Fibra ligadora de Kuraray VPB105-2-PVA para fabricação de papel (dissolve a 60 ° C)

Kuraray VPB105-2 PVA Binder Fiber for Paper Making, specified to dissolve at 60 °C, is a polyvinyl alcohol fiber supplied for wet-laid papermaking and nonwoven processes. The grade is designed to place its activation point inside the drying section of conventional paper machines while requiring controlled wet-end temperature below 45 °C. The product is typically supplied as a 1.0 dtex fiber cut to 5 mm; because fineness and cut length control retention and bridging, incoming fiber dimensions should be checked against the certificate of analysis and the actual furnish. In wet-laid systems, VPB105-2 contributes dry tensile, internal bond, and surface integrity without the emulsion destabilization and volatile organic compound load associated with latex binders.

The polymer backbone is a fully hydrolyzed PVA, with hydrolysis degree for low-temperature water-soluble grades typically in the range 98.0–99.0 mol%. The dissolution response is not a melt transition; it is the solvation of a semicrystalline PVA structure and is governed by water temperature, shear, pH, and residence time. At neutral pH, macroscopic dissolution begins near 60 °C, but stock temperatures above 45 °C can soften the fiber and increase tackiness on forming fabrics. Because the gap between the safe wet-end limit and the activation threshold is only 15 °C, the grade has a narrower processing window than high-dissolution PVA binder fibers.

What are the critical fiber dimensions and dissolution thresholds for VPB105-2?

At 5 mm and 1.0 dtex, VPB105-2 is long enough to bridge multiple cellulosic fibers but fine enough to distribute across the sheet without severe wire marking. The 60 °C dissolution threshold distinguishes VPB105-2 from general-purpose PVA binder fiber grades that require 80–95 °C. The lower threshold can reduce steam demand in the dryer section; however, it also eliminates the option of running a hot wet end. Recirculated white water above 50 °C may initiate dissolution in chests, causing viscosity build-up and couch roll adhesion. Stock temperature should therefore be measured at the fan pump discharge rather than inferred from the machine chest setpoint.

Wet-end addition rates for binder fibers typically range from 3 wt% to 10 wt% on bone-dry furnish, depending on target strength and porosity. VPB105-2 is normally added after refining and close to the fan pump, because extended exposure to refiner temperature and mechanical shear can shorten fiber length and accelerate dissolution. Retention is primarily mechanical, but dissolved PVA can increase anionic load in the white water, measurable with a particle charge detector, and reduce retention aid efficiency. Jar tests with mill stock and white water are required before changing retention aid dose. Freeness and drainage should be monitored according to ISO 5267-1 or with a dynamic drainage analyzer when addition levels exceed 5 wt%.

Compared with latex binders, VPB105-2 is a dry, repulpable fiber additive. Latex emulsions introduce film-forming polymer into the wet sheet and can reduce bulk and increase drying energy. VPB105-2 remains in fiber form through the forming section and activates only in the dryer, preserving wet-web openness and depositing binder preferentially at fiber crossings. Against starch or cellulose nanofibrils, VPB105-2 adds synthetic fiber bridging and does not increase refining load; however, it does not provide the same surface sizing or cationic demand response, so the wet-end programme must be recalibrated.

Another relevant comparison is with thermoplastic bicomponent binder fibers. Those fibers require melt bonding at 130–160 °C and form discrete bond points without water interaction. VPB105-2 instead solubilizes in water at 60 °C and reprecipitates into a continuous adhesive phase. The selection between them depends on whether the process can tolerate water-based binder migration and whether the product must be repulpable. In repulpable paper grades, VPB105-2 is often preferred because it does not leave a thermoplastic melt residue; in dry-laid nonwovens, bicomponent fibers are commonly preferred because the web can be bonded without adding water.

When VPB105-2 replaces latex in filtration media, the retention and porosity response must be rebalanced

In filtration grades, binder addition is evaluated against tensile index, air permeability, maximum pore size, and dusting. Handsheets should be formed according to ISO 5269-2 and tensile index measured according to ISO 1924-2; air permeability can be tested according to ISO 5636-3. Because VPB105-2 activates only when the sheet reaches 60 °C, the binder film is concentrated at fiber crossings rather than across the full surface. This can preserve air permeability at a given tensile level, but the response is furnish-dependent. Published data for this specific product in filtration grades is limited; direct side-by-side handsheet trials are recommended before commercial use.

Strength verification should use ISO 1924-2 for tensile index and ISO 16260 or TAPPI T 569 for internal bond. Burst strength can be measured according to ISO 2758. These methods should be applied to handsheets formed from the production furnish, not only to finished sheet samples, to separate fiber effects from machine-direction orientation and basis-weight variation.

Dryer-section activation requires the sheet temperature, not the dryer can surface temperature, to exceed 60 °C. On multi-cylinder dryers, the sheet may remain near the wet-bulb temperature during the constant-rate drying phase; measurable activation usually begins after free water has been removed and sheet temperature climbs in the falling-rate phase. In through-air dryers, exhaust temperature can overstate sheet temperature. Infrared pyrometry or contact thermocouples on the sheet are preferred for process verification. Once activated, PVA forms an adhesive phase at fiber intersections; excessive drying can darken cellulosic furnishes and consume steam without proportional strength gains.

Quality control for incoming VPB105-2 should include dissolution onset, linear density, and cut length. The dissolution temperature is commonly determined by controlled heating of a fiber suspension and observation of fiber disappearance, or by differential scanning calorimetry. Linear density can be tested according to ISO 1973, and fiber length by optical fiber length analysis. Hot water insoluble residue after treatment at 60 °C can indicate whether drying-section temperature was insufficient or whether fiber crystallinity differs from the standard grade. Batch-to-batch variance in dissolution onset can shift activation by a few degrees; mills should compare incoming lots when dryer conditions are fixed.

Because VPB105-2 is a fiber, its addition changes furnish freeness and formation. At addition levels below 5 wt%, the effect on formation is usually small; at levels above 10 wt%, the longer fiber component can produce wire marks if the stock is not adequately dispersed. Headbox consistency and jet-to-wire ratio should be adjusted when the binder fiber dose is increased. Formation can be evaluated with a beta-radiographic formation tester or visual formation standards; sheet grammage and thickness should be measured according to ISO 536 and ISO 534 so that basis-weight variation does not obscure the strength response.

The difference between 60 °C and 80–95 °C activation should be quantified against dryer-section steam consumption, not assumed. A mill trial can compare steam demand at constant machine speed and basis weight with VPB105-2 versus a high-dissolution PVA grade. Because lower activation may allow reduced dryer steam pressure or increased machine speed, the economic comparison should also measure strength development at the reel. Published mill energy data for this specific grade is limited; direct measurement is required.

Repulping, effluent load and food-contact boundary conditions

Because VPB105-2 is water-soluble, broke repulping is generally straightforward under neutral or alkaline conditions. However, dissolved PVA remains in the white-water loop and can increase chemical oxygen demand and viscosity if the mill operates with a closed water system. Mills with low purge rates should monitor white-water total organic carbon and viscosity before increasing addition rates. For food-contact paper and paperboard, use of PVA binder fibers must be confirmed against the relevant regulatory framework, such as FDA 21 CFR 176.170 or FDA 21 CFR 176.180, or applicable national legislation. Compliance is formulation-dependent; the fiber supplier’s regulatory statement should be obtained for the specific furnish and end use.

On inclined-wire wet-laid lines and cylinder paper machines, premature dissolution has been observed when stock chests are located near dryer hood exhaust or when warm white water returns directly to the machine chest. The failure mode typically appears as sticky deposits on couch rolls and reduced fabric drainage. Operators can reduce this risk by isolating VPB105-2 addition to the fan pump, using cold fresh water for dilution, and bypassing hot broke storage during trials. These measures are more important when the machine operates with high white-water closure.

Do not combine VPB105-2 with borate-containing additives in the wet end unless a compatibility trial has been completed. Borate ions can complex with dissolved PVA and generate high-viscosity gels that foul forming fabrics and press felts. Cationic retention aids may also interact with dissolved PVA under high shear; optimal dose should be determined by drainage tests using ISO 5267-1 or a dynamic drainage analyzer. The approach system should be maintained below 45 °C, and the fiber should be stored dry below 30 °C and protected from high humidity to prevent blocking.