Alkali-Free Adhesive for Recycled Paper

Recycled liner and medium take adhesive differently from a stable virgin kraft. Fines, a more open sheet, and reel-to-reel moisture swings let a thin, alkaline starch strike through the flute tip or sit on the surface and never grab. Caustic soda, used in many traditional corrugating formulas to drop gelatinization temperature, swells that open sheet further and shortens the time the bond line stays where you put it. The alkali-free adhesive series on /products/alkali-free-adhesive is built without caustic soda. This page is how to try that series on recycled paper. It is not a licence to copy the mix sheet of another Xuegong powder.

Keep the product identity straight before you weigh anything. The alkali-free series is the laminating, core, and facing family: no caustic soda, a Stein-Hall viscosity window of about 30–60 seconds, a gelatinization band of about 58–62°C, and a powder shelf life of about 12 months when sealed. The all-purpose alkali-free powder is a different concentrate. It still needs native corn starch, with a preferred dry ratio of concentrate to starch of 1:2. The water-only corrugator powder is a third product, about 50–75 kg of room-temperature water per 25 kg bag, and no extra starch. Paper-tube glue and honeycomb facing glue have their own water figures. None of those ratios is the recipe for this series. If the bag name does not match the series, stop and re-identify the delivery before the kitchen mixes it.

Caustic is the variable this series takes off the recycled sheet, not a promise that every defect disappears. On a porous recycled medium, caustic opens fibres and can drive adhesive deeper than the flute tip, which shows up as high consumption, a dry-looking bond, and washboarding. It also corrodes glue-system metal and is a burn hazard in the kitchen. Removing it does not remove wax, stickies, or a reel that arrived at the wrong moisture. Those still have to be held at the mill-roll stand and in the warehouse. What you should expect to compare is strike-through, roll corrosion, and whether the bond forms inside the series temperature band — not a universal gain in edge crush. Any stronger-bond wording on a catalog page stays a discussion point until the plant’s own paired reels say so.

Start viscosity in the upper half of the stated window when the sheet is hungry. For a recycled medium that drinks adhesive, begin around 45–60 seconds Stein-Hall, still inside the 30–60 second series range, and move down only if the bond is starving at the flute tip. The lower half, about 30–45 seconds, is a better first try on a tighter, better-sized recycled liner that is not striking through. Do not add water because the mix “looks thick” in the tank. Thickness in the tank and penetration on the sheet are different. Confirm with a peel or an iodine stain on left, centre, and right, using the method in recycled-paper-adhesive-penetration-control. If the stain is deep and the peel is weak, you are too thin or the gap is too open. If the stain sits on the tip and the peel is weak, you are too heavy or too cold, not automatically too thick.

Use the gelatinization band as a temperature target, not as a speed claim. The series is specified at about 58–62°C. A traditional caustic formula is often pushed hotter because the sheet and the glue were designed around that heat. On wet recycled medium, extra hot-plate temperature drives moisture out unevenly and can curl the sheet after it looked bonded on the bridge. Record the single-facer and hot-plate temperatures you actually run, next to the Stein-Hall number. If the bond fails while the glue is still inside 30–60 seconds and the paper is inside its moisture window, look at heat and gap before you rewrite the formula. Do not assume a lower gel point means the order can jump from 150 m/min to 250 m/min. Speed stays a result of the trial.

Moisture still outranks the formula. Hold incoming liner and medium near the plant window, commonly about 6–9%, and treat a liner-to-medium gap above about 2 percentage points as a warp flag. A cross-web spread above about 1.5 points on one sheet is a process flag even when the average looks fine. Those limits are in board-moisture-testing-corrugator-quality-lab. A wet recycled medium is not fixed by opening the glue gap or by dropping viscosity below the series window. Extra adhesive on a wet sheet makes a wetter bond line. A dry edge and a wet centre are a wrap or storage problem. Change the reel path or the preheater before you change caustic — and on this series you are not adding caustic back to “make it like the old glue.”

Coat weight is where recycled paper quietly wastes adhesive. An open sheet plus a cautious operator often means a wider glue gap “so it sticks.” Consumption then rises, the bond line floods, and the board washboards. Set the gap with the plant’s feeler or gauge, run long enough to weigh adhesive against tonnes or square metres, and only then move viscosity inside 30–60 seconds. A useful paired check is adhesive kilograms per tonne of board, or grams per square metre, on the same grade at the same speed, old formula versus alkali-free. One bucket dipped at the start of the shift is not that number. If consumption drops but pin adhesion on the drive side falls, the gap or the cross-web load is uneven. Fix alignment before you call the formula weak.

Write the trial so the numbers can be defended. Use one reel family, not a splice from virgin to recycled in the middle of the hour. Run at least a full order, or about two hours if the order is short, at the speed you intend to sell. Record Stein-Hall at the start, middle, and end; kitchen temperature; single-facer and hot-plate temperature; adhesive weight; pin adhesion or peel on left, centre, and right; and warp off the stack after it has cooled, not only on the bridge. A green bond on the bridge that warps an hour later is a fail. Repeat on a second reel before anyone writes “recycled paper solved.” If the two reels differ by more than about 2 percentage points of moisture, they are not the same trial.

Separate what a catalog can say from what this plant measured. The series page can say the adhesive contains no caustic soda and can quote the 30–60 second and 58–62°C windows. It should not be turned into a fixed edge-crush percent, a fixed glue saving, or a fixed speed for every recycled mill. Recycled fibre varies with the local waste stream. A plant that records, for example, less strike-through and a lower kilograms-per-tonne figure on its own grade has a result. A plant that only has a supplier slide does not. Put the paired numbers in the trial file with the reel numbers. If a number cannot be tied to a reel, it does not go in the customer report.

White-top, coated, or lightly printed recycled liners need an extra choice. Caustic formulas can yellow a light surface. Alkali-free is the first candidate when the complaint is colour or corrosion and the sheet is still a normal corrugating liner. A coated or heavily inked face may need the neutral adhesive grade instead, because coating chemistry is not the same problem as an open recycled medium. Do not blend the two products in one tank to “cover both.” Pick one, run the trial, and keep the other as the next test. Residual caustic in a tank that previously held traditional glue will contaminate an alkali-free batch. Flush and confirm the tank is clean before the first recycled trial, and do not add a caustic or borax sachet to this series to make it “stronger.”

Kitchen discipline is part of the formulation. Powder is charged so the viscosity lands inside 30–60 seconds Stein-Hall for that variant — laminating, core, or facing — and the variant matches the bond station. A core adhesive on the liner station is the wrong product even if both are alkali-free. Mix long enough to clear lumps, then measure. Do not hold a batch overnight and assume yesterday’s 50 seconds is still 50 seconds; recycled-starch mixes can change as they cool, and a northern winter kitchen below about 15°C will thicken the same formula. Warm the kitchen or adjust water inside the window, and write the temperature next to the cup result. If the cup and the method are not named, the viscosity is not a record.

High-speed or unusual recycled mixes are a custom question, not a reason to leave the window. If the line is chasing the top of its speed on a high-fines medium and the series, inside 30–60 seconds and 58–62°C, still strikes through or starves after gap and moisture are correct, stop editing the tank. That is the point to ask for a reviewed grade rather than adding caustic, borax, or a handful of another powder. Bring the trial sheet: furnish, speed, moisture, Stein-Hall, temperatures, consumption, and peel. A verbal “it doesn’t stick on our waste paper” is not enough to design the next batch. The next batch still has to be identified as series, concentrate, or water-only, in writing, before it is shipped.

Xuegong New Materials Group can match the alkali-free series to a recycled furnish after that sheet exists. Final bond, consumption, and speed remain the plant’s paired trial, not a catalog percentage. Use /products/alkali-free-adhesive for the series windows, recycled-paper-adhesive-penetration-control for how to read strike-through, and board-moisture-testing-corrugator-quality-lab for the oven check. Do not paste a 1:2 concentrate ratio or a 50–75 kg water-only ratio onto this adhesive. On recycled paper, the formulation is the right series, inside its own viscosity and gel window, on a reel you have actually measured. If the mix sheet, the reel number, and the cup value do not match, that comment is not written up as a trial that passed. The oncoming shift checks the cup value and the reel number before it keeps the previous batch.