ELVANOL 52-22

ELVANOL 52-22 is a partially hydrolysed poly(vinyl alcohol) resin supplied by Kuraray Co., Ltd. The grade identity denotes a nominal 4 % aqueous solution viscosity of 20–26 mPa·s at 20 °C measured with a Brookfield LVF viscometer at 60 rpm, and a hydrolysis level of 87–89 mol% according to JIS K6726. The residual acetyl content therefore lies between 11 mol% and 13 mol%, which is the primary structural factor distinguishing this grade from fully hydrolysed poly(vinyl alcohol) products. Dry-powder specifications include volatile content ≤5.0 wt%, ash as Na₂O ≤0.5 wt%, and pH of a 4 % aqueous solution from 4.5 to 7.0. The material is supplied as a white to off-white granular powder. Primary industrial uses include textile warp sizing, paper coating and surface sizing, remoistenable adhesives, vinyl acetate emulsion polymerisation as protective colloid, ceramics binder, and water-soluble transfer films.

Why Does the Hydrolysis Range of 87–89 mol% Constrain Cold-Water Dissolution?

Residual acetate groups in ELVANOL 52-22 disrupt interchain hydrogen bonding and reduce crystallinity, allowing dissolution in water at 80–90 °C. At 20–40 °C, the granules swell and form a lumpy dispersion, but complete molecular dissolution is not achieved without prolonged high-shear mixing. The nominal viscosity of 20–26 mPa·s at 4 % solids and 20 °C is therefore measured only after a heating and cooling cycle. For solution preparation in a jacketed vessel, the powder is sifted into the vortex of ambient water under slow agitation, typically 30–60 rpm with an anchor impeller, then the batch is heated to 85–90 °C and held for 30–45 min. Temperatures above 95 °C are unnecessary and may cause surface skinning and foam stabilisation. Because the hydrolysis level is below 90 mol%, the resin retains surface activity that supports emulsion stabilisation and wetting of hydrophobic fibres. In alkaline media above pH 9, deacetylation proceeds gradually; as residual acetyl groups are removed, the solution becomes more fully hydrolysed and can develop turbidity or increased viscosity during storage. Caustic soda additions beyond 1 % of solution mass are therefore avoided unless the process is buffered. Published data for the cold-water dissolution rate of this grade at 20 °C is limited, but the structural constraints are well documented for partially hydrolysed poly(vinyl alcohol) analogues.

Thermal Degradation Onset, Melt-Processing Window, and Extruder Operating Limits

Partially hydrolysed poly(vinyl alcohol) begins to evolve absorbed water and acetic acid below 200 °C, while main-chain scission accelerates above 250 °C under inert gas. For melt processing of ELVANOL 52-22, plasticisation is mandatory because the crystalline melting range and the incipient degradation range overlap. Glycerol, sorbitol, trimethylolpropane, or water are used as plasticisers, typically at 15–30 phr of resin mass. On a co-rotating twin-screw extruder with an L/D ratio of at least 40:1, barrel set points are maintained between 180 °C and 220 °C, with residence time below 120 s. Closed-loop temperature control is critical because the processing window narrows to approximately ±5 °C around 200 °C for formulations without destabilising additives. At 230 °C or above, discolouration and gel particles appear in production-scale compounding, and screw torque becomes erratic due to crosslinking and volatile generation. Water-activated purge compounds are preferred for shutdown; amine-containing purges are avoided because alkaline conditions accelerate acetate cleavage and produce brown residues. Pre-drying at 50–60 °C for 2–4 h in a dehumidified hopper dryer is required when the powder has been stored at relative humidity above 60 %. Failure to pre-dry causes steam evolution in the feed throat, unstable torque, and surface bubbles in extruded profiles. Published data for the exact degradation profile of ELVANOL 52-22 on laboratory micro-compounders is limited, but the stated limits follow manufacturer processing guidance for medium-viscosity partially hydrolysed grades.

When ELVANOL 52-22 Replaces Fully Hydrolysed Grades in Adhesive and Paper Sizing

In remoistenable adhesives, the partial hydrolysis of ELVANOL 52-22 provides lower interfacial tension on coated paper, faster fibre penetration, and higher wet tack than fully hydrolysed grades, but the dried film possesses lower moisture resistance and lower tensile strength. A comparative evaluation according to TAPPI T 494 om-01 can be used to distinguish adhesive failure from fibre tear on porous substrates; however, published data for this specific formulation is limited. When replacing ELVANOL 71-30, crosslinking is generally required to recover water resistance. Glyoxal at 1–3 wt% of resin solids is a common insolubiliser; it reduces pot life and must be maintained below pH 5.5 to prevent premature gelation. In textile warp sizing, the grade is applied from a single-box slasher at 8–12 % solids. The viscosity of 20–26 mPa·s at 4 % provides sufficient film strength while limiting excessive yarn penetration. Differences from ELVANOL 51-05 become apparent in high-humidity weaving rooms: the higher molecular weight of 52-22 retains size film cohesion at 75 % RH and 30 °C, while ELVANOL 51-05 may soften and accumulate on reed wires. The selection boundary is therefore molecular weight and viscosity rather than hydrolysis, because 51-05 and 52-22 share a similar 88–89 mol% hydrolysis range.

In paper coating and surface sizing, ELVANOL 52-22 is used as a carrier for optical brightening agents and as a surface-sizing binder. A size press formulation at 3–6 % solids is applied to linerboard at 50–70 °C; the low ash content minimises deposit formation on drying cylinders. Surface sizing with partially hydrolysed medium-viscosity grades improves glueability of the sized sheet and reduces porosity, but does not provide the same water resistance as 99–100 mol% hydrolysed grades unless combined with a styrene-acrylate or starch insolubiliser. The viscosity stability of the size press solution is monitored with an in-line falling-piston viscometer because temperature and shear affect the apparent viscosity. Published data for porosity reduction on specific substrate grades is limited.

In vinyl acetate emulsion polymerisation, ELVANOL 52-22 is charged as a protective colloid at 2–6 wt% of monomer mass. A stirred tank reactor with pitched-blade turbine agitation at 150–250 rpm is used. The 10 % stock solution is prepared separately and cooled to 40 °C before monomer addition. The partial hydrolysis contributes surface activity that affects poly(vinyl acetate) particle size distribution compared with fully hydrolysed colloids at equivalent concentration. Polymerisation pH is held between 4.5 and 6.5 to avoid deacetylation of the colloid; amine-based buffers are avoided, and sodium acetate or sodium bicarbonate is used at 0.1–0.3 wt% of monomer mass. Reaction temperature is controlled at 70–80 °C with an initiator feed of potassium persulfate at 0.05–0.2 wt% of monomer mass. Published data for this exact grade in semi-batch emulsion polymerisation is limited, but the operating window is consistent with medium-viscosity partially hydrolysed poly(vinyl alcohol) colloids.

For water-soluble transfer films, ELVANOL 52-22 is blended with glycerin at 10–20 phr and cast from a 10 % aqueous solution onto a polyethylene terephthalate release liner. Drying is carried out in a three-zone forced-air oven with zone temperatures of 70 °C, 90 °C, and 110 °C. Residual moisture is controlled to 8–12 wt% to preserve flexibility. The partially hydrolysed structure reduces crystallinity and improves heat-seal response relative to fully hydrolysed grades, but published tensile data for this grade under ASTM D882-18 is limited and must be generated on the target line. The grade is not recommended for end uses requiring sustained water resistance unless a crosslinker or overprint varnish is applied.

Regulatory status must be verified for the intended jurisdiction and end use. Poly(vinyl alcohol) is exempt from registration under REACH EC 1907/2006, Article 2(9), but the monomers used in its manufacture must be registered by the supplier. For adhesives intended for food packaging, the base resin may fall under 21 CFR 175.105; for paper and paperboard coating, 21 CFR 176.170 and 21 CFR 176.180 may apply, subject to migration and extractives limits in the finished article. RoHS 2011/65/EU does not list poly(vinyl alcohol) as a restricted substance, but residual catalysts and additives must be assessed at component level. The powder is combustible as an organic dust; transfer lines should be grounded and dust concentrations controlled below applicable combustible dust thresholds. No specific occupational exposure limit is established for poly(vinyl alcohol); airborne dust is managed as inert nuisance particulate.