Fibra ligadora de Kuraray VPB105-1-PVA para fabricação de papel (dissolve a 70 ° C)

Kuraray VPB105-1-PVA Binder Fiber for Paper Making (Dissolves at 70 °C) is a polyvinyl alcohol binder fiber supplied for papermaking furnishes in which the binder must remain a discrete staple fiber through stock preparation and sheet forming, then dissolve at a defined aqueous temperature of 70 °C. The grade is added as a dry furnish component, not as a pre-dissolved PVOH solution. Polyvinyl alcohol in fiber form has a density near 1.26–1.30 g/cm³; this range is consistent with published PVOH solid-state data and is relevant to stock-settling and retention calculations. Because the product is a fiber, its retention on the forming fabric depends on mechanical entanglement and sheet formation, not on adsorption of a dissolved polymer chain. Batch-specific fiber length, linear density, moisture, and ash values appear on the Kuraray certificate of analysis. Users should verify those values before setting refiner clearances and screen-slot dimensions.

Pilot evaluations typically use laboratory sheets formed according to ISO 5269-2:2004 to compare VPB105-1 addition levels against a control furnish. The addition level cannot be transferred directly from handsheet data to production because pilot drying conditions often differ from full-scale contact or through-air dryers. Handsheet dryers may reach 70 °C more rapidly than a heavy commercial sheet, so the observed bonding benefit may overstate the production response. Conversely, paper machine dryers with high evaporative load may under-develop the binder if steam pressure is limited. Any dose-response screening should therefore include tensile index according to ISO 1924-2:2008 and internal bond strength according to TAPPI T 569 after controlled drying, not solely after ambient air drying.

What Limits Premature Dissolution in Warm Wet-End Systems?

Premature dissolution is governed primarily by stock water temperature and residence time below the forming wire. At wet-end temperatures below 50 °C, VPB105-1 remains largely undissolved; if the stock reaches 70 °C in a pulper, machine chest, or broke system, the fiber can soften and produce tacky PVOH domains. A temperature-controlled approach below 60 °C is therefore recommended for mills that operate closed white-water loops with elevated process-water temperatures. Sustained exposure near the dissolution point should be avoided, especially in hot repulping of broke that has already passed through the dryer. Partially hydrated PVOH can coat deflaker plates, pressure-screen baskets, and forming fabric surfaces. Thermocouple data from the machine-chest discharge and headbox manifold provide the required verification.

Mechanical refining of VPB105-1 is not recommended as a primary action because it reduces fiber length and may generate PVA fines that escape into white water. On a disc refiner with standard cast alloy plates, the fiber is exposed to high shear and localized heating that can soften the material at loads below fiber damage thresholds for cellulosic fiber. Where refining is unavoidable, addition at the post-refiner chest is preferable to addition at the pulper. Pressure screens should be monitored for plugging when slot widths are below 0.2 mm; if rejects rise, stock dilution and higher screen rotor speed may be required.

Dry VPB105-1 addition eliminates the viscosity increase, cooking step, and foaming often associated with high-molecular-weight PVOH solution make-down. On the paper machine, the dry fiber can be fed by a loss-in-weight screw feeder into the pulper or post-refiner chest. Retention before the dryer is mechanical rather than adsorption-driven; in high-speed gap formers, formation, retention, and drainage must be balanced against fiber length and cut length distribution. Aqueous PVOH solution is subject to unretained-polymer losses that increase chemical oxygen demand in the white water, whereas retained VPB105-1 remains in the sheet until thermal activation. However, the dry-fiber route shifts bond development to the dryer section, so the wet-web tensile response is governed by refining and wet-end starch rather than thermal binder activation.

When the Dryer Section Fails to Reach 70 °C Through the Sheet Z-Direction

Thermal activation is not achieved when the web surface temperature alone reaches 70 °C; the entire z-directional cross-section must exceed the threshold for uniform binder dissolution. On multi-cylinder contact dryers, shell temperatures of 90–110 °C are common, but web core temperature depends on basis weight, incoming moisture, machine speed, and condensate removal. Through-air dryers provide direct hot-air penetration and can reach the dissolution threshold more uniformly in high-bulk grades, but at higher energy demand. Infrared dryers or air caps can accelerate surface heating in the initial dryer sections.

To verify bonding development, internal bond strength should be tested according to TAPPI T 569 or tensile index according to ISO 1924-2:2008 after dryer-section changes. If the sheet remains below 70 °C through the core, VPB105-1 remains partially in fiber form and the expected PVA film-bridge contribution is reduced. Wet-lap or heavy caliper boards are particularly sensitive because conductive heat transfer through the wet web is slower than in tissue or lightweight paper grades. Machine speed trials should record steam pressure, dryer surface temperature, sheet surface temperature, and final internal bond values before changing addition level.

Substituting Dry PVA Fiber for Conventional Binder Systems

Compared with starch, VPB105-1 does not introduce the same biochemical oxygen demand when retained, but dry PVA fiber must undergo thermal dissolution before it develops its final binding structure. Starch and PVOH solution wet-end binders develop hydrogen bonding as water is removed, without a phase-change dissolution step in the dryer. Compared with bicomponent thermoplastic binder fibers, such as polyethylene/polypropylene sheath-core grades, VPB105-1 does not leave a discrete hydrophobic synthetic domain in the finished sheet. The PVA phase is water-soluble at its activation temperature, which supports repulpability but also means the dry bond is water-sensitive unless protected by wet-strength resins, internal sizing, or coating. Wet tensile strength after immersion can be evaluated according to TAPPI T 456 or ISO 3781:2011.

Fiber Geometry, Ash, and Conformance Data

The cut length and linear density of VPB105-1 should be selected for the forming geometry, headbox consistency, and drainage capacity of the target machine. Longer cut lengths improve mechanical retention but can create formation defects on high-speed fourdrinier wires; shorter lengths reduce formation risk but may pass through the forming fabric with fines. PVOH density near 1.26–1.30 g/cm³ reduces settling compared with denser synthetic fibers. Ignition residue is measured according to ISO 1762:2019 at 525 °C to verify that the PVA fiber does not raise furnish ash beyond the grade specification. Because PVOH is largely organic, it is consumed during ignition; only inorganic residues from the fiber or additives remain. The ash balance should be checked when VPB105-1 is combined with filler grades that contain calcium carbonate or kaolin.

For food-contact paper and paperboard, the specific VPB105-1 grade must be reviewed against the supplier regulatory statement and the intended food type. Polyvinyl alcohol may be used in paper and paperboard intended for food contact under the relevant national and regional frameworks, including FDA 21 CFR 176.170 for U.S. conditions of use and BfR Recommendation XXXVI for European paper and board. The user must confirm migration status, temperature of use, and any food-type restrictions with Kuraray regulatory documentation. For European workplace and supply-chain compliance, the current safety data sheet and REACH Regulation (EC) No 1907/2006 registration should be checked.

Thermal Solubility Class of VPB105-1 Amid Kuraray PVA Binder Fibers

VPB105-1 occupies a 70 °C dissolution class. Lower-temperature PVA binder fibers may dissolve at 60 °C or below, reducing dryer demand but increasing the risk of premature dissolution in warm wet-end loops. Higher-temperature PVA binder fibers may require a larger dryer heat load and longer residence. Selection of the 70 °C grade is generally appropriate when the wet-end temperature remains below 60 °C and the dryer section can reliably raise the whole sheet to 70 °C. In tissue and towel machines with high-speed through-air dryers, the threshold can be achieved rapidly; on heavily loaded paperboard machines with thick calipers, the z-directional heat transfer must be confirmed. Published data for specific production-scale configurations of VPB105-1 is limited; pilot trials on a pilot paper machine are required to determine the actual dose-response.

Borate-containing wet-end additives should be avoided with VPB105-1 because borate ions form reversible PVOH–borate gel networks that can increase viscosity, reduce solubility, and create insoluble deposits. If borate is present in felt-cleaning chemicals or mill water treatment, the degree of interaction should be evaluated in laboratory stock-jar tests before production use. The fiber should be stored in dry conditions; PVOH is hygroscopic, and at relative humidity above 60 %, pre-drying or sealed storage is required to prevent surface tackiness and feeding issues in loss-in-weight equipment.