commercial antioxidant or the neat PE, the addition of the larger amount of DKL and DHL did not increase the cost of the PE blends. Instead, the material cost of a PE blend that contains a larger amount of DKL (2.5 wt%) or DHL (5 wt%) is actually lower than that of a PE blend with a smaller amount of commercial antioxidant (0.5 wt%).

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