GOHSENOL EG-05P

GOHSENOL EG-05P is supplied as a granular powder of partially hydrolysed polyvinyl alcohol. The product specification includes a 4% aqueous solution viscosity of 4.8–5.8 mPa·s at 20°C measured under JIS K6726, and a degree of hydrolysis of 86.5–89.0 mol%. Volatile content is controlled to ≤5.0%, ash to ≤0.5%, and solution pH to 5.0–7.5. Because the hydrolysis degree remains below 90 mol%, the polymer hydrates in cold water under high shear and forms films with reduced crystallinity after drying. The low solution viscosity indicates a low molecular weight relative to other GOHSENOL grades; this property controls the grade’s selection in applications where shear viscosity, re-wetting speed, or emulsion reactor viscosity must remain low.

The residual acetate groups within the 86.5–89.0 mol% vinyl alcohol unit content disrupt interchain hydrogen bonding after film drying. This leaves sufficient hydroxyl functionality for adhesion to cellulose and mineral pigments while preventing the dense crystalline packing seen with fully hydrolysed polyvinyl alcohol. The consequence is a dried film that re-wets more readily than a 98–99 mol% grade, while sacrificing part of the tensile strength and water resistance of the fully hydrolysed polymer.

For solution preparation, EG-05P is metered into the vortex of a high-speed disperser in water at 25–30°C before steam or jacket heating to 60–70°C. The slurry is held for 30–45 min to complete hydration. Overheating above 80°C can cause granule surface gelation and lump formation. Filtration through 100–150 µm screens is recommended before metering in size press or coating applications. Solutions held at 20–25°C for more than 24 h require biocide protection because partially hydrolysed polyvinyl alcohol is biodegradable.

What Limits the Use of 4.8–5.8 mPa·s PVOH in High-Speed Metered Size Presses?

On a metered size press running starch-PVOH surface size, the low viscosity of EG-05P allows higher formulation solids without exceeding the pressure limit of the metering rod or blade. The viscosity is measured at low shear; in transfer roll nips, extensional viscosity also influences film split. Low-molecular-weight PVOH solutions remain Newtonian over a wider shear range than high-molecular-weight grades, so shear heating and pressure-driven viscosity drop are less pronounced. This improves runnability but does not necessarily improve film split. Published full-scale data for EG-05P on high-speed metered size presses are limited; mill experience indicates that replacing a 20 mPa·s grade with EG-05P reduces doctor blade deposit and misting at the applicator roll, but the wet film is more susceptible to thinning on porous raw stock.

The main processing constraint is surface strength development. Under TAPPI T 530, surface sizing agents are evaluated by pick strength of the dried sheet. A low-viscosity PVOH can produce a discontinuous binder film if the coat weight is too low or if the sheet porosity withdraws water before film formation. To avoid this, EG-05P is usually blended with oxidised or cationic starch at ratios between 1 and 5 parts PVOH per 100 parts starch solids. At addition levels above 5 parts, the solution viscosity remains manageable, but the dry film may become too water-sensitive unless sizing agents or insolubilisers are added.

The lower viscosity also imposes a limit on holdout. In size press applications requiring oil and grease holdout, a purely low-molecular-weight PVOH film may lack the film cohesion needed to block penetration. Formulators therefore add fluorochemicals or acrylic latexes when barrier performance is required; the role of EG-05P in such systems is adhesion promotion and film formation rather than barrier function.

Unlike fully hydrolysed polyvinyl alcohol, EG-05P does not require heating above 80°C to complete dissolution. The partially hydrolysed structure reduces crystallinity in solution and in the dried film, which is the basis for its use in remoistenable adhesive formulations. However, the same property increases water sensitivity and limits use in wet-end papermaking where retention and water resistance are critical.

In remoistenable adhesive compounding, EG-05P takes advantage of fast cold-water re-wetting. The dried adhesive layer is applied by gravure, roller, or slot die at solids from 10% to 30%; the low solution viscosity permits clean gravure wiping and uniform coat weight. Because the hydrolysis range is 86.5–89.0 mol%, the film remains water-soluble without heating above 40°C, which is essential for envelope and label adhesives. However, this same water sensitivity means that the film softens under high humidity; blocking resistance is acceptable only when coat weight and paper porosity are controlled.

Humidity stability is a boundary condition. At relative humidity above 70%, dried EG-05P films absorb moisture and can develop surface tack, causing blocking in stacked sheets. The effect is reversible by drying, but it limits the use of unmodified EG-05P in tropical packaging without moisture barriers or high-porosity paper.

When Partial Hydrolysis Outperforms Full Hydrolysis in Flexible Remoistenable Coatings

When the end-use film must re-wet under low moisture availability, fully hydrolysed 98–99 mol% polyvinyl alcohol can form crystalline zones that retard water uptake. EG-05P, with 86.5–89.0 mol% hydrolysis, retains acetate groups that reduce crystallinity and permit faster water penetration. This difference is measurable by ISO 535 Cobb water absorption and by re-wetting time tests, although the specific re-wetting time depends on coat weight, paper type, and drying history. The trade-off is lower dry tensile strength and lower water resistance after drying.

Compared with higher-viscosity partially hydrolysed grades, EG-05P offers lower solution viscosity at equal solids. This permits higher solids application in gravure or slot-die coating without exceeding viscosity limits, reducing drying load. The lower molecular weight also reduces solution stringiness, which can improve transfer roll release but weakens the adhesive film’s wet tack on vertical surfaces. For non-vertical paper-to-paper bonding, EG-05P alone is generally sufficient; for carton side-seam adhesives with high initial tack requirements, a blend with a higher-viscosity PVOH is required.

Rheological Boundaries for Blade Coating Without Binder Migration

Blade coating of porous paperboard imposes a lower viscosity limit below which the coating formulation drains into the substrate before immobilisation. EG-05P at low addition levels provides only limited water retention because its low molecular weight contributes little to the low-shear viscosity of pigmented coatings. In pigmented coating colours containing clay or calcium carbonate, water retention must be supplied by starch, carboxymethylcellulose, or high-molecular-weight PVOH. Without these additives, blade-coating defects include binder depletion at the surface and low pick strength, measured by TAPPI T 499 or IGT pick tests.

The grade is therefore used as a secondary binder and viscosity stabiliser rather than as the primary water-retention agent. In addition, the partially hydrolysed structure improves adhesion to coated paper and reduces dusting, but the dosage is typically kept below 1.5% of pigment weight because higher levels increase coating colour viscosity only slightly and may increase water sensitivity of the finished sheet.

During vinyl acetate emulsion polymerisation, partially hydrolysed polyvinyl alcohol acts as a protective colloid at the monomer-water interface. EG-05P reduces reactor viscosity relative to higher-molecular-weight protective colloids because the water-phase chain length is shorter. This permits higher monomer conversion before mixing torque becomes limiting. In a jacketed reactor with an anchor impeller at 80 rpm, a high-viscosity PVOH grade can raise bulk viscosity above 2,000 mPa·s at intermediate conversion; EG-05P extends the operating window and can support final solids above 55% in fine-particle emulsion systems. Particle size distribution measured by ISO 22412 depends on stirring, feed rate, and PVOH concentration, not solely on PVOH viscosity.

The hydrolysis range influences grafting of vinyl acetate onto the PVOH backbone. Partially hydrolysed PVOH contains acetate groups that participate in radical transfer and can become grafted, altering the stabilisation efficiency and water sensitivity of the dried emulsion film. Because the molecular weight is low, EG-05P provides less steric stabilisation for coarse emulsions above 1,000 nm; it is therefore suited to fine and medium particle-size emulsions rather than as the sole stabiliser for large-particle dispersions.

In textile warp sizing, EG-05P is applied from a 6–8% solution at 50–60°C by size box or kiss roll. The low viscosity promotes yarn bundle penetration without excessive surface film, which is useful for fine-count cotton and polyester-cotton yarns. Desizing is performed with hot water at 80–90°C because the partially hydrolysed polymer remains water-soluble after drying. The film strength is lower than that of medium-viscosity PVOH, so the grade is often combined with starch or acrylic binders when high-speed weaving requires maximum yarn abrasion resistance.

At high loom speeds, the low molecular weight can limit sized warp strength development. Weaving trials have shown that EG-05P alone may be sufficient for low-twist staple yarns, but for continuous-filament yarns or high-abrasion fabric constructions, a higher-viscosity PVOH or starch blend is necessary to maintain weaving efficiency.

Compliance boundaries are set by FDA 21 CFR 176.170 and 176.180

Regulatory status for EG-05P should be confirmed against the specific food-contact application. Polyvinyl alcohol of this type is referenced for use as a component of paper and paperboard intended for aqueous and fatty food contact under FDA 21 CFR 176.170 and FDA 21 CFR 176.180, and as an adhesive component under FDA 21 CFR 175.105. These regulations are conditional, not blanket approvals; the finished paper or board must meet extraction limits applicable to the intended food type. The user should also confirm compliance with Framework Regulation EC 1935/2004 for paper and board intended for food contact in the European Union.

For industrial non-food applications, the polymer itself is generally exempt from EU REACH registration under the polymer exemption, but monomers and manufacturing additives must be registered. Formulated products must be reviewed for SVHC concentrations above 0.1% w/w and for applicable RoHS restrictions under Directive 2011/65/EU if the finished article enters electrical and electronic equipment. The user is responsible for verifying that the selected grade is listed or cleared for the intended jurisdiction and food type.