Sinopec-SVW SS-7-fibra PVA solúvel em água de baixa temperatura

Sinopec-SVW SS-7-Low-Temperature Water Soluble PVA Fiber is a polyvinyl alcohol staple fiber designed for ambient-water dissolution in temporary binder, fugitive yarn, and sacrificial-spacer applications. The product is supplied in cut lengths of 4 mm, 6 mm, and 12 mm with a nominal linear density of 1.7 dtex ± 0.2 dtex measured under ISO 1973:2021. Its low-temperature designation derives from a dissolution onset near 20 °C, in contrast to conventional hot-water PVA grades that require 60 °C to 80 °C. The fiber is intended for dry-lay nonwovens, wet-lay papermaking, stitch-bonded fabrics, and composite preforms where temporary support must be removed without exposing the core substrate to thermal stress exceeding 40 °C.

The polymer matrix is a partially hydrolyzed polyvinyl alcohol with an alcoholysis degree in the 88–92 mol% range. This compositional window reduces crystallite size and increases the amorphous fraction available for water ingress relative to fully hydrolyzed ≥99 mol% grades. The fiber is wet-spun and drawn under controlled conditions that preserve dissolution latency while maintaining sufficient tensile integrity for carding and needle-punching. Dry tenacity is intentionally set at 3.8–4.6 cN/dtex; this is below the 5.5–7.0 cN/dtex typical of high-crystallinity PVA staple and must be considered when temporary fabrics carry mechanical load during forming.

What Dissolution Behavior Is Observed in Cold-Water Extraction?

Under laboratory conditions using 1% w/w fiber in deionized water at 20 °C and 200 rpm agitation, SS-7 disintegrates within 30 min and yields a clear solution in 90–120 min. Dissolution rate increases as pH shifts from neutral to mildly alkaline; at pH 8–9, complete dissolution time falls to 45–60 min. Acidic baths below pH 4 slow swelling and may produce a gel residue unless shear is maintained. The dissolved polymer contributes to chemical oxygen demand in process water; closed-loop systems should monitor COD load because PVA is biodegradable under specific acclimated activated sludge conditions but is not removed in short conventional flocculation without biological adaptation.

Dissolution kinetics follow a two-stage mechanism: initial water diffusion into amorphous domains and subsequent disentanglement of polymer chains at the fiber surface. The apparent activation energy for dissolution in the 10–40 °C interval is dominated by polymer chain mobility rather than chemical degradation. In a pilot-scale continuous dissolution tank with a 1.5 m³ working volume and a pitched-blade turbine at 120 rpm, a 1% w/w SS-7 slurry is reported to reach greater than 95% single-fiber disappearance in 25 min at 25 °C; the same tank requires 45–60 min when the agitator is reduced to 60 rpm, indicating that shear-assisted removal of the hydrated surface layer is rate-limiting once the fiber has swollen.

Mechanical, Thermal, and Regulatory Specification Range

The values in the following table are manufacturer-published typical data for SS-7 staple, not batch release guarantees. They are intended for process design; actual results may vary with cut length, finish level, and conditioning history.

Production-scale dry-lay processing is sensitive to moisture content and crimp stability. On a roller-top card with cylinder speed 80–120 m/min, conditioning SS-7 at 20 °C and 55% RH for 24 h is recommended to reduce fly and static clumping. If ambient RH drops below 35%, non-ionic antistatic agents should be evaluated for compatibility with PVA dissolution residue. Cationic antistats can precipitate anionic sizing or contaminant fractions in recycled water and are not recommended without filtration trials. Crimp loss above 30% of incoming crimp frequency during prolonged recirculation can reduce web uniformity, particularly at cut lengths of 4 mm.

In wet-laid nonwovens, addition of 2–10 wt% SS-7 provides temporary green strength. A subsequent cold-water extraction at 15–25 °C removes the PVA component without the curling or shrinkage typical of hot-water extraction above 60 °C. The dissolved fiber can increase viscosity of the white water; for sheet forming on a 300 mm laboratory sheet former, a 5 wt% addition is reported to increase wet-web tensile index by 15–20% relative to the all-cellulose control. After full dissolution, tensile index returns to control levels; published data for this specific configuration is limited to laboratory forming and the effect is dependent on basis weight and refining level.

When Cold-Water Solubility Replaces Heat-Activated Binder Systems

SS-7 is deployed when heat-activated PVA or hot-water-soluble fibers would impose unacceptable thermal load on heat-sensitive substrates. In embroidery backing and water-soluble nonwoven interlinings, the fiber is processed into a support web and then removed in a cold-water rinse at 20 °C after stitching. For stitch-bonded fabrics, the fiber may be used as a fugitive insertion yarn; the final composite is scoured in a rotary drum washer at a bath temperature of 20 °C to 25 °C with a residence time of 20–40 min, depending on fabric weight and liquor ratio. A liquor ratio of 1:20 is typical; lower ratios require circulation rather than static soaking because the dissolved PVA creates a viscous boundary layer at the fiber surface. High-shear dispersion of SS-7 in aqueous slurry should be conducted at ≤ 15 °C if immediate dissolution is not intended; above 20 °C, the fiber surface hydrates rapidly and prolonged mixing can foul impellers with stringy gel phase.

Because the fiber dissolves at 20 °C, it can be combined with heat-sensitive fibers such as polylactic acid, polyhydroxyalkanoate, or protein-based fibers that would hydrolyze or denature in hot-water extraction. The spin finish applied to SS-7 is a non-ionic surfactant system selected to be water-soluble and to leave minimal residue after dissolution. Finish-on-fiber is typically 0.2–0.5% by weight. In high-purity wet-lay applications, a pre-wash at 10 °C for 5 min removes surface finish before the final dissolution step, reducing foam and COD load in the extraction bath.

The principal difference from conventional hot-water PVA fiber is the trade-off between dissolution temperature and dry tenacity. SS-7 exhibits dry tenacity of 3.8–4.6 cN/dtex, while fully hydrolyzed PVA staple typically reaches 5.5–7.0 cN/dtex. In a comparative immersion test under ISO 5079:2020 wet-conditioning, SS-7 retains less than 20% of its dry tenacity after 60 s in water at 30 °C, whereas conventional hot-water PVA retains over 80%. Against plasticizer-modified cold-water PVA copolymer fibers, SS-7 avoids fugitive plasticizer additives and maintains plasticizer content below 0.1% w/w, which reduces migration and surface tack during storage.

SS-7 is not an ethylene-vinyl alcohol copolymer fiber; EVOH is not water-soluble and is used as an oxygen barrier. SS-7 is also distinct from polyvinyl acetate fiber, which is hydrophobic and requires solvent or saponification. These distinctions are relevant when specifying sacrificial fibers for water-removable composites because only PVOH with controlled hydrolysis and crystallinity displays the required cold-water fugitive behavior.

Avoid Borate Additives, Excessive Humidity, and Oxidizing Agents in SS-7 Processing

SS-7 should be stored in sealed polyethylene-lined containers at or below 30 °C and 60% relative humidity. Moisture regain at 65% RH is 8–12%; absorbed water plasticizes the fiber and can cause premature surface tackiness, which degrades carding and opening. If bags are exposed to high humidity for more than 24 h, pre-drying in a forced-air oven at 50 °C for 4 h is advised. Pre-drying temperatures should not exceed 70 °C because the fiber surface may soften and fuse at cut ends.

Borate-containing additives, including borax and borated flame retardants, are contraindicated because borate crosslinks the PVA diol groups and shifts the dissolution temperature upward. Strong oxidizing agents such as sodium hypochlorite above 0.5% active chlorine degrade the polymer backbone and reduce fiber tenacity before dissolution. The fiber is not recommended for continuous use in acidic baths below pH 4 unless high-shear dissolution is designed, because gel residues may form. It is also not suitable for load-bearing wet applications after immersion; wet tenacity falls rapidly and the fiber loses structural function once swelling begins.

The supplier provides an SDS indicating no classification under EU CLP and no SVHC above 0.1% w/w under REACH. For food-contact uses, the final article must be evaluated by the converter against the relevant authorization in 21 CFR 177.1670, because fiber residues and dissolution by-products are article-specific. Airborne fiber dust should be controlled under local dust explosion guidance; combustible dust testing according to ASTM E1226 provides explosion severity data when the fiber is dry and finely divided. The dissolved polymer exhibits a Brookfield viscosity of 20–28 mPa·s for a 4% aqueous solution at 20 °C, determined with a spindle LVT viscometer at 60 rpm. This viscosity is low enough for subsequent filtration through 10 µm absolute filters but high enough to alter white water rheology at concentrations above 1%; process engineers should account for viscosity when specifying extraction pumps and heat exchangers.