June 2007
By David Jones, industry specialist, Buckman Laboratories of Canada Ltd
Enzymes are widely used in many industries including pulp and paper. A fairly recent and intriguing new development is in the use of enzymes to modify the quality of fiber. This application is growing but has still only scratched the surface of the overall potential. Here, enzymes are used to "refine" fiber to give the desired paper qualities. You can look at the enzymes as widening the refining window, allowing paper quality specifications to be met and/or production costs to be decreased.
The enzymes used in this application are from the cellulase family. The cellulases break down the cellulose in the fiber. This leads to the delamination of the cell walls, causes cell walls to collapse and starts fibrillation. Of course, this is exactly what is done with mechanical refiners. However, the enzymes can give a gentler, targeted refining. A concern with mechanical refining is the generation of fines. The use of enzymes makes balancing the positives and negatives of refining easier. The cellulases can be used in conjunction with mechanical refining or may replace mechanical refining completely.
Copying mill parameters
Buckman is working with the family of cellulase enzymes. The various cellulases have different actions and in some cases work on different wood species. Two major types are the exocellulases and endocellulases. Exocellulases act on the end of the cellulose chain, cutting bonds on the ends of the fiber. Endocellulases act in the middle of the cellulose chains. This means that the selection of the appropriate cellulase is important. The selection is done in the lab by treating pulp with various cellulases, putting them through a lab refiner and then making handsheets. The handsheets can then be tested for the desired sheet properties. The lab work is always done in the same pH and temperature as the mill process.
Process knowledge is an important aspect in the use of any enzyme. Enzymes have specific pH and temperature ranges where they are most effective. The temperature and pH ranges vary from enzyme to enzyme and can be quite different. Other concerns are contact time and inhibiting chemicals. All of these parameters must be taken into account when developing the fiber modification enzyme application. The wrong conditions will lead to an ineffective or failed program. A point to remember is that given the right conditions, an enzyme will always catalyze or drive the reaction it is designed to do.
Fiber modification enzymes can be used to achieve sheet qualities that a mill's mechanical refiners may not be able to. The enzyme can also be used to allow less expensive pulps to be used to reduce production costs. An example is a mill that is making a napkin grade with deinked MOW pulp and softwood kraft. The enzyme allows the mill to produce the grade with 100% deinked pulp resulting in a production cost reduction. Other benefits will surely be discovered as more mills start to investigate this technology.
Set clear goals
As with all development programs, it is essential that clear goals be set for the project. What are you trying to achieve and what measurements will be used to determine success or failure? Numbers are the key: you want to reduce production costs by increasing the percentage of a less expensive pulp. What actual percentage increase is required to realize a positive ROI? You want to have this calculated before the evaluation. An evaluation action plan that covers all aspects of the project is an important tool in maximizing the chances for success.
Fiber modification enzyme research is being done with many different pulp types and paper grades. Some are proving to be more of a challenge than others. In bleached kraft, the enzymes have been proven effective and are in daily use in a number of mills. Mechanical pulps such as TMP are proving more difficult to obtain positive results. The problem may be the temperature and/or pH of the system, or it may be that the higher extractive levels of mechanical pulps block the enzymes from reaching the cellulose. Research continues and this will result in an expansion of the application of fiber modification enzymes to different pulp types and for new benefits.
The use of enzymes to "refine" or modify fiber is proven; a number of mills around the world are already reaping the benefits. It is sure that the use of fiber modification enzymes will grow. As more mills investigate this exciting new technology, previously unthought of uses will emerge. The proper selection of the enzyme and a well thought out and documented evaluation plan will maximize the chances for success.
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