What crystallisation control strategy is required for bottle-grade PET polymerised from SMPC PTA?

In continuous bottle-grade PET melt polymerisation, purified terephthalic acid from Siam Mitsui (SMPC) is combined with monoethylene glycol in a high-shear slurry mixer to form a paste with an EG/PTA molar feed ratio maintained between 1.15:1 and 1.25:1. The paste is transferred to a multi-zone esterification reactor where operating temperatures of 260–270 °C and absolute pressures of 120–150 kPa produce an oligomer stream with esterification conversion above 96%. Isophthalic acid is metered as a co-monomer at 1.5–3.0 mol% of the acid fraction to depress crystallisation, and diethylene glycol generation is controlled to 1.0–1.5 wt% of the final polymer to reduce spherulite density without lowering top-load strength. Antimony trioxide catalyst is typically present at 150–300 mg Sb/kg polymer, stabilised with a phosphorus compound to prevent grey discoloration. The amorphous melt is pelletised and subjected to solid-state polycondensation at 200–220 °C under nitrogen or vacuum, raising intrinsic viscosity from 0.60–0.65 dL/g to 0.80–0.85 dL/g measured by ASTM D4603-18. Food-contact compliance for the resulting bottle resin is assessed under FDA 21 CFR 177.1630, EU Regulation (EU) No 10/2011, and regional positive lists; melt flow stability is checked using ISO 1133-1:2022. Terminal package types produced from this feedstock include carbonated soft drink bottles, hot-fill containers, edible oil bottles, pharmaceutical vials and cosmetics containers, each requiring preform injection at 100–120 °C and stretch blow moulding at a blow pressure of 30–40 bar.

Process bottlenecks observed on bottle-resin lines are dominated by acetaldehyde regeneration during preform injection and by gate haze formation when local barrel residence time exceeds 120 s at 270–285 °C. The esterification paste ratio is therefore not adjusted in isolation; it is coupled to DEG suppression and antimony catalyst activity because elevated EG excess increases DEG formation and lowers thermal stability. The critical threshold is the solid-state polycondensation temperature window: below 200 °C the end-of-polycondensation carboxyl end-group population remains above 30 meq/kg, and above 220 °C pellet sintering increases fines and colour shift. Published process data for individual SMPC PTA campaigns indicate that controlling raw PTA particle-size distribution is essential to avoid paste viscosity drift at the slurry pump.

The staple fibre and filament extrusion route from SMPC PTA differs from bottle-grade processing primarily in intrinsic viscosity target and delustering additive loading. Continuous polycondensation is operated to an intrinsic viscosity of 0.60–0.68 dL/g under ASTM D4603-18; titanium dioxide is dispersed into the esterification or polycondensation stage at 0.30–0.50 wt% for semi-dull to full-dull yarn grades, and the paste molar ratio EG/PTA is maintained at 1.15:1, with PTA representing approximately 86.4 wt% of the polymer repeat unit. Spin finishes are selected under ZDHC MRSL V3.1 and REACH restrictions and applied at 0.3–0.8% by fibre weight immediately below the quench zone. Melt spinning at 282–295 °C through spinnerets with hole diameters from 0.15 mm to 0.40 mm is followed by drawing ratios of 3.0:1 to 4.5:1; crimping and heat setting at 130–170 °C stabilise staple fibre geometry. Production-scale failure on tandem drawing lines is usually precipitated by filter-pack differential pressure above 350 bar or by cyclic oligomer deposition at the spinneret face. Finished fibre products include apparel and home textile filament, staple fibre for ring and rotor spinning, needle-punched nonwoven geotextile, seat-belt yarn, and tyre-cord fabric substrate. Textile compliance is normally assessed against Oeko-Tex Standard 100 product classes and REACH Annex XVII restrictions for aromatic amine release, not against food-contact standards.

When Biaxially Oriented Film Production Demands Low Oligomer Content from PTA Feedstock

In biaxially oriented polyester film production, the cyclic oligomer population and diethylene glycol concentration in the melt are the main PTA-linked variables causing chill-roll sticking, haze, and capacitor dielectric defects. The polymerisation route uses an EG/PTA molar ratio of 1.15:1, with diethylene glycol suppressed to 0.8–1.0 wt% and slip/anti-block silica additions of 0.02–0.50 wt% depending on film handling requirements. Melt extrusion at 270–285 °C through a flat film die is followed by electrostatic pinning on a quench drum and sequential biaxial orientation: machine-direction draw ratios of 3.0:1–3.5:1 at 85–100 °C, transverse-direction draw ratios of 3.5:1–4.0:1 at 100–120 °C, and heat setting at 220–240 °C with 3–8% relaxation. Cyclic trimer deposition on the MDO rolls and haze above 3.0% are the critical production boundaries; melt filtration through 10–20 µm sintered metal or depth media is therefore specified. Food-contact and electrical-grade film conformance relies on FDA 21 CFR 177.1630, EU Regulation (EU) No 10/2011, and IEC 60674-3-2 for capacitor dielectric films. Terminal film types include flexible packaging film, metallised barrier film, capacitor dielectric film, release liner, photographic base, and solar backsheet core layers. For capacitor-grade film, thickness tolerance and oligomer content are more restrictive than for packaging film, and the observed batch-to-batch variance in PTA iron and bulk density can shift dielectric dissipation factor.

Direct esterification of SMPC PTA with 1,4-butanediol to polybutylene terephthalate (PBT) requires a higher glycol excess than PET because tetrahydrofuran is formed as a side product. Industrial esterification runs at 220–250 °C with a BDO/PTA molar ratio of 1.3:1–1.5:1; tetrabutyl titanate catalyst is introduced at 50–150 mg Ti/kg and the subsequent polycondensation step is carried out at 250–260 °C under 0.5–1.0 mbar to reach an intrinsic viscosity of 0.80–1.00 dL/g for compounding grades. Carboxyl end-group concentration is maintained below 40 meq/kg because residual titanate residues accelerate hydrolytic degradation if end-capping is incomplete. Compounding on a co-rotating twin-screw extruder with L/D 44:1 uses glass fibre loadings of 15–30 wt% and flame-retardant packages selected to achieve UL 94 V-0 at 0.8 mm and 1.6 mm. Typical melt volume-flow rates for injection moulding grades are 10–20 cm³/10 min at 250 °C under 2.16 kg load according to ISO 1133-1:2022. Compliance for end parts is assessed against IEC 60243-1 for dielectric strength, REACH, and RoHS Directive 2011/65/EU where applicable. Production-scale failures in PBT moulding include surface blistering at barrel temperatures above 265 °C, and screw fouling from carbonised flame-retardant packages when screw speed exceeds 300 rpm without adequate cooling. Terminal finished parts include electrical connectors, automotive sensor housings, relay components, pump housings, and brush holders.

Two-Stage Titanate Catalysis in DOTP Esterification from PTA

Dioctyl terephthalate (DOTP) is manufactured by direct esterification of SMPC PTA with 2-ethylhexanol under titanate catalysis. The stoichiometric alcohol-to-acid ratio is 2:1, but industrial charge ratios are maintained at 2.3:1–2.5:1 to drive conversion and replenish alcohol lost to isomerisation or water entrainment. Tetrabutyl titanate or tetraisopropyl titanate is charged at 0.05–0.2 wt% of PTA; the reaction is operated at 180–220 °C initially at atmospheric pressure and then under progressive vacuum, with water removal controlled to avoid 2-ethylhexanol carryover into the reflux system. The crude ester is neutralised to an acid value below 0.07 mg KOH/g, vacuum-stripped at 180–200 °C and 0.5–2.0 kPa, and filtered through 5–10 µm media to remove catalyst residues. DOTP product used as a non-phthalate plasticiser in flexible PVC is assessed under REACH, RoHS Directive 2011/65/EU, and EN 71-3 migration testing for toy applications; food-contact use additionally requires EU Regulation (EU) No 10/2011 evaluation. In downstream PVC compounding, DOTP exhibits lower solvation power than DINP, so plastisol formulations require fine-particle suspension PVC grades and higher fusion temperatures; typical flexible PVC additions range from 30–70 phr. Process interruptions are most common at the neutralisation stage when residual acidity is allowed to exceed 0.10 mg KOH/g, causing elevated colour and ester decomposition during stripping. Terminal finished products include wire and cable insulation, automotive interior skins, flooring, coated fabrics, and medical tubing.

Polyester polyol synthesis from SMPC PTA for rigid polyurethane and polyisocyanurate foams is operated as a bulk esterification with diethylene glycol and, where required, modifying glycols or aliphatic diacids. PTA is charged at 25–45 wt% of the finished polyol; the glycol-to-acid hydroxyl excess is set to deliver a hydroxyl value of 250–450 mg KOH/g and an acid value below 2.0 mg KOH/g. The esterification temperature window is 200–230 °C, with vacuum applied to remove water and free glycol until the acid value reaches the specified endpoint. The aromatic ester content imparts dimensional stability and char formation in rigid foam, but high PTA content raises polyol viscosity, requiring blending with lower-viscosity polyether polyols before use in high-pressure impingement mixheads. Foam processing with polymeric MDI at an isocyanate index of 100–250 and hydrocarbon or hydrofluoroolefin blowing agents yields closed-cell insulation with apparent density and thermal conductivity measured under ASTM D1622 and ASTM C518; flame-spread classification is assessed by ASTM E84. Production-scale issues include phase separation during polyester polyol capping and acid value drift above 3.0 mg KOH/g when water removal is insufficient. Published data for this specific configuration is limited; formulation development therefore relies on pilot foam trials and not solely on polyester polyol quality indicators. Terminal products include metal-faced sandwich panels, pour-in-place appliance insulation, spray-applied foam, adhesives, and coatings. Compliance for these rigid foam formulations is governed principally by REACH and the regional building-code test standards, with selected applications requiring ASTM E84 Class I or Class II ratings.