CCP PVA BF-17W

When BF-17W is Adopted as the Sole Protective Colloid in Semi-Continuous VAc Feed Systems

Semi-continuous addition of vinyl acetate monomer into a pre-heated aqueous phase containing BF-17W and an oxidising initiator triggers graft polymerization at the acetate side chains of the polyvinyl alcohol. This mechanism is well documented and differs fundamentally from the behaviour of hydroxyethyl cellulose or polyacrylamide-based stabilisers. The so-formed PVA-PVAc graft copolymer orients at the monomer-swollen particle surface, creating a steric barrier that prevents coalescence during the exothermic peak that typically occurs at 65–75°C. Control of the feed rate is critical: exceeding 3.5 kg monomer per hour per litre of aqueous phase in a stirred reactor with 4-pitch impeller, tip speed ≤ 3.2 m/s, can cause localised grafting deficiency and visible grit formation in the final emulsion. The recommended initial charge holds 4.5–6.0 wt% of BF-17W (dry basis on total monomer) dissolved in deionised water at ≥ 92°C until full solubilisation, then cooled to 70°C before monomer feed begins. Typical initiator used is ammonium persulphate at 0.15–0.25 wt% on monomer, often paired with a sodium bicarbonate buffer at 0.05–0.10 wt% to maintain pH in the 4.0–5.5 window; drift below pH 3.8 accelerates acid-catalysed hydrolysis of both monomer and PVA backbone, reducing colloidal stability. The resulting polyvinyl acetate homopolymer dispersion shows a Brookfield viscosity range of 8000–30 000 mPa·s (spindle #6, 20 rpm, 25°C, per ISO 2555:2018) depending on the PVA grade and concentration, and a particle size distribution (D₅₀) between 0.8 µm and 2.5 µm when measured by laser diffraction (ISO 13320:2020). Such emulsions serve as base binders for woodworking adhesives that must comply with durability class D3 according to EN 204:2016 or for paper converting adhesives covered by FDA 21 CFR 175.105 for incidental food contact. Residual vinyl acetate monomer must be reduced to < 0.5 wt% via post-polymerisation stripping with a redox pair (typically t-butyl hydroperoxide/sodium metabisulfite) at 60°C under reduced pressure. Experience from 1000-litre stirred-tank reactors reveals that batch-to-batch viscosity reproducibility tightens significantly when the dissolved oxygen in the initial water charge is reduced below 2 mg/L by nitrogen sparging. A processing incompatibility exists with multivalent metal salts: addition of > 0.05 wt% aluminium chloride or zinc nitrate coagulates the dispersion instantly.

Viscosity and water resistance trends in VAc homopolymer emulsions stabilised solely with CCP PVA BF-17W (batch size 500 L, constant initiator level)

BF-17W concentration, wt% on VAc	Brookfield viscosity, mPa·s (ISO 2555:2018)	D₅₀ particle size, µm	D₃ wet bond strength after 24 h water soak (EN 204, N/mm²)
3.0	4200–6500	1.9–2.4	0.9–1.2
5.0	12 000–18 500	1.1–1.6	1.4–1.9
7.0	24 000–31 000	0.7–1.1	2.1–2.7

Water-remoistenable adhesive formulations demand a balance between dry tack-free film storage stability and rapid re-tack development upon re-wetting. BF-17W with its 87–89 mol% hydrolysis degree and medium molecular weight delivers a desirable open time for high-speed envelope and label converting lines. A typical formulation combines BF-17W as the primary film former at 12–16 parts per hundred parts water, a plasticiser such as glycerol at 2–4 phr (on dry PVA), a humectant (sorbitol or polyethylene glycol 400) at 1–2 phr, and a defoamer at 0.1–0.3 phr. Dissolution of all solids is executed in a jacketed dissolver with high-shear rotor-stator at 1300–1500 rpm and heating to 88–93°C for 45–60 minutes; insufficient dissolution time leaves microgel particles that block the 60-mesh filter before the coating head. The adhesive is applied via direct gravure or reverse gravure rolls onto siliconised release liner or direct to paper substrates, targeting a dry coat weight of 6–10 g/m². Coated webs run through a forced-air tunnel dryer where web surface temperature must not exceed 105°C to prevent PVA crystallinity loss that reduces re-moistenable tack. End products include peel-and-seal envelopes, postage stamps, and self-adhesive labels used under postal regulations that mandate compliance with EN 13236:2019 for remoistenable gums. Operational boundaries: relative humidity in the drying section below 30% causes excessive surface skinning, blocking water penetration; above 65% the dried film absorbs moisture and becomes blocking-prone in stacked storage. An incompatibility is noted with polyamide-based anti-block agents that interfere with re-wetting kinetics. The dried film remains non-tacky at ≤ 30°C and rewets within 2–5 seconds when exposed to a water film of 10–15 µm thickness.

At What Solids Level Does BF-17W Film Form Cause Excessive Hardness in 65/35 Polyester/Cotton Sized Yarn?

Textile sizing on ring-spun polyester/cotton blends requires a film that reduces hairiness and improves abrasion resistance during weaving yet breaks down efficiently during oxidative or enzymatic desizing. BF-17W alone forms a film with a tensile strength of 38–46 MPa and elongation at break of 160–220% at 23°C, 50% RH (conditioned to ISO 291:2008), which when applied at high add-on levels can cause excessive stiffness, shedding, and loom dust generation. In a typical size mix, BF-17W is blended with an acid-modified starch (e.g., thin-boiling corn starch) in a ratio of 30:70 to 50:50 dry basis. The size solution is prepared by dispersing the starch in cold water, heating to 95–98°C, then adding BF-17W pre-dissolved separately at 90°C. Final solids content in the size box is maintained at 8–11 wt% for filling yarn and 11–14 wt% for warp yarn depending on yarn count; for yarn of Ne 40, a size pick-up of 10–12% on yarn weight is targeted. Squeeze roll pressure must be set to 14–18 kN/m on the warp sizing machine to remove excess liquor without stripping the protective film. Drying cylinder temperatures are staged from 120°C to 95°C; the first cylinder must stay below 125°C to avoid skin formation that traps moisture and leads to mildew growth in wound beams. Sizing performance is evaluated by abrasion resistance per ASTM D4158-08 (Stoll-Q test) with a target of > 800 cycles before yarn break. Field data from projectile weaving machines operating at 520–580 rpm indicates that size pick-up exceeding 13% on Ne 40 P/C yarn causes needle wear and increased warp break frequency due to film rigidity. Desizing is carried out with an oxidative non-silicate system (hydrogen peroxide 2–4 mL/L at 85°C) or with amylase enzyme at 60°C, achieving > 95% size removal within 20 min. It is important to note that BF-17W is not recommended for 100% viscose sizing because the alkaline washing step causes irreversible yellowing of the PVA film. Finished woven fabrics must pass ISO 105-E01:2013 for water bleeding fastness, unaffected by residual PVA. In cementitious tile adhesives classified under C2 per EN 12004:2017, addition of BF-17W at 0.3 wt% of dry mix functions as a secondary water-retention agent and rheology modifier, working in tandem with a cellulose ether such as methyl hydroxyethyl cellulose (MHEC). In a standard dry-mix formulation containing ordinary Portland cement 35–40 wt%, silica sand (0.1–0.5 mm) 58–62 wt%, calcium carbonate filler 5–8 wt%, and an MHEC at 0.35 wt%, the partial substitution of 0.1 wt% MHEC with BF-17W powder improves open time from 20 min to 28 min as tested per EN 1346:2007 under a 5 kg weight. The PVA powder must be redispersible and milled to a particle size distribution with 98% < 500 µm to avoid stratification in silo storage. Mixing with water at a ratio of 0.22–0.26 generates a pot life exceeding 2 h; shear thinning behaviour allows trowelling at 1.5–2.5 m/s linear speed without slump. Tensile adhesion strength after water immersion, per EN 1348:2007, remains above 1.0 N/mm² when the PVA addition does not exceed 0.5 wt%. Higher loadings risk air entrapment and foam stabilisation that lower density and compressive strength. A processing limitation: dry-mix blends containing BF-17W must be stored in moisture-impermeable bags and used within 9 months; exposure to cyclical humidity above 70% RH initiates caking that cannot be reversed by re-milling. Final cured tile adhesive mortar must comply with EN 12004 durability requirements and must not release formaldehyde above the limit set in EN 15251:2007 for indoor air quality—PVA BF-17W is inherently formaldehyde-free but can react with residual crosslinkers if an incompatible styrene-butadiene redispersible powder is used.

Co-application of BF-17W and Enzyme-Converted Starch — Surface Pick Strength Improvement Metrics

Surface sizing of packaging linerboard and corrugating medium with a size press blend of BF-17W and enzyme-converted starch enhances IGT surface strength and reduces splitting during corrugator preheating. A commercial operating window involves a size solution at 65°C applied via puddle-type size press to a paper web at 8–12% moisture content, running at 400–600 m/min. The solution contains oxidized or enzyme-thinned starch at 7.0–9.0 wt% solids and BF-17W at 0.8–1.5 wt% on dry starch. The PVA must be cooked separately at 16–20 wt% concentration in an agitated make-down unit at 93–96°C for a minimum of 30 minutes before blending into the starch feed line. An in-line static mixer with 12 elements ensures uniform mixing without shear degradation. Size pick-up is controlled to 1.2–1.8 g/m² dry per side. Final paper bonding strength is tested by the Scott Internal Bond method (TAPPI T 569) targeting a minimum of 250 J/m² for linerboard of 150 g/m² grammage. The presence of BF-17W also raises the IGT picking velocity from 1.8 to 2.5 m/s when measured with a low-viscosity oil on uncoated board (ISO 3783:2006). An upper addition limit exists: beyond 2.0 wt% on starch, the film becomes hydrophobic enough to retard aqueous coating penetration in downstream conversion, causing mottle on flexo-printed surfaces. Furthermore, broke re-pulping efficiency drops significantly when the PVA content exceeds 2.2 wt% in the recycled furnish because the PVA film does not disperse under standard neutral de-inking conditions. The end product finds use in high-performance shipping containers under EN 12281:2002 for transport packaging.

Processing Window for BF-17W-Based Blown Film in Humidity-Buffered Packaging

Extruding BF-17W into a water-soluble blown film requires a narrow processing window to avoid melt fracture and thermal crosslinking. The raw granules must be pre-conditioned to a moisture content of 9.5–12.0 wt% (Karl Fischer titration, ISO 760:1978) and fed to a single-screw extruder with a screw L/D ratio of 30:1 and a compression ratio of 3.5:1. Formulation commonly incorporates glycerol as a plasticiser at 8–14 phr and a non-stick slip agent (glycerol mono-stearate) at 0.5 phr to lower die adhesion. Barrel temperature zones from feeding to die are set at 140, 175, 195, 205, 195°C, and die temperature is held at 190±3°C. Exceeding 210°C causes dehydrochlorination-like discolouration even though no chlorine is present; rather, it triggers acetic acid elimination and crosslinking that raises melt viscosity and produces gel specks. The extruder must be vented at the compression zone with a vacuum of -0.06 MPa to remove residual acetic acid vapour. Blowing ratio is maintained at 2.5:1 to 3.5:1 to yield a film with balanced machine-direction and transverse-direction tensile strength. Resulting film at 30 µm thickness exhibits a tensile strength of 28–35 MPa (MD) and 18–24 MPa (TD) when conditioned at 23°C, 50% RH per ISO 527-3:2018. Water solubility is evaluated by immersion in demineralised water at 20±1°C under gentle magnetic stirring; complete dissolution of a 30 cm² film piece should occur within 75–120 seconds. This film is suitable for unit-dose packaging of granular detergent, agrochemical water-soluble sachets, and textile auxiliary dosage bags subject to OECD 301B ready biodegradability assessment. A practical incompatibility arises with cationic surfactants and quaternary ammonium compounds that plasticise the film uncontrollably, causing premature softening and seam failure in heat-sealed sachets. Storage must be in heat-sealed aluminium-laminate pouches with desiccant to maintain moisture content; a relative humidity exceeding 65% in storage accelerates carbonyl formation and reduces tensile strength by up to 30% within 6 months.

Effect of glycerol content on mechanical and dissolution properties of BF-17W cast film (conditioned to 23°C, 50% RH, tested per ISO 527-3 and in-house dissolution protocol)

Glycerol, phr	Tensile strength MD, MPa	Elongation at break MD, %	Water dissolution time (30 µm film, 20°C), s
8	38–43	180–230	95–125
12	28–33	290–350	65–90
16	18–24	410–480	40–60