Kuraray POVAL 30-88 is a partially hydrolysed polyvinyl alcohol grade defined by two primary specifications: a nominal
4% aqueous solution viscosity of
30 mPa·s at
20°C and a nominal degree of hydrolysis of
88 mol%. The product is supplied as a white to off-white granular powder that is soluble in hot water; it is not cold-water soluble at
25°C. Under
JIS K6726:1994, the control ranges typically presented for this grade include a viscosity of
27.0–33.0 mPa·s, a hydrolysis level of
87.0–89.0 mol%, volatile matter not exceeding
5.0%, ash as Na₂O not exceeding
0.5%, and a pH between
5.0 and
7.0 for a
4% solution. The combination of moderate chain length and partial hydrolysis places the material between low-viscosity surface-active PVOH grades and high-viscosity fully hydrolysed grades. Residual acetate groups depress crystallinity and reduce the energy required for dissolution relative to a
98–99 mol% hydrolysed grade, while the
88 mol% hydroxyl content retains sufficient interchain hydrogen bonding to form a coherent cast or coated film after drying.
| Property |
Typical value |
Test basis |
| Degree of hydrolysis |
87.0–89.0 mol% |
JIS K6726:1994 |
| Viscosity of 4% aqueous solution |
27.0–33.0 mPa·s at 20°C |
JIS K6726:1994 |
| Volatile matter |
≤ 5.0% |
JIS K6726:1994 |
| Ash as Na₂O |
≤ 0.5% |
JIS K6726:1994 |
| pH of 4% solution |
5.0–7.0 |
JIS K6726:1994 |
In solution preparation, the solid is typically introduced through a low-shear eductor or centrifugal sifter into a jacketed stainless steel vessel containing water at
85–90°C. If dry powder is dumped directly into a high-speed vortex without sifting, hydrated gel layers form around undissolved cores, producing fish-eye defects that can persist through
150 μm filters. For incoming inspection, viscosity testing alone is not sufficient to detect low-level crosslinked gels. A typical quality control protocol includes visual inspection of a
10% solution after passing through a
150 μm sieve, with gel particle counts reported as number per
100 g of solid. The alcoholysis degree is verified by saponification value; residual acetyl content may also be measured by hydrolysis and titration.
How Do Molecular Weight and Residual Acetate Distribution Influence Solubility and Film Tensile Response?
The prefix “30” indicates a longer average chain length than grades such as
22-88 or
5-88. At equal hydrolysis, higher molecular weight raises the viscosity of a
4% solution and increases extensional viscosity in the film split during roll application. In a
5,000 L jacketed dissolution vessel with a bottom-mounted axial-flow impeller running at
40–60 rpm, a
10 wt% batch is normally fully dissolved in
90–150 min at
85°C. If the heating ramp is shortened or the vessel is operated below
80°C, residual gel particles can be carried downstream and appear as streaks in a subsequent coating nip.
The
88 mol% hydrolysis level also controls solubility and film properties. Fully hydrolysed PVOH requires holding temperatures above
90°C and longer swelling times because dense hydrogen-bonded crystalline domains resist water ingress. In
30-88, randomly distributed acetate groups interrupt crystallite growth and allow a lower dissolution temperature, but they also reduce ultimate water resistance of the dried film. A dried film formed from
30-88 will exhibit measurable swelling and softening in cold water, whereas a fully hydrolysed grade remains intact until hot water is applied. Tensile testing of cast films under
ASTM D882-18 typically shows that
30-88 films are more extensible than fully hydrolysed PVOH and stronger than
5-88 films at equal plasticiser content. Published data for specific plasticiser formulations is limited; observed industrial behaviour varies with plasticiser type and drying temperature.
Where
30-88 is used as a protective colloid in vinyl acetate emulsion polymerization, the addition level is commonly
3.0–3.5 wt% on total monomer. In a
500–1,000 L glass-lined reactor with a pitched-blade turbine at
80–120 rpm, the colloid stabilises growing latex particles and reduces coagulum build-up on the vessel wall. The residual acetate groups participate in radical grafting to the PVOH backbone; this grafting alters the stabiliser layer and produces pseudo-plastic flow in the finished latex. Increasing the PVOH fraction from
3.0 wt% to
5.0 wt% raises low-shear Brookfield viscosity at
20 rpm and may shift the particle size distribution measured by laser diffraction toward larger mean diameters.
Scale-up from laboratory glassware to a
1,000 L reactor is not linear. The lower surface-to-volume ratio changes heat removal, and persulfate initiator addition must be ramped accordingly. If the exotherm is not controlled within ±
2°C, grafting density changes and batch-to-batch low-shear viscosity can vary by more than
20%. At comparable addition levels,
30-88 produces higher latex viscosity and better wet-tack than
5-88 because the longer chains bridge adjacent particles more effectively. However, the increased low-shear viscosity can complicate handling in high-solids formulations; pumps, filters, and filling lines must be sized for shear-thinning behaviour. Rheological evaluation under
ISO 3219:1993 or
DIN 53019-1:2008 is recommended when shifting from a low-viscosity grade to
30-88.
Grade-Differentiating Properties in Aqueous Adhesive and Barrier Coating Applications
In paper surface sizing, a
6.0–8.0% solids solution of
30-88 maintained at
70–80°C on a film press can deposit dry coat weights of
3–5 g/m² when metered with a rod or smooth-roll applicator. The grade’s viscosity contributes to a stable film split and reduces spattering compared with lower-molecular-weight PVOH, but the solids window narrows above
9.0% because the solution can become too viscous for uniform transfer at
600 m/min line speeds. Surface strength is often assessed via
ISO 3783 IGT pick resistance; comparative trials show that PVOH addition at
3.0–5.0% of coating solids improves dry pick resistance, while wet pick resistance depends on the cure of the co-binder and the base-sheet internal size.
Aqueous adhesive formulations exploit similar film-formation and colloidal stabilisation behaviour. In remoistenable adhesives,
30-88 can be compounded with plasticisers and defoamers; the higher molecular weight increases bond strength relative to
22-88 but raises the viscosity of a
20% solids formulation. Formulators typically dilute by
2–5% additional water when transitioning from
22-88 to
30-88 to maintain identical coating viscosity.
| Grade |
Nominal 4% viscosity at 20°C (mPa·s) |
Nominal degree of hydrolysis (mol%) |
Processing consequence in aqueous formulation |
| POVAL 30-88 |
30 |
88 |
Higher film cohesion than 22-88 at equal solids; requires heating to 80–85°C |
| POVAL 22-88 |
22 |
88 |
Lower viscosity at equal solids; reduced wet pickup on cylinder presses |
| POVAL 5-88 |
5 |
88 |
Easier cold-water handling; lower tensile strength of cast film |
| Fully hydrolysed PVOH |
27–33 |
98–99 |
Higher water resistance after drying; dissolution above 90°C |
On textile warp sizing lines processing polyester–cotton blends, a
10–13% solids solution of
30-88 is applied in size boxes at
75–85°C. The higher viscosity of the grade provides adequate size add-on at squeeze pressures of
0.3–0.5 MPa on a two-roll padder, reducing the need for high add-on from low-viscosity grades. Desizing is carried out with hot-water washing at
80°C because the size film must be removed before dyeing; the partially hydrolysed PVOH re-dissolves more readily than fully hydrolysed size, but is not removable in cold water. Yarn tensile strength retention after sizing is typically evaluated under
ISO 2062:2009; the PVOH film increases abrasion resistance during weaving as measured by loom stop counts per
100,000 picks. Published data for specific weave-room stop counts is formulation-dependent and limited.
When a Low-Moisture Melt Process Replaces Hot-Water Solution Preparation
Partially hydrolysed PVOH is not commonly processed as a neat melt because the temperature window between flow initiation and thermal degradation is narrow. For
30-88, the crystalline melting range is below that of fully hydrolysed PVOH, but thermal degradation accelerates above
200°C. If a twin-screw compounding line is selected, plasticiser incorporation of
15–30 phr is required to bring the melt temperature into a processable range. In a co-rotating twin-screw extruder with an
L/D ratio of
40:1, a barrel temperature profile from
90–170°C and a die temperature below
180°C can be used for plasticised formulations.
Without sufficient plasticiser, shear heating in the kneading blocks raises the melt temperature above
200°C, producing yellowing, generation of acetic acid, and gel formation. These observations are consistent with the known thermal degradation pathway of PVOH, but published data for this specific melt-processing configuration is limited. Aqueous solution processing remains the standard route for
30-88 in high-volume coating lines.
Regulatory data sheets for Kuraray POVAL 30-88 list the substance as polyvinyl alcohol under
CAS 9002-89-5. Under
REACH, the grade is registered as a polymer, and exposure controls address dust containment rather than acute toxicity. For food-contact use, polyvinyl alcohol films and coatings may be evaluated under
FDA 21 CFR 177.1670 or
21 CFR 175.300 depending on the final article; end-use migration testing is required because the grade itself does not establish compliance limits.
Storage should be in sealed bags at relative humidity below
60% and below
30°C. Moisture uptake above
60% RH increases caking and can alter gravimetric feeding; pneumatic transfer lines should be designed for a bulk density near
0.40–0.60 g/cm³, but the exact packed density depends on particle-size distribution and consolidation. In aqueous formulation,
30-88 should be protected from strong oxidizing agents and from excessive alkaline hydrolysis at pH above
10 during prolonged hot storage. Addition of borate salts at even
0.1% by weight can produce reversible but high low-shear viscosity increases through borate-diol complexation; crosslinked gels can block filters and coating lines. These incompatibility boundaries are reversible under acidic pH adjustment but are difficult to reverse once films are dried.
