| HS Code | 158149 |
| Product Name | KURARAY POVAL L-508W |
| Chemical Family | Polyvinyl Alcohol (PVA) |
| Cas Number | 9002-89-5 |
| Appearance | White to pale yellow powder |
| Physical Form | Powder |
| Viscosity 4 Aqueous Solution 20 C | 4.8 - 5.8 mPa·s |
| Degree Of Hydrolysis Saponification | 86.5 - 89.5 mol% |
| Ph 4 Aqueous Solution | 5.0 - 7.0 |
| Ash Content | ≤ 0.5% |
| Volatile Content | ≤ 5.0% |
As an accredited KURARAY POVAL L-508W factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | KURARAY POVAL L-508W is supplied in 25 kg net multi-ply paper bags with a moisture-proof polyethylene inner liner. |
| Container Loading (20′ FCL) | 20′ FCL loading of KURARAY POVAL L-508W: palletized polyethylene vinyl alcohol bags, securely stowed, moisture-protected, weight-capped for safe transport. |
| Shipping | KURARAY POVAL L-508W is a white, granular polyvinyl alcohol resin. It ships as a non-hazardous material in sealed multi-layer paper bags on pallets. Protect from moisture, rain, and excessive humidity during transit. Store in a cool, dry area away from heat sources to preserve flowability and product quality. |
| Storage | Store KURARAY POVAL L-508W in a cool, dry, well-ventilated area away from direct sunlight and moisture. Keep containers tightly sealed when not in use to prevent caking or clumping. Avoid generating dust; keep away from ignition sources. Maintain temperatures below 30°C and protect from humidity for optimal stability. |
| Shelf Life | Shelf life is typically 2 years from manufacture if stored unopened in a cool, dry place away from moisture. |
When partially hydrolysed polyvinyl alcohol is introduced as the primary protective colloid in vinyl acetate-ethylene dispersion polymerisation, the reactor-side variables—solution preparation, grafting kinetics, and heat removal capacity—determine whether the final dispersion remains pumpable and coagulum-free. In this role, KURARAY POVAL L-508W has a 4 % aqueous solution viscosity of 5.0–6.0 mPa·s and a degree of hydrolysis of 87.0–89.0 mol%, placing the grade in the low-molecular-weight, partially hydrolysed segment used for fine particle stabilisation without the high continuous-phase viscosity that would limit shell-side heat transfer in a jacketed batch reactor. The powder is pre-dissolved at 10–15 % solids in demineralised water at 80–90 °C for 60 min, then cooled to 35–40 °C before being metered into the reaction vessel; undissolved gels are removed by filtration through a 80 mesh screen because residual gel particles act as seeds for grit formation during the early monomer-feed phase. In vinyl acetate-ethylene recipes, the typical POVAL L-508W charge ranges from 2–5 wt% on total monomer mass; at the lower end dispersion risk is lower but particle size rises, and at the upper boundary continuous-phase viscosity increases to the point where agitator power draw and reactor wall fouling become process-limiting. The colloid functions through grafting of vinyl acetate radicals onto the partially hydrolysed PVA backbone, which converts a water-soluble polymer fraction into a bound stabiliser layer; the 87.0–89.0 mol% hydrolysis window provides sufficient residual acetyl content for hydrophobic chain segments while retaining water solubility. Reaction temperature in VAE polymerisation is normally held at 75–85 °C with an oxygen-free monomer feed, and initiator selection is restricted to persulfate or hydrogen peroxide–metal redox couples because organic peroxides can abstract hydrogen from the PVA backbone and produce excessive viscosity drift. The measured dispersion viscosity after neutralisation to pH 4.5–5.5 with sodium hydroxide or sodium acetate is frequently performed according to ISO 2555; solids content is determined by ISO 3251. In industrial practice, high-ethylene VAE dispersions stabilised with POVAL L-508W can be formulated to 55–65 % solids for wood adhesive and construction applications, but the actual maximum solids depends on ethylene pressure, agitator geometry, and the residual monomer stripping step. The use of an external cooling loop with a plate heat exchanger is recommended when the batch volume exceeds 10 000 L; failure to remove the exotherm results in local hot spots that promote broad particle-size growth and increase coagulum on the baffles. Quantitative grafting-efficiency data for this specific grade under full-scale ethylene pressure reactor conditions are not published in a directly comparable form; the operational ranges described here are industrial practice, not batch-specific certificates.
Remoistenable envelope and label adhesives based on POVAL L-508W rely on the reversible absorption of water by a dried polyvinyl alcohol film that contains sufficient residual acetyl content to soften at room temperature without blocking under normal office humidity. The grade is typically compounded with dextrin, plasticiser, and a small amount of sulfosuccinate wetting agent; dry-film coat weights are maintained at 2–5 g/m² on paper substrates because heavier films increase blocking at 50 % RH and slow reactivation speed on high-speed mailing lines. POVAL L-508W is pre-dissolved at 20–25 % solids, then added to the cooked dextrin batch at 50–60 °C; the mixing vessel is equipped with a low-shear anchor agitator because high-shear rotor-stator dispersion can mechanically degrade the dextrin component more than the PVA fraction. Boric acid is sometimes introduced as a wet-tack modifier, but the addition must remain below the gelation threshold of the PVA-polysaccharide system; borate crosslinking raises viscosity and can generate insoluble aggregates if injected as a concentrated slug. The reactivation test is performed by applying a controlled water film to the dry adhesive layer and measuring peel adhesion after 5–15 s open time; ASTM D1876 T-peel geometry is used for comparative purposes, while blocking resistance is tested under a 0.5 kPa load at 40 °C and 50 % RH for 24 h. In mailing machines with vacuum pick-up, adhesive-coated envelopes exhibit misfeed if the adhesive layer swells before vacuum suction releases, a condition that occurs when the coating is applied at more than 5 g/m² or when glycerol plasticiser exceeds 10–12 % of the dry PVA/dextrin mass. The coated paper should be fully dried in a tunnel at 90–110 °C for 2–4 s; residual moisture above 1.5 % in the adhesive layer increases blocking in stacked storage.
| Reference | Relevant condition |
|---|---|
| 21 CFR 175.105 | Adhesives for food-contact surfaces and packaging |
| 21 CFR 176.170 | Components of paper and paperboard in contact with aqueous and fatty foods |
| 21 CFR 176.180 | Components of paper and paperboard in contact with dry food |
| EU 10/2011 | Plastic materials and articles intended to come into contact with food; overall migration limits apply |
| REACH Annex XVII | Restriction check for substances in adhesive articles |
On slasher sizing machines running 65/35 polyester–cotton warp yarns at 80–120 m/min, POVAL L-508W is dosed into the size box as a 4–8 % solids solution blended with corn starch or a starch/acrylic size. The low solution viscosity allows the blend to penetrate the yarn bundle without excessive size-box foaming, but the bath temperature must be held at 85–90 °C because cooling below 80 °C produces a surface skin that transfers as visible size pick faults. Squeeze roll pressure is adjusted to achieve 8–12 % wet pickup on the warp; the dried size film adds abrasion resistance during weaving and reduces hairiness measured by ASTM D2256 yarn tensile loss after flexing. Warp-sizing formulations with POVAL L-508W are designed to be partially desized through hot water, and the main operational incompatibility arises when the size recipe is overdosed with styrene-acrylic size above 30 % of total size solids, because the acrylic fraction restricts water solubilisation and increases desizing cost. Reported mill practice indicates that size films containing more than 8 % POVAL L-508W on total dry size can crack in low-humidity weave rooms below 35 % RH; therefore the PVA fraction is commonly limited to 4–6 % when the yarn run includes high-density plied warp.
Surface sizing on fine paper at a metering size press with a pond width of 4.2 m and machine speed of 900 m/min uses POVAL L-508W in combination with oxidised corn starch at total solids of 6–9 %. The PVA fraction increases IGT pick resistance and reduces dusting, but the film-split behaviour at the metering nip becomes unstable if the solution temperature falls below 55 °C or if the PVA fraction exceeds 30 % of total solids. Cobb values according to ISO 535 are used to verify that the PVA film does not excessively hydrophilise the sheet; when the sizing mixture contains POVAL L-508W above 1.5 % of total sheet dry weight, water absorption can exceed target values for offset printing grades. The application is a cost-sensitive partial replacement of oxidised starch; no separate bonding process is required.
For alumina and zirconia slip systems intended for spray drying, POVAL L-508W functions as a green-body binder at 0.5–3.0 mass% of dry powder. The dispersion is ball-milled for 12–24 h with polyacrylate deflocculant, then spray-dried with an inlet temperature of 180–220 °C and outlet temperature of 90–110 °C. The low-viscosity PVA binder does not raise slip viscosity as severely as medium-viscosity PVOH grades, allowing 50–65 % solids slips to remain pumpable for peristaltic feed to the atomiser. During pressing at 50–150 MPa, the binder increases green strength, but binder migration at high drying rate or relative humidity above 60 % can create soft shells and non-uniform density in the pressed compact. Thermogravimetric analysis of POVAL L-508W under air shows two major mass-loss events: the first at 200–350 °C associated with side-group oxidation and the second at 350–500 °C for backbone decomposition; the ash content of 0.4 % maximum leaves limited inorganic residue, but for alkali-sensitive titanate dielectrics the sodium fraction in the ash must be controlled by binder selection or washing. Green density and water absorption are measured on the fired body according to ASTM C373; pressed compacts fail by lamination if binder content is below 0.5 mass% or if the spray-dried granule size distribution contains more than 20 % fines below 20 µm. Published data for POVAL L-508W in dielectric layers under reducing atmospheres are limited.
Thin-bed cementitious tile adhesive formulations use POVAL L-508W as a water-retention co-modifier at 0.5–2.0 % by mass of cement, normally in combination with cellulose ether and a redispersible VAE polymer powder. The PVA dissolves rapidly in the mixing water and reduces surface crusting during the open-time window; EN 1346 open-time measurements on non-porous substrates track the effect of PVA content on adhesive transfer. At PVA additions above 2.0 %, the fresh mortar becomes increasingly sticky, and the 28 d compressive strength may decrease because the PVA film disrupts early hydration at the aggregate-paste interface. The compatibility boundary appears when the mortar is mixed with high-sulfate cements or rapid-hardening calcium aluminate cement; concentrated PVA solutions can coagulate in the presence of high ionic strength mixing water, producing lumps that are visible after trowel application. Mixing equipment is typically a forced-action paddle mixer at 300–400 rpm; high shear above 800 rpm entrains air and increases PVA foam formation, which reduces adhesive tensile strength after 28 d curing. Water retention is quantified by a vacuum suction method or by EN 1348 shear adhesion after specified open times; actual values depend on cement type, cellulose ether grade, and sand morphology. The hardened mortar is classified according to EN 12004; PVA addition changes fresh-mortar workability but not the classification if the redispersible polymer powder content remains within the formulation envelope.
When applied by air-assisted spray to polished stainless steel or precision glass, POVAL L-508W forms a temporary peelable masking film at 6–10 % solution solids. The wet film is deposited at 60–100 µm thickness, dried at 20–30 °C and 35–55 % RH, and must achieve a continuous pinhole-free layer before machining, etching, or handling. Low-viscosity solutions permit suction-feed spray guns with nozzle diameters of 0.8–1.2 mm; air pressure below 0.3 MPa reduces overspray and film build-up on edges. Film removal is performed by peeling at ambient temperature; the residual acetyl content of POVAL L-508W reduces crystallinity and improves wet peel from glass surfaces without leaving oily residue. The film is not intended for outdoor exposure beyond 72 h because condensation and UV exposure degrade the PVA layer and can make removal brittle. Dimensional change of the film under tension is measured according to ISO 527-3; however, published data for this specific grade as a peelable masking film are limited.
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KURARAY POVAL L-508W is a low-viscosity, partially saponified polyvinyl alcohol resin manufactured by controlled alcoholysis of polyvinyl acetate. The residual acetyl content in the polymer is approximately 11–13 mol%, corresponding to a degree of saponification of 87.0–89.0 mol%. This compositional window distinguishes the grade from fully saponified polyvinyl alcohol resins, where residual acetyl content is typically below 2 mol% and dissolution requires heating to 85–95°C. L-508W retains sufficient hydroxyl functionality for hydrogen bonding and film formation, while the acetate groups disrupt crystallisation and reduce the thermal energy required for solvation. The product is supplied as white to off-white granules or powder, with the granular form preferred in automated dosing systems because it generates less dust than fine powder. Within the Kuraray Poval L-series, the designation L-508W identifies a partially saponified product positioned for applications requiring cold-water dissolution, moderate film strength, and compatibility with aqueous formulation components.
The release properties in the following table follow the batch certificate-of-analysis framework. The viscosity is measured on a 4 mass% aqueous solution at 20°C, not on the dry resin.
| Property | Test method | Typical value or range |
|---|---|---|
| Appearance | Visual inspection | White to off-white granules or powder |
| Degree of saponification | JIS K6726 | 87.0–89.0 mol% |
| Residual acetyl content | Calculated from degree of saponification | 11–13 mol% |
| Viscosity of 4 mass% aqueous solution at 20°C | JIS K6726 | 5.0–6.0 mPa·s |
| Volatile matter | JIS K6726 | ≤5.0 mass% |
| Ash content as Na₂O | JIS K6726 | ≤0.5 mass% |
| pH of 4 mass% aqueous solution | JIS K6726 | 5.0–7.0 |
Because aqueous polyvinyl alcohol solutions are non-Newtonian at higher concentrations, the 4 mass% value should not be extrapolated linearly to process concentrations. A 10 mass% stock solution prepared under the same conditions will display shear-thinning behaviour at low shear rates and higher apparent viscosity than a simple linear scaling suggests. For gravimetric dosing in plant operations, the volatile matter limit of ≤5.0 mass% is applied; when storage exceeds 60% relative humidity, moisture uptake can alter the as-received mass and shift the calculated solids content of the final batch.
Direct charging of dry granules into water heated above 60°C is the most frequent source of gel fisheyes in manufacturing. The outer surface of each granule hydrates rapidly and forms a viscous film that blocks water ingress, trapping unhydrated polymer in a gel envelope. For L-508W, the preferred dissolution sequence is to pre-slurry the granules in demineralised water at 10–20°C while maintaining agitation at 500–1000 rpm in a vessel equipped with a high-speed disperser or bottom-entry rotor-stator mixer. Once the dispersion is uniform and free of floating agglomerates, steam-jacket heating raises the batch to 85–90°C and holds it under low-shear stirring for 30–60 min. The batch is then cooled to 20°C before viscosity adjustment or release testing.
Continuous dissolution systems using a twin-screw dissolver with an L/D of 30:1 and barrel zones at 90/90/85°C can process 4–8 mass% solutions, provided the granular feed is metered into the first zone with water at 20°C. Viscosity verification is performed after cooling to 20.0±0.5°C because polyvinyl alcohol solution viscosity is strongly temperature-dependent. A 4 mass% solution measured at 25°C will read lower than the 20°C limit. If pre-drying is necessary because bags were stored at RH>60%, granules should be dried in a dehumidified air stream at 40–50°C for 2–4 h; the material should not be exposed to temperatures above 120°C for extended periods because discolouration and molecular-weight degradation may occur.
During vinyl acetate and vinyl acetate–ethylene emulsion polymerisation, L-508W functions as a protective colloid rather than a primary surfactant. The partially saponified structure provides adsorption at the monomer–water interface while maintaining steric stabilisation of growing oligomeric particles. The low solution viscosity of 5.0–6.0 mPa·s allows post-polymerisation letdown and spraying without excessive shear deformation of the latex. In a 2 m³ glass-lined reactor equipped with a retreat-blade impeller operating at 90–120 rpm, addition levels of 2.0–6.0 mass% based on total monomer are typical for batch emulsion polymerisation. At the lower end of the range, the latex particle size tends to be larger and the free-PVA aqueous phase concentration is lower; at the higher end, the emulsion exhibits finer particle size and greater shear resistance but also higher water sensitivity of the dried film.
Processing bottlenecks on production lines commonly involve foam generation and heat transfer. Polyvinyl alcohol stabilises air bubbles at the reactor surface, and excessive foam can cause pump cavitation in continuous loops or interfere with jacket heat removal. Antifoam selection must be compatible with the emulsion end-use; silicone-based defoamers may reduce foam efficiently but can introduce film defects in downstream coating. Published data for L-508W-specific particle-size distributions and scale-up kinetics is limited, and formulations should be validated in pilot reactors before transfer to full-scale campaigns.
Surface sizing formulations containing L-508W are prepared at 2.0–8.0 mass% solids and applied at the size press or film press. At 5.0–6.0 mPa·s the base solution viscosity is low enough to permit co-blending with oxidised starch, styrene-acrylic latices, or alkyl ketene dimer emulsions without exceeding the viscosity limits of the press circulation system. In rod-metering size presses running at 100–400 m/min, the partially saponified grade contributes film strength, fibre pick resistance, and oil hold-out. The film does not develop the same water resistance as fully saponified grades, but the reduced crystallinity gives cleaner film splitting and less dusting on drying cylinders.
Oil hold-out can be evaluated by the TAPPI T 559 cm-02 kit test, while water absorption can be measured by ISO 535 Cobb method. L-508W should not be used as the sole water-barrier resin in high-humidity packaging. For wet-strength or high-humidity service, blends with crosslinkers such as glyoxal or zirconium ammonium carbonate are required, and the borate compatibility boundary described below must be observed.
Polyvinyl alcohol containing residual 1,2-diol units reacts with borate ions to form didiol complexes, producing a reversible gel. In L-508W, the gelation response is usable only within narrow limits because uncontrolled addition of sodium tetraborate to a 4.0 mass% solution at pH 8.0–9.5 increases viscosity rapidly and can generate non-pourable gel plugs. For formulations requiring alkaline viscosity adjustment, the borate solution must be diluted to 0.1–0.5 mass% and metered under high-shear mixing; the total borate concentration should remain below 0.05 mass% unless the process is specifically designed for gel casting or structured-fluid rheology.
Strong oxidising agents and persulfate initiators can reduce molecular weight if held at reaction temperature. Hypochlorite solutions above 2.0 mass% can cause chain scission and should not be used for tank cleaning without complete rinsing. The pH of L-508W solutions is 5.0–7.0; prolonged exposure to strong alkali can accelerate acetate hydrolysis and shift the degree of saponification, altering solubility and film properties.
Compared with a fully saponified polyvinyl alcohol of matching 4 mass% solution viscosity, L-508W exhibits lower film crystallinity, lower tensile strength, higher elongation, greater cold-water solubility, and better adhesion to hydrophobic substrates. Compared with a higher-viscosity partially saponified grade, L-508W contributes less thickening at equal solids, permitting faster filtration, easier spraying, and smaller pressure drops in pipe transport.
| Characteristic | L-508W | Fully saponified low-viscosity reference grade | Higher-viscosity partially saponified reference grade |
|---|---|---|---|
| Degree of hydrolysis | 87.0–89.0 mol% | 98.0–99.0 mol% | 87.0–89.0 mol% |
| 4 mass% solution viscosity at 20°C | 5.0–6.0 mPa·s | 5.0–6.0 mPa·s | 24.0–30.0 mPa·s |
| Dissolution temperature with pre-slurry | 20–30°C | 85–95°C | 20–30°C |
| Protective colloid efficiency in emulsion polymerisation | High | Low to moderate | High; high solution viscosity limits handleability |
| Film water resistance | Moderate | High | Moderate |
| Water sensitivity of dried film | Higher than fully saponified grades | Lower | Higher than fully saponified grades |
Table values are typical published ranges from supplier technical literature and comparison grades; exact values should be verified against the batch certificate of analysis. The primary reason to select L-508W over a fully saponified grade is low-temperature solubility without ammonia or caustic additives. The primary reason to select L-508W over a higher-viscosity partially saponified grade is the lower thickening contribution at equal solids. The trade-off is reduced film strength and greater water sensitivity, which must be offset by formulation design when final film properties are critical.
For indirect food-contact applications, use of L-508W requires verification against specific national and regional provisions. The grade is supplied when requested with documentation covering REACH registration for the European Union, and the resin may be listed in other chemical inventories. Formulators must not rely on a single grade designation as proof of compliance; the end use, layer structure, temperature, and food type determine the applicable migration test. Where published data for L-508W in a specific food-contact matrix is limited, migration testing under the intended use is the controlling requirement. For paper and board, compliance considerations often include 21 CFR 176.170 and 21 CFR 176.180; for adhesives, 21 CFR 175.105 may apply to the formulated adhesive rather than to the polyvinyl alcohol alone. The converter must confirm residual monomer and volatile matter meet the relevant specification for the intended application.
