CCP PVA BF-17W

Designation CCP PVA BF-17W identifies a partially hydrolysed polyvinyl alcohol resin (CAS 9002-89-5) produced by Chang Chun Petrochemical Co., Ltd. The grade is delivered as a white to off-white granular powder with a degree of hydrolysis of 87.0–89.0 mol% (determined per ISO 15023-1:2001), a 4% aqueous solution viscosity at 20 °C of 20.0–26.0 mPa·s (ASTM D1343-95, Brookfield LVF, spindle No. 1, 60 rpm), and a solution pH of 5.0–7.0. Residual volatile matter does not exceed 5.0 wt% (ISO 3251:2019), and sulphated ash is held below 0.5% (ISO 3451-1:2019). In contrast to fully hydrolysed CCP PVA types such as BF-05 (degree of hydrolysis 98.0–99.0 mol%) or high-viscosity BF-24 (43.0–49.0 mPa·s), the residual acetyl content of 11–13 mol% in BF-17W reduces inter-chain hydrogen bonding density, lowering the crystalline fraction to approximately 30–40% and enabling cold-water solubility. Films cast from 10% aqueous solution and dried at 23 °C/50% RH exhibit a tensile strength of 48–52 MPa and elongation at break of 180–220% (ASTM D882-18), while fully hydrolysed grades under identical conditions typically develop tensile strengths exceeding 70 MPa with elongation values near 100%. The combination of moderate molecular mobility and controlled hydrophilicity positions BF-17W as a protective colloid in emulsion polymerisation and as a flexible film former in textile sizing where adhesion to hydrophobic fibres must be balanced against size removal efficiency.

In surfactant-free vinyl acetate homopolymerisation conducted in a jacketed 50 L glass-lined reactor equipped with a pitched-blade turbine agitator operating at 120–150 rpm, BF-17W is fed as a 10% aqueous solution into the initial charge at 4.0–6.0 wt% relative to the total vinyl acetate monomer. Semi-batch monomer addition over 3.5–4.0 h at 68–72 °C with a redox initiator system (H₂O₂/tartaric acid, molar ratio 1:0.6) triggers grafting of poly(vinyl acetate) chains onto the PVA backbone via hydrogen abstraction at the methine carbon. The resulting amphiphilic graft copolymer adsorbs irreversibly onto nascent polymer particles, generating a steric stabilisation layer that limits particle diameter to 200–350 nm Z-average as measured by photon correlation spectroscopy (ISO 22412:2017). When the same charge of fully hydrolysed PVA (e.g., BF-05) is substituted under identical conditions, the lower grafting frequency—attributable to the higher crystallite content in the aqueous phase—yields a broader particle size distribution spanning 400–800 nm and a viscosity inversion point delayed by 25–35 min. Finished emulsions stabilised with BF-17W consistently deliver a low coagulum fraction (<0.05% on total solids, ISO 4576:1996) and maintain an apparent viscosity of 3 000–8 000 mPa·s (Brookfield RVT, spindle No. 4, 20 rpm) at 55% solids content without the addition of anionic surfactants. The absence of free surfactant minimises foam formation during application and permits direct formulation of wood adhesives meeting EN 204-D3 durability requirements after addition of a 0.5% aluminium chloride crosslinker.

What Limits the Minimum Film Formation Temperature of BF-17W Compared to Fully Hydrolysed Copolymer Grades?

The minimum film formation temperature (MFFT) of an aqueous BF-17W dispersion, measured on a gradient-heated copper bar per ISO 2115:1996, registers at <0 °C when plasticised with 5–10 wt% glycerol or triethylene glycol. In the same test, a fully hydrolysed PVA of equivalent viscosity grade requires a plasticiser loading of 15–20 wt% to depress the MFFT below 10 °C. The difference originates from the acetyl side groups, which act as internal plasticisers, expanding free volume and shifting the glass transition temperature of the amorphous phase from approximately 85 °C (dry BF-05) to 55–60 °C for BF-17W as measured by differential scanning calorimetry at 10 K/min under nitrogen (ISO 11357-2:2020). Below 5 °C, however, water plasticisation becomes dominant, and the mechanical coherence of the coalesced film depends on the degree of hydrolysis rather than added plasticiser content. Oscillatory shear rheometry on a stress-controlled rheometer (parallel-plate geometry, 25 mm diameter, 1 mm gap) reveals that a 15% aqueous BF-17W solution exhibits a gelation onset temperature of 8–12 °C at 1 Hz and 1% strain, whereas a comparable BF-05 solution gels at 28–32 °C. These thresholds dictate the lower temperature boundary for slot-die coating of paper where a coherent wet film must be maintained: BF-17W can be applied at stock temperatures as low as 15 °C, while fully hydrolysed grades demand pre-heating to 40 °C to avoid premature gelation in the coating head. Despite this advantage, the presence of residual acetate groups imparts a measurable cold-water tack that increases blocking tendency in re-reeled paper stored at pressures above 0.5 MPa and temperatures exceeding 30 °C, a limitation addressed through surface dusting with maize starch at 0.2 g/m² or incorporation of 3–5 wt% urea into the coating formulation.

Warp Sizing on High-Speed Air-Jet Looms

Articles defined by the combination of high film elongation and moderate tensile strength make BF-17W a candidate for warp sizing of 100% cotton and polyester/cotton (65/35) ring-spun yarns processed on air-jet weaving machines operating at insertion rates beyond 1 200 m/min. In a typical size box configuration—two-cylinder squeeze unit, squeezing pressure 0.6–0.8 MPa, size temperature 85–90 °C, and a size concentration of 8–10% solids—BF-17W deposits a uniform film with add-on ranging from 8–12% owf. The film exhibits a hairiness index reduction of 65–80% (Zweigle G 566) and a yarn-to-metal friction coefficient (μ) of 0.22–0.28 measured at 100 m/min against a polished steel peg (ASTM D3108/D3108M-13). In comparative weaving trials monitored under identical loom settings (Picanol OMNIplus 800, 850 rpm, 60 ends/cm), published data for this specific configuration is limited; however, laboratory abrasion testing using a reciprocating yarn-on-yarn abrasion tester (stroke 5 cm, 60 cycles/min) indicates that BF-17W-sized yarns withstand 2.2–2.8 times more cycles to failure than yarns sized with oxidized corn starch at equivalent add-on, a result attributed to the lower cohesive energy density of the partially acetylated film allowing inter-fibre movement at shed crossing without adhesive rupture. Because polyvinyl alcohol lacks specific adhesion to polyester, a 20% blend of an acrylic copolymer size (Tg −10 °C) is required to achieve adequate adhesion on 65/35 blends; the final size paste maintains a viscosity below 50 mPa·s at 85 °C (Brookfield LVF, spindle 1, 60 rpm) and does not skin in the size box, even after 4 h continuous running. Desizing is accomplished with hot water at 80 °C in a single wash step, leaving residual size content below 0.2% owf, meeting the requirements for subsequent reactive dyeing with Remazol-type dyes.

In remoistenable adhesive applications, a 35% aqueous solution of BF-17W is cast onto 80 g/m² kraft liner at a coat weight of 12–15 g/m² (dry) using a reverse gravure coater. Open time at 23 °C/50% RH reaches 25–30 s before the film loses tack, a window sufficient for envelope sealing on high-speed insertion lines. Bond strength to paper, measured as 90° peel adhesion (ASTM D3330/D3330M-04, method F), ranges from 2.8–3.5 N/cm, with paper substrate failure observed above 3.2 N/cm. By comparison, a fully hydrolysed grade such as BF-05 fails to redisperse in cold water and requires activation temperatures above 60 °C, rendering it unsuitable for ambient- use remoistenable coatings. The hygroscopic nature of BF-17W, however, necessitates storage of coated sheets at relative humidity below 60% to prevent premature activation and blocking; if ambient humidity exceeds 65%, pre-drying the base paper to 3% moisture content and packing with silica gel desiccant sachets are required.

When Ambient Relative Humidity Exceeds 70%: Blocking and Storage Instability

Exposure of BF-17W films to 30 °C/75% RH for 48 h leads to water absorption of 18–22% relative to dry film weight and a reduction in tensile modulus from 1.2 GPa to 0.2 GPa. Under these conditions, stacked sheets of sized yarn or coated paper develop interfacial adhesion exceeding 0.4 N/cm², resulting in tearing upon separation. This behaviour contrasts with fully hydrolysed PVA films, which absorb less than 5% moisture under the same conditions and retain a modulus above 1.0 GPa. To mitigate blocking, formulators often incorporate 2–4 wt% of a hydrophobic ester plasticiser such as triacetin or treat the film surface with a 0.5% calcium stearate dispersion. In emulsion polymerisation post-processes, dried resin powder stored in unlined multi-wall paper bags at tropical sites ( 30 °C, 85% RH) can undergo cold sintering within 72 h, producing agglomerates that fail to disperse in standard 15% solution make-down without high-shear mixing at 5 000–8 000 rpm. Consequently, bulk handling protocols recommend immediate transfer to sealed silos with a nitrogen purge and silo wall temperature maintained 2–3 °C above the local dew point.

Regulatory Compliance Matrix

Workers involved in dust-generating transfer operations should observe an occupational exposure limit of 10 mg/m³ for inhalable dust (OSHA PEL) and wear a P95 filtering facepiece. Combustible dust propagation tests according to ASTM E1226-19 indicate a deflagration index K_St below 50 bar·m/s when moisture content exceeds 5%, classifying the powder as St 1; conductive earthing of all transfer piping remains necessary to prevent electrostatic accumulation.

Extended exposure to amine-functional or highly alkaline additives (pH>9.5) triggers partial deacetylation of BF-17W in aqueous solution, manifested by a 15–30% viscosity rise over 24 h at 50 °C and subsequent gelation. Formulations requiring pH adjustment should employ weak organic acids (citric or acetic) rather than ammonium salts to avoid this autohydrolysis cascade. In co-formulation with natural starches, the tendency of BF-17W to retrograde when cooked pastes are held below 10 °C for 6 h can generate a granular precipitate that blocks size-box filters; maintaining the circulation loop at 75–80 °C and incorporating 0.05% sorbitan monolaurate eliminates this filtration issue.