A Sinopec PVA 095-28 identifies a partially hydrolysed polyvinyl alcohol resin manufactured by Sinopec Group, characterised by a nominal degree of polymerisation (DP) approximating
950 ± 50 and a hydrolysis level of
95.0 ± 1.5 mol% (determined by back-titration per GB/T 12010.2‑2010). The 4 % aqueous solution viscosity at
20 °C is controlled within
28 ± 3 mPa·s (Brookfield LV, spindle 2, 60 rpm; GB/T 12010.3‑2010), placing it between low‑DP grades such as 05‑88 and fully hydrolysed grades such as 17‑99. Volatile matter typically remains below
5.0 wt% and ash content below
0.5 wt% (GB/T 12010.4‑2010). The grade is supplied as a white, free‑flowing granular powder with a bulk density of
0.45–0.60 g/cm³. This combination of molecular weight and residual acetate content yields a balance of cold‑water dispersibility, film tensile strength, and adhesive performance suitable for textile warp sizing, emulsion polymerisation, and paper surface treatment.
What Differentiates 095-28 from Fully Hydrolysed Grades in Aqueous Solution Behaviour?
The critical distinction lies in the dissolution temperature window and solution stability. While fully hydrolysed polyvinyl alcohol (≥
99 mol%) typically requires heating above
85 °C and prolonged agitation to achieve complete dissolution, PVA 095-28 begins hydration at
20–25 °C and dissolves completely between
60 °C and
75 °C under continuous low‑shear mixing. This permits direct addition to ambient process water in textile sizing kitchens without pre‑heating, reducing energy input by approximately
30 % compared with 17‑99 grade in identically configured jacketed mixing vessels. The residual acetate groups disrupt inter‑ and intra‑molecular hydrogen bonding sufficiently to lower the cloud point of the aqueous solution, yet not so extensively as to compromise water resistance of the deposited film after desizing. On an industrial scale, operators report that a
5 wt% stocking solution of 095-28 exhibits no visible gel bodies after
45 minutes in a
500 L vessel with a twin‑blade agitator rotating at
120 rpm, while a comparable 17‑99 batch may retain microgel.
Solution viscosity stability over time is another observable difference. Measurements over
8‑hour holding periods at
50 °C show viscosity drift below
2 % for 095-28 when preserved with
0.05 wt% sodium dehydroacetate, whereas 17‑99 solutions can undergo a secondary structuring that increases apparent viscosity by
5–8 % within the same interval due to enhanced hydrogen bonding. This constancy is essential for metering pumps feeding size boxes on high‑speed weaving looms, where viscosity fluctuation directly alters size add‑on.
When the relative humidity in storage exceeds
60 %, the powder of 095-28 must be pre‑dried at
80 °C for a minimum of
4 hours in a forced‑air tray dryer to bring moisture content below
0.8 % before melt‑extrusion compounding or precision gravimetric feeding. Failure to do so leads to bubble formation in cast films and irregular pellet quality in masterbatch production.
When the Viscosity Drift Exceeds ±2 mPa·s in Size Box Replenishment
In continuous filament warp sizing on single‑end sizing machines — typically a Zell or Karl Mayer configuration with multi‑cylinder drying — the
4 % solution viscosity directly governs size add‑on and penetration into the yarn bundle. A drift beyond
±2 mPa·s from the target
28 mPa·s triggers a measurable shift in size pick‑up: an increase of
3 mPa·s correlates with approximately
1.2–1.5 % higher dry add‑on on polyester‑cotton
45 Ne yarn in a size box maintained at
85 °C and a nip pressure of
12 kN/m of roller width. Such drift, if uncorrected, elevates weaving shed stickiness and complicates desizing. Published data for this specific grade under alkali‑oxidative desizing conditions are limited; however, plant‑scale trials indicate that a
21 ± 2 % add‑on level produces adequate weaving efficiency when the size film is removed with a
2.0 % sodium hydroxide plus
0.5 % hydrogen peroxide bath at
90 °C for
120 seconds (desizing efficiency>
98 % by weight per GB/T 2912.1‑2009 formaldehyde extraction reference method). The partial hydrolysis enables the film to swell and disintegrate without the high caustic concentrations demanded by fully hydrolysed sizes, thus reducing chemical oxygen demand in the desizing effluent by an estimated
18–22 % compared with a 17‑99 size at equivalent add‑on.
Operators compensate for viscosity drift by adjusting the makeup water flow rate. A
0.5–1.0 % reduction in solids concentration typically restores the target viscosity. In practice, batch‑to‑batch viscosity variation within the
±3 mPa·s specification window is absorbed without process interruption, provided the size kitchen is equipped with an in‑line viscometer (Brookfield TT‑100 or similar) feeding back to a dosing unit with
±0.5 L/min accuracy.
The hot‑conditioned film on the yarn surface, when tested as a free film cast under identical conditions and evaluated per ASTM D882‑18 at
23 °C and
50 % RH, reveals a tensile strength of
37–42 MPa and an elongation at break of
120–150 %. These properties are insensitive to minor hydrolysis shifts but fall sharply if the dried film absorbs moisture above
8 wt%, a limitation that mandates conditioned storage of sized beams prior to weaving.
Without a heading, a separate application zone emerges.
In surface sizing of fine paper grades, the addition of PVA 095-28 at a wet‑end addition of
0.8–1.2 kg/tonne of paper raises the IGT pick velocity (ISO 3783:2006) by
12–15 % relative to an unsized control, without generating the film brittleness observed with fully hydrolysed 17‑99 at the same addition level, because the residual acetate groups impart sufficient plasticisation to prevent micro‑cracking under printing press conditions.
Evaluating Film Tensile Evolution under Variable Humidity
Dynamic mechanical analysis of solution‑cast films (
50 µm dry thickness, conditioned to equilibrium at
25 %, 50 %, and 75 % RH ) reveals that the storage modulus at
25 °C decreases by approximately
40 % when relative humidity rises from
50 % to
75 %, a behaviour common to partially hydrolysed PVAs. The tan δ peak, associated with the glass‑to‑rubber transition of the amorphous phase, shifts from
62 °C at
50 % RH to
48 °C at
75 % RH. These transitions are critical for warp sizing because the glass transition temperature must remain above the weaving‑room temperature (
28–32 °C) to prevent tack; the data confirm that PVA 095-28 retains adequate modulus under all but the most humid mill conditions. Fully hydrolysed 17‑99 exhibits a tan δ peak above
80 °C across the same humidity range, providing a wider safety margin but at the expense of the solubility advantages previously discussed.
Film oxygen barrier performance, measured as oxygen transmission rate (OTR) per ASTM D3985‑17 at
23 °C, 0 % RH, sits around
0.8–1.2 cm³·µm/(m²·day·atm) for a
20 µm film, roughly double that of 17‑99 films, due to higher free volume introduced by the acetate pendants. For paper coating applications where a moderate barrier is acceptable and the primary function is surface strength, this trade‑off is immaterial. In composite food packaging laminates, the grade is typically used in tie‑layer formulations rather than as a barrier layer.
Why Ash Content Must Remain Below 0.5% for Emulsion Polymerisation Applications
Residual sodium acetate, the primary contributor to ash in partially hydrolysed grades, functions as an electrolyte that collapses the electrical double layer around polymer particles in radical emulsion polymerisations. In continuous stirred‑tank reactors producing polyvinyl acetate homopolymer emulsions, an ash level above
0.5 wt% in the PVA protective colloid correlates with a measurable increase in coagulum formation: sieve residue (
100 mesh) rises from
<0.1 % to
0.3–0.5 % of total latex solids. Furthermore, the electrolyte shifts the particle size distribution toward larger mean diameters (from
300 nm to
450 nm at identical stirring intensity) due to reduced electrostatic stabilisation, altering the shear viscosity and film formation properties of the final adhesive. For these reasons, Sinopec PVA 095-28 is supplied with a typical ash content of
0.35–0.45 wt%, verified by muffle furnace ignition at
700 °C for
2 hours. When the application demands an even lower electrolyte burden, e.g., in emulsion‑derived medical‑grade adhesives, an additional washing step is advised.
The same grade is unsuitable for compounding with borax or heavy‑metal salts such as copper(II) sulfate, as these induce rapid gelation even at concentrations below
0.1 wt%, a behaviour exploited in structured fluid applications but detrimental to sizing and coating stability.
A comparative summary of core specification parameters is provided in the table below.
Sinopec PVA 095-28 technical specification vs. a typical fully hydrolysed grade
| Property | Test Method | PVA 095-28 | PVA 17-99 (reference) |
|---|
| Polymerisation degree (nominal) | GB/T 12010.2‑2010 | 950 ± 50 | 1700 ± 50 |
| Hydrolysis (mol%) | GB/T 12010.2‑2010 | 95.0 ± 1.5 | ≥ 99.0 |
| Viscosity (4% aq., 20°C, mPa·s) | GB/T 12010.3‑2010 | 28 ± 3 | 28 ± 3 (for 17‑99L; 17‑99H: 45–55) |
| Ash (wt%) | GB/T 12010.4‑2010 | ≤ 0.5 | ≤ 0.8 |
| Volatile matter (wt%) | GB/T 12010.4‑2010 | ≤ 5.0 | ≤ 5.0 |
| Dissolution temperature (°C, complete) | In‑house method | 60–75 | ≥ 90 |
Interactive effects between residual acetate content and the chosen plasticiser system also bound the adhesive compounding space. Glycerol, added at
5–15 wt% on dry resin, reduces film tensile strength by
20–30 % but improves flexibility at sub‑zero temperatures, making the grade adaptable to cold‑storage label stock when paired with an acrylic emulsion. In contrast, sorbitol‑based plasticisers can migrate to the surface at loadings above
8 wt%, leaving a tacky residue that attracts dust — a failure mode documented in roll‑to‑roll converting lines. No such migration is observed with polyethylene glycol
400 up to
10 wt%, provided the film is aged below
40 °C.
Application-driven performance comparison across selected Sinopec PVA grades
| Criterion | 095-28 | 05-88 | 17-99L |
|---|
| Cold‑water solubility (20°C) | Partial; full dissolution at 60°C | Rapid; full dissolution at 20°C | Negligible; gel at 20°C |
| Film tensile strength (MPa, ASTM D882) | 37–42 | 25–30 | 55–60 |
| Film elongation at break (%) | 120–150 | 180–220 | 60–80 |
| Desizing energy demand | Moderate | Very low | High |
| Adhesion to polyester (warp sizing) | Good | Excellent (low DP aids wetting) | Moderate |
| Coagulum risk in PVAc emulsion | Low at ash ≤0.5% | Low | Moderate (higher electrolyte) |
Storage in a dry, ventilated warehouse at
≤ 30 °C and away from direct sunlight is required to preserve flowability and keep volatiles within specification over the labelled shelf life of
12 months. Bags should be kept sealed after opening to avoid caking in high‑humidity environments; if caking occurs, the material may be passed through a
2 mm screen before use, but solution filtration is recommended to catch gel specks that form when moisture penetration initiates localised hydrolysis inhomogeneities.
