Cellulase for Pulp and Paper — Fiber Modification, Drainability Improvement, and Recycled Fiber Processing

The key to cellulase's beneficial effect on drainability without strength loss is its selective action on the outermost exposed cellulose microfibrils on the fiber surface and on the ultra-fine fiber fragments (fines) that contribute most to drainage resistance. By modifying the surface of swollen, fibrillated fibers and partially degrading the most drainage-reducing fines, cellulase reduces the specific filtration resistance of the fiber network without hydrolysing the main fiber body that provides tensile and tear strength. The critical control is dose — too low a dose gives insufficient drainage improvement; too high a dose begins to attack the fiber body, reducing strength. The practical dosing window where drainage improves without meaningful strength loss is validated at bench scale before production implementation.

Reported energy savings from cellulase pre-treatment in pulp refining vary by application. For recycled fiber drainability improvement in containerboard, the indirect energy benefit from reduced refining to reach target freeness is typically 15–25% of the refining electrical energy for that pulp fraction. For mechanical pulp with enzymatic pre-treatment, direct refining energy savings of 5–15% per tonne have been reported in bench-scale studies, with plant-scale results ranging from modest to significant depending on wood species, pulp target quality, and refiner configuration. Mill-scale validation with a defined pilot program is recommended before committing to production-scale enzyme procurement based on energy savings calculations.

Cellulase enzyme for pulp and paper is typically applied as a dilute aqueous solution added to the pulp stock in the machine chest, blend chest, or a dedicated pre-treatment vessel before the paper machine. The enzyme contact is managed at pH 4.5–5.5 and 45–55°C for 30–120 minutes before the stock proceeds. After the treatment contact time, the enzyme is diluted and largely inactivated by the paper machine's alkaline retention chemistry and temperature management. Cellulase is generally compatible with standard wet-end chemistry — starch, retention aids, and sizing — but specific compatibility should be verified with the mill's wet-end chemistry supplier. Avoid adding cellulase simultaneously with strong cationic polymers that may bind and inactivate the enzyme.

Activity grade selection for pulp and paper depends on the target application and available contact time. For drainability improvement with 30–60 minutes contact, grades of 50,000–100,000 U/g allow dosing at 100–300 U/kg dry pulp with a relatively small mass of enzyme added to the pulp — important for minimizing enzyme protein addition to the furnish. For applications with longer contact times (60–120 minutes in a pre-treatment vessel), lower activity grades (10,000–30,000 U/g) at proportionally higher mass doses are also effective. The practical guidance is to specify based on the target dose in U/kg dry pulp and the available contact time, then select the enzyme activity grade that delivers that dose in a convenient liquid addition volume for the mill's dosing system.