Application of Cellulase in Papermaking

The pulp and paper industry is one of the important pillar industries of the national economy, but the current pulp and paper industry is faced with the shortage of raw materials, energy shortages, and serious pollution, which restrict its development.

In recent years, people have successively studied and applied a series of new methods and new technologies in the pulp and paper industry, hoping to solve these unfavorable factors that plague the development of the pulp and paper industry through technological progress and innovation. The research and application of cellulase is undoubtedly an effective way to achieve this goal. It mainly includes cellulase deinking of waste paper, cellulase treatment to improve pulp performance and paper quality.

1. Deinking of waste paper.

The conventional deinking method is to use some chemicals to separate the ink from the fiber under a certain temperature and appropriate mechanical action, and then use the flotation and/or washing process to remove the peeled ink from the pulp. Enzymatic waste paper deinking and recycling of secondary fibers is a brand-new biotechnology. Currently, the enzyme preparations used for deinking research include cellulase, lipase, esterase, pectinase, amylase, hemicellulase and lignin degrading enzyme.

The enzyme treatment method uses enzymes to attack the surface of the ink or fiber, in which lipase and esterase can degrade vegetable oil-based ink. Pectinase, amylase, hemicellulase, cellulase and lignin degrading enzymes change the connection bonds on the fiber surface or near the ink ions, so that the ink is separated and removed by washing or flotation. Compared with traditional chemical deinking, enzymatic deinking has obvious advantages. It can reduce energy consumption and reduce environmental pollution, and the deinking rate is higher than chemical deinking.

Laboratory research and industrial-scale experiments have confirmed that enzymatic deinking is an effective and economically feasible method for waste paper deinking. Compared with conventional alkaline deinking pulp, enzymatic deinking pulp has the advantages of high freeness, good water filtration performance, excellent physical properties, high whiteness and low residual ink volume. More importantly, enzymatic deinking can control the size distribution and shape of ink particles by changing the composition, dosage, treatment time, pH and adding some additives, so enzymatic deinking can effectively improve the flotation deinking effect. So it can effectively remove large particle size, flat and rigid ink.

Recently, Welt and Dinus proposed several possible mechanisms for cellulase deinking:

• The enzyme partially hydrolyzes and degrades the cellulose fiber that fixes the ink to separate them from each other, and the ink particles are separated during the pulping process;
• Enzyme treatment reduces the bonding force between fibers by improving the fibrillation or removing the surface layer of single fibers, and then separates the ink;
• Enzyme-catalyzed hydrolysis is not the main thing. The important thing is that

cellulase can degrade the fiber surface to a certain degree, thereby separating the ink in the pulp;

• Cellulase peels off the fine fibers from the fiber surface to disperse the ink particles into the suspension;
• The role of enzymes is indirect. It improves the filtration performance of pulp and promotes washing or flotation by removing fine fibers and small components;
• Cellulase and hemicellulase decompose and remove the residual fibers on the ink particles that have been peeled off, increase the hydrophobicity of the ink particles, and improve the subsequent flotation treatment effect;
• Mechanical action distorts the cellulose molecular chain on the fiber surface or on the fiber, thereby increasing the accessibility and erodibility of enzymes. Therefore, mechanical action is very important and necessary for enzyme deinking.

2. Cellulase treatment improves the properties of pulp.

Enzyme treatment to improve pulp properties includes reducing the energy consumption of mechanical pulp refining, improving the beating performance of chemical pulp and improving the properties of pulp fibers. Enzyme treatment can also improve the refining performance. Before the pulp is refined, pretreatment with cellulase and hemicellulase can improve the refining effect.

Generally used in mechanical pulp, rarely used in chemical pulp. The main reason for the poor filterability of waste paper pulp is the high content of fine fibers and fillers, and cellulase can selectively hydrolyze the fine fibers in waste paper pulp, thereby improving the drainage performance of waste paper pulp. At present, the industrial application of enzymatic treatment to improve the filtration performance of waste paper pulp has made certain progress.

Enzyme-treated waste paper pulp, because of its improved water filtration performance, can not only increase the speed of the paper machine to increase production capacity, but also reduce the concentration of the head box to improve the uniformity of the paper and maintain good mechanical strength. This improves the paper quality. After the waste paper pulp is treated with enzymes, the ratio of waste paper pulp in the production of kraft liner board is increased by 32%, which reduces the production cost.

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