Wanwei PVA 17-95(L) (PVA 095-27)

Anhui Wanwei Group designates this partially hydrolysed polyvinyl alcohol as PVA 17-95(L), alternatively coded PVA 095-27. It occupies the intermediate alcoholysis window between fully saponified homopolymers and the highly water-sensitive 88 mol% grades, with a nominal degree of polymerisation of 1700 and a hydrolysis degree controlled to 95.0 ± 1.0 mol%. The “L” suffix denotes a low-methanol-extraction post-treatment, resulting in reduced residual vinyl acetate monomer and an ash ceiling of 0.2%, which distinguishes this grade from standard 17-95 material in applications where ionic contamination compromises dielectric performance or adhesive bond stability. Film cast from 4% aqueous solution exhibits tensile strength at break in the range 40–50 MPa (GB/T 1040.3, conditioning at 23 °C, 50% RH) with elongation at break 250–350%, reflecting the balance between amorphous domain mobility and residual crystalline anchoring contributed by retained acetate groups.

Specifications and Analytical Compliance Matrix

What Differentiates a 95 mol% Hydrolysed PVA from Fully Saponified and Low-Hydrolysis Grades?

Fully saponified grades such as 17-99 (hydrolysis ≥ 98.5 mol%) require dissolution temperatures above 90 °C and yield films with minimal cold-water sensitivity and tensile modulus exceeding 4.5 GPa. At the opposite end, 17-88 (88 mol%) dissolves readily in water at 10–15 °C but exhibits high surface tack and tensile strength below 30 MPa. The 95 mol% structure in 17-95(L) balances solubility onset at 40–50 °C with a storage modulus G’ plateau in the semi-dilute regime approximately 2.3 kPa (6% solution, 25 °C, oscillatory frequency 1 Hz), providing sufficient chain entanglement for cohesive film formation without the severe crystallinity-driven brittleness observed in fully hydrolysed analogues. Residual acetate groups reduce hydrogen-bond-driven ordering, preserving ductility under cyclic loading relevant to flexographic plate mounting tapes and repulpable splicing adhesives.

In textile warp sizing lines operating at slasher speeds above 80 m/min, the size liquor composed of 6–8% PVA 17-95(L), 3% acrylic copolymer, and 0.8% tallow wax is maintained at 85–88 °C in a Sucker Müller SMR size box. Delivered add-on on Ne 30 ring-spun cotton warp is 10–12% dry weight. If box temperature drops below 80 °C, surface skinning on the immersion rolls produces gel specks that deposit within the reed dents, causing warp-end abrasion on air-jet looms operating at 900 picks/min. Film abrasion resistance, measured by Zweigle G55 Gauge with 400-cycles under 50 g load, shows a mass loss ≤ 2.5 mg for films cast from liquors conditioned at 88 °C. Migration of the size film during quiescent storage in weaving sheds where humidity exceeds 85% RH leads to blocking; pre-drying warp sheets to 6–8% moisture content before lease separation is mandatory.

When 17-95(L) Replaces Higher-Viscosity Grades in Emulsion Polymerisation Protective Colloids

In the suspension polymerisation of vinyl acetate monomer initiated by azobisisobutyronitrile (AIBN) at 0.05% on monomer, PVA 17-95(L) is dosed at 1.2–1.8% (w/w monomer) into the aqueous phase. The low ash content minimises interference with the free-radical initiation sequence, while the narrow hydrolysis distribution reduces polydispersity-driven partitioning effects that would otherwise widen the particle size distribution. Post-polymerisation analysis by laser diffraction (ISO 22498) confirms a volume median diameter Dv50 of 80–120 µm when the agitation is set to produce a tip speed of 3.5 m/s in a 3 m³ glass-lined reactor with a Pfaudler retreat-blade impeller. Substitution of a 17-99 grade under identical conditions raises Dv50 to 180–240 µm and increases coarse fraction (>500 µm) due to poor interfacial tension reduction, while 17-88 over-stabilises the dispersion and generates excessive fines (Dv50 < 20 µm) that raise emulsion viscosity beyond pumpable limits.

Processing Temperature Limits and Degradation Kinetics in Twin-Screw Extrusion

Compounding PVA 17-95(L) with glycerol (15 phr), urea (8 phr), and stearamide (0.5 phr) for water-soluble blown film requires a co-rotating twin-screw extruder with L/D = 40:1 and a modular screw profile incorporating two kneading blocks of 45° stagger angle followed by a reverse-flighted intensive mixing zone. Barrel temperature profile: Zone 1 90 °C, Zone 2 130 °C, Zone 3 155 °C, Zone 4 165 °C, die adapter 170 °C. Plasticising must be complete before Zone 2; residual crystalline domains entering Zone 3 create viscosity heterogeneities that manifest as ±15% thickness variation in the final film (ASTM D6988). Degradation onset detected by DSC at 200 °C (ramp 10 K/min, nitrogen purge) produces acetic acid, which autocatalytically accelerates chain scission. Residence time is therefore restricted to < 120 s, monitored by a graphite tracer pulse. Pre-drying of the powder in a desiccant hopper dryer at 80 °C for 4 h until residual moisture is < 0.5% is mandatory; otherwise, steam devolatilisation at the vent port creates bubble defects and reduces film dart impact by 40–50% (ISO 7765-1). Purging with linear low-density polyethylene at shift end prevents carbonised deposits at the die lips.

In low-solids oilfield fluid loss pills, 0.8% PVA 17-95(L) is hydrated in 2% KCl brine, after which controlled crosslinking with sodium tetraborate decahydrate at 0.015% generates a shear-reversible gel. Gel time at 25 °C is 18 min, reaching an equilibrium storage modulus G’ of 420 Pa (vane rheometer, stress 5 Pa). Concentrations exceeding 0.03% borax produce syneresis within 6 hours static aging at 80 °C, rendering the pill ineffective for loss zone sealing. This system is incompatible with amine-based shale inhibitors; pH drift above 8.2 deacetylates the polymer backbone, shifting cloud point and collapsing the gel network.

Comparative Profiles of Selected Wanwei Polyvinyl Alcohol Grades

For a simple repulpable bookbinding adhesive, PVA 17-95(L) is dissolved at 12% solids in water heated to 60 °C and blended with acid-modified corn starch in a 1:1.2 ratio.