ÇKP PVA BP-17N

CCP PVA BP-17N is a partially hydrolysed polyvinyl alcohol grade produced by continuous saponification, supplied as free-flowing, dust-controlled granules. The grade is characterised by a nominal 4 % aqueous solution viscosity of 28–32 mPa·s (Brookfield LV, 20 °C, 60 rpm, determined in accordance with ASTM D 3591‑17) and a residual acetyl content corresponding to a degree of hydrolysis of 87–89 mol% (JIS K 6726 back-titration method). Ash content, measured as sodium oxide, is controlled to ≤ 0.5 % by mass, and the pH of a 4 % solution at 25 °C falls in the range 5.0–7.0. The intermediate molecular weight and partial hydrolysis position BP‑17N between fully water-soluble cold-dispersible grades and highly crystalline, hot-water-soluble grades, allowing it to function as a versatile temporary or permanent binder, film-former, and protective colloid in applications where rapid hydration, controlled open time, and moderate moisture resistance are required.

In adhesive compounding, the granulated form permits direct addition into high-shear mixer tanks equipped with a rotor-stator device or a saw‑tooth dissolver operating at tip speeds above 18 m/s. When dry-blended with starches, dextrins, or extenders at filler-to-PVA ratios up to 1.5:1, the grade’s narrow particle size distribution (95 % passing 1.0 mm sieve, 10 % maximum retained on 0.15 mm sieve) suppresses segregation during pneumatic conveying, a failure mode commonly observed in plants using powdered fully hydrolysed PVA with a broader span. Solution make‑up should target a solids content between 8 % and 20 % by mass; cold water (10–25 °C) disperses the granules without lumping, but hydration is completed only after heating to 92–96 °C under gentle agitation for a minimum of 30 minutes. Premature cooling below 70 °C before full solubilisation leads to microgel carry‑over that can generate fisheyes in downstream coating or casting processes.

When viscosity build‑up in starch‑PVA size press formulations becomes a critical constraint, BP‑17N offers a narrower rheology drift window than oxidised starches blended with fully hydrolysed PVA. On a production‑scale film‑press line (Voith SpeedSizer AT, 1 200 m/min web speed), a 7 % solids blend containing 30 % BP‑17N on dry starch displayed a Brookfield viscosity of 110–125 mPa·s at 60 °C immediately after make‑down, with a rise of only 8–12 % over a 4‑hour hold at 55 °C under mild circulation. Under identical conditions, a comparable fully hydrolysed grade shifted from 135 mPa·s to 210 mPa·s, causing streaking on the metering bar. The controlled retrogradation behaviour is attributed to the residual acetate groups of BP‑17N, which interfere with inter‑molecular hydrogen bonding between PVA and starch amylose. Operators should nevertheless avoid calcium‑containing water hardness above 350 ppm as CaCO₃, because divalent ions accelerate syneresis in starch‑PVOH films and can precipitate sodium lignosulfonate-based dispersants often co‑formulated in industrial starch grades.

How does BP-17N compare with low‑viscosity and fully hydrolysed grades when used as a protective colloid in vinyl acetate emulsion polymerisation?

The grade’s hydrophobe-hydrophile balance, expressed through a Hansen solubility parameter δ_h of approximately 23 MPa^½, promotes grafting of vinyl acetate monomer onto the PVA backbone during radical initiation, yielding latices with mechanical stability that can exceed 6 months at 25 °C in non‑agitated storage, as measured by ASTM D 7149‑05. Compared with low‑viscosity partially hydrolysed grades (nominally 4–6 mPa·s), BP‑17N requires a higher feed rate to achieve equivalent particle size; typical use levels range from 1.5 % to 4.0 % by weight of total monomer, depending on the target particle size of 0.5–2.0 µm (D 50, laser diffraction, ISO 13320:2020). The higher chain length of BP‑17N improves wet scrub resistance of architectural coatings based on the resulting latex, accompanied by a measured improvement in Taber abrasion loss (CS‑17 wheel, 1 000 g load, 500 cycles) from 65 mg for a 5 mPa·s PVA colloid to 48 mg for a BP‑17N-based latex, as evaluated under ASTM D 4060‑19. However, the higher viscosity of the water phase during polymerisation elevates reactor torque by approximately 15–20 % during the initial monomer pre‑emulsion stage, so drives must be sized for peak loads of at least 1.3 kW/m³ in 10 000‑L pilot‑plant vessels with anchor‑helix agitation at 60 rpm. Published data for this specific reactor configuration in open literature is limited, but multiple producers have confirmed the torque trend during technology transfer trials.

In textile warp sizing, the removal (desizing) efficiency after atmospheric steam treatment constitutes a differentiating attribute. Cotton warps sized with a 9 % BP‑17N solution, dried on a cylinder set at 130 °C surface temperature, and subsequently desized in a continuous open-width washer at 80 °C for 90 s showed ≥ 99 % size removal, verified by iodine‑boric acid spot test, compared with 92 % for a fully hydrolysed grade of equivalent viscosity. The partial hydrolysis reduces crystallinity from approximately 55 % (XRD, peak deconvolution, 2θ = 19.6°) to 38–42 % in dried annealed film, allowing rapid ingress of wash water. Consequently, integrated mills employing enzymatic desizing with α‑amylase can lower enzyme dosage by up to 20 % without increasing residual size on fabric beyond 0.3 % owf (on weight of fabric). The granules can be directly metered into high‑speed cooking units (e.g., IBT Flexipro) along with lubricants and waxes; when soot‑cooked at 105 °C and 3 bar for 20 min, the solution achieves a Hess‑Philip number indicative of complete solution, and no undissolved particle count exceed 2 per 100 mL as determined by wet screen analysis using a 63 µm mesh.

Film mechanical behaviour under varying relative humidity

Cast films of BP‑17N conditioned according to ISO 291 (23 °C, 50 % RH) yield a tensile strength of 45–52 MPa and elongation at break of 220–260 % (ASTM D 882‑18, 50 mm/min grip separation). At 80 % RH, the elongation increases to 290–330 % while tensile strength drops to 28–33 MPa, reflecting plasticisation by absorbed water, which reaches an equilibrium moisture content of 9–11 % by mass. The transition is reversible over three humidity cycles with less than 5 % hysteresis in modulus. In contrast, films of a fully hydrolysed PVA with similar 4 % solution viscosity show a drop from 70 MPa to 20 MPa over the same range, with permanent elongation set of 12 % after the first cycle, indicating BP‑17N’s superior dimensional recovery under cyclic humidity, a key parameter for water‑soluble packaging films that must remain robust through tropical shipping yet disintegrate in cold‑water washing machines at 20 °C.

When BP‑17N is employed as a binder in high‑green‑density ceramic slip casting, interactions with boric acid or borax must be screened. Even at 0.05 % w/w borax addition based on PVA, viscosity of a 5 % BP‑17N solution rises from 30 mPa·s to 250 mPa·s within 60 seconds at 25 °C, forming a non‑reversible gel unusable for tape casting. This crosslink occurs through diol‑borate complexation with the 1,3‑diol configuration of residual acetate‑hydrolysed segments and is more pronounced than with fully hydrolysed grades because the random distribution of acetate groups creates longer sequences of vicinal hydroxyls available for complexation. Formulators can suppress gelation by adding a low‑molecular‑weight polyol such as glycerol at a glycerol:borax molar ratio of 3:1, but the benefit must be weighed against the resulting reduction in green strength. For aqueous tape casting of alumina substrates, a migration‑free binder approach uses BP‑17N in combination with plasticised PVAc emulsion, circumventing borate‑based crosslinkers.

When tetrahydrofuran replaces water as the carrier solvent in barrier coating formulations

While BP‑17N is insoluble in most organic solvents, blends with polyvinyl butyral in THF‑ethanol mixed solvents (80:20 v/v) have been evaluated in patent literature for oxygen‑barrier films. The BP‑17N component is introduced as a pre‑formed aqueous dispersion emulsified into the non‑aqueous phase using a non‑ionic surfactant (HLB 10–12) at 2 % on total resin. Resulting dry films cast at 80 °C and 20 µm dry thickness exhibit oxygen transmission rates (OTR) below 0.8 cm³/(m²·day·bar) at 23 °C, 0 %RH (ASTM D 3985‑17), a value competitive with EVOH‑based systems but without the moisture sensitivity penalty typical of EVOH; at 80 %RH, OTR rises to 2.4 cm³/(m²·day·bar), versus 12.0 for an EVOH (32 mol% ethylene) control under identical conditions. This indicates that BP‑17N can function as a humidity‑tolerant barrier component when domain size is controlled below 400 nm in the dried film, verified by scanning electron microscopy of cryo‑fractured cross‑sections. Processing demands high‑shear rotor‑stator emulsification with a minimum energy density of 2 × 10⁷ J/m³ to achieve the target particle size; batch‑to‑batch OTR variation increases from ±0.1 to ±0.4 cm³/(m²·day·bar) if the specific energy input falls below 1.5 × 10⁷ J/m³, a direct consequence of coalesced PVA domains causing micro‑voids at the film surface. Published data for this specific configuration is limited, but pilot‑scale trials on a 300‑L IKA Dispax‑reactor loop confirm the energy input threshold.

For extrusion‑grade compounds based on polyvinyl alcohol, storage of the granules under ambient conditions requires vigilance: at relative humidity exceeding 60 %, the equilibrium moisture of BP‑17N can surpass 5.5 % within 48 hours, sufficient to generate steam voids when fed directly into a twin‑screw extruder with barrel temperatures above 180 °C. Pre‑drying in a desiccant dryer to a moisture content ≤ 0.3 % is mandatory when the compound is processed through a 25 mm co‑rotating twin‑screw extruder (L/D = 40) with a melt temperature target of 195–210 °C; failure to do so leads to surging at the die with a pressure fluctuation amplitude exceeding 25 % of setpoint. The partial hydrolysis advantage—lower melting point (180–190 °C versus 228 °C for fully hydrolysed grades) and wider processing window—allows co‑extrusion with heat‑sensitive biodegradable polyesters at screw speeds of 200–250 rpm without transesterification catalysts, preserving melt strength measured via a Gottfert Rheotens run at 190 °C and acceleration of 6 mm/s².

In paper coating, BP‑17N is frequently blended with styrene‑butadiene latex to modify rheology and grease resistance. A 100 µm coating layer applied to 230 g/m² bleached board at a coat weight of 14 g/m² (dry) using a bent‑blade coater at 800 m/min exhibited a kit‑value improvement from 6 to 9 (TAPPI T 559 cm‑12) after the addition of 5 % BP‑17N to the binder share. Simultaneously, the ink gloss after offset printing increased by 7 points (60° gloss meter) due to the film‑forming capacity of the PVA under the calender nip. The reformulated coating displayed shear‑thinning behaviour with a capillary viscosity extrapolated to infinite shear of 0.22 Pa·s, compared with 0.35 Pa·s for the pure latex coating, enabling stable runnability without misting at the blade. This benefit is not observed with the fully hydrolysed analogue BP‑17S, which produces micro‑flocs with the latex at alkaline pH 8.5–9.0 typical of precipitated calcium carbonate‑based coatings, causing visible blade streaks.

Table 2. Regulatory compliance matrix for CCP PVA BP-17N

Operational boundaries of BP‑17N extend to its interaction with cationic compounds. The grade carries a low anionic charge density (0.8–1.2 meq/100 g, measured via polyelectrolyte titration with poly‑DADMAC at pH 7.0), but should not be co‑dissolved with primary or secondary amines in hot solution because the slight alkalinity combined with residual sodium acetate can catalyse saponification‑like chain scission, leading to a viscosity loss of 8–12 % per hour at 90 °C. When cationic starch is deployed in the same size press circuit, a polyaluminium chloride pretreatment of the starch at a dose of 0.3 % on dry starch reduces charge‑driven precipitation with BP‑17N, maintaining runnability documented on a Beloit flooded‑nip size press running at 1 100 m/min with a pickup of 4.2 % on dry fibre over 72‑hour continuous operation.