| HS Code | 206820 |
| Product Name | Vinyl Acetate Monomer (VAM) inhibited with Hydroquinone (HQ) 20-30 ppm |
| Chemical Formula | C4H6O2 |
| Cas Number | 108-05-4 |
| Molecular Weight | 86.09 g/mol |
| Appearance | Clear colorless liquid |
| Inhibitor Content | 20-30 ppm hydroquinone |
| Purity | >=99.9% |
| Boiling Point | 72.7 °C |
| Melting Point | -93.5 °C |
| Flash Point | -8 °C (closed cup) |
| Relative Density | 0.934 at 20 °C |
| Solubility In Water | 20 g/L at 20 °C |
As an accredited VAM HQ 20–30 ppm factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | VAM HQ 20–30 ppm is supplied in 200 kg steel drums, with nitrogen blanketing and sealed lids to ensure stability. |
| Container Loading (20′ FCL) | Load VAM HQ (20–30 ppm) into a 20-foot FCL container, secure properly, ventilate, and prevent contamination during transit. |
| Shipping | Ship as UN 1301, Vinyl Acetate Monomer, stabilized, Hazard Class 3, Packing Group II. Use approved drums or IBCs; ground and bond equipment. Maintain inhibitor at 20–30 ppm, keep away from heat/ignition sources, and segregate from oxidizers. Include proper labeling, documentation, and certificate of analysis. |
| Storage | Store VAM HQ 20–30 ppm in a cool, dry, well-ventilated area away from heat, sparks, and open flames. Keep containers tightly closed and protected from direct sunlight, ideally under a nitrogen blanket to inhibit polymerization. Maintain temperatures below 30°C to preserve the hydroquinone inhibitor. Use grounded, explosion-proof equipment and segregate from oxidizing agents and acids. |
| Shelf Life | Vinyl acetate monomer inhibited with 20–30 ppm hydroquinone typically retains stability for 6–12 months when stored cool, dark, and under inert atmosphere. |
An incoming VAM stream stabilised with hydroquinone 20–30 ppm is assessed in downstream operations as a kinetic input rather than a generic monomer specification. In polyvinyl acetate homopolymer wood-adhesive manufacture, the inhibitor must be consumed by primary radicals before the propagation phase stabilises. The relevant compliance framework includes EN 204 durability classes D3/D4 for wood bonding, ASTM D5751 for adhesives in non-structural laminated lumber products, and FDA 21 CFR 175.105 where the dried adhesive function is indirect food contact. Formulation addition ratios in this segment place VAM at 100% of the monomer charge for a homopolymer backbone or at 75–85 wt% of total monomer when a plasticising comonomer is used; polyvinyl alcohol protective colloid is added at 4–8 parts per 100 parts monomer, sodium acetate buffer at 0.1–0.4 phr, and potassium persulfate initiator at 0.08–0.20 phr. The downstream production process is a semi-batch stirred-tank emulsion polymerisation at 68–80 °C, with VAM fed over 3–5 h into an aqueous phase already containing colloid, buffer, and seed latex. At 20–30 ppm hydroquinone, the induction period is measurable before persulfate-derived radicals can sustain a constant particle number; plant-scale experience with 5–20 m³ glass-lined reactors indicates that raising persulfate to 0.15–0.20 phr without adjusting jacket cooling can produce an overshoot exotherm above 80 °C, increasing coagulum on the wall and reducing heat-transfer capacity. After the monomer feed is complete, the dispersion is typically chased at 75–80 °C with 0.05–0.10 phr tert-butyl hydroperoxide and 0.05–0.10 phr sodium metabisulfite before steam stripping under vacuum to lower residual VAM. Terminal finished product types include D3 and D4 wood assembly adhesives, flat-panel lamination glues, paper-tube winding adhesives, bookbinding emulsions, and packaging dispersion binders. The operational boundary is that a change from a 30 ppm supply to a 20 ppm supply with the same persulfate charge can increase unreacted monomer in the dispersion unless conversion monitoring or headspace GC is in place. Storage of this VAM grade should be maintained under air rather than nitrogen because the hydroquinone inhibitor requires dissolved oxygen to function; oxygen-free blanketing can shorten storage stability.
In vinyl acetate–ethylene (VAE) emulsion polymerisation for re-dispersible polymer powder and construction latex, the hydroquinone load is not a simple initiator offset because the oxidised quinone also consumes the reducing side of the redox couple. The compliance standards for this downstream segment are EN 12004 for ceramic tile adhesives, EN 998-1:2016 for render and plastering mortar, ASTM C1059 for bonding fresh to hardened concrete, and ISO 15824 for polymer-modified waterproofing slurry. Formulation addition ratios place VAM at 70–85 wt% of monomer mass, ethylene at 15–30 wt%, polyvinyl alcohol protective colloid at 5–10 parts per 100 parts monomer, and a redox initiator system at 0.05–0.25 phr based on ammonium persulfate plus sodium metabisulfite or sodium formaldehyde sulfoxylate. The polymerisation is carried out in a high-pressure stirred reactor at 60–85 °C and 30–70 bar ethylene partial pressure, with VAM fed continuously or semi-continuously against the backpressure. At 20–30 ppm hydroquinone in the VAM feed, the induction behaviour is non-linear because hydroquinone is oxidised to p-benzoquinone, which competes with the initiator for the reducing agent; adding more persulfate without increasing the reducing feed can generate a temporary oxidising environment that destabilises the protective colloid and changes particle size distribution. Plant-scale VAE reactors therefore monitor redox potential, residual monomer, and latex viscosity after particle formation rather than relying on temperature alone. After polymerisation, the latex is neutralised, filtered, and either shipped as a liquid or spray-dried into a redispersible polymer powder at inlet temperatures of 120–180 °C, outlet temperatures of 50–70 °C, and anticaking agent addition of 5–15 wt%. Terminal finished product types include C1 and C2 tile-adhesive powders, self-leveling underlayment binders, external thermal insulation composite base coats, concrete repair mortars, and polymer-modified waterproofing slurries. Published data for the exact induction shift at 60 bar and 20–30 ppm hydroquinone in commercial VAE recipes is limited; the usual plant correction is a controlled persulfate pre-oxidation at 55–60 °C before ethylene feed is initiated, rather than an unconditional increase in the main redox charge.
Architectural coatings based on vinyl acrylic binders consume VAM because the monomer balances hardness, adhesion, and cost per litre of dry binder, but low-temperature redox initiation makes the hydroquinone load a critical radical-budget term. The governing standards for this application are EU Directive 2004/42/EC for VOC content, ISO 11998 for wet scrub resistance classification, and ASTM D6886 for aqueous coating VOC speciation. The formulation addition ratio typically places VAM at 15–25 wt% of total monomer, butyl acrylate at 45–55 wt%, methyl methacrylate at 20–30 wt%, and acrylic acid at 1–2 wt%, with the balance to 100 wt% adjusted through the butyl acrylate or methyl methacrylate ratio; surfactants are charged at 2–4 wt%, and the initiating system is a redox couple such as tert-butyl hydroperoxide with sodium sulfoxylate at 0.10–0.30 phr. Because the reaction runs at 55–70 °C, the thermal radical generation rate is low, so the 20–30 ppm hydroquinone entering with VAM must be oxidised and consumed before the main monomer feed can establish steady conversion. Batch behaviour on low-temperature lines shows a characteristic conversion stall at 8–15% monomer conversion when the reducing agent-to-initiator molar ratio is held at 1:1; the lag disappears only after the quinone inventory is depleted. The downstream production process uses a semi-batch monomer pre-emulsion fed over 3–4 h, followed by a chase at 65–70 °C and neutralisation with ammonia or sodium hydroxide to pH 7.5–8.5. Terminal finished product types include interior and exterior flat, matte, and satin architectural paints, dry-film primers, and low-sheen wall coatings. The operational boundary is that the reducing agent charge should not be increased in direct proportion to total VAM without accounting for residual reducing agent that can survive into the final latex and cause after-polymerisation or viscosity drift during storage.
For ethylene–vinyl acetate pellet, extrudable resin, and hot-melt base polymer operations, VAM is copolymerised with ethylene in high-pressure autoclave or tubular reactors where the inhibitor does not remain confined to the liquid monomer phase. The relevant standards are FDA 21 CFR 177.1350 for ethylene-vinyl acetate copolymers in food-contact applications, ASTM D1238 and ISO 1133-1:2022 for melt flow rate, and REACH registration for the finished polymer. The polymerisation feed ratio is set by the target VAM content in the finished resin: 5–15 wt% for clarity film and extrusion grades, 18–28 wt% for hot-melt adhesive grades, and 28–33 wt% for solar encapsulant sheets. The VAM feed contains hydroquinone at 20–30 ppm, but at 1,200–2,500 bar and 120–250 °C the inhibitor partially decomposes and can accumulate in low-pressure recycle monomer streams if the recovery distillation is not adequately purged. This accumulation is a process variable because recycled quinone species can increase the apparent inhibitor load above the fresh-feed specification, shifting molecular weight distribution and altering melt flow rate. Downstream production includes single- or multi-zone autoclave reactors with peroxide initiator injection, high-pressure separator trains, and pelletising under nitrogen. Finished product types are hot-melt adhesives for packaging and bookbinding, EVA lamination film, solar encapsulant sheet, and foamed sheet for footwear and gasketing. The operational boundary is that purchased VAM used in high-pressure EVA should not be assumed to retain a single hydroquinone concentration through the recycle loop; the plant should monitor recycle-stream inhibitor concentration by UV-Vis or GC and adjust purge rate or fresh monomer feed to keep the polymerisation zone below the point where inhibitor-derived side reactions degrade clarity and raise gel level. Moisture in the VAM feed should be controlled below 50 ppm for high-pressure service to reduce corrosion stress on the compressor train.
Because polyvinyl alcohol requires a polyvinyl acetate precursor with controlled molecular weight and low gel, methanol solution polymerisation of VAM treats the 20–30 ppm hydroquinone load as a subtraction from initiator efficiency rather than as a storage-only parameter. Compliance anchors for this route include FDA 21 CFR 177.1670 for polyvinyl alcohol film, the current USP polyvinyl alcohol monograph for pharmaceutical-grade material, and relevant pharmacopoeia impurity limits where the grade is used in regulated healthcare packaging. Formulation addition ratios in this process commonly use VAM at 50–70 wt% of the methanol solution, methanol at 30–50 wt%, and azobisisobutyronitrile at 0.02–0.15 mol% relative to VAM. The polymerisation is conducted at 60–75 °C under reflux, and the hydroquinone introduced with VAM remains largely in the PVAc solution unless a low-temperature finishing step is used before saponification. During saponification with sodium hydroxide at a molar ratio of 0.02–0.08 to acetyl groups at 40–50 °C, oxidised hydroquinone can form quinoid colour bodies that appear as yellowing in partially hydrolysed grades; this is controlled by washing the methanol-swollen gel with methanol/water mixtures. The downstream process includes monomer stripping, saponification, neutralisation, solvent recovery, drying, and milling. Terminal product types are fully hydrolysed 98–99 mol% PVOH for paper surface sizing, partially hydrolysed 87–89 mol% PVOH for emulsion polymerisation protective colloids, and film-grade PVOH for water-soluble unit-dose packaging. Published data on the exact yellowing threshold at 20–30 ppm hydroquinone in continuous PVOH lines is limited; industrial control is based on gel fraction and post-saponification colour rather than on the incoming hydroquinone value alone.
Vinyl acetate copolymer latexes for paper coating, paperboard converting, and textile reinforcement consume the same 20–30 ppm HQ VAM stream, but the inhibitor management depth is lower because the binder is formulated into an aqueous application system rather than a polymer melt or dry mortar. Relevant compliance instruments include 21 CFR 176.170 for paper and paperboard in contact with aqueous and fatty foods, EU 1935/2004 for food-contact materials, and Oeko-Tex Standard 100 where textile binders must meet residual monomer and sensitiser limits. The formulation addition ratio in this segment places VAM at 50–90 wt% of total monomer, with a flexible comonomer such as butyl acrylate or dioctyl maleate at 10–50 wt%, and a protective colloid or nonionic surfactant at 2–8 pphm. The production process is a conventional emulsion polymerisation at 65–80 °C, followed by post-reaction stripping and formulation into size-press or blade-coating baths. Terminal finished product types are paper coating binders for coated board, nonwoven binders for wipes and hygiene products, and textile finishing resins for backing and stiffening. The primary limitation is not polymerisation kinetics but residual hydroquinone oxidation products in the aqueous binder, which can darken under alkaline paper coating conditions; therefore the post-stripping pH is held below 8 until the binder is formulated with optical brighteners.
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Vinyl acetate monomer stabilized with hydroquinone at 20–30 ppm by mass is a polymer-grade unsaturated ester supplied for free-radical polymerization and copolymerization processes. The designation VAM HQ 20–30 ppm identifies the inhibitor species and the certified concentration band. The base monomer CAS registry number is 108-05-4 and the stabilizer CAS registry number is 123-31-9. The liquid is clear and water-white, with a closed-cup flash point of -8 °C, a boiling point of 72.7 °C at 101.3 kPa, and a density near 0.934 g/cm³ at 20 °C. The proper shipping name is “vinyl acetate, stabilized,” with UN 1301, Class 3, Packing Group II. The vapor pressure at 20 °C is approximately 12.3 kPa. The vapor density relative to air is approximately 3.0, and the autoignition temperature is approximately 402 °C.
Representative acceptance limits for bulk tank deliveries are given below.
| Parameter | Method | Limit/typical value |
|---|---|---|
| Vinyl acetate assay | ASTM D2191-22 | 99.9 wt% min |
| Hydroquinone inhibitor | ASTM D2193-22 | 20–30 mg/kg |
| Water | ASTM D1364-22 | 0.05 wt% max |
| Acidity as acetic acid | ASTM D1613-17 | 0.005 wt% max |
| Color, Pt-Co | ASTM D1209-00(2019) | 5 max |
| Distillation range at 101.3 kPa | ASTM D1078-11(2019) | 71.8–73.0 °C |
| Nonvolatile residue | ASTM D1353-13(2021) | 0.005 wt% max |
The specification set is not a single analytical snapshot. Hydroquinone must be measured on the as-received liquid without distillation because the inhibitor is intentionally present and distillation would remove it. Water and acidity are controlled because residual moisture accelerates acetolysis in downstream purification trains and increases the load on distillation columns. The nonvolatile residue limit is an indirect screen for low-molecular-weight polymer that may have formed during transit or storage. If a delivery fails the nonvolatile residue test, the cause is usually oxygen starvation in a previous tank or a dead leg with poor circulation, not high hydroquinone content.
Incoming bulk shipments of VAM HQ 20–30 ppm are normally tested against ASTM D2191-22 for vinyl acetate assay, ASTM D2193-22 for hydroquinone, ASTM D1364-22 for water, and ASTM D1613-17 for acidity. Color is reported in Pt-Co units under ASTM D1209-00(2019), and distillation range is determined under ASTM D1078-11(2019). The hydroquinone method is specific to the active inhibitor and should not be substituted with a generic phenol titration, which can over-report if benzoquinone or other oxygenated by-products are present. Sampling points should be located below the liquid surface after at least two tank turnovers to avoid stratification caused by top-off inhibitor addition.
Because the product is stabilized with a phenolic inhibitor, the certificate of analysis should state both the inhibitor concentration and the date of shipment. A hydroquinone result near 20 mg/kg may be acceptable at the factory, but a plant receiving the monomer after two weeks of tropical transport should verify that the value has not fallen below the working minimum. If the value falls below 20 mg/kg, the material may still be used immediately in a controlled polymerization campaign, but long-term storage is no longer assured.
Because hydroquinone is an aerobic inhibitor, a storage tank blanketed with nitrogen can lose its protective action even when the analytical hydroquinone concentration remains within 20–30 mg/kg. Hydroquinone traps propagating radicals in the presence of oxygen and is converted to benzoquinone; the quinone species is the active radical trap, and oxygen is required to maintain the quinone reservoir. Under oxygen-deficient conditions, hydroquinone is consumed by side reactions and the monomer can polymerize exothermically in the vapor space and around internal fittings.
The critical control parameter is not hydroquinone concentration alone but the paired measurement of headspace oxygen and dissolved oxygen. In bulk storage, the headspace should be maintained with a controlled air sweep rather than nitrogen blanketing. At temperatures below 15 °C, inhibitor consumption is slow; above 30 °C, consumption accelerates and periodic re-inhibition may be required in extended warm-climate storage. A plant may use periodic reinjection of hydroquinone into recirculating storage tanks to hold the lower segment of the 20–30 mg/kg band. Published data for this specific configuration is limited; each tank farm should establish re-inhibition frequency by field trial using ASTM D2193-22 as the control method.
The aerobic inhibition mechanism involves reversible oxidation of hydroquinone to benzoquinone. In a non-aerated monomer, the semiquinone intermediate can dimerize or react with monomer, consuming the inhibitor without regenerating the active quinone. This is why inert blanketing is not merely unnecessary but directly destabilizing. Storage tanks should therefore be vented through desiccant dryers to avoid drawing in humid air, because water promotes acetolysis and can reduce hydroquinone effectiveness at the liquid surface.
Increasing the hydroquinone concentration from 3–7 mg/kg to 20–30 mg/kg extends the safe storage window for long-haul transport and reduces the risk of low-molecular-weight polymer formation during railcar or ISO tank shipment in warm weather. The higher inhibitor concentration does not eliminate the need for oxygen, but it increases the buffer against short oxygen interruptions. In a well-aerated tank, the additional hydroquinone produces a longer induction period when the monomer is subsequently charged to a batch reactor. The actual induction delay is determined by temperature, oxygen partial pressure, and free-radical initiator concentration; a fixed universal induction time cannot be assigned without reactor-specific calorimetric testing.
| Characteristic | VAM HQ 20–30 ppm | VAM HQ 3–7 ppm | VAM MeHQ 5–15 ppm |
|---|---|---|---|
| Inhibitor chemistry | hydroquinone | hydroquinone | 4-methoxyphenol |
| Inhibitor concentration | 20–30 mg/kg | 3–7 mg/kg | 5–15 mg/kg |
| Dominant use profile | extended bulk storage and long-haul transport | short internal loop and immediate processing | low-color organic continuous systems |
| Water solubility of inhibitor | high | high | moderate to low |
| Inhibitor removal before PVOH | recommended for low-color film grade | often removed | distillation or adsorption may be needed |
A plant that switches from a 3–7 mg/kg hydroquinone grade to this 20–30 mg/kg grade may observe longer induction periods in small batch reactions. This can be managed by increasing the initiator concentration or by sparging the monomer with air before use, but oxygen sparging can also increase peroxide formation. The preferred approach is to maintain the higher inhibitor grade for storage tanks and to distill the monomer only when a low-color or low-inhibitor process requires it.
In batch emulsion polymerization of vinyl acetate at 60–80 °C, the VAM HQ 20–30 ppm grade is commonly charged directly to the reactor without preceding distillation. The hydroquinone contributes a short induction period that is compensated by adjusting the redox initiator shot; the required compensation is site-specific and should be determined by isothermal reaction calorimetry or sealed-ampoule induction tests. In high-pressure ethylene-vinyl acetate copolymerization, the inhibitor effect is reduced by the high free-radical flux from peroxide initiators at elevated temperature, but the oxygen history of the monomer remains important because oxygen can participate in unwanted side reactions.
In polyvinyl acetate latex production, hydroquinone also affects the nucleation stage. A delayed nucleation can change the particle size distribution and the final latex viscosity; therefore the redox initiator, surfactant, and seed charge are adjusted on the basis of the measured induction time. This is a routine process control adjustment, not a product deficiency, when the monomer grade is changed. In ethylene-vinyl acetate copolymer synthesis, the VAM stream may be mixed with high-pressure ethylene in a stirred autoclave; the inhibitor is consumed rapidly at reaction temperature, and the broader effect on molecular weight distribution is controlled by the chain-transfer agent feed.
For polyvinyl alcohol production, the same monomer is first polymerized to polyvinyl acetate and then alcoholized. Residual hydroquinone can carry into the methanolysis mother liquor and contribute to color formation in low-color PVOH film grades. Plants that target low yellowness index values therefore install pre-distillation or adsorption before polymerization. The spent inhibitor is then transferred into an aqueous or solvent-rich stream that must be treated by oxidation or activated carbon before discharge; ordinary steam stripping may not fully mineralize the hydroquinone.
Storage of this grade is governed by the conflict between flammability control and inhibitor preservation. Vinyl acetate has a lower explosive limit of 2.6 vol% and an upper explosive limit of 13.4 vol%. At 20 °C, the saturated vapor concentration is approximately 12 vol%, which places the headspace inside or near the flammable envelope. Nitrogen blanketing would reduce flammability but would remove the oxygen required by hydroquinone. Therefore tank facilities use explosion-proof motors, flame arrestors on vents, and controlled air aspiration rather than oxygen-free inerting. Air addition must be managed so that the mixture does not remain in the optimum combustion region during filling, emptying, or tank breathing. The facility design should follow NFPA 30 and local fire codes.
For bulk tanks above 25,000 L, recirculation loops with low-shear pumps are preferred for homogenizing inhibitor after top-up. High-shear rotary pumps should not be used for extended recirculation because local heating in seal chambers can initiate polymer formation. Stainless steel or aluminum is used for wetted parts; copper alloys should be avoided unless a compatibility study demonstrates acceptable color and polymerization behavior. Elastomer seals should be selected from fluoroelastomer or PTFE rather than ethylene-propylene diene monomer rubber if prolonged contact is expected. Sampling after top-up should occur after at least two tank turnovers to avoid a false high inhibitor result near the dip tube.
During tank filling, the displaced vapor should be routed to a flare or a scrubbed vent, not simply released to atmosphere, because the vapor is flammable and has a strong odor. During emptying, dry air should be admitted through a flame arrestor to maintain inhibitor activity. If a tank is temporarily idled, it should not be sealed under nitrogen for a period that exceeds the oxygen-starvation threshold determined by ambient temperature and tank insulation. In hot summer locations, tank surface temperatures can locally exceed the bulk liquid temperature, which accelerates inhibitor consumption even when the liquid bulk remains within the normal storage band.
Compared with 4-methoxyphenol-inhibited vinyl acetate, the hydroquinone-inhibited grade has a higher inhibitor water solubility. This difference is relevant when the monomer is water-washed to remove inhibitor residues; hydroquinone partitions rapidly into the aqueous phase, whereas 4-methoxyphenol may remain in the organic phase in low-water systems. The selection between grades is therefore driven by the downstream process: water-based emulsion polymerization and PVOH processes tend to favor hydroquinone because water removal is integrated; non-aqueous or low-color systems may select 4-methoxyphenol to avoid water contact and color carryover. Both stabilizer systems require oxygen; a monomer that is stripped with nitrogen immediately before use can become thermally unprotected even if the certificate of analysis still reports the original inhibitor content.
