ÇKP PVA BP-17L

CCP PVA BP‑17L is a partially hydrolysed polyvinyl alcohol grade produced by Chang Chun Petrochemical Co., Ltd. The resin is supplied as a free‑flowing white powder with a bulk density typically in the range 0.40–0.55 g/cm³ and a volatile content below 5.0 % when measured under ISO 3251 (105 °C, 3 h). The polymer backbone derives from polyvinyl acetate with a controlled degree of alcoholysis, giving residual acetyl groups that depress crystallinity and broaden the cold‑water solubility window. The grade is routinely deployed as a primary protective colloid in vinyl acetate and vinyl‑versatate emulsion polymerisation, as a temporary binder in ceramics, and as a film‑former in water‑soluble packaging where dissolution rate and mechanical integrity must be balanced. In all these functions the essential difference from fully hydrolysed PVA grades is the lower degree of hydrolysis, which shifts the cloud point downward and permits processing in cold‑water systems without the high‑temperature dissolution steps (>85 °C) required by grades with >98 mol% hydrolysis.

What Distinguishes BP‑17L from Conventional Partially Hydrolysed PVA Grades?

The resolution of a partially hydrolysed PVA into a specific viscosity–hydrolysis combination determines its protective‑colloid activity and secondary film properties. BP‑17L occupies an intermediate position. The nominal degree of hydrolysis, determined by titration according to ISO 1597, falls between 87.0 mol% and 89.0 mol%. At this acetal‑shadowed balance, the polymer retains sufficient residual acetyl groups to prevent gel‑phase separation when cooled below 15 °C in aqueous solution, while still providing the interfacial tension reduction needed for small‑particle latex stabilisation. The dynamic viscosity of a 4 % (m/m) aqueous solution at 20 °C, measured with an Ubbelohde capillary viscometer under ISO 3104, is controlled to 4.5–6.5 mPa·s. This viscosity range is deliberately lower than that of the manufacturer’s BP‑20 (20.0–26.0 mPa·s) and higher than BP‑05 (4.0–5.0 mPa·s), placing BP‑17L in the zone where reactor fluid mechanics can be optimised without excessive increase in mix‑motor torque during the latter stages of batch emulsion polymerisation, when free monomer is depleted and viscosity climbs sharply due to particle crowding.

High‑Shear Stability and Particle Size Control in Emulsion Polymerisation

In vinyl acetate‑based emulsion formulations where the protective colloid is the sole stabiliser, the molecular weight distribution of BP‑17L influences both the nucleation period and the resistance to shear‑induced coagulation during the growth stage. Pilot‑scale data from a 250‑L glass‑lined reactor equipped with a two‑stage anchor impeller (80–120 rpm) show that at an addition level of 5 wt% relative to monomer, the final latex particle size falls within 350–600 nm (z‑average, ISO 22412) with a polydispersity index <0.15 when the initiator is fed over 4 h at 70 °C. Compared with grades of higher viscosity, BP‑17L reduces the incidence of macro‑gel formation in the reactor volume by approximately 30–50 %, evaluated by filtration through a 100 µm sieve after the hold period. The rheological signature of the reaction mass, monitored by a torque‑linked agitator drive, shows a flatter profile during the final conversion ramp, reflecting the lower solution viscosity of the aqueous phase. This behaviour allows the solids content to be pushed above 55 % without exceeding the drive’s continuous rating of 2.2 kW.

Operational limits: when the protect‑colloid loading drops below 3 wt% on monomer, the particle size distribution broadens and a secondary population above 1 µm appears, detectable by disc‑centrifuge photosedimentometry. Above 8 wt% loading, the Brookfield viscosity of the finished latex (spindle LV‑3, 12 rpm) approaches 12 000 mPa·s, which can impede let‑down and pumping. Pre‑dissolution of BP‑17L must be performed in demineralised water at 20–25 °C with a high‑dispersion dissolver at a tip speed of at least 18 m/s; incomplete dissolution yields microgel seeds that act as nucleation centres during polymerisation. The dissolved colloid solution should be used within 24 h to prevent microbial slime formation that can block downstream filters.

In water‑based adhesive formulations, the product demonstrates rapid cold‑water tack development on porous substrates. Draw‑down films of a 10 % aqueous solution conditioned at 23 °C and 50 % RH yield a tensile strength at break of 35–45 MPa (ISO 527‑3, specimens type 5, testing speed 100 mm/min) and an elongation at break of 180–250 %. By comparison, fully hydrolysed grade BP‑24 (hydrolysis degree >98.5 %) requires dissolution at >90 °C and develops ultimate tensile strength values above 70 MPa but with elongation reduced to <50 %. The higher flexibility of BP‑17L films makes them preferable for paper‑to‑paper laminations where differential shrinkage of the substrate can otherwise cause curl. During production, pre‑drying of the powder is recommended when ambient relative humidity exceeds 60 %, as the equilibrium moisture uptake at 65 % RH exceeds 8 % and leads to bridging in the feed hopper of a loss‑in‑weight dosing unit.

If Calcium‑Based Filler Compatibility Is Critical for Paper Coating

In paper surface‑sizing formulations containing precipitated calcium carbonate, BP‑17L imparts water‑retention values that exceed those of oxidised starches at equivalent pick‑up weights. Cobb60 water absorption (ISO 535) on a 100 g/m² wood‑free base paper drops from 35 g/m² to 14–18 g/m² when a 5 % PVA solution is applied at a size‑press nip pressure of 15–25 kN/m and a drying‑cylinder surface temperature of 75 °C. The rheology of the size‑press bath, recorded with an in‑line process viscometer, remains within 30–80 mPa·s over a temperature window of 45–65 °C, which is sufficiently wide to avoid viscosity spikes during machine stops. A known incompatibility exists with borate‑containing crosslinkers: the addition of borax at molar ratios exceeding 0.02 mol boron per mol of vinyl alcohol unit induces rapid gelation, making the size formulation unusable after 30 s of circulation. Therefore, wet‑strength must be developed by incorporating a polyamide‑epichlorohydrin resin (added separately just before the size press) rather than through board‑like PVA‑borate complexation.

The difference from fully hydrolysed grades is most evident in calcium‑ion tolerance. BP‑17L solutions maintain clarity and Newtonian flow behaviour at Ca²⁺ concentrations up to 500 mg/L, whereas a 4 % solution of a 99 %‑hydrolysed grade develops turbidity above 100 mg/L. This is attributed to the acetate‑rich short blocks that suppress lattice‑like ionic crosslinking, a property that directly extends felt‑side runnability on paper machines using hard water.

Migration Resistance in Water‑Soluble Films

Water‑soluble packaging manufactured by cast‑film extrusion from BP‑17L produces films with a dissolution time, tested according to the internal method derived from ISO 14852 (framed for biodegradation but adapted here for disintegration under shear), typically in the range 25–40 s for 30 µm thickness at 20 °C in still water. The dissolution profile exhibits a lag phase of 5–8 s followed by rapid mass loss as the film reaches a plasticised state. For detergent pod applications, where resistance to cold wash cycles is required, the film can be blended with a higher‑hydrolysis grade (e.g., BP‑24) in a 70:30 ratio, shifting the cold‑water disintegration point below 10 °C. Migration of plasticiser (glycerol added at 8–12 phr) to the film surface, measured gravimetrically after 7 d at 40 °C and 75 % RH, is less than 2 mg/dm², a value that falls within the acceptance criteria for secondary packaging in contact with food‑grade detergent pouches. The film’s oxygen transmission rate at 23 °C and 0 % RH (ISO 15105‑2) is <1 cm³/(m²·d·bar), providing sufficient barrier to slow the oxidation of fragrances during shelf‑life.

When incorporated as a temporary binder in ceramic injection‑moulding feedstocks, BP‑17L permits debinding cycles in air without the evolution of corrosive by‑products. Thermogravimetric analysis (heating rate 5 °C/min, air flow 50 mL/min) shows the onset of thermal decomposition at 230 °C and complete burn‑off by 500 °C, leaving an ash residue below 0.5 % (ISO 3451‑1). That residue level is significantly lower than that obtained with polyvinyl butyral binders processed under identical conditions, reducing carbon‑rich defects in sintered alumina components sintered at 1600 °C. The powder‑binder mixture, prepared on a twin‑screw extruder with an L/D ratio of 20, exhibits a melt‑flow index of 6–12 g/10 min (190 °C, 2.16 kg, ISO 1133‑1) when plasticised with 15 wt% polyethylene glycol. Storage of the feedstock under dry nitrogen at <25 °C is essential, as absorbed moisture above 0.3 % leads to steam porosity during moulding. The binder system is not suitable for use with oxide powders that exhibit acidic surface groups (isoelectric point <3), where accelerated acetal formation can embrittle the green part.