Fibra estrutural VPB103-PVA de Kuraray para fabricação de papel

Kuraray VPB103 is a polyvinyl alcohol (PVA) structural fiber for paper making, supplied as a cut-fiber furnish additive rather than as a dissolved polyvinyl alcohol solution or powder. The fiber is a high-hydrolysis PVA homopolymer with a degree of hydrolysis above 98 mol%. The 103 designation identifies a papermaking-grade cut length of 3 mm and a low-temperature dissolution profile in neutral water; within the manufacturer’s KURALON PVA fiber range, VPB103 is positioned as a binder fiber that remains discrete through stock preparation and sheet forming, then activates during drying. This dual behavior contributes a reinforcing skeleton before thermal activation and adhesive film formation after the wet web reaches the dissolution threshold. Typical applications include wet-laid filter media, tea bag paper, decorative paper, and grades that require wet tensile without formaldehyde-based wet-strength resins. The lot certificate of analysis remains the controlling specification; the values below are manufacturer-published typical data.

Kuraray VPB103 Chemical Identity and Typical Lot Specifications

The fiber is a non-fibrillating homopolymer with uniform cross-section and no sheath-core differentiation. This distinguishes VPB103 from sheath-core binder fibers because dissolution occurs across the entire fiber rather than only in a low-melting sheath. The product is not intended for melt processing; thermal softening in papermaking is water-mediated. Table 1 lists the typical lot properties.

Variation in water hardness, pH, or dissolved salts can shift dissolution onset. Alkaline whitewater conditions may extract low-molecular-weight PVA fractions below the listed threshold. The product should not be predispersed in tanks equipped with steam sparging above 50 °C. Within the manufacturer’s VP series, the 103 grade is differentiated from higher-numbered binder grades primarily by dissolution temperature and cut length. Higher-activation PVA grades remain fibrous longer in the dryer and may be preferred where wet web strength must survive higher temperatures before bonding. VPB103 is also distinct from polyvinyl acetate emulsion binders and polyvinyl alcohol powder; the fiber form eliminates dusting, meters like a cellulosic furnish component, and creates a temporary reinforcement phase before dissolution. Because VPB103 dissolves uniformly, it should not be used where a non-dissolving reinforcing fiber is required throughout the finished sheet, since a portion of the fiber loses fibrous identity during drying.

How Does VPB103 Function in the Wet End of a Paper Machine?

The fiber is first dispersed in water at 10–25 °C; dissolution is negligible at this temperature, so conventional pulpers and machine chests are acceptable. Dispersion should avoid high-shear refining because VPB103 does not fibrillate and mechanical refining reduces fiber length and generates fines that dissolve prematurely. If refining is required for the cellulosic furnish, VPB103 should be introduced after refiners and before the machine chest. Dispersion consistency below 2 wt% in dedicated pulpers reduces agglomeration. Do not recirculate the dispersed fiber through centrifugal cleaners for extended periods, because fiber length can be lost; forward cleaners may remove some PVA fibers, although the density of 1.26–1.30 g/cm³ is less problematic than aramid or glass fiber.

Addition rates of 3–10 wt% on dry furnish are typical for specialty grades. Above 15 wt%, drainage and formation often degrade; published data for this specific configuration is limited. Retention is governed primarily by mechanical filtration and hydrogen bonding rather than charge neutralization because the fiber exhibits low surface charge density. In filled or high-freeness furnishes, a cationic polyacrylamide retention aid at 0.02–0.05% on dry fiber is typically used. Headbox pH should be maintained between 6.5 and 7.5. Acidic conditions below 4.5 promote acid-catalyzed hydrolysis; alkaline conditions above 9.0 increase surface swelling and can produce tacky deposits on forming fabrics. Whitewater loops operating with high closure may accumulate dissolved PVA oligomers, which raise foam stability and interfere with cationic demand titration. Defoamer dosage often requires adjustment because dissolved PVA is surface active.

On the forming section, the fiber behaves as a relatively stiff but non-fibrillating cut fiber. On a twin-wire former, typical retention efficiencies of 60–85% have been reported for similar cut-length synthetic fibers when the retention aid is applied in the thin-stock loop; actual values are furnish-specific and should be confirmed by mass balance. Wet web tensile before activation is lower than that of refined cellulosic furnish, so open draws should be set with reduced tension to prevent edge flutter and open-draw breaks. In press sections operating at linear loads of 80–120 kN/m, the PVA fiber flattens and increases interfiber contact, but excessive wet pressing to solids above 48–50% can reduce bulk and may make the sheet denser than required for filter and tea bag applications.

Activation of the fiber occurs in the dryer section when sheet temperature reaches approximately 60–70 °C and residual moisture still allows PVA chain mobility. Below 55 °C, the fiber remains largely intact and contributes mechanical entanglement rather than adhesive bonding. Above 70 °C, dissolved PVA migrates into interfiber contacts and forms film-like bridges upon drying. This transition creates a narrow processing window in the early dryer section. If the wet web contacts a dryer can hotter than 80 °C before its moisture content falls below 60%, PVA film can transfer to the can surface and cause picking. Mills running VPB103-containing grades therefore schedule a gradual drying ramp and may reduce first-group can temperatures by 10–15 °C relative to standard conditions. Calendering should be kept below 90 °C; higher surface temperatures can soften PVA at the sheet surface and produce blackening or sticking during machine stops. Final sheet moisture should remain within normal limits of 4–8% depending on basis weight and end use.

The following directional changes are commonly observed in PVA binder fiber systems; exact values are furnish-specific. In ISO 5269-2 handsheets from bleached softwood kraft at 5 wt% VPB103, dry tensile index measured by ISO 1924-2 can increase by 5–15% after thermal activation; wet tensile index rises more substantially because PVA film bridges fiber intersections. Bursting strength measured by ISO 2758 can increase by 10–20% in the same typical range, while tear index measured by ISO 1974 may remain unchanged or decrease slightly if the PVA bond restricts fiber pull-out. Air permeability measured by ISO 5636-3 decreases with increasing PVA content because the film-forming phase occupies interfiber pores; this is often desirable for tea bag and filter papers but can reduce absorbency. Wet tensile after 24 h water immersion remains higher than untreated cellulose but lower than high-dose melamine-formaldehyde or urea-formaldehyde wet-strength resin systems. PVA bonding is not covalent or thermosetting, so some loss under prolonged soaking should be expected. A 5 wt% addition can reduce Canadian Standard Freeness by 20–50 mL under ISO 5267-1, depending on refine level and filler content.

Deposit formation is the main process conflict. Dissolved PVA is surface active and can precipitate on felt surfaces if whitewater pH drops sharply or salt concentration increases. Mills counter this with nonionic felt detergents and periodic alkaline boil-outs. High doses of cationic fixatives should be avoided because PVA-fixative complexes can form white pitch-like deposits. Residence time in chests above 50 °C should be limited to 30–60 min; above 55 °C, the fiber surface becomes sticky and agglomerates can form in chest corners and on level sensors. Transfer lines after steam mixing points should be inspected for accumulated film if the furnish is heated before the headbox.

When VPB103 Replaces Synthetic PET or Aramid Reinforcement in Specialty Paper Formulations

Compared to polyethylene terephthalate (PET) fiber, VPB103 offers a thermal response that is compatible with water-based papermaking rather than melt bonding. PET fiber has a melting point near 255–260 °C and does not bond to cellulosic fiber without an additional latex or sheath. Para-aramid fiber has no practical thermoplastic bonding window and is hydrophobic. VPB103 becomes adhesive at 60–70 °C only in the presence of water and can form bonds without latex, but this also limits high-temperature performance: PVA bonds soften under high humidity and are not suitable for continuous service above 120 °C. For food-contact paper, VPB103 is not a direct substitute for fluorochemical grease-resistance additives or for high-temperature aramid insulation papers. The choice between VPB103 and PET fiber often depends on whether the end product must survive hot humid conditions; PET maintains dimensional stability better above 120 °C, but VPB103 avoids the need for a latex binder in many wet-laid grades.

The comparative data are drawn from general polymer and fiber literature; the VPB103 values should be confirmed against the lot certificate because surface finish and degree of hydrolysis can shift dissolution and bonding. In direct substitution trials, a pilot-scale paper machine trial is necessary because formation, retention, and dryer deposition cannot be predicted solely from fiber properties. Published data for direct substitution of VPB103 in flame-retardant aramid papers is limited; if such a substitution is attempted, the upper service temperature and hot-wet tensile of the resulting paper will be controlled by the PVA fraction.

Open bales should be conditioned at 20–25 °C and 50–65% RH for at least 24 h before use to reduce static and feeding variability. If moisture exceeds 8%, the fiber may clump in metering screws; material exposed to RH above 80% should be pre-dried at 40 °C for 2–4 h. Storage near steam lines or open water is unsuitable. Borate-containing additives can crosslink dissolved PVA even at low concentrations and form gel specks; strong oxidizing agents such as hypochlorite above 500 ppm residual chlorine cause chain scission and loss of fiber tenacity. Prolonged exposure to pH above 10 at temperatures above 50 °C should be avoided. For food-contact paper, the product’s suitability must be established under FDA 21 CFR 176.170 and 176.180, with migration testing according to EN 1186-1 or equivalent. The current REACH status and specific SDS should be confirmed for each shipment.

Incoming inspection typically verifies cut length distribution by optical microscopy, linear density by ISO 1973:2021, and dissolution behavior by a hot-water check at 60 °C: a discrete fiber should lose its fibrous form within 10–15 min under mild agitation. This simple test distinguishes VPB103 from higher-activation PVA grades that remain discrete at 60 °C. Repulping of off-spec paper containing VPB103 is possible in hot pulpers above 60 °C; cold repulping will leave fibrous PVA fragments. Lot-to-lot cut length distribution should show a coefficient of variation below 15%. If wet tensile after thermal activation at 70 °C does not meet target, dryer temperature profile should be checked before increasing binder dose.