| HS Code | 137463 |
| Product | KURARAY POVAL 5-98 |
| Chemical Name | Polyvinyl alcohol |
| Cas Number | 9002-89-5 |
| Appearance | White granular powder |
| Degree Of Hydrolysis | 98.0 - 99.0 mol% |
| Viscosity 4 Aqueous Solution 20 C | 5.0 - 6.0 mPa·s |
| Average Degree Of Polymerization | Approximately 500 |
| Average Molecular Weight | Approximately 22,000 |
| Ph 4 Aqueous Solution | 5.0 - 7.0 |
| Ash Content | ≤ 0.7 wt% |
| Volatile Content | ≤ 5.0 wt% |
| Solubility | Soluble in hot water; insoluble in most organic solvents |
As an accredited KURARAY POVAL 5-98 factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | KURARAY POVAL 5-98 is supplied in 25 kg multi-wall paper bags, lined with polyethylene, ensuring dry, safe handling and storage. |
| Container Loading (20′ FCL) | KURARAY POVAL 5-98 polyvinyl alcohol packed in 20′ FCL, securely stowed, protected from moisture, clean and dry. |
| Shipping | KURARAY POVAL 5-98 is a polyvinyl alcohol powder shipped in sealed multi-layer paper bags or drums to protect against moisture. It is generally non-hazardous for transport, but should be kept dry, handled with dust control, and stored away from ignition sources. |
| Storage | Store in a dry, cool, well-ventilated area away from heat, moisture, and direct sunlight. Keep the original container tightly closed to prevent humidity absorption, as KURARAY POVAL 5-98 is water-soluble. Avoid dust accumulation and contact with strong oxidizers. Ensure proper labeling and handle with clean equipment to maintain product purity. |
| Shelf Life | Store in a cool, dry place. Shelf life is typically 2 years from manufacture when kept in original sealed packaging. |
In surface-sizing operations on fine paper machines running above 1,200 m/min, the selection of KURARAY POVAL 5-98 as a co-binder with cationic starch is determined less by film formation alone than by the need to hold size-press solids at 6–9 wt% without exceeding 150–250 mPa·s at 55 °C in the transfer-roll nip. The grade is fully hydrolysed at 98–99 mol%, and its low viscosity of 5.0–6.0 mPa·s as a 4 wt% aqueous solution at 20 °C permits high-solids size preparation without the shear-transfer instability that occurs when a 20 mPa·s grade is blended with oxidised starch at 55 °C. In a rod-metered film press with roll hardness 0–5 P&J and rod pressure 0.8–1.2 bar, the size formulation typically contains 0.5–1.5 parts of 5-98 per 100 parts cationic starch on dry basis, corresponding to a dry PVA pick-up of 0.2–0.8 g/m² per side. The size solution is prepared by dispersing POVAL 5-98 in cold water with agitation, heating to 88–95 °C for 30 min, and then cooling to 55 °C before starch addition; this sequence prevents residual gel fish-eyes from forming on the rod and reduces blade scratches. On the downstream sheet, the PVA fraction increases surface strength and reduces lint build-up on offset blanket cylinders, and the film-press runnability window narrows if the starch/PVA blend is held for more than 45 min at 55 °C because of retrogradation-related viscosity drift. Direct mixing with borax or boric acid is not practised because fully hydrolysed PVA forms a three-dimensional diol-borate gel above pH 8.0. Compliance is anchored to ISO 535:2023 Cobb60 for water absorptiveness, ISO 8791-4:2021 Parker PrintSurf for surface roughness, FDA 21 CFR §176.170 for paper and paperboard components intended for aqueous and fatty food packaging, and EU Regulation 1935/2004 Articles 3, 15, and 17 for overall migration and good manufacturing practice. Terminal products from this configuration include inkjet coated base paper, lightweight coated offset grades, envelope base paper, and label facestock. Process limitations are linked to drying capacity; the infrared air-flotation dryers after the size press must reach a sheet surface temperature of 85–105 °C within 0.8–1.5 s to prevent blocking when 5-98 is used at the upper addition level.
In remoistenable adhesive coating for high-speed envelope converting, KURARAY POVAL 5-98 is used at 8–12 wt% of solution solids, with dextrin at 20–35 wt%, urea or glycerin plasticizer at 2–4 wt%, and water to balance. The dried adhesive film typically contains 25–35 wt% PVA on dry solids, with the remainder being dextrin and plasticiser. Application is performed by a roller coater or doctor knife at 15–25 g/m² wet film weight on envelope lines running at 80–150 m/min, followed by infrared drying at 120–140 °C and forced air cooling to 25–30 °C before stacking; if stack temperature exceeds 35 °C, blocking occurs because the fully hydrolysed film remains thermoplastic above its glass transition temperature of 75–80 °C. The remoistening unit then re-wets the adhesive with 5–10 g/m² water, and initial tack develops within 3–8 s. Viscosity control at 25 °C using a Brookfield RVT #4 spindle at 20 rpm should remain at 1,500–3,500 mPa·s; above 14 wt% total solids the mix can enter a hydrogen-bond-driven viscosity plateau that complicates levelling and increases strikethrough on low-grammage papers, a condition observed on batch mixers where the circulation pump is undersized for the final equivalent diameter of hydrated dextrin-PVA clusters. Formulation compatibility is bounded by borate-containing tackifiers; the fully hydrolysed 5-98 crosslinks rapidly at pH > 8.0, producing a stiff gel that cannot be applied by roller coaters. Compliance for the adhesive route is based on FDA 21 CFR §175.105 for adhesives used in food packaging laminates and EU REACH Annex XVII for restricted substances in consumer articles. Terminal products are remoistenable envelope flaps, stamp gum, paper labels, and wallpaper border adhesive.
Before a polyester/cotton warp enters the weaving shed at speeds of 160–240 m/min, the size formulation applied in the slashing room must produce a continuous film on the yarn surface with sufficient abrasion resistance to survive reed impact and harness friction. KURARAY POVAL 5-98 is metered into the size mix at 30–50 wt% of the total film-former, with acid-thinned starch or oxidised starch comprising 50–70 wt%, wax at 0.2–0.5 wt%, and pH held between 6.5 and 7.5; the size box solids are typically 8–12 wt% depending on yarn count and loom speed. The size kitchen preparation starts with dispersion of POVAL 5-98 in cold water, heating to 88–95 °C in a jet cooker with a 20–30 min hold to eliminate undissolved gel particles, then cooling to 75–85 °C before mixing with starch. On the slasher, the warp passes through a size box with squeeze roll load of 16–22 N/mm², and the wet pick-up is controlled to 80–120% on yarn mass; drying cylinder profiles are set to 105–130 °C to bring residual moisture to 3–5% without overheating the PVA film. Weaving performance depends on the ability to remove the size after greige fabric production; the starch portion is hydrolysed with α-amylase at 60–70 °C, while the PVA fraction requires oxidative desizing with hydrogen peroxide or sodium persulfate at 80–95 °C, and incomplete removal leads to redeposition on reeds and higher warp breaks during subsequent wet processing. Regulatory alignment for the size formulation is based on Oeko-Tex Standard 100 Annex 4 Class I for textile finishes, ZDHC MRSL Version 3.1 for wastewater-relevant sizing agents, and EU REACH Annex XVII entry 72 for restricted substances. Terminal woven products served by this route include cotton/polyester shirting, denim, twill workwear, and filament blend wovens. The operational boundary is sharp: at squeeze roll pressure below 12 N/mm², the size pick-up becomes too high, drying is incomplete, and the warp becomes tacky on the headstock beams, whereas above 22 N/mm² the low-viscosity 5-98 film is over-squeezed and abrasion protection drops measurably on high-speed air-jet looms.
KURARAY POVAL 5-98 enters ceramic tape casting as a green-body binder for aqueous alumina and zirconia slips, where its low solution viscosity of 5.0–6.0 mPa·s at 4 wt% allows binder solutions of 4–6 wt% to be added without pushing slurry viscosity above 2,000–4,000 mPa·s at 5 s⁻¹. The binder is charged at 1.0–2.5 wt% of dry ceramic powder mass, with a plasticiser such as PEG 400 at 20–30 wt% of the PVA dry weight, defoamer at 0.1–0.3 wt%, and dispersant such as Darvan C-N at 0.5–1.0 wt%; the ceramic solids loading is held at 50–55 vol% for aqueous tape formulations. Slurry preparation is carried out in a ball mill with alumina or zirconia media for 16–24 h, followed by deairing under vacuum at 50–100 mbar to prevent pinholes. The tape is cast with a doctor blade gap of 100–500 µm and a carrier speed of 0.5–2.0 m/min; drying at 50–80 °C in a three-zone air flotation oven removes water without forming a surface skin, and the PVA binder bonds the ceramic particles until burnout. Thermal removal of 5-98 is performed in air or nitrogen with a hold at 450–500 °C for 2–4 h, and residual ash must be controlled because the sodium content in some PVA batches can shift sintered dielectric properties. Compliance for finished ceramics is assessed through ASTM C373-18 for water absorption, ISO 14604:2012 for advanced ceramic coatings, and EU REACH for organic binder constituents. Terminal products manufactured from this route include alumina substrates, LTCC multilayer low-temperature co-fired ceramic tapes, zirconia oxygen sensor elements, and porous ceramic membranes. The process window is particularly sensitive to blade gap drift; a movement of more than 5 µm in the doctor blade gap changes wet tape thickness by more than the allowed 10% tolerance and alters green density, which in turn shifts sintered shrinkage and camber on cutting lines.
At 0.3–0.8 wt% of dry mix, KURARAY POVAL 5-98 functions in gypsum-based joint compounds and skim coats as a water-soluble polymer that retards moisture loss at the trowelling face and reduces crusting under hot, low-humidity site conditions. The powder is blended in a forced-action mixer with hydrated calcium sulfate, limestone filler, and cellulose ether; water demand is adjusted to maintain a water-to-dry-mix ratio of 0.45–0.60 depending on spread rate. Application is by trowel over gypsum board joints, with initial setting controlled by the gypsum system rather than the PVA, and the PVA residue at 0.3–0.8 wt% does not form a coalesced latex film because it is water-soluble and is distributed in the hydrated matrix. Compliance is based on ASTM C474-15 for joint treatment materials, EN 13963:2014 for gypsum plaster products, and EU REACH for the polymer constituent. Terminal products are drywall joint compounds, gypsum skim coats, and patching plasters. The boundary condition is that increasing 5-98 above 1.0 wt% can increase open time but may soften the cured surface under humid conditions because the fully hydrolysed film remains hygroscopic.
Release liner converting uses KURARAY POVAL 5-98 as an aqueous pre-coat at 4–7 wt% solids on clay-coated or supercalendered kraft base stock before the thermally cured silicone top coat. The dry pre-coat weight is 0.3–0.8 g/m², and the coating is run on an air-knife or rod coater at 150–300 m/min with drying at 100–120 °C; the PVA film blocks silicone migration into the base paper and provides a uniform surface for the subsequent solventless silicone layer. The downstream process uses a five-roll solventless silicone coater with addition of 0.8–1.5 g/m² thermal silicone, and the cure is run at 120–150 °C for 5–10 s. Release performance is checked by peel force at 180° and 30 cm/min, with typical target release of 5–15 cN/25 mm for label applications, and by indicator stain tests for holdout. If the PVA pre-coat holdout falls below 85%, silicone strike-in causes release force drift and adhesive deadening on pressure-sensitive labels. Compliance includes FDA 21 CFR §176.170 for indirect food contact, EU 1935/2004, and ISO 8791-4 for surface roughness. Terminal products include silicone release liners for pressure-sensitive labels, tape backings, medical plasters, and industrial laminates. The main incompatibility is with cationic water chemistry at pH < 4.5, which can precipitate the PVA and reduce holdout.
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Hydrolysis degree is not an aesthetic classification. In polyvinyl alcohol, residual acetate groups interrupt interchain hydrogen bonding and reduce crystallinity. A partially hydrolysed grade such as POVAL 5-88 carries a degree of hydrolysis of 87.0–89.0 mol%; the residual acetate is sufficient to permit dissolution at 20°C and to lower the surface tension of the aqueous solution. In POVAL 5-98, the 98.0–99.0 mol% hydroxyl content removes most residual acetate, increases the glass transition of the dry polymer, and produces a film with higher tensile strength at equivalent thickness. The operational trade-off is thermal: the 5-98 grade must be heated to 90–95°C and held under agitation for complete solution, whereas a partially hydrolysed grade of the same viscosity class dissolves without thermal input.
Degree of hydrolysis is measured by saponification value in accordance with JIS K6726, which reports residual acetyl content as a proportion of the original polyvinyl acetate. The molecular weight of polyvinyl alcohol is not commonly sold as an exact weight-average molecular weight. Instead, the 4% solution viscosity under standard conditions is the operationally decisive parameter. Because the grade 5 viscosity is low, the polymer has a lower molecular weight than fully hydrolysed grades carrying a higher initial numeral. This reduces chain entanglement in solution, lowers extensional viscosity, and allows transfer through positive displacement pumps at lower backpressure. In adhesive compounding, this is relevant when the formulation is applied by engraved roller or spray nozzle; droplets and ribs are less stable than those from higher-viscosity grades.
On production-scale adhesive lines, this solubility difference changes vessel selection. Cold-water-dispersible grades can be pre-mixed in atmospheric tanks at 20–25°C. Fully hydrolysed 5-98 requires a jacketed vessel with condenser or a steam-sparged mixing unit. In high-solids solutions above 10 wt%, end-point clarity should be checked by passing a sample through a 100 μm filter or by inspecting the solution for gel specks under transmitted light. Undissolved microgels can reduce the adhesive bond area and create visible coat defects. Published data for the exact lap-shear value of a starch/PVOH blend at a given coat weight is limited; qualification trials on the target substrate are therefore required.
During heating of a 4 wt% aqueous slurry of POVAL 5-98, the powder first swells and the viscosity remains low until the mixture reaches 70–80°C. The solution clears between 90°C and 95°C. If the heating profile is too rapid, the outer layer of the swollen particles gelatinises before the interior dissolves, producing a stable dispersion of gel skins that cannot be filtered economically. A heating rate of 1–2°C/min with propeller agitation at 200–400 rpm is therefore preferable in atmospheric batch tanks. Once the polymer is fully dissolved, the solution should be cooled slowly. Below 40°C, high-solids solutions of fully hydrolysed PVOH can undergo thermoreversible gelation, which raises apparent viscosity and interferes with levelling in downstream coating.
The typical specification ranges for the product are given below.
| Property | Range | Test basis |
|---|---|---|
| Viscosity of 4% aqueous solution at 20°C | 5.0–6.0 mPa·s | JIS K6726, rotational viscometer |
| Degree of hydrolysis | 98.0–99.0 mol% | JIS K6726, saponification |
| Volatile matter | ≤ 5.0 wt% | JIS K6726, drying |
| Ash as Na₂O | ≤ 0.5 wt% | JIS K6726, ignition |
| pH of 4% solution | 5.0–7.0 | Glass electrode |
The low ash specification is relevant in electronic-grade binder applications and in adhesive systems where ionic contamination can reduce corrosion resistance on bare metallic substrates. In those applications, lot-specific powder washing and handling records should be reviewed before release to production.
In adhesive compounding, POVAL 5-98 is used as a structural binder or as a co-binder with starch, dextrin, and polymer emulsions. The low solution viscosity permits higher wet film weight in rod-metering and spray coating. Film tensile properties are typically assessed on cast films per ASTM D882; fully hydrolysed PVOH films from 98 mol% grades show higher tensile strength and lower elongation at break than films of similar thickness from 88 mol% grades. Water resistance of the dried adhesive film can be ranked by immersion testing per ISO 62, with time to visible whitening being measurably longer than for partially hydrolysed control films. These comparisons are directionally consistent with the increase in crystallinity and hydrogen bond density caused by the higher hydroxyl content.
Paper surface sizing trials with PVOH and starch blends typically run on puddle size presses or metering size presses at 60–120 m/min. At 6 wt% total solids, the low viscosity of 5-98 reduces rod pressure and misting compared with high-viscosity grades. Cobb water absorption is measured per ISO 535; the grade contributes to a lower Cobb value when applied as a continuous surface film. In textile warp sizing, the dry film is evaluated for size add-on, hairiness reduction, and desizing efficiency. Desizing in hot water at 80–90°C is effective because the size film dissolves under the same thermal conditions used in fabric preparation.
In emulsion polymerisation, fully hydrolysed PVOH functions as a protective colloid but with lower surface activity than partially hydrolysed grades. The 5-98 grade is therefore selected when the resulting emulsion must form a more water-resistant dry film. The viscosity contribution of the colloid remains manageable because the 4% solution viscosity is low; this supports higher reactor solids without exceeding maximum agitator torque or impairing heat transfer through the reactor jacket.
Because the viscosity class is fixed at 5.0–6.0 mPa·s, substitution of 5-98 for a higher-viscosity fully hydrolysed grade such as 20-98 changes application rheology before it changes dry film strength. At equal solids, the low-viscosity grade penetrates porous substrates more deeply and produces thinner films under the same coat weight. In contrast, substitution of 5-98 for a partially hydrolysed grade changes water interaction and dry film strength while leaving the 4% solution viscosity essentially unchanged. These distinctions are summarised below.
| Parameter | POVAL 5-98 | POVAL 5-88 | Higher-viscosity fully hydrolysed grade |
|---|---|---|---|
| Viscosity of 4% solution at 20°C | 5.0–6.0 mPa·s | 5.0–6.0 mPa·s | 20.0–24.0 mPa·s |
| Degree of hydrolysis | 98.0–99.0 mol% | 87.0–89.0 mol% | 98.0–99.0 mol% |
| Cold-water solubility at 20°C | Insoluble; requires heat | Soluble | Insoluble; requires heat |
| Film tensile strength at equivalent thickness | Higher than 88 mol% | Lower than 98 mol% | Higher than 88 mol% |
| Film water resistance | Higher than 88 mol% | Lower than 98 mol% | Higher than 88 mol% |
| Solution viscosity at equal solids | Low | Low | High |
Film formation from a 98 mol% PVOH solution proceeds through gelation and evaporation. The dried film is harder and less tacky under humid conditions than a partially hydrolysed film of comparable thickness. However, the same hydrogen bonding density that improves water resistance also narrows the compatibility window with hydrophilic plasticisers. If plasticiser addition exceeds 15 phr in a cast film formulation, blocking under compression at 40°C may occur; this is an operational boundary rather than a molecular-weight failure.
Polyvinyl alcohol powders are hygroscopic and equilibrate with ambient moisture. Bulk storage of POVAL 5-98 in unlined silos at relative humidity above 60% RH increases the volatile matter content and reduces flowability. Bridging in hoppers and build-up on screw conveyors are the dominant failure modes reported on continuous compounding lines. Pre-drying at 60–70°C for 1–2 hours in a dehumidified hopper dryer restores flowable moisture levels before feeding into hot-water dissolution systems. The product should not be exposed to open steam during powder conveying because condensation forms surface lumps that are difficult to disperse.
Because the grade is fully hydrolysed, solution pH drift during prolonged storage is lower than in partially hydrolysed grades with higher residual acetate, but antimicrobial preservation is still mandatory for aqueous solutions held above 24 hours at 20–30°C. The product should not be combined with strong oxidising agents due to the risk of chain scission and viscosity loss. For food-contact applications, compliance must be confirmed against lot-specific regulatory certification; the material is commonly reviewed under FDA 21 CFR 175.105 for adhesives and under EU Regulation 10/2011 where applicable. No statement in this technical description substitutes for lot-specific verification against the finished article specification.
