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

Sinopec-SVW SS-4(L)-Low-Temperature Water Soluble PVA Fiber is supplied by Sinopec Sichuan Vinylon Works as a polyvinyl alcohol staple fibre engineered for temporary binder and sacrificial reinforcement functions in low-temperature aqueous process environments. The model designation SS-4(L) identifies a low-temperature dissolution grade; the parenthetical L is the supplier’s marker for a dissolution onset below 40 °C in neutral deionised water under gentle mechanical agitation. Representative manufacturer-published values include a linear density of 1.5 dtex ± 0.2 dtex measured by ISO 1973:1995, cut lengths of 4 mm and 6 mm, dry tenacity not lower than 3.5 cN/dtex and elongation at break between 20 % and 30 % under ISO 5079:1995. The product is used in wet-laid nonwoven, papermaking, hydroentangled preform, textile sizing, and embroidery backing processes. All values are representative lot data, not specification limits; current batch certificates should be reviewed for the exact dissolution profile, residual acetyl content, and cut-length distribution.

The product is not a direct substitute for high-tenacity structural PVA fibre. Dry tenacity is lower because molecular orientation is deliberately reduced to permit low-energy dissolution. The grade should be specified only when cold-water removal or low-temperature binder activation is the controlling process variable.

What Low-Temperature Dissolution Threshold Distinguishes SS-4(L) from Standard Water-Soluble PVA Staple Fibre?

Standard water-soluble PVA staple fibre typically requires process water at 60 °C to 95 °C to lose fibrous geometry, while SS-4(L) dissolves at or below 40 °C. The lower activation threshold is produced by a higher degree of hydrolysis and lower crystalline order; the supplier does not publish the full comonomer or thermal history. This difference reduces the wet-end energy required for binder activation but also removes the safety margin that higher-temperature grades provide against incidental heat. The fibre is therefore specified only when the downstream process can hold forming, pressing, and recirculation temperatures below 35 °C. In systems that can do so, SS-4(L) replaces starch or latex binders and avoids the need for steam-heated white water. The lower dry tenacity of ≥ 3.5 cN/dtex is a further differentiator: high-tenacity water-insensitive PVA fibre commonly reports 6–9 cN/dtex, so SS-4(L) is not a load-bearing reinforcement substitute.

The dissolution-onset test is supplier-specific because no ISO method fully captures the transition from intact staple to homogeneous solution under mill conditions. Users should request the internal method, stirring speed, and endpoint definition. Published data for exact current SS-2 series values should be confirmed against the Sinopec-SVW technical data sheet.

Hydroentangled and Needle-Punched Preform Reinforcement

For drylaid preforms that are subsequently hydroentangled, SS-4(L) is blended with polyester or polypropylene staple at 5 wt% to 15 wt%. The fibre remains coherent during opening, carding, and pre-needling; dry frictional heating at needle densities above 800 punches/cm² may soften the fibre surface, though published data for this specific configuration is limited. Hydroentanglement at water pressures from 80 bar to 120 bar requires process water below 35 °C to avoid dissolved PVA accumulation in the recirculation loop. Jet strips should be inspected every 4 h during long runs because PVA surface gel can accumulate in nozzle tips and reduce jet impact force. Fabric breaking force is evaluated by ISO 9073-3 or ASTM D5035-11. This grade is limited to preforms in which final cold-water extraction is acceptable; residual surface dissolution can alter fabric hand and increase stiffness variability across the web.

Wet-laid nonwoven manufacturing uses SS-4(L) as a partial or complete binder fibre at 2 wt% to 20 wt% on dry furnish. The fibre disperses in water at 0.1 % to 0.5 % consistency without surfactant pre-treatment when dispersion temperature is kept at 20–30 °C. A stock temperature above 40 °C initiates surface gelation and raises white-water viscosity. After sheet formation, binder activation is carried out at 60–90 °C for 30–120 s in the drying section; the resulting tensile index is measured by ISO 1924-2 and water absorption by ISO 535. Dryer activation at 70–80 °C for 60 s is typical for lightweight sheets at 20–40 g/m² basis weight; heavier sheets require longer dwell. The dryer profile should include a gradual ramp rather than a rapid shock to avoid binder migration to the sheet surface. The principal process conflict is recirculated white water: if tray water approaches 40 °C, dissolved PVA raises Brookfield viscosity and increases wire contamination. At 5 wt% dissolved PVA in water at 25 °C, viscosity can exceed 50 mPa·s, causing sheet defects and press-section picking.

When Excess Process Heat and Humid Storage Compromise the Dissolution Window

Excess process heat is the primary boundary condition for SS-4(L). Headbox temperatures should be held at 25–30 °C on twin-wire formers; vacuum pump heat and drying-hood blow-back can add 5–10 °C to the white-water loop, pushing the system toward the 40 °C dissolution threshold. If dissolved PVA accumulates, the wet-web tensile index decreases and felt cleaning frequency increases. Storage is a second boundary: the fibre should be kept in sealed moisture-barrier packaging at ≤ 30 °C and relative humidity below 60 %. Exposure to RH above 60 % for more than 24 h can produce tacky fibre surfaces and clumping in bale openers. Pre-drying may be required at 40–50 °C for 2 h before use, but drying air must remain below 50 °C to avoid premature fibre gelling. Conditioning for physical property verification should follow ISO 291 atmosphere A or B. Warehouse management should follow first-in-first-out inventory because aged fibre may show a widening dissolution temperature distribution if the moisture barrier is compromised.

Borate-Mediated Complexation Delays Aqueous Dissolution in Sacrificial Textile Structures

Controlled addition of sodium tetraborate or boric acid retards the dissolution of SS-4(L) through didiol complexation with the 1,3-hydroxyl groups of PVA. This mechanism is used to retain temporary strength during intermediate processing and then remove the fibre by cold-water washing. A borate concentration of 0.1 wt% to 0.5 wt% on fibre weight shifts the observed dissolution onset upward by 15–30 °C, depending on pH and calcium hardness. The treatment bath should be maintained between pH 8.5 and 9.5; below pH 8.0 complexation is weak, and above pH 10.0 fibre surface swelling becomes excessive. Bath pH is measured by ISO 10523. Uncontrolled borate carryover from other additives can cause gel specks in wet-laid sheet and should be monitored through white-water total organic carbon and sludge dewatering tests. Published data for this specific configuration is limited, so mill trials should include worst-case pH and temperature excursions.

In textile sizing and embroidery backings, SS-4(L) functions as a temporary strength carrier that is removed in a cold-water scour at 20–30 °C. Warp sizing formulas containing 10–20 g/L of the fibre or its dissolved PVA can be removed without enzymatic desizing, reducing chemical oxygen demand compared with starch or acrylate sizes. Conventional textile PVA sizes require scour baths at 80–95 °C; the low-temperature grade therefore reduces energy input but yields a lower film strength. High-speed weaving above 800 m/min or abrasive warp yarns may require a secondary reinforcing polymer, because the dry film strength of the low-temperature grade is below that of high-tenacity PVA size films. Slash room humidity should be controlled below 60 % to prevent tack development on sized yarns.

White-water and effluent treatment from SS-4(L) processing must account for dissolved PVA as a soluble organic fraction. Dissolved PVA is poorly removed by conventional chemical coagulation unless aluminium sulfate or polyaluminium chloride is applied; membrane bioreactor degradation is possible, but kinetic data are site-specific. The dissolved PVA contributes to chemical oxygen demand and can increase foaming in activated sludge. Published data for this specific configuration is limited, and discharge permits should be reviewed before large-scale substitution.

Compliance documentation should include a current REACH registration and a supplier safety data sheet. The product is not classified as dangerous under CLP Annex I, but the supplier SDS must be checked for any national variations. Food-contact use is not automatic; verification under EU 10/2011 migration testing or a relevant national food-contact regulation is required. No medical implant use should be assumed, and no USP Class VI data is supplied for this fibre grade.