| HS Code | 685920 |
| Product Name | KURARAY POVAL 3-98 |
| Chemical Family | Polyvinyl alcohol |
| Appearance | White granular powder |
| Viscosity 4 Percent Solution 20c | 3.0 ± 0.4 mPa·s |
| Degree Of Hydrolysis | 98.0 ± 0.5 mol% |
| Ph 4 Percent Solution | 5.0 - 7.0 |
| Ash Content | ≤ 0.5% |
| Volatile Matter | ≤ 5.0% |
| Bulk Density | 0.4 - 0.6 g/cm³ |
| Solubility | Soluble in hot water; practically insoluble in organic solvents |
| Cas Number | 9002-89-5 |
As an accredited KURARAY POVAL 3-98 factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | KURARAY POVAL 3-98 is supplied in 25 kg multi-layer paper bags, palletized and shrink-wrapped for safe handling and storage. |
| Container Loading (20′ FCL) | Load 20′ FCL with palletized 25kg bags of KURARAY POVAL 3-98, ensuring stable stacking, proper segregation, and secure bracing for safe transit. |
| Shipping | KURARAY POVAL 3-98 is a polyvinyl alcohol powder shipped in sealed multi-layer paper or polyethylene bags, typically palletized and stretch-wrapped. It is non-hazardous under transport regulations, but moisture-sensitive, so it should be kept dry, protected from direct sunlight, and handled to avoid dust generation. |
| Storage | Store KURARAY POVAL 3-98 in a cool, dry, well-ventilated area away from direct sunlight and moisture. Keep containers tightly closed when not in use to prevent caking or contamination. Avoid dust generation and incompatible materials such as strong oxidizers. Maintain stable temperature and humidity, and follow local regulations for safe handling and storage. |
| Shelf Life | Shelf life is typically 2 years from manufacture when stored in original unopened containers in a cool, dry place. |
In slasher sizing of ring-spun cotton and 65/35 polyester/cotton yarns, a 12.0% solids size liquor containing 6.0–8.0 wt% KURARAY POVAL 3-98 relative to total size solids is cooked in a steam-injected jet cooker at 95–98°C for 25–30 min to obtain a particle-free solution with a flow cup viscosity of 9–13 s (ISO 2431, 4 mm cup at 20°C). The grade’s nominal viscosity of 3.2–3.8 mPa·s in 4% aqueous solution at 20°C (JIS K6726) permits high size-box pickup without overcuring the yarn sheet. A two-size-box slasher running at 60–80 m/min with nip pressure of 18–25 N/mm deposits 8–12% dry add-on on polyester/cotton yarns and 5–8% on 100% cotton yarns, depending on yarn count and size-box solids. POVAL 3-98 forms a strongly hydrogen-bonded film at the fibre surface; abrasion resistance of sized yarn tested by ASTM D3885-07A improves by 40–60% relative to starch-only size, although published mill data for this exact grade is limited. Size shed data measured on a Reutlingen Webtester can be suppressed below 0.5 mg/kg yarn when a post-drying wax overcoat is applied. Compatibility limits must be observed: borax or boric acid additions above 0.2 wt% of PVA solids cause irreversible gelation through diol-borate complexation, and process water above 25°dH promotes calcium-stearate precipitation if wax-based overcoats share the same size box. Desizing of the woven fabric uses hot water at 70–80°C and a 0.5–1.0 g/L amylase or oxidative desizing bath; residual PVA is quantified by the iodine-boric acid colorimetric method according to DIN 54280. On production-scale slashers, the main bottleneck is foam formation when return liquor is blended with fresh liquor; many lines require 0.05–0.10 wt% of an EO/PO block copolymer defoamer to maintain size-box level control.
Rod-metering size presses operating at 400–600 m/min on 80–120 g/m² recycled linerboard show a distinct rheological shift when 3-98 replaces oxidized starch at 2.0–4.0 wt% solution concentration. The starch pseudoplastic profile transitions to a Newtonian low-viscosity profile measured at 15–35 mPa·s at 50°C by ISO 2555. At 3.0 wt% solids, the film press deposits a dry coat weight of 1.5–2.5 g/m²/side, with wet film thickness of 8–12 µm/side controlled by rod pressure and backing roll hardness. Oil and grease resistance evaluated by TAPPI T559 kit rating reaches kit 5–7 after 2.0 g/m² dry coat weight on recycled substrate; published data for this exact configuration is limited. Water absorption by ISO 535 Cobb 60 is reduced from 28–35 g/m² to 6–10 g/m² on kraft liner. Because 3-98 is a 98.0–99.0 mol% hydrolysed PVOH, the dry film is less moisture-sensitive than 88 mol% grades, but the resin requires cooking at 90–95°C and cannot be dispersed cold. Dilution water hardness above 20°dH can produce insoluble calcium-PVA interfacial films; mills using hard water typically add 0.2–0.5 g/L tetrasodium EDTA. Continuous runnability is limited by PVOH solution surface tension of 45–50 mN/m at 3.0 wt%, which is lower than oxidized starch and can cause misting above 800 m/min; high-molecular-weight polyethylene oxide anti-misting additives at 0.05 wt% are introduced only where line speed demands.
| Standard / regulation | Relevant provision | Measured property |
|---|---|---|
| FDA 21 CFR §176.170 | Components of paper and paperboard in contact with aqueous and fatty foods | Extractives limit |
| REACH Annex XVII | Restriction on boron compounds in treated paper | Boric acid content |
| TAPPI T559 | Grease resistance kit test | Kit rating |
| ISO 535 | Cobb water absorptiveness | g/m² after 60 s |
Aqueous polyvinyl acetate and vinyl acetate-ethylene dispersion polymerisation introduces 3-98 as the primary or co-protective colloid at 2.0–6.0 wt% based on total monomer. The low molecular weight of the grade produces a low-viscosity aqueous phase that permits higher reactor solids before heat transfer becomes limiting; 55–65% solids VAE dispersions with 2,500–5,000 mPa·s Brookfield viscosity at 25°C (ISO 2555, spindle 4, 20 rpm) are produced in 10–20 m³ stainless steel reactors with anchor impeller tip speeds of 1.5–2.5 m/s. Polymerisation is initiated at 65–75°C with a redox pair of hydrogen peroxide and sodium formaldehyde sulfoxylate, with delayed monomer feed over 3.5–5.0 h. Because 3-98 has a degree of hydrolysis of 98.0–99.0 mol%, the resulting dispersion shows low water sensitivity and high wet adhesion in wood glue and paper-to-paper laminates. Grafting efficiency of the PVOH onto polyvinyl acetate is higher at the late stage of monomer addition when free monomer concentration remains above 5.0 wt%; below this value, ungrafted PVOH accumulates in the serum and raises minimum film-forming temperature. Coagulum levels on production lines stay below 0.05 wt% if the PVOH solution is pre-cooked at 90°C, filtered through 100 µm bag filters, and fed continuously at a rate matched to monomer feed. The principal operational incompatibility is with carboxylic acid monomers: methacrylic acid or acrylic acid above 1.0 wt% can complex with hydroxyl groups and increase dispersion viscosity beyond the reactor impeller motor limit. In such formulations a lower-hydrolysis PVOH is blended with 3-98 to restore shear stability.
Alumina substrates for thick-film circuits are tape-cast from aqueous slips in which 3-98 functions as the primary sacrificial binder phase. The resin is dissolved at 6.0–8.0 wt% in deionised water and added to the slip to yield 4.0–7.0 wt% PVOH on dry alumina powder. The low ash content of the grade, below 0.5 wt%, limits sodium and potassium contamination; sodium levels above 150 ppm in the binder can depress sintered alumina resistivity and are avoided in thick-film circuit substrates. Milling proceeds in a 50–100 L polyurethane-lined ball mill with 10 mm yttria-stabilised zirconia media at 55–70% critical speed for 16–24 h. After vacuum de-airing to below 2.0 kPa absolute pressure, the slip is cast with a doctor blade gap of 150–300 µm onto a Mylar carrier at 0.3–1.0 m/min; viscosity at the casting shear rate is 1,500–3,500 mPa·s by ISO 3219. Drying at 55–65°C for 20–40 min produces green tape with 0.5–1.5% residual moisture and green density of 2.2–2.5 g/cm³. Debinding follows a two-stage profile: 0.5–1.0°C/min to 300°C with a 2 h hold, then 1.0–2.0°C/min to 600°C with a 1 h hold in air. A critical processing window exists at 220–260°C; heating rates above 1.5°C/min in this range cause delamination and blistering because PVOH decomposition is autocatalytic. Fired density measured by ASTM C373-18 reaches 3.85–3.92 g/cm³ after sintering at 1,550–1,600°C.
| Slip component / property | Low-binder slip | High-binder slip |
|---|---|---|
| Alumina powder (d50 0.8 µm) | 100.0 parts by weight | 100.0 parts by weight |
| 3-98 solution (8.0 wt%) | 50.0 parts | 87.5 parts |
| Dry binder level | 4.0 wt% of alumina | 7.0 wt% of alumina |
| Plasticizer (PEG 400) | 1.0 wt% of binder solids | 2.0 wt% of binder solids |
| Viscosity ISO 3219 at 100 s⁻¹ | 1,800–2,400 mPa·s | 2,800–3,500 mPa·s |
| Green density | 2.30–2.40 g/cm³ | 2.20–2.30 g/cm³ |
At the two-roll metering system on a continuous filament E-glass forming line, 3-98 forms the film-forming base at 3.0–8.0 wt% of the aqueous size bath. The bath is prepared by cooking the PVOH at 90°C, then adding a silane coupling agent, typically γ-methacryloxypropyltrimethoxysilane at 0.3–0.8 wt% of size, followed by a lubricant and antistatic agent. The metering roll gap is set to maintain 0.4–0.8% loss on ignition on the roving, measured by ISO 1887. Drying is performed in a forced-air oven at 120–140°C for 8–15 s; overdrying above 150°C causes insoluble PVOH skin formation on the strand surface and reduces composite interlaminar shear strength. 3-98 provides a medium film elongation and adequate strand integrity; the low molecular weight lowers size bath viscosity to 20–50 mPa·s at 25°C, allowing uniform strand split after application. In pultruded profiles tested by ISO 14125, resin wet-out is influenced by PVOH level: below 0.3% LOI, strand fuzz generation during creel pay-off increases by 25–40%, but above 1.0% LOI the PVOH film reduces vinyl ester resin dissolution at room temperature. A production bottleneck is the interaction of PVOH with pH-sensitive silane hydrolysis; the size bath must be held at pH 4.0–5.0 with acetic acid because above pH 6.0 the methoxy silane condenses prematurely and PVOH-borosilicate glass surface adsorption becomes uneven.
Spiral paper core winding at 80–120 m/min requires an adhesive whose low-shear viscosity is high enough for wet tack but whose roll-applied shear viscosity remains below 1,500 mPa·s; 3-98 cooked at 12.0–16.0 wt% solids meets this condition when compounded with 10–20 wt% kaolin or calcium carbonate filler on dry polymer, 5–10 wt% glycerol or sorbitol plasticizer, and 0.2–0.5 wt% defoamer. Cooking proceeds in batch mixers at 85–90°C, and the adhesive is held at 55–65°C and transferred by gear pump to a roll applicator. Viscosity at 25°C measured by ISO 2555 is 4,000–10,000 mPa·s at 20 rpm, but under roll shear it drops to 500–1,500 mPa·s. Open time on 200–300 g/m² coreboard is 10–20 s; wet tack reaches 8–12 N/25 mm at 180° peel. Setting speed is controlled by moisture release; cores with 8–10 plies reach 60–70% of final crush strength within 2 h at 23°C and 50% RH. The principal limitation is the equilibrium moisture regain of PVOH at high relative humidity; cartons stored above 70% RH show adhesive softening and a 20–30% reduction in TAPPI T811 edgewise crush compared with conditioned samples at 50% RH. Insolubilisation with 1–3 wt% glyoxal on dry PVOH improves water resistance but shortens pot life to 4–6 h at 55°C; production batches must be sized to line consumption to avoid viscosity drift.
In cemented carbide powder granulation, 3-98 is introduced as a pressing lubricant and binder at 1.0–2.5 wt% of powder mass before spray drying. The PVOH is pre-dissolved at 5.0–8.0 wt% in deionised water at 90°C and blended into a WC-Co slurry containing 70–80 wt% solids. Spray drying uses a rotary atomiser at inlet 180–200°C and outlet 90–100°C, producing granules with 50–150 µm median particle size and residual moisture below 0.5%. Pressing at 100–200 MPa yields green compacts with uniform density; the low ash content of 3-98 keeps residual sodium and potassium low enough for hardmetal sintering. Debinding proceeds at 10–15°C/h to 450°C under a flowing 95% N₂ / 5% H₂ atmosphere with a 2 h hold; residual carbon after debinding is held below 0.05 wt%. Sintered transverse rupture strength is evaluated by ISO 3327 and density by ASTM B311. Incompatibility occurs with iron salt contamination in the slurry, which accelerates PVOH crosslinking and raises granule hardness; chelating agents are not recommended because they leave metallic residue in the sintered compact. The main process boundary is the low molecular weight of 3-98: at binder levels above 2.5 wt%, green machinability improves but ejection force drops below the level required for clean pressing because the low-viscosity solution reduces particle-to-particle friction.
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Kuraray Poval 3-98 is a fully hydrolysed polyvinyl alcohol (PVOH; CAS 9002-89-5) manufactured by controlled alcoholysis of polyvinyl acetate. The grade designation separates two governing properties: the first numeral 3 denotes a nominal viscosity class for a 4% aqueous solution at 20°C, and the suffix 98 denotes a degree of hydrolysis of 98.0–99.0 mol%. Under JIS K6726, the material is released against degree of hydrolysis, solution viscosity, volatile matter, and ignition residue. The 98.0–99.0 mol% hydrolysis level leaves only a small residual acetyl fraction; this low acetyl content distinguishes fully hydrolysed PVOH from partially hydrolysed grades and produces a denser hydrogen-bonded network, higher crystallinity, and reduced cold-water solubility of the dried film. The product is supplied as a white to light-yellow granulate or powder. Because the powder is hygroscopic and can compact under silo mass flow, gravimetric feeding lines may require hopper liners, aeration pads, and moisture ingress control; particle-size distribution is not typically a certificate-of-analysis parameter under JIS K6726 and must be qualified separately for continuous dosing.
| Property | Method | Controlled value |
|---|---|---|
| Degree of hydrolysis | JIS K6726 | 98.0–99.0 mol% |
| Viscosity of 4% aqueous solution at 20°C | JIS K6726 | 3.2–4.0 mPa·s |
| Volatile matter | JIS K6726 | ≤5.0 wt% |
| Ignition residue | JIS K6726 | ≤0.5 wt% |
| pH of aqueous solution at 20°C | JIS K6726 | 5.0–7.0 |
The 3.2–4.0 mPa·s viscosity at 4% solids is the low end of the fully hydrolysed 98-series viscosity range. This low viscosity is not simply a concentration effect; it reflects the shorter chain length and lower hydrodynamic volume of the grade. The practical consequence is that Poval 3-98 is selected when the dried film must retain the higher strength and water resistance of a fully hydrolysed PVOH, but the liquid feed system cannot tolerate the solution viscosity of 4-98, 5-98, or 6-98 at the same solids. The reverse consequence is lower film tensile strength and lower solution extensional viscosity than in longer-chain grades; this must be considered in curtain coating, roll transfer, and adhesive fibre formation where extensional viscosity controls film splitting and web transfer.
Fully hydrolysed PVOH chains contain a dense sequence of secondary hydroxyl groups. The resulting intra- and inter-chain hydrogen bonds increase crystallite density; water penetrates the amorphous regions but does not dissolve the crystallites at room temperature. A standard preparation procedure begins with dispersion of the powder in water at 20–25°C under low-shear agitation at 200–500 rpm. The slurry is then heated in a jacketed stainless-steel vessel at 1–2°C min⁻¹ to 85–95°C and held for 30–60 min. For precision coating use, the solution is filtered through a 100–200 mesh screen; residual microgels are more common if the initial dispersion is too rich or if direct steam injection creates local overheating. Once dissolved, the solution should be held at 60–80°C with slow agitation. Fully hydrolysed PVOH solutions can form structured gels, skins, or crystalline domains during standing at room temperature, particularly at solids above 10 wt%.
Rheology is nearly Newtonian at the 4% reference viscosity and becomes shear-thinning at higher solids. Low-viscosity Brookfield spindles should be calibrated at 20°C because the 4% solution is near the lower torque reliability threshold of high-viscosity spindles. The solution pH is typically 5.0–7.0, but pH affects long-term hydrolysis stability; strong acids or bases can hydrolyse residual acetate groups and alter viscosity over time. Sulphates and phosphates can reduce hydration and raise clouding; borate ions cause reversible di-diol crosslinking, producing a sharp viscosity increase that may be beneficial in gelled adhesives but is an incompatibility in standard size presses and paper coating colour systems.
In comparison with higher-viscosity fully hydrolysed grades such as 4-98, 5-98, and 6-98, Poval 3-98 produces the lowest aqueous-solution viscosity at constant solids. This permits solids increases from 8 wt% to 12 wt% or more before the viscosity exceeds the operating window of a metering size press or positive-displacement pump. The lower chain length also lowers dry-film tensile strength, elongation at break, and solution extensional viscosity. When films are conditioned at 50% relative humidity and 23°C and tested under ISO 527-2 or ASTM D638-14, longer-chain fully hydrolysed grades generally produce higher tensile values; the difference becomes more pronounced at high strain rates. Against partially hydrolysed grades such as 22-88, the 98.0–99.0 mol% hydrolysis level raises the crystalline fraction and reduces equilibrium moisture uptake at 65% relative humidity. The fully hydrolysed film is therefore stiffer, stronger, and more resistant to polar-oil pickup, but it is less cold-water-soluble and has lower elongation unless plasticised. Glycerol, triethylene glycol, or sorbitol at 5–15 phr lowers the glass-transition and increases elongation; the trade-off is a reduction in tensile strength and an increase in moisture uptake. Published comparative data for all substrate and plasticiser combinations is limited; drawdowns on the intended substrate remain necessary.
On high-speed paper machines, film-press and metering size press applications operate within a narrow viscosity band, typically 20–50 mPa·s at process temperature. Poval 3-98 is blended with oxidised starch at 4–8 wt% total solids and 0.5–2.0 wt% PVOH on dry fibre. The low-viscosity PVOH fraction raises film strength and reduces surface dusting without moving the circulating size outside the runnable viscosity window. The size is maintained at 60–70°C to prevent starch retrogradation and PVOH gelation; filters are selected for 100–150 µm retention to protect the metering elements. The sized sheet is evaluated for water absorption by ISO 535 and for tensile strength by ISO 1924-2. The fully hydrolysed PVOH contributes lower equilibrium moisture uptake than a partially hydrolysed grade, but at the low add-on levels used in surface sizing it modifies the fibre surface rather than closing all pores.
In cotton and polyester-cotton warp sizing, the size is cooked in a jet cooker or pressure cooker at 120–130°C and applied at 6–10 wt% solids. The low molecular weight of Poval 3-98 permits a size pickup of 8–14% on warp yarns while maintaining penetration into the yarn bundle. Abrasion resistance is tested on a Zweigle warp-sizing tester, and isolated size films are conditioned at 65% relative humidity and 20°C before tensile measurement. Desizing requires hot water above 80°C; if starch is present, enzymatic or oxidative desizing is used first, followed by hot washing to remove the PVOH fraction.
For remoistenable and hot-water-activated paper adhesives, Poval 3-98 is formulated at 10–20 wt% solids with a plasticiser and, where controlled gelling is needed, a metered borate crosslinker. The low solution viscosity allows higher solids in roller-coating and extrusion-coating feed systems without exceeding the transfer system viscosity limit. The dried film is harder and more water-resistant than a partially hydrolysed PVOH of comparable viscosity class; activation therefore relies on heated rolls or hot water rather than cold-water rewetting. Uncontrolled borate addition creates filter-plugging gels, so borate should be injected only at controlled pH and under continuous viscosity monitoring.
Films cast from Poval 3-98 and dried between 50°C and 80°C develop high crystalline order because the low residual acetyl content permits close chain packing. The effect is increased modulus and tensile strength relative to partially hydrolysed PVOH, but also lower elongation and greater drying stress. At 50% relative humidity, equilibrium moisture uptake is lower than for an 88 mol% hydrolysed grade; at 80% relative humidity, all PVOH films plasticise substantially and lose tensile strength. Plasticisers such as glycerol at 5–15 phr suppress the glass-transition and reduce internal stress, but they also increase moisture uptake and can migrate in contact with paper or board. Without crosslinking, fully hydrolysed PVOH remains soluble in hot water and should not be specified as a permanent water barrier.
Poval 3-98 may be considered where a low-viscosity PVOH is used as an oxygen-barrier coating on oriented polypropylene or polyester at 0.5–2.0 g/m² dry coat weight. Oxygen transmission rate is evaluated by ASTM D3985 at 23°C and 0% relative humidity; barrier performance falls as humidity rises because water acts as a plasticiser. The low chain length of 3-98 permits higher coating solids, but the dry film is slightly weaker than that of 5-98; coating weight or crosslinking may need to compensate. Because the residual acetyl content is very low, surface activity at oil/water interfaces is lower than in partially hydrolysed grades. Poval 3-98 is therefore not the first-choice protective colloid for vinyl chloride suspension polymerisation, where grades in the 70–80 mol% hydrolysis range are typically used.
At storage relative humidity above 60%, the powder absorbs atmospheric moisture and may clump; pre-drying is required when gravimetric dosing or moisture-sensitive compounding is involved. The dry product forms combustible organic dust, and process equipment should be grounded with dust collection complying with local combustible-dust standards. Aqueous solutions are susceptible to microbial growth; preservative selection must be checked for compatibility with PVOH and with the borate/plasticiser system. Food-contact applications require grade-specific regulatory confirmation; polyvinyl alcohol may be referenced in FDA 21 CFR §175.300, §176.170, and §176.180, but the specific end-use temperature and simulant type must be evaluated under current listings and supplier certificates. Melt extrusion of this fully hydrolysed grade without plasticiser is constrained by thermal degradation before flow; solution casting and aqueous coating are the standard conversion routes. Published melt-processing data for Poval 3-98 is limited, and extrusion trials require plasticiser pre-blending and screw configurations designed to minimise shear heating.
