SUPERVISOR: Georg M. GÜBITZ

PROJECT ASSIGNED TO: Maximilian HUEMER

Nature offers an abundant reservoir of enzymes modifying biopolymers, which can serve as a biocatalytic toolbox for technologists, e.g. in the context of dissolving wood pulp and cellulosic fiber production. These enzymes may replace environmentally harmful chemistries and/or increase the selectivity of reactions, e.g. at the cellulose surface. However, the application of enzymes in industrial environments continues to produce erratic outcomes and continuous cellulosic fiber modification processes are severely underdeveloped. As an example, dissolving wood pulp can be treated with hydrolases, such as lipases or xylanases, to improve its purity and the quality of cellulosic fibers spun from the dissolving pulp.

Lipases are serine hydrolases that are capable of hydrolyzing tri-, di-, and monoglycerides at the surface of an oil-water interface, thereby releasing glycerol and free fatty acids. Such glycerides are non-structural components of wood and can disturb pulping and fiber processes or deteriorate pulp and fiber quality.

 

Figure 1: Hydolysis of triglycerides by lipase

While it is generally accepted that “enzymatic pulp bleaching” can replace hazardous chlorine chemistry, previous studies have failed to provide detailed insight into the interactions of lipase with other low molecular weight biomass constituents and compounds resulting from wood pulping. More specifically, there is a lack of data about the effects of influencing factors like cations, anions, phenols and lignosulfonates on the lipase activity. When such data exists, the respective studies typically failed to offer mechanistic explanations for the observed activity changes. As a result, the performance of lipases with cellulose fibers and under process conditions remains hard to predict and many pulp mills continue to use harsh chemistries for jobs that could be performed biocatalytically.

Similarly, carbohydrate active enzymes, such as lytic polysaccharide monooxygenases, could be employed to replace fiber-modifying chemistries, which rely on potentially environmentally harmful chemicals. By contrast, enzymes are environmentally compatible and might even offer the benefit of higher specificity. This project therefore seeks to provide mechanistic insight into the interactions of activity modifying pulp extractives (alone and in combination) on hydrolase activity, as exemplified by a lipase from Candida antarctica and to advance the underdeveloped concept of enzymatic fiber modification.

Cellulose oxidizing enzymes will be employed to study the possibility to integrate enzyme-mediated surface functionalization of cellulose fibers into continuous fiber production settings and to deepen the understanding of cellulose surface oxidation on fundamental fiber properties and fiber behavior.