| HS Code | 206289 |
| Product Name | Polymer Grade MEHQ 10-15 ppm (Low-Yellowing Textile Vinylon Fiber) |
| Chemical Name | 4-Methoxyphenol |
| Cas Number | 150-76-5 |
| Molecular Formula | C7H8O2 |
| Molecular Weight | 124.14 g/mol |
| Appearance | White crystalline solid |
| Purity | 99.0% min (polymer grade) |
| Recommended Dosage | 10-15 ppm based on vinyl monomer |
| Melting Point | 52.5-54.5 °C |
| Boiling Point | 243 °C |
| Density | 1.13 g/cm3 at 20 °C |
| Solubility | Soluble in water, alcohols, ketones, and vinyl monomers |
| Flash Point | 132 °C (closed cup) |
| Color Stability | Low yellowing profile in textile Vinylon fiber processing |
| Storage Conditions | Store in a cool, dry, ventilated area; keep below 40 °C |
| Shelf Life | 12 months when properly stored |
As an accredited Polymer Grade MEHQ 10–15 ppm (Low-Yellowing Textile Vinylon Fiber) factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Supplied in 25 kg sealed fiber drums with nitrogen purge, ensuring stability and low-yellowing quality. |
| Container Loading (20′ FCL) | 20' FCL loading: Place Polymer Grade MEHQ (10–15 ppm) drums on pallets, secure with bracing, ensure dry, ventilated, and temperature-controlled container. |
| Shipping | Polymer Grade MEHQ (10–15 ppm) is shipped as a stabilized inhibitor to prevent premature polymerization. Pack in sealed, moisture-proof containers, away from heat, ignition sources, and direct light. Store in a cool, dry, ventilated area. Ensure proper labeling and compliance with hazardous material transport regulations. |
| Storage | Store in a cool, dry, well-ventilated area away from direct sunlight, heat, and ignition sources. Keep container tightly sealed to prevent moisture absorption and contamination. Avoid contact with strong oxidizers and acids. Maintain temperatures between 5–30°C. Ensure proper labeling and segregation from incompatible materials. Use appropriate personal protective equipment when handling. |
| Shelf Life | Store in a cool, dry, well-ventilated area away from light. Shelf life is 12 months from manufacture when sealed. |
Polymer-grade MEHQ at 10–15 ppm functions as the aerobic phenolic inhibitor in vinyl acetate monomer that is subsequently polymerized into fibre-grade polyvinyl alcohol for low-yellowing textile vinylon fiber. At the import terminal or plant tank farm, vinyl acetate monomer designated for fibre-grade polyvinyl alcohol is received with 10–15 ppm 4-methoxyphenol inhibitor, and this concentration is maintained during bulk storage through continuous recirculation under a controlled oxygen partial pressure. The formulation ratio 10–15 ppm is not arbitrary: MEHQ behaves as a radical scavenger requiring dissolved oxygen in the liquid phase to regenerate the phenoxy radical after it terminates a growing polyvinyl acetate chain. In fixed-roof carbon steel storage tanks fitted with pressure/vacuum vents and side-entry recirculation pumps, the monomer is kept below 28°C and the oxygen concentration in the vapour space is managed without full nitrogen inerting because nitrogen blanketing would deactivate the inhibitor. ASTM D2190 Table 1 is the relevant monomer specification for vinyl acetate inhibitor content, and the European REACH registration for the material requires the safety data sheet to state the MEHQ concentration in the 10–15 ppm band. The downstream production process is the transfer of inhibited vinyl acetate to the continuous polymerization train; the terminal finished product type is a stabilized polymer-grade vinyl acetate stream that will later become fibre-grade polyvinyl alcohol and low-yellowing textile vinylon staple.
Recovered vinyl acetate streams from the polyvinyl alcohol train present a fouling risk profile that differs from fresh monomer because light ends, acetaldehyde, acetic acid and dissolved methanol concentrate in the recovery column overheads. In a vacuum distillation system operating with a reflux drum at 120–180 mbar and a forced-circulation reboiler at 70–85°C, MEHQ is dosed as a make-up solution into the reflux line at 5–15 ppm relative to the recovered vinyl acetate mass, supplementing the 10–15 ppm already present in fresh-monomer inventories. The inhibitor partitions between the liquid and vapour phases; column top trays and overhead condenser lines are the most likely locations for popcorn polymer accumulation when the local MEHQ concentration falls below 5 ppm. Compliance is governed by the same ASTM D2190 monomer specification after blending with fresh vinyl acetate, and the recovered monomer is not returned to storage without confirming the inhibitor concentration by gas chromatography. The downstream production process is the redistillation and inhibitor make-up operation in a mother-liquor recovery train; the terminal finished product type is a clarified, inhibited recovered vinyl acetate stream suitable for reuse in fibre-grade polyvinyl acetate synthesis.
In batch solution polymerization of vinyl acetate in methanol, the incoming MEHQ concentration functions as a radical inventory buffer rather than an inert spectator, and commercial reactor logs show that 10–15 ppm in the fresh monomer produces a measurable induction period before the azo initiator establishes steady-state radical flux. The polymerization is carried out in a stainless steel jacketed stirred reactor at 60–65°C with a reflux condenser and a feed ratio of methanol to vinyl acetate between 10:90 and 25:75 by mass; azobis(isobutyronitrile) initiator is metered separately at 0.02–0.05 wt% of vinyl acetate. MEHQ at 10–15 ppm consumes a portion of the initial free radicals, delaying the exotherm onset and shifting the molecular weight distribution toward a higher weight-average molecular weight at a given conversion because fewer initiator fragments participate during the early polymerization stage. Published data for this specific configuration is limited; therefore, reactor control in practice relies on exotherm-onset time and final viscometric average molecular weight rather than on a fixed kinetic equation. The practical control band is bracketed by 8 ppm and 15 ppm: below 8 ppm the safety margin against premature polymerization during vinyl acetate preheating narrows, while above 15 ppm the induction time increase and the potential for quinoid yellowing downstream become difficult to offset by initiator adjustment alone. Compliance for the monomer remains ASTM D2190, while the resulting polyvinyl acetate solution is characterized by solids content and viscosity according to the plant’s internal standard operating procedure aligned with ISO 9001. The downstream production process is the controlled solution polymerization of vinyl acetate to intermediate polyvinyl acetate; the terminal finished product type is a 40–50% solids polyvinyl acetate solution in methanol, ready for alkaline saponification to fibre-grade polyvinyl alcohol.
Methanolysis mother liquor generated during the sodium hydroxide–catalysed saponification of polyvinyl acetate contains residual methyl acetate, sodium acetate, water, and unreacted vinyl acetate that can carry MEHQ back to the solvent recovery system. No fresh MEHQ is added at this stage; instead, the recycle concentration is controlled by purging a portion of the recovered methanol and by washing the polyvinyl alcohol gel with fresh methanol to keep the residual inhibitor below 2 ppm in the dried resin. The production process is a continuous belt saponification and methanol washing operation in which the 40–50% solids polyvinyl acetate solution is mixed with sodium hydroxide in methanol at 35–45°C, then the precipitated polyvinyl alcohol is swollen, washed, and centrifuged before drying at 100–120°C. Pre-drying is required when ambient relative humidity exceeds 60% to control residual moisture before dissolution. The relevant compliance standard for colour stability of the resulting polyvinyl alcohol is ISO 105-B02 when the final fibre is tested for light-induced yellowing; the monomer entering the saponification train remains specified by ASTM D2190. The terminal finished product type is a low-yellowing polyvinyl alcohol flake or granular resin with residual acetyl content adjusted to the 1–2 mol% range, which is the feedstock for wet-spun vinylon fibre.
| Control point | Standard or test code | MEHQ or residual specification | Terminal product type |
|---|---|---|---|
| Bulk vinyl acetate storage | ASTM D2190 | 10–15 ppm | Stabilized vinyl acetate feedstock |
| Vinyl acetate recovery column | ASTM D2190, plant GC method | 5–15 ppm make-up | Recovered inhibited vinyl acetate stream |
| PVAc solution polymerization | ISO 9001 process control | 10–15 ppm in fresh monomer | PVAc solution for saponification |
| PVA saponification and washing | ISO 105-B02 | <2 ppm residual in PVA | Low-yellowing PVA flake |
| Vinylon wet spinning | ISO 105-B02, ISO 13934-1 | <1 ppm residual in fibre | Textile vinylon staple or filament |
When a wet-spinning line produces low-yellowing textile vinylon staple from polyvinyl alcohol that originated from 10–15 ppm MEHQ-inhibited vinyl acetate, the trace phenolic residues survive the saponification and washing sequence only at sub-ppm levels, but their photochemical behaviour becomes measurable in fibre heat setting and in subsequent textile laundering. The spinning process begins by dissolving the low-yellowing PVA flake in hot water at 88–95°C to form a 15–20% dope, which is filtered and deaerated before extrusion through a spinneret into a coagulation bath of sodium sulfate at 380–420 g/L and 40–50°C. The resulting filaments are wet-drawn, heat-treated, and optionally acetalized to improve hot-water resistance. Residual MEHQ is not an intentional formulation component at this stage; however, the specification linkage back to 10–15 ppm in vinyl acetate is critical because oxidation products of MEHQ can lower the CIE whiteness index after 80–120°C heat setting and after ISO 105-B02 xenon arc exposure. Compliance for the final textile fibre includes ISO 105-B02 for light-induced yellowing and ISO 13934-1 for tensile properties of the woven fabric. The terminal finished product type is low-yellowing vinylon staple or filament yarn for woven and knitted textile applications, including workwear, linings, and technical textiles.
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Polymer Grade MEHQ 10–15 ppm (Low-Yellowing Textile Vinylon Fiber) is a refined 4-methoxyphenol inhibitor and stabilizer for vinyl acetate monomer and downstream polyvinyl alcohol feedstock in textile vinylon production. The product is identified by the descriptive grade designation rather than a proprietary model code; procurement specifications reference CAS 150-76-5, EC 205-769-8, molecular formula C7H8O2, and molecular weight 124.14 g/mol. The loading range of 10–15 ppm in vinyl acetate distinguishes this grade from higher-dosage inhibited vinyl acetate grades intended for adhesives or emulsion polymers. The low-yellowing textile vinylon grade is release-controlled for hydroquinone, water, and solution color because trace phenolic carryover can form quinonoid chromophores during saponification, wet spinning, and formalization.
This polymer-grade product is an industrial polymerization inhibitor, not a pharmaceutical or food-contact additive. Certificates of analysis report impurity limits relevant to continuous vinyl acetate polymerization lines. The grade is added to distilled vinyl acetate after distillation and before storage; it is not applied as a finish to the vinylon fiber.
Wet-spun vinylon fiber is sensitive to trace phenolic residues because the polyvinyl alcohol dope is processed in hot aqueous acid and then acetalized with formaldehyde. Residual 4-methoxyphenol at 10–15 ppm in the original vinyl acetate feed is depleted primarily during polymerization and saponification, but the unconverted fraction can follow the polymer into the spinning dope. The formalization bath operates at 60–75 °C with 30–50 g/L formaldehyde and 200–300 g/L sulfuric acid. Under these conditions, residual phenolic species may undergo acid-catalyzed condensation and oxidation to conjugated quinonoid structures with absorbance in the 400–450 nm region. The low-yellowing grade therefore restricts the vinyl acetate stabilizer to 10–15 ppm, below the carryover level associated with visible yellowing after heat stretching and acetalization.
Yellowness is measured on finished fiber or on compression-molded polyvinyl alcohol film according to ASTM E313-20. Optical white textile vinylon staple is also evaluated after xenon arc exposure according to ISO 105-B02 for color fastness. Published data for this specific configuration is limited, but industrial specifications for low-yellowing vinylon yarn frequently reject lots with CIE whiteness below 80 or yellowness index above 3.0 when tested on conditioned fiber. These numerical limits are customer-defined release criteria, not universal ISO specifications.
| Parameter | Test method | Specification |
|---|---|---|
| Appearance | Visual inspection | White to off-white crystalline powder or flakes |
| 4-Methoxyphenol assay | HPLC-UV, 254 nm | ≥99.5 wt% |
| Hydroquinone content | HPLC-UV, 254 nm | ≤0.05 wt% |
| Water content | Karl Fischer titration | ≤0.10 wt% |
| Color, 50 wt% methanol | ASTM D1209 | ≤30 APHA |
| Solidification point | ASTM D1519 | 54.0–56.0 °C |
| Sulfated ash | Combustion at 650 °C | ≤0.05 wt% |
Batch release records for this grade typically report 4-methoxyphenol assay by HPLC-UV at 254 nm, water by Karl Fischer titration, and color by ASTM D1209. Hydroquinone is limited because it has two phenolic hydroxyl groups and can form p-benzoquinone more readily than monomethyl ether derivatives. The methoxy substituent of 4-methoxyphenol blocks one ring position and reduces the probability of fully aromatic quinone formation. This difference is significant in molten or acidic polyvinyl alcohol processing, where color body formation is kinetic rather than thermodynamic. At 10–15 ppm inhibitor loading, the hydroquinone limit of ≤0.05 wt% keeps total color-forming impurity mass below 0.008 mg/kg in the final vinyl acetate stream.
Storage conditions also influence product color. The product should be kept in sealed bags under nitrogen and protected from temperatures above 30 °C. Prolonged exposure to air, relative humidity above 60%, or contact with copper alloys accelerates oxidation to colored species. Carbon steel is acceptable for short-term transfer only if the vessel is clean and dry; 316L stainless steel is preferred for recirculation loops. The inhibitor should not be mixed with strong oxidizers, peroxides, or concentrated nitric acid. Pre-drying of feed hoppers and transfer lines is required at relative humidity above 60%.
The function of 4-methoxyphenol in vinyl acetate is sacrificial radical quenching. The phenolic O–H bond transfers a hydrogen atom to an alkyl or peroxy radical, yielding a stabilized phenoxyl radical. The methoxy substituent increases electron density on the aromatic ring and introduces steric hindrance, which makes the inhibitor effective at 10–15 ppm without completely stopping polymerization after thermal initiator addition. In bulk vinyl acetate storage at 15–25 °C, this loading is sufficient to prevent runaway polymerization in clean 316L tanks under inert gas.
At higher loadings, the induction period in continuous polymerization can be extended unevenly across the reactor. The low loading range reduces the need for additional azo or peroxide initiator and limits the formation of oligomeric side products that affect polyvinyl alcohol molecular weight distribution. Viscosity of polyvinyl alcohol dope is typically measured at 4 wt% in water at 20 °C according to JIS K6726 or equivalent methods. For textile vinylon, a narrow viscosity range is required for stable wet spinning; published data for the exact induction time shift at 10–15 ppm in vinyl acetate plants is limited because it depends on oxygen partial pressure, temperature, and inhibitor distribution.
If the MEHQ concentration in vinyl acetate rises above 15 ppm, the main process risk is not disappearance of inhibition but accumulation of unconverted inhibitor or its oxidation products in the acetalization bath. The bath is reused continuously, so color body concentration can increase with bath age. Spent formalization liquor from low-yellowing textile vinylon lines is monitored for UV absorbance at 420 nm; an absorbance increase in the 400–450 nm window correlates with yellowing of the fiber. Once the residual inhibitor exceeds the target range, bath blowdown and fresh acid replenishment are required to restore optical properties. The upper control limit of 15 ppm is therefore a feed-forward control point for color consistency across multiple spinning positions.
In polyvinyl alcohol powder, off-target MEHQ carryover can also lower thermal stability during drying. Polyvinyl alcohol drying air temperatures are often 120–140 °C in continuous belt dryers. Phenolic species that survive saponification can oxidize in this thermal environment and contribute to yellowing before the fiber is spun. Because textile vinylon is used in white fabrics, industrial processes prefer the 10–15 ppm MEHQ grade over higher-dosage inhibited vinyl acetate grades intended for adhesives or emulsion polymers.
Production-scale transfer of polymer-grade MEHQ into 40 m³ vinyl acetate storage tanks uses a closed addition hopper with nitrogen purge at 10–25 kPa. The inhibitor is added after monomer distillation and before storage; in-line static mixers with 30–60 s residence time are used to avoid local inhibitor concentration above 100 ppm at the injection point. Batch-to-batch deviation of hydroquinone content in supplier certificates is typically between 0.01 wt% and 0.05 wt%, with corresponding APHA color shifts from 20 to 40 in 50 wt% methanol. This variance is acceptable for low-yellowing vinylon only when the vinyl acetate feed is sampled at the polymerization reactor inlet and adjusted to maintain the 10–15 ppm window. Stagnant zones in unagitated storage tanks can retain local concentrations above 30 ppm even when average feed is 12 ppm; therefore circulation before transfer is required.
Hydroquinone, 4-tert-butylcatechol, and phenothiazine are not direct drop-in replacements for the low-yellowing vinylon grade. Hydroquinone is more water-soluble and forms p-benzoquinone under oxidative conditions, which produces a stronger yellow color than the corresponding 4-methoxyphenol oxidation products. 4-tert-Butylcatechol is effective in styrene and butadiene systems but may form highly colored metal complexes with iron or copper in polyvinyl alcohol processing. Phenothiazine contains sulfur and nitrogen, may impart amber color at low concentration, and is generally reserved for acrylic monomer stabilization.
| Property | Polymer-grade MEHQ 10–15 ppm | Hydroquinone | 4-tert-Butylcatechol | Phenothiazine |
|---|---|---|---|---|
| CAS number | 150-76-5 | 123-31-9 | 98-29-3 | 92-84-2 |
| Principal use | Vinyl acetate and polyvinyl alcohol grade inhibitor | Styrene stabilizer; antioxidant | Styrene and butadiene inhibitor | Acrylic and methacrylic inhibitor |
| Color risk in acidic acetalization | Low at 10–15 ppm; rises above 15 ppm | Moderate to high due to benzoquinone | Moderate; metal chelation risk | High; amber sulfur and nitrogen by-products |
| Solubility in vinyl acetate | Fully soluble at 20–25 °C | Lower; may require heated mixing | Soluble | Partially soluble |
| Suitability for low-yellowing textile vinylon | Preferred within stated loading | Not recommended | Not recommended | Not recommended |
Because the vinylon formalization bath contains 200–300 g/L sulfuric acid and 30–50 g/L formaldehyde, inhibitor-derived chromophores are generated at high ionic strength and moderate temperature. The polymer-grade MEHQ product is therefore differentiated from hydroquinone and phenothiazine grades by lower conjugated quinone formation at equivalent antioxidant activity, not by higher radical quenching strength alone.
Regulatory documentation for this grade includes REACH registration for 150-76-5 and a safety data sheet compliant with EC 1907/2006. The product is classified as harmful if swallowed and may cause skin sensitization; local exhaust ventilation is required during open handling. It is not approved for direct food-contact use under EU 10/2011 or FDA 21 CFR for this application. Waste material should be incinerated in a licensed facility at ≥850 °C with secondary combustion. These boundaries are included because the low-yellowing vinylon grade is an industrial polymerization inhibitor, not a textile finishing agent.
