Lignocellulosic Materials and their Interactions with Proteins and Surface Active Molecules

Publication year: 2016
Authors: Fritz C.

BiCMat Group, North Carolina State University

Published in: Doctoral dissertation, North Carolina State University

Lignocellulosic biomass is a highly valuable resource for the development of value-added biobased chemicals and other materials. However, the efficient utilization of this biomass regards on understanding the different interactions among other components. For example, proteins interactions are relevant in several applications, where enzymatic hydrolysis is needed to obtain different products, especially sugars. Moreover, the heterogeneity and complex chemical and physical structure of this biomass have been identified as the major drawbacks during lignocellulose bioconversion. On the other hand, surface active molecules have been used during bioconversion processes; however, the fundamental interactions with lignocellulose are not fully known. Therefore, this work systematically investigates the interactions among proteins, surfactant, and the most abundant biopolymers in nature, namely cellulose and lignin.

Pretreatment of biomass is performed in order to deconstruct the cell wall and open the structure for subsequent stages. Several different pretreatments have been investigated but they are usually done at high temperature and pressure. A novel approach using complex systems for green biomass pretreatment is investigated under atmospheric pressure and low temperature. It is hypothesized this system can overcome the complex structure of wood by taking advantage of the hydrophobic interactions between the mainly components (lignin, surfactants, oil, proteins). A ternary diagram is built and an appropriated microemulsion formulation is analyzed and used. The effects of this pretreatment on woody material are analyzed by crystallinity, thermogravimetric analysis, and spectroscopy techniques. Sugar products are quantified after enzymatic hydrolysis. Overall, microemulsions affect the chemical-physical properties of biomass in a larger extent compared with aqueous systems.

Moreover, the non-productive interactions between lignin and enzymes are monitored in situ and in real time using sensitive surface techniques, as quartz crystal microbalance and surface plasmon resonance. Other interactions are also investigated, such as proteins-cellulose, surfactant-cellulose, surfactant-lignin, proteins-surfactant-cellulose, and proteins-surfactant-lignin. As a result, surfactant binds to lignin mainly due to hydrophobic interactions. Remarkably, the enzyme affinity towards lignin is reduced by using surface active molecules without affecting enzyme digestibility.

Understanding self-aggregation and colloidal properties of lignin in aqueous conditions is relevant since there is a growing interest to use kraft lignin in other applications rather than burning it. Here, the colloidal stability of lignin in solution is tested under the addition of surfactants and salts by monitoring changes in size and rheological properties. It is demonstrated the disruptive effect of salt, whereas the interaction with a non-ionic surfactant can improve stability. These results may open new opportunities on applications where a control over aggregation is needed, for example, filtration and separation of lignin from wastewater and lignin nanoparticles formation.

MP-SPR keywords: cellulose nanofibrils (CNF), different lignin substrates, effect of non-ionic surfactants, lignin - enzyme interaction, thickness of the film