Wanwei PVA 20-99 (H) (PVA 100-35)

Wanwei PVA 20-99(H), identified under the alternate product code PVA 100-35 in DP-viscosity nomenclature, is a fully hydrolyzed polyvinyl alcohol (PVOH) resin engineered for applications demanding high tensile strength, solvent resistance, and low migration tendency. Viscosity of a 4% aqueous solution at 20°C falls within 20.0–28.0 mPa·s (GB/T 12010.2-2010, Brookfield LV, 60 rpm), while the degree of hydrolysis is 98.0–99.0 mol% as determined by saponification value titration (GB/T 12010.7-2010). The (H) suffix indicates a high-purity variant with residual sodium acetate controlled to ≤0.3%, ash content ≤0.5% (GB/T 12010.3-2010), and volatile matter ≤5.0% (GB/T 12010.4-2010), minimizing plate-out during thermal processing of aqueous solutions. A pH of 5–7 (GB/T 12010.8-2010) in solution permits compatibility with neutral-to-slightly-acidic formulation systems without triggering hydrolysis reversal. The powder presents as white to off-white granules with a bulk density of approximately 0.4–0.6 g/cm³; retained on 20 mesh sieve is typically ≤1.0%. This grade is frequently specified where film toughness, adhesion to cellulosic substrates, and hot-water solubility must be balanced against solution processability—attributes that position it between the lower-viscosity 17-99 series and the higher-viscosity 24-99 series within Wanwei’s fully hydrolyzed portfolio.

How Does the Hydrolysis Degree Influence Film Solubility and Thermal Resistance?

A hydrolysis level of 98.0–99.0 mol% places 20-99(H) solidly in the fully hydrolyzed category, where residual acetyl groups are minimal. This elevates crystallinity to approximately 50–55% (X-ray diffraction, Cu Kα) and raises the glass transition temperature (Tg) to 78–82°C (DSC, 10°C/min). Consequently, dissolution in water requires heating to 90–95°C with shear; cold-water swelling is negligible. The high crystallinity imparts solvent resistance to greases, oils, and hydrocarbons, and restricts oxygen transmission through cast films to 0.5–1.5 cm³·20 µm/m²·day·atm at 0% RH (ASTM D3985). In contrast, a partially hydrolyzed counterpart such as the 17-88 series (hydrolysis 86–89 mol%) dissolves readily at 20–30°C but yields films with oxygen permeability an order of magnitude higher. The near-complete hydrolysis of 20-99(H) also delays thermal decomposition: onset of weight loss in TGA (N₂, 10°C/min) occurs at 270–290°C, which broadens the processing window for hot-melt extrusion with plasticizers. However, extended exposure above 140°C in air can induce polyene formation and yellowing; thus drying of films should not exceed 120°C surface temperature. In blow-film operations for water-soluble packaging, processors pre-heat the resin with glycerol (10–15 phr) in a high-speed mixer to 85°C before extrusion through a L/D 30:1 single-screw extruder, where barrel zone temperatures are profiled from 160°C at the feed throat to 200°C at the die. Published data for specific melt rheology under simultaneous moisture evaporation in a twin-screw devolatilization setup is limited; pilot-scale validation with a co-rotating ZSK 26 mm extruder is recommended when incorporating this grade into biodegradable mulch film compounds.

Applicable migration limits for food-contact paperboard are met when the surface-applied coating weight does not exceed 2.5 g/m² of dry film. Under FDA 21 CFR 176.170, components of paper in contact with dry foods may be used provided extractives remain compliant. The resin has been tested against EU Regulation 10/2011 (simulant A, B, D2) for overall migration, with results ≤10 mg/dm² under conditions of 40°C/10 days for aqueous simulants and 20°C/10 days for isooctane. Nevertheless, the grade does not carry a formal EU FCM approval letter as a standalone substance; instead, formulators rely on the raw material supplier’s Certificate of Conformity referencing the relevant positive lists (e.g., FCM No. 1040 for vinyl alcohol).

Textile Warp Sizing Efficiency and Loom Productivity

In cotton and polyester/cotton blend weaving, 20-99(H) is delivered into a warp-sizing cook tank as granules that are pre-slurried in cold water (10–15% solids) and then steam-injected to 95°C for 45–60 min under continuous recirculation. The resulting cooking liquor, typically formulated at 8–12% solid content, develops a Brookfield viscosity of 30–80 mPa·s at 85°C. The fully hydrolyzed backbone yields a stiff, tough size film with tensile strength of 45–55 MPa (GB/T 1040.3-2006, 50% RH conditioning), which reduces hairiness and filament breakage on high-speed shuttleless looms operating at weft insertion rates above 800 m/min. Compared with the lower-viscosity 17-99 grade (viscosity 16.0–20.0 mPa·s), 20-99(H) offers superior yarn coverage per unit addition, allowing a slight reduction in size add-on from 12% to 10% while maintaining weaving resistance. The principal trade-off, observed on a Tsudakoma ZAX9100 air-jet loom processing Ne40 ring-spun cotton, is a marginally higher loom-shed drop rate—approximately 2.3 vs. 1.8 stops/10⁵ picks—when the size film is over-dried above 130°C, as embrittlement raises warp breakage. Desizing is executed with α-amylase or oxidative desizing agents at 80–90°C; the residual ash from the PVA’s sodium acetate left after neutralization must be rinsed thoroughly to avoid interference with optical brighteners applied downstream. Mills frequently blend 20-99(H) with oxidized corn starch in a 70:30 ratio to balance cost and re-weavability, though compatibility requires buffering the mixture to a pH of 6.5–7.0 using acetic acid to prevent starch retrogradation in the size box sump.

When Fully Hydrolyzed Grades Replace Starch-PVA Blends in High-Speed Sizing Machines

The replacement of all starch with 20-99(H) in warp sizing recipes on a Karl Mayer sizing machine equipped with a dual-squeeze roller system (nip pressure 15 N/cm²) produces a size film modulus of 2.0–2.5 GPa at 65% RH, approximately 30% higher than a starch-dominant blend. This stiffening effect is beneficial for zero-twist filament polyester, where filament cohesion prevents slippage, but it demands precise control of the drying cylinder temperature cascade from 110°C (first cylinder) to 100°C (final cylinder) to avoid case hardening. Operators have documented a 12–15% reduction in sizing agent consumption per linear meter of warp when switching from a PVA/starch mix to a neat 20-99(H) formulation at identical 10% add-on, attributable to the elimination of starch retrogradation losses during overnight shutdowns. However, the solution’s higher cooling viscosity, which can reach 400 mPa·s at 40°C, risks cavity formation in the size box if agitation is insufficient, leading to uneven pickup. Thus, a low-shear mixer operating at 30 rpm is mandatory in the trough. The recovered PVA from effluent ultrafiltration retains effective sizing properties, with a viscosity drop of ≤5% after three thermal cycles through a Koch membrane system (10 kDa cutoff), making in-plant reclamation feasible.

Comparative property benchmarks among three fully hydrolyzed Wanwei grades are presented in Table 1. All measurements performed on films cast from 10% aqueous solution and conditioned at 23°C/50% RH for 48 h.

From the table, the inter-grade viscosity increment directly correlates with film toughness but inversely with ease of solution handling; for example, the 24-99 film exhibits roughly 15% higher tear strength than 20-99(H) yet requires dissolution temperatures near the boil with a higher propensity for gel skins in unagitated tanks.

Paper Surface Sizing and Coating Binder Performance

In fine paper production, 20-99(H) is applied via a film press or size press at concentrations of 4–6% solids to impart surface strength and oil hold-out. Pick resistance (IGT Dry Peel, ISO 3783) values increase by 1.8–2.4 m/s at a dry pickup of 1.2 g/m², surpassing the gain achievable with starch-only formulations under identical machine conditions. The degree of hydrolysis ensures that the film remains insoluble in cold fountain solution encountered in offset lithography, preventing blanket piling. Specification sheets for this application require the surfactant-free grade to avoid foam interference on the wire, and 20-99(H) meets the foam height limit of ≤20 mm after 1 min in a dynamic foam cell test (internal method). The resin is also employed as a primary binder in pigmented inkjet paper coatings, where silica pigments (e.g., fumed silica of 200 m²/g BET) are bound at a binder-to-pigment ratio of 15:100 by weight. The high crystalline fraction prevents rapid water uptake during high-speed printing, yielding a 60° gloss of 25–35 GU on a Fogra-certified proofing substrate, sufficient without additional matte agent. Published results on fine-surface rheology indicate that coating colors containing 20-99(H) exhibit a shear-thinning profile of 500 mPa·s at 100 s⁻¹ (Anton Paar MCR 302, cone-plate) and a short time-dependent structure recovery, enabling clean doctoring in a bent-blade coater running at 1200 m/min.

Material Handling, Stability, and Incompatibilities

Unopened bags (25 kg multiwall paper with PE liner) stored at 5–35°C and RH <60% maintain specification viscosity for 24 months from the date of manufacture. Once a bag is opened, the powder absorbs atmospheric moisture, and lumping may occur within 48 h at RH>65%; partial pre-drying at 60°C for 4 h is recommended before fed into a loss-in-weight feeder if lump diameter exceeds 5 mm. Aqueous solutions prepared at 10% concentration without biocide develop microbiological growth within 72 h at 25°C, visible as a foul odour and viscosity drop; sodium benzoate at 0.1% w/w extends pot life to 7 days. The fully hydrolyzed PVA is compatible with nonionic surfactants (HLB 12–16), plasticizers such as glycerol, sorbitol, and PEG 400, and many cellulosic thickeners. It gels irreversibly in the presence of borates, borax, or boric acid even at concentrations as low as 0.05%, forming a rubbery mass unsuitable for coaters or spray nozzles. Cationic wet-end additives commonly used in papermaking, including poly-DADMAC and alum (aluminium sulfate), can precipitate PVA from solution if added without sufficient charge neutralization adjustment; thus sequence of addition in the blending tank must be strictly enforced to avoid forming filter-plugging coacervates.

For temporary ceramic binder applications, a 5% solution is spray-dried onto alumina powder pre-mix. The burnout profile in air demands a holding stage at 350°C for 2 h to remove carbon residue without cracking green bodies, as determined by simultaneous thermal analysis. Ash residue after burnout is ≤0.3%, which is critical for high-purity electronic substrates where sodium contamination must remain below 50 ppm. The limitation in this use-case is the exothermic decomposition peak at 430°C, which can create localized overheating in thick-walled alumina tubes processed in a throughput tunnel kiln; operators mitigate this by limiting the batch layer thickness to ≤15 mm during the de-binding ramp.