Industrial polyvinyl alcohol (PVA) binder powder

01

Pick the degree of hydrolysis and the 4% viscosity grade

Kuraray explains that in its grade names the first number is the viscosity of the 4% aqueous solution at 20 °C, as a relative measure of molar mass, and the second is the degree of hydrolysis of the polyvinyl acetate it is made from. Its data sheet lists partially hydrolyzed 5-88 at 4.6–5.4 mPa·s and 86.5–89.0 mol%, 22-88 at 20.5–24.5 mPa·s and 87.0–89.0 mol%, medium-hydrolyzed 17-94 at 14.5–18.5 mPa·s and 92.5–94.5 mol%, and fully hydrolyzed 28-98 at 25.0–31.0 mPa·s and 98.0–99.0 mol%. [1] Kuraray's FAQ gives its viscosity range as about 3 to 225 mPa·s (4% solution, 20 °C) and groups hydrolysis as partially (about 87–89 mol%), intermediately (about 92–96 mol%) and fully hydrolyzed (about 98–99 mol%). [2]

Sekisui's Selvol brochure uses the same 4% viscosity as its measure of molecular weight: 3–6 cP corresponds to a degree of polymerization of 150–650 and a weight-average molecular weight of 13,000–50,000; 22–30 cP to 1000–1500 and 85,000–124,000; 45–72 cP to 1600–2200 and 146,000–186,000. It classes partially hydrolyzed grades at 87.0–89.0 mol%, fully at 98.0–98.8 and super at 99.3+. [3]

Chinese makers name grades differently. Wanwei lists more than thirty PVA grades including PVA17-99, PVA26-99, PVA04-99, PVA05-99, PVA17-88 and PVA05-88, and defines the polymer as (CH3CHCOOCH3)x(CH2CHOH)y, where x + y is the degree of polymerization and y/(x + y) the degree of alcoholysis. [4] Editorial note: because Kuraray's first number is a viscosity and the Wanwei page does not state viscosity for its grades, ask any supplier of a 17-88 or 24-88 grade for the measured 4% viscosity at 20 °C and the alcoholysis range on the certificate of analysis rather than comparing grade names.

Give the supplier the binder use (adhesive, paper or pigment coating, textile size, ceramic pressing), the target degree of hydrolysis in mol%, the 4% solution viscosity range at 20 °C, volatiles, ash and pH limits with the test method, the form (granules, flakes or fine powder) and any particle-size requirement, methanol limit, packaging, and quantity.

02

Set volatiles, ash and pH limits, form and dissolution

Kuraray's standard grades carry volatiles ≤5.0%, ash ≤0.4% (≤0.6% for the low-viscosity fully hydrolyzed 3-98, 5-98 and 11-98) and pH 5.0–7.0, and its low-ash grades go to ≤0.09% ash; it states non-volatile content of at least 95% after 3 hours at 105 °C and methanol under 3%. [1] Selvol standard grades list volatiles 5.0% max, ash 0.5–1.2% max expressed as Na2O, methanol 0.9% max, and pH 4.5–6.5 for partially hydrolyzed and 5.0–7.0 for fully hydrolyzed grades, all on a 4% solution. [3]

Form: Kuraray supplies granules and fine powder with defined grain size, including fine-powder S2 versions of 5-88, 22-88, 30-88, 44-88 and 28-98 with the same viscosity and hydrolysis ranges as the standard grades. [1] Wanwei describes PVA as white flake, granular or powder solid, or a white flocculent solid depending on the alcoholysis process, with specific gravity 1.23–1.31 g/cm³ and bulk density 0.42–0.52 g/cm³ for flake versus 0.20–0.27 g/cm³ for flocculent PVA; it notes no marked change below 40 °C, gradual colouring with long heating above 160 °C and decomposition above 220 °C. [4]

Dissolution depends on hydrolysis. Kuraray's FAQ says fully hydrolyzed grades are added to room-temperature water with stirring and heated for about 60 minutes after reaching about 95 °C, while partially hydrolyzed grades, which dissolve readily in cold water and can form lumps, should be charged below 25 °C and held at 93–95 °C for 30–60 minutes. [2] Kuraray's data sheet adds that dissolution slows as the 4% viscosity rises, and that the powder must be kept dry because it absorbs moisture and can form blocks. [1]

For ceramics, a Kuraray patent on a compression-molding binder (US 6,737,013 B1) describes drying an aqueous kneaded mix of ceramic powder, water and a modified vinyl alcohol polymer binder into granules, pressing the granules and sintering, with 0.1 to 20 weight parts of binder per 100 weight parts of ceramic powder (0.2 to 15 preferred), and a polymerization degree of 200 to 2,000 for its polymer. [5]

03

Grade table, certificate of analysis and form to request from each PVA bidder

When requesting quotations, ask each supplier for its grade table with hydrolysis and 4% viscosity ranges, a certificate of analysis, test methods, available forms (granules, flakes, fine powder), packaging and samples.

04

Vinyl alcohol and residual acetate units, chain length, volatiles and ash

The first three rows are what a grade name encodes: in Kuraray's 22-88, 22 reads chain length as 4% solution viscosity and 88 is the degree of hydrolysis, the share of acetate units converted to vinyl alcohol. [1]

05

Hydrolysis, 4% viscosity, ash, volatiles, pH and bulk density for a PVA order

Ash needs its basis stated: Kuraray quotes ≤0.4% for standard grades and ≤0.09% for low-ash grades, while Selvol's 0.5–1.2% maxima are given as Na2O. [1] [3]

06

Send the grade, limits and process together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Grade: [hydrolysis mol%; 4% viscosity mPa·s at 20 °C]
Limits: [volatiles; ash; pH; methanol]
Form: [granules; flakes; fine powder; particle size]
Use: [adhesive; paper coating; textile size; ceramic pressing]
Supply: [packaging; quantity; CoA]

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