| HS Code | 175309 |
| Product Name | SELVOL Polyvinyl Alcohol WS-724 |
| Chemical Name | Poly(vinyl alcohol) |
| Cas Number | 9002-89-5 |
| Molecular Formula | (C2H4O)n |
| Appearance | White to off-white powder or granules |
| Degree Of Hydrolysis | 72-74 mol% |
| Viscosity | Approximately 24 mPa·s (4% aqueous solution, 20°C) |
| Ph | 5.0 to 7.0 (4% aqueous solution) |
| Solubility | Soluble in water, including cold water at low hydrolysis |
| Density | Approximately 1.19 to 1.31 g/cm³ |
| Ash Content | Less than or equal to 0.5% by weight |
| Volatile Content | Less than or equal to 5% by weight |
| Glass Transition Temperature | Ranges from approximately 70 to 90°C depending on moisture content |
| Molecular Weight | Medium molecular weight grade |
| Biodegradability | Biodegradable under aerobic aqueous conditions |
As an accredited SELVOL Polyvinyl Alcohol WS-724 factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | SELVOL Polyvinyl Alcohol WS-724 is supplied in 25 kg multi-ply paper bags with a moisture-proof polyethylene liner. |
| Container Loading (20′ FCL) | 20′ FCL loading of SELVOL WS-724: palletized bags stowed securely, evenly distributed, braced to prevent shifting during transit. |
| Shipping | SELVOL Polyvinyl Alcohol WS-724 is a water-soluble resin shipped as a non-hazardous material. Packed in sealed multi-layer bags or fiber drums to prevent moisture pickup. Store in a cool, dry area away from direct heat. Standard truck or container transport is suitable; no special dangerous goods declaration required. Keep secured during transit. |
| Storage | Store SELVOL Polyvinyl Alcohol WS-724 in its original, tightly sealed container in a cool, dry, well-ventilated area. Protect from moisture, excessive heat, and direct sunlight. Keep away from ignition sources and incompatible materials. Avoid creating dust; use proper handling controls. Under recommended conditions, shelf life is typically two years. |
| Shelf Life | SELVOL WS-724 has a shelf life of two years from manufacture if stored unopened in original packaging in cool, dry conditions. |
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.
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.
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.
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.
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SELVOL Polyvinyl Alcohol WS-724 is supplied as a white to off-white granular intermediate identified by CAS 9002-89-5. The WS designation places the product in warp-sizing service, and the numerical suffix positions it in a medium-viscosity class used when a slasher size solution must maintain a stable viscosity reservoir at elevated solids. The grade is differentiated from general-purpose polyvinyl alcohol by a controlled hydrolysis window, reduced ash burden, and a particle form selected for cold-water slurry formation without fisheye generation during transfer to a jet cooker or open kettle.
The polymer backbone is represented by the repeat unit (–CH2–CHOH–)n after saponification of the precursor poly(vinyl acetate). Residual –OCOCH3 groups are retained deliberately to reduce crystallite density relative to a fully hydrolyzed grade. This structural feature is relevant in warp sizing because the dried size film must remain flexible enough to survive loom reed friction, yet must release from greige fabric in a subsequent hot-water desizing bath. The exact balance depends on degree of hydrolysis, viscosity-average molecular weight, and the thermal history imposed during drying on cylinder cans or in hot-air ovens. Published data for this specific configuration are limited; mill trials are used to confirm formation performance against a given yarn count, twist coefficient, and beam width.
In single-size-box slashers operating above 200 m/min, the limiting variable is the relationship between solution viscosity in the size box and the hydrodynamic force available to wet the yarn sheet before the nip. A 4% aqueous reference solution of WS-724 typically falls within the Brookfield LVF viscosity class 22–27 mPa·s at 20 °C when measured according to ISO 15023-2. At size-box solids between 8 wt% and 12 wt%, the apparent viscosity is higher and shear-thinning; the size box should therefore be equipped with a level controller and a slow-turning agitator rather than high-shear dispersion blades to avoid entrained air. Nip load should be regulated so that add-on remains between 8% and 14% on yarn weight, with the exact target established by mill correlation. Excessive nip pressure starves the yarn bundle and produces a low film thickness that increases size shedding at the heald frame, while insufficient pressure floods the sheet and increases drying load on the cylinder section.
Process water quality alters solution behavior more severely than the raw polymer specification. Residual hardness ions above 150 mg/L as CaCO3 can stabilize calcium acetate species that cloud the solution and reduce film clarity; water should therefore be softened or demineralized before slurry charging. The dissolution vessel should be heated at 2 °C/min to 90–95 °C, held for 30–45 min, and then passed through a 150 µm basket strainer before transfer to the storage tank. Steam sparging is acceptable only when sparge pressure is maintained below 0.2 MPa; higher energy input induces localized overheating and polymer chain scission that appears as viscosity loss after the first hour of circulation.
Unlike fully hydrolyzed low-viscosity grades such as Selvol 103 and Selvol 107, WS-724 retains sufficient residual acetyl content to delay film crystallization during drum drying. This allows the size film to remain receptive to water during desizing while still providing yarn-to-yarn cohesion at low add-on. Compared with high-viscosity partially hydrolyzed grades such as Selvol 853, WS-724 permits higher solids content at the same apparent viscosity, which is advantageous when a warp of fine-count polyester is prone to size penetration rather than surface coating. The trade-off is that the lower chain length reduces dry film strength and narrows the drying window; if cylinder surface temperature exceeds 120 °C, the film may become brittle and deposit hard size on the reed. The grade differs from low-ash specialty PVOH used in paper coating by its intended solution concentration and by the size-kitchen filtration point; paper-coating control often relies on flow-cup dilution rather than the ISO 15023-2 Brookfield viscosity method used in warp sizing.
The specification is generally built around four control parameters: solution viscosity, degree of hydrolysis, volatile matter, and ash residue. Viscosity is measured on a 4% by weight aqueous solution at 20 °C using a Brookfield LVF viscometer; the degree of hydrolysis is determined by the residual acetate saponification method described in JIS K6726. The table below gives representative industrial control ranges for a commercial partially hydrolyzed PVOH of this viscosity class. Actual lot certificates for SELVOL Polyvinyl Alcohol WS-724 may be narrower than the class ranges shown because the supplier releases the product against a controlled recipe and may adjust the nominal viscosity within the band to compensate for chain-transfer effects during polymerization.
| Parameter | Test method | Typical control range |
|---|---|---|
| 4% aqueous solution viscosity | ISO 15023-2 / JIS K6726 | 22–27 mPa·s at 20 °C |
| Degree of hydrolysis | ISO 15023-2 / JIS K6726 | 87.0–89.0 mol% |
| pH | ISO 15023-2 / JIS K6726 | 5.0–7.0 |
| Volatile matter | ISO 15023-2 / JIS K6726 | ≤5.0% |
| Ash as Na2O | ISO 15023-2 / JIS K6726 | ≤0.5% |
For critical warp-sizing trials, the relevant value is not the dry-powder specification but the filtered solution viscosity after complete hydration and cooling to the size-box temperature. A solution that appears within specification at 20 °C can deviate at 80 °C if the dissolution protocol leaves microgel from undispersed particles; therefore the size kitchen should record the temperature-compensated torque of the transfer pump or the pressure drop across the final filter as an indication of solution homogeneity. Volatile matter above 5% can reduce the accuracy of solids-weight calculations and should be corrected by predrying when the bag has been stored in an uncontrolled warehouse. Ash is minimized because sodium acetate is a known plasticizer for dried PVOH film and can increase size pick-up variability between beams.
In mills that run both cotton and polyester warps, the grade is often cross-blended with starches or acrylic binders to adjust cost-performance. WS-724 is generally compatible with oxidized corn starch in the size box when the starch is cooked separately and blended after cooling to 80 °C; incompatibility appears as a viscosity spike if the two components are charged simultaneously into an unheated mixer. The blend ratio is established by comparing slashing strength and elongation on sized yarn rather than by relying on the PVOH viscosity specification alone. Sized yarn tensile properties can be measured according to ASTM D2256, with sample conditioning at 23 °C and 65% RH for at least 4 h before testing; this standard provides a comparative basis for choosing between WS-724 and alternative high-solids sizing agents.
After a machine stop or shift change, the contents of the size box cool and the WS-724 solution may enter a gelation regime if the concentration exceeds the critical overlap concentration at quiescent temperature. This behavior is not a defect; it is reversible upon reheating to 85 °C with gentle agitation. However, repeated thermal cycling removes water by evaporation and raises the effective solids level, producing a surface skin that can block the return line from the size box to the storage tank. Operators should therefore maintain a continuous low-flow recirculation loop during any stop longer than 20 min and should not add cold water directly to the size box because the resulting thermal shock can precipitate a gel layer on the rolls.
The desizing response is also determined by the thermal history of the dried film. Woven fabric sized with WS-724 and dried at cylinder temperatures below 110 °C generally releases the film in a conventional hot-water desizing bath held at 85–95 °C containing a mild wetting agent. If the fabric is heat-set above 160 °C before desizing, the partially hydrolyzed structure can undergo additional dehydration and crystallite growth, making removal slower. In such cases, a short enzymatic or oxidative pre-wash may be necessary. This boundary should be checked against the specific singeing and heat-setting sequence used downstream; published data for this exact grade after high-temperature heat-setting is limited, so a laboratory desize test on a fabric swatch is advised before full-width processing.
Regulatory documentation for SELVOL Polyvinyl Alcohol WS-724 is typically aligned to indirect food-contact adhesive and paper/paperboard component standards where the grade is used as an aqueous film former or binder. Under 21 CFR 175.105, polyvinyl alcohol may be used as an adhesive component in articles intended for contact with food; under 21 CFR 176.170 and 21 CFR 176.180, components may be used in paper and paperboard in contact with aqueous and fatty foods, subject to conditions of use. The SELVOL product line is not a direct food additive; such applications require separate approval of the formulated final article. For the European market, the finished compound supplier must verify that the polymer monograph and any residual vinyl acetate monomer levels meet Commission Regulation (EU) No 10/2011 migration limits if the final article is a plastic food-contact material.
Warehouse storage requires dry, sealed packaging at ≤30 °C because the granular solid is hygroscopic and will form lumps at relative humidity above 60%. If the product has adsorbed moisture, predry at 60–70 °C for 4 h in a desiccant dryer before pneumatic transfer; do not predry above 100 °C because prolonged exposure can color and partially dehydrate the polymer, reducing dissolution clarity. Strong acids, strong bases, and oxidizing agents should not be combined with the dry powder or concentrated solution. Borate salts are a known incompatibility: borate ions crosslink the poly(vinyl alcohol) through didiol formation and convert the solution into a non-pumpable gel even at low addition levels. This interaction is used deliberately in some water-soluble film applications but must be avoided in a sizing kitchen unless a controlled thickening response is designed into the formulation.
Outside warp sizing, WS-724 can be used as a film-forming binder in remoistenable adhesives, water-soluble temporary protective coatings, and paper coating formulations that require a controlled redispersibility boundary. In adhesive compounding, the dry powder should be dispersed in cold water before addition of plasticizers such as glycerol or polyethylene glycol; adding the plasticizer before full hydration can slow water uptake and produce grainy films. The optimal plasticizer level is typically determined by measuring the glass transition temperature of the cast film by differential scanning calorimetry or by a loop-tack test; however, the specific value for WS-724 at each plasticizer ratio should be generated internally because it is influenced by residual humidity and drying rate. For paper coating, the medium-viscosity class increases wet pick resistance without the excessive starch viscosity that limits blade-coater speed.
The dried film shows a tensile strength that is governed primarily by degree of hydrolysis, orientation, and residual moisture, not by nominal solution viscosity alone. A cast film conditioned at 23 °C and 50% RH for 24 h can be tested according to ISO 527-3; however, elongation at break for partially hydrolyzed PVOH shifts with relative humidity because water acts as a plasticizer. Film generated from WS-724 is expected to be weaker than a fully hydrolyzed high-viscosity grade but more flexible than a fully hydrolyzed low-viscosity grade. This intermediate position matches the requirement of a warp size that must survive shed opening and reed beat-up yet release during desizing without requiring aggressive chemical oxidation.
The drying step is a critical threshold because the film must reach a final moisture content below 10% but must not be over-dried. On a conventional seven-cylinder slasher, the first cylinders are set at 80–95 °C to remove free water, and the final cylinders at 100–115 °C to plateau the film without creating blisters. If the final cylinder temperature exceeds 120 °C, the surface of the size film can develop a glassy skin that traps moisture underneath and reduces beam hardness. Operators monitor exhaust humidity and beam surface temperature rather than the heater setpoint alone; this practice prevents lot-to-lot viscosity drift from being misinterpreted as a drying failure.
Stainless steel construction of the size kitchen is required because PVOH solutions are mildly acidic after storage, with pH in the range 5.0–7.0, and will corrode unprotected carbon steel over repeated steam-out cycles. Transfer pumps should be low-pulsation, positive-displacement or progressive-cavity types rather than centrifugal pumps operated against a closed discharge at high speed; the latter can cause mechanical shear degradation of the polymer and raise the fine-gel load on the final filter. Final filter media should be 100–150 µm, placed after the heat exchanger and before the size-box return line. These equipment selections are based on observed batch-to-batch variance on production slashers rather than on dry-powder specifications.
