KURARAY POVAL 20-98 LA is a polyvinyl alcohol grade produced by controlled alcoholysis of polyvinyl acetate, with a specified degree of hydrolysis of 98.0–99.0 mol% and a nominal viscosity of 20.0–24.0 mPa·s for a 4 wt% aqueous solution at 20°C measured according to JIS K6726. The LA suffix denotes a low-ash variant, with ash content specified at ≤ 0.2 wt% compared with ≤ 0.5 wt% commonly assigned to the corresponding standard 20-98 grade. The product is directed toward ceramic green-body binder systems, paper surface sizing, textile warp size, and water-soluble adhesive compounds where inorganic residue and solution rheology are controlled parameters. Because the degree of hydrolysis is high, cold-water solubility is limited; dissolution requires heating to 85–90°C.

KURARAY POVAL 20-98 LA: Product Identity and Viscosity Specification

Typical lot-release specifications are listed in Table 1. The viscosity window of 20.0–24.0 mPa·s is a manufacturing control range for a 4 wt% aqueous solution at 20°C, and the 4 mPa·s span is not instrument error; it is intentional lot-to-lot variation that downstream compounding must absorb through adjustment of make-up water or polymer solids. The pH specification of 5.0–7.0 is measured on the same 4 wt% solution after cooling to 20°C. For incoming inspection, viscosity is determined on a Brookfield viscometer spindle 1 at 60 rpm after 30 min at 85°C and cooling to 20°C. The degree of hydrolysis is determined by saponification back-titration under JIS K6726. Ash is determined by ignition at 700°C to constant weight.

For dissolution, the powder is first dispersed in cold water at 5–20°C under low-shear agitation. Direct powder addition to water above 50°C causes gel-coated lumps and prolonged filtration time. After dispersion, the batch is heated to 85–90°C and held for 30–60 min until the solution is clear. Equipment should be stainless steel or epoxy-lined; carbon steel can contaminate the solution with iron oxide. After dissolution, the solution is filtered through a 100 µm bag filter or equivalent screen. If a rotor-stator mixer is used for dispersion, tip speed should stay below 2.0 m/s because higher shear entrains air and requires vacuum deaeration at 50–100 mbar absolute. Dissolution below 70°C is an operational boundary; incomplete hydration can leave gel particles that block slot dies in ceramic casting.

The viscosity of the 4 wt% solution decreases with increasing temperature. Solutions may be held at 60–70°C for coating or casting when viscosity reduction is necessary, but exposure above 95°C for more than 2 h can accelerate hydrolysis of residual acetate groups and increase solution color. Within the 20.0–24.0 mPa·s specification, batch-to-batch variation is typically compensated by adjusting polymer concentration by 0.2–0.3 wt% for each 1 mPa·s deviation from the target viscosity.

In ceramic tape casting of alumina substrates, the 20-98 LA grade functions as the primary thermoplastic binder in slurries containing ceramic powder, plasticizer, defoamer, and a polyelectrolyte dispersant. Binder concentration is typically 4–8 wt% of the dry ceramic mass. The low ash content of ≤ 0.2 wt% limits alkali metal introduction during burnout; residual sodium or potassium from higher-ash PVOH can depress the density of sintered alumina after firing above 1550°C. During debinding, the polymer decomposes in air between 450°C and 600°C, leaving an inorganic residue that should remain below 0.2% of the binder mass. In zirconia tape casting, the same grade can be used, but the debinding profile must be extended because zirconia green tape has lower through-plane thermal diffusivity than alumina. Published data for this specific LA configuration in lanthanum-doped barium zirconate titanate systems is limited; users should validate burnout residue on a production tunnel kiln before qualification.

Does Low Ash Content Shift Deflocculant Demand in Alumina Slurries?

The reduction in ash content from ≤ 0.5 wt% to ≤ 0.2 wt% does not eliminate ionic strength effects in electrostatically stabilized alumina slurries. The product retains a pH of 5.0–7.0 in 4 wt% solution, so adding binder to an alkaline slurry can shift the apparent surface charge of the alumina. Formulators re-titrate the dispersant demand after binder addition using a zeta potential probe on a 0.1 vol% suspension. In a 25 wt% solids alumina slip, replacement of standard 20-98 with 20-98 LA can lower the required ammonium polyacrylate dispersant addition by 0.05–0.10 wt% of the ceramic mass while maintaining a low-shear viscosity below 1000 mPa·s at 10 s⁻¹. The exact shift depends on the surface area and impurity profile of the ceramic powder; published data for this specific configuration is limited. The mechanism is attributed to reduced residual acetate salt carry-over, not a change in the adsorption density of the PVOH chain on the alumina surface.

If the slurry is processed on a twin-screw extruder with an L/D of 25:1 and a die pressure below 40 bar, binder solution viscosity should be trimmed to keep the total shear stress below the extruder drive limit. A 20.0–24.0 mPa·s 4% solution does not predict the viscosity at a 20 wt% binder solution concentration; the concentration dependence is strongly non-linear, and plant trials must generate a viscosity-concentration curve using the actual batch. Foam entrainment in ceramic slurries is a production-scale failure mode when dissolved PVOH is pumped through centrifugal mixers. The low-ash grade does not eliminate foam; defoamer selection should be based on dynamic surface tension rather than static surface tension. A polyether-modified siloxane defoamer at 0.1–0.3 wt% of slurry is commonly used, but excess defoamer above 0.5 wt% can cause craters in the cast tape.

For paper surface sizing under alkaline conditions, the 20-98 LA grade is dissolved at 6–10 wt% solids and applied on a film press or size press at 50–60°C. The low-ash attribute reduces deposit formation on metering rods and drying cylinders compared with standard 20-98 in closed-loop broke systems with high conductivity. Viscosity at the application temperature is maintained below 50 mPa·s to prevent film splitting and misting. The grade is combined with starch or styrene-acrylate surface sizing agents; at PVOH addition levels above 0.5 wt% of the size formulation, dynamic surface tension should be measured with a bubble pressure tensiometer and kept below 45 mN/m to prevent ribbing. Calcium carbonate slurry should be added only after complete PVOH dissolution because divalent cations can bridge residual sulfate groups and increase low-shear viscosity to an extent that the size press feed pump cannot manage. Size press roll hardness should remain below 40 Shore D when running continuous PVOH/starch formulations to avoid film build-up on the roll edges.

In textile warp sizing of polyester/cotton blends, 20-98 LA is used at 8–12 wt% solids with lubricant and wax additives. The low ash content reduces reed deposits on air-jet looms running at weft insertion rates above 1000 m/min. Warp size viscosity is controlled at 80–120 mPa·s at 60°C measured on a Brookfield LVT spindle 2 at 30 rpm. The film forms a water-resistant size that can be removed after weaving only by enzymatic desizing with amylase if starch is present, or by a 80–90°C water wash for PVOH. In continuous desizing ranges, wash water temperature below 70°C results in incomplete size removal. Published data for this specific LA configuration on high-speed rapier looms is limited.

In water-soluble adhesive compounds for paper tubes and cores, 20-98 LA is compounded with plasticizers such as glycerol or sorbitol at 10–20 wt% of PVOH solids to reduce film brittleness. The low ash content supports stable wet tack on recycled board; high-ash PVOH can promote adhesive skin formation in glue pots. Adhesive viscosity is adjusted to 2000–5000 mPa·s at 25°C using a Brookfield RVT spindle 6 at 20 rpm. The product is not recommended for cold-water laundry bags because a higher hydrolysis grade dissolves too slowly at 20°C; a partially hydrolyzed grade should be used instead for cold-water release applications.

When Volatile Content Exceeds 5.0 wt% at High Humidity

The volatile matter specification of ≤ 5.0 wt% is a storage and handling boundary, not a limit for final product performance. PVOH is hygroscopic; at relative humidity above 60%, powder adsorbs moisture and becomes cohesive, causing caking in silos and bridging in screw feeders. A desiccant-bed hopper dryer set at 40–50°C with a dew point of -20°C restores flow. Moisture uptake above 5.0 wt% reduces effective polymer solids per unit mass; if make-up water is not corrected, the batch viscosity falls below the lower limit of 20.0 mPa·s for a 4 wt% solution and affects green strength. Handling systems should meet the requirements of NFPA 654 for combustible dust. Flexible intermediate bulk containers must be grounded; transfer through ungrounded polypropylene pipe is not recommended because static charge can accumulate and ignite dust clouds. Storage in unlined carbon steel silos is also not recommended because moisture and residual acetate can promote corrosion staining of the powder.

Differences Between Poval 20-98 LA and Partially Hydrolyzed Grades

The 20-98 LA grade differs from partially hydrolyzed PVOH with hydrolysis degrees of 87–89 mol% in dissolution temperature, crystallinity, and water resistance. At 98.0–99.0 mol% hydrolysis, the polymer requires heating to 85–90°C for complete dissolution, whereas 87–89 mol% grades dissolve at 20–40°C. The higher hydrolysis level raises water resistance after drying and promotes crystallinity, but the polymer is not melt-processable without plasticizer because thermal decomposition begins near 200°C. Films formed from 20-98 LA after drying at 100°C are insoluble in water at 20°C but swell; they dissolve only upon reheating. The product is therefore selected over partially hydrolyzed grades when the final article must withstand humid or aqueous contact after drying.

A second comparative boundary is the ash difference between 20-98 LA and standard 20-98. For applications with high-surface-area alumina or zirconia, the shift from ≤ 0.5 wt% to ≤ 0.2 wt% reduces the total alkali burden by 60% relative to the standard grade. The viscosity and hydrolysis specifications remain identical, so substitution does not require a change in dissolution equipment or solution concentration. The standard 20-98 grade can be used where ash level is not process-limiting; the LA variant becomes necessary only when inorganic residue affects sintering, optical clarity, or electrical loss. In both grades, residual acetyl groups amount to 1.0–2.0 mol%.

For food-contact use, the product may be referenced against FDA 21 CFR 175.105 for adhesives and FDA 21 CFR 176.170 for paper and paperboard in contact with aqueous and fatty foods, subject to extractive limitations and end-use testing. Under REACH Regulation (EC) No 1907/2006, polyvinyl alcohol is registered. The grade is not classified as hazardous under CLP Regulation (EC) No 1272/2008. The Restriction of Hazardous Substances Directive 2011/65/EU does not restrict the polymer itself; end-use articles must be assessed for total lead, cadmium, mercury, and hexavalent chromium if sold in the EU. No statement of biocompatibility for implantable medical devices is made for this industrial grade.