| HS Code | 850941 |
| Product Name | KURARAY POVAL 25-88 KL |
| Chemical Type | Partially saponified polyvinyl alcohol |
| Cas Number | 9002-89-5 |
| Appearance | White granular powder |
| Viscosity 4 Percent Aqueous Solution 20c | 24.0 - 28.0 mPa·s |
| Saponification Degree | 87 - 89 mol% |
| Ph 4 Percent Solution | 5.0 - 7.0 |
| Ash Content | ≤ 0.3 wt% |
| Volatile Content | ≤ 5.0 wt% |
| Average Degree Of Polymerization | ~2400 |
As an accredited KURARAY POVAL 25-88 KL factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | KURARAY POVAL 25-88 KL is supplied in 25 kg multi-walled paper bags with a polyethylene liner for moisture protection. |
| Container Loading (20′ FCL) | 20′ FCL shipment of KURARAY POVAL 25-88 KL in sealed bags on pallets, properly secured, protected from moisture and contamination. |
| Shipping | KURARAY POVAL 25-88 KL is supplied as a white granular polyvinyl alcohol powder. It is non-hazardous and not regulated as dangerous goods for shipping. Packed in moisture-proof multi-layer bags or bulk containers, it requires dry, ventilated transport and protection from rain, humidity, and contamination. |
| Storage | Store KURARAY POVAL 25-88 KL in a cool, dry, well-ventilated area, away from direct sunlight, moisture, and heat sources. Keep the container tightly sealed when not in use to prevent clumping or degradation. Avoid contact with oxidizing agents. Maintain stable temperatures and protect from humidity to preserve product quality. |
| Shelf Life | Shelf life is typically 2 years when stored unopened in a cool, dry place, protected from moisture. |
In continuous vinyl acetate–ethylene (VAE) emulsion polymerisation, KURARAY POVAL 25-88 KL functions primarily as a high-molecular-weight protective colloid, not as a rheology modifier alone. The nominal 88 mol% hydrolysis leaves sufficient residual acetyl groups to depress the oil/water interfacial tension at the vinyl acetate monomer–water boundary, while the 25 mPa·s viscosity of a 4% aqueous solution at 20 °C reflects a degree of polymerisation high enough to form an adsorbed layer with measurable surface shear elasticity. The polymer is predissolved in demineralised water at 80–85 °C under low-shear agitation, cooled to reactor temperature, and metered into the aqueous phase before monomer addition or fed simultaneously with a delayed monomer stream. In production-scale 20–30 m³ stainless steel reactors equipped with anchor or Pfaudler-type impellers, the aqueous-phase PVOH concentration is typically maintained within a range that prevents starved protective colloid conditions; excessive feed rates produce local gel specks that are not resolvable by post-filtration. During radical initiation, chain transfer from the propagating PVAc-graft-PVOH chain transfers to the PVOH backbone and consumes a fraction of the water-soluble polymer as graft copolymer, shifting the molecular weight distribution of the dispersing phase and raising low-shear latex viscosity. That shift is measured by ISO 2555 Brookfield apparent viscosity at 20 °C and can be misinterpreted as solids drift if the PVOH charge is not held constant across campaigns. The terminal VAE copolymers are used in packaging adhesives, carpet backing, and construction mastics, where the contribution of 25-88 KL is observed as reduced coarse particle count after 100 µm filtration and improved wet bonding to cementitious substrates. Operational boundaries include the incompatibility of partially hydrolysed PVOH with high levels of borate ions, which can form viscoelastic transient networks rather than useful flow improvement, and the need to verify food-contact status under 21 CFR 175.105 for adhesive applications rather than assuming clearance from the polymer specification alone. Pilot batch comparisons against 72 mol% grades are advised for low-odour packaging lines where residual stabiliser type also influences finished film odour.
Beyond emulsion polymerisation, the same 88 mol% hydrolysis window is exploited in vinyl chloride suspension polymerisation, where the interfacial activity of partially hydrolysed PVOH determines primary grain size, droplet coalescence rate, and final PVC resin porosity. In a baffled 10–30 m³ autoclave, 25-88 KL is typically charged as a prefiltered aqueous solution at 80–90 °C and allowed to cool before initiator injection; the high molecular weight produces a protective film that is less desorbed under the 50–70 °C polymerisation exotherm than low-viscosity fully hydrolysed grades. The grade is combined with a low-hydrolysis grade in the 72 mol% region to create a bimodal stabilisation package: the lower hydrolysis component increases droplet coalescence and porosity, while 25-88 KL suppresses runaway coalescence during the pressure-drop phase. Suspension properties are evaluated by cold plasticiser absorption, bulk density, and K-value according to ISO 1628-2, ISO 60, and ISO 1624; off-spec porosity usually appears as a drop in dry-blend plasticiser uptake rather than as a change in particle size alone. The terminal PVC is used in window profiles, pipe fittings, and rigid film calenders; the resin grain stability contributed by 25-88 KL is most visible in high-K-value grades where loss of the primary suspending agent during the final 15–20% conversion window causes grain collapse. Because the aqueous solution of this grade approaches practical pumping limits at ambient temperature, transfer piping above 60 °C and a 200 µm basket filter are standard to prevent skinning at pipe walls. Published data for this specific grade in 70 m³ autoclave configurations are limited; suspension trials should compare against the current dual-grade package rather than replacing it based on nominal hydrolysis alone.
Because the 25 mPa·s viscosity of a 4% aqueous solution already forces a low solids ceiling, surface size presses running 25-88 KL are usually configured with rod metering rather than pond transfer. In high-speed fine paper applications at 900–1,200 m/min, 25-88 KL is dissolved at 6–8% solids and blended with oxidised starch or styrene-acrylate surface size at a starch-to-PVOH ratio of 2:1 to 4:1; the partial hydrolysis imparts lower intrinsic water resistance than a 98 mol% grade, but the high degree of polymerisation reduces size penetration and improves surface holdout. The practical upper solids limit is controlled by Brookfield viscosity at 55 °C measured with ISO 2555; above approximately 120–150 mPa·s at application temperature, rod streaking and back-flow misting become line-stopping defects on high-speed film transfer. Water resistance is quantified by ISO 535 Cobb60 and oil barrier by TAPPI T 559; the 25-88 KL contribution is observed as a 2–4 g/m² reduction in Cobb60 when replacing a low-viscosity partially hydrolysed grade at equal dry pick-up, although exact values depend on base sheet porosity. Terminal products include grease-resistant folding cartons, release liners, and inkjet coating base papers where dimensional stability under rewetting is required. Because high viscosity limits runnable concentration, converters operating at low drying capacity should set the size press sump temperature at 55–60 °C and avoid mixing with fully hydrolysed PVOH at pH 4, where interpolymer association can raise filtration pressure and create surface gel defects. Food-contact structures must be evaluated under 21 CFR 176.170 for the paper component and 21 CFR 175.105 for the adhesive component, not solely on the PVOH certificate of analysis.
On slasher sizing lines for 65/35 polyester–cotton woven constructions, 25-88 KL is typically pumped from a vacuum cooker at 85 °C into a two-box slasher maintained at 75–80 °C; the high-viscosity grade forms a lubricating film that reduces warp end hairiness during high-speed air-jet weaving. Size add-on is controlled gravimetrically at 8–12% on warp yarn weight, with the formula adjusted by weaving room relative humidity and loom speed. In blends of PVOH with corn starch or acrylic co-size, 25-88 KL contributes the largest share of film toughness, measured as single-yarn tenacity retention after 10,000 cycles on an abrasion tester according to ASTM D2256 and ASTM D3885. The terminal woven product is a dyed apparel or workwear fabric, and the size is removed before bleaching by hot-water washing at 80–90 °C; because the desizing liquor contains high molecular weight PVOH, ultrafiltration recovery is preferred over direct sewer discharge where local COD limits apply. The limiting operational variable is not dissolution temperature but stagnation skimming: at low loom scheduling, the surface of the size box can form a skin below 70 °C, causing slub defects after restart. The use of 25-88 KL in starch blends above 50% PVOH on dry solids may also raise shed dust in high-reed pick looms, and this effect is best evaluated on the target slasher rather than transferred from a laboratory cook test.
Ceramic tape-casting slip formulations based on 20–30% solids in MEK/ethanol utilise 25-88 KL as the primary binder because the high degree of polymerisation raises green tensile strength at low binder content, reducing the burnout burden. In doctor-blade tape casting, a typical nonaqueous formulation contains alumina powder, menhaden fish oil dispersant, 2–5% PVOH on ceramic solids, and 2–4% butyl benzyl phthalate as external plasticiser; the 25-88 KL solution is prepared separately in water or hydroalcoholic solvent and added slowly to avoid shock precipitation. Green tape properties are measured on punched bars using ASTM D882 tensile and ASTM D638-14 for thicker films; the target is typically 2–4 MPa tensile strength with 10–20% elongation at break before burnout. The terminal product is a multilayer ceramic capacitor dielectric, alumina substrate, or piezoelectric actuator tape, where binder burnout must leave ash below a specified limit; the KL grade designation is normally selected for controlled ash, but lot-specific ash analysis by thermogravimetric residue at 600 °C should be checked against the converter’s specification. The burnout profile is the critical processing boundary: PVOH decomposes rapidly through 180–240 °C, and the furnace ramp must hold at 400–600 °C for complete carbon oxidation without disrupting the ceramic particle network. Slip viscosity measured by ISO 2555 at 20 °C should not exceed a range that allows degassing without air entrapment; high-viscosity binder batches may require deaeration under 50 mbar for 30–60 min. Published data for the exact burnout kinetics of 25-88 KL in barium titanate systems are limited, so thermogravimetric profiling on the production tape is required.
When a lithographic envelope line shifts to synthetic gumming, 25-88 KL is dissolved at 20–30% solids in warm water and blended with dextrin, urea or glycerin plasticiser, and a preservative; the high molecular weight raises dry film cohesion to resist wheel tracking on high-speed envelope folding sections, while the residual acetate units moderate water re-wetting speed. Application is by rotary gravure or roller coater with a dry coat weight of 5–8 g/m²; remoistening speed is tested by the time to reach a measurable tack after a 0.1 mL water drop is applied, although the industry also uses automated remoistening testers under controlled nip pressure. Bond performance is quantified by ASTM D1876 T-peel on the paper substrate and by block resistance tests at 50 °C for 24 h. The terminal products include window envelopes, stamps, and tamper-evident closure labels. Borax is a known gelation trigger for partially hydrolysed PVOH because the borate ion complexes with 1,3-diol units; if borax is used to shorten open time, it must be added only after the PVOH is fully hydrated and below 0.5 phr, otherwise the mix will climb in viscosity and may set in the coater pan. At ambient relative humidity above 70%, dusting with silica or starch is necessary to prevent blocking, but the dusting agent reduces remoistening speed proportionally.
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KURARAY POVAL 25-88 KL is a partially hydrolysed polyvinyl alcohol resin supplied as a white to pale-yellow granular powder. The grade designation encodes a nominal solution viscosity of 25 mPa·s measured as a 4% aqueous solution at 20 °C and a nominal degree of hydrolysis of 88 mol%. The KL suffix identifies a manufacturer-controlled low-ash variant intended for cation-sensitive emulsion polymerisation, ceramic green-body binding, remoistenable adhesives, and paper saturation. The product is identified by CAS RN 9002-89-5 and EINECS 209-183-3. Because polyvinyl alcohol is a polymer, REACH registration obligations rest primarily with the vinyl acetate monomer rather than the final macromolecule. Manufacturer certificates of analysis should be consulted for lot-specific release limits, because the KL designation carries additional residual-ash constraints over standard 88 mol% grades.
The technical release profile for KURARAY POVAL 25-88 KL is defined through solution viscosity, degree of hydrolysis, volatile content, ash as sodium oxide, and aqueous pH. Viscosity is determined on a 4% by mass aqueous solution at 20 °C using capillary viscometry under ISO 3105 or the historical JIS K6726 method. The nominal viscosity of 25 mPa·s places the grade between the adjacent 22-88 and 30-88 products; batch certificates provide the exact acceptance interval rather than a single fixed value. Degree of hydrolysis is measured by saponification and back-titration according to ISO 15023-2. For 88 mol% grades, the target hydrolysis interval is commonly 86.0–89.0 mol%, although lot-specific ranges must be verified. Aqueous pH at 4% solids is typically controlled within 4.5–6.5. Volatile matter after drying at 105 °C is generally controlled to ≤5.0%. Ash as Na₂O is controlled to ≤0.4% for standard grades, while the KL variant is additionally constrained to reduce alkali-metal carryover. Published data for the exact KL ash ceiling is limited; procurement specifications should therefore state the maximum allowable sodium and potassium by inductively coupled plasma optical emission spectrometry after ashing.
Operational boundaries follow from the resin’s partial hydrolysis and powder morphology. At relative humidity above 60%, moisture uptake promotes particle agglomeration. Pre-drying at 40–50 °C for 2–4 h is required before controlled feeding or dry blending under such conditions. The powder should not be subjected to direct high-temperature contact with strong mineral acids, because acid-catalysed ester hydrolysis shifts the effective degree of hydrolysis and can alter cold-water solubility. For aqueous stock preparation, the polymer is first dispersed in demineralized water at 25–30 °C under high-shear agitation, then heated to 85–90 °C and held for 30–60 min. Direct steam sparging is avoided because local temperatures above 95 °C may produce gel skins or degrade the polymer.
In emulsion polymerisation, the grade functions as a protective colloid rather than as a passive thickener. The partially hydrolysed chain carries residual acetate segments that anchor to polyvinyl acetate particle surfaces, while the hydroxyl-rich segments extend into the aqueous phase and provide steric stabilisation. A typical charge lies between 2% and 6% by mass relative to monomer, depending on target particle size, latex viscosity, and shear stability. In a 500 L glass-lined reactor equipped with an anchor impeller operating at 40–60 rpm, the resin is usually introduced as a 10% pre-dissolved aqueous solution before monomer addition. The 88 mol% hydrolysis level avoids the high crystallinity and reduced water compatibility of fully hydrolysed 99 mol% grades, while retaining sufficient grafting activity during vinyl acetate polymerisation. The low-ash KL property becomes relevant when the finished dispersion contacts carboxylated thickeners, cation-sensitive stabilisers, or conductivity-limited coating baths. Standard PVOH with ash near 0.4% as Na₂O can raise ionic strength after drying or dilution; the KL variant reduces this transfer. Published data for this specific configuration is limited, but the comparative ionic-strength effect can be estimated from the ash delta and the formulation dilution factor.
Grade selection in the 88 mol% series is driven by solution rheology, final adhesive viscosity, and ash residue. The 25-88 KL midpoint sits between lower-viscosity 22-88 and higher-viscosity 30-88. Lower-viscosity grades reduce mixer torque at equal solids and are preferred when formulation solids must increase without exceeding a fixed viscosity ceiling. Higher-viscosity grades provide stronger protective-colloid function but can raise high-shear viscosity in final water-based adhesives and coatings. The KL variant is specified when the process requires a 25 mPa·s nominal film former and a constrained ash budget in the same grade. Differences in hydrolysis are small among adjacent 88 mol% products; differences in solution viscosity and ash carryover are more significant in production.
| Grade designation | Nominal 4% viscosity at 20 °C | Nominal hydrolysis degree | Ash control | Typical selection driver |
|---|---|---|---|---|
| 22-88 | 22 mPa·s | 88 mol% | standard | lower solution viscosity at high solids |
| 25-88 KL | 25 mPa·s | 88 mol% | low ash | cation-sensitive emulsion polymerisation and low-residue ceramic binding |
| 30-88 | 30 mPa·s | 88 mol% | standard | higher colloidal protection and adhesive film toughness |
| 28-99 | 28 mPa·s | 99 mol% | standard | reduced cold-water sensitivity in dried films |
Preparation of a stock solution differs from simple dilution because partially hydrolysed polyvinyl alcohol swells before dissolution. The powder is added to demineralized water at 25–30 °C under high-shear agitation to separate grains and prevent lump formation. The slurry is then heated to 85–90 °C with continued agitation and held for 30–60 min. Filtration through a 100 µm bag filter removes residual gel specks. Stock solutions at 10–15% solids are stable for extended periods if preserved against microbial growth; unpreserved solutions can lose viscosity through biological degradation. The powder is incompatible with borate ions: sodium tetraborate at concentrations as low as 0.1% in solution can induce a marked viscosity increase through diol-borate complexation. This property is exploited in some gel systems but must be avoided in standard adhesive and emulsion processes unless intentionally formulated.
For ceramic green-body extrusion and tape casting, residual ash from PVOH binders can form fluxing phases during sintering. The KL variant is selected when the fired body must retain dimensional tolerance and low alkali contamination, as in alumina, zirconia, or barium titanate dielectric layers. Binder burnout is typically conducted in air or nitrogen with ramp rates of 0.5–2 °C/min to 450–600 °C. Residual sodium from a standard 0.4% ash grade can produce glassy phases at grain boundaries, shifting dielectric loss and reducing electrical resistivity. The KL grade reduces this residue, although quantitative tan δ improvement must be confirmed on the target ceramic formulation because firing atmosphere, particle size distribution, and binder loading dominate the final ash distribution. The use of 25-88 KL as a binder at 2–5% solids in slip or extrusion batches provides green strength from the 25 mPa·s viscosity film former without excessive die pressure. Bulk density and open porosity after firing can be checked using ISO 18754 or ASTM C20-00, but those methods do not independently isolate binder ash effects.
Remoistenable paper adhesives and water-based laminating adhesives use 25-88 KL as a primary binder. A 15–25% solids solution produces a tacky film with moisture-triggered rebonding capability. The partial hydrolysis level limits cold-water solubility compared with fully hydrolysed 99 mol% grades, but retains sufficient fluidity at application viscosity. In paper saturation, the grade is applied at 8–12% solids; tensile strength retention can be measured by ISO 1924-2 on conditioned paper strips before and after treatment. Ash content influences adhesive clarity in thin films; low-ash KL material reduces haze in dried films compared with standard 88 mol% grades. The relationship between ash and haze is nonlinear and is best assessed by ASTM D1003 haze measurement on cast films. For indirect food-contact uses, relevant compliance may be evaluated under 21 CFR 175.300 and 21 CFR 176.170, but supplier confirmation is required for the specific grade and lot before such use is authorised.
| Parameter | Designation or method | Application constraint |
|---|---|---|
| Chemical identity | CAS RN 9002-89-5; EINECS 209-183-3 | polyvinyl alcohol, partially hydrolysed |
| Solution viscosity | ISO 3105 / JIS K6726 | 4% aqueous solution at 20 °C |
| Degree of hydrolysis | ISO 15023-2 | nominal 88 mol% |
| Ash control | manufacturer-specific low-ash route | residual sodium and potassium constrained for KL grade |
| Indirect food contact | 21 CFR 175.300; 21 CFR 176.170 | supplier confirmation required before use |
| REACH | polymer; monomer obligations apply | no polymer registration number required |
