CCP PVA BF-24

Designated under the model code BF-24 in the Chang Chun Petrochemical (CCP) polyvinyl alcohol portfolio, this partially hydrolyzed grade is engineered for aqueous solution applications where low solution viscosity at ambient and moderately elevated temperatures must coexist with controlled surface activity. Published datasheets for the BF-24 grade cite a degree of hydrolysis in the range 86.0–89.0 mol% and a 4% aqueous solution viscosity of 4.5–6.0 mPa·s at 20°C determined by ISO 15023-2 or Brookfield methodology per ASTM D1343. The residual acetyl content, typically 11–14 mol%, disrupts interchain hydrogen bonding sufficiently to depress the gelation temperature and impart cold-water solubility, a characteristic that distinguishes BF-24 from fully hydrolyzed grades such as CCP PVA BF-17 (hydrolysis > 98.5 mol%) which require heating to 80–90°C for complete dissolution. Ash content as Na₂O is held below 0.5% by weight under routine production quality control, a value that meets the optical clarity requirements for most clear film and overprint lacquer end-uses.

How Does BF-24’s Macromolecular Architecture Differ From Standard PVOH Homopolymers?

The primary structural distinction lies in the sequencing of residual acetate groups along the vinyl alcohol backbone. In the 86–89 mol% hydrolysis window, the polymer transitions from a blocky distribution of acetate units—typical of grades hydrolyzed without solvent-phase randomization—toward a more statistical distribution achieved through controlled saponification conditions. This sequencing affects interfacial tension at the air–water and oil–water boundaries. Dynamic surface tension measurements on 4% solutions at 25°C using a Wilhelmy plate tensiometer (ASTM D1331) yield equilibrium values of 48–50 mN/m. The absence of long hydrophobic blocks prevents excessive foaming during high-shear transfer, a processing advantage observed on rotary screen printing tables operating at squeegee pressures above 1.5 bar.

On a typical slasher sizing machine running 70–80 m/min with single-end fine-count cotton or polyester/cotton blend yarns, the size box concentration of BF-24 is maintained between 6.0% and 8.5% total solids. Below 6.0%, the add-on level on the warp sheet falls below 8% dry weight, leading to insufficient abrasion resistance as measured by the Zweigle G 552 Hairiness Tester. Above 8.5% solids, viscosity build-up in the size box—exacerbated by evaporative water loss across an eight-hour production shift—can exceed the operational window of the size pump, which is typically a positive-displacement gear pump rated for fluids up to 120 mPa·s at 85°C. Cooker configuration matters: a continuous jet cooker operating at 150°C and 3.5 bar with a residence time of 45–60 seconds yields a fully solubilized, grit-free size with fewer undispersed gel particles than batch atmospheric cooking kettles. The viscosity of a 7.5% BF-24 solution measured at 85°C with a Brookfield LV spindle No. 1 at 60 rpm typically reads 45–55 mPa·s immediately after cooking and gradually declines by 10–15% over 6 hours under gentle mechanical agitation due to shear-induced chain scission, a behavior that requires periodic replenishment with fresh size to maintain film integrity.

When Is a Partially Hydrolyzed Grade Preferable Over Fully Hydrolyzed PVA in Emulsion Polymerization?

In vinyl acetate and vinyl acetate-ethylene emulsion polymerizations, the protective colloid efficiency of BF-24 stems from its balanced hydrophilic-lipophilic character. The acetate segments adsorb onto the growing polymer particle surface, while the vinyl alcohol segments extend into the aqueous phase, providing electrosteric stabilization. Grafting of PVOH onto the poly(vinyl acetate) core occurs through chain transfer to polymer, and the grafting efficiency—quantified by solvent extraction in acetone/water mixtures—is lower for partially hydrolyzed grades compared to fully hydrolyzed analogues due to the reduced number of abstractable tertiary hydrogens adjacent to hydroxyl groups. However, the lower grafting tendency results in less viscosity drift during storage of the finished latex. A 4% solution of BF-24 used as a sole protective colloid in a semi-batch vinyl acetate homopolymerization at 70°C with potassium persulfate initiator yields a latex with a particle size D₅₀ of 1.2–1.8 µm (laser diffraction, ISO 13320) and a Brookfield viscosity of 2,000–4,000 mPa·s at 55% solids. In contrast, a fully hydrolyzed grade at identical colloid loading produces a bimodal distribution with a coarse fraction above 5 µm, a size regime prone to settling and screen clogging on 80-mesh filters. The operational limitation is the temperature ceiling: BF-24 begins to phase-separate from aqueous solution above 45°C when salts such as sodium sulfate exceed 0.5 mol/L, a condition encountered in redox-initiated recipes with high persulfate loading. Therefore, in processes requiring electrolyte tolerance, a grade with hydrolysis <80 mol% may be substituted.

Adhesive formulators evaluating BF-24 for high-speed paper converting lines—envelope folding, tube winding, and carton side-seam gluing—observe open times that are tunable by blending with fully hydrolyzed grades or by adjusting the plasticizer ratio. A simple formulation comprising 12% BF-24, 2% glycerol (on wet weight), and 0.1% defoamer shows an open time of 25–35 seconds on 80 g/m² uncoated Kraft paper at 23°C and 50% relative humidity, measured by the finger-tack method. Setting speed on a Nordson slot-coater running at 200 m/min is sufficient to achieve fibre tear within 1.5 seconds of compression when the glue film thickness is controlled to 25–30 µm wet. The critical process constraint with BF-24 is its interaction with borate ions: even 0.3% borax decahydrate added as a tackifier triggers a rapid viscosity climb into the 10,000–20,000 mPa·s range through didiol complex formation, demanding precise metering and immediate flushing of lines during stoppages to avoid solidified gel plugs in 6 mm ID delivery hoses.

Volatile Matter and Ash Content Specifications Relative to Optical-Grade Films

For cast film applications where optical haze must remain below 2% per ASTM D1003, the combination of low ash content and controlled volatile matter in BF-24 is critical. Residual sodium acetate from the saponification process, if ash exceeds 0.5%, nucleates crystalline regions during film drying that scatter light and elevate haze to 4–6%. The as-received powder, with a bulk density of 0.45–0.60 g/cm³ and a particle size distribution where 95% passes through a 60-mesh screen (250 µm), must be pre-dried to <0.5% moisture if stored in ambient humidity above 60% RH to prevent clumping in loss-in-weight feeders servicing single-screw extruders with a 24:1 L/D ratio. Drying at 80°C for 4 hours in a dehumidifying hopper dryer is standard practice on film lines running at outputs of 150–250 kg/h.

In cast film extrusion, BF-24 is frequently blended with plasticizers such as glycerol or trimethylolpropane at 20–30 phr. The partially hydrolyzed character provides a broader processing window than fully hydrolyzed grades because the melt flow index (MFI, 190°C/2.16 kg, ISO 1133-1) of a compound with 25 phr glycerol is 8–12 g/10 min, compared to 2–4 g/10 min for an equivalent fully hydrolyzed formulation. However, the oxygen barrier of films derived from BF-24 at 50% RH is 1.5–2.5 cm³·mm/m²·day·atm, roughly twice that of a fully hydrolyzed film, a trade-off acceptable in secondary packaging but disqualifying for high-barrier food packs requiring an oxygen transmission rate below 0.5 cm³·mm/m²·day·atm per ASTM D3985.

Impact of Hard Water Cations on Solution Clarity and Gelation

Dissolution of BF-24 in water with total hardness exceeding 150 ppm as CaCO₃ leads to an increase in turbidity due to salting-out of the acetate-rich segments. Turbidity measured by nephelometric method (ISO 7027) on a 4% solution prepared in water of 250 ppm hardness can exceed 20 NTU, which is above the 10 NTU acceptance limit for clear overprint varnishes. To counteract this, the addition of 0.05% phosphoric acid (85%) chelates calcium ions and restores clarity to <5 NTU. In textile size recovery operations by ultrafiltration, the permeate flux of a 7.5% BF-24 solution through a 50 kDa polysulfone membrane at 5 bar trans-membrane pressure is 25–35 L/m²·h initially but declines by 40% over 8 hours if calcium ion concentration rises above 200 ppm, necessitating daily acid cleaning cycles.

In paper surface sizing at the size press of a fine-paper machine producing 80–120 g/m² copy paper, BF-24 is typically co-applied with starch at a ratio of 1:4 to 1:6 PVA to oxidized starch solids. The total size pick-up is 2–3 g/m² per side. At these levels, the Hercules Size Test (TAPPI T 530) shows an increase from <2 seconds for unsized paper to 15–25 seconds. The main processing hazard is the intermixing of BF-24 with cationic wet-end additives carried over from the wire section: residual poly-DADMAC or cationic starch at concentrations above 50 ppm in the size press circulation water precipitates PVOH, causing white specks in the finished sheet detectable by image analysis systems set to reject defects larger than 0.3 mm². Bleed control from size press to dryer cylinders is achieved by maintaining BF-24 solution viscosity below 80 mPa·s at 60°C, which falls within the grade’s viscosity-temperature profile.