GOHSENOL EG-40C

GOHSENOL EG-40C is a partially hydrolysed polyvinyl alcohol (PVOH/PVA) powder manufactured under the GOHSENOL line by Nippon Gohsei. The grade is controlled by a 4 wt% aqueous solution viscosity of 40.0–46.0 mPa·s at 20°C, hydrolysis degree of 86.5–89.0 mol%, volatile matter of ≤5.0%, ash of ≤0.5% calculated as Na₂O, and pH of 5.0–7.0 in the same solution. The analytical basis for these release limits is JIS K6726:1994. This composition leaves 11.0–13.5 mol% residual vinyl acetate units, which lower interchain hydrogen bonding and confer cold-water dispersibility while limiting dry-film water resistance relative to fully hydrolysed PVOH.

What Molecular Parameters Distinguish EG-40C from Fully Hydrolysed PVOH Grades?

Partial hydrolysis in EG-40C leaves 11.0–13.5 mol% residual vinyl acetate units distributed along the polyvinyl alcohol backbone. These acetate side groups interrupt the regular hydrogen-bonded lattice that dominates fully hydrolysed grades with hydrolysis above 98 mol%. Consequently, EG-40C dissolves more readily in cold water but produces films with greater equilibrium moisture sorption and lower tensile modulus. The medium viscosity specification of 40.0–46.0 mPa·s indicates a high molecular weight fraction that increases chain entanglement; this is advantageous for protective-colloid efficiency but raises pressure drop in transfer lines. Crystallinity differences between EG-40C and fully hydrolysed reference films can be quantified by differential scanning calorimetry according to ISO 11357-3:2018, where the partially hydrolysed grade exhibits a lower heat of fusion and a broader melting endotherm.

Dissolution of EG-40C is performed in a jacketed stainless-steel vessel equipped with a draft-tube disperser or a low-shear turbine. Powder is educted into ambient demineralised water at 25–35°C under agitation of 300–600 rpm to prevent lump formation. The slurry is heated at 1–2°C/min to 85–90°C and held for 30–45 min; direct steam sparging is avoided because localised heating above 95°C produces gel specks. After cooling to 40–50°C, the solution is passed through a 100–150 µm bag filter. Solutions held longer than 48 h at ambient temperature require a preservative or chilled storage below 10°C.

Protective-colloid performance in semi-batch vinyl acetate polymerisation is sensitive to the ratio of EG-40C to monomer and to initiator feed profile. At colloid loadings below 2 pphm, latex particle size can exceed 1.0 µm and coagulum in a baffled 4 L glass reactor equipped with an anchor stirrer at 120–180 rpm increases when the initiator pulse is introduced before the emulsion pre-charge reaches reaction temperature. At loadings above 8 pphm, latex viscosity rises sharply because excess water-soluble polymer remains in the serum, reducing heat transfer in a 4 m³ stainless-steel reactor. The processing window is therefore narrow; users should map particle size by dynamic light scattering (ISO 22412:2017) and residual monomer by gas chromatography (ISO 13741-1) across the intended colloid range. In vinyl acetate–ethylene systems, EG-40C alone may not provide sufficient interfacial area control, so a supplementary anionic surfactant at 0.1–0.5 pphm is often used. Higher anionic surfactant addition competes with the grafted PVOH layer and can increase grit formation. Persulphate initiation at 70–85°C promotes chain transfer to PVOH and anchors the colloid to the particle; redox initiation at 60–65°C leaves a larger water-soluble PVOH fraction in the serum and increases low-shear latex viscosity.

When EG-40C Is Substituted for Fully Hydrolysed PVOH in Water-Resistant Adhesive Compounding

Substitution of fully hydrolysed PVOH with EG-40C in adhesive compounding reduces solution make-up temperature but also reduces the equilibrium wet strength of the dried adhesive film. In paper tube winding and remoistenable labelling, the partially acetylated grade contributes faster tack development and lower crystallisation-induced shrinkage on porous substrates. Unmodified films derived from EG-40C absorb water and lose cohesive strength, so wet-service formulations require addition of a crosslinker such as glyoxal, a polyisocyanate, or zirconium ammonium carbonate. Bond strength is evaluated by lap-shear adhesion testing on paper-based adherends under TAPPI T 494 or ISO 1924-2:2008, with specimens conditioned to equilibrium at 23°C and 50% RH as defined in ISO 187. In a production laminating line with a slot-die applicator, insufficient drying below 80°C leaves residual moisture at the bond line and produces delamination under reel tension.

At the size press, EG-40C is applied as a 3–6 wt% solution at 40–60°C using a metering size press or film press. The grade functions as a film-forming binder that reduces surface dusting and improves IGT pick resistance of uncoated fine paper; performance is evaluated by ISO 3783:2006 using a medium-viscosity oil at specified printing speed. Because the 4 wt% solution viscosity is already 40.0–46.0 mPa·s, recirculation loops require positive displacement or progressive cavity pumps; centrifugal pump selection at line sizes below 50 mm risks cavitation and uneven flow distribution across the press width. At 3 wt% application solids, a rod-metering size press deposits 0.3–0.8 g/m² dry binder depending on rod pressure and base sheet absorption. If the base sheet is internally sized with alkyl ketene dimer above 0.15% oven-dry pulp, solution holdout increases but the failure mode may shift from fibre tear to interfacial binder detachment.

Rheological Limits, Borate Sensitivity, and Biological Stability

EG-40C solutions are pseudoplastic at industrial concentration; apparent viscosity declines with increasing shear rate in blade and roll applicators. The colloid is incompatible with borate salts and boric acid, which crosslink with the 1,3-diol segments of PVOH and produce gelation or precipitate in the mixing head. Recycled process water from papermaking should be monitored for residual borate or hardness ions because gel aggregates above 0.1 mm can block slot-die lips and cause coating streaks. Storage of unstabilised solutions at ambient temperature beyond 48 h risks microbial growth; a preservative compatible with nonionic polymers is required, or the solution should be held at 60–70°C under low agitation. Viscosity loss during storage may also indicate oxidative main-chain scission if the solution is exposed to copper or iron ions; stainless steel or plastic wetted parts are specified.

Regulatory Status Is Governed by Specific Monograph Conditions

Use of EG-40C in food-contact adhesives and paper coatings requires formulation-specific verification against regional positive lists. Polyvinyl alcohol grades may be used in adhesives intended for food packaging under FDA 21 CFR §175.105 and as a component of paper and paperboard under FDA 21 CFR §176.170 and §176.180, subject to extraction limitations and good manufacturing practice. In the European Union, compliance with Commission Regulation (EU) No 10/2011 must be verified for the final article by migration testing according to EN 1186-1:2002 and EN 1186-3:2002. The grade is supplied with a REACH-compliant safety data sheet; users must confirm registration for the relevant tonnage band and ensure no national restriction applies.

Why Does Fines Generation Compromise Continuous Emulsification Feed Accuracy?

Pneumatic transfer of EG-40C powder through dilute-phase conveying systems generates fines when line velocity exceeds 20–25 m/s and when elbow radius is below 5D. Fines accumulation in receiving vessels alters bulk density and can shift gravimetric feeder output by ±3–5% in continuous emulsification. A closed-loop nitrogen conveying system with dew point below -40°C reduces hygroscopic clumping. Bulk bags should be stored at ≤30°C and ≤60% RH; opened bags should be resealed because exposure to humidity above 60% RH can increase moisture content and reduce dissolution consistency. If the powder is pre-blended with starch in dry adhesive mixes, the difference in bulk density between EG-40C and native starch requires separate venturi pick-up points to avoid segregation in the feed hopper.

EG-40C is also used as a temporary binder in ceramic green tape and as a suspension stabiliser in water-based pigment dispersions. In ceramic tape casting, a 8–12 wt% solution is blended with inorganic powder and plasticiser; the dried tape must exhibit no surface skinning, which is suppressed by humidifying the drying air to 50–60% RH. Because the grade is partially hydrolysed, it burns out at lower ash residue than fully hydrolysed PVOH if the ash specification is maintained; this is relevant for electronic ceramic formulations where sodium content must not exceed 0.5% as Na₂O. Published data for EG-40C-specific burnout behaviour in multilayer ceramic processing is limited, so formulators should validate residue by thermogravimetric analysis in air according to ISO 11358-1:2022.