SELVOL Álcool Polivinílico 205S

In jacketed batch reactors running vinyl acetate-ethylene copolymer dispersion at 80–85°C jacket temperature and 15–45 bar ethylene partial pressure, SELVOL Polyvinyl Alcohol 205S is typically charged as a 10 wt% aqueous solution before monomer feed begins. The grade carries a manufacturer-published 4% aqueous viscosity of 5.2–6.2 mPa·s at 20°C and a hydrolysis range of 87.0–89.0 mol%, placing it in the low-molecular-weight partially hydrolysed PVOH class. Low-molecular-weight PVOH does not build aqueous viscosity as rapidly as higher-viscosity grades in the wet section of the polymerisation kettle, yet the residual acetate groups provide interfacial activity sufficient to cover vinyl acetate droplets. Reactor fouling on internal cooling coils is reduced when the colloid is pre-dissolved at 85°C for 45 min using a propeller agitator at 150–250 r/min and then cooled to 30°C before feed. The 205S solution should be filtered through a 100 µm screen to remove undissolved skins; otherwise, the skins are transported into the pre-emulsion tank and cause seed coalescence. Monomer consumption rate, measured by calorimetry, remains linear during the propagation phase when the PVOH loading is held between 2.0 pphm and 5.0 pphm on vinyl acetate.

The polymerisation is initiated with potassium or sodium persulfate at 0.15–0.30 pphm, buffered with sodium bicarbonate to keep pH between 4.0 and 5.5; below pH 4.0, the 205S colloid can undergo acid-catalysed acetate hydrolysis and gradually lose protective surface activity. These conditions are matched to a stirred batch reactor with a turbine impeller tip speed of 2.5–5.0 m/s and a condenser returning unreacted ethylene. The resulting dispersion reaches 50–55% solids and exhibits a Brookfield viscosity in the range of 3,000–7,000 mPa·s at 25°C, depending on monomer ratio and post-stabilisation additives. It is post-formulated with benzyl alcohol, dibutyl phthalate, or citric acid ester plasticisers at 2–10% of wet dispersion to produce packaging adhesives, paper-to-film laminating adhesives, and VAE-based carpet backing compounds. The adhesive film is evaluated by ASTM D882 for tensile properties and by ASTM D3163 for lap shear on polystyrene substrates. Because 205S is a partially hydrolysed grade, adhesive films remain redispersible in water at 25°C, which supports mechanical cleaning of returnable containers without organic solvents. Where food-contact packaging is involved, the applicable regulatory reference is FDA 21 CFR 175.105 for adhesives used as components of food-contact articles; the grade also falls within REACH registration obligations for nonyl phenol-free polyvinyl alcohol supplied in the EU.

Plant-scale failure is typically batch-to-batch viscosity drift when the pre-emulsion is aged beyond 6 h at 30°C, because the partially hydrolysed PVOH can continue to swell and agglomerate. The corrective action is to hold pre-emulsion solids below 62% and feed within 4 h. Oxygen must be excluded by nitrogen purge to below 50 ppm dissolved oxygen; otherwise, inhibition extends induction time and causes sticky polymer deposition on thermowells. The terminal products from the 205S-stabilised dispersion class are spiral paper tube adhesives, furniture lamination adhesives, cigarette filter plug wrap adhesives, and VAE copolymers for nonwoven wipes.

Stabilising Vinyl Chloride Monomer Droplets in PVC Suspension Polymerisation

Suspension-grade poly(vinyl chloride) reactors operating at 50–65°C and 7–13 bar VCM pressure use a two-dispersant package containing a high-hydrolysis primary grade and SELVOL Polyvinyl Alcohol 205S as the low-molecular-weight secondary dispersant. The 205S grade hydrates at 20°C without hot-water cooking because its hydrolysis level is 87–89 mol%, but resistance to phase separation at the reactor temperature is maintained by the acetate group blockiness. A 5 wt% aqueous solution is prepared in a separate feed tank with agitated baffles and is dosed at 0.05–0.20 pphm on VCM, depending on the target K-value of the suspension resin and the desired plasticiser absorption capacity. The combination of primary and secondary PVOH controls VCM droplet coalescence during the critical particle identity point at 20–30% monomer conversion; underdosing the 205S secondary dispersant below 0.05 pphm produces coarse grains with a high fraction of agglomerates retained on a 250 µm sieve. Overdosing above 0.20 pphm can over-stabilise droplets and shift the mean particle size toward 80–100 µm, which is below the preferred suspension resin range for extrusion compounding. The autoclave is equipped with a Pfaudler-type retreat-curve impeller, draft tube, and reflux condenser; wall fouling is monitored by pressure-drop rise across the jacket and by clear-wall sections after each batch.

After VCM stripping to below 1 ppm residual monomer under vacuum at 70°C, the dried resin is evaluated by ISO 1628-2 for K-value, ASTM D1755 for PVC resin specification classification, and ISO 4608 for plasticiser absorption at 20°C. The 205S-derived grain morphology increases the specific surface area for plasticiser uptake but does not leave inorganic residues if ash content is below 0.5% by the manufacturer’s specification. The terminal suspension PVC grades are converted into rigid pipe, window profiles, cable insulation, and medical tubing. Pipe-grade formulations are processed on twin-screw extruders with L/D 36:1 to 44:1 at melt temperatures of 185–195°C; the residual PVOH layer on the PVC grain does not introduce amine or sulfur compounds that would otherwise degrade thermal stability during extrusion. Compliance for medical tubing includes ISO 10993-1 biological evaluation guidance and EU Medical Device Regulation 2017/745 for finished articles; the PVOH dispersant itself is controlled under REACH with the grade’s SDS carrying no SVHC classification.

How Much 205S at the Metering Size Press Preserves IGT Dry Pick Resistance Above 1.5 m/s Without Reducing Air Permeability?

At a metering size press running 600–1,200 m/min web speed with rod pressure set to 20–40 kN/m, the surface sizing formulation balances film strength against liquor pickup. SELVOL Polyvinyl Alcohol 205S is prepared as a 8–12 wt% stock solution at 80°C for 45 min, then diluted at the size press to 0.5–3.0 wt% active PVOH in the working size. The low-molecular-weight grade limits Brookfield viscosity of the stock solution to 250–500 mPa·s at 70°C, which helps maintain a stable film split between the applicator roll and the paper surface without misting. The dry pick resistance of sized fine paper is measured by TAPPI T 477 or ISO 3783; a coated woodfree sheet moving from 0.8 m/s to 1.5 m/s pick velocity represents an improvement from weak surface strength to acceptable offset-printing runnability. Because 205S is partially hydrolysed with residual acetate groups, the dried surface film is less brittle than fully hydrolysed grades and does not crack at fold creases during converting. Air permeance measured by ISO 5636-3 should remain above 100 mL/min for porous release liner base or above 300 mL/min for bag paper; excessive PVOH loading above 3.0 wt% in the working size closes surface pores and reduces air permeance by film blocking. Process control therefore uses a ratio of surface sizing agent to starch of 1:10 to 1:4 on dry chemicals, depending on furnish.

The size press liquor is held at 60–70°C in a circulation loop with 100 µm in-line filtration; stable temperature prevents viscosity drift from retrograded starch-PVOH complexes. Coagulation occurs when the aluminum sulfate level in the size press loop exceeds 50 ppm Al³⁺, because PVOH reacts with polyvalent cations; mills operating alum in wet-end chemistry should flush the size press loop before switching to PVOH-containing surface size. The sized web is dried on after-sections at 90–100°C to reach a moisture content of 5–7%; above 115°C, the PVOH film can undergo dehydration and become less redispersible, which reduces repulpability of broke. Finished grades include offset uncoated printing paper, envelope base, release liner, inkjet conversion paper, and folding carton board. Surface-sized board also passes FDA 21 CFR 176.170 for paper and paperboard components in contact with food when the PVOH grade is used in accordance with good manufacturing practice. The following table summarises the regulatory and test references for the surface sizing application.

Tape casting of alumina-based low-temperature co-fired ceramic dielectric layers requires a slurry with 40–55 vol% solids loading and a viscosity range of 1,500–3,000 mPa·s at 10 s⁻¹, measured on a rotational rheometer with cone-plate geometry at 25°C. SELVOL Polyvinyl Alcohol 205S is introduced as a 4–7 wt% binder on ceramic powder after the powder has been dispersed in a ternary solvent system of toluene, ethanol, and methyl ethyl ketone. The grade is pre-dissolved in the aqueous phase before solvent exchange or is added as a dry powder to the mill; dry addition requires a high-shear disperser at 1,000–2,000 r/min to avoid soft binder agglomerates. The low ash content of the grade, specified below 0.5% by the manufacturer, is critical for LTCC dielectric layers sintered at 850–900°C; residual sodium or sulfate above 100 ppm in the final green sheet can affect loss tangent at 1 MHz. After ball milling for 12–24 h with 3 mm zirconia media, the slurry is de-aired under 0.2–0.5 kPa vacuum for 15–30 min and cast onto a polyester carrier with a doctor blade gap of 150–300 µm. The green tape is dried at 45–60°C in a cleanroom controlled at ISO 14644-1 Class 7 or better to prevent particle inclusion.

The dried green sheet is laminated at 60–80°C under 10–30 MPa hydraulic pressure to build multilayer structures. The 205S binder controls interlayer adhesion and prevents delamination during cutting and via punching. The burnout profile is critical because the partially hydrolysed grade decomposes by thermo-oxidative chain scission starting near 200°C and completes carbon-free burnout by 450°C under air flow of 2–5 L/min. Published data for this specific configuration is limited, but PVOH binders measured by thermogravimetric analysis under 10 K/min air purge typically show 90–95% mass loss below 400°C. The furnace ramp rate is held below 2°C/min between 100°C and 400°C to prevent tape blistering; held dwells at 250°C and 350°C allow binder decomposition products to escape through the porous alumina network before the matrix densifies. Sintered LTCC substrates are used in high-frequency RF modules, automotive radar sensors, and multilayer ceramic capacitors. Since the binder must not disturb the final dielectric constant and loss factor, the 205S is selected for its low ash, low alkali, and chlorine-free profile under RoHS Directive 2011/65/EU.

When Slasher Room Relative Humidity Exceeds 70% at 30°C

When slasher room relative humidity exceeds 70% at 30°C, spun cotton warp yarn sized with starch alone loses flexibility and becomes susceptible to static yarn breaks during weaving. SELVOL Polyvinyl Alcohol 205S is used as a co-binder in the size box with native starch at 15–25 parts PVOH per 100 parts starch on dry solids. The total size-box solids are maintained at 9–12% and the sizing machine is a multi-cylinder slasher with 8–12 drying cylinders; pre-drying cylinder surface temperature is set to 110–120°C, and final cylinders to 80–90°C. The 205S grade dissolves at 25–30°C, which permits low-temperature cooking of the size bath without the steam demand of fully hydrolysed grades; the solution is heated to 60°C for 30 min to complete hydration. For 20 Ne cotton yarn at a slasher speed of 60–80 m/min, size deposition is controlled between 8% and 12% add-on. The PVOH film reduces abrasion damage at the reed and improves weaving efficiency, particularly on high-speed air-jet looms operating above 600 weft insertions per minute. The film property is checked by the tensile strength of a cast film using ASTM D882, with elongation at break above 200% to tolerate weaving flexure.

Desizing uses a 50–60°C water bath with 0.5–1.0 g/L nonionic wetting agent for 10–15 min; the 205S portion redissolves without enzyme action, while starch requires amylase if enzymatic desizing is specified. Overdrying above 130°C on the slasher cylinders produces a water-insoluble skin on the yarn, which increases desizing time and creates fabric dyeing defects; moisture at the final drying cylinder is therefore maintained at 6–8%. The high relative humidity in the weaving shed is an operational boundary because PVOH film absorbs atmospheric moisture, reducing tensile strength and increasing tack. The size bath should not be mixed with strong borax solutions above 0.2% of PVOH, because borate crosslinking raises viscosity and may gel in the size box return loop. Terminal woven goods include cotton shirting, denim, home textile sheeting, and industrial workwear. The textile sizing operation aligns with ZDHC Manufacturing Restricted Substance List requirements for sizing agents; PVOH is free of alkylphenol ethoxylates, and its COD in desize effluent is conventionally managed by aerobic treatment because PVOH is biodegradable in acclimated activated sludge under OECD 301B test conditions.

Paper Tube Lamination Adhesive Viscosity and Borax-Driven Tack Development

Spiral-wound paper tube lines running at 40–70 m/min require an adhesive with a Brookfield RVT viscosity of 800–2,000 mPa·s at 20°C, 20 r/min, spindle 3, to transfer cleanly through serrated applicator rollers and to hold open lap seams within 2–3 s of contact. SELVOL Polyvinyl Alcohol 205S is dissolved at 15–18% solids in a jacketed mixer at 30–40°C, then blended with mineral filler, starch, and a borax tackifier solution. The borax-to-PVOH ratio is kept between 0.1 and 0.5 parts borax per 100 parts dry PVOH; at the upper boundary, the adhesive builds a reversible tack gel that improves wet grab on high-density kraft board without freezing the circulation pump. Exceeding 0.5 pphm borax leads to an irreversible elastic gel that cannot be pumped through 50 µm adhesive filters and must be scrapped. The 205S grade is selected because its low molecular weight permits 30% more solids than medium-viscosity grades while remaining below pump shear limits; high solids reduce water penetration into the paperboard and shorten the drying time in the tube mandrel. The adhesive is applied by a 2–4 g/m² wet film, then the paper web is wound on a spiral tube mandrel at roll pressure of 0.4–0.8 MPa.

Adhesion is measured after 24 h conditioning at 23°C and 50% relative humidity by TAPPI T 808 for bond strength of corrugated or solid fiberboard; for spiral tubes, the flat crush and radial crush are tested by ISO 11093-9. The terminal articles include spiral paper cores for stretch film, edge protectors, industrial cores, yarn carriers, and paper composite cans. Since the laminate adhesive remains on the paper substrate, the relevant food-contact regulation for packaging composite cans is FDA 21 CFR 175.105; for corrugated board used in indirect food-contact, FDA 21 CFR 176.170 also applies. Operational boundaries include storage of prepared adhesive below 35°C; above this temperature, PVOH solutions support microbial activity and require biocide preservation. The preserved adhesive should be consumed within 48 h; prolonged storage without agitation permits separation of starch and PVOH phases, which then requires re-homogenisation at 300–500 r/min before the next run.