Solução de álcool polivinil SELVOL 24-203

SELVOL Polyvinyl Alcohol 24-203 Solution is an aqueous delivery form of the partially hydrolyzed polyvinyl alcohol grade SELVOL 24-203, CAS 9002-89-5. The underlying dry-grade polymer is controlled within a 4.0–5.0 mPa·s viscosity window for a 4% aqueous solution at 20 °C, measured by falling-ball technique under ISO 12058, and a degree of hydrolysis of 87.0–89.0 mol%, determined by saponification-based chemistry in accordance with JIS K6726. The pH of the solution is normally 4.5–6.5 when measured by ISO 976, and ash content is specified at ≤0.5% by ISO 3451-1. Because the material is supplied as a solution, the active polymer concentration is not a universal constant; it is set by supply specification, commonly 10–25 wt%, and must be confirmed by non-volatile residue gravimetry under ISO 3251 before the solution is metered into viscosity-sensitive processes.

The 87.0–89.0 mol% hydrolysis range leaves 11–13 mol% residual acetate groups along the polymer backbone. Those acetate groups disrupt interchain hydrogen bonding enough to permit cold-water dissolution at 20–25 °C, whereas fully hydrolyzed grades in the 98–99 mol% range generally require heating above 80 °C and extended hold time for complete hydration. The acetate content also alters the interfacial tension and steric stabilization behavior of the polymer; partially hydrolyzed PVOH is a more effective protective colloid in many emulsion systems than a fully hydrolyzed material of equivalent viscosity. The trade-off appears in dried-film performance: residual acetate reduces tensile strength and hot-water resistance relative to a fully hydrolyzed grade. The 24-203 solution therefore functions between low-viscosity surfactant-like stabilizers and high-molecular-weight fully hydrolyzed film formers.

What Distinguishes 24-203 Solution from Fully Hydrolyzed PVOH in Aqueous Processing?

The principal processing difference is the temperature required for full solubility. A 4% stirred batch of 24-203 solution can be prepared without heat when the water is deionized and temperature is maintained at 20–25 °C; this is not the case for fully hydrolyzed PVOH grades with equivalent viscosity, which generally require slurry heating to 80–95 °C and a minimum hold time. The viscosity response is also different after complete dissolution: 24-203 builds viscosity in a more linear relationship with concentration at low solids, while fully hydrolyzed grades can form stronger hydrogen-bonded networks and develop higher gel strength as temperature drops. In hot coating lines, the partially hydrolyzed grade retains lower hot-water resistance, which can be either a limitation in water-resistant barrier coatings or an advantage in repulpable paper grades.

The temperature coefficient of the solution’s viscosity is negative and non-linear. When the solution is cooled toward 5 °C, low-shear viscosity rises as intermolecular hydrogen bonding increases; when it is heated to 60–70 °C, viscosity drops and the solution again approaches Newtonian behavior. This has direct consequences for sizing and coating lines because a cold morning start-up may require higher pump pressure or reduced line speed even when solids content is unchanged. Inline temperature-compensated viscosity measurement is therefore preferable to simple dip-tube or efflux cup methods for process control.

When borate crosslinkers are introduced into an adhesive or coating formulation, the 1,3-diol residues in the polyvinyl alcohol chain react with borate ions to form a reversible monodiol/di-diol complex. Viscosity increases rapidly with pH and borate concentration; production lines using 24-203 solution with boric acid or borax therefore require pH-stat control and inline viscosity monitoring because the product’s pH window of 4.5–6.5 shifts upward during borax addition and can pass through an irreversible precipitation boundary if the dose is uncontrolled. This sensitivity differs from plasticizer-thickened starch adhesives, which do not show the same borate-diol complexation response.

Paper-coating and water-remoistenable adhesive operations use the product as a film-forming binder where cold dissolution and remoistenability are more important than permanent water resistance. In these converting lines, the solution is metered into a pigment coating color at low PVOH addition levels, typically below 2 parts per hundred parts pigment, and dried surface strength is assessed by IGT pick-resistance testing under ISO 3783. The remoistening step later reintroduces water through a lick roll or spray bar; partial hydrolysis lowers the rewet temperature needed to develop tack. However, dried films remain water-soluble unless a crosslinker is added. The operational limit is therefore clear: permanent water resistance must be designed through crosslinking or overcoating, not expected from the base polymer.

When 24-203 Solution Is Introduced into Emulsion Polymerization as a Protective Colloid

In vinyl acetate, vinyl acetate-ethylene, and acrylic emulsion processes, the solution is introduced as the protective-colloid phase to control particle size, shelf stability, and end-use rheology. The product’s partial hydrolysis and 4.0–5.0 mPa·s viscosity at 4% solids mean that it can be pre-diluted and fed without hot dissolution. The feed configuration should avoid localized high-concentration zones at the monomer addition nozzle; direct feed into a stirred monomer-rich region can create transient viscous skins that later hydrate incompletely. Jacketed stainless steel reactors with pitched-blade agitation are typical; the PVOH phase is usually charged as an initial reactor heel or as an aqueous feed stream, depending on whether the target particle-size distribution is monomodal or bimodal.

The continuous phase viscosity in the final emulsion is governed by PVOH concentration, molecular weight, and the degree of graft formation during polymerization. At higher PVOH solids in the aqueous phase, low-shear Brookfield viscosity rises and shear-thinning becomes more pronounced; inline process viscometers must be calibrated against the specific formulation because the 24-203 solution itself is Newtonian at 4% but the compounded emulsion is not. In published vinyl acetate-acrylic systems, medium-viscosity partially hydrolyzed PVOH levels are commonly observed in the 2–6 phm range, but this window is not a universal specification; particle-size distribution, coagulum, and dry-film water sensitivity must be rebalanced for each monomer set. Published monomer-specific formulation data for 24-203 is limited to supplier technical service trials and production records; therefore, reactor trials are required when replacing a fully hydrolyzed grade or a low-viscosity partially hydrolyzed grade.

The solution’s pH 4.5–6.5 range is close to the optimum decomposition window for persulfate initiators at typical reaction temperatures of 70–85 °C. If the pH is shifted upward by ammonia or sodium bicarbonate buffers, the hydrolysis rate of vinyl acetate increases, and the graft level between PVOH and vinyl acetate can change. The resulting changes in particle-size distribution and latex viscosity are usually larger than those introduced by small variations in the PVOH feed rate. This is a critical threshold conflict in continuous or semi-batch processes where pH control and temperature control interact.

On slasher sizing lines for spun cotton and polyester-cotton yarns, the solution is blended with starch or acrylic size binders at size-box temperatures of 65–85 °C. Typical size-box solids are maintained by refractometric control; PVOH contributes film adhesion to the yarn surface and reduces hairiness without requiring a separate wax or lubricant. Yarn tensile retention is measured by ASTM D2256, and abrasion resistance is evaluated by ASTM D3885 or equivalent loom-stop records. The partial hydrolysis level is an advantage in desizing because the size film can be removed by hot-water washing; however, complete removal requires sufficient water temperature and mechanical action, and residual PVOH on the fabric can interfere with later optical brightener pickup if desizing is incomplete. Desizing of woven fabrics containing 24-203-based size is performed with hot-water washes above 70 °C; cold water below 40 °C rewets the size film but does not fully dissolve it. In reuse systems, the dissolved PVOH can accumulate in the desize bath and alter liquor viscosity, requiring overflow dilution or membrane filtration.

Regulatory Ingredient Limits and Quality-Control Points in Converting Operations

The polyvinyl alcohol ingredient under CAS 9002-89-5 may be referenced in food-contact regulations where PVOH is cleared as an indirect additive, including 21 CFR 175.105, 21 CFR 176.170, and 21 CFR 176.180, but end-use compliance is formulation-specific and depends on the finished article, extractives limits, and use conditions. The solution form does not automatically confer food-contact clearance; converters must obtain the appropriate regulatory declaration from the supplier for the specific lot and application.

Storage of aqueous PVOH solution requires a closed, agitated or recirculated tank at 5–35 °C. Prolonged holding at ambient temperature without biocide protection permits microbial growth, which can reduce viscosity and produce organic acid by-products. Repeated freeze-thaw cycles are outside the product’s operational boundary; freezing can cause local polymer enrichment or phase separation that is not fully reversible by simple remixing. The solution should be pre-filtered through a 100–250 µm bag or cartridge filter before use in coating or spraying operations to remove any skin or gel particles formed during storage. Long-term viscosity drift in aqueous PVOH solutions is normally slow when the solution is stored under nitrogen or another inert gas and protected from light. However, polyvinyl alcohol solutions are sensitive to metal-ion contamination, especially iron and copper, which can catalyze oxidative degradation. Storage tanks and piping for the solution should be constructed of 316L stainless steel or compatible plastics; carbon steel should be avoided unless fully lined because corrosion products accelerate viscosity loss.

Concentrated oxidizing acids, hypochlorite-based cleaning agents, and peroxide-containing oxidizers are incompatible because oxidative chain scission breaks the polyvinyl alcohol backbone and lowers solution viscosity. Equipment cleaned with these materials must be rinsed to neutral pH and confirmed free of residual oxidizer before the product is reintroduced.