Endoglucanase and accessory enzymes facilitate high yield pulp fibrillation into lignin-containing cellulosic nanofibrils

High-yield fibers, containing much of the original composition of woody biomass, includes mechanical and chemi-thermomechanical pulps. Collectively, they represent major products derived from Canadian softwoods, which are traditionally used to produce newsprint. These processes have the advantages of lower production costs and significantly lower environmental impact compared to chemical processes. Given the decline in the demand of newsprint and writing grades the demand for high-yield pulps has been in dramatic decline. It is therefore of pressing urgency to expand the portfolio of products that can be derived fromhigh-yield pulps. In contrast, the markets of cellulose nanofibrils products have been growing steadily. For uses in packaging, nanocomposites and nanopapers. To date, most nanofibrils have been produced by defibrillating chemical pulps. Little work has been done on assessing the potential of fibrillating high lignin-containing, high-yield fibers. At the same time the potential of enzyme-mediated fibrillation of mechanical pulps has not received much attention to date.

In this work, lignin-containing cellulose nanofibrils (LCNFs) were produced from mechanical fibers by enzymatic treatments followed by mechanical disintegration. Subsequently, how the selective addition of enzymes might enhance mechanical pulp fibrillation was assessed. Different combinations of enzymes including endoglucanase (EG), xylanase, mannanase and lytic polysaccharide monooxygenase (LPMO) were added to the fibers, followed by mechanical treatments. It was apparent that the crystallinity of enzymatical treated pulp increased with enzyme treatment while the yield, surface charge and thermostability of the LCNFs increased with a decrease in particle size.

Carbohydrate-binding modules which specifically recognize and bind to different supramolecular structures within lignocellulose substrates (e.g. crystalline/ paracrystalline cellulose, xylan and mannan) were successfully used to quantify fiber changes and elucidate the synergistic action of different enzymes. It was apparent that the combined action of the hemicellulases and LPMO increased EG accessibility to the paracrystalline cellulose regions, resulting in enhanced fibrillation. Surface-sensitive techniques such as quartz crystal microgravimetry and surface plasmon resonance were used to better elucidate more fundamental aspects while the benefits of high-yield nanofibrils in a number of applications were also described.