How Does the Viscosity-to-Hydrolysis Ratio in This Grade Influence Water Solubility and Desizing Efficiency?
Sundy PVA 098-08, the commercial designation for Sinopec’s partially hydrolyzed polyvinyl alcohol produced at the Sichuan Vinylon Works, is defined by a narrow process window in the medium-hydrolysis, mid-viscosity segment. The polymer carries a degree of hydrolysis in the range of
87.0–89.0 mol% and a viscosity, measured on a
4% aqueous solution at
20°C by the Brookfield method per
ISO 15023-2, of
8.0–10.0 mPa·s. This combination places the grade between fully hydrolyzed products that require hot-water dissolution and low-hydrolysis grades that trade film strength for cold-water solubility. The balance of residual acetate groups and chain length determines both the thermal dissolution profile and the shear stability of the resulting aqueous solution. Ash content (ignition residue) determined by
ISO 3451-1:2019 is held below
0.5%, and the volatile matter content, measured as mass loss after
3 h at
105°C, remains under
5.0%. The pH of the
4% solution is maintained between
5.0 and 7.0, ensuring compatibility with enzyme-based desizing formulations without excessive acid catalysis of ester linkages.
The standard property envelope, verified on multiple production campaigns, is assembled from batch release documentation and independent quality audits and is given in Table 1.
| Property | Typical Value | Test Standard |
|---|
| Viscosity (4% aq., 20°C) | 8.0–10.0 mPa·s | ISO 15023-2 (Brookfield LV, 60 rpm) |
| Degree of hydrolysis | 87.0–89.0 mol% | ISO 15023-1:2001 (back-titration) |
| Ash content (as Na₂O) | ≤0.5% | ISO 3451-1:2019 |
| Volatile matter | ≤5.0% | ISO 787-2 (3 h at 105°C) |
| pH of 4% solution | 5.0–7.0 | ISO 976 (glass electrode) |
| Bulk density | 0.45–0.55 g/cm³ | ISO 60:1977 |
In woven fabric sizing operations on a Zell slasher running at
600 m/min, the dissolution kinetics of PVA 098-08 become the primary control variable. Size box solids are typically maintained at
10–12%, with the cooking kettle operating at
90–95°C for
30–45 min to ensure complete swelling of the cold-water-soluble granules. If the cooking time is shortened below
20 min, microscopic gel nuclei persist and manifest as intermittent size film breaks across the split rods, raising warp end breakage rates from the baseline of
1.2 per 10⁶ picks to over
4 per 10⁶ picks on high-tension filament yarns. The grade’s
8–10 mPa·s viscosity provides moderate film strength that is insufficient for unsized fine-count polyester warps when used alone; therefore, mill recipes commonly blend PVA 098-08 with a high-polymerization-degree PVA 1799 (viscosity
25–31 mPa·s) in a ratio of
30:70 by dry weight. This blend exploits the low-viscosity component’s rapid wet-out of the yarn sheet and the high-DP fraction’s abrasion resistance during the weaving shed. Residual size removal in an open-width Benninger washer is completed in less than
30 s at
90°C using an
α-amylase enzyme bath, as measured by the hot-water solubility test per
ISO 15023-1 Annex B. The
88% hydrolysis level allows rapid enzyme penetration, unlike grades above
95% hydrolysis that require extended dwell times at
95°C and often necessitate oxidative post-desizing.
When the Protective Colloid Function Overrides Surfactant Demand in Vinyl Acetate Emulsion Polymers
In the semi-batch homopolymerization of vinyl acetate at
65–70°C inside a
5 m³ jacketed stainless steel reactor equipped with a low-shear anchor agitator rotating at
60 rpm, PVA 098-08 is introduced as a
10% aqueous solution at a level of
1.5–2.5 wt% on monomer. The grade’s relatively short chain length (
≈900 polymerization degree) and
88% hydrolysis generate a grafting efficiency during the radical-initiated stage that limits particle size broadening. Monitoring with a focused beam reflectance measurement (FBRM) probe reveals that the square-weighted mean chord length stabilizes at
1.2–1.5 µm after the
60% monomer feed point, compared to
1.8–2.3 µm when a higher-DP protective colloid (PVA 1788, viscosity
20–26 mPa·s) is substituted at equal concentration. The narrower particle size distribution translates into a Brookfield RVT viscosity drop from
2200 mPa·s to
1400 mPa·s (spindle 6,
20 rpm) at
55% solids content, while coagulum retained on a
200-mesh screen remains below
0.05%. This enables post-polymerization compounding with less thickening agent, an advantage when formulating for high-speed knife-over-roll coating lines where levelling demands a pseudoplastic flow curve with a low-shear viscosity between
800 and 1200 mPa·s.
A critical processing boundary exists regarding the redox initiator system. If the exotherm is miscontrolled and the reacting mass reaches
85°C for more than
15 min, the water layer surrounding the grafted PVA chains undergoes partial dehydration, visible as an abrupt increase in backscatter signal on a Turbiscan instrument and a corresponding rise in the coagulum fraction to
0.2–0.3%. This degradation mode is absent in grades with a hydrolysis degree above
98%, which retain a tighter hydration shell, but those grades require higher energy dissolution and impart a strong temperature-dependent viscosity hysteresis in the emulsion. In continuous monomer addition mode, PVA 098-08 is incompatible with premature addition of amine-functional additives (e.g., hexamethoxymethyl melamine) because residual acetate groups can undergo transamidation at the feed port, generating insoluble particles that block the static mixer upstream of the reactor. Therefore, post-reaction adjustment of pH and addition of crosslinkers must be conducted after the latex has been cooled below
40°C and transferred to a blend-down vessel.
Blade Metring Dynamics and Immobilization Time Under High-Shear Paper Coating Conditions
A coating color formulated with
65% solids, comprising a
70:30 weight blend of GCC (
60% <2 µm, Hydrocarb 90) and fine kaolin, uses PVA 098-08 as the sole synthetic co-binder at
2.0 parts per hundred pigment. In laboratory blade coater tests run at
1 m/s and a blade angle of
22°, the immobilization time—determined by the inflection point of transmitted light through the wet film—decreases to
0.38 s at
25°C ambient. For coating heads operating at
1200 m/min on a Valmet OptiCoat Jet unit, this immobilization point must be extended beyond
0.6 s to avoid blade scratches and micron-scale streaks. Mill trials therefore incorporate
0.3–0.5 parts of a low-molecular-weight plasticizer such as sorbitol or triacetin, which interacts with the hydrated PVA segments and retards the capillary-driven dewatering. The adjustment returns the open time to
0.65–0.75 s without sacrificing wet-pick resistance. Dry pick strength, measured by the
IGT AIC2-5 tester in accordance with
ISO 3783:2006, improves by
18% compared to a starch-only control, while surface resistivity measured by
ASTM D257-14 remains within the acceptable range for reprographic papers.
The grade’s limited thickening efficiency at high shear becomes an asset in short-dwell application systems where a severe dilatancy risk exists if long-chain PVA is employed. Extensional viscosity measurements on a capillary break-up extensional rheometer show a relaxation time below
1 ms for the PVA 098-08 solution at
12% solids, preventing filament formation at the blade lip. When the same formulation is run with PVA 2488 (viscosity
44–50 mPa·s), spatter marks appear on the coated sheet at speeds above
800 m/min. This difference dictates that high-speed LWC (
40–55 g/m²) coating stations preferentially select the mid-viscosity grade to maintain runnability over a shift length of
12 h without blade change.
When evaluated alongside other Sinopec partially and fully hydrolyzed grades, the property window of PVA 098-08 reveals distinct processing advantages in applications demanding intermediate cold-water solubility without excessive viscosity build. Table 2 summarizes standardized data for four representative grades routinely compared in bench-scale formulation studies.
| Grade | Polymerization Degree (approx.) | Hydrolysis (mol%) | Viscosity, 4% aq. (mPa·s, 20°C) | Typical Processing Niche |
|---|
| Sundy PVA 098-08 | 900 | 87.0–89.0 | 8.0–10.0 | Warp sizing, VAc protective colloid, paper co-binder |
| PVA 1788 | 1700 | 86.0–89.0 | 20.0–26.0 | High-strength emulsion adhesive, ceramic binder |
| PVA 1799 | 1700 | 98.0–99.0 | 25.0–31.0 | Hot-water soluble film, high-temperature mold release |
| PVA 0588 | 500 | 86.0–89.0 | 4.5–6.0 | Low-viscosity protective colloid, warped napkin adhesive |
Adhesive compounding for cellulose-based substrates leverages the grade’s re-wettability and open time, but imposes specific formulation boundaries. In a wood-to-wood laminating adhesive conforming to
EN 204 D1 durability class, PVA 098-08 is pre-dissolved at
15% solids and blended with a vinyl acetate-ethylene copolymer emulsion at a ratio of
20:80 on a dry-weight basis. The addition of
0.5% of a non-ionic polyurethane thickener (Borchi Gel 0620) brings the mixture to a final Brookfield viscosity of
12,000–15,000 mPa·s (TF spindle,
2.5 rpm), providing a press assembly time of
8–10 min at
23°C and
50% RH. Under these conditions, the adhesive achieves a dry shear strength exceeding
10 N/mm² on beech test blocks conditioned to
12% moisture content, as determined by
EN 205. However, water resistance is limited: after
24 h immersion in cold water (
23±1°C), bond strength drops to less than
1 N/mm², precluding use in exterior or wet-area applications. Pre-drying of the granular resin at
60°C for
2 h is mandatory when ambient relative humidity exceeds
60%, as absorbed moisture retards dissolution and can produce graininess in the final film. The product is registered under
REACH and meets the heavy-metal limits set forth in
RoHS Directive 2011/65/EU, as confirmed by third-party ICP-MS screening of
29 regulated elements.
