SELVOL Álcool Polivinílico WS-53NF

On high-speed air-jet weaving platforms exceeding 1,100 picks/min and running warp-beam widths above 220 cm, the sized yarn is subjected to oscillatory tension cycles in the 30–50 cN/tex range at the heald frames and recurrent reed impact frequencies above 18 Hz. Selvol Polyvinyl Alcohol WS-53NF is introduced as the primary film former in warp-size mixes because its 4 % aqueous solution viscosity of 5.0–6.0 mPa·s at 20 °C and hydrolysis degree in the 86.0–89.0 mol% band produce a dry film with sufficient cohesion for spun cotton and cotton/polyester blends without excessive stiffness at normal weaving-shed humidity. The size film must remain continuous under elongation cycling; film tensile values measured on isolated PVOH films are generally in the 30–55 MPa break-stress range with elongation at break between 80 % and 150 % when cast from 7 wt% aqueous solution and conditioned at 23 °C and 50 % RH according to ASTM D882 specimen preparation adapted for solution-cast films. Such elongation values are materially above the 1.5–3.0 % elongation of raw ring-spun cotton yarn at first break, which allows the size film to deform with the yarn rather than crack at maximum curvature on the reed. The operational boundary for storage is that unopened bags should be kept below 30 °C and below 60 % RH; if material is stored in an uncontrolled warehouse above 60 % RH, pre-drying at 40 °C for 2 h is required before high-shear dispersion to avoid agglomerates that reduce filter life in the size kitchen.

Size-mix preparation on production-scale jet cookers requires initial cold-water dispersion at 25–30 °C in a high-shear disperser, followed by indirect steam heating to 90–95 °C for 30 min under continuous agitation. Holding temperatures below 80 °C in the size box reduce skinning on the box surface; however, viscosity increases as the solution approaches 40 °C because of strong hydrogen bonding and partial gel network formation. Typical size-box solids for WS-53NF range from 6.0 wt% to 9.0 wt% for fine ring-spun counts in the 30–60 tex range, with lower solids on air-jet looms and higher solids on water-jet looms only when the size film is protected by a cationically modified starch co-binder. The size-box viscosity is commonly controlled between 60 mPa·s and 120 mPa·s at 60 °C, measured with a Brookfield viscometer at 20 rpm using an LV spindle set per ISO 2555. Add-on targets for continuous filament polyester are typically 6–9 % dry solids on yarn mass, whereas spun cotton warps require 10–14 % add-on. Because residual moisture above 8 wt% in the dried size film lowers the effective hardness and can produce blocking on the first drying cylinders, the dry-can surface temperature profile is commonly set between 110 °C and 130 °C, with the final can no higher than 140 °C to avoid film yellowing. Production warping tensions after sizing should not exceed 0.15 cN/tex because a moisture-plasticised film can block on the warp beam if wound at excessive tension.

Desizing of WS-53NF-based size films is carried out in continuous pad-steam or pad-batch washers with oxidative or enzymatic stages. Because the product is soluble in water above 70 °C, a wash train consisting of four counterflow boxes with final liquor temperature above 80 °C normally removes more than 98 % of the size film before bleaching, as measured by mass loss before and after treatment. Complete removal is critical when the fabric enters downstream inkjet pre-treatment or coating steps because residual PVOH can interfere with optical brightener absorption and produce localised surface energy differences. The sizing solution must not be mixed with borax, boric acid, or sodium metaborate at elevated pH, since borate ions crosslink the diol units and produce an irreversible viscosity increase or gel formation in the size box. Published data for specific loom-shed humidity thresholds for this grade are limited; however, operational practice is to maintain weaving-room relative humidity between 65 % and 75 % to prevent film embrittlement at low humidity and blocking at high humidity.

Why Do Paper Mills Replace Oxidised Starch with PVOH in Film-Press Coatings?

Metering size presses running at 1,200–1,800 m/min on fine paper machines impose shear rates above 1 × 10⁶ s⁻¹ in the transfer nip. Oxidised starch solutions in the same solids range undergo shear degradation and permanent viscosity loss, whereas a partially hydrolysed PVOH such as WS-53NF maintains molecular integrity because its aqueous solution rheology at 10 % solids is pseudoplastic but not chain-scission-sensitive under the short nip residence times, which are below 10 ms. The material is added at 2–5 parts per hundred dry fibre in size-press starch formulations to raise surface strength without reducing bulk. If the paper machine uses a film press with rod-metering or bent blade, the final coating colour viscosity of 300–800 mPa·s at 60 °C is normally targeted, measured by Brookfield LVT at 60 rpm. The transfer film is controlled by adjusting the solids to 12–15 % in the size press; above 15 % solids, transfer can become uneven because the high-viscosity film splits before deposition. Surface sizing efficiency is evaluated by the Hercules size test per TAPPI T 530 and by Cobb water absorptiveness per ISO 535, with typical targets of 20–30 g/m² Cobb for coated packaging liner. In pigmented coating, WS-53NF can function as co-binder at 0.5–1.5 parts per hundred dry pigment; its role is to increase picking resistance as measured by the IGT pick test per ISO 3783. The addition of WS-53NF into a coating colour containing clay or ground calcium carbonate should be carried out after complete dissolution and cooling to below 50 °C, because hot PVOH solution can shock the binder dispersion and produce micro-gels that appear as blade streaks on the coated sheet.

The main limitation in paper applications is the incompatibility of PVOH with glyoxal-based insolubilisers at low pH. Glyoxal reacts with hydroxyl groups and can crosslink the film prematurely in the size-press circulation loop if the pH falls below 4.0. Circulation pH is therefore maintained between 5.5 and 6.5 when PVOH is present with starch. Since the PVOH solution can foam under high-speed pumping, defoamer additions of 0.05–0.15 wt% on total wet formulation are used, but excess defoamer above 0.3 wt% can produce eye-specks in the dried sheet. Published data on the specific film-press transfer behaviour of this grade on commercial fine paper machines are limited, but the use window is derived from known PVOH rheology and mill practice with partially hydrolysed grades in coated papers.

Remoistenable Adhesive Film Formation on Polyethylene-Coated Kraft

Roll-coating remoistenable gum onto polyethylene-coated kraft at line speeds up to 800 m/min deposits a wet film that is subsequently dried in a forced-air tunnel with zone temperatures between 70 °C and 110 °C. WS-53NF is used as the colloid and film former in the gum formulation because its 4 % solution viscosity of 5.0–6.0 mPa·s yields low high-shear stringiness at the coating head, which reduces the incidence of coating mist at high machine speeds. A representative gum formulation includes 30–40 wt% PVOH solids, 10–20 wt% plasticiser such as polyethylene glycol, and 0.5–1.0 wt% defoamer on total dry solids; the total coating solids are adjusted to 25–35 % for gravure roll application. If the wet film is deposited at 8–12 g/m² dry coat weight, the resulting adhesive is non-blocking at 40 °C and 70 % RH when the re-moistenable surface is stored against uncoated paper, but blocking can occur if the stack pressure exceeds 35 kPa at the bottom of tall pallets. The open time after moistening is typically 5–10 s on commercial envelope sealing machines running at 400–800 pieces/min; this window is determined by the plasticiser concentration and the ambient relative humidity. A viscosity drift beyond ±10 % of the initial Brookfield reading at 25 °C after 24 h indicates microbial growth or incomplete dissolution, requiring filtration through a 100 µm mesh screen before further coating.

Compliance anchors for indirect food contact in remoistenable adhesive applications refer to FDA 21 CFR 175.105 when the dried adhesive remains on the exterior of closed packaging and is not intended for direct food contact. The use of WS-53NF in this application is not a direct food-contact declaration; the grade is applied only as a non-contact adhesive in converting operations. Methanol content in the PVOH affects workplace emission during drying; WS-53NF is generally selected when residual methanol in the wet adhesive is specified below 0.5 wt% of wet formulation to satisfy printing-sector air-emission permits. The adhesive film must not be formulated with cationic polyelectrolytes or high levels of aluminium salts because coagulation can occur at pH values above 6.5. Operational practice is to maintain final adhesive pH between 5.0 and 6.5 and to store coated stacks at or below 25 °C to preserve re-moistenability over a 12-month shelf life.

The binder system in ceramic tape-casting lines producing alumina substrates for thick-film circuits must deliver a stable slurry viscosity of 1,500–3,000 mPa·s at 20 rpm Brookfield LV and a cast green tape with an elongation of at least 4–6 % during carrier release and punching. Selvol Polyvinyl Alcohol WS-53NF is dissolved at 8–12 wt% solids in a solvent mixture, typically water with a small percentage of a nonionic defoamer, and then blended with submicron alumina powder at 60–70 wt% solids on total slurry. The slurry is milled in a ball mill with 3–5 mm zirconia media for 18–24 h; final slurry viscosity is then reduced by vacuum deairing to remove entrained air bubbles that would otherwise form pinholes in the green tape. The doctor blade gap is set between 300 µm and 650 µm depending on the required green sheet thickness after drying, which is typically 50–150 µm. Tape drying is performed in a three-zone air float dryer with zone temperatures of 50 °C, 70 °C, and 90 °C, and residual moisture is held below 1.5 wt% before winding.

Binder burnout is the critical process window. WS-53NF begins thermal decomposition near 200 °C, and the binder removal profile for a 100 µm green tape should not exceed a heating rate of 1 K/min between 250 °C and 450 °C to avoid delamination or carbon residue. The ash content of the PVOH is measured by ISO 3451-1 at 600 °C; low ash is required because residual sodium oxide above 0.05 wt% of the ceramic mass shifts sintering behaviour of dielectric layers. Documented failure modes on production-scale lines include edge curl when the drying rate in the first zone exceeds 0.5 g/m²·s and blocking on the roll when the green sheet is wound at tension above 0.3 N/mm. The compatibility of WS-53NF with polyacrylate dispersants and with ammonium polyelectrolyte deflocculants is acceptable at pH 8.0–9.5; below pH 6.5, the slurry may thicken because the partially hydrolysed PVOH adsorbs less water as ionisation decreases. Published comparative data for this specific grade in tape-cast dielectric systems are limited; the above operating window is derived from general PVOH binder practice in the multilayer ceramic capacitor and thick-film substrate industries.

When Emulsion Polymerisation Requires a Low-Methanol Protective Colloid

Vinyl acetate-ethylene and vinyl acetate-acrylic emulsion polymerisation processes use PVOH as a protective colloid because it controls particle size during the radical polymerisation and stabilises the finished latex against storage coagulation. In a 5,000 L stirred reactor running a semi-batch vinyl acetate feed at 60–70 °C, WS-53NF is prepared as a 10 wt% stock solution and added at 3–6 parts per hundred monomer; the initial charge is dissolved in deionised water and sparged with nitrogen for 30 min. The use of a low-methanol grade is relevant when the final latex must meet volatile organic compound limits for interior low-emission paints, because residual methanol in conventional PVOH can contribute to total VOC measured by ISO 17895 gas chromatography. The particle size of the resultant latex is typically in the 0.5–2.0 µm range when the polymerisation is run under low shear with only PVOH as stabiliser; smaller particle sizes require the addition of anionic surfactants, which changes the rheology profile to more Newtonian at high shear. Reactor pH is maintained between 4.0 and 6.0, because above pH 7.0 the acetate groups of the PVOH undergo alkaline hydrolysis and the colloid becomes more hydrophilic, increasing water sensitivity of the formed films.

During polymerisation, the PVOH participates in grafting reactions with vinyl acetate radicals, and the degree of grafting affects the clarity and water resistance of the dried film. Residual monomer reduction using a redox pair of tert-butyl hydroperoxide and sodium metabisulfite at 70 °C should not exceed 1.0 wt% of the product mass, because excess sulfite can react with the PVOH and produce an off-gassing issue during storage. The finished latex solids are measured per ISO 3251, and the viscosity is measured at 25 °C with a Brookfield viscometer at 20 rpm. Incompatibility is known with borate salts, aluminium sulfate, and some zirconium crosslinkers at concentrations above 0.1 wt% of the latex; these additives can induce gel particles or complete coagulation. When the latex is used in low-VOC architectural coatings, the residual methanol contribution from the protective colloid is measured in the liquid coating by gas chromatography and reported against the product limit established under the relevant local air-quality regulation. No direct food-contact status is assigned to WS-53NF in this polymerisation route; the grade is used as an industrial colloid for technical dispersions and construction coatings where FDA 21 CFR 175.105 is not part of the end-use specification.