SELVOL Álcool Polivinílico 504

SELVOL Polyvinyl Alcohol 504, a partially hydrolysed grade of 87–89 mol% hydrolysis and Brookfield viscosity of 4.0–5.0 cP for a 4 wt% aqueous solution at 20 °C, enters vinyl acetate-ethylene (VAE) and polyvinyl acetate (PVAc) latex polymerisation as the primary protective colloid. The charge is 2.0–5.0 phm for VAE and 3.0–6.0 phm for PVAc homopolymer in batch reactors. The grade is pre-dissolved in demineralised water to a 15 wt% stock solution at 90 °C for 45–60 min, cooled to 40 °C, and metered into the reactor before initiator feed begins. Brookfield viscosity of the stock solution is confirmed by ISO 2555 using a Brookfield LV, spindle 2, at 12 rpm and 20 °C. The partially hydrolysed structure maintains interfacial surface excess at the monomer-swollen polymer particle, restricting particle coalescence during the constant-rate nucleation window. In 50–100 m³ batch reactors with anchor impellers operated at 40–80 rpm, semi-continuous addition of vinyl acetate monomer over 3–5 h yields latex median particle sizes from 800 nm to 1.8 µm; the final diameter depends on the initiator system and seed concentration. Excessive charge above 6 phm raises latex viscosity above 5000 mPa·s and can destabilise the reactor during monomer stripping. Coagulum is assessed on a 150 µm sieve after steam distillation, and residual vinyl acetate monomer is controlled below 500 ppm by combined vacuum and purge. For indirect food packaging adhesive applications, latex formulated with SELVOL 504 may be reviewed under 21 CFR 175.105 and 21 CFR 176.170. In formulations requiring wet tack and fast setting on paper, SELVOL 504 is partially replaced with fully hydrolysed grades; complete replacement in water-resistant adhesives is not recommended because acetate-rich chain segments remain sensitive to humid peel.

Cold-Water Film Casting Requires Glycerol at 12–18 phr to Suppress Blocking

For water-soluble packaging films used in detergent unit doses and agrochemical sachets, SELVOL 504 is formulated at 100 parts by dry weight with glycerol at 12–18 phr, sorbitol at 5–8 phr, and a silicone-free defoamer at 0.1–0.3 phr. The aqueous dope is prepared at 18–22 wt% total solids and heated to 85–90 °C for 60 min under low-shear mixing, then deaerated under 200–400 mbar vacuum before being cast onto a polyethylene terephthalate belt with a slot die. Because the grade has 87–89 mol% hydrolysis, residual acetate groups break intra-chain hydrogen bonding and permit film disintegration in deionised water at 5 °C without an alkali wash. Cast webs are dried in three zones: 70 °C for setting, 95–110 °C for evaporative drying, and 40 °C for conditioning to 8–12 wt% residual moisture. The dry film is converted by kiss cutting; edge trimming is reprocessed as regrind at up to 20 wt% without blocking the slot die. Tensile properties are evaluated by ASTM D882; the absence of plasticizer exudation is checked after 7 days at 40 °C and 75% RH. In-line thickness is controlled to ±2 µm by beta gauge. When relative humidity in converting exceeds 60%, the film absorbs surface moisture and blocks on the rewinder; preconditioning of the slitting room below 45% RH is therefore mandatory. Combination with amine-based additives is avoided because alkaline amine residues accelerate acetate hydrolysis and reduce shelf stability. Published data for dissolution time specific to SELVOL 504 in finished unit-dose film is limited; converting lines therefore set disintegration windows using an internal protocol at 5 °C in deionised water before commercial release.

How Does SELVOL 504 Function as a Remoistenable Adhesive for Paper Converting?

Remoistenable envelope flap coatings rely on the fast re-wetting and tack development of partially hydrolysed PVOH when a low-viscosity grade carries a high solids loading without stringing during roll transfer. A converting formulation typically combines SELVOL 504 at 100 parts, glycerol or polyethylene glycol 400 at 5–10 phr, and a modified starch extender at 0–20 phr. The adhesive is prepared at 30–38 wt% solids and held at 45–55 °C in a jacketed tank. Application proceeds by reverse gravure or smooth roll at coat weights of 0.8–2.5 g/m² dry. The coating is dried with forced air at 80–110 °C to a moisture content below 6 wt% before rewinding. Because the grade contains acetate groups at 12–13 mol% of the repeating unit, the film rehydrates on a wet sponge without elevated temperature on standard white wove envelope paper; published data for specific SELVOL 504 re-wetting kinetics is limited. Bond performance is quantified by ASTM D1876 T-peel on conditioned substrates at 23 °C and 50% RH, with fibre tear required for acceptable converting. High relative humidity above 70% causes pre-activation of the dry adhesive and early blocking in stacked blanks. The formulation must not be stored with borax or amine-containing wetting agents because borate crosslinking raises the re-wetting time and amine residues shift the pH above 6.5, accelerating ester hydrolysis in storage.

In vinyl chloride suspension polymerisation, SELVOL 504 is metered as the secondary suspending agent at 0.05–0.25 g/L of aqueous phase alongside a primary fully hydrolysed PVOH at 0.30–0.60 g/L. The distinction is functional: the high hydrolysis grade controls vinyl chloride monomer droplet coalescence, while the partial grade lowers interfacial tension at the reacting monomer-PVC particle and moderates free-radical entry into the growing grain. The ratio of primary to secondary PVOH is maintained between 2:1 and 4:1 by mass, depending on the target K value and cold plasticizer absorption of the PVC resin. In 50–120 m³ autoclaves with turbine agitators, tip speed is held at 1.5–3.0 m/s and polymerisation temperature at 55–65 °C; heat removal is controlled by reflux condenser and jacket. SELVOL 504 is charged before the monomer phase to avoid localised high-viscosity pockets that would generate fine particles below 50 µm. The suspension is monitored by in-situ focused beam reflectance measurement, with volume median droplet size kept within 100–160 µm for pipe-grade PVC. Final resin particle size distribution is measured by dry sieving under ISO 1624, and K value by ISO 1628-2. Excess secondary PVOH above 0.30 g/L reduces grain size, raises fines, and depresses plasticizer absorption below specification. The same grade cannot be used as the sole suspending agent because the partially hydrolysed molecule lacks sufficient graft stabilisation to prevent droplet coalescence at high conversion.

When Slasher Speed Exceeds 250 m/min, Size Bath Viscosity Must Be Rebalanced

Textile warp sizing of ring-spun polyester/cotton blends uses SELVOL 504 in a size bath at 6–12 wt% solids supplemented with a fatty acid wax at 2–5 wt% of the PVOH dry weight and a defoamer at 0.05–0.10 wt%. The size is prepared in a pressure cooker at 110–130 °C for 30–40 min to dissolve the PVOH completely, then transferred to the slasher box at 80–85 °C. A double-box slasher with Teflon-coated squeeze rolls applies the size to warp yarns at 10–14 kN nip load; add-on on cotton-rich yarns is controlled at 8–12 wt% dry on yarn, while polyester-rich yarns are sized to 6–10 wt%. If slasher speed exceeds 250 m/min, bath viscosity must be reduced toward the lower end of the working range to prevent size splash, doctor blade deposit, and uneven transfer. Yarn abrasion resistance is evaluated on a Zweigle abrasion tester; tensile strength and elongation at break are measured by ASTM D2256. Desizing is carried out in enzyme-free hot water at 70–80 °C for cotton blends, with complete removal assessed by iodine stain. SELVOL 504 is not appropriate as the sole size for high-twist continuous polyester filament because the partial hydrolysis grade gives lower adhesion to hydrophobic filament than fully hydrolysed or modified PVOH grades. The material must be protected from high-humidity storage; caked size flakes above 60% RH form lumps that block the pressure cooker feed screw.

Pigmented Coating Rheology and Starch Compatibility Limits

In blade-coated paper and paperboard finishes, SELVOL 504 serves as a co-binder and water retention modifier in pigmented coatings at 0.5–2.0 parts per 100 parts dry pigment. The grade is pre-dissolved at 15–20 wt% solids and metered into the coating colour after starch cooking but before pigment slurry addition; injection into hot starch above 85 °C is avoided because localised thermal stress can form microgels. The coating formulation is run at 58–65 wt% solids with Brookfield viscosity measured by ISO 2555; high-shear viscosity must be matched to the blade coater model and backing roll speed. The PVOH improves surface strength, dry pick resistance, and optical brightening agent retention without the water-retention drop observed with low-molecular-weight starch alone. Coated sheet is printed on an IGT pick tester; wet pick strength is judged by the number of passes before blistering on a heated web. Because the grade is partially hydrolysed and carries residual acetate groups, it interacts less strongly with borate than fully hydrolysed PVOH, but glyoxal and zirconium ammonium carbonate insolubilizers must be dosed after pH stabilisation to avoid premature crosslinking. At addition levels above 2.5 parts, the coating colour shifts into the dilatant regime and blade scratches appear on high-speed coaters. The use of 0.05–0.10 parts of an anionic dispersant before PVOH addition prevents pigment shock and agglomeration.