GOHSENOL KH-17

Poly(vinyl alcohol) grade GOHSENOL KH-17, manufactured by Mitsubishi Chemical Corporation, is a partially hydrolysed poly(vinyl acetate) derivative supplied as white to off-white powder or granular material. The product code specifies a hydrolysis band of 78.5–81.5 mol% and a viscosity of 25.0–31.0 mPa·s for a 4 wt% aqueous solution at 20.0°C. These values are determined by the methods in ISO 15023-2:2019 and JIS K6726:1994; each production lot is certified for hydrolysis, viscosity, volatile matter, ash, and pH. The residual acetate content of 18.5–21.5 mol% lowers crystallinity and increases cold-water wettability relative to fully saponified grades, making the polymer suitable as a suspension dispersant and protective colloid. When stored below 60% relative humidity, the material remains free-flowing; beyond this condition, moisture uptake can produce lumps that reduce gravimetric feeding accuracy.

What Distinguishes KH-17 from Fully Saponified Poly(Vinyl Alcohol) Grades?

Fully saponified PVA grades with hydrolysis above 98.0 mol% require heating to 80–95°C for complete dissolution because interchain hydrogen bonding creates crystalline domains. KH-17, with hydrolysis of 78.5–81.5 mol%, has a less ordered microstructure and reaches full dissolution at 60–85°C under moderate shear. The residual acetate groups also increase adsorption at oil-water interfaces, which is relevant in suspension polymerization. Fully saponified grades tend to produce more water-resistant films after drying; KH-17 films remain water-soluble unless crosslinked. This does not represent a quality difference but a selection boundary: cold-water solubility and interfacial activity are obtained at the cost of dry-film water resistance. In adhesive compounding, KH-17 solutions are less likely to form semidilute gel networks at room temperature than fully saponified grades of equal 4 wt% concentration, although solvent and pH conditions dominate this behavior.

Production-scale suspension polymerization of vinyl chloride in reactors of 30–200 m³ working volume generally operates at 50–70°C and 0.8–1.2 MPa. In this process, KH-17 is charged as an aqueous solution at 0.04–0.12 wt% relative to vinyl chloride monomer; the optimum addition depends on agitator power number, baffle configuration, and target PVC K-value. Because the polymer solution has a viscosity of 25.0–31.0 mPa·s at 4 wt%, it can provide sufficient interfacial film strength to limit coalescence of monomer droplets during the early polymerization phase. If the dose is below the lower boundary, the suspension phase can become unstable and produce coarse agglomerates; if the dose is excessive, the polymer may reduce primary grain porosity and lower plasticizer absorption. Published reaction-engineering data for KH-17 in a single named reactor geometry are limited; pilot-scale trials using a two-turbine agitator system and glass-lined baffles are the standard method for setting a site-specific dispersant loading.

Dispersion and Dissolution Procedure for Aqueous Formulations

KH-17 powder is dispersed in cold water at 25–40°C under agitation to wet the particle surfaces and prevent agglomerate formation. The slurry is then heated to 80–90°C and held for 30–60 min at low shear; a 4 wt% solution cooled to 20.0°C should fall within the certified viscosity band. When steam injection is used, local hot spots above 95°C should be avoided because acid-catalyzed hydrolysis or oxidative yellowing may occur, particularly if pH is below 3.0. For gravimetric feeding in humid plants, pre-drying at 30–50°C in a fluid-bed dryer is recommended when relative humidity exceeds 60%. Aqueous solutions are prone to microbial growth after 48–72 h if stored at ambient temperature without biocide; process tanks should be cleaned with alkaline flushing to prevent biofilm buildup.

Rheological measurements on 4 wt% solutions show a temperature-dependent viscosity reduction of approximately 40–60% when the solution is heated from 20.0°C to 60.0°C, though the exact reduction depends on degree of hydrolysis and ash. Because of this, transfer lines and filters should be sized for the cold-start viscosity 25.0–31.0 mPa·s, not the operating temperature viscosity. Centrifugal pumps with low-shear impellers are preferred over high-shear gear pumps, because prolonged mechanical shear can reduce apparent viscosity by chain scission in the presence of dissolved oxygen.

Within the GOHSENOL KH series, KH-17 is selected for low-to-mid viscosity requirements; higher-viscosity grades KH-20 and KH-23 provide approximately 35–43 mPa·s and 44–52 mPa·s under the same 4 wt% conditions, while retaining a similar hydrolysis band. KH-17 is therefore preferable when a high-solids feed stream must be pumped through narrow-line heat exchangers or slot dies without exceeding a back-pressure limit. Compared with grade GH-17, which has a hydrolysis band near 86.5–89.0 mol%, KH-17 is more hydrophilic and more surface-active in suspension polymerization, but the dried film is less water resistant. Compared with fully saponified NH-18, which has hydrolysis above 98.0 mol%, KH-17 dissolves at lower temperature and produces lower solution viscosity for equal concentration. These comparisons should be verified against current manufacturer certificates, because grade specifications can change with production site and national standard revision.

If Water Resistance Becomes a Design Requirement, KH-17 Requires Crosslinking or Blending

Because KH-17 retains 18.5–21.5 mol% residual acetate, a film cast from this grade alone softens rapidly on water immersion and loses tensile integrity. Water resistance for paper coatings or adhesives can be increased by adding glyoxal at 1.0–5.0 wt% of PVA solids, but the resulting viscosity build occurs within 24–48 h and must be neutralized or consumed before application. Dialdehyde starch and melamine-formaldehyde resins offer alternative crosslinking, with cure temperatures of 120–150°C typical on coated paper. Borax is not a crosslinker for this polymer in the covalent sense but forms reversible complexes with 1,2-diol units; addition of sodium tetraborate at 0.1–0.5 wt% of wet formulation increases viscosity sharply, and above this range gel particles can block slot-die lips and gravure cells. Formulators using KH-17 in water-resistant laminating adhesives therefore pre-compound the PVA with colloid-stabilized dispersions rather than relying on the dry film alone.

Textile warp sizing uses KH-17 at 8–14 wt% solids in the size box, held at 65–75°C to control pickup on cotton, polyester/cotton, and regenerated cellulose yarns. The cooled film exhibits sufficient tensile strength for loom shed conditions, but elongation remains high enough to withstand repeated cyclic bending at yarn intersections. Desizing is performed with hot water at 60–85°C or with amylase/oxidative desizing baths; because PVA is not starch, enzyme-only desizing does not remove the film, and a washing step is required. The film tensile properties of PVA are commonly tested by ASTM D638 or ISO 527 on cast specimens, although converted textile laboratories often use yarn-level tensile retention after sizing.

Vinyl Acetate Emulsion Polymerization Uses KH-17 as a Protective Colloid

Emulsion polymerization of vinyl acetate homopolymers and vinyl acetate-ethylene copolymers at 50–80°C can be stabilized with partially hydrolysed PVA. KH-17 is dissolved in the aqueous phase at 4–6 wt% on total reactor charge, and monomer is added under high-shear dispersion to create a pre-emulsion. The polymer increases continuous-phase viscosity and provides steric stabilization at the monomer-water interface, which reduces reactor wall coagulum and impeller fouling. Finished dispersions stabilized with KH-17 are typically pseudoplastic, with lower viscosity under high shear and recovery at low shear. Because the hydrolysis band is 78.5–81.5 mol%, the colloid has lower crystalline content than fully saponified PVA, which may improve freeze-thaw stability in some formulations; however, published data for this specific grade in ethylene-modified emulsions is limited. Coagulum is measured in production by filtration through a 40–80 µm sieve, and lot acceptance is often set at 0.05–0.10 wt% of total dispersion dry mass.

In paper surface sizing, KH-17 can be applied at 2–5 wt% solids by a size press or film press to increase the surface strength measured by TAPPI T530. The low degree of hydrolysis reduces the solution viscosity at equal solids, allowing a higher size-press speed without misting or skip coating. However, the dried film does not develop the water resistance of fully saponified PVA; therefore, papermakers often combine KH-17 with styrene-acrylate surface sizes or crosslinking agents to meet oil and grease holdout requirements.

In ceramic tape casting, KH-17 may be used as a temporary organic binder at 5–10 wt% of ceramic powder; burnout in air at 400–600°C leaves an ash contribution of ≤0.4%, which must be included in dielectric loss calculations. This application exploits the clean burnout of PVA and its film toughness, but the sodium salt content in the ash may preclude use in low-loss microwave dielectric tapes. Compatibility with inorganic fillers such as kaolin, calcium carbonate, and titanium dioxide is generally acceptable at neutral pH. Strong acids below pH 2.5 accelerate hydrolysis of residual acetate groups and reduce solution viscosity over time. Strong oxidizing agents such as persulfates at high concentrations can oxidize the secondary alcohol groups, leading to chain scission and discoloration.

Typical certificate of analysis for KH-17 includes viscosity, degree of hydrolysis, volatile matter, ash, and pH. The viscosity test uses a 4.00 g dry-basis sample dissolved to 100 mL total volume in deionized water. The sample is heated at 90°C for 1 h, cooled to 20.0°C, and measured with a rotational viscometer at 30 rpm; this method aligns with JIS K6726:1994. Incoming inspection should use water with conductivity below 5 µS/cm to avoid ionic interference in pH and viscosity results. Ash above 0.4% can lead to salt spotting on coated surfaces after drying, and volatile matter above 5.0% can indicate insufficient drying during production. If viscosity is below the lower band, the polymer may have undergone chain scission; if above, contamination with a higher-molecular-weight grade or moisture-swollen aggregate may be present. Users should quarantine non-conforming lots and request manufacturer re-certification before use in regulated applications.

GOHSENOL KH-17 is not classified as hazardous under GHS in the supplied powder form, but the dust can form explosive mixtures; process equipment should be bonded and grounded in accordance with IEC 60079-10-2 or local equivalent. For food-contact applications, users should verify that the final article meets FDA 21 CFR 176.170 and EU Regulation 10/2011 migration limits, because the polymer itself does not provide a global food-contact approval. The ash residue of ≤0.4% must be considered in dielectric or optical applications where residual sodium salts alter electrical properties.