SELVOL Álcool Polivinílico 502

SELVOL Polyvinyl Alcohol 502, with a 4 % aqueous solution viscosity of 5.0–6.0 cP at 20 °C and a hydrolysis degree of 87–89 mol%, is used in aqueous surface sizing of fine paper and recycled linerboard where the target is to shift Cobb values below 22–25 g/m² on sized sheets. The size press bath is built by first dissolving PVOH 502 in demineralised water at 90 °C for 30 min to a stock solution of 12–18 wt%, then allowing the solution to cool to 55–60 °C before blending with oxidised corn starch at a dry binder ratio of 0.5–2.0 parts PVOH 502 per 100 parts starch. The final size press bath is held at 3.0–7.0 wt% total solids and applied through a film press or metering size press at 45–60 °C; typical dry pick-up is 0.3–1.5 g/m² per side on fine paper and 1.0–3.0 g/m² per side on recycled linerboard. Viscosity at the metering nip is controlled between 20 mPa·s and 80 mPa·s using Brookfield LV spindle 2 at 60 rpm, because below 40 °C the starch component retrogrades and the blended film becomes brittle, while above 80 °C the starch thins excessively and pickup collapses. Compliance for food-contact grades follows 21 CFR 176.170 for paper and paperboard in contact with aqueous and fatty foods and EU Regulation 1935/2004 with supporting compliance under Council of Europe Resolution AP(2002)1; water resistance is measured by ISO 535:2023 Cobb test. Process failure data from high-speed paper machines shows mottling and reel curl when the PVOH/starch ratio exceeds 2.0 parts per 100 parts starch at line speeds above 1,200 m/min, primarily because the film-split pattern at the metering rod becomes unstable; terminal products are inkjet papers, release base papers, sized printing papers, and recycled containerboard for corrugated packaging.

Why Does Coagulum Formation in VAE Reactor Trains Accelerate When PVOH 502 Drops Below 2 Parts per 100 Parts Monomer?

In emulsion polymerisation of vinyl acetate homopolymers, vinyl acetate-ethylene (VAE) copolymers, and acrylic ester dispersions, PVOH 502 serves as a partially hydrolysed protective colloid, with grafting of monomer at the polymer-water interface generating a grafted PVOH layer that stabilises particles. The addition ratio is constrained to 2–6 parts PVOH 502 per 100 parts total monomer, with the polymer pre-dissolved at 90–95 °C in demineralised water at 8–12 wt% solids and then post-fed to the reactor. In a 20–40 m³ batch stirred tank with a dual 45° pitched-blade turbine operating at 60–90 rpm, the PVOH solution is charged before initiation or metered during the first 30–45 % of monomer feed; the polymerisation temperature is held at 65–75 °C for VAE and 75–85 °C for acrylic systems. VAE processes inject ethylene to 0.4–0.8 MPa over the vapour space. Coagulum weight on 200 µm filter screens rises when PVOH 502 drops below 2 parts per 100 parts monomer, because the graft layer becomes discontinuous and the latex particles undergo shear-driven aggregation at the impeller tip. Reactor pH is maintained between 4.0 and 5.5; process data show coagulum weight increases sharply when pH drifts below 3.5 because the partially hydrolysed acetate groups are further hydrolysed, shrinking the steric barrier. Conversely, addition above 6 parts per 100 parts monomer increases aqueous-phase viscosity above 150 mPa·s at 55 °C, reducing heat transfer and causing monomer pooling in the reactor bottom. Compliance for adhesives and nonwoven binders follows REACH (EC) 1907/2006 and, where applicable, 21 CFR 175.105 for indirect food-contact adhesives; dispersion viscosity is measured by ISO 2555:2018 Brookfield method, pH by ISO 976:2013, and residual monomer by gas chromatography. Terminal products include VAE wood adhesives for finger-joint and lamination, acrylic nonwoven binders for air-laid mats, redispersible powders for dry-mix mortars, and architectural interior wall paint formulations.

In water-soluble unit-dose film production, PVOH 502 is dry-blended with plasticisers and processing aids at a ratio of 65–80 wt% PVOH 502, 8–20 wt% plasticiser such as glycerol, sorbitol, or propylene glycol, and 0.1–1.0 wt% nonionic surfactant; starch or polyether polyol may replace up to 10 wt% of PVOH for cost reduction if cold-water dissolution below 20 °C is not required. The blend is dissolved in demineralised water at 25–35 wt% total solids under vacuum degassing at −0.08 MPa relative pressure, then cast onto a PET carrier belt at 200–600 mm/s and dried in zones from 75 °C to 105 °C. Alternatively, partially pre-plasticised compound is melt-extruded through a slot die at 170–190 °C and drawn to target thickness before conditioning. The resulting film is conditioned to 35–45 % RH before slitting; storage above 60 % RH requires pre-drying at 45–60 °C for 4–6 h because absorbed moisture blocks the sealing jaw and shifts the seal initiation temperature. Seal initiation temperature for PVOH 502 film is typically 105–125 °C at 0.7 N/mm² jaw pressure, and film tensile properties are tested by ISO 527-3:2018 with tear propagation by ASTM D1922-23. Compliance for detergent packaging falls under EU Regulation 648/2004 and, for agricultural packaging, national pesticide container regulations; the polymer itself is registered under REACH. Production-line failure data show pinholes and casting streaks when dope viscosity at 25 °C exceeds 4,000 mPa·s or when the degassing vacuum fails, because residual air bubbles nucleate defects at the metering lip. Terminal product types are single-dose laundry detergent pouches, dishwasher detergent pouches, water-soluble agrochemical sachets, and embroidery topping films.

When High-Squeeze Nip Pressures and PVOH 502 Dry Add-On Limits Interact in Slasher Sizing

In slasher sizing of cotton, cotton/polyester, and regenerated cellulose warps, PVOH 502 is compounded with native corn starch, modified starch, or carboxymethyl cellulose and wax lubricant. The size box bath is maintained at 80–85 °C with 2–6 wt% PVOH 502 on bath weight and total solids of 8–12 wt%; the dry size add-on is clamped between 8 wt% and 15 wt% for cotton warps and 6 wt% and 10 wt% for polyester/cotton blends. A high-pressure squeeze nip at 3–5 kN/m line load removes excess bath before the yarn sheet enters a drying section of 12–16 cylinders at 120–135 °C surface temperature and 35–60 m/min warp speed. High-squeeze pressure above 5 kN/m combined with PVOH 502 content below 2 wt% produces dry add-on below 6 wt%, which field records associate with filamentation and dropped ends on air-jet looms above 800 ppm insertion speed. Conversely, PVOH 502 above 6 wt% in the bath creates film bridging between adjacent ends, especially on high-density cotton poplin with 110–140 ends/inch, and the size film becomes difficult to remove during desizing at 60–70 °C. Compliance for commercial textiles follows ZDHC MRSL v3.1 and OEKO-TEX Standard 100 substance restrictions; residual size is checked by iodine staining and mass loss after enzymatic desizing in a laboratory jigger. Terminal products are denim greige, cotton shirting, poly/cotton workwear fabrics, and home-textile sheeting.

Remoistenable adhesive coating for envelopes, paper tape, and stamp backing is produced by dissolving PVOH 502 at 10–30 wt% dry solids into a water-based adhesive batch containing 2–10 wt% plasticiser and optional dextrin at 0–20 wt%; the adhesive is applied at 8–20 g/m² by forward roll or Mayer rod, dried at 70–90 °C, and rewetted with water to activate tack. For indirect food-contact packaging, the adhesive is formulated under 21 CFR 175.105; block resistance is evaluated by a 1 kg /50 cm² dead-weight test at 40 °C for 24 h after film formation. Terminal products are remoistenable envelopes, paper parcel tape, wallcovering joints, and label papers.

Alumina Tape-Casting Slip Viscosity Ceiling and Green Tape Edge Cracking Threshold

For aqueous tape casting of alumina, zirconia, or barium titanate green sheets, PVOH 502 functions as a temporary binder that decomposes during the binder burnout step. The binder addition ratio is 0.8–2.5 wt% of dry ceramic powder mass, with PVOH 502 first dissolved at 85–95 °C and then combined with deionised water, ammonium polyacrylate dispersant at 0.2–0.6 wt%, PEG 400–600 plasticiser at 20–40 wt% of PVOH solids, and ceramic powder to a final slurry solids loading of 55–65 wt%. Slip viscosity measured on a rotational viscometer at 10 s⁻¹ and 25 °C is held below 2,500 mPa·s; edge cracking during casting onto silicone-coated polyester carrier increases when viscosity exceeds 3,000 mPa·s or when the doctor blade gap is advanced beyond 400 µm in a single pass. The wet tape is dried at 20–25 °C and 45–55 % RH for 12–24 h, then binder burnout follows a ramp of 0.5–1 °C/min from 20 °C to 450 °C, with a hold of 2–4 h at 450 °C. Residual ash of PVOH 502 is specified below 0.5 % as Na₂O, which limits ion contamination in electronic ceramic layers. Compliance for ceramic substrates intended for electronic assemblies follows RoHS 2011/65/EU for restricted substances, and green strength is compared to ASTM C1161-18 flexural data after machining of test bars. Published data for this specific PVOH 502 configuration is limited; therefore the viscosity ceiling and burnout profile are drawn from PVOH grades with equivalent 4 % solution viscosity and hydrolysis range. Terminal product types are alumina electronic substrates, multilayer ceramic capacitor green tapes, LTCC glass-ceramic sheets, and zirconia dental framework blanks.