A novel enzymatic approach to nanocrystalline cellulose preparation.

In this work, conditions for an enzymatic pretreatment prior to NCC isolation from cotton linter were assessed. Different cellulase doses and reaction times were studied within an experimental design and NCC were obtained. At optimal enzymatic conditions (20U, 2 h), a total yield greater than 80% was achieved and the necessary enzymatic treatment time was reduced 90%. Different intensities of enzymatic treatments led to proportional decreases in fiber length and viscosity and also were inversely proportional to the amount of released oligosaccharides. These differences within fibers lead to quantitative differences in NCC: increase in acid hydrolysis yield, reduction of NCC surface charge and crystallinity increase. Benefits produced by enzymatic treatments did not have influence over other NCC characteristics such as their sulfur content (≈1%), size (≈200 nm), zeta potential (≈-50 mV) or degree of polymerization (≈200). Evidence presented in this work would reduce the use of harsh sulfuric acid generating a cleaner stream of profitable oligosaccharides.

An enzyme-catalysed bleaching treatment to meet dissolving pulp characteristics for cellulose derivatives applications.

Bleached cellulose with good end-properties (≈ 90% ISO brightness and 62% cellulose preservation) was obtained by using a totally chlorine-free biobleaching process (TCF). Unbleached sulphite cellulose was treated with Trametes villosa laccase in combination with violuric acid. This enzymatic stage (L) was followed by a chelating stage (Q) and then by a hydrogen peroxide stage reinforced with pressurized oxygen (Po), resulting to an overall LQPo sequence. The use of violuric acid was dictated by the results of a preliminary study, where the bleaching efficiency of various natural (syringaldehyde and p-coumaric acid) and synthetic mediators (violuric acid and 1-hydroxybenzotriazole) were assessed. The outstanding results obtained with laccase-violuric acid system fulfil most of the characteristics of commercial dissolving pulp, totally acceptable for viscose manufacturing or CMC derivatives, with the added advantage that the enzymatic treatment saved 2h of reaction time and about 70% of hydrogen peroxide consumption, relative to a conventional sequence (Po).

Obtaining biobleached eucalyptus cellulose fibres by using various enzyme combinations.

Various combinations of laccases, xylanase and cellulase were used to biobleach cellulose fibres from eucalyptus. The Trametes villosa and Myceliophthora thermophila laccases were used in combination with violuric acid (VA(TvL) system) and methyl syringate (MeS(MtL) system), respectively, as mediator. A dissimilar mode of action of the two systems was found: the VA(TvL) treatment released both hexenuronic acids and lignin, whereas the MeS(MtL) released lignin alone. Pulp properties were further improved by applying the mediator before the enzyme during treatment. Pulp properties comparable to those provided by industrial TCF sequences were obtained by inserting a xylanase pretreatment before VA(TvL), but no significant effect was observed after the cellulase pretreatment. As an added value, the resulting enzymatically bleached fibres possess a reduced hexenuronic acid content. The chemical oxygen demand of the effluents from each stage was also assessed.

A new procedure for the hydrophobization of cellulose fibre using laccase and a hydrophobic phenolic compound.

A new biotechnological procedure using laccase in combination with a hydrophobic phenolic compound (lauryl gallate) for the hydrophobization of cellulose fibres and internal sizing of paper was developed. Cellulose fibres from hardwood kraft pulp were incubated with laccase (Lac), in combination with lauryl gallate (LG). The Lac-LG treatment resulted in the internal sizing of paper, and also in significantly reduced water penetration in the handsheets and wettability of the paper surface. Paper was found not to be effectively rendered hydrophobic by LG alone. SEM images of the fibre network revealed the presence of the sizing agent: a product of the reaction between laccase and lauryl gallate. Binding of lauryl gallate to cellulose fibres was suggested by the increase in kappa number of the pulp and further confirmed by IR spectroscopy.