ÇKP PVA BP-17S

CCP PVA BP‑17S is a partially hydrolyzed polyvinyl alcohol resin manufactured through continuous alcoholysis of polyvinyl acetate under controlled alkalinity. Its nominal degree of hydrolysis spans 87–89 mol% and the average degree of polymerization is 1,700–1,800, producing a 4 % aqueous solution viscosity of 25–31 mPa·s when measured at 20 °C with a Brookfield RVT viscometer (spindle #2, 20 rpm) following JIS K6726. The resin is supplied as a white, free‑flowing powder with a bulk density of typically 0.4–0.6 g/cm³ and a residual volatile content not exceeding 5 % when dried to constant mass at 105 °C. A condensed set of typical physical‑chemical benchmarks is given below.

When Partial Hydrolysis and 1,700 Degree of Polymerization Converge

The combination of an intermediate hydrolysis level and a medium‑high polymerization degree dictates the aqueous dissolution kinetics and rheological fingerprint. BP‑17S disperses rapidly in cold water (20–25 °C) without the extended heating required for fully hydrolysed grades; a translucent solution is obtained after stirring for 30–60 min at moderate shear. The apparent viscosity of a 10 % solution at 20 °C typically lies in the range 1 500–2 500 mPa·s, reflecting strong inter‑chain hydrogen bonding through residual acetate groups which disrupt crystallinity while preserving enough hydroxyl functionality for extensive water interaction. Above 15 % solids, the solution exhibits pronounced shear‑thinning behaviour and a measurable first normal stress difference in rotational rheometry (ISO 3219). The Huggins constant obtained from dilute‑solution capillary viscometry (ISO 1628-3) is on the order of 0.5–0.6, indicating a moderately good solvent environment at ambient temperature. When the solution is cooled below 10 °C, gelation can occur if the concentration exceeds 12 %, a threshold that shifts to lower solids with increased hydrolysis or higher molecular weight. In high‑shear make‑down equipment—a rotor‑stator device operating at 3 000 rpm—the addition rate of powder to the vortex must be controlled at 10–12 kg/min for a 500 L vessel to avoid the formation of partially hydrated agglomerates; once formed, these fish‑eyes cannot be fully eliminated without prolonged heating above 80 °C.

How Does Partially Hydrolyzed PVA Stabilize Vinyl Acetate Emulsion Droplets?

In emulsion polymerization, BP‑17S functions as a protective colloid through a graft‑stabilization mechanism that is highly sensitive to both molecular weight and residual acetate content. During vinyl acetate homopolymerization initiated by a water‑soluble persulfate (0.1–0.5 wt% on monomer), the 1,2‑diol and terminal carbonyl groups on the PVA backbone serve as sites for hydrogen abstraction, generating polymer‑radicals that graft vinyl acetate branches onto the PVA. Grafting efficiencies measured by selective solvent extraction under 60 °C reflux typically reach 45–75 % for a 88 mol% hydrolysis grade, falling to below 30 % when hydrolysis drops to 80 mol% and decreasing to 50–60 % when it exceeds 92 mol% due to reduced backbone solubility in the monomer‑swollen particle. The grafted copolymer locates at the particle‑water interface, providing electrosteric stabilization; zeta‑potential values measured in 0.01 M KCl remain around −5 to −12 mV, so the principal repulsive contribution is steric. Particle size distributions measured by dynamic light scattering after 4 h of semi‑batch feed exhibit a monomodal character with a z‑average diameter of 200–400 nm when BP‑17S is used at 4–6 wt% based on total monomer. A lower‑molecular‑weight analog such as CCP PVA BP‑05 (degree of polymerization ≈500, identical hydrolysis window) yields smaller primary particles but provides insufficient mechanical stability during high‑shear let‑down; shear‑induced coagulation is observed in a Cowles disperser at tip speeds above 12 m/s, whereas BP‑17S‑stabilized latices tolerate at least 18 m/s before significant grit formation occurs. Conversely, the fully hydrolysed grade CCP PVA BF‑17 (hydrolysis ≥98 mol%) requires dissolution at 85–95 °C and, when used as sole colloid, generates coarse particles with broad polydispersity because the dense grafting layer retards radical entry and chain propagation at the particle surface. The narrow processing window for BP‑17S in vinyl acetate‑acrylic copolymerizations spans 60–75 °C; at temperatures above 80 °C the grafting density declines, and residual ungrafted PVA can phase‑separate as gel domains during neutralization to pH 8–9.

Addition of a 10 % pre‑dissolved BP‑17S solution to the reactor heel along with deionized water and a non‑ionic surfactant (0.2–0.5 phm) establishes an initial viscosity plateau of 80–150 mPa·s at 60 °C. Upon commencement of the monomer feed, the torque on an anchor agitator (60 rpm) climbs within 20–30 min as the particle number concentration surpasses 10¹⁵ particles/mL. A batch‑to‑batch variation in PVA degree of hydrolysis of only ±0.3 mol% has been correlated with a ±18 nm shift in the final latex particle size in a 2 000 L production reactor, underscoring the need for tight incoming quality control. Operators report that the delayed addition of the PVA stream—introducing 70 % of the total colloid only after 30 % monomer conversion—narrows the particle size distribution and raises the film‑forming minimum film‑formation temperature to ≈3 °C above that of a single‑shot charge, a useful lever for pressure‑sensitive adhesive rheology.

Film Tensile Strength and Elongation Under 23 °C, 50 % RH Conditioning

Cast films of BP‑17S dried from aqueous solution exhibit a tensile strength at break of 35–45 MPa and an elongation at break of 150–250 % when tested according to ASTM D882 (50 µm thickness, crosshead speed 50 mm/min). The film displays a glass‑transition temperature of approximately 85 °C by differential scanning calorimetry (10 K/min heating rate, second scan), and the water contact angle after 24 h conditioning is 52–58°, confirming a hydrophilic surface that can be heat‑sealed to paper and cellulosic substrates at 120–140 °C under 0.3 MPa pressure. At equilibrium moisture uptake (≈8–10 wt% at 50 % RH), the tensile modulus drops to roughly 60 % of the dry value, a property that must be accommodated when the grade is specified for water‑soluble packaging or embroidery stabilizers. Films plasticized with 10 % glycerol show a drop in Tg to 45 °C and an increase in elongation to 400 %, but the plasticizer migrates over 30 days to the surface under 40 °C, 75 % RH storage, limiting long‑term flexibility.

Ash Content, Transparency, and the “S” Designation

The “S” suffix in BP‑17S designates a low‑ash variant produced by intensified washing steps. Ash content is controlled to ≤ 0.3 % versus ≤ 0.5 % for the standard BP‑17 grade, a difference that reduces the yellowness index of aqueous solutions measured per ASTM E313 by 2–3 units and virtually eliminates insoluble gel specks in 50 µm adhesive films. In heat‑seal adhesives applied to medical packaging, the lower ionic residue retards corrosion on aluminium foil under accelerated aging at 60 °C and 90 % RH; pit formation observed by optical microscopy after 14 days is <5 pits/cm² compared with 15–25 pits/cm² for the higher‑ash homologue. The clarity of the 4 % solution, measured as percent transmittance at 550 nm wavelength, attains ≥95 % 10 min after dissolution completion, making the grade suitable for over‑print varnishes where haze must remain below 2 %.

Polyethylene‑lined multi‑wall paper bags should be stored in a dry environment at <25 °C and <60 % relative humidity. The product forms flammable dust‑air mixtures; conveying and blending equipment must be electrically grounded and located in areas classified as Zone 21 under IEC 60079‑10‑2.