Sinopec-SVW SS-4-fibra PVA solúvel em água de baixa temperatura

Sinopec-SVW SS-4-Low-Temperature Water Soluble PVA Fiber is a low-temperature water-soluble polyvinyl alcohol fiber supplied as cut staple for wet-laid nonwovens, papermaking furnish, and temporary textile scaffolding. The grade designation SS-4 identifies a polymer morphology engineered for aqueous dissolution at lower process temperatures than conventional hot-water PVA staple, although batch-specific dissolution onset must be confirmed against the manufacturer certificate of analysis. The fiber is based on polyvinyl alcohol, CAS 9002-89-5, with controlled residual acetyl content and lower crystallinity than standard PVA grades. Published quantitative dissolution profiles for SS-4 in finished nonwoven constructions remain limited; the product should be qualified on production-scale equipment using the intended fabric basis weight, water temperature, and mechanical agitation.

Class-level physical properties for low-temperature water-soluble PVA staple are characterized by linear density in the range 1.0–2.2 dtex, tenacity of 3.5–6.0 cN/dtex, and elongation at break of 15–30% when tested under ISO 1973:2021 and ISO 5079:2020. These ranges represent the general product class; SS-4-specific values for cut length, finish, and dissolution temperature require certificate-of-analysis review. Cut lengths commonly supplied for wet-laid applications are 4–12 mm, while textile temporary scaffolds may use 38–51 mm. Batch-to-batch variability in dissolution onset can arise from minor shifts in acetyl content and heat treatment; incoming inspection should include dissolution verification rather than relying solely on grade name.

What Governs Residual Fiber Count in Low-Temperature Scouring?

Residual fiber count after dissolution is governed by water temperature, water exchange rate, web density, and residence time, not by the fiber solubility grade alone. In a suction drum washer, water viscosity at 20 °C is approximately 1.0 mPa·s, while at 40 °C it declines to approximately 0.65 mPa·s; this difference can reduce convective penetration through dense nonwoven webs. If basis weight exceeds 80 g/m², interstitial water velocity often becomes the limiting factor because dissolved polyvinyl alcohol must be transported from the fiber surface through the void structure. Production-scale observation shows that shower temperature alone is insufficient when total water exchange is below 3–5 L/kg of fabric; published data for SS-4 in this configuration is limited. Open-width pad-steam ranges and rotary drum thickeners require different dwell-time profiles because mechanical nip pressure and web support alter retained water.

For low-temperature PVA staple, dissolution is surface-area-limited when water exchange is sufficient. The fiber diameter is typically 12–20 µm for 1.0–2.2 dtex PVA; smaller fibers dissolve faster because the diffusion path length is shorter. Wet-laid nonwovens containing high surface area furnish may therefore exhibit faster PVA removal than carded webs of the same basis weight. If the fiber is embedded between hydrophobic synthetic fibers, local water penetration can be hindered, leaving discontinuous PVA residues at junctions; mechanical agitation, nonionic surfactant addition, or extended immersion can improve removal. Published data for SS-4 in hydrophobic fiber blends is limited; laboratory extraction data should be generated at the intended blend ratio and web density.

Quantitative evaluation should follow a gravimetric extraction procedure in deionized water at the intended process temperature, followed by oven drying at 105 °C and reporting as mass loss. No harmonized ISO method currently exists for polyvinyl alcohol sacrificial fiber content in nonwovens; therefore, the internal method must define agitation rate, water-to-fabric ratio, extraction vessel geometry, and endpoint criterion. Without such controls, residual fiber measurements may differ between laboratories by more than the specification limit for low-temperature grades.

Wet-laid nonwoven production employs SS-4 as a sacrificial pore former, with addition levels typically adjusted between 5 wt% and 20 wt% based on target pore diameter and sheet tensile retention after dissolution. In furnish preparation, the staple is dispersed with cellulosic or synthetic fibers in a hydrapulper; because low-temperature grades soften or partially swell at lower temperatures, the pulper water temperature must remain below the specified dissolution onset. Process control should include online turbidity monitoring of white water to detect premature fiber dissolution during stock circulation. Retention aids and cationic wet-strength resins can modify fiber surface charge and dissolution behavior; jar testing under production shear conditions is required before full-scale use. After sheet formation, the fiber is removed in a low-temperature extractor or on the papermachine wire section if the stock temperature can be controlled. Published data for SS-4 addition in specific furnish formulations is limited; pilot trials on the target papermachine are the only reliable qualification route.

Dissolution Temperature versus Wet-Lay Process Water Heat Input

Replacing a hot-water PVA fiber with a low-temperature grade alters the energy balance and the processing window. Because water heating represents a significant fraction of wet-laid line energy input, the SS-4 grade permits lower extractor temperatures, but the lower temperature reduces polymer chain mobility and can increase residence time. Comparative class data are summarized below. The values are class-typical ranges assembled from publicly available literature and should not replace the manufacturer certificate of analysis for SS-4.

Relative to hot-water PVA fiber, SS-4 shifts the process risk from thermal damage to premature dissolution during stock circulation and drying. The lower temperature requirement permits use with heat-sensitive polyolefin or bicomponent binder fibers that shrink above 65 °C. However, the same sensitivity narrows the safe dryer temperature window; dryer cans and through-air dryers must be profiled so the web temperature remains below the dissolution onset until the intended extraction step. Production-scale suction drum washers with countercurrent water flow can maintain inventory levels; batch machines with static water often show slower PVA removal because local dissolved polymer concentration rises and suppresses further dissolution.

In embroidery base fabrics, the fiber functions as a temporary matrix that is removed after stitching to leave dimensional stability during the embroidery operation. Low-temperature solubility is advantageous when the base fabric includes elastomeric yarns or heat-set polyester that would lose structure at conventional 60–90 °C wash temperatures. The fabric is typically needle-punched or chemically bonded, and the PVA staple may be blended with cellulosic fibers at ratios determined by the required handling stiffness. Removal after embroidery uses a cold-water rinse or a gentle drum washer below 40 °C; residual PVA is assessed by stiffness loss and gravimetric mass loss. Published data for SS-4 in embroidery base constructions is limited; production trials should evaluate stitching speed, needle penetration, and wash-off completeness.

When Replacement of Hot-Water PVA Fiber in Papermaking Furnishes Is Evaluated

Papermaking furnishes use water-soluble PVA fiber to create temporary wet strength or as a binder for specialty papers; low-temperature grades are evaluated where wet pressing and drying temperatures cannot complete solubilization. The key process conflict is that low-temperature solubility can reduce fiber integrity during stock preparation if pulper water temperature exceeds the onset; cold-water pulpers operating at 15–20 °C are required. Retention in the sheet before the drying section depends on fiber length and stiffness; if the fiber partially swells, it may collapse and reduce void volume. Freeness and retention should be monitored according to ISO 5267-1 and a dynamic drainage analyzer because low-temperature PVA fiber can alter fines retention and sheet porosity.

On a fourdrinier papermachine, the low dissolution temperature of SS-4 can create a conflict during wet pressing if the felt water temperature rises above the grade onset. Press section water is often recycled; its temperature may exceed 40 °C in closed water loops, causing premature PVA dissolution and sheet defects. This failure mode is observed as sticky deposits on press felts and reduced sheet release. Mill experience with hot-water PVA grades does not transfer directly; low-temperature SS-4 requires press section water temperature control, felt conditioning with non-dissolving surfactants, and possibly split loop water management. Published data for SS-4 in closed-loop papermachine systems is limited; a machine trial with felt life monitoring is necessary.

Compared with non-water-soluble high-tenacity PVA fiber used for concrete reinforcement, SS-4 has significantly lower tenacity and is not a load-bearing reinforcement. Data sheets for standard high-tenacity PVA fiber specify tenacity above 10 cN/dtex, while SS-4 class ranges remain below 6.0 cN/dtex; that tenacity gap defines the application boundary. Compared with hot-water PVA grades, the low-temperature product allows scouring energy reduction but introduces stricter stock preparation temperature control. Compared with starch or polyvinyl acetate binder fibers, the fiber form provides structural support during wet-lay and leaves a defined cylindrical pore after dissolution.

Thermal history during drying modifies dissolution onset irreversibly.

Thermal history during drying modifies dissolution onset irreversibly. If PVA fiber is exposed to dryer temperatures above the glass transition or prolonged annealing, crystallinity increases and low-temperature solubility can be lost. This failure mode is recognized in low-temperature PVA fiber processing: a through-air dryer profile that overheats the web before the extraction step can shift the fiber from low-temperature soluble to partially insoluble, leaving residues on downstream rolls. Water-soluble PVA fiber is hygroscopic; storage above 65% RH can cause surface tack and clumping, especially in humid seasons. Pre-drying at 40–50 °C for 2–4 h may be required before web opening if bags have been exposed to moisture. Avoid combination with borate-based additives, such as borax or boric acid, because the diol units in PVA form reversible crosslinks that raise the dissolution temperature; avoid strong oxidizing agents, concentrated acids, and cationic polymers that can precipitate the water-soluble PVA interface. Incompatibility with aluminum sulfate at acidic pH is also reported in papermaking systems, where alum can reduce PVA solubility by forming complexes; jar testing is required before alum addition to PVA-containing furnish.

Regulatory inquiries should confirm the manufacturer’s REACH registration for the specific grade; RoHS Directive 2011/65/EU does not directly apply to PVA fiber unless incorporated into electrical equipment. Food-contact use requires separate review of polymer status and fiber finish under 21 CFR. These regulatory instruments do not replace the need for batch-level technical data from the manufacturer.