GOHSENOL EG-48P

GOHSENOL EG-48P is a partially hydrolyzed polyvinyl alcohol powder supplied under the GOHSENOL trade name by Nippon Gohsei, Ltd., a Mitsubishi Chemical Group company. The grade is positioned in the medium-viscosity segment of the EG series, with a 4 % aqueous solution viscosity of 46.0–54.0 mPa·s at 20 °C and a degree of hydrolysis of 86.0–89.0 mol %. Volatile moisture is controlled to ≤5.0 % and ash to ≤0.7 % when tested according to JIS K6726. These values define a partially hydrolyzed polyvinyl alcohol with sufficient residual acetate groups to depress crystallinity and enable cold-water dispersion, while the chain length provides elevated solution viscosity and film cohesion. The powder is used as a protective colloid in emulsion polymerization, as a binder in paper and nonwoven systems, and as a film former in water-based adhesives and remoistenable coatings.

What Constrains the Dissolution and Shear Stability of EG-48P?

Dissolution of EG-48P is governed by the hydration rate of residual polyvinyl acetate blocks and the particle size distribution of the powder. Typical preparation involves dispersing the powder in cold water at 20–30 °C under sustained agitation, then heating to 80–90 °C for 30–45 min at moderate shear. In an in-line rotor-stator reconstitution system with a tip speed of 10–15 m/s, undisintegrated agglomerates can produce gel-like microgels if the powder is added faster than the hydration front. Solution viscosity measured at 20 °C by JIS K6726 is not a direct indication of molecular weight but is the principal grade release criterion. Shear degradation is negligible in aqueous processing below 60 °C; above 80 °C, oxidative chain scission can occur in aerated systems unless hold time is kept below 60 minutes. For high-shear preparation, cooling jacket control at 45–60 °C is recommended after complete hydration to reduce viscosity drift during storage.

In semi-batch vinyl acetate-ethylene and vinyl acetate-acrylic emulsion polymerizations, the protective colloid effect of EG-48P is achieved by pre-dissolving the polymer at 10–15 % solids and charging the solution into a jacketed glass-lined reactor before monomer addition. Protective-colloid loadings of 2.5–5.0 % by mass on total monomer are reported in formulation literature for medium-viscosity partially hydrolyzed PVOH grades; within this range, higher loadings reduce mean particle diameter but increase continuous-phase viscosity. Reactor installations with pitched-blade turbine agitation at 120–180 rpm and a reactor temperature of 55–85 °C require slow addition of the PVOH solution to the initial reactor charge to avoid local viscosity stratification. The residual acetate content reduces grafting efficiency compared with fully hydrolyzed grades but improves low-temperature particle stability. Nitrogen purging at 0.2–0.5 L/min per kg of reactor charge is used to control dissolved oxygen and to retard chain-transfer side reactions during the first hour of monomer feed. Batch-to-batch ash content below 0.7 % is relevant for low-electrolyte formulations because residual sodium acetate buffers the aqueous phase and may shift particle size distribution if not controlled.

When Partially Hydrolyzed PVOH Replaces Fully Hydrolyzed Grades in Surface Sizing and Barrier Coating

Partially hydrolyzed EG-48P is selected over fully hydrolyzed grades where cold-water solubility and lower film sealing temperatures are more important than maximum water resistance. In a size-press formulation containing oxidized starch and PVOH at 0.5–2.0 % PVOH on dry fiber, the EG-48P component alters surface strength as measured with an IGT AIC2-5 printability tester under ISO 3783; published EG-48P-specific pick values are limited, so formulation trials are used to define starch displacement. Films cast from EG-48P require a thermal fusion step at 90–120 °C to develop acceptable water resistance; fully hydrolyzed grades develop higher tensile strength and lower equilibrium moisture at equivalent film thickness. The trade-off is a lower hot-water resistance because residual acetate groups leave the dried film more water-sensitive.

Film casting from EG-48P on a polyethylene terephthalate support at a wet thickness of 200 µm and drying at 120 °C for 10 min produces films that remain redispersible in water at 25 °C. Mechanical testing according to ASTM D882-18 after conditioning at 23 °C and 50 % relative humidity for similar medium-viscosity partially hydrolyzed PVOH grades typically reports tensile strength in the range of 35–50 MPa and elongation at break of 150–250 %. EG-48P-specific data under identical casting conditions is limited; therefore, these values are screening references rather than guaranteed product performance. Higher film tensile strength can be obtained with higher-viscosity fully hydrolyzed grades, but those require dissolution at 80–95 °C and exhibit higher blocking tendency.

Comparative Viscosity and Hydrolysis Ranges Across GOHSENOL EG-Series Powders

Product differentiation within the GOHSENOL EG series is primarily controlled by 4 % aqueous solution viscosity and degree of hydrolysis. EG-48P has a viscosity range of 46.0–54.0 mPa·s, which is higher than the lower-viscosity EG-series range of 40.0–46.0 mPa·s at the same 20 °C test condition. This viscosity increment corresponds to longer polymer chains and contributes to higher film tensile strength, higher adhesive cohesion, and increased solution thickening per unit mass. The degree of hydrolysis for both categories is 86.0–89.0 mol %, so differences in cold-water solubility are less pronounced than differences in final solution rheology. Table 2 compares EG-48P with a lower-viscosity partially hydrolyzed category and a fully hydrolyzed reference category.

Adhesive compounding with EG-48P requires formulation-specific control of plasticizer migration and borate-induced gelation. In water-activated adhesive coatings, plasticizer addition of 10–20 phr based on dry resin reduces minimum film-forming temperature and improves adhesion to clay-coated board, but film blocking can occur above 25 °C when plasticizer exceeds 25 phr. The interaction between borax and PVOH is a critical boundary: sodium tetraborate in alkaline aqueous media forms reversible diol-borate crosslinks, and gelation can begin at borax levels as low as 0.2 % on solution mass; however, published gel-point data for EG-48P in adhesive formulations is limited. Borax-compatible formulations require metered addition and pH control between 7.0 and 8.5. Polyvalent salts, especially aluminium sulfate, can precipitate or destabilize EG-48P solutions in papermaking process water. Do not combine with strongly oxidizing acids or hypochlorite-based biocides because exothermic oxidative degradation of PVOH can occur.

Thermal Degradation Thresholds in Aqueous EG-48P Solutions

Thermal exposure of aqueous EG-48P solutions causes two distinct degradation responses. In the absence of oxygen, solutions remain visually clear but undergo slow acid-catalyzed hydrolysis of remaining acetate groups, shifting pH to 4.0–5.0 after prolonged storage at 40 °C. In aerated storage tanks, oxidative chain scission reduces the 4 % solution viscosity at 20 °C by 10–20 % after 72 hours at 60 °C when no antioxidant is present; published accelerated aging data for similar partially hydrolyzed PVOH grades support this range, but EG-48P-specific data under identical conditions is limited. Storage of prepared solutions at 20–25 °C with a biocide is limited to 72–96 hours because of microbial degradation. Dried EG-48P powder stored above 75 % relative humidity can absorb moisture and cake in hoppers; pneumatic transfer with air at a dew point below 10 °C is used to maintain flow. The product should not be exposed to temperatures above 200 °C in dry form, because thermal decomposition accelerates sharply and releases volatile carbonyl compounds.