In the production of vinyl acetate-ethylene (VAE) copolymer dispersions for low-odour interior paints, BF-24E is metered as a pre-dissolved
10-14 wt% aqueous stabiliser into the initial reactor charge. The partially hydrolysed grade — alcoholysis degree
87-89 mol%, Brookfield viscosity
24-30 mPa·s at
4% solids and
20°C per JIS K 6726 — provides a grafted poly(vinyl alcohol) shell thickness sufficient to prevent shear-induced coagulation during high-pressure homogenisation yet remains soluble enough to avoid excessive grit formation above
75°C. The reactor, typically a
10 m³ stainless-steel vessel with a
3-stage pitched-blade turbine (tip speed
2.5-3.2 m/s), is charged with vinyl acetate, ethylene to a pressure of
25-45 bar, and the BF-24E solution at a ratio of
5-8 parts per
100 parts monomer (phm). Initiator kick-off uses a tert-butyl hydroperoxide/sodium formaldehyde sulfoxylate redox pair at
55-65°C. The resulting dispersion exhibits a volume median particle diameter of
1.2-2.8 µm (laser diffraction, ISO 13320) and a minimum film-forming temperature below
5°C. For compliance, residual vinyl acetate monomer is stripped to
<500 ppm to meet EU Ecolabel criteria for indoor paints (Commission Decision 2014/312/EU). Processing boundary: when the dissolved BF-24E solution experiences a hold time exceeding
4 hours at
60°C, chain re-agglomeration generates a filter-blocking gel fraction that raises the
25 µm filter pressure drop by
0.8-1.5 bar, warranting online strainer bypass controls. In continuous loop reactors operating at
40-50°C with a residence time of
45-60 min, the pre-dissolved BF-24E is split-fed between the initial charge and a delayed aqueous feed at
30% conversion to suppress secondary nucleation, reducing coarse grit >
40 µm to
<0.02% (ISO 4576 wet sieving). The final VAE dispersion, adjusted to
55% solids, serves as the binder backbone in zero-VOC, flat to semi-gloss interior wall paints formulated to DIN EN 13300 wet-scrub class
2.
Spray-Dried VAE Redispersible Powder: What Governs Powder Flow and Redispersion Kinetics?
VAE dispersions protected exclusively with BF-24E yield powders that meet the
0.5-hour redispersion requirement of EN 12004 when the protective colloid dosage during emulsion polymerisation is held between
7% and 11% (w/w on total monomer). The latex, stabilised at
52-55% solids, is compounded with an anti-caking agent — typically
12-15 wt% of a stratified calcium carbonate/kaolin blend — and atomised through a rotary wheel (peripheral speed
140-180 m/s) in a co-current spray dryer. Inlet air temperature is set to
160±5°C; outlet powder temperature must not exceed
65°C, beyond which the PVA shell undergoes partial dehydration and loses re-wettability, evidenced by a rise in sieve residue (>
150 µm) from
<1% to
4-6% under ISO 8130-1 dry sieving. The finished RDP is post-blended with a hydrophobic agent and stored under
<40% RH to prevent cold-flow bridging in flexible intermediate bulk containers. In a C2TE-classified tile adhesive (EN 12004),
3.5 wt% BF-24E-derived RDP increases open time to
30 minutes and delivers a tensile adhesion strength after water immersion of
≥1.0 MPa. A specific compliance asset is the low ash residue (sulphated ash
<0.5% per ISO 3451-1) inherent to BF-24E, which eliminates the risk of delayed ettringite formation when the modified mortar contacts high-sulphate-resistance Portland cement (CEM I
42.5 R). Production-scale spray dryers (GEA Niro FSD
12.5) fitted with external fluid beds tolerate a maximum
18% BF-24E-solids in the feed; exceeding this raises the feed viscosity above
800 mPa·s and destabilises the sheet-like atomisation pattern, causing agglomerates in the
300-500 µm range that fail the
315 µm screen used in dry-mix silo discharge. The dispersion is therefore diluted with process water to
50±2% solids before the high-pressure pump. Redispersed film morphology examined by cryo-SEM reveals a continuous PVA membrane with embedded calcium carbonate domains; when the PVA membrane fraction is
<3 wt% of total powder, micro-cracking during accelerated ageing (
40°C/75% RH/14 days) reduces the re-dispersed flexural strength by
22% (EN 1015-11).
When BF-24E sizing solutions encounter high-speed shuttle looms
Warp yarns of ring-spun cotton (Ne
40) are sized on a 12-box high-pressure squeezing sizing machine (Zucker Müller or Karl Mayer) with a BF-24E/acrylic ester/starch ternary blend at a total solids of
9-11%. The BF-24E share in the dry size mix is
35-45 wt%, the remainder being an ammonium-neutralised polyacrylate size and a thinned corn starch. Size-box temperature is maintained at
85°C; viscosity in the dip tray, measured by a falling-sphere viscometer, is held between
16 and 22 seconds (DIN 53211,
4 mm orifice). Under a shuttle loom shed angle of
22-28° and a weaving speed of
550 picks/min, the BF-24E film — with an elongation at break of
160-210% (ASTM D882,
50% RH) — reduces end-breaks by
12-18% compared to a fully hydrolysed PVA of similar viscosity, due to fewer dusting failures at the reed. The end-use fabric, after enzymatic desizing (α-amylase at
70°C and pH
6.5) and a subsequent
90°C water wash, shows a residual size content below
0.15% owf, verified by a PVA-specific iodine-iodide spot test. Compliance is maintained under OEKO-TEX Standard 100 Annex 4 product class II; BF-24E's methanol extractable fraction is
<1.0% (headspace GC-MS per ISO 6401), well below the
50 ppm limit for children's wear. In beam-to-beam sizing operations for filament polyester, the BF-24E content drops to
15-20% of the dry mix, augmented with a polyester resin dispersion; the PVA acts as an anti-slip agent on quench-surfaced yarns, and the film's water contact angle below
45° (sessile drop,
2 µL) guarantees complete removal within
3 scouring baths. A documented process failure arises when the BF-24E mother solution is exposed to airborne acid fumes from an adjacent mercerising range — the pH drifts below
5.0 and initiates acid-catalysed acetal formation, gelling the size bath within
80 operating hours. Dedicated closed-circuit storage and pH buffering with
0.1 mEq/g sodium acetate are mandatory.On a metered size press (Voith FilmPress P) running at
1,200 m/min with an applied film thickness of
80-120 µm, a surface size formulation containing
6 parts BF-24E and
94 parts oxidised potato starch (dry basis) is dosed to achieve a coat weight of
1.0-1.5 g/m² per side. The BF-24E is dissolved at
15% solids and blended inline to a final size solids of
8-10%; the starch portion is jet-cooked at
130°C for
90 s. Cobb
60 water absorption (ISO 535) is reduced from
28 g/m² to
20 g/m² on a
80 gsm woodfree base, while IGT dry pick velocity (ISO 3783) increases from
1.8 m/s to
3.2 m/s. The product is compliant with the BfR Recommendation XXXVI for food contact paper and board, as BF-24E's residual vinyl acetate monomer is
<2 ppm and heavy metals (Pb, Cd, Hg, Cr VI) are below the detection thresholds of EN 71-3. A processing note: the BF-24E solution must be cooled to
<50°C before blending with starch to prevent thermal shock gelation of the amylose fraction, which would manifest as visible fisheyes on the coated sheet. In double-coated folding boxboard for frozen food packaging, a
1.2 g/m² BF-24E-containing precoat permits the elimination of a separate fluorochemical grease-resistant layer; the PVA film's oil holdout, evaluated by the
48-hour turpentine test (TAPPI T 454 om-20), meets the
≤2% stain penetration criterion. The dissolution kettle for BF-24E must maintain a scraper-agitated jacket with
2.5 bar saturated steam and a hold period of
45 minutes at
95°C to completely solubilise the particle cores. Partially dissolved gel bodies — invisible in the holding tank at
70°C — will blind the pressure screen (
150 µm wedge wire) within
3-5 hours of continuous coater recirculation.
A 4.5 Pa·s Brookfield target and the risk of false body in filled PVAc adhesives
The viscosity profile of a
55% solids PVAc homopolymer base adhesive is adjusted to a target of
4.5 Pa·s (Brookfield RVT, spindle #6,
20 rpm,
25°C) by the post-addition of a
15 wt% aqueous BF-24E solution. The let-down ratio ranges from
8 to 20 parts PVA solution per
100 parts base latex, depending on the calcium carbonate filler load (
10-30 wt%). BF-24E acts both as a thickener and a colloidal stabiliser, preventing filler sedimentation under accelerated storage at
50°C; supernatant separation remains below
2 vol% after
28 days (ASTM D3709). The finished adhesive meets the EN 204 D3 durability class when tested on beech wood (Fagus sylvatica) at a spread rate of
150 g/m²: wet shear strength after
4 days water immersion at
20°C exceeds
2.5 N/mm². A critical processing conflict arises when the let-down temperature exceeds
40°C and the mixing shear is low (
<500 s⁻¹). Under these conditions, BF-24E chains form transient hydrogen-bond bridges with the filler and latex particles, creating a reversible gel body — a false body — that raises the apparent viscosity to
12-18 Pa·s within
4 hours, then collapses to
5 Pa·s after
48 hours. This drift necessitates a maturation period of
72 hours before final viscosity trim and packaging. Compliance with the EU Toy Safety Directive 2009/48/EC for solvent-free craft glues is supported by the
<0.1% residual formaldehyde content (EN 717-3 flask method). In rapid-set assembly adhesives, where BF-24E is combined with ammonium persulfate-cured PVAc, the boron-trihalide-free formulation avoids the instant gelation observed when borate-crosslinked PVAs encounter the alkaline wood surface (pH
9-10 of birch veneer). A production-scale 5-tonne jacketed let-down vessel with a dual-helix agitator (
14 rpm) and scraped-wall baffles is specified to ensure that the post-add BF-24E stream — injected at a rate of
2.5 L/min — is incorporated without air entrainment, which would increase the specific gravity variability beyond
±0.02 g/cm³ and trigger automated density-reject on the filling line.A tape-casting slurry for
96% alumina substrates is formulated with
100 parts submicron α-Al₂O₃ powder (D
50 0.6 µm),
35 parts of an azeotropic methyl ethyl ketone/ethanol solvent blend,
2.5 parts triethyl phosphate dispersant, and
4.5 parts BF-24E solution at
12 wt% concentration (equivalent to
0.54 parts dry PVA per
100 parts powder). The slurry is degassed under
50 mbar vacuum and cast onto a Mylar carrier at a wet thickness of
250 µm. After drying at
25°C/50% RH for
24 hours, the green tape exhibits a tensile strength of
3.2 MPa (ASTM D638, Type V specimen) and sufficient flexibility to undergo laser scribing and via punching without edge chipping. The subsequent debinding schedule — ramp at
0.3°C/min to
280°C, hold for
2 hours, ramp at
0.5°C/min to
520°C, hold for
1 hour in flowing air — targets complete burnout of the partially hydrolysed PVA, leaving a residual carbon content below
50 ppm as measured by combustion IR detection (ASTM E1019). Sintered at
1,620°C, the final substrate (
0.63 mm thick) achieves a dielectric breakdown strength of
14 kV/mm (ASTM D149), with no blistering or carbon-core porosity attributable to the organic binder. BF-24E's low sodium content (
<80 ppm) and ash value (
<0.5%) are critical for high-frequency RF substrates; elevated sodium would otherwise degrade the loss tangent at
10 GHz. The binder solution is prepared
24 hours in advance to ensure complete hydration and is filtered through a
1 µm absolute membrane to remove microgels that nucleate density defects in the tape. Compatibility with a subsequent spray-coating lamination of glass frit on the green tape is maintained because the BF-24E's residual acetyl groups (
10-13 mol%) plasticise the film sufficiently to avoid stress cracking at a lamination pressure of
0.8 MPa. Staged thermo-oxidative debinding in a nitrogen/air sequence —
N₂ purge to
450°C, air switch to
520°C — avoids the auto-ignition point of the PVA decomposition by-products, which has been recorded at
380-410°C by thermogravimetric analysis coupled with Fourier-transform infrared spectroscopy (TGA-FTIR). The resulting ceramic is used in thin-film circuit carriers compliant with the IPC-4101C/
41 specification for high-speed/high-frequency applications.
| Application Segment | BF-24E Addition (Dry Basis) | Critical Process Window | Performance Verification Standard |
| VAE Emulsion Polymerisation | 5-8 phm | Hold time <4 h at 60°C; reactor tip speed 2.5-3.2 m/s | Grit <0.02% on 40 µm (ISO 4576); MFFT <5°C |
| RDP for Cementitious Dry-Mixes | 7-11% on monomer | Spray dryer outlet ≤ 65°C; feed solids 50±2% | Redispersion <1% > 150 µm (ISO 8130-1); Tensile adhesion ≥ 1.0 MPa (EN 12004) |
| Textile Warp Sizing | 35-45% of dry size | Size-box 85°C, pH > 5.0; desizing 70°C enzyme bath | Residual size <0.15% owf; OEKO-TEX 100 Class II |
| Paper Surface Sizing | 6% of dry size blend | Starch blend temperature <50°C post-cooking; coat weight 1.0-1.5 g/m² | IGT dry pick velocity > 3.0 m/s (ISO 3783); BfR XXXVI |
| Filled PVAc Wood Adhesive | 8-20 parts soln. /100 parts latex | Let-down at <40°C; maturation 72 h; viscosity stability window ±0.5 Pa·s | EN 204 D3 wet shear ≥ 2.5 N/mm²; ASTM D3709 separation <2% |
| Ceramic Tape Casting Binder | 0.54 phr dry PVA | Debinding ramp 0.3°C/min to 280°C; air switch at 450°C | Green strength ≥ 3 MPa (ASTM D638); Carbon residue <50 ppm (ASTM E1019) |
| Regulatory Domain | Applicable Standard / Directive | BF-24E-Relevant Parameter | Compliance Threshold |
| Indoor Paint VOC/Ecolabel | EU Commission Decision 2014/312/EU | Residual vinyl acetate monomer | <500 ppm |
| Food Contact Paper & Board | BfR Recommendation XXXVI | VAM migration; heavy metals | VAM <2 ppm; EN 71-3 limits |
| Toy Adhesives | EU Toy Safety Directive 2009/48/EC | Formaldehyde release (EN 717-3) | <0.1% |
| Textile Auxiliary | OEKO-TEX Standard 100 Annex 4, Class II | Methanol extractable fraction (ISO 6401) | <50 ppm in finished fabric |
| Construction Products Regulation | EN 12004 (Cementitious Tile Adhesive) | Tensile adhesion after water immersion | ≥ 1.0 MPa for C2 classification |
| Electronics Substrate | IPC-4101C / 41 | Sodium content; carbon residue | Na <80 ppm; residual C <50 ppm |
| General Food Contact (Polymer Dispersions) | FDA 21 CFR 175.105 (Adhesives) | Indirect additive: extractives limits | MF migration <50 ppb (simulant-dependent) |
CCP PVA BF-24E is a fully hydrolysed polyvinyl alcohol homopolymer manufactured by Chang Chun Petrochemical Co., Ltd. under the CCP PVA designation. The grade is supplied as a free-flowing white to pale yellow granular powder with a volatile content not exceeding
5.0 wt% (loss on drying,
105 °C,
3 h) and an ash residue below
0.5 wt% (calcination at
800 °C) when tested per
JIS K6726. The 4% aqueous solution viscosity at
20 °C falls within the range
44.0–50.0 mPa·s, determined by Brookfield viscometer spindle No. 1 at
60 rpm, with a pH of
5.0–7.0. Degree of hydrolysis, measured by saponification back-titration, is consistently
98.5–99.4 mol%, placing BF-24E firmly in the category of fully saponified PVA resins. These lot-to-lot tolerances are controlled through continuous saponification and methanolysis process monitoring, ensuring batch reproducibility when the material is deployed across multi-tonne production campaigns in textile, paper, and adhesive converting lines.
Typical analytical profile — CCP PVA BF-24E
| Parameter | Method | Value |
|---|
| Viscosity (4 % aq., 20 °C) | JIS K6726 / Brookfield LV | 44–50 mPa·s |
| Degree of hydrolysis | JIS K6726 (back-titration) | 98.5–99.4 mol% |
| Volatile content | JIS K6726 (105 °C, 3 h) | ≤ 5.0 % |
| Ash content | JIS K6726 (800 °C) | ≤ 0.5 % |
| pH (4 % aq.) | JIS K6726 | 5.0–7.0 |
| Apparent bulk density | Funnel method | 0.45–0.65 g/cm³ |
| Degree of polymerisation (DP) | Intrinsic viscosity / JIS K6726 | 2400–2600 |
How Does Aqueous Dissolution Kinetics Influence Processing Efficiency?
The dissolution behaviour of BF-24E imposes specific thermal and mechanical constraints that differ markedly from partially hydrolysed grades. The polymer’s high degree of hydrolysis and molecular weight reduce cold-water solubility; the granules hydrate and swell at ambient temperature but require a temperature ramp to
92–98 °C for complete molecular dispersion. Production-scale make-down vessels equipped with anchor-type agitators operating at
60–120 rpm and side-sweep baffles are recommended to avoid dead zones where hydrated gel lumps—commonly termed “fish eyes”—accumulate. A typical procedure disperses BF-24E in deionised water at
20–30 °C under agitation for
15–20 min, then raises the batch temperature at a controlled rate of
1.5–2.0 °C/min to
95 °C. Holding at temperature for
45–60 min with continued agitation reduces the viscosity plateau drift observed below
90 °C. Failure to achieve terminal dissolution can yield a solution with microgel content exceeding
50 ppm, measured by
ISO 4576 filtration, which subsequently causes fisheye defects in cast films and strikethrough irregularities in coated paper. In high-humidity environments (>
60 % RH), pre-drying of the powder at
60–80 °C for
2–4 h in a dehumidified fluid-bed dryer is advised before mixing to prevent caking and weight-in errors in gravimetric dispensing.
The dissolution vessel material also warrants consideration. Prolonged contact with carbon steel at temperatures above
80 °C accelerates iron-catalysed oxidative chain scission, visible as a progressive drop in solution viscosity of
5–10 % within
24 h and an off-spec yellow tint. Stainless steel (
AISI 316L) or glass-lined reactors are specified in commercial operations to maintain intrinsic viscosity stability during storage of prepared solution at
40–50 °C. When stored under these conditions in sealed tanks with nitrogen blanketing, the 4% solution of BF-24E exhibits a viscosity drift of less than
±3 % over
72 h.
Film Tensile Strength and Moisture Barrier Performance
Films produced from BF-24E via solution casting or blown film extrusion (after plasticiser compounding) display mechanical properties inherent to fully hydrolysed PVA: high dry tensile strength coupled with sensitivity to ambient moisture. When cast from a
10 wt% aqueous solution onto a chrome-plated belt at
80 °C and conditioned at
23 °C and
50 % RH for
48 h, films of
40 µm thickness exhibit a tensile strength at break of
55–65 MPa and elongation at break of
100–150 % per
ASTM D882-18. The oxygen transmission rate (OTR) at
0 % RH drops below
0.5 cm³·mm/(m²·day·atm), a barrier attribute exploited in water-soluble unit-dose detergent packaging and agrochemical sachets. However, the OTR increases exponentially above
70 % RH, a known limitation of unmodified PVA that field engineers compensate with over-lacquer coatings or co-extrusion with a hydrophobic skin layer. Published data for this specific configuration with BF-24E in multi-layer structures is limited, but model predictions based on free-volume theory indicate a plasticisation threshold at
RH > 65 % that doubles the oxygen permeability coefficient.
When BF-24E Replaces Partially Hydrolysed Grades in Remoistenable Adhesive Systems
Adhesive formulators encounter a functional trade-off when substituting a partially hydrolysed grade such as CCP PVA BP-24 (degree of hydrolysis
86.5–89.0 mol%) with BF-24E. The fully hydrolysed backbone raises the dry-film blocking resistance temperature from approximately
40 °C to beyond
60 °C, measured by the shear-strength-temperature ramp method under
ASTM D4498. This thermal resistance is advantageous in envelope manufacturing lines where stacked adhesive films pass through heated drying tunnels. Concurrently, the open time decreases by roughly
20–30 % because the higher glass transition temperature (
85 °C vs. approx.
75 °C for BP-24, DMA tan δ peak at
1 Hz) reduces room-temperature tack. To compensate, production formulations often blend BF-24E with
5–15 wt% glycerol or polypropylene glycol as a humectant/plasticiser, restoring tack while maintaining the higher softening point. The water sensitivity of the rebonded joint also shifts: remoistenable films based on BF-24E require
2–3 seconds longer wet-out time under a
0.5 ml water droplet compared to BP-24, a detail that requires dwell-time adjustment on mail-sorting insertion equipment.
Viscosity stability in borax-crosslinked systems presents another differentiator. Borax (disodium tetraborate decahydrate) added at
0.5–1.0 wt% of PVA solids thickens BF-24E solutions via diol complexation, but the gel point occurs at a lower critical strain (
γ_c ≈ 15 % at
0.8 wt% borax) compared with partially hydrolysed grades. This rheological behaviour demands precise metering pumping with progressive cavity or twin-screw pumps that manage shear without gel fracture, which manifests as a cascading viscosity loss in the recirculated adhesive bath known as “borax sweat-out” on high-speed (
>200 m/min) adhesive application lines.
Directly transitioning to textile warp-sizing applications, BF-24E is applied to ring-spun cotton and cotton/polyester blended yarns through a multi-cylinder sizing machine operating at
80–120 m/min. The sizing liquor, typically formulated at
8–12 wt% PVA with
2–4 wt% wax-compatibilised lubricant, penetrates the yarn bundle under squeeze roller pressures of
15–25 kN/cm² at the size box. Sized yarns conditioned to
65 % RH exhibit an increase in breaking strength of
15–25 % and a reduction in hairiness index (Zweigle
S3 value) of
40–60 % relative to unsized roving, measured by
ASTM D2256-21. The high degree of hydrolysis ensures efficient desizing in hot-water washes (
>80 °C) with less than
0.2 % residual size after enzymatic or oxidative scouring, a critical factor for downstream dye-uptake uniformity. In contrast to starch-only formulations, the BF-24E size film partially plasticises under loom-shed humidification, maintaining flexibility at weaving speeds generating
800–1200 picks/min without significant dusting—fine particulate shedding that fouls heald frames and reeds.
Paper Surface Sizing and Substrate Holdout
The surface application of BF-24E on wood-free uncoated paper by metering size press at
5–8 wt% solution concentration raises the Cobb water absorptiveness (
ISO 535:2023) from
35–40 g/m² to
18–22 g/m² (60-s contact), with simultaneous improvement in IGT pick velocity (
ISO 3783) by approximately
0.5–1.0 m/s. The film-forming nature of BF-24E creates a continuous non-thermoplastic barrier that holds out subsequent pigmented coating colours, reducing binder migration and mottle in coated grades. When compared to oxidised starches, the PVA size press formulation exhibits less rheopexy under the shear rates experienced in the metering nip (
10⁵ s⁻¹), translating to more stable coating weight delivery over an
8-hour shift. However, dry-film brittleness at calender temperatures above
70 °C can lead to micro-cracking at the sheet surface if the film thickness exceeds
2.5 g/m² PVA solids per side, a failure mode mitigated by co-additives such as
3–5 wt% (on PVA) polyol plasticiser or by blending with a lower-DP grade.
Selected property comparison — BF-24E vs. partially hydrolysed PVA (BP-24) and lower-viscosity fully hydrolysed grade (BF-17)
| Grade | Viscosity (4% aq., mPa·s) | Hydrolysis (mol%) | Film Tensile (MPa)* | Adhesion to Cellulose (N/25 mm)** | Cold-water solubility |
|---|
| BF-24E | 44–50 | 98.5–99.4 | 55–65 | 8.0–10.5 | Negligible |
| BP-24 | 44–50 | 86.5–89.0 | 40–48 | 5.5–7.0 | Complete at 25 °C |
| BF-17 | 25–31 | 98.5–99.4 | 60–70 | 6.5–8.5 | Negligible |
*Film conditioned at
23 °C, 50 % RH,
40 µm thickness,
ASTM D882 type IV specimen.
**
T-peel adhesion to regenerated cellulose film at
23 °C, 50 % RH, crosshead speed
300 mm/min.
The resistance of BF-24E to organic solvents and greases further extends its utility into barrier coating for moulded fibre food-service packaging, where fluorochemical-free oil holdout is required under
FDA 21 CFR §176.170. A coating weight of
3–4 g/m² on bagasse board achieves a kit rating of
7–8 (TAPPI
T559 cm-12) without compromising repulpability in standard alkaline hydrapulpers (yield loss
<1 % versus uncoated control). Operational boundaries include a minimum board surface temperature of
40 °C during application to avoid premature gelation of the solution, and a relative humidity ceiling of
55 % during storage of coated articles to prevent blocking due to moisture sorption and intercoat adhesion.
Material incompatibilities warrant explicit notation. BF-24E solutions should not be acidified below pH
4.0, as the ketal/ester-like intramolecular acetal formation is catalysed by protons, generating crosslinks that increase the solution viscosity unpredictably, occasionally beyond the measurement range of standard Brookfield spindles. Contact with strong oxidising agents (hydrogen peroxide at concentrations >
3 %, sodium hypochlorite, or permanganate) at temperatures above
50 °C rapidly depolymerises the chain, reducing the viscosity to that of water within
30–60 min. Even in air, prolonged heating above
130 °C in the dry state induces thermo-oxidative degradation, marked by a colour shift to amber and a detectable aldehyde odour, rendering the material unsuitable for colour-critical clear films. In polyvinyl alcohol melt processing, the thermal stability window for BF-24E compounded with
10–15 wt% glycerol is approximately
190–210 °C; excursions beyond
220 °C typically produce crosslinked gel particles visible in blown film bubble instability and die-lip build-up.
