Alpek (Mexico) PTA is supplied as a dry-flowing crystalline powder for continuous polyester condensation routes where the feedstock is expected to hold 4-carboxybenzaldehyde at or below 25 ppm, p-toluic acid at or below 150 ppm, ash residue in the low single-digit ppm range, and a b* color coordinate not exceeding 1.5. The application scope below is restricted to real downstream polyester and copolyester production environments: bottle resin, fiber and filament, biaxially oriented film, glycol-modified sheet, glass-reinforced compounds, and PBT engineering resin. PTA is not evaluated here as a direct filler, pigment, coating additive, or fuel component.

Alpek PTA entering a continuous bottle-resin polymerization line is first converted to a pumpable slurry with ethylene glycol at an EG:PTA molar feed ratio between 1.10 and 1.15. The excess glycol is not lost from the process but is recovered in the ethylene glycol distillation columns and returned to the slurry preparation vessel, which limits free glycol carryover into the esterifier off-gas. Antimony trioxide is metered as the polycondensation catalyst at 250–300 ppm Sb on the melt, with a phosphorus-based thermal stabilizer added at 15–25 ppm P to suppress catalyst-induced thermal degradation during finisher operation. Esterification is carried out in a two-reactor cascade at 240–260°C and 1.2–2.5 bar(a), with the first reactor achieving an esterification degree above 90% and a carboxyl end-group concentration below 150 mmol/kg. Melt polycondensation follows at 275–285°C and absolute pressure below 1.5 mbar, using a horizontal ring-cage finisher to produce melt-phase pellets with an intrinsic viscosity of 0.60–0.65 dL/g as measured by ASTM D4603. Bottle-grade resin then passes through solid-state polycondensation at 205–215°C under a countercurrent nitrogen stream to raise intrinsic viscosity to 0.78–0.84 dL/g and reduce acetaldehyde to below 1 ppm under ASTM F2013-10. Industry compliance for food-contact bottle formats requires FDA 21 CFR 177.1630 for aqueous, acidic, and carbonated beverage packaging, EU 10/2011 with an overall migration limit of 10 mg/dm², REACH 1907/2006 SVHC control below 0.1 wt%, and China GB 4806.6-2016 for food-contact plastics. Terminal product types are injection-stretch-blow-moulded carbonated soft drink bottles, still water containers, hot-fill juice bottles with heat-set mould temperatures of 115–135°C, and monolayer edible oil bottles requiring high aldehyde suppression. An operational boundary is the residual 4-carboxybenzaldehyde level in the PTA feed: above 25 ppm, it acts as a chain terminator and shifts the molecular weight distribution toward low-IV oligomers, reducing SSP rate and broadening the final melt rheology window.

Can 4-CBA Below 25 ppm in Alpek PTA Maintain High-Speed Polyester Fiber Spinning Without Pre-SSP Finishing?

Because spin-draw winding at 3000–3500 m/min demands a melt with low gel content, controlled carboxyl end-group levels, and stable extensional viscosity, the PTA slurry for fiber-grade polyester is prepared at an EG:PTA molar ratio of 1.13–1.15 and is not elevated above this range; excess ethylene glycol increases diethylene glycol formation during esterification and lowers thermal stability in the final fiber. Titanium dioxide delustrant is injected as a 30 wt% dispersion in ethylene glycol rather than as dry powder to prevent agglomerates. The final TiO₂ content for semi-dull fiber is 0.30–0.50 wt%, while full-dull staple requires 2.0–2.5 wt%; TiO₂ levels above 3.0 wt% increase spinneret pressure and produce filament breaks at the pack face. Melt-phase polymerization is stopped at an intrinsic viscosity of 0.62–0.68 dL/g under ASTM D4603, and the melt is filtered through 20 μm sintered metal filtration media before extrusion through spinnerets at 285–295°C. Quench air is controlled at 0.3–0.6 m/s across the filament bundle, and winding speeds are set between 3000 m/min for coarse denier partially oriented yarn and 3500 m/min for fine-denier POY, above which orientation-induced crystallinity increases dramatically and drawability drops. Draw texturing is performed at draw ratios of 1.55–1.75 with heater temperatures of 170–190°C for drawn textured yarn, while staple fiber production uses a two-stage draw line with crimping and heat-setting at 135–150°C. Industry compliance for textile and industrial polyester fiber spans OEKO-TEX Standard 100 Annex 4 for harmful substances, REACH Annex XVII restrictions for azo colorants and phthalates, ZDHC MRSL for auxiliary chemicals, and China GB 18401-2010 for textile safety categories. Terminal products are semi-dull POY, drawn textured yarn, full-dull staple fiber for ring and open-end spinning, and high-tenacity industrial filament used in seat belts and geotextiles where tenacity above 7 cN/dtex is specified.

When the target is an optically clear 23 μm BOPET film, the Film-grade PET derived from Alpek PTA is polymerized to a lower intrinsic viscosity of 0.58–0.62 dL/g and a controlled diethylene glycol content of 0.7–1.2 wt% to suppress spherulite growth during casting and orientation. The PTA-to-ethylene glycol molar ratio is held at 1:1.13, and the melt is discharged through a gear pump into a flat die at 275–285°C before quenching on a chilled casting drum at 40–55°C. Orientation is carried out sequentially at machine-direction draw ratios of 3.2–3.8 and transverse-direction draw ratios of 3.5–4.0, with heat-setting at 210–225°C to lock in dimensional stability and reduce thermal shrinkage below 1.5% at 150°C. The film-grade formulation includes fumed silica anti-blocking agent at 0.05–0.20 wt% and an optical brightener-free antioxidant package to minimize extractables. Terminal product types cover 12–23 μm metallized film for flexible packaging, 50–250 μm electrical insulation film, and 125–350 μm solar backsheet base film. Compliance for food-packaging film requires FDA 21 CFR 177.1630 and EU 10/2011; electrical insulation film is specified under IEC 60674-3 with breakdown voltage testing, while solar backsheet laminates are qualified under IEC 61215. A documented boundary is resin moisture during extrusion: dried pellets must contain less than 30 ppm water before entering the flat die, because moisture above this level hydrolyzes the ester linkages at melt temperature and increases carboxyl end-groups, causing die-face build-up and film haze.

When CHDM Replaces 30 mol% Ethylene Glycol in the Alpek PTA Feed Stream

In continuous glycol-modified copolyester production, the diol feed is split between ethylene glycol and cyclohexanedimethanol at a CHDM content of 30–35 mol% of total diol, which is sufficient to suppress crystallization and produce an amorphous sheet with a glass transition temperature near 81–85°C as measured by differential scanning calorimetry. The diol:PTA molar ratio is controlled at 1.05–1.10, and esterification is conducted at 225–240°C before melt polycondensation; the resulting copolyester is solidified by strand pelletizing rather than underwater pelletizing because the amorphous strands are tacky and block easily in water baths. Extrusion into sheet is performed at 210–240°C on a single-screw extruder with barrier screw design and polished roll temperatures of 50–80°C to remove residual stress without inducing crystallization. Terminal product types are thermoformed medical device trays, cosmetic jar inner liners, point-of-sale display sheet, and refrigerator crisper trays where clarity, impact resistance, and solvent resistance are required without post-mold annealing. Industry compliance for food-contact glycol-modified polyester adheres to FDA 21 CFR 177.1315 for ethylene-1,4-cyclohexylene dimethylene terephthalate copolymers, EU 10/2011, and ISO 10993-5 for cytotoxicity when the sheet is converted into medical packaging. The main process limitation is that CHDM content exceeding 50 mol% of total diol raises melt viscosity and reduces melt-phase polycondensation efficiency; below 20 mol%, the material begins to develop strain-induced crystallization, which reduces thermoforming latitude.

Compounding Glass-Reinforced PET from Alpek-Resourced Base Resin through Twin-Screw Extrusion

Base PET resin sourced from Alpek PTA is first solid-state polymerized to an intrinsic viscosity of 0.85–0.95 dL/g under ASTM D4603, because lower-IV base resin does not retain sufficient melt strength during glass fiber feeding and leads to screw slippage at 280°C. The base resin is dried to below 50 ppm moisture and compounded with 30 wt% E-glass chopped strand at a barrel temperature profile of 260–285°C, using a co-rotating twin-screw extruder with L/D ratio of 40:1 and vacuum venting at 50–100 mbar to remove volatile glycol and water. Nucleating agent is added at 0.1–0.5 wt% to accelerate crystallization during injection molding, and a flame-retardant package is compounded at 10–15 wt% to achieve UL 94 V-0 performance at 0.8 mm. Injection molding is carried out with mold temperatures of 120–140°C to complete PET crystallization; mold temperatures below 110°C leave amorphous surface regions with reduced chemical resistance and poor dimensional stability at 150°C. Terminal product types are electrical relay sockets, automotive sensor housings, microwave oven crisper trays, and heat-resistant pump components where continuous use temperature reaches 150°C and short-term peaks reach 180°C. Compliance requirements are UL 94 V-0 for flammability, IEC 60112 for comparative tracking index above 250 V, RoHS 2011/65/EU for restricted substances, and REACH for SVHC disclosure.

Direct esterification of Alpek PTA with 1,4-butanediol on a titanium-catalyzed continuous line is more sensitive to tetrahydrofuran formation than ethylene glycol-based PET; therefore the reactor pressure and residence time must be tightly managed to keep THF loss below 0.5 wt% of the butanediol feed. The PTA:BDO molar feed ratio is set at 1:1.25–1.30, with tetrabutyl titanate catalyst injected at 50–150 ppm Ti and a hindered phenol stabilizer added at 0.05–0.15 wt% to reduce thermo-oxidative carboxyl end-group accumulation. Esterification is carried out at 215–230°C and 1.0–1.5 bar(a), followed by polycondensation at 245–255°C and absolute pressure below 1 mbar to reach an intrinsic viscosity of 0.80–1.20 dL/g. The molten PBT is filtered and extruded into strands through a water bath, with pellet drying below 0.02 wt% moisture before compounding or injection molding. Terminal product types are automotive wiring harness connectors, electronic sensor housings, pump impellers, and industrial gear covers requiring dimensional stability, chemical resistance to hot oils, and continuous use temperature up to 120–140°C. Industry compliance includes UL 94 HB or V-0 depending on the reinforced compound, IEC 60112 for comparative tracking index above 600 V in halogen-free grades, and ISO 7792-1:2021 for PBT designation. Published data for this specific configuration using Alpek PTA in titanium-catalyzed BDO direct esterification is limited; the values above are drawn from commercial PBT direct esterification lines using high-purity terephthalic acid with equivalent 4-CBA control.