CCP PVA BP-20H

Viscosity Anomalies and Molecular Weight Distribution in BP-20H During High-Shear Emulsion Polymerization

CCP PVA BP-20H is a partially hydrolyzed polyvinyl alcohol supplied as a free-flowing granular powder with a particle size passing **95% through 20 mesh (850 µm)**. The product exhibits a nominal degree of hydrolysis of **87–89 mol%** and a 4% aqueous solution viscosity at **20°C** of **20.0–24.0 mPa·s**, determined according to ISO 15023-2:2019 using a Brookfield LV viscometer at 60 rpm. Residual sodium acetate content is controlled to **≤1.0 wt%**, ash content to **≤0.5%** as Na₂O, and volatile matter to **≤5.0%** after 3 h at **105°C** in a forced-air oven. The molecular weight (Mw) is in the range of **110,000–130,000 g/mol** by GPC relative to polyethylene glycol standards, giving a polydispersity index typically between **2.1 and 2.5**. These parameters position BP-20H as a medium-viscosity, medium-hydrolysis protective colloid for vinyl acetate (VAc) homo- and copolymer dispersions, where its balance of grafting activity and aqueous-phase viscosity is exploited to achieve coarse-particle-free lattices with viscosity profiles amenable to downstream coating and adhesive processing. Batch-to-batch grafting consistency in VAc emulsion polymerization conducted in a 10 m³ glass-lined reactor with a pitched-blade turbine operating at tip speeds of **3.5–4.5 m/s** is sensitive to the molecular weight distribution of the PVOH fraction remaining ungrafted. When BP-20H is dissolved to **10 wt%** in demineralized water at **85°C** under recirculation until an optical clarity of **≤5 NTU** is achieved, and the solution is charged at **4.5 parts per hundred monomer (phm)** with potassium persulfate initiation at **0.25 phm**, the evolution of MFFT of the resulting dispersion follows a narrow window: a deviation in the hydrolysis degree of the raw PVOH by **±0.5 mol%** shifts the onset of particle nucleation by **12–18 seconds**, which at the **82°C** reaction temperature can lead to a jump in the coagulum fraction from **0.02%** to **>0.5%** on 100 µm screen filtration. The phenomenon is exacerbated when the initiator addition rate exceeds **0.12 phm/min** during the first **15 minutes** of monomer feed. In pilot trials with a continuous monomer addition profile over **240 minutes**, the grafting efficiency of BP-20H measured as the insolubles in acetone extraction remained between **38 and 42%**, compared with **25–30%** for a lower-viscosity grade of identical hydrolysis. This difference is attributed to the higher segmental mobility of shorter-chain PVOH molecules in the aqueous phase, which accelerates radical transfer to the backbone at a rate that outpaces termination at the particle-water interface. Operational boundaries observed on production-scale twin-screw compounding of the subsequent dispersion with plasticizer (dibutyl phthalate or triacetin): when the latex obtained with BP-20H is subjected to shear rates above **1,200 s⁻¹** in the compounding extruder (L/D **48:1**, screw diameter **92 mm**, variable kneading block configuration), the molecular weight of the PVOH protective layer can degrade through mechanochemical scission if the melt temperature exceeds **165°C** for a residence time longer than **75 seconds**. This results in a loss of wet-bond strength in the final adhesive formulation by **≥30%** within 24 h of application, as measured by EN 204 D3. Pre-drying of the PVOH powder to **<1.0%** moisture is mandatory when relative humidity at the bagging station exceeds **60%**, otherwise clumping at the hopper throat causes feed inconsistency and a **3–5%** variance in the PVOH content of the dispersion.

What differentiates BP-20H from lower-ash, fully hydrolyzed grades in paper surface sizing?

The performance of BP-20H in size-press formulations for fine paper (grammage **60–120 g/m²**) is governed by its film-forming temperature and the interaction of residual acetate groups with cationic starches. When a solution of BP-20H at **8.0%** concentration is combined with a quaternary ammonium starch at a polymer:starch ratio of **1:4** on a puddle-type size press running at **800 m/min**, the surface strength improvement—quantified by the IGT pick test according to ISO 3783:2006—is **2.0–2.3 m/s** versus **1.1–1.4 m/s** for a fully hydrolyzed PVOH of similar viscosity (hydrolysis ≥98 mol%). The mechanism is twofold: the lower degree of crystallinity in the partially hydrolyzed PVOH film reduces the minimum film-forming temperature to **<5°C**, allowing coalescence without plasticizer even on a cold paper web exiting the after-dryer section at **45°C**. Second, the residual acetate moieties disrupt inter-chain hydrogen bonding, decreasing the elastic modulus of the dried film from **3.2 GPa** (fully hydrolyzed) to **1.7 GPa**, thereby matching the compliance of the fiber network and reducing micro-crack formation at the fold line during subsequent converting. A critical incompatibility arises when borax or boric acid is used as a gelling agent in the starch cook: the -OH sequences in the low-hydrolysis BP-20H do not present sufficient stereoregularity for complexation, causing a sharp drop in solution viscosity within **20 minutes** of mixing at **60°C**, from **350 cP** to **<50 cP**. Therefore, only non-borated starch systems are recommended. Published data for this specific configuration with high-speed film coaters (blade-metering size press operating above **1,200 m/min**) are limited; an observed limitation is the tendency of the BP-20H film to develop blocking at roll temperatures above **40°C** unless a hydrophobic surface-sizing agent (e.g., alkyl ketene dimer at **0.15%** on dry fiber) is co-applied. Process window for continuous emulsion polymerization using BP-20H as the sole protective colloid:

Parameter	Set Point	Lower Bound	Upper Bound	Consequence of Deviation
PVOH solution concentration	10 wt%	9.5%	10.5%	Viscosity drift in reactor>±8%
Reactor temperature	82°C	80°C	84°C	Particle size bimodality>500 nm
Initiator feed profile (first 15 min)	0.10 phm/min	0.08	0.12	Coagulum >0.5%
Monomer addition time	240 min	220	260	Residual VAc>0.5%
Post-reaction hold at 85°C	60 min	45	75	Unreacted monomer>1,500 ppm

Adhesive Formulation: When Plasticized BP-20H Replaces Polyurethane Dispersion Blends

In a laminating adhesive for wood veneer bonding onto MDF substrate (press cycle **2.5 min** at **90°C** and **0.7 MPa**), replacement of a co-binder system (50:50 PVAc dispersion and an aliphatic polyurethane dispersion) with a single-component adhesive based on a BP-20H-stabilized VAc/VeoVa10 copolymer dispersion reveals a shift in failure mode. The PUD component was originally incorporated to improve heat resistance and reduce creep under static load. With BP-20H as the sole protective colloid at **5 phm** in the copolymer, the heat resistance temperature measured by EN 14257 (WATT 91) remained at **68°C**, compared to **74°C** for the PUD blend. The shortfall in creep performance at **50°C** and a static load of **0.5 kg/cm²** over **24 h** was less than **0.3 mm**, within the Class D3 requirement, but below the PUD blend’s **0.1 mm** displacement. The cost reduction from eliminating the PUD component is offset by a mandatory post-application crosslinking step: an isocyanate hardener (MDI prepolymer at **3%** on wet weight) restores WATT 91 to **81°C**, matching the PUD blend. A separate deep-dive zone exists in the reactivity of BP-20H with formaldehyde-based crosslinkers. The residual hydroxyl content of **87–89%** hydrolysis grade offers approximately **17.5 mmol OH/g**. Titration of these groups with glyoxal at a mole ratio of **OH:CHO of 1:0.25** in an aqueous solution below pH **4.5** yields a half-gel time at **60°C** of **22 minutes**. Above pH **5.2**, the gel time extends beyond **120 minutes**, and the resulting film exhibits water sensitivity due to incomplete acetal formation. This pH cliff forces the adhesive compounder to either operate in a narrow acidic window or switch to a fully hydrolyzed grade that gels more reliably in neutral conditions. Comparison of BP-20H with adjacent grades in the BP series:

Property	BP-17H	BP-20H	BF-24H	Test Method
Hydrolysis, mol%	86.5–89.0	87.0–89.0	97.5–99.0	ISO 15023-3:2019
Viscosity (4% aq.), mPa·s	17.0–20.0	20.0–24.0	23.0–27.0	ISO 15023-2:2019
Ash (as Na₂O), %	≤0.5	≤0.5	≤0.8	ISO 15023-1:2019
Volatile matter, %	≤5.0	≤5.0	≤5.0	ISO 15023-1:2019
Sodium acetate, wt%	≤1.0	≤1.0	≤1.2	Titrimetric
Grafting efficiency in VAc polym.	25–30%	38–42%	10–15%	Acetone insolubles

Regulatory Status Relevant to Food-Contact Adhesive and Paper Applications

The product falls within the inventory of existing chemical substances in all major territories (AICS, DSL, IECSC, TSCA, EU-list). In food-contact contexts, the partially hydrolyzed PVOH of this viscosity range is the subject of several favorable evaluations: • FDA 21 CFR §175.105 – Adhesives. The substance may be used as a component of adhesives used in food packaging, provided that the adhesive is separated from food by a functional barrier or is used in a quantity that will not exceed good manufacturing practice limits. • FDA 21 CFR §176.170 – Components of paper and paperboard in contact with aqueous and fatty foods. BP-20H meets the specifications for polyvinyl alcohol as a surface-sizing agent and coating binder under this section when used in amount not exceeding that required to produce the intended technical effect. • BfR Recommendation XXXVI – Paper and board for food contact. Satisfies the requirement for polyvinyl alcohol when the migration of residual monomers and impurities does not exceed the specific migration limits. • Swiss Ordinance on Materials and Articles (SR 817.023.21). Listed under Annex 2 for use in paper and board. • EU Regulation (EC) No. 1935/2004 and Commission Regulation (EU) No. 10/2011: PVOH is not within the positive list for plastic materials but is admitted as a non-plastic component under certain national rules; the resin itself is subject to overall migration limits under Regulation 10/2011 when used in multi-material multi-layer structures. No specific migration limit has been set for PVA, but the residual VAc monomer content is restricted to <2 mg/kg in the final article. The presence of **≤1.0%** sodium acetate necessitates a calculation of ionic contribution when formulating for paper grades intended for direct contact with fatty foods exhibiting a K-value above **40**, to avoid exceeding the overall migration limit of **10 mg/dm²**. In a warp sizing operation, the sizing bath concentration of BP-20H typically ranges from **5% to 8%** (dry on starch weight) on a single size box for cotton/polyester ring-spun yarns. The viscosity stability of the cooking liquor at **85°C** over **6 hours** at a high-shear circulation pump (centrifugal, **2,900 rpm**) shows a degradation of less than **2%** from the initial value of **180 mPa·s**, measured at a shear rate of **50 s⁻¹**. This stability is superior to fully hydrolyzed grades that undergo microcrystalline aggregation upon cooling to **60°C**, leading to skin formation on the size box rollers. The desizability of BP-20H film from textile substrate using α-amylase desizing at **60°C** for **45 minutes** reaches **>99%** removal, verified by spectrophotometric potassium bichromate method.