Enzyme for Sticky Control


Stickies are tacky, hydrophobic, pliable organic materials found in recycled paper systems. They exhibit a broad range of melting points and different degrees of tackiness depending on their composition. Stickies are composed of a variety of materials including adhesives, styrene-butadiene latex, rubber, vinyl acrylates, polyisoprene, polybutadiene, and hot melts. Stickies come from adhesives, plastics, inks, coatings, glues, binders and other additives that enter the mill furnish during the papermaking process .

Stickies can cause runnability and quality problems, and their variable nature makes them difficult to control. The problem with stickies is that they cling together and tend to build up into globs or strings. Because they are deformable, they cannot be completely excluded by pressure screens. They can adhere to papermaking equipment, they can fill felts, and they can make spots in the product. There ways to deal with stickies include avoiding them (by selecting the kind of pulp source), removing them during deinking of the wastepaper (easier said than done), or adding enough talc to the system to overcome their tackiness.

The current approach used for stickies control typically involves both mechanical and chemical systems. Various pieces of equipment in the deinking plant and paper mill are designed to clean and/or mechanically remove contaminants. Screening, cleaning, flotation, dissolved air flotation (DAF) systems and washing are all designed to remove contaminants, which can include dirt, shives, or stickies, but none of these processes can deal with all types of stickies that a mill might encounter. Removes stickies by screening is difficult due to their ability to deform and become extruded through very small holes. Also, high levels of shearing action during processing of wastepaper can result in micro-stickies that are not easily retained.

The same limitation is true for chemical control programs. Chemical control has mainly involved the use of three types of products: dispersants, polymers, and absorbents. Chemical approaches to stickies control can tie up stickies in the furnish or clean stickies off surfaces once they are deposited, but these programs are not always completely successful.

A different approach to stickies control is a system that would break down the macro-stickies into smaller micro-stickies. A new system based on the use of enzymes to break down stickies has been developed. Enzyme helps degrade and remove chemical buildup that can foul processing equipment and lead to lower quality products. The enzyme formulation is inherently safer to transport and handle than organic solvents and surfactants currently used for most paper recycling, and it provides economic benefits by boosting paper production. Enzyme not only degrades stickies, but also removes stickies from fiber.

There are kinds of enzyme that usually used to control stickies: esterase, cellulase, hemicellulase, xylanase.

 

Esterase :

Composition of stickies reveals that most contain a number of ester-type chemical bonds that link the basic building blocks of the sticky together. This directed the search to esterase-type enzymes, an enzyme product for stickies control that catalyzes the breaking of ester bonds. A number of esterase-type enzyme mixtures were studied to find the one that had the ability to break down stickies. Breaking the ester bonds reduces the size of the sticky by breaking it into smaller components. Esterase is also catalyzes hydrolysis of the vinyl acetate materials, converting them to water-soluble vinyl alcohols and acetic acid that are removed in the process water. A key advantage of this approach is that once broken down, the chance of the particles reagglomerating further along in the process is greatly reduced. In other approaches, such as those using talc or other materials to coat the surface of the sticky to make it passive, the talc can be dislodged by shear forces in the process, which can lead to reagglomeration.

 

Cellulase and hemicellulase :

able to dislodge stickies by degrade fibrils without degrade the fibers. Xylanase are used to partly break down the xylan, so it can remove lignin.

 

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