| HS Code | 626991 |
| Product Name | VAM HQ 4-6 ppm |
| Chemical Name | Vinyl Acetate Monomer |
| Chemical Formula | C4H6O2 |
| Cas Number | 108-05-4 |
| Molecular Weight | 86.09 g/mol |
| Appearance | Clear colorless liquid |
| Purity | ≥99.8% |
| Inhibitor | Hydroquinone (HQ) |
| Inhibitor Concentration | 4-6 ppm |
| Boiling Point | 72.7 °C |
| Flash Point | -8 °C (closed cup) |
| Density | 0.934 g/cm³ at 20 °C |
| Melting Point | -93 °C |
As an accredited VAM HQ 4–6 ppm factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | VAM HQ 4–6 ppm is packaged in 20 ft ISO tank containers, holding approximately 24 metric tons per container. |
| Container Loading (20′ FCL) | Load VAM HQ (4–6 ppm) into 20′ FCL with secure drum placement, proper segregation, grounding, and ventilation per SDS. |
| Shipping | Ship as UN1301, Vinyl Acetate Monomer, stabilized, Class 3 flammable liquid. Verify hydroquinone inhibitor is 4–6 ppm before loading. Use approved drums or ISO tanks, ground equipment, and keep away from heat, sparks, and oxidizers. Ensure proper ventilation, segregation, and hazard labeling on all transport documentation. |
| Storage | Store VAM HQ (vinyl acetate monomer inhibited with 4–6 ppm hydroquinone) in tightly sealed, carbon steel or stainless steel containers under inert gas blanketing. Keep in a cool, dry, well-ventilated area away from sunlight, heat, ignition sources, oxidizers, and catalysts. Maintain inhibitor effectiveness to prevent polymerization, and use proper grounding and bonding during transfer. |
| Shelf Life | Shelf life is typically 12 months from manufacture when stored unopened, under nitrogen, and protected from light and heat. |
Vinyl acetate monomer supplied with hydroquinone inhibitor at 4–6 ppm is handled as a free-radical-scavenger-stabilized monomer. At this loading, the inhibitor suppresses thermal polymerization during ambient storage but is consumed rapidly by dissolved oxygen and radical initiators in controlled polymerization. Downstream process design therefore addresses induction time, initiator correction, and residual monomer specifications rather than inhibitor removal in most emulsion and solution polymerization routes. Under REACH Regulation EC 1907/2006, hydroquinone is registered as an intentionally added stabilizer, and downstream formulators must account for the corresponding exposure and trace-substance obligations.
Semi-batch jacketed reactors of 10–30 m³ operating volume convert vinyl acetate monomer containing hydroquinone at 4–6 ppm into polyvinyl acetate homopolymer emulsions. The standard charge includes vinyl acetate at 35–50 wt% of total batch, polyvinyl alcohol protective colloid at 2–6 wt%, anionic surfactant at 0.1–1.0 wt%, ammonium persulfate initiator at 0.1–0.5 wt% on monomer, and buffer to maintain pH 4.0–6.0. The monomer is fed over 2–5 h at 60–80 °C; the hydroquinone extends the induction period, so 40–60% of the initiator is charged initially and the remainder is metered with the monomer feed. Final emulsion properties are controlled to solids 50–65%, Brookfield viscosity 5,000–50,000 mPa·s at 20 rpm, and mean particle diameter 300–1,200 nm. The production process operates as a semi-batch emulsion polymerization with delayed monomer addition to control exotherm and particle nucleation. Industry compliance for adhesive durability is anchored to EN 204:2016 classes D3 and D4 and FDA 21 CFR 175.105 for indirect food-contact use. Terminal products include D3 interior furniture adhesives, D4 water-resistant assembly glues, paper-lamination adhesives, and wood filler binders. Batch-to-batch variation in emulsion viscosity is managed by controlling residual hydroquinone consumption, initiator feed profile, and final pH; storage above 35 °C in containers with high headspace oxygen can increase coarse gel formation.
In high-pressure ethylene–vinyl acetate copolymerization, trace hydroquinone in vinyl acetate monomer at 4–6 ppm must be accounted for because the inhibitor consumes primary radicals and alters the effective initiator yield in autoclave and tubular reactors operating at 1,400–2,200 bar and 180–280 °C. Photovoltaic encapsulant grades are produced with vinyl acetate comonomer content 28–33 wt% and melt flow index 15–45 g/10 min measured at 190 °C/2.16 kg per ISO 1133-1:2022 or ASTM D1238. The EVA base resin is compounded in a co-rotating twin-screw extruder with an L/D ratio of 40:1 and a barrel temperature profile from 80 °C to 110 °C. The formulation addition ratios are EVA base resin 100 phr, organic peroxide 0.4–1.5 phr, methacryloxy silane coupling agent 0.1–0.5 phr, and hindered phenolic antioxidant 0.05–0.3 phr. The compounding window is narrow: melt temperature must remain below 110 °C to avoid premature peroxide decomposition; a ±5 °C overshoot increases gel content and reduces film clarity. The compounded granulate is cast into film at 85–130 °C with a slot die to a thickness of 400–600 µm. Module lamination is run at 145–155 °C for 10–20 min under vacuum; crosslink density is measured by xylene extraction to a gel content of 75–95%. Compliance is anchored to IEC 61215-1:2021, IEC 61730-2, and ISO 1133-1:2022. Terminal product types include mono-facial and bifacial photovoltaic encapsulant films and building-integrated PV interlayers. Published data for the exact initiator correction required by 4–6 ppm hydroquinone in commercial high-pressure vinyl acetate feed is limited; reactor operators adjust initiator injection based on melt flow index and density feedback.
Continuous solution polymerization trains for polyvinyl alcohol receive vinyl acetate containing hydroquinone at 4–6 ppm mixed with methanol to a monomer fraction of 55–70 wt%. The polymerization is performed in a stirred tank chain at 60–70 °C with azo or perester initiator metered at 0.01–0.1 wt% on monomer; the inhibitor is consumed during the induction phase and influences low-conversion molecular weight distribution. Raw polyvinyl acetate solution at 35–60 wt% solids is stripped and hydrolyzed with sodium hydroxide or sodium methoxide in methanol. Saponification degree is set at 85–99 mol% for film-forming and sizing grades. For downstream conversion, the polyvinyl alcohol resin is compounded with plasticizer at 5–15 wt% for water-soluble film, or supplied as 2–6 wt% protective colloid into emulsion polymerization of vinyl acetate and other monomers. Compliance for industrial and food-contact use is referenced to FDA 21 CFR 176.170, FDA 21 CFR 177.1670, and JIS K6726. Terminal product types include water-soluble packaging film, textile warp size, paper size, and polyvinyl butyral intermediate for laminated glass. Operational boundary: residual sodium acetate must not exceed 2.0 wt% for clear-film thermal stability; methanol recovered from the alcoholysis stage must be controlled below 0.2% moisture before reuse.
For cementitious tile adhesive dry mixes containing redispersible polymer powder, deformability derives from vinyl acetate–ethylene latex polymerized with vinyl acetate monomer containing hydroquinone at 4–6 ppm. Pressure-resistant stirred reactors or loop reactors operate at 25–80 bar and 40–70 °C with monomer feeds of vinyl acetate 70–90 wt% and ethylene 10–30 wt%; hydroquinone at this level delays latex particle nucleation, so persulfate or redox initiator pre-charge is reduced accordingly. The latex is produced at 50–60% solids, 200–3,000 mPa·s Brookfield viscosity, pH 4.0–6.0, and glass transition temperature -10 to +15 °C. Spray drying at inlet 120–180 °C and outlet 55–75 °C converts the latex to redispersible powder; anticaking agent is added at 5–15 wt% on polymer solids. In cementitious tile adhesive formulation, the redispersible polymer powder is dosed at 2–8 wt% of total dry mix. The production process for the adhesive includes dry blending cement, silica sand, cellulose ether, and redispersible polymer, followed by addition of water on site. Industry compliance is tested per EN 12004-1:2017 for cementitious adhesives, including C2 classification. The table below lists the conditioning regimes and minimum tensile adhesion values for C2 products.
| Conditioning regime | Test method | Minimum tensile adhesion |
|---|---|---|
| Standard climate 28 d | EN 12004-1:2017 | 1.0 N/mm² |
| Water immersion 21 d + recovery 7 d | EN 12004-1:2017 | 1.0 N/mm² |
| Heat ageing 14 d / 70 °C | EN 12004-1:2017 | 1.0 N/mm² |
| Freeze-thaw 25 cycles | EN 12004-1:2017 | 1.0 N/mm² |
Terminal product types include C2/C2E floor and wall tile adhesives, self-leveling underlayments, and ETICS base coats. Operational boundary: VAE powders are not suitable for use with sulfate levels outside 2.5–4.0% SO₃ because late ettringite formation can reduce adhesion; storage above 35 °C and relative humidity above 60% accelerates blocking and loss of redispersibility.
When blade coating speed exceeds 1,200 m/min, vinyl acetate–acrylate and vinyl acetate–maleate dispersion binders are formulated to immobilise coating color without surface picking. In this segment, vinyl acetate monomer containing hydroquinone at 4–6 ppm is copolymerized by semi-batch emulsion polymerization at 55–80 °C with a monomer feed of vinyl acetate 60–85 wt% and acrylate or maleate 15–40 wt%. The finished latex at 45–60% solids is compounded into coating color at 10–16 parts dry binder per 100 parts dry pigment; final coating color solids are 55–65%, viscosity 800–2,500 mPa·s at 100 rpm, and pH 7.5–9.0. Paper and board are metered by blade or roll applicator at web speeds of 800–1,800 m/min and dried to 4–7% moisture. Compliance is referenced to FDA 21 CFR 176.170, ISO 2470, and ISO 5626. Terminal product types include coated folding carton board, label paper, thermal base paper, and inkjet receptor sheets. The operational boundary is wet-rub resistance under plasticizer migration; the binder content should not be reduced below 10 parts per 100 parts pigment when surface picking is critical.
Styrene–vinyl acetate and acrylate–vinyl acetate copolymer dispersions for nonwoven binders are polymerized from vinyl acetate monomer containing hydroquinone at 4–6 ppm. The monomer feed is vinyl acetate 50–85 wt%, styrene or acrylate 15–50 wt%, and functional monomer 0.5–5.0 wt% such as N-methylolacrylamide or acetoacetoxyethyl methacrylate. Redox initiation at 40–65 °C consumes the hydroquinone during the first stage; residual free monomer in the final dispersion is controlled below 0.5%. The latex is applied to wet-laid, carded, or air-laid webs at binder add-on 10–25% dry on fibre, followed by drying and curing at 140–160 °C for 1–3 min. Industry compliance includes OEKO-TEX Standard 100 and ISO 14184-1 with formaldehyde release below 16 mg/kg for baby articles and 75 mg/kg for direct skin contact. Terminal product types include nonwoven interlinings, industrial wipes, hygiene topsheet binders, glass mat binder, and upholstery web. The operational boundary is pH compatibility: these self-crosslinking dispersions must not be blended with cationic fixing agents below pH 3.0 because premature gelation occurs.
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VAM HQ 4–6 ppm is a vinyl acetate monomer grade stabilized with hydroquinone (CAS 123-31-9) at a nominal concentration of 4–6 mg/kg. The parent monomer (CAS 108-05-4, EC 203-545-4) has the molecular formula C4H6O2 and a molecular mass of 86.09 g/mol. The product is supplied as a clear, water-white liquid for free-radical polymerizations and copolymerizations in which the stabilizer level must balance ambient storage stability against initiator demand. Test methods referenced in ASTM D2190 are applied for release testing, with hydroquinone determined by ASTM D2193, water by ASTM D1364, acidity as acetic acid by ASTM D1613, color by ASTM D1209, and density by ASTM D4052. The grade designation is not a formulated mixture grade; hydroquinone is present as a dissolved stabilizer and no separate inhibitor phase exists at the specification limit.
| Parameter | Test method | Specification |
|---|---|---|
| Vinyl acetate purity | ASTM D2190 gas chromatographic procedure | ≥ 99.8 mass % |
| Hydroquinone | ASTM D2193 | 4–6 mg/kg |
| Water | ASTM D1364 | ≤ 0.05 mass % |
| Acidity as acetic acid | ASTM D1613 | ≤ 0.005 mass % |
| Color | ASTM D1209 | ≤ 10 Pt-Co |
| Density at 20 °C | ASTM D4052 | 0.933–0.936 g/cm³ |
| Dynamic viscosity at 20 °C | ASTM D7042 | 0.59 mPa·s |
| Boiling point at 101.3 kPa | ASTM D1078 | 72.7 °C |
The 4–6 ppm hydroquinone window is among the narrowest common inhibitor bands in merchant VAM. A lower limit of 4 ppm is maintained because hydroquinone is consumed slowly by trace peroxides and by oxygen diffusing across conservation vents; below that value, the induction time measured by differential scanning calorimetry at 80 °C falls below 24 h, which is insufficient for railcar logistics. The upper limit of 6 ppm is set for polymer-grade customers whose automated initiator dosing loops are calibrated for a maximum inhibitor burden corresponding to 6 mg/kg. Water and acidity limits protect downstream hydrolysis processes where excess water shifts the saponification mass balance and excess acetic acid consumes sodium methoxide in polyvinyl alcohol production.
At bulk storage scale, the practical hazard boundary is set by dissolved-oxygen mass transfer, headspace inerting, and inhibitor depletion rather than by the nominal hydroquinone concentration alone. Vertical carbon steel tanks with an internal unreactive coating are kept under nitrogen at 2–5 kPa gauge, and recirculation piping is specified for 0.5–1.0 m/s linear velocity to eliminate stagnant zones. Under these conditions, the 4–6 ppm hydroquinone level supports storage at 25–30 °C for 6 months, provided dissolved oxygen in the liquid is maintained below 5 mg/kg and the vapor phase is kept inert. Inline spectrophotometric analyzers on tank discharge lines commonly record inhibitor depletion of 0.2–0.4 ppm per month during summer operations at 35 °C with minor oxygen ingress; published data for specific terminal configurations is limited. The storage envelope is reduced to 60–90 days when the liquid is exposed to repeated pumping through non-dedicated lines and when loading arms are not purged with nitrogen before connection. Stainless steel 316L is preferred over carbon steel for fittings in contact with vapor because trace iron from corrosion accelerates hydroquinone conversion to benzoquinone, which is measured as visible yellowing before the hydroquinone value drops below specification.
The consequence of hydroquinone in a continuous vinyl acetate–ethylene emulsion line is not a simple induction delay but a shift in the radical flux balance at the beginning of each reactor pass. In a train of three 30 m³ stirred reactors operating at 55–65 °C, an inhibitor concentration of 5 ppm consumes approximately 8 × 10⁻⁶ mol of propagating radicals per mol of VAM when a two-radical termination stoichiometry is assumed. With a typical persulfate redox feed at 0.05–0.15 wt% of monomer, that scavenging effect can reduce first-pass conversion by 2–5 percentage points and shift the molecular weight distribution toward a higher weight-average value because low-molecular-weight chains are selectively suppressed. Process control therefore uses hydroquinone offset correction on the initiator dosing loop: an increase from 4 ppm to 6 ppm corresponds to an additional 2–4 mol% persulfate demand in the first reactor, depending on the vinyl acetate–ethylene ratio and the emulsifier system. Published data for this specific reactor configuration is limited, but the stoichiometric basis remains the same across free-radical polymerization processes.
Hydroquinone content is determined by ASTM D2193 using an ultraviolet spectrophotometric finish after extraction; the method does not require derivatization and is calibrated against certified hydroquinone standards in anhydrous VAM. Sample lines are fitted with 0.45 µm PTFE filters and chilled to 5 °C to suppress polymerization during transport to the analyzer; a hold time longer than 30 min at ambient temperature can produce low results because the monomer may polymerize and consume inhibitor. When the measured value falls below 4 ppm, the tank may be re-inhibited through a metered hydroquinone solution in VAM at the recirculation eductor. Addition above 6 ppm is avoided for polymer-grade deliveries because downstream initiator demand shifts outside the calibrated range of the customer's automated dosing system. A certificate of analysis reports hydroquinone to the nearest 0.1 ppm, water to the nearest 0.01 wt%, and acidity to the nearest 0.001 wt%. Total chloride is kept below 1 mg/kg to protect noble-metal catalysts in downstream processes; published data for this specific configuration is limited.
The selection of 4–6 ppm hydroquinone over a more heavily inhibited grade becomes operationally important when ethylene–vinyl acetate copolymers are produced in high-pressure tubular reactors operating at 140–180 °C and 200–300 MPa. At those temperatures, residual hydroquinone is not merely a radical scavenger; it can undergo thermal oxidation to benzoquinone and oligomeric quinone-type species that contribute to preheater fouling and yellowing. A higher inhibitor load is therefore rejected for film-grade EVA with a yellowness index requirement below 1.5 per ASTM E313. The 4–6 ppm product maintains a stoichiometric inhibitor-to-monomer molar ratio below 4 × 10⁻⁶, corresponding to a low fouling tendency on the reactor preheater when oxygen is excluded. The same level is insufficient for prolonged unrefrigerated shipment through tropical marine routes; for that service, a manufacturer-approved 12–15 ppm hydroquinone grade is substituted, and the receiving plant compensates with added initiator or an extended induction period. Published comparative data for the 200–300 MPa configuration is limited, but the difference in outlet color and preheater fouling between low and high inhibitor grades is consistently observed in high-pressure ethylene copolymerization units.
Uninhibited vinyl acetate is available only as a short-life monomer for immediate captive polymerization. Without hydroquinone, its storage envelope at 10 °C is typically 24–48 h in a dedicated lined tank with continuous recirculation and a 0.5 vol% oxygen-free nitrogen sweep; trace peroxide formation remains a source of quality drift. The 4–6 ppm hydroquinone grade extends the same storage envelope to 6 months at 25 °C under nitrogen. At the opposite end, the 12–15 ppm hydroquinone grade is specified for long-haul bulk transport and hot-climate tank farms, but its use in polyvinyl acetate formulations requires a 10–20% increase in thermal initiator feed to restore the same time-to-peak exotherm. The table below summarizes typical commercial profiles:
| Grade | Inhibitor system | Storage envelope | Initiator demand relative to VAM HQ 4–6 ppm | Typical handling note |
|---|---|---|---|---|
| VAM HQ 4–6 ppm | hydroquinone 4–6 ppm | 6 months at 25 °C under nitrogen | baseline | standard polymer-grade VAM |
| Uninhibited VAM | none | 24–48 h at 10 °C | lower | immediate captive polymerization only |
| VAM HQ 12–15 ppm | hydroquinone 12–15 ppm | extended tropical marine | higher by 10–20% | long-haul or hot-climate storage |
| VAM MEHQ-stabilized | 4-methoxyphenol | not directly comparable | variable | limited comparative published data |
MEHQ-stabilized VAM, where available, is not interchangeable in the ASTM D2193 hydroquinone release method because the analyte differs; published data for direct comparisons in high-pressure copolymerization service is limited.
In vinyl chloride–vinyl acetate suspension copolymerization, the 4–6 ppm hydroquinone load is low enough to allow direct reactor charging without pre-distillation, but the induction period must be corrected for the radical scavenging contribution. At a polymerization temperature of 55–65 °C, azobisisobutyronitrile or diacyl peroxide initiators with a half-life of 1–2 h are typically added at 0.08–0.20 wt% of the combined monomers. A hydroquinone increase from 4 ppm to 6 ppm adds roughly 30–60 s to the induction period in a 20 m³ suspension autoclave; the exact value depends on oxygen content and the vinyl chloride-to-vinyl acetate ratio. If the hydroquinone is not accounted for, the reactor may show a delayed exotherm and a skewed particle size distribution because nucleation starts unevenly. Some suspension-grade users therefore request a reduced hydroquinone certificate of 4–5 ppm, while maintaining the 4 ppm lower limit for logistics.
Polyvinyl alcohol producers hydrolyzing polymerized VAM are sensitive to hydroquinone because hydroquinone oxidation products can contribute to color in the final resin. In a saponification train operating with sodium methoxide in methanol at 40–50 °C, residual hydroquinone from the PVAc feed is largely converted to ionic species and separated in the methanol recovery column. If upstream re-inhibition has raised the feed monomer above 6 ppm, the additional aromatic compounds can accumulate in recycled methanol and raise the APHA color of a 4 wt% aqueous PVOH solution above 20 per ASTM D1209. For this reason, some PVOH operations set an internal receiving limit of 5.5 ppm for hydroquinone in VAM even though the commercial grade allows 6 ppm. The lower bound of 4 ppm is maintained because below that value the storage induction time measured by differential scanning calorimetry at 80 °C drops below 24 h, which is insufficient for normal railcar logistics.
Regulatory classification of VAM HQ 4–6 ppm is not altered by the hydroquinone content because the stabilizer is below the CLP threshold for mixture classification under Regulation (EC) No 1272/2008; the substance is classified as Flam. Liq. 2 with H225, Acute Tox. 4 with H332, and Carc. 2 with H351. Storage vessels must meet ATEX zone requirements for the vapor space, and flame arresters are specified under ISO 16852. The lower explosion limit of VAM in air is 2.6 vol% and the upper explosion limit is 13.4 vol%, measured per ASTM E681 at 100 kPa and 20 °C. The hydroquinone does not reduce flammability; its sole function is inhibition of free-radical polymerization. Transfer pumps are specified as centrifugal sealless units with a suction line velocity below 1.5 m/s to avoid static discharge, and grounding resistance below 10 Ω is maintained at loading racks. Contact with strong oxidizing agents, peroxides, or free-radical initiators must be excluded because those substances consume hydroquinone and can initiate polymerization even when the monomer is within specification.
