SELVOL Álcool Polivinílico WS-724

What Fails First When Oxidized Starch Is Replaced with PVOH in High-Speed Warp Sizing?

In a high-pressure jet cooker operating at 2.5 bar and 130°C for a 20 min hold, SELVOL Polyvinyl Alcohol WS-724 is cooked as a replacement for oxidized starch in cotton and cotton–polyester warp sizing. The dry addition is maintained at 45–80 kg per 1000 L of cooked size, corresponding to 8–14% dry-on-dry pick-up on sized yarn. The size box is held at 68°C ± 5°C; the nip load at the squeeze rollers is set to 2–3 bar, and the drying cylinder surface temperature is graduated from 110°C in the first bank to 140°C in the final bank. The size mix is filtered through an 80-mesh screen before entering the size box, and the size box pH is maintained between 6.5 and 7.5 because acid hydrolysis below pH 5.0 reduces chain length and lowers film tensile strength. Sized yarn tensile retention is assessed against ISO 2062:2010, while final woven fabric tensile and elongation are tested under ISO 13934-1:2013. Sizing efficiency on production looms is judged by warp stops per 100,000 picks; acceptable runs on air-jet looms running 900–1200 rpm generally require fewer than 3 stops per 100,000 picks. Terminal output includes 100% cotton sheeting, cotton–polyester blended shirting, denim greige fabric, and home textile base cloth. Operating boundaries are narrow at the size box: below 63°C the liquor surface film viscosity rises above 50 mPa·s and causes non-uniform pick-up, while above 73°C the liquor skims and deposits on the first drying cans; borax addition above 0.1 wt% of dry size solids is not recommended because the resulting borate–diol gel network increases size-box viscosity and produces hard size on the yarn sheet.

For Ne 30 ring-spun cotton warps, the dry-on-dry pick-up is kept between 10% and 13%; for Ne 20 open-end cotton warps, the pick-up is reduced to 8–10% to avoid over-stiffening. The size recipe is adjusted by on-line refractometer to maintain dry solids within 0.5% of target, and the size box level is held steady by a flow-through circulation loop with a residence time below 4 h because extended heating above 80°C can cause viscosity loss of more than 10% during prolonged hold. After loom weaving, the size is removed in a continuous desizing range with an enzymatic or oxidative step at 60–90°C followed by alkaline scour and peroxide bleach; the resulting warp yarn tensile loss must remain below 5% relative to greige yarn. Sized-yarn abrasion resistance is measured on a Zweigle G 552 yarn abrasion tester with 30 threads under 50 g load; sized yarns must withstand 150–250 strokes before break to prevent loom shedding faults.

Running at 1100 m/min on a Speedsizer AT metering size press, WS-724 is metered as 5–25 parts per 100 parts of cationic starch dry solids in a surface size formulation that is supplied to the press at 4.0–8.5% total solids and 62°C. The film transfer roll speed differential is maintained at 1.2:1, producing a single-side pick-up of 1.5–4.0 g/m² before the sheet enters the after-dryer section, where the web surface temperature reaches 105–120°C. This surface sizing operation is performed on paper and paperboard grades that require food-contact compliance under FDA 21 CFR 176.170; water absorptiveness is controlled according to TAPPI T 441 using a 60 s Cobb test, and optical brightness is measured under ISO 2470-1:2016. The downstream production sequence includes metering size press application, soft calender finishing at 70–90 kN/m line load, and rewind to jumbo rolls for sheet-fed or roll-fed printing. Terminal products include offset printing papers, inkjet bond grades, linerboard for corrugated packaging, and silicone-coated release base papers. The critical operating boundary is the high-shear viscosity in the metering nip: if the formulation exceeds 45 mPa·s at 1500 s⁻¹, misting and film split defects appear at the press; if it falls below 8 mPa·s, pick-up control deteriorates and Cobb values rise above 35 g/m².

For matte inkjet bond grades, a 1:1 blend of WS-724 and low-viscosity cationic starch is applied at 0.5–2.0 g/m² per side immediately before an ink-receptive coating layer, and sheet tensile strength is verified under ISO 1924-2 while internal bond is tested according to TAPPI T 569. Air permeance is measured by the Gurley densometer method under TAPPI T 460, with targets of 15–30 s/100 mL on surface-sized inkjet base paper to control strike-through without creating calender blackening. The PVOH fraction also acts as a barrier to silicone holdout on release liner base papers; on-machine viscosity checks at 1500 s⁻¹ are used to reject batches that deviate by more than ±5% from the standard curve, because such drift alters film split uniformity on the speed-differential rolls.

Colloid Retention, Grafting Efficiency and Reactor Brookfield Viscosity in Semi-Batch Vinyl Acetate Polymerisation

A 4 m³ semi-batch reactor fitted with a two-stage anchor impeller operating at 80–120 rpm is charged with WS-724 as protective colloid at 3–6 wt% based on total vinyl acetate monomer. The initial aqueous phase is buffered with sodium acetate at 0.1–0.3 wt% of the reactor charge to hold pH between 3.5 and 4.5 during polymerisation, and initiation is supplied by potassium persulfate at 0.2–0.5 wt% on monomer. Monomer is fed by delayed addition over 4–5 h at 65–75°C, while the reaction mass is held at a Brookfield LVF viscosity of 8,000–25,000 mPa·s at 20°C, spindle 4, 60 rpm; the final dispersion is adjusted to 54–58% solids with a residual monomer content below 0.5 wt%. Grafting efficiency and colloid retention are assessed by Soxhlet extraction of the dried film in water at 80°C for 8 h, with target insolubles of 35–55 wt% for packaging adhesive grades. Compliance for the resulting polyvinyl acetate homopolymer adhesive is established under FDA 21 CFR 175.105 for indirect food contact, and for moisture resistance classification under EN 204/205 D2 and D3 according to the end-use bond test. Terminal product types are PVAc woodworking adhesives, paper sack and carton side-seam adhesives, and laminating adhesives for flexible packaging. The reactor operation has a narrow shear-stability boundary: if the agitation tip speed exceeds 3.0 m/s, free colloid is stripped from the newly formed particle surface and the dispersion destabilizes, producing coagulum larger than 100 µm that must be removed by 100-mesh filtration. Pre-drying of WS-724 at 50°C for 2 h is required when storage RH exceeds 60% before its use in volumetric powder dosing, because caked material causes batch-to-batch viscosity drift in the seed stage.

The seed stage is controlled by charging 10–15% of the total monomer at 65°C with 25–30% of the total initiator before the delayed feed is started; the remaining monomer is pumped at a linear rate that avoids exotherm overshoot above 75°C. After the monomer feed is completed, the batch is held at 75°C for 45–60 min, then vacuum-stripped at 0.2 bar and 70°C for 1 h, and treated with a redox chase of tert-butyl hydroperoxide and sodium metabisulfite at 0.05 wt% on monomer each to reduce residual monomer. The cooled dispersion is filtered through a 100-mesh steel screen and filled into HDPE drums. Shear stability is checked on a Red Devil shaker for 30 min continuous shaking; sedimentation after 24 h must remain below 1 vol%. D3 wood bonds prepared under EN 205 are tested after 4 h cold water immersion at 20°C; the pass criterion determines the minimum WS-724 dosage for packaging and assembly adhesives.

During suspension polymerisation of vinyl chloride in a 30 m³ stainless steel reactor fitted with a retreat-curve impeller operating at 350–500 rpm, WS-724 is metered as a primary suspending agent at 0.08–0.15 wt% on monomer, with a secondary suspending agent at 0.02–0.08 wt%; the water-to-monomer charge ratio is 1.2:1 and the initiator is di(2-ethylhexyl) peroxydicarbonate at 0.04–0.08 wt% on monomer. Polymerisation proceeds at 57–65°C and 7.5–11 bar until conversion reaches 80–90% over 5–7 h. The slurry is then transferred to a vented stripping vessel at 0.2–0.5 bar and 70–80°C for residual monomer removal, dewatered in a continuous centrifuge, and dried in a two-stage fluid bed at 50–120°C. The resin is classified by cell class under ASTM D1784-20 using K-value, apparent bulk density, porosity, and plasticizer absorption; pipes made from the resin are qualified by tensile and hydrostatic testing under ISO 6259-1 and ISO 1452-2. Terminal products are rigid PVC pressure pipe, window profile compounds, cable jacket compounds, and calendered flooring. The droplet coalescence boundary is determined by fish-eye counts in the finished compound: below 0.06 wt% primary suspending agent on monomer, the droplet size distribution broadens and plasticizer absorption falls below 20 g/100 g resin; above 0.30 wt%, the particle size becomes too fine and the slurry filtration rate slows, causing centrifuge overload and higher dryer residence time.

Droplet size distribution is monitored by Coulter counter after 15% conversion and again before transfer; the primary slurry should contain 90% of particles between 50 µm and 250 µm with a median diameter of 120–160 µm. Finished resin K-value targets are typically 65–72, apparent bulk density 0.46–0.58 g/cm³, plasticizer absorption 20–30 g/100 g, and sieve retention on 250 µm below 5%; residual VCM monomer after stripping must be below 5 ppm for most compound grades. Fish-eye counts in a clear calendered sheet are kept below 5 per 1000 g of compound, because higher counts indicate droplet coalescence caused by inadequate suspending agent coverage or agitator shear. Reactor wall fouling is removed after each campaign by high-pressure water jetting; if the PVOH charge is increased too quickly above 0.15 wt% on monomer, the aqueous phase viscosity rises and heat transfer at the cooling coils deteriorates, forcing longer reaction time and reducing throughput.

When the Doctor Blade Gap Drops Below 0.6 mm in Alumina Tape Casting

A 0.6 mm doctor blade gap on a polyester carrier moving at 0.5 m/min is used to cast 96% alumina tape with WS-724 as the green body binder at 3–8 wt% of the aqueous slurry solids. The slurry is prepared in a ball mill with 10 mm alumina grinding media for 12–18 h, after which the viscosity is adjusted to 4,000–8,000 mPa·s at 20 s⁻¹ before casting. The tape is dried in a three-zone tunnel at 40–80°C to a residual moisture of 0.5–1.5 wt%, then the binder is removed in a forced-air kiln at 300–500°C with a ramp rate not exceeding 10°C/min; final sintering for fixed substrates is carried out at 1550°C under air. Fired water absorption and bulk density are measured according to ASTM C373-18, and flexural strength of machined test bars is measured under ASTM C1161-18. For ceramic insulating components, fired-body material properties are screened under IEC 60672-3 before release. Terminal pieces include alumina substrates for thick-film circuits, zirconia oxygen sensor bodies, and porcelain insulator components. The operating boundary in electronic substrate production is residual carbon after debinding: if the burnout plateau is shortened below 2 h or the oxygen partial pressure is reduced in a nitrogen-purged furnace, residual carbon exceeds 0.05 wt% and alters dielectric loss in the fired ceramic, so air flow above 1.5 m/s across the ware is maintained during the 450°C hold.

After drying, the green tape is blanked or laser-cut with alignment holes, and via punching is performed at 40–60°C under a hard tool to avoid edge delamination; green density is maintained at 2.30–2.50 g/cm³ for 96% alumina. The debinding schedule includes a 250°C soak for 2 h to remove plasticizer and a 450°C soak for 2 h to decompose the PVOH binder; heating between these soaks is limited to 10°C/min to prevent internal pressure from organic vapour. Fired camber after sintering is measured over a 100 mm span and is typically held below 0.2 mm; substrates outside this limit are rejected before thick-film metallisation because paste printing thickness cannot be maintained within ±5 µm. The fired surface roughness is checked with a stylus profilometer at 0.5 µm Ra maximum for screen-printed conductor lines. Terminal uses therefore depend on both mechanical and surface specifications, not solely on green strength.

Operating at 14,000 rpm, the rotary atomizer of a co-current spray dryer converts a vinyl acetate–ethylene dispersion containing WS-724 as protective colloid at 4–12 wt% on polymer solids into redispersible polymer powder at an inlet air temperature of 140–180°C and an outlet temperature of 65–85°C. The feed stream is pre-homogenised at 60°C and 100–150 bar to prevent pre-gelation in the atomizer wheel, and the resulting powder is post-blended with precipitated silica at 5–15 wt% of the dry powder to block premature moisture uptake. Final moisture content is held below 1.5 wt% by coulometric titration, and the powder is discharged from the cyclone at 20–30°C. In dry-mix manufacture, the redispersible powder is added at 0.5–3.0 wt% of total dry mortar, with the finished tile adhesive tested for tensile adhesion after water immersion and freeze–thaw cycles under EN 12004:2012; cementitious repair products are qualified under EN 1504-3:2005. Terminal products are C2-class tile adhesives, self-leveling underlayments, polymer-modified repair mortars, and external thermal insulation composite system base coats. The limiting operating condition is the outlet air temperature: below 65°C the powder sticks to the dryer sidewall and cyclone inlet, while above 85°C the protective colloid loses re-emulsification capacity, producing mortar water retention values below 92% and reducing open time in tile adhesives.

Redispersibility is assessed by mixing 10 g of powder into 90 g deionised water at 20°C with an overhead stirrer at 500 rpm for 2 min, then filtering through a 100-mesh screen; residue must remain below 1 wt% of the powder charge. Powder bulk density is controlled between 400 g/L and 600 g/L, and sieve retention on 0.8 mm is held below 1% to avoid dosing problems in continuous mortar mixing. In tile adhesives tested under EN 12004:2012, C2 products must achieve tensile adhesion of at least 0.5 N/mm² after water immersion, after freeze–thaw cycling, and after heat ageing; these values create the effective upper addition limit in dry-mix formulations because excessive powder above 3.0 wt% may reduce compressive strength and increase creep. The spray dryer campaign is stopped if cyclone outlet moisture rises above 1.5 wt% for 30 min, because wetted powder at the discharge rotary valve leads to blockages and batch contamination with agglomerates larger than 2 mm.

Slot-Die Casting of PVOH Film for Unit-Dose Detergent Products Operates within a Narrow Viscosity Window

WS-724 is dissolved in deionised water at 15–25% solids in a jacketed stainless steel vessel at 80–90°C with slow-speed paddle agitation; the solution is deaerated under 50 mbar vacuum for 30 min before being delivered to a slot die with a 0.6 mm lip gap. The wet film is cast onto a polished chrome-plated belt or moving polymer carrier at 0.5–2.0 m/min and dried in a multi-zone tunnel at 65–85°C to a residual moisture of 4–8 wt% in the final film. The dry-film formulation contains PVOH at 70–95 wt%, polyol plasticizer at 5–15 wt%, and surfactant release agent at 0.1–1 wt%; final film thickness is controlled between 38 µm and 100 µm by die lip adjustment and casting speed. Compliance for food-contact use of the polyvinyl alcohol film is supported by FDA 21 CFR 177.1670, while detergent unit-dose films are assessed for compatibility with finished product stability under the EU Detergent Regulation EC 648/2004 and the film supplier’s dissolution protocol at 20°C and 40°C. Terminal products include dishwasher detergent pods, laundry powder pouches, agrochemical water-soluble sachets, and water-soluble transfer printing film. The critical processing boundary is the solution viscosity at the slot die: below 2,000 mPa·s at 70°C, ribbing and edge neck-in occur; above 8,000 mPa·s, die internal pressure exceeds 20 bar and the wet film cannot be drawn to 38 µm without tearing. Sealing of the cast film is performed at 170–190°C using heated jaw sealers with 0.5–2.0 s dwell; storage above 60% RH causes plasticizer migration to the film surface and increases blocking force, so finished rolls are conditioned at 20–25°C and 25–35% RH before slitting.

Dissolution rate of the finished film is evaluated in a 1.5 L vessel with a perforated basket stirrer at 20°C and 40°C; for unit-dose detergent pouches, the film must open and release the pack contents within 60 s at 40°C and within 180 s at 20°C under the in-house protocol aligned to EC 648/2004. Film tensile properties are measured under ISO 527-3 using 15 mm wide strips at 200 mm/min; typical values are 35–55 N/mm² tensile strength and 200–350% elongation at break. Tear resistance is measured by the Elmendorf method under ISO 6383-2, and the films are conditioned at 25°C and 30% RH for 24 h before testing. Seal strength after a 0.5 s dwell at 180°C must exceed 15 N/25 mm for detergent pod integrity. Moisture uptake in storage is kept below 2.5 wt% by packaging the slit rolls in aluminium composite film, because plasticizer migration and blocking increase sharply at ambient humidity above 60% RH.