GC-M PTA (PTTGC 74% / Mitsui 26%) is metered into the esterification stage of continuous polyester fibre lines as a dry crystalline solid. The mole ratio of ethylene glycol to terephthalic acid is held between 1.15 and 1.30 during esterification at 260–280 °C and 1.5–3.0 bar. Water formed by direct esterification is removed through a distillation column with reflux control, with overhead temperature kept near 100–110 °C under the stated pressure. The esterified prepolymer is transferred to a pre-polycondensation vessel operating at 270–280 °C and 20–50 mbar, followed by a finisher reactor at 280–290 °C and 0.5–2.0 mbar. Antimony trioxide is added at 150–300 ppm Sb on a PTA basis, and a phosphorus-based thermal stabilizer is metered at 10–60 ppm P to suppress discoloration. Titanium dioxide delustrant is introduced as a dispersed ethylene glycol slurry at 0.02–0.50 wt% TiO2 in the final polymer. Batch-to-batch variance in 4-carboxybenzaldehyde below the typical 25 ppm ceiling has a disproportionate influence on catalyst demand, although published data for this specific GC-M PTA configuration is limited. The polycondensation endpoint is controlled by intrinsic viscosity measured according to ASTM D4603; staple fibre is typically discharged at 0.60–0.64 dL/g and filament at 0.65–0.72 dL/g.

Spinning is performed through spinnerets with 48–288 capillary holes. Extruder melt temperature is 285–295 °C, and quench air temperature is maintained at 18–24 °C with 0.4–0.8 m/s cross-flow velocity. Drawing and texturing conditions vary by end product. Partially oriented yarn is drawn at ratios from 1.5:1 to 1.8:1 while false-twist texturing runs on high-speed friction discs at 600–900 m/min. End products include spunlace nonwoven, automotive interior fabrics, sports and leisure knitwear, terry towelling, and sewing thread. Finished textile quality control references ISO 105-B02 for light fastness, ISO 6330 for dimensional stability, and ASTM D5034 for breaking strength of woven fabrics. REACH obligations in this downstream segment apply primarily to fibre finishes and spin finishes rather than to the PTA-derived polymer itself. Processing bottleneck data from production lines show that elevated 4-CBA in PTA increases carboxyl end groups in the melt, reducing melt filtration pack life and raising break frequency in draw warping.

What Controls Solid-State Polycondensation Throughput for Bottle-Grade PET?

Bottle-grade PET based on GC-M PTA requires a copolymer-modified backbone to control crystallization and stretch behaviour. Isophthalic acid is co-fed at 1.0–3.0 wt% on total acid, and diethylene glycol is allowed to form during esterification to a concentration of 0.8–1.5 wt%. Melt-phase polymerization is terminated at an intrinsic viscosity of 0.60–0.65 dL/g using the ASTM D4603 solvent system. The amorphous pellets are crystallized at 130–160 °C and fed to a solid-state polycondensation rotary vacuum dryer or continuous column. SSP operates at 205–220 °C and 0.5–1.0 mbar for 12–20 h to raise intrinsic viscosity to 0.80–0.84 dL/g. Acetaldehyde concentration after SSP is controlled below 2 ppm because higher residual acetaldehyde impairs sensory properties in mineral water and carbonated soft drinks. The SSP reaction is surface-area controlled; pellet size distribution between 2.0 mm and 3.5 mm with a standard deviation near 0.2 mm prevents channeling and moisture pockets.

Preform injection moulding follows with a 300 t clamp pressure machine and hot runner temperatures of 270–280 °C. Barrel residence time is limited to 5–8 min to avoid thermal generation of acetaldehyde. The preform is then stretch blow moulded at a preform temperature of 100–110 °C and a blow pressure of 30–40 bar. End products include carbonated soft drink bottles, still water bottles, hot-fill containers and pharmaceutical syrup containers. Migration and regulatory compliance uses the following matrix:

Cast film lines processing PTA-derived PET for biaxially oriented polyester film require low diethylene glycol and low carboxyl end group concentrations to prevent bubble instability during sequential stretching. The base resin is polymerized from GC-M PTA and ethylene glycol to an intrinsic viscosity of 0.60–0.65 dL/g, with silica slip agent added at 500–3000 ppm as an ethylene glycol slurry. The dried resin is fed to a twin-screw extruder with L/D 33:1 and melt temperature 275–285 °C. The melt passes through a filtration pack with 15–25 µm cut size and is cast onto a chilled drum at 30–40 °C. Electrostatic pinning wires are operated at 6–8 kV to eliminate air entrapment between film and drum. Sequential orientation is performed at 90–110 °C in machine direction with a draw ratio of 3.0–3.5:1, then at 100–120 °C in transverse direction with a draw ratio of 3.5–4.0:1. Heat setting at 200–220 °C for 3–6 s reduces shrinkage to 0.5–1.5% at 150 °C when measured according to ASTM D1204.

The film is wound in rolls with thickness tolerance of ±2%. End products include capacitor dielectric film, flexible packaging laminates, thermal transfer ribbons, solar backsheets and release liners. Haze is controlled below 3% using ASTM D1003, and tensile strength is verified by ASTM D882. For capacitor-grade film, dielectric strength is tested under IEC 60674-2, and the minimum breakdown voltage is specified for 1–5 µm films. Polyester film production with this PTA grade is sensitive to carboxyl end group levels because residual acid accelerates hydrolytic degradation during hot-fill or autoclave lamination conditions. Published data for this specific configuration is limited, but film producers commonly request carboxyl end group values below 30 mmol/kg.

When PTA Replaces DMT in Direct Esterification for PBT Resins

Polybutylene terephthalate synthesis from GC-M PTA and 1,4-butanediol follows direct esterification rather than transesterification. The mole ratio of 1,4-butanediol to terephthalic acid is kept at 1.3–1.7:1 because excess diol suppresses the tetrahydrofuran side reaction during the initial hold. Esterification is carried out at 220–250 °C under atmospheric or slightly reduced pressure. Water is removed continuously through a packed column with forced reflux, and the overhead water is monitored for tetrahydrofuran content. Tetrabutyl titanate is dosed at 50–120 ppm Ti on PTA. After esterification, pressure is reduced stepwise to 0.5–2.0 mbar and temperature is increased to 245–255 °C for polycondensation. Final intrinsic viscosity for injection-moulding PBT is 0.85–1.05 dL/g measured by ISO 1628-5. The process is stopped when melt viscosity or screw torque reaches target because intrinsic viscosity alone can mask thermal degradation caused by insufficient vacuum.

The replacement of DMT with PTA eliminates methanol recovery and changes the byproduct profile to water and tetrahydrofuran, which must be separated in a low-boiler distillation train. Insufficient 4-CBA control in the PTA raises carboxyl end group concentration and lowers hydrolytic stability. Moulding compounds require drying to 0.02 wt% moisture before extrusion. End products include electrical connectors, relay housings, sensor bodies and fibre optic loose tubes. Flame-retardant grades are evaluated under UL 94 V-0 at 0.8 mm thickness and glow-wire ignition according to IEC 60695-2-13. Tensile properties are tested with ISO 527-2 at 50 mm/min, flexural modulus with ISO 178, and melt volume-flow rate with ISO 1133-1 at 250 °C and 2.16 kg.

Esterification of GC-M PTA with 2-ethylhexanol in a batch train produces di-2-ethylhexyl terephthalate, used as a non-phthalate general-purpose plasticizer. The batch reactor is charged with a mole ratio of 2.2–2.8:1 2-ethylhexanol to PTA. Tetrabutyl titanate or tetrabutyl zirconate is added at 0.05–0.15 wt% on PTA. The reaction is operated at 200–230 °C with continuous water removal through a reflux condenser and decanter. To reach conversion above 99.5%, pressure is progressively reduced to 50–100 mbar in the final stage. The endpoint is based on acid value below 0.10 mg KOH/g measured by ASTM D1045 or GB/T 1668. Excess alcohol is removed by steam stripping at 160–190 °C and 10–30 mbar, followed by filtration through a 5–10 µm filter to remove catalyst residues. Colour is controlled below 30–50 APHA according to ASTM D1209.

The plasticizer is formulated into flexible PVC at 30–60 phr for wire and cable insulation, artificial leather, coated textiles and automotive interior skins. Dry blending uses a high-speed mixer at 90–120 °C followed by twin-screw compounding at 160–180 °C. Volatility is checked with ASTM D2288, density with ASTM D4052, and migration resistance with ASTM D3291 for certain food-contact applications. Regulatory compliance is assessed under REACH and EU Regulation No 10/2011 for food-contact plasticizers where applicable. DOTP from PTA does not contain phthalic anhydride-derived byproducts; however, residual 2-ethylhexanol and unreacted terephthalic acid must be stripped below 0.05 wt% to prevent exudation in finished PVC sheet.

Hydrolysis Resistance in Unsaturated Polyester Resin Formulations

Unsaturated polyester resins based on GC-M PTA, maleic anhydride and propylene glycol are produced by a two-stage fusion cook. In the first stage, PTA is reacted with propylene glycol at a glycol excess of 5–15 mol% at 190–210 °C. In the second stage, maleic anhydride is added at a molar ratio of 0.3–0.6 mol PTA per 1.0 mol maleic anhydride, and esterification continues at 200–220 °C with nitrogen sparging or xylene azeotropic reflux. The endpoint is an acid value of 15–30 mg KOH/g measured by ISO 2114. The melt is then dissolved in styrene at 30–40 wt% monomer to yield a resin with viscosity between 300 mPa·s and 900 mPa·s measured by ISO 3219. Hydrolysis resistance is influenced by the aromatic acid content; higher PTA content reduces water absorption and improves resistance to alkaline and acidic chemical environments but increases resin brittleness if styrene bridging density is not adjusted.

The resin is compounded for sheet moulding compound on a machine with a 1.83 m wide carrier film and 6.0 m/min line speed. Fillers such as calcium carbonate are added at 150–250 phr, glass fibre chopped to 25 mm length is layered at 20–30 wt%, and thickening agents raise paste viscosity over 3–5 days to 20,000–40,000 mPa·s. End products include corrosion-resistant storage tanks, sanitary ware, marine stringers and electrical insulator parts. Mechanical properties are measured in accordance with ISO 527-4 for tensile strength, ISO 178 for flexural strength, and ASTM D2583 for Barcol hardness. The styrene carrier imposes workplace exposure limits under local regulations; vinyl toluene or acrylic monomers may replace styrene only if resin reactivity and viscosity are revalidated. High aromatic PTA content can reduce exotherm peak temperature by 5–15 °C in thick-section castings, but published data for this specific configuration is limited.