| HS Code | 807535 |
| Product Name | Kuraray K-II WN7 41 Water Soluble PVA Fiber |
| Material | Polyvinyl alcohol (PVA) |
| Chemical Family | Synthetic water-soluble vinyl polymer fiber |
| Dissolution Temperature | 70 °C |
| Fiber Form | Staple fiber, cut to short lengths |
| Fineness Dtex | 4.1 dtex |
| Specific Gravity | 1.26 |
| Appearance | White fibrous solid |
| Moisture Regain | Approximately 5% at standard humidity |
| Tensile Strength | Approximately 4.0-5.5 cN/dtex |
| Elongation At Break | Approximately 15-20% |
| Alkali Resistance | Good against dilute alkali |
| Acid Resistance | Resistant to dilute acid; decomposed by concentrated strong acids |
| Solvent Resistance | Insoluble in common organic solvents |
| Biodegradability | Biodegradable; dissolves in water before biological decomposition |
As an accredited Kuraray K-II WN7 41-Water Soluble PVA Fiber (Dissolves at 70°C) factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Available in 20 kg sealed, moisture-proof bags, clearly labeled Kuraray K-II WN7 41 water-soluble PVA fiber dissolving at 70°C. |
| Container Loading (20′ FCL) | 20′ FCL container loading of water-soluble PVA fiber, K-II WN7 41, dissolved at 70°C, safely packed for transit. |
| Shipping | Ship as non-hazardous dry cargo in sealed moisture-proof packaging to prevent premature dissolution. Avoid exposure to humidity and temperatures near 70°C during transit. Use standard freight with proper labeling; keep cool, dry, and away from water sources. Include handling instructions for safe delivery. |
| Storage | Store in a cool, dry, well-ventilated area, away from moisture, humidity, and direct sunlight. Keep in original sealed packaging or a tightly closed container to prevent water exposure and fiber clumping. Avoid storage above 40°C, as elevated heat and moisture may compromise integrity. Ensure area is clean and free from spills. |
| Shelf Life | Store in a cool, dry area away from moisture and heat. Shelf life is typically two years from date of manufacture. |
Kuraray K-II WN7 41 fibre is converted into a water-soluble nonwoven for sealed isolation laundry bags used in hospital and clinical waste handling. The specification centres on a dissolution threshold of 70 °C, which corresponds to the holding phase of operational washer-disinfectors; the nonwoven is manufactured from a 100% PVA fibre furnish at mass per unit area 50–70 g/m². Seam construction uses impulse sealing jaws at 140–150 °C with dwell 0.6–1.2 s; the absence of adhesive prevents insoluble seam residue in drain lines. Compliance within healthcare laundry processing is referenced to EN 14065:2016 for biocontamination control, while physical integrity is evaluated according to ISO 9073-5:2008 burst strength and ASTM D5034-09 grab tensile. Production-scale drying requires a multi-zone flatbed dryer with first-zone temperature no higher than 45 °C, second zone 55 °C, and third zone 62 °C; if any drying zone exceeds 65 °C in the presence of free moisture, the fibre surface becomes tacky and roll blocking occurs within 20–30 min of contact. Storage at relative humidity above 60% demands vapour-barrier wrapping and desiccant inserts because fold creases absorb atmospheric moisture and pre-dissolve before the bag reaches the washer.
The downstream terminal article is a water-soluble isolation bag filled with contaminated surgical drapes, bed linen, or laboratory coats. The filled bag is placed directly into the washer-disinfector without opening; the 70 °C water dissolves the substrate during the wash cycle and releases the load while the PVA liquor passes into the effluent system. Washer programmes operating below 70 °C leave residual seam fragments and gusset gel, a known failure mode on hospital laundry lines with older equipment. The material is unsuitable for steam-autoclave pre-sealing because wet steam at the seal station introduces free water and reduces seam strength. The nonwoven also exhibits incompatibility with continuous hot-melt adhesives: adhesive-bonded seams remain insoluble and create filter blockages. Typical terminal product types include isolation sacks, maternity ward linen bags, and single-use collection bags for laboratory coats.
Machine embroidery on cap fronts, uniform logos, and fashion garments requires a temporary stabiliser with sufficient hoop tension and needle resistance, but removable without leaving fibre residue in dense satin stitch coverage. K-II WN7 41 is formed into carded nonwovens at 25–40 g/m² from 100% PVA fibre. Web formation is carried out by flat carding followed by hydroentanglement at 40–60 bar; a final calender pass at 100–120 °C under 40–60 kN/m line pressure produces a smooth embroidery face and reduces fuzzing. Compliance is anchored to OEKO-TEX Standard 100, product class I or II depending on final garment type, and to Regulation (EC) No 1907/2006 Annex XVII for residual vinyl acetate monomer control. Rinsing after embroidery uses a 70–80 °C bath with 120–300 s dwell; lower-temperature rinse cycles leave stabiliser residue in intersections of high-stitch-density embroidery.
On production-scale multi-head embroidery machines operating at 800–1,200 stitches/min, the backing is applied either as an underlay or as a top sheet depending on seam structure. The primary process bottleneck is premature surface tack when shop-floor humidity exceeds 65% RH; pre-drying at 45 °C for 2 h is required before loading onto the machine. Exposure of the nonwoven to glycol-based machine cleaners must be avoided because glycols plasticise the PVA surface and reduce hoop tension response. After embroidery, the stabiliser is removed in the heated rinse bath; effluent pH is maintained between 6.0 and 8.5 to prevent acid-catalysed acetal formation and to keep dissolution linear. Terminal finished products include embroidered caps, uniform emblems, wedding lace overlays, badge patches, and decorative towel borders.
In wet-laid industrial filter media manufacture, Kuraray K-II WN7 41 is introduced as a low-cut fibre at 2–6 wt% of the dry furnish, with the balance composed of refined wood pulp and, in certain grades, glass or synthetic short-cut fibre. The PVA fibre functions as a temporary wet-lap binder during sheet formation and early drying; after initial drying it can be leached at 70 °C to generate a controlled pore network before resin saturation. Formation trials are conducted according to ISO 5269-2:2004, while dry tensile is checked by ISO 1924-2:2008. Production stock preparation is held at 35–40 °C water temperature to avoid dissolving the fibre before web formation. Headbox consistency is maintained at 0.2–0.5%; the sheet is formed on an inclined wire and passed through a multi-zone dryer where the first zone at 80 °C activates surface tack and the final zone at 120 °C fixes the web structure.
After initial drying, the web is immersed in hot water at 70–80 °C for 10–20 min to remove the PVA fibre, leaving elongated pores that increase filtration permeability while preserving sheet closure. The leached paper is then saturated with phenolic or epoxy resin, cured, and reeled. This downstream sequence is used for automotive oil and fuel filter papers, industrial air intake media, extraction thimbles, and battery separator base papers. The known operating boundary is repulping temperature: if the pulper water is maintained above 60 °C, discrete PVA fibre disappears and binder uniformity drops, so cold or 40 °C repulping water is used. The process is not intended for food-contact tea or coffee paper because full dissolution at brewing temperature would release fibre-derived material into the infusion.
In fully fashioned knitwear production, temporary separation courses are knitted from K-II WN7 41 multifilament between garment panels or at linking edges. The yarn is 100% PVA filament, with linear density 56–112 dtex and filament count 12–24; its wet tenacity is tested by ASTM D2256/D2256M-10. The separation course maintains panel orientation through steam pressing, linking, and initial wet finishing, then is intentionally dissolved after final linking. Garment washing and dimensional change are evaluated according to ISO 6330:2012 and ISO 5077:2007. All wet processing before intentional separation is maintained below 60 °C; any dyeing machine excursion to 70 °C or above destroys the separation yarn prematurely, causing panel misalignment, rework, and stitch distortion. After final linking, the garment is agitated in a 70–80 °C bath for 5–10 min to remove the PVA course. Terminal articles include fully fashioned sweaters, socks, gloves, and linked collar assemblies.
The fibre is incompatible with hot alkaline scouring steps above 60 °C prior to separation; such scouring causes uncontrolled dissolution and knitted panel separation. Batch-to-batch variance in knit tension is controlled by maintaining a yarn package moisture content below 7%; over-conditioned packages develop fibre surface tack and increase knitting resistance. After separation, residual PVA liquor is discharged through standard textile effluent handling, and the final garment is inspected for residual yarn fragments under ultraviolet illumination.
| Application sector | Typical loading | Compliance anchor | Critical processing boundary |
|---|---|---|---|
| Healthcare laundry bag | 100% PVA fibre, 50–70 g/m² | EN 14065:2016; ISO 9073-5:2008; ASTM D5034-09 | Dry below 65 °C; seal at 140–150 °C for 0.6–1.2 s |
| Embroidery backing | 100% PVA fibre, 25–40 g/m² | OEKO-TEX Standard 100; REACH Annex XVII | Rinse at 70–80 °C for 120–300 s; pre-dry at 45 °C for 2 h |
| Industrial filter media | 2–6 wt% of dry furnish | ISO 5269-2:2004; ISO 1924-2:2008 | Repulping water ≤40 °C; leach at 70–80 °C for 10–20 min |
| Knit separation yarn | 100% filament, 56–112 dtex | ISO 6330:2012; ISO 5077:2007; ASTM D2256/D2256M-10 | Wet processing below 60 °C before separation |
| Composite microchannels | 0.5–2.0 vol% of preform | ISO 527-4:2021; ASTM D2734-16 | Cure plateau 150–180 °C; leach bath changed every 2 h |
| Porous ceramics | 1–5 vol% on dry solids | ASTM C373-18 | Green drying 45–60 °C; leach at 70 °C for 30–60 min |
Co-curing a sacrificial PVA weft within carbon/epoxy preforms imposes a narrow processing window between the fibre’s 70 °C aqueous dissolution and the onset of PVA thermal decomposition. K-II WN7 41 is woven or stitched into dry preforms at 0.5–2.0 vol%; the assembly is laid up or injected with a low-viscosity epoxy system and cured at a plateau of 150–180 °C for 60–120 min. The laminate mechanical compliance anchor is ISO 527-4:2021, while void volume before and after dissolution is measured according to ASTM D2734-16. Post-cure immersion in demineralised water at 70 °C for 4–12 h removes the PVA weft and opens channel networks. If the water bath is not exchanged every 2 h, saturation slows dissolution and leaves unbranched channel mouths. Published data for this specific fibre configuration remains limited outside aerospace research and thermal-management laboratory programmes; channel dimensions are therefore verified on each batch by optical microscopy rather than assumed from loading fraction alone.
Terminal product types include composite laminates with embedded microvascular networks for heat exchange, dielectric fluid circulation, and self-healing agent delivery. The known thermal boundary is the cure exotherm: if the laminate temperature exceeds 200 °C, acetic acid evolution and fibre discolouration occur, reducing channel quality. The process is not applicable to matrices requiring post-cure above 180 °C, and the leach cycle must use demineralised water to avoid mineral deposition inside the formed channels.
During porous ceramic green-body preparation, the fibre is mixed into an aqueous alumina or silicon carbide slurry at 1–5 vol% on dry solids; the slurry is either tape-cast onto a polymer carrier or extruded through a single-screw ceramic extruder at 5–10 bar die pressure. The green tape is dried at 45–60 °C, below the dissolution threshold, to retain fibre dimensions. The dried body is then immersed in softened water held at 70 °C for 30–60 min, during which the PVA fibre dissolves and leaves interconnected cylindrical voids. Compliance for porosity is determined by ASTM C373-18 water absorption and bulk density. Terminal products include porous ceramic filter elements, catalyst support substrates, and refractory burner media. A production-scale failure mode is non-uniform leaching when stacked green sheets exceed 10 mm in the bath; spacers of 3–5 mm are required between sheets. Leach water hardness above 100 mg/L as CaCO₃ reduces dissolution rate by surface precipitation, so softened water is specified for the dissolution tank.
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Kuraray K-II WN7 41 is a water-soluble polyvinyl alcohol staple fiber intended for temporary structural support, sacrificial binding, and fiber removal applications in wet-laid nonwovens, papermaking, and textile support systems. The WN7 designation corresponds to dissolution in deionized water at approximately 70°C; the 41 suffix is a producer configuration identifier for cut length and linear density, and the lot certificate should be consulted because secondary published data for the exact suffix may be limited. In neutral-pH aqueous systems, the fiber retains its filamentary identity and mechanical function below 55°C. This thermal headroom permits warm furnish handling, vacuum dewatering, and low-temperature drying before the fiber is deliberately removed in a hot-water extraction stage. The material is not a low-melting binder fiber; its functional transition is solvent-induced dissolution rather than melting, and dissolved PVA remains in the aqueous phase as a polymer solution.
At the molecular level, water diffuses first into the amorphous regions of the PVA fiber, disrupting interchain hydrogen bonds and releasing oriented polymer into solution. The 70°C grade is more thermally resistant than cold-water-soluble PVA grades because the crystalline domains require additional thermal energy and time for water penetration. This characteristic is exploited in production lines where the intermediate web must experience warm processing temperatures without losing the temporary fiber. The dissolution process should be monitored as a function of water temperature, mechanical shear, bath ratio, water hardness, and dissolved polymer concentration, not as a simple melting event.
Dissolution accelerates as free-water temperature rises above 70°C, but practical extraction systems operate at 75–80°C to balance dissolution rate, evaporation, and solution viscosity. In a laboratory immersion test, 1 g of loose fiber in 100 mL deionized water under mild agitation typically loses fiber form within several minutes once the bath reaches 70°C; in dense nonwoven or paper webs, the rate-limiting step is often water ingress through the void structure. Production-scale extraction therefore uses counterflow drum washers, spray bars, or high-shear pulpers that continuously remove the viscous PVA boundary layer from the dissolving fiber surface. In recirculating loops, ultrafiltration or dissolved air flotation may be used to control suspended and dissolved solids. When dissolved PVA concentration approaches 5 wt%, solution viscosity rises and dissolution slows; overflow, dilution, or polymer recovery should be designed into the loop. Water hardness caused by calcium and magnesium ions can retard dissolution and interact with residual finish oils, so softened water is preferred for repeatable cycle times. Keep bath pH between 5 and 8 for routine processing; strong acid hydrolysis or hot alkaline degradation can reduce PVA molecular weight and alter extraction behavior. Boron-containing compounds, including borate salts, should not be present in the dissolution bath because they can crosslink PVA into a gelled network that prevents complete fiber release.
Receiving inspection for the fiber typically includes linear density, cut length, tensile tenacity, elongation at break, moisture content, finish content, and hot-water residue. Conditioning before mechanical testing is performed at 20 ± 2°C and 65 ± 4% relative humidity in accordance with ISO 139. Linear density can be determined by ISO 1973, single-fiber tensile properties by ISO 5079 or ASTM D3822, and moisture content by ASTM D2654. Because the fiber is hygroscopic and becomes tacky at high humidity, storage should be maintained at 10–30°C and not more than 65% RH. Condensation exposure or partial wetting before use can create fiber-to-fiber adhesion that survives conventional dispersion and produces sheet defects. A hot-water residue test can be run by dispersing 5 g of fiber in 500 mL deionized water at 70 ± 2°C for 30 min under mild agitation, then filtering through a 75 µm sieve and drying the retained material at 105°C to constant mass.
| Parameter | K-II WN7 41 | Lower-temperature water-soluble PVA grade | Non-water-soluble high-tenacity PVA fiber |
|---|---|---|---|
| Dissolution onset in deionized water | 70°C | 40–60°C depending on grade | Insoluble below 100°C |
| Maximum wet-processing temperature before fiber loss | 55°C typical | 30–45°C typical | Not limited by aqueous dissolution; thermo-oxidative degradation above 180°C in air |
| Tensile tenacity range | 4.0–6.0 cN/dtex | 3.5–5.5 cN/dtex | 6.0–10.0 cN/dtex |
| Elongation at break | 12–20% | 12–20% | 6–12% |
| Primary selection criterion | Thermal headroom before 70°C release | Low-temperature removal with limited hot processing | Permanent fiber reinforcement without aqueous extraction |
K-II WN7 41 differs from colder-water-soluble PVA grades primarily in the maximum temperature at which the intermediate web can be processed before fiber loss. Grades that dissolve at 25–40°C are unsuitable for furnishes above approximately 35°C because partial dissolution increases white-water viscosity and deposits binder solids on forming fabrics. The 70°C grade permits furnish temperatures of 35–50°C, which lowers water viscosity and improves formation without initiating dissolution. Compared with non-water-soluble high-tenacity PVA fiber, the K-II WN7 41 is unsuitable for durable reinforcement in concrete, curable composites, or geotextiles exposed to water above 50°C because the fiber is intended to dissolve. The selection between WN7 41 and other water-soluble PVA grades should therefore be made by comparing the thermal profile of forming and drying against the dissolution onset, not simply by tensile strength or cut length.
In wet-laid nonwovens, battery pasting papers, and filtration support papers, the fiber is introduced at 0.1–3.0 wt% of furnish solids to provide temporary sheet strength before a permanent binder or coating is cured. Because the cut length is suitable for wet-laid dispersion, it is generally pre-dispersed in a side tank equipped with a high-speed disperser and then metered into the machine chest. On inclined-wire formers running basis weights from 30 g/m² to 120 g/m², the fiber remains intact through vacuum dewatering and through-air drying at web temperatures up to 55°C. The extraction bath is then maintained at 75–80°C with counterflow dilution to keep dissolved solids below 5 wt%. If the dry web has high basis weight or high density, dissolution time is extended; the line speed, drum washer length, or spray-bar flow rate must be adjusted accordingly. Heavy needlepunched batts may require several minutes of submerged residence time because water penetration controls the release rate. After extraction, dissolved PVA accumulates in white water; recirculation viscosity should be monitored, and downstream dryer surfaces should be inspected for film formation that can cause sticking.
In textile support and separation yarns, the fiber can be spun or plied into temporary yarns for embroidery toppings, drawstrings, and hollow-composite mandrel aids. The supporting yarn survives scouring and dyeing operations that remain below 60°C, then dissolves during a final hot rinse at 75–80°C. This behavior is distinct from cold-water yarns that may fail during warm wash cycles and from non-water-soluble PVA yarns that cannot be removed by laundering. In hollow composite ducts, the fiber is placed or braided as a temporary core or mandrel, the resin is cured at a temperature below the dissolution threshold, and hot water is used to remove the core while the surrounding laminate remains intact. The removal step requires access to the fiber surface; closed laminates with limited water exchange may retain undissolved PVA gel if the bath is not replenished or if the laminate cross-section is excessively thick.
The fiber is not recommended for products that must remain dimensionally stable in wet service above 50°C. Aqueous exposure combined with free boron compounds, strong oxidizing agents, or concentrated formic acid can degrade or gel the PVA and should be avoided unless the process specifically anticipates those effects. If storage relative humidity has exceeded 65%, pre-drying and re-opening should be performed before blending or web formation. For food-contact paper and nonwoven end uses, the finished article must be evaluated under FDA 21 CFR 176.170 or EU 10/2011 as applicable; fiber grade alone does not establish compliance. In applications requiring organic solvent resistance or permanent hydrolysis resistance, non-water-soluble PVA or alternative synthetic fibers should be selected.
