PVOH 735'in

Model designator PVOH 735 identifies a partially hydrolyzed polyvinyl alcohol resin whose 4 % (w/w) aqueous solution dynamic viscosity spans 5.5–7.5 mPa·s (Brookfield LV, spindle No. 1, 60 rpm, 20 °C, JIS K6726). The residual acetate content, determined by saponification-back titration, ranges from 11–13.5 mol%, placing the hydrolysis degree between 86.5 and 89 mol%. This molecular architecture—substantial acetate blocks interrupting the vinyl alcohol backbone—retards intra- and inter-chain crystallisation, conferring cold-water solubility and a solution gelation temperature below 10 °C even at 15 % solids. Ash residue (as Na₂O) is held below 0.5 % (JIS K6726), while volatiles at 105 °C for 3 h rarely exceed 5 %. In granule form the bulk density approximates 0.4–0.6 g/cm³, and the material is supplied in 25 kg multi-wall paper sacks with an inner polyethylene liner. Because PVOH 735 dissolves readily in unheated water, it serves as a temporary binder, warp-sizing agent, and water-responsive film former across paper, textiles, and single-use packaging.

How Rapidly Does a 50 µm Cast Film Disintegrate at 20 °C?

A continuous film prepared on a laboratory draw-down coater (wet gap 400 µm, drying at 85 °C for 6 min) yields a dry thickness of 48–52 µm. When a 20 mm × 20 mm coupon of this film is immersed in 1 L of deionised water at 20±1 °C stirred at 100 rpm, complete disintegration (no visible fragments retained on a 2 mm sieve) occurs inside 45–60 s. This rapid dissolution, coupled with the absence of toxic monomers, meets the disintegration criterion of ISO 16929:2021 for compostable plastics but is measured here in a simplified immersion test that isolates hydrodynamic shearing from biological action. At water temperatures below 10 °C, dissolution decelerates markedly—residual film fragments persist beyond 120 s—because the polymer-solvent interaction parameter shifts closer to a theta condition as the lower critical solution temperature is approached. In industrial converting, this behaviour governs machine runnability: on a Faustel® pilot coater-laminator running at 150 m/min, an inline remoistenable glue seam based on PVOH 735 dried within 2 s of contact with a cold-water mist, whereas fully hydrolysed PVOH 117 required a 78 °C heated nip roll to achieve comparable tack development.

Adhesive Compounding: High-Torque Dispersion and Viscosity Stability

In the preparation of aqueous paper-laminating adhesives, PVOH 735 is added through a high-speed disperser (DINO C 1520, 7.5 kW, 400-L vessel) to deionised water preheated to 25 °C while the saw-tooth disc operates at 1200 rpm. Powder is sifted through a 500 µm inline sieve to eliminate fish-eye agglomerates. Once the target solids of 12±0.5 % is reached, the batch is stirred at reduced speed (300 rpm) for an additional 30 min under vacuum (−0.8 bar) to deaerate. Viscosity, measured with a Brookfield DV2T LV spindle No. 2 at 30 rpm, typically reads 1800–2200 mPa·s immediately after makeup and drifts less than 7 % over 24 h when stored at 23 °C in a closed container. The low ash content suppresses unwanted ionic interactions with cationic wet-strength resins such as polyamide-epichlorohydrin (PAE), a frequent partner in paperboard laminates. Production-scale experience on a 2000 t/year adhesive line indicates that substituting PVOH 735 for a higher-viscosity grade (4 % viscosity 28–34 mPa·s) reduces coating weight by 12–15 % while maintaining identical T-peel adhesion values on corrugated medium (tested per TAPPI T 838).

In contrast, when PVOH 735 is formulated with filler clay slurries for pigmented paper coatings, the system must be augmented with a high-solids latex binder; the polyvinyl alcohol alone at 2.5 phr raises low-shear viscosity too little to control blade pressure on a flooded-nip coater, whereas PVOH 705 with its 3.0–3.8 mPa·s viscosity allows a coating colour solids of 65 % without exceeding a Brookfield viscosity of 1400 mPa·s. The choice between the two grades therefore hinges on the balance between required film integrity and runnability at high solids.

What Limits the Melt Extrusion Window for PVOH 735-Based Compounds?

PVOH 735 can be melt-processed only when plasticised. A typical formulation contains 25 phr glycerol, 10 phr sorbitol, and 0.3 phr processing aid (stearamide). Prior to feeding the co-rotating twin-screw extruder (Coperion ZSK 26 Mc18, 26 mm screw diameter, L/D 44, segmented screw with two kneading blocks at 90° offset), the granular PVOH 735 must be dried in a desiccant-bed dryer at 80 °C for 3–4 h to a residual moisture below 0.15 % (Karl Fischer titration). Feeding moisture-rich granules into the extruder causes drastic melt fracture at the die lip, visible as microscopic shark-skin, because steam generation in the metering zone (180–195 °C) leads to localised expansion and tearing. The stable processing window is narrow: barrel temperatures from the feed throat to the die must profile 140–170–185–190 °C; exceeding 205 °C at any zone induces acetaldehyde and crotonaldehyde release from thermal dehydration of residual acetate and hydroxyl groups, causing yellow-brown discolouration and an objectionable odour. Torque typically runs 55–65 % of maximum drive load (9.2 kW motor). The strand pelletised compound exhibits a MFI of 8–14 g/10 min (190 °C/2.16 kg, ASTM D1238-20) and can be injection-moulded using a clamp force of 800 kN and a cold mould at 15 °C. Publications from polymer processing laboratories caution against the use of boric acid as a crosslinker in this grade because it triggers gel particles in the melt at concentrations above 0.05 %, blocking screen packs of 80 mesh. Amine-bearing additives, including certain secondary antioxidants, are similarly incompatible, accelerating chromophore formation at typical compounding residence times of 45–90 s.

When PVOH 735 is cast directly from aqueous solution onto a release liner and dried at 110 °C, the resulting film exhibits a tensile strength of 44–55 MPa and elongation at break 180–250 % at 23 °C and 50 % RH ( ASTM D882-18, 50 mm/min crosshead speed). Comparable data for fully hydrolysed PVOH 117 film reaches 70–85 MPa but with an elongation below 80 %, underlining the flexibility advantage conferred by the acetate residues.

Why PVOH 735 Replaces Viscosity-Lowering Co-Binders in Barrier Formulations

In nanoclay-based oxygen-barrier coatings applied to polyester film, a binder that dissolves completely at room temperature and provides sufficient film strength without raising coating colour viscosity above 300 mPa·s at 100 s⁻¹ is critical. PVOH 735 meets both conditions: a 10 % solution has a low-shear viscosity of 160–200 mPa·s, which allows montmorillonite platelet dispersion to remain aligned during slot-die coating. Substitution of fully hydrolysed grades demands heating the entire feed tank to 88–92 °C, while low-viscosity counterparts like PVOH 705 produce films that craze upon flexing. The oxygen transmission rate of a 2 µm dry coating containing 20 wt% PVOH 735 and 80 wt% surface-modified montmorillonite drops from 12 to 0.8 cm³/(m²·day·atm) at 23 °C, 0 % RH (ASTM D3985-17), confirming that the polymer’s molecular weight provides adequate binding without occluding the tortuous path. However, at 50 % RH the oxygen barrier degrades by a factor of 6–8; published data for this specific configuration under tropical conditions are limited, and end-users are advised to conduct shelf-life testing under their intended storage environment before commercial release.

Articles manufactured with PVOH 735 intended for single-use food-contact paper coatings fall under FDA 21 CFR 175.300 (resinous and polymeric coatings) and FDA 21 CFR 175.105 (adhesives), provided the finished coating weight does not exceed the good manufacturing practice limit. The grade also complies with the EU No 10/2011 plastic materials and articles regulation and has been assessed under REACH (EC 1907/2006) with a registration number for the substance Poly(vinyl alcohol) (CAS 9002-89-5). The following table summarises key regulatory touchpoints relevant to converters and compounders.

Storage of PVOH 735 in conditions where relative humidity exceeds 60 % without resealing the sack leads to moisture absorption above 6 %, causing caking in the hopper and erratic gravimetric feeding on loss-in-weight feeders. The powder is mildly irritating to the respiratory tract; occupational exposure limits are set at 5 mg/m³ (respirable fraction, ACGIH TLV). Dust extraction equipment is required during bag emptying at a rate of 2000 m³/h per station to maintain dust below 1 mg/m³.