A fully hydrolyzed polyvinyl alcohol homopolymer, identified by the grade designation
Wanwei PVA 15-99(L) and cross-referenced as
PVA 098-15, occupies a precise viscosity band within the manufacturer’s portfolio of suspension-polymerized PVOH resins. The numeric suffix follows the industry convention: the first two digits indicate the nominal dynamic viscosity of a
4 % (w/w) aqueous solution at
20 °C, bracketed as
12.0–16.0 mPa·s (determined by Brookfield LVF viscometry per
GB/T 12010.3), while the final two digits denote a hydrolysis degree of
99.0–99.8 mol % (back-titration against
GB/T 12010.5). The parenthetic
(L) suffix signals a low‑methanol, low‑ash manufacturing route optimized for applications where residual catalyst and volatile organic content impose upper limits below the generic
15-99 specification. This product is distributed by Anhui Wanwei Group Co., Ltd. as a free-flowing granular powder with a bulk density typically
0.40–0.55 g/cm³, shipped in
25 kg multi-wall paper sacks with an inner polyethylene liner to maintain a volatiles content below
5.0 % at point of use.
What Distinguishes the (L)-Designated Product from Standard 15-99?
The primary differentiator is the ceiling imposed on two purity parameters that remain uncontrolled in the conventional grade. For
Wanwei PVA 15-99(L), residue on ignition (ash) measured by muffling at
700 °C in accordance with
GB/T 12010.7 is held to a maximum of
0.05 %, whereas generic
15-99 typically reports ash values up to
0.5 %. Simultaneously, residual methanol content, quantified by headspace gas chromatography following
GB/T 12010.12, is guaranteed not to exceed
0.5 %. These reductions are not cosmetic; they directly affect optical homogeneity in drawn films and the uniformity of crosslinking reactions, where ionic ash components can act as heterogeneous nucleation sites. The combination of tight molecular-weight distribution (
polydispersity index ≤ 2.2 by GPC) and the controlled ash profile makes the
(L) variant the supplier’s designated feedstock for polarized light-element films, high-clarity adhesive interlayers, and emulsion polymerization runs requiring low coagulum counts.
Typical lot-release data — Wanwei PVA 15-99(L)
| Property |
Specification |
Test Method |
| Viscosity (4 % aq., 20 °C) |
12.0–16.0 mPa·s |
GB/T 12010.3 (Brookfield LVF, spindle 1, 20 rpm) |
| Hydrolysis degree |
99.0–99.8 mol % |
GB/T 12010.5 (alkali titration) |
| Ash content |
≤ 0.05 % |
GB/T 12010.7 (700 °C, 2 h) |
| Residual methanol |
≤ 0.5 % |
GB/T 12010.12 (HS‑GC) |
| Volatile matter (as packed) |
≤ 5.0 % |
GB/T 12010.4 (105 °C, 3 h) |
| pH (4 % solution) |
5.0–7.0 |
GB/T 12010.8 |
| Particle size (retained on 40 mesh) |
≤ 1.0 % |
GB/T 12010.2 (dry sieving) |
Dissolution Kinetics and Solution Stability in Demineralized Water Systems
Preparation of a
4 % stock solution from
Wanwei PVA 15-99(L) powder proceeds through a mandatory cold-water swelling phase before thermal dissolution. When ambient relative humidity exceeds
60 %, the granular product should be pre-dried at
80 °C for
2 h to avoid clumping during wet-out. In a jacketed vessel equipped with a low-speed anchor agitator (
60–80 rpm, tip speed ≤
1.5 m/s), the powder is dispersed into demineralized water at
20–25 °C under moderate agitation for
30 min to permit particle swelling without forming gelatinous fisheyes. The jacket temperature is then ramped to
90–95 °C at a rate not exceeding
2 °C/min; rapid heating above
100 °C is contraindicated because localized overheating triggers foam formation and deposits a partially dehydrated skin on the vessel wall. A Rushton-type high-shear disperser operating at
1500 rpm may be inserted during the initial dispersion step if powder addition is continuous, but prolonged high-shear after the solution reaches
80 °C risks chain scission, evidenced by an irreversible viscosity drop exceeding
10 % of the target value.
Freshly prepared solutions display Newtonian behavior up to concentrations of
8 %. Once cooled to
25 °C and held in a closed container, the viscosity drift over
24 h is less than
3 % provided the solution pH remains within
5.0–7.0. Because the homopolymer lacks bio-resistance, solutions stored beyond
48 h at ambient temperature require addition of a preservative, typically sodium benzoate at
0.1–0.3 % on solution weight, or continuous refrigeration at
5–10 °C. Blending with other water-soluble polymers (e.g., starch, CMC) is best conducted by co-dissolution at
90 °C to avoid phase separation; the optimum mass ratio of PVA to oxidized starch for surface-sizing formulations is
1:3 to
1:5 on a dry-solids basis.
Compatibility with plasticizers, crosslinkers, and nonionic surfactants is generally uncomplicated; excessive polyol addition above
5 wt % on dry PVA may reduce tensile strength.
In the fabrication of iodine-type polarizing films, the low ash content of
15-99(L) directly influences boric acid crosslinking homogeneity during the wet‑stretching process. Polyvinyl alcohol film cast from a
10–15 % aqueous solution is first uniaxially stretched to a draw ratio of
3.5–4.5× in a dyeing bath containing iodine and potassium iodide at
30 °C ±
1 °C. Ash residues exceeding
0.08 % have been shown to nucleate sodium borate crystallites within the amorphous PVA matrix, producing point defects that scatter visible light and depress single-pass transmittance below
42 % (illuminant C,
2° observer,
JIS Z 8701). With
15-99(L), transmittance values consistently fall in the
42.5–43.8 % range and the polarization efficiency measured according to
JIS Z 8722 exceeds
99.9 %. The lower methanol specification also reduces plasticization during the drying step, preserving the glass‑transition temperature above
85 °C, which is critical for maintaining dimensional stability under the
≥ 250 W/m² irradiance of a xenon-arc fadeometer. In contrast, a higher-viscosity fully hydrolyzed grade such as
20-99 demands a draw ratio approaching
5.0× to achieve equivalent orientation, elevating the risk of fibrillation at the tenter-clip line; conversely,
10-99 does not generate sufficient green strength to survive the transverse stretch without edge tearing. Published data for the specific iodine‑PVA complex stoichiometry obtained with the
(L) low‑ash variant is limited, but industrial production runs on tenter‑frame lines (web width
1.6–2.2 m) indicate a process window of
± 2 °C for the boric acid crosslinking bath when the film residence time is
120 s.
When the Role of Protective Colloid Demands Viscosity Gap between 10-99 and 15-99(L)
In vinyl acetate emulsion polymerization, the molecular weight of the protective colloid dictates both the grafting efficiency and the final emulsion rheology.
Wanwei PVA 15-99(L), with its intermediate solution viscosity of
12.0–16.0 mPa·s, provides sufficient chain length to generate a robust steric barrier around poly(vinyl acetate) particles while maintaining a manageable continuous‑phase viscosity. When the polymerisation is initiated by a redox pair (e.g., ammonium persulfate/sodium metabisulfite at
0.5 % on monomer) at
65 °C, the degree of grafting measured by acetone‑extraction‑insoluble fraction reaches
18–22 % using
15-99(L), compared with
12–15 % for a lower-viscosity
10-99 (viscosity
8–12 mPa·s) and
24–28 % for
17-99 (
20–28 mPa·s). The lower grafting efficiency of
10-99 correlates with greater coagulum formation (>
0.3 % on total solids) during high-shear finishing on a Silverson L5M in-line mixer operating at
8000 rpm, whereas emulsions stabilized with
15-99(L) produce coagulum below
0.08 %. Meanwhile,
17-99 raises the emulsion Brookfield viscosity beyond
2000 mPa·s at
50 % solids, restricting pumpability in heat-exchanger-cooled loops. The low‑ash signature of
15-99(L) additionally suppresses the formation of ionic centers that can destabilize carboxylated latexes during pH adjustment cycles.
Comparative profile of Wanwei PVA grades in protective-colloid service
| Grade |
4 % viscosity (mPa·s) |
Hydrolysis (mol %) |
Ash (max, %) |
Graft efficiency (%) |
Coagulum at 50 % solids (%) |
| 10-99 |
8–12 |
99.0–99.8 |
≤ 0.5 |
12–15 |
≤ 0.35 |
| 15-99(L) |
12.0–16.0 |
99.0–99.8 |
≤ 0.05 |
18–22 |
≤ 0.08 |
| 17-99 |
20–28 |
99.0–99.8 |
≤ 0.5 |
24–28 |
≤ 0.15 |
| 17-88 (partially hydrolyzed) |
20–28 |
87.0–89.0 |
≤ 0.5 |
— |
— |
On high-speed air-jet looms operating at weft insertion rates above
800 picks/min, a warp-sizing formulation containing
8 % PVA solids achieves a size add-on of
12–14 % after single‑end sizing on a Zell or Sucker‑Müller slasher. The tensile strength of a dried
15-99(L) film, tested according to
ISO 527-3 at
23 °C and
50 % RH, reaches
55–65 MPa at break with an elongation of
180–220 %, sufficient to suppress warp-end breaks on polyester/cotton blends to below
0.15 stops per 10⁵ weft insertions. Desizing of the fully hydrolyzed polymer requires a hot-water scour at
85–90 °C for
20–30 min; partially hydrolyzed grades such as
17-88 dissolve at
60 °C but impart lower film toughness, shifting the failure mode from cohesive film rupture to adhesive failure at the fiber interface. Consequently, mills processing high‑twist yarns frequently specify the
15-99(L) low‑ash type to reduce eyelet‑guide residue accumulation on the drying cylinders, where carbonate deposits from standard grades can score the chrome surface.
Surface sizing of fine paper grades using a metered film press (e.g., Voith SpeedSizer, rod‑metering geometry, nip load
20–40 kN/m) with a
6–10 % PVA solution results in a Cobb60 value of
18–22 g/m² when measured per
ISO 535, a reduction of approximately
35 % relative to an oxidized-starch-only baseline. The low‑ash characteristic of
15-99(L) is reported by mill operators to minimize calender‑roll dusting during subsequent gloss finishing (line speed
1200 m/min, chrome‑roll surface temperature
140 °C). Where permanent water resistance is required, glyoxal is added at
3–5 % on PVA dry weight, catalyzed by ammonium chloride at
0.5 %, and cured for
3–5 s at
180 °C in the after‑dryer section; the crosslinked film maintains IGT pick resistance above
3.0 m/s (
ISO 3783, spring‑driven mode) with no measurable re‑wetting at the offset printing blanket.
