| HS Code | 463499 |
| Product Name | Wanwei VAM LI Low Inhibitor Grade |
| Chemical Name | Vinyl Acetate Monomer |
| Cas Number | 108-05-4 |
| Chemical Formula | C4H6O2 |
| Molecular Weight | 86.09 g/mol |
| Appearance | Clear, colorless liquid |
| Odor | Sweet, fruity odor |
| Purity | ≥ 99.9% |
| Inhibitor Hydroquinone Content | ≤ 10 ppm |
| Water Content | ≤ 0.02% |
| Acidity As Acetic Acid | ≤ 0.005% |
| Boiling Point | 72.7 °C (162.9 °F) |
| Melting Point | -93 °C (-135 °F) |
| Flash Point | -8 °C (17.6 °F) closed cup |
| Specific Gravity | 0.932 at 20 °C |
| Vapor Pressure | 115 hPa at 20 °C |
| Solubility In Water | 2.5 g/100 mL at 20 °C |
| Auto Ignition Temperature | 427 °C (800 °F) |
As an accredited Wanwei VAM LI Low Inhibitor Grade factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Wanwei VAM LI Low Inhibitor Grade is supplied in 200 kg steel drums or bulk ISO tankers for industrial polymerization use. |
| Container Loading (20′ FCL) | 20′ FCL container loading of Wanwei VAM LI Low Inhibitor Grade ensures safe, secure transport with proper ventilation and temperature protection. |
| Shipping | Wanwei VAM LI Low Inhibitor Grade ships as a flammable liquid (UN 1301, Class 3, PG II) requiring controlled temperature, adequate ventilation, and storage away from heat, sparks, and oxidizers. Use approved drums, ISO tanks, or dedicated tankers; ensure inhibitors remain effective and emergency spill protocols are ready. |
| Storage | Store Wanwei VAM LI Low Inhibitor Grade in tightly sealed, approved containers under inert nitrogen blanketing in a cool, dry, well-ventilated area away from heat, sparks, open flames, direct sunlight, and oxidizing agents. Maintain storage temperature below recommended limits, typically ≤20°C, and use promptly to prevent polymerization. Ensure grounding, secondary containment, and adequate ventilation. |
| Shelf Life | Store below 25°C, protected from light and air; use within six months to prevent polymerization and maintain inhibitor effectiveness. |
In continuous VAE emulsion trains where Wanwei VAM LI Low Inhibitor Grade is stored in nitrogen-blanketed stainless day tanks below 25 °C and metered to the pre-emulsion vessel, the reduced MEHQ burden shortens the induction interval in the persulfate/metabisulfite redox couple, and the conversion slope is stable enough that residual monomer samples taken at 30 min intervals remain within 3% of the scheduled delayed-feed profile. Production-scale equipment typically includes a 10–20 m³ stainless jacketed reactor with external tubular loop cooling, a 3-blade pitched turbine operating at 80–120 rpm, and an ethylene booster compressor supplying 20–60 bar partial pressure; a processing bottleneck occurs when the hold-up time in the pre-emulsion exceeds 90 min, because vinyl acetate coalescence raises coagulum loading on the 150 µm basket strainer and forces a cleaning cycle when differential pressure exceeds 2.5 bar. The formulation window is VAM 70–92 wt% of total monomer, ethylene 8–30 wt%, stabilising colloid 3–8 wt% on dispersion, and an acrylic acid functional feed at 0.3–2.0 wt%; pH is maintained between 4.5 and 5.5 with buffered electrolytes to protect the colloid against alkaline hydrolysis. Low-inhibitor material should not be held in unblanketed atmospheric storage; oxygen in the presence of metal ions can generate acetic acid and downstream pH drift, so day tanks are blanketed with 99.5% nitrogen. For redispersible powder grades, the post-reaction residual monomer is steam-stripped to 0.1 wt% max and the dispersion is spray-dried at inlet 180–220 °C and outlet 70–90 °C, with 8–15 wt% anticaking filler added before atomisation. Compliance is assessed under EN 12004, ISO 13007-2, and EN 15824 for tile adhesives and external rendering; volatile organic content is measured by ASTM D3960 and must sit below the 2004/42/EC waterborne phase limit. Terminal product types include carpet-backing laminating dispersions, cementitious tile adhesive powders, bottle-labelling adhesives, and flexible waterproofing slurries.
The induction period observed in low-inhibitor vinyl acetate homopolymerization is governed by the inhibitor-to-initiator molar balance in the first reflux stage; with reduced MEHQ, full exothermic onset can occur within 8–15 min at 70–80 °C, rather than the longer delay seen with standard-inhibitor monomer. The total VAM fraction in the finished emulsion is 35–55 wt%, with solids target at 45–65 wt%; the seed charge is 5–10 wt% of total VAM, the aqueous phase contains 3–8 wt% PVOH protective colloid on total formulation, and potassium or ammonium persulfate is charged at 0.2–0.4 wt% on VAM. Plasticizer addition is 5–15 wt% on solids where dibutyl or benzyl butyl phthalate is specified. A production kettle for polyvinyl acetate homopolymer emulsions is typically a 5–25 m³ glass-lined or stainless reactor fitted with a 45° four-blade pitched turbine, a vertical reflux condenser, and a jacket capable of removing 80–120 kW peak heat duty; the delayed monomer feed runs 3–5 h, and the exotherm is controlled by throttling jacket water rather than by stopping the feed, because feed-stopping widens the batch particle-size distribution. Operators monitor free monomer with an on-line near-infrared probe; the delay feed is terminated when conversion exceeds 92–95 wt%, and a post-cook stage with a second initiator spike reduces residual VAM below 0.15 wt%. Adhesive qualification requires shear strength testing under ASTM D905-08 and ASTM D5751-99, with classification under EN 204/205 for D2 and D3 service; preservative packages must comply with EU 528/2012 when aqueous products are labelled for long-term storage. Finished goods include D2 interior woodworking white glue, D3 exterior-grade wood assembly adhesive, high-solids paper-laminating dispersion, and low-VOC school glue; the low-inhibitor grade reduces batch-to-batch persulfate feed adjustments to within ±0.05 wt% on VAM across a multi-plant monomer supply.
Across high-pressure low-density polyethylene plants retooled for ethylene-vinyl acetate copolymerization, low-inhibitor vinyl acetate is injected after the secondary compressor into a stirred autoclave or tubular reactor operated at 1,800–2,800 bar and 180–260 °C; because MEHQ residues can accumulate in the high-pressure recycle wax separation and interfere with free-radical initiation, the low-inhibitor grade reduces visible fouling on the letdown valve and permits run lengths beyond 168 h before hot-zone inspection. The VAM feed ratio is the primary control for crystallinity and service temperature. Photovoltaic encapsulant grades are produced at 28–33 wt% VAM, hot-melt adhesive grades at 18–28 wt% VAM, and footwear foam grades at 15–22 wt% VAM. Melt index is controlled with chain transfer agents, typically at 25–45 g/10 min for hot-melt EVA and 5–20 g/10 min for film extrusion; density ranges from 0.930 to 0.950 g/cm³ for low-VAM grades to 0.950–0.980 g/cm³ for high-VAM grades. Downstream processing of encapsulant film uses cast film lines with 300–500 mm slot die widths and winding tension below 50 N to prevent blocking; pelletizing is conducted underwater after a high-pressure separator and low-pressure degasser, with pellet water temperature held at 5–10 °C to prevent amorphous high-VAM pellets from agglomerating. Testing for photovoltaic encapsulant is governed by IEC 61215-1:2021 and IEC 62788-1-1, with optical transmittance measured by ASTM D1003 and melt flow by ASTM D1238; hot-melt adhesive compounds are evaluated by ASTM D3835 for viscosity and ASTM D1876 for T-peel resistance.
| Target grade | VAM feed (wt%) | Melt flow (g/10 min) | Density (g/cm³) | Primary downstream |
|---|---|---|---|---|
| Photovoltaic encapsulant | 28–33 | 5–20 | 0.950–0.980 | Solar module encapsulant film |
| Hot-melt adhesive | 18–28 | 25–45 | 0.930–0.950 | Packaging hot-melt |
| Footwear foam | 15–22 | 8–25 | 0.930–0.950 | Crosslinked midsole |
Because the low-inhibitor monomer shortens the initiation lag in the solution polymerisation step, the first reactor’s residence time distribution remains narrower when continuous stirred-tank trains are used for polyvinyl acetate precursor synthesis; the polymerisation charge comprises vinyl acetate at 20–60 wt% in methanol, azobisisobutyronitrile or peroxide at 0.02–0.1 wt% on monomer, and a hold-up time of 4–8 h at 60–80 °C. The critical control in the subsequent methanolysis is the sodium hydroxide-to-acetyl molar ratio: partial hydrolysis for stabiliser grades is run at 0.05–0.15 mol NaOH per mol acetyl, whereas fully hydrolysed textile film grades require 0.9–1.0 mol per mol acetyl, producing methyl acetate as a recoverable by-product. Belt or screw saponifiers process the polymer-methanol paste with residence times of 15–45 min, and the precipitate is pressed, dried under vacuum at 80–120 °C, and milled to 50–200 µm particle size; residual sodium is reduced with countercurrent alcohol wash to 0.1 wt% max. Material conformity is checked under ISO 15023-1:2017 for designation and specification, USP-NF Polyvinyl Alcohol for pharmaceutical excipient grades, and FDA 21 CFR 177.1670 where the grade is intended for food-contact film; ash content is controlled to 0.5 wt% max for packaging grades. Downstream product types include cold-water-insoluble fully hydrolysed textile sizing film, paper-surface size, detergent unit-dose water-soluble film, and partially hydrolysed grades used as emulsion stabilisers and adhesive remoisteners.
A pre-emulsion feed ratio of VAM to butyl acrylate at 65:35, corrected by the Fox equation, places the copolymer glass transition temperature near 5 °C; lower VAM fractions below 50 wt% produce tackier pressure-sensitive adhesives, while higher VAM fractions above 80 wt% force post-addition coalescents to maintain film formation in architectural coatings. The production process is seeded semi-batch: an initial seed charge using 5–10 wt% of total monomer is heated to 65–75 °C, then a pre-emulsion of VAM, butyl acrylate, 0.5–2.0 wt% anionic/nonionic surfactant mixture, and water is fed over 3–4 h with a separate persulfate/metabisulfite stream. Reaction pH is held at 4.0–5.5, and the pre-emulsion is cooled to 15–25 °C to prevent premature polymerisation in the feed tank; residual monomer stripping is performed in a vacuum post-reactor at 55–65 °C until free VAM falls below 0.1 wt%, after which the latex is adjusted with ammonia to pH 8.0–8.8 for thickener compatibility in paint. Standards for finished architectural coatings include ASTM D2486 scrub resistance, ASTM D4828 practical washability, and ISO 11998 wet-scrub classification; PSA film performance is tested by ASTM D3330 for peel adhesion and ASTM D3121 for rolling ball tack, with VOC content below the 2004/42/EC waterborne limit. Terminal end products are interior low-odor paints, exterior flat and semi-gloss finishes, removable label adhesives, and repulpable paper tapes.
After the seed latex has stabilised, the vinyl versatate-rich third feed is introduced to form a hydrophobic shell, and any inhibition delay in the early VAM exotherm would shift the seed particle size and reduce the surface area available for the later hydrophobic monomer feed; the low-inhibitor VAM is therefore charged in the initial seed and first growth phases to maintain the nucleation schedule. The formulation is typically VAM 55–75 wt%, vinyl versatate (VeoVa) 25–45 wt%, and a carboxylic acid functional monomer at 0.3–1.5 wt%; the VeoVa fraction is delayed to the last 20–30% of the monomer feed, and the reactor is run semi-batch at 70–80 °C with a pre-emulsion make-up vessel held at 10–20 °C. The final dispersion is neutralised to pH 8.0–8.5 and formulated with 10–25 wt% mineral filler for textured masonry paints. Compliance is tested with EN 1062-1:2004 for exterior masonry coating classification, ISO 7783-2 for water-vapour transmission, and ISO 11507 for artificial weathering; fire performance for external thermal insulation composite systems is assessed under EN 13501-1 when the coating is part of the system. Terminal product types are elastomeric wall coatings, high-build protective masonry paint, EIFS base coats, and synthetic stucco finishes.
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The product designated Wanwei VAM LI Low Inhibitor Grade is a vinyl acetate monomer identified by CAS 108-05-4 and molecular weight 86.09 g/mol. The LI designation denotes a reduced inhibitor fraction relative to standard inhibited shipments, not an inhibitor-free monomer. It is supplied as a clear, colorless liquid with a commercial VAM assay of ≥99.9 wt% by gas chromatography, water content of ≤0.05 wt% by Karl Fischer titration, acidity as acetic acid of ≤0.005 wt%, and color of ≤5 Pt-Co. The stabilizer is ordinarily hydroquinone or hydroquinone monomethyl ether and is specified by agreement under ASTM D2190-07(2021). The exact inhibitor concentration is lot-specific and must be obtained from the certificate of analysis. At atmospheric pressure, the distillation range is 71.5–73.5 °C, and the density is approximately 0.932 g/cm³ at 20 °C. The low-inhibitor formulation is intended for downstream polymerization systems in which a standard inhibitor loading would extend induction time and raise initiator consumption.
Storage stability of low-inhibitor VAM is governed by three coupled variables: inhibitor concentration, dissolved oxygen, and temperature. In lightly inhibited vinyl acetate, radical-chain polymerization can initiate in the bulk liquid when thermal or trace-metal initiation events generate free radicals. Quinoid inhibitors such as hydroquinone and monomethyl ether of hydroquinone function as radical traps; a reduction from 12–17 mg/kg to 3–8 mg/kg therefore narrows the consumption safety margin. The monomer should not be held as a completely oxygen-free liquid unless the stabilizer system has been qualified for that condition, because dissolved oxygen can act as a retarder and may also assist regeneration of aromatic stabilizer species. Published lot-specific storage-stability data for the Wanwei LI designation is limited; the following operational limits are derived from general VAM stabilization practice and should be verified against the storage installation.
At bulk storage scale, the product is typically maintained in stainless steel or aluminum vessels at or below 25 °C. Venting and dilution systems are arranged to keep vapor below the lower flammable limit of 2.6 vol% and the upper flammable limit of 13.4 vol% in air. Nitrogen blanketing is used only after the stabilizer package has been validated for reduced oxygen service; otherwise a controlled oxygen concentration is maintained in the vapor space. Liquid transfer lines should avoid dead legs, pump-cavitation heating, and local surface temperatures above 40 °C. Recirculation loops, if used, are low-shear centrifugal arrangements with thermal relief and no static mixers that generate localized high shear.
In emulsion and solution polymerization, the induction period before the exothermic reaction begins is not a simple function of inhibitor concentration. Dissolved oxygen and initiator decomposition efficiency contribute parallel radical-consuming loads. Quinoid inhibitors may consume two radicals per inhibitor molecule, so a decline from 15 mg/kg to 5 mg/kg does not produce a threefold reduction in induction time if oxygen ingress remains uncontrolled. At typical persulfate initiation temperatures of 65–80 °C, the low-inhibitor grade permits target molecular weight to be reached with a lower initiator charge, but the processing window becomes less forgiving of oxygen leakage through monomer feed lines, pump seals, and extraction vents. Reactor operators report that batch-to-batch induction-time variance is more sensitive to the low-inhibitor grade when the feed system admits air. This is an operational boundary, not a product defect.
The product is used in continuous and semi-batch production of polyvinyl acetate homopolymer emulsions, polyvinyl alcohol, vinyl acetate-ethylene copolymers, and vinyl acetate-acrylic copolymers. In a conventional PVAc emulsion train with stirred reactors of 2:1 to 3:1 height-to-diameter ratio, the monomer addition profile must compensate for the shortened inhibition period. Initiator feed is typically split between the reactor charge and the monomer feed line; with the low-inhibitor grade, control of head-space oxygen ingress can be as important as adjustment of the persulfate rate. The exact ratio is plant-specific and is determined by reaction calorimetry rather than by fixed rule.
Continuous emulsion polymerization of vinyl acetate at production scale requires the monomer to be fed at a rate that matches radical generation. The Wanwei LI grade is specified for such trains because its lower stabilizer burden reduces accumulation of aromatic inhibitor in the aqueous phase. Such accumulation can suppress the polymerization rate in later reactors or contaminate wastewater with phenolic species. The performance difference is most evident in multi-stage trains operating with total residence time of 3–6 h and jacket temperatures from 65 °C to 85 °C. Published data for the exact Wanwei LI grade in such continuous trains is limited; however, the specification range is consistent with low-inhibitor VAM applications in which monomethyl ether of hydroquinone is maintained below 10 mg/kg.
| Parameter | Wanwei VAM LI Low Inhibitor Grade | Standard inhibited VAM | Test method |
|---|---|---|---|
| Assay as vinyl acetate | ≥99.9 wt% | ≥99.9 wt% | ASTM D2190-07(2021) / GC |
| Water | ≤0.05 wt% | ≤0.05 wt% | ASTM D1364 |
| Acidity as acetic acid | ≤0.005 wt% | ≤0.005 wt% | ASTM D1613 |
| Color | ≤5 Pt-Co | ≤5 Pt-Co | ASTM D1209 |
| Inhibitor as HQ/MeHQ | 3–8 mg/kg | 12–17 mg/kg | UV/HPLC; supplier C of A |
| Distillation range at 101.3 kPa | 71.5–73.5 °C | 71.5–73.5 °C | ASTM D1078 |
Because inhibitor content is specified by agreement in ASTM D2190-07(2021), the 3–8 mg/kg and 12–17 mg/kg windows in the table are order-management values rather than absolute quality limits. The certificate of analysis for each Wanwei lot records the measured inhibitor concentration and supersedes the general table. The low-inhibitor grade is not an uninhibited VAM; the product remains stabilized, but the margin to spontaneous polymerization is lower.
In vinyl acetate-ethylene emulsion polymerization, ethylene is absorbed into the monomer phase under pressure, typically in the range of 30–90 bar depending on the target ethylene content. Oxygen and inhibitor effects in the VAM feed become coupled with ethylene mass transfer. A low-inhibitor VAM stream reduces the radical scavenger concentration entering the reactor, but it does not compensate for oxygen contamination from the ethylene supply. The reactor—usually a stirred autoclave with 4:1 to 6:1 effective length-to-diameter ratio and a multi-zone jacket—must provide sufficient interfacial area for ethylene transfer while avoiding hot spots that would consume the reduced inhibitor margin. In such processes, the LI grade is selected because standard inhibitor burden can contribute to long induction periods, especially in low-temperature redox-initiated formulations at 45–55 °C.
The grade also differs from standard VAM in logistics sensitivity. Because the stabilizer level is lower, residence time in tank farms and railcars should be minimized, and inventory should be consumed under a first-in, first-out schedule. If the material is transferred to an intermediate day tank, the tank should be clean, dry, and free of rust or water. Water in vinyl acetate slowly hydrolyzes the ester to acetic acid and acetaldehyde, increasing acidity and aldehyde content. Closed-loop transfer under dry gas or controlled oxygen is used in installations where relative humidity exceeds 60%. The low-inhibitor grade does not differ from standard VAM in hydrolysis chemistry, but the reduced inhibitor content means that any contamination generating radicals or acids will have a proportionally larger effect on shelf life.
In batch polymerization, the low-inhibitor grade allows lower initial persulfate or redox initiator addition. A comparative process observation is that at 0.2 wt% ammonium persulfate and 70 °C, monomer containing 5 mg/kg monomethyl ether of hydroquinone typically shows a shorter pre-reaction quiescent period than the same monomer containing 15 mg/kg; however, the magnitude of the shift is installation-specific because oxygen ingress, reactor surface condition, and agitator shear modify the radical budget. Published data for this specific configuration is limited. The shortened induction period can be used to raise throughput, but it also requires a fast-acting reactor interlock.
For incoming quality control, the laboratory should measure water, acidity, and inhibitor content rather than rely on appearance. Vinyl acetate is colorless, and low inhibitor concentration cannot be visually verified. Gas chromatography with a capillary column and internal standard confirms the main assay; Karl Fischer coulometry gives water content in the ≤500 mg/kg range. Inhibitor results can vary with sampling point because stabilizer is consumed in the sample unless the sample is immediately chilled and protected from light. The certificate should state the inhibitor species and concentration; the LI classification should be confirmed against that species, not against a generic hydroquinone equivalent.
Vinyl acetate is a flammable liquid with a closed-cup flash point of -8 °C and is classified as a GHS Category 2 flammable liquid. The LI designation does not alter the transport classification of vinyl acetate. Emergency relief sizing should account for the heat release of vinyl acetate self-polymerization. Because low-inhibitor VAM can generate heat if polymerization initiates, storage and reactor relief devices are sized for the monomer’s exothermic runaway scenario rather than for normal fire exposure only.
The critical process limit is not solely the average inhibitor concentration; the spatial distribution of inhibitor in the monomer feed matters. If a low-inhibitor VAM stream is mixed with recycled monomer that contains aged inhibitor or with a higher-inhibitor heel, local gradients can produce inconsistent induction times. For this reason, operations using the LI grade often pre-mix the monomer in temperature-controlled day tanks with slow agitation and measure inhibitor concentration before reactor feed. The day tank is equipped with a platinum resistance temperature sensor and a low-velocity agitator; dead zones in the tank can retain lightly inhibited monomer and undergo slow polymerization. That failure mode is detectable as a viscosity increase and acidity drift, and it is the main reason that low-inhibitor VAM is not simply blended into an existing standard-VAM tank without an equipment review.
