SELVOL Polyvinyl Alcohol 310

On high-speed envelope blank converting lines, SELVOL Polyvinyl Alcohol 310 is cooked as a 15–22 wt% aqueous solution in a jacketed mix tank fitted with a dual-shaft disperser. The grade is a partially hydrolysed PVOH with a degree of hydrolysis of 87–89 mol% and a 4% aqueous solution viscosity of 10–13 cP at 20 °C, measured per ISO 2555. Solution make-up proceeds at 85–90 °C for 30–45 min under 400 rpm disperser agitation, followed by cooling to 45–50 °C and filtration through a 90-mesh screen. The resulting remoistenable adhesive is applied by engraved roll or slot die to envelope flap gumlines at line speeds of 250–350 m/min. Viscosity at application is commonly held between 1,200 and 2,500 cP at 25 °C using a Brookfield LVT viscometer at 60 rpm, in accordance with ASTM D1084. Dry film rewettability is evaluated by remoistening with water at 20 °C and measuring adhesive transfer to paper under 0.5 kPa contact pressure for 3 s. Plasticiser addition, usually glycerol or polyethylene glycol, is limited to 5–15 phr on dry PVOH to retain film block resistance at warehouse temperatures up to 35 °C. Boric acid or borax may be used as a thixotrope, but addition above 1.0–1.5 wt% on PVOH at a system pH above 8.0 produces a thermoreversible gel that can set in storage tanks and block transfer pumps. Borax-thickened batches are therefore held below pH 7.5 and are consumed within 24 h. Preservation with a benzisothiazolinone or methylisothiazolinone solution at 0.1–0.3 wt% on wet adhesive is required if the batch is held above 35 °C for more than 24 h, because aqueous PVOH is susceptible to microbial attack. Defoamer addition of 0.1–0.2 wt% on wet adhesive prevents foam in the application pan. The application roll is chrome-plated and engraved at 45–60 lines/cm to deposit 2–5 g/m² dry coat weight, and drying is performed in a gas-fired oven at 120–160 °C for 0.5–2.0 s. PVOH 310 is used where low solution viscosity is required at high solids, but it is not recommended for structural paperboard lamination where fibre tear is specified without adhesive failure. The finished adhesive is assessed under FDA 21 CFR 175.105; paper and paperboard applications may reference FDA 21 CFR 176.170 or 176.180 depending on the food-contact condition.

What Limits High-Shear Stability in VAE Emulsion Polymerization When Low-Viscosity PVOH Is Used at 3–6 wt%?

In semi-batch vinyl acetate-ethylene emulsion polymerisation, SELVOL Polyvinyl Alcohol 310 is pre-dissolved in deionised water at 85 °C for 60 min and charged to a pressure reactor at 3–6 wt% on total monomer. The reactor is buffered with sodium bicarbonate to maintain pH 4.0–5.5. Vinyl acetate is dosed over 4–6 h at 80–90 °C and, in VAE production, under ethylene pressure of 30–45 bar. The 87–89 mol% hydrolysis level and residual acetate blocks provide surface-active anchoring at the monomer-water interface, while the 10–13 cP solution viscosity permits high-solids emulsions without the high mixing torque associated with higher-viscosity PVOH grades. The measured emulsion viscosity at 55% solids typically falls between 1,500 and 6,000 cP at 25 °C when tested by ASTM D2196. Mean particle size by laser diffraction is often 0.6–1.5 µm; this distribution remains sufficiently shear-stable for most post-processing but is not intended for homogenisation above 10,000 s⁻¹. The medium molecular weight of PVOH 310 contributes steric stabilisation that prevents coagulation during vinyl acetate starvation, yet final viscosity is lower than that produced by high-DP colloids at the same solids.

Grafting of PVOH with vinyl acetate occurs via hydrogen abstraction on the polymer backbone and at acetate side groups. With PVOH 310 the graft ratio is governed by initiator concentration, temperature, and monomer feed rate. Persulfate or redox initiators at 0.05–0.2 wt% on total monomer are recommended. High initiator concentration and temperature above 85 °C increase grafting and can reduce particle size, but grit formation occurs if colloid loading falls below 3 wt%. Filtration through a 150 µm in-line basket strainer is standard before the product storage tank. Alkaline pH is controlled because pH above 7.0 accelerates acetate hydrolysis and shifts the effective degree of hydrolysis enough to change colloidal stability. Cationic surfactants and polyamines are not added to PVOH 310-stabilised VAE without prior compatibility testing. Long-term storage is monitored for viscosity change by ISO 2555 and for coagulum by 100 µm screen retention.

A size mix based on SELVOL Polyvinyl Alcohol 310 for textile warp sizing of spun cotton and polyester-cotton blends is cooked at 8–12% solids in a jet cooker with a hold time of 15–20 min at 110–120 °C. The size box is maintained at 75–80 °C with viscosity of 80–180 mPa·s measured by spindle viscometer at 100 rpm. Squeeze rolls operate at 1.5–3.0 bar pneumatic pressure; wet pick-up on the yarn is held at 8–14%, while after-drying add-on is typically 6–9% on yarn weight. A wax or tallow component at 0.5–1.0% on dry PVOH reduces yarn-to-metal friction in split rods and heddle eyes. PVOH 310 is blended with oxidised maize starch at dry PVOH-to-starch ratios between 30:70 and 50:50 where lower cost is required; below 30% PVOH, the size film loses cohesion and weaving dust increases. The film formed by PVOH 310 is water-soluble at 80–90 °C, allowing desizing with hot water and nonionic surfactant at 0.2–0.5 g/L without enzyme addition, provided starch is not a dominant component. Size-box skinning is controlled by maintaining high relative humidity near the immersion roll and by using a slow-turning roll. The dried size film is examined by a film solubility test in water at 80 °C; insoluble gel specks indicate overcooking or water hardness above 200 ppm CaCO₃. The medium viscosity of the grade reduces foam and skinning compared with fully hydrolysed grades, but tensile strength of the cast film is lower, so high-count filament yarns may require a higher-DP PVOH grade.

Surface Sizing Response of Lightweight Coated Base Paper to PVOH 310 in an Oxidised Starch Size Press

Trials on woodfree base paper with basis weight 70–80 g/m² use a size press solution containing 0.5–2.0 dry parts of SELVOL Polyvinyl Alcohol 310 per 100 dry parts oxidised starch at total solids of 6–10%. The size bath is held at 60–70 °C with Brookfield viscosity of 10–40 mPa·s at 100 rpm. PVOH 310 is pre-cooked at 15–20% solids and metered into the starch dilution line after the starch has been cooled below 70 °C to prevent excessive viscosity rise. The size press nip load is set to 20–40 kN/m; the sheet enters at 8–10% moisture and exits at 12–15% moisture before drying. PVOH 310 improves film continuity and reduces starch dusting on calender stacks and sheet-cutoff knives. Print pick resistance is evaluated by IGT test at 0.5 m/s acceleration; improvement over the starch-only control depends on base sheet sizing, but mill data often show an increase of 0.3–1.2 m/s in dry pick velocity. Cobb water absorption is measured per ISO 535; PVOH 310 does not provide the water resistance of a styrene acrylate surface size, so internal sizing with AKD or rosin is required when the finished paper must meet a Cobb value below 22 g/m². PVOH 310 addition also improves size press runnability at machine speeds above 1,200 m/min, where misting and fibre contamination are concerns.

As a secondary dispersant in vinyl chloride suspension polymerisation, a grade with hydrolysis 87–89 mol% and 10–13 cP solution viscosity is used at 0.02–0.08 wt% on VCM. The primary dispersant is normally a lower-hydrolysis PVOH in the 70–74 mol% range; the secondary PVOH 310 narrows particle size distribution and reduces the <63 µm fines fraction. The polymerisation is run in a 50,000–150,000 L jacketed autoclave at 55–65 °C with a VCM-to-water mass ratio near 1.0:1.2, stirred at 200–300 rpm. Initiator, such as di(2-ethylhexyl) peroxydicarbonate, is charged at 0.03–0.08 phr; pressure is maintained at 8–12 bar until the pressure drop at 80–85% conversion. The finished PVC slurry is stripped, dried, and classified; typical K-value of 66–70 and mean particle size of 120–160 µm are controlled mainly by the primary dispersant, while PVOH 310 reduces coarse tailings and fisheye formation in plasticised film. The PVOH solution must be filtered through a 90 µm screen before charging; undissolved gel specks from incomplete cooking create fisheyes in downstream calendering. Charging more than 0.08 wt% on VCM can increase slurry viscosity and hinder stripping, so the secondary dispersant dosage is not raised as a sole response to particle size drift. Published data for the exact particle size shift attributable to a secondary dispersant in a specific reactor configuration is limited; the effect is typically evaluated by laser diffraction and sieve retention per internal quality procedures rather than a single public standard.

When Ceramic Green Tape Binder Loading Is Restricted to 2–5 wt% in Alumina Slurries

Ceramic green tape casting for multilayer alumina substrates uses SELVOL Polyvinyl Alcohol 310 as a temporary binder at 2–5 wt% of dry ceramic powder. The grade is dissolved separately at 8 wt% in deionised water at 85–90 °C and cooled to 25–30 °C before addition to the milling vessel. The slurry formulation starts with an aqueous suspension of alumina powder at 55–65 wt% solids, an ammonium polyacrylate dispersant at 0.5–1.0 wt% of powder, and a plasticiser such as glycerol or PEG 400 at 0.5–1.0 wt%. Ball milling proceeds for 4–6 h with zirconia media, followed by vacuum de-airing at 20–30 kPa gauge for 30 min. The slip is cast onto a silicone-coated PET carrier at 0.3–0.8 m/min with a doctor blade gap of 150–350 µm. Drying is staged from 25 °C to 60 °C over 20–40 min to avoid skinning. The resulting green tape is evaluated for tensile strength per ISO 527-3 and elongation at break; green density of 2.2–2.5 g/cm³ for alumina tape is common but depends on slurry solids and lamination pressure. Green sheets are laminated at 20–40 MPa and 60–70 °C for 1–3 min. Thermal debinding of PVOH is carried out at 350–450 °C with a ramp rate not exceeding 1 °C/min until 600 °C; residual carbon must be held below 0.2 wt% to prevent sintering defects. The advantage of PVOH 310 over starch-based binders is lower ash and clean burnout, but the grade is not recommended for freeze-dried granulation because partially hydrolysed PVOH can show lower green strength than high-DP PVOH.