KURARAY POVAL 44-88 S2

KURARAY POVAL 44-88 S2 is applied in size-press surface treatment of uncoated woodfree and recycled liner grades where surface strength, porosity regulation, and gluability are simultaneous requirements. The grade is prepared as an aqueous solution at 6–9 wt% solids in a jet cooker or steam-injection dissolver; dissolution is completed at 90–95 °C for 45–60 min with continuous agitation at 300–500 rpm. Because the 4% aqueous viscosity at 20 °C is 40.0–48.0 mPa·s, a size-press working formulation at 7 wt% PVOH typically exhibits Brookfield viscosity in the range 800–1,500 mPa·s at 40 °C, depending on the proportion of oxidised starch or carboxymethyl cellulose in the blend. The high degree of polymerisation, corresponding to a nominal DP of approximately 4,400, increases film tensile strength and reduces migration of the size into the sheet, which is critical on high-speed metering size presses running above 900 m/min. Surface strength after treatment is monitored by IGT pick resistance in accordance with ISO 3783 and by dry lint propensity measured on a Heydenreich tester; typical target values for offset printing grades are 2.8–3.5 m/s IGT and Cobb 60 water absorptiveness of 25–35 g/m² per ISO 535:2014. The partially hydrolysed structure, with 86.5–89.0 mol% vinyl alcohol units, maintains solubility at size-press temperatures while reducing excessive water retention compared with fully hydrolysed grades. Operational limitations include viscosity rise during hold times longer than 6 h at 60 °C and film blocking when the dried PVOH content in the sheet exceeds 1.2 g/m² per side. Addition rates are therefore metered at 0.8–1.0 wt% absolute dry PVOH on fibre, and pH is maintained at 6.0–7.5 to avoid acid-catalysed acetate hydrolysis.

What Governs Grafting Efficiency and Coagulum Formation When 44-88 S2 Serves as Primary Protective Colloid in Vinyl Acetate/Ethylene Emulsion Polymerisation?

In continuous and batch emulsion polymerisation of vinyl acetate/ethylene, KURARAY POVAL 44-88 S2 functions as the primary water-soluble protective colloid, establishing initial particle nucleation, steric stabilisation, and final viscosity. The degree of hydrolysis at 88 mol% provides sufficient residual acetyl groups for interfacial activity without the strong chain association observed at hydrolysis levels above 92 mol%; this assists latex stability during ethylene stripping and final storage. Grafting of PVOH onto poly(vinyl acetate) proceeds via chain transfer from PVAc macroradicals to the PVOH backbone and through initiation at the acetate methyl group, with grafting efficiency increasing at reaction temperatures from 70 °C to 85 °C but declining above 90 °C because of accelerated acetate hydrolysis and premature chain association in the aqueous phase. Industrial VAE recipes based on 4–6 wt% PVOH on total monomer yield final emulsions at 54–56% solids with Brookfield viscosity of 3,000–6,500 mPa·s at 25 °C when measured at 20 rpm with spindle 4; the high molecular weight of 44-88 S2 pushes the upper end of this range compared with PVOH grades of DP 2,000 or lower. Coagulum control requires delayed addition or split-charge protocols: adding more than 60% of the total colloid in the initial charge can create local viscosity hot spots and starved dispersion at impeller tips, especially in reactors with glass-lined jackets and anchor impellers operating below 1.5 m/s tip speed. Residual vinyl acetate is reduced to below 1,000 mg/kg by post-reaction steam stripping at 80–85 °C, and pH is adjusted to 4.5–5.5 with sodium hydroxide or ammonia before discharge. The addition of 0.5–1.0 wt% of a nonionic surfactant such as an alcohol ethoxylate can reduce coarse grit on 180 µm filters, but exceeding this level may depress water resistance of the final adhesive film. This formulation space is validated for food-contact adhesives under FDA 21 CFR 175.105 and for paper and paperboard components under 21 CFR 176.170; REACH registration of the polymer grade is maintained by Kuraray, and residual methanol is controlled below 1 wt% in the PVOH as supplied.

Heat transfer is the dominant scale-up constraint for this grade because the high continuous-phase viscosity reduces jacket heat removal coefficient to roughly 300–500 W/(m²·K) in a 10 m³ reactor. When the PVOH charge exceeds 6 wt% on monomer, the final emulsion may reach 8,000 mPa·s, making discharge through 2-inch diaphragm pumps slow and increasing the risk of skinning in headspace areas. Production-scale lines therefore generally operate at 4.5–5.5 wt% PVOH and compensate for lower colloid content by raising ethylene pressure to 20–35 bar to achieve target T_g depression. In semi-batch acrylic or styrene-acrylic formulations, 44-88 S2 is not typically used as the sole stabiliser because anionic surfactants provide lower particle size; however, it can be post-added at 0.5–1.5% of finished latex solids to raise viscosity for formulated adhesives. Published data for high-pressure VAE copolymerisation with this specific S2 particle-size variant are more limited than for standard 44-88, but industrial batch records indicate the particle-size specification mainly improves dust control and pneumatic conveying into pre-slurry hoppers without altering dissolution kinetics.

In PVAc wood adhesive compounding, KURARAY POVAL 44-88 S2 is often incorporated as a 10–15 wt% aqueous solution to lift viscosity, extend open time, and contribute to D3 water resistance when used with aluminium chloride or polymerised isocyanate crosslinkers at 0.5–2.0 wt% on wet adhesive. The grade dissolves slowly below 80 °C, so adhesive plants prepare the solution in jacketed make-down vessels with high-shear rotor-stator mixers at 1,500 rpm for 60–90 min. Finished assembly adhesives formulated with 8–12% PVOH solids display cold Brookfield viscosity of 15,000–30,000 mPa·s and are applied with roller coaters or extruders at 120–180 g/m². The high DP of 44-88 S2 extends open time by 3–5 min relative to medium-viscosity PVOH when tested at 23 °C and 50% relative humidity, but the same molecular weight reduces penetration into low-porosity beech and maple, requiring a lower-viscosity PVOH or a wetting agent at 0.1–0.3% for cold-press lamination. Mechanical performance is assessed by EN 204 D3/D4 classification after the conditioning sequences of ISO 9142; tensile shear strength is determined to EN 205 with species-specific minimum values for D3 and D4 qualification. Processing boundaries include pH limits of 3.0–6.0 in acid-catalysed systems and avoidance of borax addition above 0.2% because the borate-diol crosslink with 1,3-diol units produces a sharp viscosity jump that can gel the adhesive in the pot.

When the Size Box Temperature Falls Below 60 °C in Polyester/Cotton Warp Sizing

KURARAY POVAL 44-88 S2 is used in filament and spun-yarn sizing as a partial replacement for starch or modified starch in formulations for high-density cotton/polyester blends. The size paste is prepared at 10–12% total solids by cooking under 90–95 °C; the PVOH fraction is normally 30–50% of dry size solids, with the balance being starch, acrylic size, and a wax lubricant at 0.5–1.5% on total solids. The high-DP grade delivers a stronger cohesive film and better abrasion resistance on high-speed shuttleless looms, where warp yarn tension reaches 0.4–0.6 cN/dtex during shed opening. Size add-on is controlled at 8–12% on yarn weight by adjusting squeeze roll pressure to 10–20 kN/m depending on yarn count; the wet pickup in the size box is maintained at 70–90% to avoid warp streaks. If the size box temperature falls below 60 °C, the high-DP PVOH solution undergoes a rapid viscosity increase and can form surface skins at the liquid-air interface; this results in size film deposits on drying cylinders and a measurable increase in warp breakage rate above 0.15 breaks per 100,000 picks on air-jet looms. Desizing is performed enzymatically for starch fractions or by hot-water washing at 70–80 °C for PVOH, with residual size on greige fabric after scouring assessed by iodine-borate staining; acceptable residual PVOH is below 0.05% on fabric weight. Tensile strength retention after sizing is verified to ASTM D2256-21 on single yarns, with target breaking force retention of 95–105% relative to unsized yarn. Drying cylinder surface temperature must be controlled: surface temperatures above 140 °C can cause film embrittlement and loss of elongation, while temperatures below 100 °C leave tacky PVOH films that block warp ends on the beam.

Ceramic Green Tape Binder Burnout Requires Heating Rates Below 1.0 °C/min

In aqueous tape casting of alumina substrates, KURARAY POVAL 44-88 S2 functions as a temporary organic binder in slurries containing 60–70 wt% alumina powder, 0.5–1.0 wt% dispersant such as ammonium polyacrylate, and 4–7 wt% PVOH on dry ceramic. The slurry is milled in a ball mill at 30–40 rpm for 12–24 h, then de-aired under 50 mbar vacuum. The high molecular weight of the grade increases green tape tensile strength to 1.5–2.5 MPa at 3% strain, measured by a universal testing machine at a crosshead speed of 10 mm/min. Binder burnout is carried out in air at 450–600 °C with a heating rate of 0.5–1.0 °C/min; residual carbon after burnout is controlled below 0.05 wt% to prevent dielectric loss in co-fired substrates. Slurry viscosity is the main process parameter because this PVOH grade is high in molecular weight; a fine-particle S2 specification assists dispersion by reducing undissolved gel specks during low-shear make-down.

Cementitious Tile Adhesive Water-Retention and Shear-Adhesion Trade-Off Under EN 12004 Classification

KURARAY POVAL 44-88 S2 is dry-blended into cementitious tile adhesives at 0.2–0.8% by total dry weight to reduce water loss into absorptive concrete substrates and to extend open time. The PVOH powder is dispersed with cement, sand, and redispersible polymer powder in a cyclic mixer at 800–1,200 rpm; the presence of the high-DP PVOH raises wet mortar viscosity, which is measured as a spread of 140–160 mm after 15 jolts on a flow table. Water retention is determined by filter-paper water uptake under 5 min contact; formulations containing 0.5% PVOH typically retain above 90% of mixing water, compared with 85% for unmodified mortars. The partially hydrolysed grade maintains higher water retention at elevated substrate temperatures of 30–35 °C than starch ethers at equivalent cost, but calcium ions in portland cement can produce PVOH-calcium interaction at pH above 12, gradually reducing open time; therefore the PVOH is combined with a retarder such as citric acid at 0.05–0.15% to shift setting time. Tensile adhesion strength after 28 days dry storage and after water immersion is tested to EN 1348:2007; values for C2 formulations generally exceed 1.0 N/mm², but PVOH alone does not confer the flexibility required for S1 classification, for which the addition of 1.5–3.0% acrylic or vinyl acetate/ethylene redispersible powder is required. Processing incompatibilities include strongly alkaline batching above 40 °C slurry temperature, which accelerates PVOH hydrolysis and can cause a drop in viscosity during extended pot life.