UC Berkeley

Applications of NIPAm Copolymers in Lignocellulosic Biomass

Depolymerization for Biofuels Production

By: Katherine Jean Mackenzie

Doctor of Philosophy in Chemistry

University of California, Berkeley

Professor Matthew B. Francis, Chair

Abstract

There is currently great interest in the use of cellulosic biomass as a source of renewable fuels. This practice generally involves the enzymatic hydrolysis of plant matter to afford soluble sugars for subsequent fermentation steps. The cost of cellulase enzymes presents a critical barrier to the commercialization of these processes. In this work, two methods to reduce enzyme costs are presented. Both are based on copolymers exhibiting a thermoresponsive lower critical solution temperature (LCST), created through the copolymerization of an aminooxy-bearing methacrylamide with N-isopropylacrylamide (NIPAm) or N-isopropylmethacrylamide (NIPMa). The design of this copolymer includes three different ways to adjust the LCST, allowing it to be readily tailored to the temperature requirements of a specific application. In the first strategy, this copolymer system is combined with a site-selective protein modification method to construct a recoverable polymer-endoglucanase bioconjugate. This bioconjugate matches the activity of unmodified enzymes on insoluble purified cellulose, and shows an increased hydrolysis yield on an industrially-relevant lignocellulosic biomass. The recycling ability of the bioconjugate was evaluated over three rounds of activity, affording significantly more soluble carbohydrates than unmodified enzyme alone on both assayed substrates. The second application of the NIPAm copolymers is as a new family of polymer additives that can increase enzyme performance substantially. When applied to an industrially relevant combination of enzymes and lignin-containing biomass, polymer additives allow a 60% reduction in enzyme loading to achieve the same level of saccharification. It was found that these polymers function through multiple mechanisms, including (1) preventing enzyme denaturation from shear and interfacial interactions, (2) preventing non-productive adsorption to lignin, and (3) altering the cellulose structure. These two applications of NIPAm copolymers were tailored specifically for use with cellulases. However, it was found that the ability of NIPAm copolymers to stabilize proteins against shear and interfacial stress extends to other, non-cellulolytic enzymes. This expands the potential use of NIPAm copolymers to a range of industrial operations