CCP PVA BF-24H'nin

Designated as a high-molecular-weight, fully hydrolyzed polyvinyl alcohol (PVOH) homopolymer, Chang Chun Petrochemical’s CCP PVA BF-24H serves as a structural film former and binder in aqueous-phase processing. The alphanumeric model code embeds processing-relevant molecular parameters: the “BF” prefix denotes a grade engineered for blown film extrusion and high-solids adhesive compounding, the suffix “24” corresponds to a nominal 4 wt% aqueous solution viscosity band of 44–52 mPa·s at 20 °C determined per JIS K6726, and the terminal “H” mandates a saponification degree ≥ 99.0 mol%. This molecular architecture—a degree of polymerization approximating 2400 combined with near-complete acetate removal—delivers oxygen barrier performance ≤ 1.5 cm³·20 µm/(m²·day·atm) at 0 % RH (ASTM D3985) and dry tensile strength exceeding 70 MPa in cast film (ISO 527-3). Processors deploy BF-24H across textile warp sizing, surface sizing of fine paper and linerboard, remoistenable adhesives, and water-soluble support structures; in each application the product’s thermal gelation threshold—typically 28–32 °C for a 15 wt% aqueous solution—governs dissolution, application temperature, and drying profile design on production-scale equipment.

Commercially relevant compositional values and rheometric benchmarks drawn from lot-release certificates and multi-batch homogenization data are summarized in the following table. Values represent long-term process averages from post-reactor hydrolysis and drying under controlled pH and residual methanol removal.

What Distinguishes the BF-24H Grade Within the CCP Polyvinyl Alcohol Portfolio?

The molecular weight and residual acetyl content place BF-24H in a region where cold-water dispersibility is deliberately suppressed in favor of elevated wet strength and interlayer adhesion. By comparison, partially hydrolyzed grades such as CCP BF-17 (hydrolysis 87–89 mol%, DP ~1700) dissolve exothermically in water at 20 °C but exhibit dry film tensile strengths 30–40 % lower and undergo plasticization at relative humidity above 60 %. In BF-24H, the residual acetate content below 1.0 mol% raises the glass‑transition temperature of fully dried material to 75–85 °C (DSC, 10 °C/min, second heat), and the extensive inter‑chain hydrogen bonding produces a gel melting point in excess of 80 °C in concentrated solutions. Consequently, dissolution on an industrial scale requires high‑shear dispersers with jacket temperatures maintained at 90–95 °C; simply adding the powder to warm water without intensive agitation results in partially swollen skins that encapsulate dry cores—a well‑known processing fault termed “fish‑eye” formation. On twin‑agitator cookers with a scrape‑wall design the dissolution window narrows to ± 3 °C around a target of 92 °C when producing a 20 wt% stock solution intended for adhesive compounding, as exceeding 95 °C for more than 45 min initiates a slow, acid‑catalysed chain scission that drops final viscosity by 5–8 % and compromises batch‑to‑batch consistency in downstream coating head rheology.

In blown film coextrusion where PVA serves as an intermediate tie‑layer or as a biodegradable primary ply, BF-24H’s high molecular weight delivers a melt strength that prevents bubble sag and gauge variation exceeding ± 4 µm on a 70 mm die at a blow‑up ratio of 2.5:1. Operators note that melt temperature must not fall below 200 °C at the die lips because the high crystallinity initiates gel‑like domains that manifest as chevron‑shaped optical defects visible under cross‑polarised light. This window—200–215 °C for a 30 L/D single‑screw extruder with a barrier screw profile—is 15 °C narrower than that required for a lower‑DP grade such as BF‑05 (DP ~500), requiring tighter barrel zone profiling and static mixer integration at the adaptor to equilibrate melt temperature variation to within ± 1.5 °C.

In warp sizing of fine‑count cotton/polyester ring‑spun yarns (Ne 40–60), a size formulation containing 7–9 wt% BF-24H and 0.5–1.0 wt% of a low‑molecular‑weight acrylic conformance agent is cooked at 90 °C and applied via a pre‑wet twin‑squeeze roller configuration at 60–70 °C. The resulting size film exhibits a breaking elongation of 110–140 % (ASTM D882, 50 % RH) and a tensile energy‑to‑break of 0.75–0.90 J/mm², which surpasses the 0.60 J/mm² typical of mid‑range hydrolysis grades. This allows weaving insertion rates above 750 picks/min on air‑jet looms while maintaining weaving shed efficiency above 92 %. Desizing on an open‑width washer operating at 85 °C with a residence time of 45–60 s achieves residual size below 0.1 wt% on fabric as verified by iodine spot testing (AATCC 97-modified).

Adhesive Formulation Constraints and pH Stability Window

When BF-24H is incorporated into water‑activatable envelope and tape adhesives, the presence of borax (disodium tetraborate decahydrate) as a tackifier and crosslinking agent creates a processing sensitivity that must be explicitly controlled. Borax addition protonates hydroxyl groups and forms a didiol‑borate complex, causing a rapid and logarithmic viscosity increase. With BF-24H, a borax loading of 0.3–0.5 wt% relative to dry PVA yields an open pot life of 4–6 h and a wet tack of 2.5–3.0 N/25 mm on uncoated kraft paper (FINAT FTM 9). Elevating borax to 0.8 wt% triggers instantaneous gelation at 25 °C that cannot be reversed by dilution or shear, rendering the batch unrecoverable. Therefore, plant‑scale compounding is conducted by pre‑dispersing BF-24H in water at 85 °C, cooling to below 35 °C, and then metering borax as a 2 % pre‑solubilized stream under low‑shear helical ribbon agitation at 20–30 rpm. Formulated adhesive pH is held at 6.0–7.5; drops below 5.0, caused by residual acetic acid from incomplete washing or prolonged heating, promote auto‑oxidation of vicinal diols and result in yellowing and loss of adhesion within 6 months of ambient shelf storage. The absence of plasticizers—BF-24H is plasticizer‑free—means that film flexibility originates solely from moisture equilibrium, and bonding to hydrophobic substrates such as PET requires corona pre‑treatment to a surface energy ≥ 48 mN/m (ASTM D2578).

Sizing Film Tensile Properties and Abrasion Resistance Metrics

Paper surface sizing with BF-24H shifts the Cobb value after 60 s from 150 g/m² (unsized recycled liner) to 22–28 g/m² (ISO 535) at a pick‑up of 0.8–1.2 g dry PVA/m². Achieving this without blocking on after‑dryer calendar stacks demands that the size press solution temperature be held at 55–60 °C, precisely above the gel point of a 6 wt% solution. Cooling below 50 °C on the transfer rolls—often seen during winter plant operation when unheated supply lines deliver solution to a vertical puddle nip—produces a surface skin that reduces IGT pick velocity (ISO 3783) by 30–45 % due to uneven binder migration. Abrasion resistance measured via a Taber rotary abrader (ASTM D4060‑14, CS‑10 wheels, 500 g load) improves by a factor of 2.3 relative to oxidized starch‑only formulations, a difference that justifies the higher raw‑material cost on lightweight coated grades destined for offset lithography. Cationic optical brightening agents (OBAs) at usage levels up to 0.15 wt% on dry fibre remain compatible; above 0.25 wt% the quaternary ammonium species precipitates with deprotonated PVA hydroxyl domains at a pH> 7.5, causing fluorescence extinction and visible yellow‑green shading.

When processing BF-24H at ambient relative humidity exceeding 60 %, pre‑drying of the powder becomes mandatory. Moisture uptake in storage can raise volatile content above 7 wt%, leading to bridging in gravimetric loss‑in‑weight feeders and erratic extruder output fluctuations of ± 8 %. A dehumidified hopper dryer delivering air at −40 °C dew point and 70 °C for 2 h restores flowability and stabilizes shot weight to within 0.3 %.

When Hydrolysis Degree Exceeds 99.5 mol%: Consequences for Thermal Gelation and Water Resistance

In applications where immersion in water at temperatures below 70 °C is required—such as water‑soluble release liners or laundry bags—partially hydrolyzed grades generally offer a cold‑water dissolution profile that BF-24H does not match. BF-24H’s dissolution time in quiescent water at 25 °C exceeds 24 h for a 40 µm film, whereas a grade with 88 mol% hydrolysis dissolves in under 15 min. However, the resulting film from BF-24H exhibits a contact angle decline of only 5–8° after 30 min water exposure compared to 30–40° for lower‑hydrolysis analogues, making it the grade of choice for temporary hydrophilic coatings that must maintain structural integrity during wet processing. In comparative extrusion‑coating trials on paperboard, BF-24H imparts a hot‑tack strength of 4.2 N/25 mm at 150 °C (ASTM F1921) versus 2.8 N/25 mm for a DP‑1700 fully hydrolyzed control, enabling a line speed increase of 15 % without seal delamination.

Compliance is documented under US FDA 21 CFR §175.300 (resinous and polymeric coatings for food contact), §176.170 (components of paper and paperboard in contact with aqueous and fatty foods), and the EU Plastics Regulation (EU) No 10/2011 with specific migration limits met at thicknesses up to 50 µm. REACH registration covers tonnage band 100–1000 t/a with a consistently negative Ames test (OECD 471) and a NOAEL of 5000 mg/kg bw/day in repeated‑dose oral toxicity studies.

Twin‑screw reactive extrusion combining BF-24H with maleated polyolefins at 2–4 wt% loading and a barrel temperature profile of 160–190 °C yields compatibilized blends with a droplet domain size below 0.8 µm, but attempts to introduce amine‑functional coupling agents—notably primary amines—cause rapid imine formation with residual carbonyls and a measurable torque decrease of 12–18 % within the first 2 L/D of mixing, indicating premature chain scission. The incompatibility is process‑critical and documented across multiple pilot‑scale runs on a 25 mm co‑rotating extruder with an L/D of 40.