Shuangxin SX-IV PVA

Shuangxin SX-IV PVA is a partially hydrolysed poly(vinyl alcohol) resin supplied as a white to pale-yellow granular solid with a bulk density of 0.40–0.60 g/cm³. The product is identified by CAS 9002-89-5 and belongs to the medium-viscosity segment of the Shuangxin PVA series. In the producer’s batch release documentation, the 4% aqueous solution viscosity at 20±0.5°C is reported as 20.0–30.0 mPa·s under GB/T 12010.3-2010, and the degree of hydrolysis is reported as 86.0–89.0 mol% under ISO 15023-2:2009. These figures place SX-IV between cold-water-soluble low-hydrolysis grades and fully hydrolysed high-water-resistance grades. The resin is used where a medium-viscosity film-forming colloid is required in aqueous systems, including surface sizing, textile warp sizing, emulsion polymerization, and water-soluble film casting. Published data for this specific configuration is limited to the producer’s batch certificates and the standard PVA test series; incoming inspection should use agreed limits against a qualified supplier certificate rather than generic literature.

What Specification Boundaries Are Reportable Under GB/T 12010 and ISO 15023-2?

The specification table below consolidates typical batch release boundaries for medium-viscosity partially hydrolysed PVA of the SX-IV class. These ranges are typical, not batch guarantees; the purchaser’s method should be qualified against the repeatability statements in the cited standards.

The Hydration Window Is Narrow Enough to Require Controlled Heating

Solution preparation with SX-IV must follow a thermal and shear sequence that avoids both incomplete swelling and thermo-oxidative degradation. Dry resin particles are slurried in ambient water at a concentration of 4–10% by weight, then heated to 85–90°C at a rate not exceeding 2°C/min in an indirect steam-jacketed vessel. Production-scale mixing should use a sawtooth-type high-speed disperser with a tip speed of 10–15 m/s or an inline high-shear mixer positioned upstream of the hold tank. Batch logs from 500 L to 2000 L vessels show that a hold at 85°C for 30–60 min is required to reach a steady Brookfield viscosity; shorter hold times result in viscosity drift greater than ±5% over the next 2 h as particle hydration completes. The critical processing window is 85±3°C for metered size presses and slot-die coaters: below 82°C undissolved gel particles accumulate at the metering blade and produce streak marks, while above 88°C evaporation thickens the puddle and causes blade-pressure oscillation. At temperatures above 95°C, the solution exhibits progressive viscosity loss and light yellowing associated with thermo-oxidative chain scission. A defoamer is usually required because air bubbles stabilize on the PVA solution surface and create pinholes in cast films.

Temperature control is also critical during transfer lines. At 4% solids, a drop from 85°C to 55°C can raise Brookfield viscosity by a factor of 1.5 to 2.0 depending on shear history. Transfer lines should therefore be heat-traced and sized for a shear rate of 100–300 s⁻¹ to avoid gel layer formation on the wall. In jacketed tanks without baffles, viscosity stratification can occur because the surface cools faster than the bulk; a low-speed gate anchor operating at 10–30 r/min is sufficient to maintain top-to-bottom uniformity.

Unlike fully hydrolysed grades such as 1799, which require solution temperatures above 90°C and are characterized by a hydrolysis level of 99.0–100.0 mol%, SX-IV hydrates at 85–90°C and forms a less crystalline dry film. The lower residual acetate content reduces the minimum film-forming temperature but also raises the equilibrium moisture uptake of the dried film. When substituted for 1799 in warp sizing, the partially hydrolysed grade produces comparable tensile strength at equal add-on but gives a softer size film; when water resistance is the controlling specification, the fully hydrolysed grade remains preferable and the trade-off must be evaluated using the mill’s desizing efficiency. Compared with low-viscosity partially hydrolysed grades in the same producer series, whose 4% solution viscosity is commonly reported in the range 4.0–6.0 mPa·s, SX-IV shows higher film tensile yield stress and lower tendency to migrate into fibrous substrates during drying. The higher viscosity also limits the maximum solids content in spray-dried or gravure coating formulations; SX-IV atomization trials typically require dilution to 4–6% solids, whereas low-viscosity grades can be atomized at 8–10% solids. In vinyl acetate emulsion polymerization, the choice between SX-IV and a lower-viscosity protective colloid shifts the final particle size distribution of the dispersion, measurable by laser diffraction under ISO 13320:2020; higher protective-colloid viscosity at equal stirring power increases the volume-median particle diameter and raises latex low-shear viscosity.

When SX-IV Replaces Starch or Hydroxyethylcellulose in Surface Sizing

When SX-IV is evaluated as a partial or complete replacement for oxidized starch or hydroxyethylcellulose in surface sizing, the controlling variables are size-press solids, puddle temperature, and metering blade loading. Typical pilot runs on a blade-metering size press use 4–8 wt% solids at a puddle temperature of 50–65°C. The PVA film former increases surface strength and reduces dusting, but the magnitude of the IGT pick improvement should be measured according to ISO 3783:2014 at constant ink tack. Because PVA forms a continuous oil-resistant film, the Cobb value measured by ISO 535:2014 may not track starch replacement linearly unless the internal sizing or cationic retention program is held constant. Trials on bleached test liner with 2 kg/t of alkenyl succinic anhydride have shown lower porosity and higher dry pick; however, published data for this specific mill configuration is limited, and each furnish requires a forward trial. The operational advantage over starch is the lower required cook solids and the elimination of enzyme degradation in the holding tank. The trade-off is higher film elongation and a greater tendency to re-wet on the dryer section if the sheet enters the size press at a sheet temperature below 40°C.

In textile warp sizing, SX-IV is used as the film-forming binder in size mixes at 8–14% solids on slashers with 2–4 size boxes. The size-box temperature is maintained at 80–85°C to keep the solution above the gel onset temperature, and the dry add-on on warp yarn is controlled by squeeze-roll pressure and reported as percent dry size on yarn. A higher proportion of SX-IV relative to starch raises abrasion resistance of sized warp yarns, but it also raises shedding and loom-friction risk if the size film absorbs ambient moisture at relative humidity above 70%. Sized-yarn abrasion is evaluated on a Zweigle abrasion tester or equivalent with the supplier’s fixed procedure; no single ISO method covers all weaving-shed conditions, so the mill should correlate laboratory abrasion to loom stops per 100,000 picks.

In remoistenable paper adhesives and water-based laminating adhesives, SX-IV is typically compounded at 8–15% solids with plasticizer levels of 5–15 phr on dry polymer. The high molecular weight of the resin extends open time, but it also raises the low-shear viscosity of the adhesive; pot viscosity at 25°C should be tracked by ISO 2555:2018 and adjusted with water to the target for roll coater or wire-wound rod application. In production trials on a roll-coater line running at 30–80 m/min, film thickness was controlled at 10–25 μm wet, and the dried adhesive showed lower blocking tendency under 40°C and 75% relative humidity than starch-based formulas. However, the PVA film remains moisture-sensitive, and packages intended for tropical storage should include a water-resistant barrier layer or a crosslinker. The use of a borate-free crosslinker, such as a low concentration of glyoxal, can increase water resistance without the irreversible gel risk posed by borax.

Emulsion polymerization uses SX-IV as protective colloid for vinyl acetate homopolymers and vinyl acetate/ethylene copolymers. The polymer is pre-solubilized at 8–12% solids and metered into the reactor so that the protective colloid concentration on total monomer is 4–10 wt% for standard wood-glue emulsions. Because the partially hydrolysed structure contains both hydrophobic acetate and hydrophilic hydroxyl groups, it adsorbs at the poly(vinyl acetate) particle interface and reduces coalescence during reaction and stripping. Reactor torque and heat-transfer data from pilot plants show that substitution of fully hydrolysed PVA with SX-IV lowers prenucleation viscosity but increases final emulsion viscosity at equal percent solids; the final viscosity should therefore be measured at 25±0.5°C with a Brookfield LVF spindle 3 at 12 r/min under ISO 2555:2018. Batch-to-batch drift in emulsion viscosity of ±10% has been observed when the PVA solution is not filtered through a 250 μm mesh before reactor charging.

Water-soluble film formulations based on SX-IV are processed by solution casting or extrusion casting from aqueous dope. The higher degree of polymerization relative to low-viscosity grades raises tensile strength measured by ISO 527-3:2018, but the casting solution must be held at 85–90°C to avoid voids and surface pits. Extruded film from partially hydrolysed PVA requires plasticizer levels of 10–20 phr glycerol or sorbitol; below this range the film is brittle at low relative humidity. The water dissolution time of a 40 μm cast film at 20°C is typically 30–90 s for a fully submerged coupon, but the value is sensitive to water circulation and film orientation. Published film dissolution data for this specific product grade is limited, so end-use validation is required under the intended wash-water temperature and agitation.

Operational Boundaries, Storage Constraints, and Chemical Incompatibilities

The resin should be stored in sealed bags at temperatures below 30°C and relative humidity below 60%. Moisture uptake at higher relative humidity can cause particle caking and weigh-feed blockage on continuous mixing lines; pre-drying is required at ambient relative humidity above 60% and is typically conducted at 40–50°C for 2–4 h in a forced-air dryer. SX-IV is incompatible with strong oxidizing agents, including hypochlorite and persulfate streams at concentrations above 1%, and should not be mixed with borax or boric acid because borate complexation crosslinks the diol segments and forms an irreversible gel. The material is stable in neutral and mildly acidic solution, but prolonged heating above 90°C in air will produce a progressive yellowing and a drop in solution viscosity due to chain scission. For metering-pump sizing lines, the solution should be filtered through a 177–250 μm stainless-steel screen immediately before the size press or coating station to protect the precision gap and reduce streaking.