In thermomechanical pulping of softwood chips, a commercial endoglucanase–xylanase preparation is introduced at the chip washing stage or into the presteaming bin at 0.08–0.15 kg/t oven-dry wood; the impregnation liquor pH is maintained at 5.0–6.5 and chip temperature between 40°C and 60°C for a hold period of 30–90 min before the chips enter a primary high-consistency disc refiner with plate diameter of 1.6–2.1 m and specific energy of 1,800–2,400 kWh/t. The enzyme-catalysed cleavage of arabinoxylan and amorphous cellulose at the fibre cell wall improves internal fibrillation while preserving fibre length; specific energy consumption determined from refiner motor power, mass throughput, and plate gap setting is typically reduced by 8%–18% against untreated chips. The process is bounded by two failure modes observed on production lines: application above 60°C for more than 45 min denatures the endoglucanase fraction and reduces specific energy savings below 3%, while addition of alkaline peroxide brightening liquor at pH above 8.5 in the same impregnation zone deactivates the xylanase component before the refiner. Compliance is evaluated under ISO 5264-2 for laboratory refining, ISO 2470-1 for brightness, and ISO 5351 for viscosity; final mechanical pulp grades include newsprint, supercalendered paper, lightweight coated base, and folding boxboard from CTMP, with market pulp grades controlled to the brightness and viscosity limits specified in the customer technical agreement.

What governs xylanase retention time in kraft brownstock prebleaching?

Washed, oxygen-delignified hardwood kraft brownstock is dosed with alkali-tolerant xylanase from glycoside hydrolase family 11 at 0.05–0.12 kg/t oven-dry pulp, pH 6.8–8.2, temperature 55–70°C, and retention time 60–120 min in a dedicated reaction tower before the first chlorine dioxide stage. The enzyme hydrolyses reprecipitated xylan on the fibre surface, increasing fibre wall porosity and improving extractability of oxidized lignin fragments in subsequent D0 and E stages. Mill-scale data sets show chlorine dioxide charge reductions of 10%–20% at equal final brightness, or brightness gains of 1–2 ISO points at equal oxidant charge; final kappa number after D0 measured by ISO 302 is typically 0.5–1.5 units lower than untreated control pulp. Retention time is governed not by biochemical saturation but by transport limitations: black liquor carryover above 4% residual alkali and dissolved lignin above 12 g/L reduce enzyme binding to the substrate, requiring an increase in residence time or a split-dose strategy across the decker repulper and post-oxygen wash press. The treatment is incompatible with upstream filtrate containing residual hydrogen peroxide above 50 mg/L because oxidative denaturation of the enzyme occurs within 15 min. Product compliance for bleached hardwood kraft grades sold into food-contact packaging requires testing under FDA 21 CFR 176.170 and EU Regulation (EC) No 1935/2004; the converted finished goods span uncoated fine paper, coated folding carton board, tissue and towel base sheets, and bleached market kraft pulp.

MDF fiber furnish enzymatic defibration and resin demand

In dry-process fibreboard manufacture, an enzyme cocktail containing cellulase, xylanase, and pectin methylesterase is applied to hardwood chips after washing and before the pressurized refiner at 0.10–0.25 kg/t dry wood, with pH adjusted to 4.5–5.5, chip temperature held at 45–60°C, and residence time 45–90 min in an insulated chip silo. The enzyme weakens the middle lamella and primary wall at the fibre separation plane, allowing the pressurized defibrator at 7–9 bar steam pressure to operate at 5%–10% lower specific energy, or at unchanged energy to produce a higher proportion of fibrillated fibre with increased surface area for resin adhesion. Urea-formaldehyde resin dosage in the blowline or blender is commonly reduced by 5%–12% while maintaining internal bond strength because improved fibre surface coverage shifts failure from resin-starved zones to the fibre cell wall; internal bond values are verified according to EN 319 or ANSI A208.2 test methods. The treated fibre is dried and formed into mats, then hot-pressed at 170–210°C and 3–6 N/mm² press pressure. The enzyme application introduces a moisture control boundary: chip moisture below 35% dry basis inhibits enzyme diffusion into the wood structure, and residual free water after treatment above 55% increases drying load and risk of refiner steam pressure instability. The primary compliance framework is EN 622-5 for MDF board specifications, EN 13986 for CE marking, CARB Phase II and TSCA Title VI for formaldehyde emission from finished panels; terminal products include furniture-grade MDF, high-density flooring underlayment, door skins, display panels, and millwork profiles.

After steam explosion pretreatment of debarked softwood chips at 190–210°C for 3–6 min, the washed slurry is cooled to 48–52°C and adjusted to pH 4.8–5.2 with 10% ammonium hydroxide before a cellulase–hemicellulase–β-glucosidase cocktail is dosed at 5–15 mg protein/g glucan, equivalent to 0.12–0.30 kg/t original dry wood depending on prehydrolysate sugar loss. Simultaneous saccharification and co-fermentation is conducted in 100,000–500,000 L stainless steel vessels with an agitation power input of 0.5–1.0 kW/m³ and residence time 72–120 h; the resulting hydrolysate typically contains 30–60 g/L glucose and 10–25 g/L xylose depending on feedstock species and pretreatment severity. The enzyme preparation is inhibited by residual furfural above 2 g/L and formic acid above 5 g/L; detoxification by ion exchange or overliming is required for steam-exploded conifer hydrolysates, and published data for this specific configuration is limited beyond these threshold observations. Final cellulosic ethanol must meet EN 15376-1 or ASTM D4806-20a for fuel ethanol blending, and production routes seeking renewable fuel credit verification are audited under ISCC EU or RSB; co-products include purified lignin for bio-based adhesives, dried distillers grains from fermentation solids, and biogas from stillage.

When chip pile temperature exceeds 45°C, lipase dosing moves from batch to in-line

At the woodyard of a mechanical printing paper mill, triglyceride-hydrolyzing lipase is applied to conifer chips before the pile is formed at 0.05–0.15 kg/t dry wood diluted in water to a spray volume of 2–4 L/t; the solution pH is kept at 6.5–7.5 and the chips are held for 24–72 h to allow hydrolysis of wood resin esters to free fatty acids and glycerol. The treatment is moved from batch to in-line when chip pile core temperature exceeds 45°C, because thermophilic wood extractive oxidation accelerates resin polymerization and creates deposits that resist post-refiner washing. On production lines, the extractive content measured by TAPPI T 204 cm-17 solvent extraction is reduced by 30%–55% relative to untreated chips, and refiner plate cleaning intervals are extended from 7–10 days to 18–30 days depending on furnish. The downstream process consists of atmospheric preheating, primary and secondary disc refining, screening, and peroxide bleaching; the hydrolyzed pitch is partially removed in the deinking or washing stage and partially remains as an emulsified surfactant-like component that improves fibre dispersion. The enzyme is incompatible with sodium hypochlorite retention above 20 mg/L active chlorine and with chip pile pH below 5.0; acidified chip storage for brightness preservation suppresses lipase activity by more than 50%. Food-contact paper compliance follows FDA 21 CFR 176.170 and BfR Recommendation XXXVI; terminal papers include newsprint, directory paper, and supercalendered magazine grades with ISO 2470-1 brightness targets.

Alkali-stable xylanase treatment of prehydrolysis kraft hardwood brownstock is carried out at 0.05–0.15 kg/t pulp, pH 6.5–8.5, temperature 60–75°C, and retention 60–120 min in a storage tower after oxygen delignification; the enzyme removes xylan from the fibre surface and improves downstream caustic extraction selectivity, increasing alpha-cellulose content by 1–3 percentage points as determined by TAPPI T 203 cm-99 and reducing alkali solubility S18 by 2–5 percentage points measured by ISO 692 or an equivalent solubility test. The production route uses prehydrolysis at 160–170°C before alkaline cooking, followed by oxygen delignification, enzyme application, and a multi-stage bleach sequence that may include chlorine dioxide, hydrogen peroxide, and ozone; the resulting dissolving pulp has a viscosity of 450–650 mL/g by ISO 5351 and an ash content of 0.05–0.10% by ISO 1762. The treatment is limited by excessive enzyme carryover into the spinning dope, where residual cellulase activity above 0.5 U/g pulp can reduce cellulose chain length during storage; therefore a final hot alkali extraction at 85°C or above, or an oxidative peroxide stage, is required to inactivate residual enzyme protein before drying. Dissolving pulp produced by this route is converted into viscose staple fibre, lyocell filament, cellulose acetate tow, cellulose ethers, and nitrocellulose derivatives; textile fibre producers specify viscosity and reactivity limits under ISO 5351 and rayon-grade pulp reactivity test protocols, and food or medical cellulose derivatives are tested under relevant pharmacopoeia or FDA 21 CFR 176.170 food-contact migration limits where applicable.