| HS Code | 177958 |
| Product Name | KURARAY POVAL 5-88 S2 |
| Chemical Family | Polyvinyl alcohol |
| Cas Number | 9002-89-5 |
| Appearance | White to slightly yellow granular powder |
| Saponification Degree | 87-89 mol% |
| Viscosity 4 Percent Solution 20c | 4.8-5.8 mPa·s |
| Ph 4 Percent Solution 20c | 5.0-7.0 |
| Bulk Density | 0.4-0.6 g/cm³ |
| Solubility | Soluble in hot water; requires heating for full dissolution |
| Volatile Content | <=5.0% |
| Ash Content | <=0.3% |
As an accredited KURARAY POVAL 5-88 S2 factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Supplied in 25 kg multi-wall paper bags. KURARAY POVAL 5-88 S2 is a white granular polyvinyl alcohol resin requiring dry storage. |
| Container Loading (20′ FCL) | KURARAY POVAL 5-88 S2 loaded in 20′ FCL: 25 kg bags, 40 bags per pallet, 20 pallets, 20,000 kg net, shrink-wrapped. |
| Shipping | KURARAY POVAL 5-88 S2 is supplied as a free-flowing powder in multi-layer paper bags or similar moisture-proof packaging. Ship in dry, ventilated containers, protected from rain and humidity. Avoid excessive dust generation; store away from ignition sources. Handle with care to prevent bag damage during transit. |
| Storage | Store KURARAY POVAL 5-88 S2 in its original, tightly sealed container in a cool, dry, well-ventilated area. Protect from moisture, direct sunlight, and heat sources. Keep away from oxidizing agents and ignition sources. Prevent dust accumulation and maintain clean surroundings. Follow manufacturer’s shelf-life recommendations and handle with appropriate PPE. |
| Shelf Life | Shelf life is typically two years from production date when stored in original, unopened containers under dry, cool conditions. |
KURARAY POVAL 5-88 S2 is processed as a primary protective colloid in semi-continuous emulsion polymerization of vinyl acetate homopolymers and vinyl acetate-ethylene copolymer dispersions. The grade has a degree of hydrolysis of 87.0–89.0 mol% and a 4% aqueous solution viscosity of 4.5–5.5 mPa·s at 20°C measured by JIS K6726. In a 10–15 m³ stainless steel reactor equipped with a pitched-blade turbine and external loop heat exchanger, the colloid solution is prepared in demineralized water at 20–40°C before initiator feed. A colloid loading of 4–6 wt% based on total monomer mass is typical for adhesive-grade dispersions. At this loading, the particle size distribution is controlled between 0.8 µm and 2.5 µm. Reducing the colloid below 4 wt% broadens the particle size distribution and raises coarse grit counts on 40 µm filter screens. Increasing above 6 wt% pushes dispersion viscosity above 15,000 mPa·s and reduces the external loop heat-transfer coefficient. Undissolved powder fines initiate seed particles and reactor wall fouling; eductor addition into a high-shear dissolver at 1,500–3,000 rpm for 20–30 min prevents fisheye formation.
The 88 mol% hydrolysis level permits sufficient grafting with vinyl acetate radicals during potassium persulfate initiation at 70–85°C. Residual acetate groups depress surface tension and improve low-temperature film coalescence of wood-adhesive and packaging-adhesive end products. Sodium acetate buffer at 0.05–0.20 wt% keeps the aqueous phase at pH 4.5–5.5. Borax, boric acid, and polyvalent metal salts are excluded from the let-down because they crosslink residual hydroxyl sites. Crosslinking appears as a viscosity spike or as gel stringers in the first let-down vessel. Defoaming with mineral-oil or silicone defoamers at 0.1–0.3 wt% is required in high-speed dispersers. Medium-shear impeller tip speeds of 2.5–4.0 m/s produce reproducible dispersion viscosity between 8,000 mPa·s and 12,000 mPa·s at 25°C. In vinyl acetate-ethylene copolymerization, ethylene pressure is held at 20–60 bar to reach 10–30 wt% ethylene content in the polymer. Residual monomer stripping at 60°C and 150–200 mbar does not destabilize the latex if pH remains above 4.0.
Fine-paper surface sizing uses KURARAY POVAL 5-88 S2 as a co-binder with oxidized starch at total solids of 2–6 wt%. Because the grade dissolves at 20–40°C, no jet cooking is required. A 4% aqueous solution viscosity of 4.5–5.5 mPa·s keeps size-press formulation viscosity below 30 mPa·s at 50°C in a metering size press. Starch replacement levels of 20–40 wt% on dry weight raise surface strength as measured by IGT pick velocity per ISO 3783. The increase is caused by the continuous film formed at the paper surface. Metering with bent-blade or rod systems gives a controlled wet film between 5 g/m² and 12 g/m², depending on base-sheet absorption. Soft-roll applicators reduce film-split patterns at machine speeds above 1,200 m/min. After-application infrared dryers must not raise sheet surface temperature above 90°C, because skinning of the PVOH film reduces surface strength gain.
Operational boundaries are defined by starch compatibility and microbial stability. If the starch fraction is enzyme-converted and the size pH drops below 4.5, PVOH phase separation can occur in long recirculation loops. Mixed size tanks holding starch–PVOH blends longer than 24 h require a preservative registered for papermaking wet-end use. High calcium hardness above 300 ppm as CaCO₃ may increase foaming in flooded nip systems. Defoamer selection must avoid silicone overdosing above 0.1 wt% of wet size, because hydrophobic spots on coated sheets cause print mottle in subsequent offset applications.
For alumina and barium titanate tape casting, binder selection requires low-foaming dissolution and controlled burnout. KURARAY POVAL 5-88 S2 is incorporated at 2–6 wt% of ceramic powder. The ceramic powder is first dispersed in water with poly(acrylic acid) ammonium salt at 0.2–0.8 wt% of solids. PVOH solution is added later to avoid competitive adsorption on the particle surface. Glycerol or polyethylene glycol 400 is introduced at 10–30 wt% of binder solids to plasticize the dried tape. Final slurry viscosity is adjusted to 1,000–4,000 mPa·s at 20 s⁻¹ for doctor-blade casting. A blade gap of 100–300 µm and carrier speed of 0.5–2.0 m/min on a polyethylene terephthalate film produce green tapes of 30–150 µm after drying at 25–60°C. The grade provides sufficient green strength for punching and via formation in multilayer ceramic capacitors.
Thermal binder removal is a critical step. In air, decomposition begins near 200°C and is completed by 450–500°C. In low-oxygen atmospheres, carbon residue can remain if the burnout profile does not hold at 350–400°C. Boric acid additions, sometimes used as sintering aids, must be delayed until after binder dissolution because borate crosslinks the PVOH and raises slurry viscosity. Additions above 0.5 wt% of ceramic solids are known to produce gelation in PVOH-based slips. Green density is checked by mercury intrusion porosimetry before sintering. Published data for this specific slurry configuration are limited; adjustment is required when changing from alumina to barium titanate due to differences in particle surface charge.
On high-speed air-jet looms, warp sizing formulations incorporate KURARAY POVAL 5-88 S2 at 5–20 wt% of total size solids to reduce broken warp ends. The PVOH is combined with native or modified starch after starch cooking. In a typical size box maintained at 60–80°C, the size liquor viscosity is held at 8–20 s through a Zahn cup #3. Cotton and cotton–polyester warps receive an add-on of 8–14 wt% owf on a multi-cylinder drying section with cylinder surface temperatures of 120–150°C. The partially hydrolyzed PVOH migrates less than fully hydrolyzed grades during drying, which reduces size film surface crusting. Modern air-jet looms operating at 800–1,200 rpm show less accumulation of size residues on drop wires and heald frames when PVOH is present. Size removal after weaving uses hot alkaline washing at 70–90°C with 2–5 g/L caustic soda and a nonionic surfactant. Enzymatic desizing with amylase addresses only the starch fraction; PVOH requires the alkaline wash step for complete removal before bleaching. Hard water above 200 ppm as CaCO₃ increases scale formation on drying cylinders when processing PVOH–starch blends. No formaldehyde is released from PVOH-containing sizing formulas because no amine-formaldehyde resin is required in this system.
Spiral paper tube winding adhesive formulations use KURARAY POVAL 5-88 S2 at 10–20 wt% of solution as the remoistenable film former. Mill humidity above 65% RH reduces tack development because the PVOH film absorbs moisture and plasticizes on the glued ply. In such conditions, solids are raised to 18–22 wt% with clay or calcium carbonate filler to accelerate wet tack. A glue-roll applicator running at 30–80 m/min line speed applies 20–40 g/m² of wet adhesive to the paper ply. Viscosity is maintained at 2,000–5,000 mPa·s at 25°C with a Brookfield viscometer. The base solution viscosity of 4.5–5.5 mPa·s allows formulation adjustments without thixotropic modifiers. Borax is excluded because it crosslinks the PVOH and shortens open time. The dried adhesive film remoistens at 20–30°C for envelope window patching. Storage tanks require heating only to 30–40°C; higher temperatures accelerate hydrolysis of residual ester groups and reduce adhesive viscosity over multi-day hold times.
In solution-cast water-soluble film production, KURARAY POVAL 5-88 S2 is formulated into an aqueous coating solution containing 10–15 wt% PVOH and a plasticizer at 2–10 wt% of PVOH solids. Slot die or knife-over-roll coating is used. Wet film thickness of 200–500 µm is cast on a release-coated polyester carrier. Drying at 60–90°C in a multi-zone forced-air oven produces films of 30–80 µm. Dissolution time in agitated water at 20°C depends on film thickness and plasticizer type. Films plasticized with glycerol dissolve more rapidly than films containing trimethylolpropane. Blocking resistance is tested under 1 kg/cm² load at 40°C and 70% RH for 24 h. Mechanical properties are measured per ASTM D882; published data for this specific formulation are limited. End-use specifications for laundry sachets commonly require cold-water dissolution below 30 s in an agitated vessel. Films above 80 µm may require perforation or elevated water temperature to meet this limit. PVOH 5-88 S2 films are incompatible with borax-containing detergent powders because borate ion crosslinks the film surface and leaves undissolved residue. High-humidity storage above 80% RH causes irreversible blocking unless the film is overpacked in moisture-barrier packaging.
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KURARAY POVAL 5-88 S2 is a partially hydrolysed polyvinyl alcohol supplied as a dry, free-flowing powder. The grade designation follows the ISO 15023-1 system: the leading numeral group identifies the nominal 4% aqueous solution viscosity, and the second numeral group identifies the nominal degree of hydrolysis. For this material, the 4% aqueous solution viscosity at 20 °C is controlled within 5.0–5.8 mPa·s when determined by capillary viscometry under ISO 15023-2:2019, and the degree of hydrolysis is controlled within 87.0–89.0 mol%. The S2 suffix identifies a handling-optimized sub-grade within the 5-88 series. Typical release data cited in supplier documentation also list pH of a 4% aqueous solution in the range 4.5–6.5, volatile matter not exceeding 5.0 wt%, and ash not exceeding 0.6 wt% by JIS K6726 or corresponding ISO 15023-2 clauses. The base polymer is a vinyl alcohol–vinyl acetate copolymer with residual acetyl groups distributed along the polymer chain; this composition lowers crystalline order, lowers the aqueous dissolution temperature, and increases cold-water solubility relative to fully hydrolysed polyvinyl alcohol grades.
The primary distinction between POVAL 5-88 S2 and standard POVAL 5-88 is not a change in the base polymer composition but a change in handling and processing behaviour. Kuraray literature associates the S2 suffix with controlled dry-powder particle size, reduced dusting during bulk transfer, and lower foam entrainment during cold-water batch make-up. Published quantitative differences between 5-88 S2 and standard 5-88 in residual catalyst ash and particle-size distribution remain limited; the certificate of analysis is the authoritative source for lot-specific values. Compared with fully hydrolysed POVAL 5-98, the 5-88 S2 grade carries approximately 12 mol% residual acetyl groups, corresponding to roughly 21 wt% vinyl acetate repeat units. These acetate groups act as internal chain defects, suppressing crystallite density and producing a more open, water-sensitive network. The comparative solution profile is summarised below.
| POVAL grade | 4% solution viscosity | Degree of hydrolysis | Function class |
|---|---|---|---|
| 3-88 | 2.8–3.5 mPa·s | 87–89 mol% | low-viscosity protective colloid |
| 4-88 | 4.0–4.8 mPa·s | 87–89 mol% | paper sizing, adhesives |
| 5-88 S2 | 5.0–5.8 mPa·s | 87–89 mol% | protective colloid, remoistenable adhesive |
| 5-98 | 5.0–5.8 mPa·s | 98–99 mol% | film, barrier, water-resistant binder |
| 8-88 | 7.0–9.0 mPa·s | 87–89 mol% | high-viscosity adhesive, binder |
At 88 mol% hydrolysis, the residual acetate content is sufficient to reduce the thermal gelation tendency that is more pronounced in fully hydrolysed grades. The practical consequence is that 5-88 S2 can be dissolved directly in cold water under high shear, while 98–99 mol% hydrolysed grades typically require temperatures above 80 °C for complete dissolution. The trade-off is reduced water resistance after film formation and higher equilibrium moisture uptake under humid conditions.
For cold-water make-up, the powder is dispersed into turbulent cold water before the slurry is heated to 85–90 °C for 30–60 min. Adding dry 5-88 S2 directly to hot water above 70 °C introduces a process risk: the particle surface hydrates rapidly and forms a gelatinous shell that retards water penetration and can produce swollen agglomerates. In a 1,000 L stainless-steel vessel equipped with a 45° pitched-blade turbine and side baffles, a specific power input of 0.15–0.30 kW/kg during the wetting phase is commonly applied, although published data for this precise configuration is limited. The function of the high-shear wetting phase is particle separation, not molecular dissolution. After heating, the solution is cooled and adjusted to the target solids content.
| Property | Typical range or limit | Reference method |
|---|---|---|
| Degree of hydrolysis | 87.0–89.0 mol% | ISO 15023-2, JIS K6726 |
| Viscosity of 4% aqueous solution at 20 °C | 5.0–5.8 mPa·s | ISO 15023-2 |
| Volatile matter | ≤ 5.0 wt% | JIS K6726 |
| Ash | ≤ 0.6 wt% | JIS K6726 |
| pH of 4% aqueous solution | 4.5–6.5 | ISO 15023-2 |
The 4% solution viscosity value is a quality-control reference and does not define the behaviour of concentrated process solutions. At 10 wt% solids, the Brookfield viscosity at 20 °C measured under ISO 2555 is considerably higher than the 4% reference value, and at 20 wt% the solution exhibits pronounced shear thinning. Specific viscosity values at concentrations above 10 wt% must be determined by rheometry because temperature history, pH, and mechanical shear all influence the final solution state. Solutions left unstirred below 15 °C may increase in viscosity and exceed the capability of low-speed centrifugal transfer pumps. Storage above 95 °C for extended periods should be avoided because residual acetate groups can undergo further hydrolysis under sustained thermal load, shifting the effective degree of hydrolysis and altering crystallisation behaviour on cooling.
Emulsion polymerisation utilises 5-88 S2 as a protective colloid in vinyl acetate, vinyl acetate-ethylene, and acrylic ester polymerisations. The polymer adsorbs at the monomer–water interface and provides steric stabilisation during nucleation and particle growth. The 87–89 mol% hydrolysis band gives sufficient amphiphilic character without the excessive interfacial rigidity that can occur with highly hydrolysed grades. For a 45–55 wt% solids vinyl acetate homopolymer or copolymer latex, protective colloid addition levels are commonly 2–6 wt% based on monomer. Typical final emulsion Brookfield viscosity ranges from 500–10,000 mPa·s, depending on reactor temperature, initiator type, and the residual monomer level. Continuous stirred-tank reactors operating at 70–80 °C with mean residence times of 2–4 h are representative, though published data for the S2 sub-grade in a specific reactor configuration is limited.
At protective colloid levels below 1.5 wt% on monomer, particle size control can deteriorate and coagulum formation may increase. Above 8 wt%, the continuous-phase viscosity may restrict monomer diffusion and reduce overall conversion. The residual 5-88 S2 remaining in the dried latex film contributes wet tack and dry adhesion but also increases water sensitivity. In addition, the ash and volatile matter limits are relevant in polymerisation because residual inorganic species can alter initiator decomposition and pH drift during batch hold. Grade-to-grade ash variance is therefore monitored by lot certificate rather than assumed from the nominal POVAL designation.
Paper surface sizing is another established use of 5-88 S2. The partially hydrolysed grade is selected over fully hydrolysed PVOH when the size-press formulation requires low foaming and reduced film blocking. The 5.0–5.8 mPa·s 4% viscosity permits low-viscosity circulation at 4–10 wt% solids in a size press. The S2 handling-optimized form is reported to lower foam entrainment during continuous metering; quantitative foam-height reduction data are supplier-specific and should be confirmed by a dynamic foam test such as ASTM D1173. Typical size-press pick-up on bleached board is 0.5–1.5 g/m², but the appropriate addition level depends on substrate porosity, surface energy, and the wet-end cationic demand of the machine.
Substituting 5-88 S2 for a fully hydrolysed grade such as 5-98 in remoistenable adhesives shifts end-use properties in two directions. The 87.0–89.0 mol% hydrolysis gives cold-water rewettability and lower film blocking, which are functional advantages in envelope and label adhesives. The same residual acetate content increases equilibrium moisture uptake and reduces wet bond strength after water exposure. In borate-containing formulations, 5-88 S2 reacts with boric acid or sodium tetraborate through reversible didiol crosslinks. At pH 8–9 and 5 wt% PVOH, borax additions below 0.5 wt% can produce a sharp viscosity increase; at pH below 5, crosslink density remains low. Uncontrolled borate addition is a process boundary because irreversible gel lumps can form rapidly in high-shear mixing zones.
Alkaline additives, including caustic and certain alkanolamines, accelerate saponification of residual acetate groups in 5-88 S2 and should be buffered if pH stability is required. Amine-based additives are not recommended in unbuffered formulations where long-term viscosity stability is critical. The material is not the preferred choice for blown-film oxygen-barrier structures because the partially hydrolysed grade does not provide the oxygen transmission resistance of fully hydrolysed PVOH or ethylene-vinyl alcohol copolymer. Melt processing without plasticiser is not recommended because the onset of thermal decomposition is near 200 °C; compounding with polyolefins requires glycerol or polyol plasticisers and may still result in phase separation. Regulatory status for food-contact uses should be verified against the specific residual monomer and catalyst profile. Polyvinyl alcohol is listed in FDA 21 CFR 175.105 for adhesive components and FDA 21 CFR 176.170 for paper and paperboard components, subject to extractives limitations. REACH registration applies to the polymer as a registered substance in the EU.
