Less Bleach, Lower Refiner Power, Fewer Stickies: Fibre Enzymes for Pulp, Board and Straw Fibre Mills
Which fibre enzyme goes where in a pulp, board or straw fibre mill: alkaline xylanase before bleaching, chip, wood-powder, stickies and sizing enzymes.
A pulp or board mill pays for fibre three times: in bleaching chemicals, in refiner electricity and in machine downtime when deposits build up. An alkaline xylanase is aimed at the first of those costs: its main use is pulp bleaching, where it lowers the amount of bleaching agent the mill needs and eases both the cost and the environmental side of the process. It works because breaking down the xylan in the pulp beforehand reduces the chemical demand of the bleaching stages that follow. This page is for the mill manager, process engineer or fibre processor who wants to know which enzyme goes where in the line, under what conditions, and what to send a supplier to get a usable trial.
What the enzyme does to the fibre
An alkaline xylanase for papermaking is an endo-xylanase from a Bacillus fermentation that cuts the long xylan chains in hemicellulose down to xylo-oligosaccharides. The fibre structure loosens, liquids penetrate more easily and the contents of the fibre dissolve out more readily. The buying claim attached to it is less lignin redeposited on the fibre and a brighter pulp. What a mill should look for in the grade is stability under alkaline conditions and a low cellulase side activity, because cellulase in the wrong place attacks the fibre you are trying to keep.
The enzymes a mill actually buys, by problem
Xylanase is rarely bought alone. The same suppliers sell a small programme of enzymes, each tied to one cost in the mill and one dosing point.
• Bleach chemical cost, brightness. Enzyme: Alkaline xylanase; Where it is added: By batch or continuously, to suit the process; Conditions printed for it: pH 5.0-9.5, 55-80 C, about an hour of reaction.
• Refiner electricity on wood chips. Enzyme: Wood-chip treatment enzyme; Where it is added: Chip washing pool, or sprayed on the chips; Conditions printed for it: 100-300 g/T of oven-dry pulp, pH 6.0-10.0, 15-65 C, eight hours or more.
• Stiff wood-powder fibre, poor formation. Enzyme: Wood-powder softening enzyme; Where it is added: Stock storage chest for the wood-powder fibre; Conditions printed for it: 100-500 g/T of oven-dry pulp, pH 6.0-10.0, 35-65 C.
• Stickies from recycled paper. Enzyme: Stickies-control enzyme; Where it is added: Pulper, the tower after pulping, or the chest before the machine; Conditions printed for it: 80-100 g/T of oven-dry pulp, pH 6.0-10.0, 15-65 C.
• Cost of modified starch for surface sizing. Enzyme: Sizing-starch enzyme; Where it is added: Starch cooking tank; Conditions printed for it: Used at 55-65 C, then inactivated by a timed hold once the cook passes 95 C.
• Pitch and resin trouble. Enzyme: Lipase; Where it is added: Sold as a papermaking aid for resin obstacles; Conditions printed for it: Ask the supplier.
• Beating and fibre development. Enzyme: Acid cellulase, 40000 U/g; Where it is added: Sold for paper beating and for fabric polishing alike; Conditions printed for it: Ask the supplier.
A liquid pectinase is also offered as a papermaking process aid.
How each one is run: Alkaline xylanase ahead of bleaching
The label dose for an alkaline xylanase is set by mill trial. Two offers of alkaline xylanase for the same job print different windows: one works at pH 5.0-9.5 and 55-80 C, the other is specified for pH 6.0-9.0 and 35-65 C. The second is a high-concentration liquid meant to be compounded into a plant-fibre treatment preparation rather than dosed as it comes. So the name on the drum does not settle the question: match the printed window of the exact product to the temperature and pH of the tower where it will sit.
How each one is run: Wood chips before refining
The chip enzyme is used to pre-treat wood chips so that the fibre takes up water and swells during refining, separates and fibrillates more easily, and the refiner draws less power. It acts on the outer layers of the fibre wall, lowering the cohesion of the fibre and leaving the wall structure looser and softer. It needs eight hours or more of contact, which is why it is added at the chip washing pool or sprayed on the chips and not in the stock line.
How each one is run: Wood-powder fibre for corrugated and board
Mills that make corrugated medium or board from wood-powder fibre use a softening enzyme that lowers the lignin content of that fibre and leaves it softer and looser, which helps sheet formation and strength. It goes into the storage chest for the wood-powder stock, by batch or continuously, and is given about an hour to work.
How each one is run: Stickies in recycled stock
The stickies-control enzyme was developed for small and medium mills whose paper machine system has no hot-dispersion equipment. It reduces sticky deposits from recycled grades such as OCC, MOW, OMG and ONP, and it is sold on a low dose, a fast effect and tolerance of low temperature. The dose is raised when the stickies load is severe.
How each one is run: Surface sizing with ordinary starch
The sizing enzyme treats ordinary starch directly so that it meets surface-sizing requirements and replaces modified starch, which is where the saving comes from. Water and starch are stirred in the cooking tank, the enzyme is added, steam is turned on and the heating curve is steered by viscosity. Once the cook passes 95 C the batch is held for the time printed on the label to inactivate the enzyme, and the paste is then used at 55-65 C.
Straw, bamboo and other plant fibre
The same alkaline xylanase is specified for the enzymatic treatment of straw, wood, bamboo, herbal raw material and feed, so a non-wood fibre line can use it on the same logic of loosening the fibre and letting the contents out.
Where mill trials go wrong
1. Dosing on the wrong basis: the chip, wood-powder and stickies enzymes are dosed per tonne of oven-dry pulp, so a dose worked out on wet stock is several times too low.
2. Too little time: a chip enzyme that needs eight hours or more will show nothing if it is added where the fibre only stays for minutes.
3. Wrong pH: the stock-line enzymes above are specified for pH 6.0-10.0, and an acid system takes them out of their window.
4. Too cold or too hot for the grade: one alkaline xylanase starts at 55 C and another stops at 65 C, so the tower temperature picks the product.
5. A xylanase with too much cellulase side activity, which trades bleach savings for fibre strength.
6. Sizing starch that keeps thinning in the size press because the enzyme was never held long enough above 95 C to be inactivated.
7. Expecting the stickies enzyme to stand in for cleaning and screening: it lowers deposits, it does not remove the contaminants from the furnish.
Shelf life is shorter than for dry food enzymes: the chip and wood-powder enzymes are marked for 6 months at room temperature, so order to your consumption and not to the price break.
What to tell a supplier
Give the furnish (wood species, chips or wood powder, straw, bamboo, or the recycled grades you pulp), the pH and temperature at the point where the enzyme would go in, and the retention time there. Say which cost you want to move: bleach chemicals, refiner power, stickies downtime or sizing starch. Ask for the working pH and temperature window of the exact grade, the dose and whether it is stated on oven-dry pulp or dry fibre, the reaction time, the form and the shelf life. Buyers of fibre enzymes commonly put a cellulase in the same order as the hemicellulase, so say what else you already run.
Next step
Email us the four numbers that decide the fit, furnish, pH, temperature and retention time, with your daily tonnage and country, and we reply with the enzyme that suits that point in your line, a starting dose window and a sample size for a mill trial. If a previous enzyme trial showed nothing, send the dosing point and conditions you used and we will tell you what to change first.
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Frequently Asked Questions
How does an alkaline xylanase lower bleaching cost?
Breaking down the xylan in the pulp beforehand reduces the chemical demand of the bleaching stages that follow. Look for stability under alkaline conditions and a low cellulase side activity, because cellulase in the wrong place attacks the fibre you are trying to keep.
What dose of alkaline xylanase should a mill use?
The label dose for an alkaline xylanase is set by mill trial. Match the printed window of the exact product to the temperature and pH of the tower where it will sit: one offer works at pH 5.0-9.5 and 55-80 C, the other is specified for pH 6.0-9.0 and 35-65 C.
Why did a wood-chip enzyme trial show nothing?
A chip enzyme that needs eight hours or more will show nothing if it is added where the fibre only stays for minutes. The chip, wood-powder and stickies enzymes are dosed per tonne of oven-dry pulp, so a dose worked out on wet stock is several times too low.
What should I send for a mill trial?
The furnish, pH, temperature and retention time at the dosing point, with your daily tonnage and country. We reply with the enzyme that suits that point in your line, a starting dose window and a sample size for a mill trial.
Planning a mill trial?
Email us the four numbers that decide the fit, furnish, pH, temperature and retention time, with your daily tonnage and country, and we reply with the enzyme for that point in your line, a starting dose window and a sample size.
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