In bottle-grade polyethylene terephthalate (PET) melt polymerization, the Lotte Chemical PTA stream is first dispersed in ethylene glycol at a molar ratio of PTA to EG in the range 1:1.15 to 1:1.25. The resulting paste is transferred to a continuous esterification train operated at 260–270 °C and 0.2–0.4 MPa gauge pressure, where the first esterification stage reaches a degree of esterification above 90 % and the second stage above 97 % before polycondensation. Water formed during esterification is stripped under vacuum, and the resulting bis(2-hydroxyethyl) terephthalate oligomer is transferred to a vacuum finishing reactor at 285–290 °C under pressures below 1 mbar. Antimony trioxide, dosed at 150–350 mg/kg as antimony, is used as the polycondensation catalyst; phosphorus-based stabilizers are added at 10–80 mg/kg as phosphorus to control thermal degradation. The esterification and finishing stages are operated as separate vessels, with the finisher designed to remove glycol, water, and acetaldehyde under final vacuum while maintaining a short melt residence time.

For bottle resin, isophthalic acid is introduced at 1.5–3.0 wt % to suppress crystallization during injection stretch blow moulding. The isophthalic acid comonomer reduces spherulite growth and widens the processing window for preform reheating, but it also lowers the glass transition temperature and tensile modulus. Melt-phase resin is pelletized at an intrinsic viscosity of 0.60–0.64 dL/g as measured by ASTM D4603-18, then transferred to solid-state polymerization. In solid-state polymerization, pellets are heated in a nitrogen-purged rotary drum at 210–215 °C for 8–16 h; nitrogen dew point is maintained below -40 °C to prevent hydrolysis. The final bottle-grade resin achieves an intrinsic viscosity of 0.82–0.87 dL/g, an acetaldehyde concentration below 3 mg/kg, and a carboxyl end group content below 25 mmol/kg. Published data for Lotte-specific solid-state lines is limited, but these ranges represent industrial operating targets for continuous bottle-grade transfer.

Acetaldehyde generation is the critical process conflict in bottle-grade PTA-based PET. Residual acetaldehyde migrates into packaged water and creates taste and odor defects; bottle preforms for mineral water typically require an acetaldehyde concentration below 3 mg/kg per headspace gas chromatography. Higher melt-phase temperatures, increased ethylene glycol residence time, and excessive antimony catalyst concentration all elevate acetaldehyde formation. Processing protocols therefore balance polycondensation rate against degradation: lowering the melt-phase temperature below 285 °C reduces acetaldehyde but extends residence time, which can make carboxyl end group concentration drift above 30 mmol/kg. The injection moulding step for preforms introduces additional shear heating; barrel zone setpoints are typically limited to 260–280 °C. Drying of bottle-grade pellets before injection moulding is mandatory when ambient relative humidity exceeds 60 %, with a closed-loop desiccant dryer set at 160–170 °C to achieve moisture below 50 mg/kg.

Staple Fibre Spinning and the Role of TiO₂ Dispersion in PTA-Based PET

Staple fibre production from PTA-based PET begins with continuous melt spinning of polymer with an intrinsic viscosity of 0.62–0.68 dL/g. The polymer is dried to below 50 mg/kg moisture and extruded through spinnerets with capillary diameters of 0.2–0.4 mm at 280–295 °C. Titanium dioxide, added at 0.30–0.80 wt %, acts as a delustering agent and requires high-shear dispersion in an ethylene glycol-based masterbatch before injection into the melt stream; undispersed titanium dioxide agglomerates above 5 µm cause filter pack pressure rise and can block spinneret holes. The spun tow is quenched with conditioned air at 18–25 °C and 0.3–0.5 m/s, drawn at a draw ratio of 2.5–3.5, crimped, and cut to staple lengths of 32–64 mm. Drawing increases crystallinity and tenacity; tenacity values for PTA-based polyester staple are typically in the range 220–550 mN/tex when tested according to ISO 5079:2020.

The main process boundary for PTA-based staple fibre is the balance between titanium dioxide addition and spinneret service life. Titanium dioxide levels above 0.80 wt % increase delustering and UV protection but shorten spinneret pack life and require more frequent screen changes. The carboxyl end group content of fibre-grade chip should remain below 35 mmol/kg; higher carboxyl end group concentration increases moisture regain and dye uptake variability, which is particularly problematic for disperse dye pad-steam processes. Fibre-grade PTA feedstocks with elevated p-toluic acid require additional ethylene glycol purge and can shift the melt pH, destabilizing the antimony catalyst system. In direct spinning lines integrated with continuous polymerization, a melt-phase intrinsic viscosity of 0.63–0.67 dL/g is targeted; for semi-dull staple, the titanium dioxide content is held at 0.30–0.50 wt % and the spinning temperature is adjusted by 3–5 °C to compensate for melt viscosity effects in the spin pack.

Biaxially oriented polyester film produced from PTA and ethylene glycol demands lower carboxyl end group concentrations than staple fibre because free carboxylic acid groups promote chain scission during orientation and reduce hydrolysis resistance in flexible packaging. The base PET is continuously melt-extruded onto a chilled drum at 30–50 °C, quenched to an amorphous sheet with a thickness of 1.5–3.0 mm, then subjected to sequential orientation. Machine-direction orientation is performed at 70–90 °C; transverse-direction stretching follows at 90–110 °C, with heat setting at 220–230 °C to lock in dimensional stability. The high orientation process requires a polymer intrinsic viscosity of 0.62–0.68 dL/g and a carboxyl end group content in the range 15–35 meq/kg; higher values cause electrostatic pinning instability and increase the frequency of film breaks at the tenter clips.

The optical performance of PTA-based biaxially oriented film depends on oligomer content and the presence of particulate contaminants. Extruded film haze is tested according to ASTM D1003-13; typical values for clear film lie below 3 %. The coefficient of friction, adjusted with silica or calcium carbonate particles, is specified in the range 0.3–0.5 static and 0.3–0.4 dynamic when tested by ISO 8295:1995. For food-contact film, migration compliance is assessed under EU Regulation (EU) No 10/2011 and FDA 21 CFR 177.1630. The use of PTA as the aromatic monomer gives a lower rate of diethylene glycol incorporation than dimethyl terephthalate-based processes; diethylene glycol mole fractions above 1.5 mol % reduce melting point below 252 °C and can alter the stretching window, requiring the tenter temperature profile to be reduced by 5–8 °C. Published data for Lotte-specific film-grade PTA is limited; these process limits are derived from commercially operated biaxially oriented film lines using continuous polymerization.

When 1,4-Butanediol Reacts with PTA in a Three-Stage Esterification Train

When 1,4-butanediol is used as the diol component for polybutylene terephthalate, the PTA-based route is preferred over dimethyl terephthalate because water rather than methanol is released, but the process has a narrow thermal window. Esterification is run at 190–220 °C with an initial 1,4-butanediol/PTA molar ratio of 1.3:1 to 1.7:1 to compensate for tetrahydrofuran formation. Tetrabutyl titanate is charged at 50–150 mg/kg as titanium; excess catalyst above 150 mg/kg accelerates tetrahydrofuran formation and causes yellowing. The esterification product is transferred to a prepolycondensation vessel at 230–245 °C and then to a final finisher at 250–260 °C under vacuum below 1 mbar. The molten polymer is pelletized and dried to below 50 mg/kg moisture before compounding.

Polybutylene terephthalate made from PTA and 1,4-butanediol exhibits an intrinsic viscosity of 0.90–1.15 dL/g when tested by ISO 1628-1:2021 and a melt mass-flow rate of 10–25 g/10 min at 250 °C and 2.16 kg per ISO 1133-1:2022. Nucleation density and crystallization rate are high; mould temperatures of 60–100 °C are used in injection moulding. For automotive connectors and housings, glass fibre at 20–30 wt % is compounded on a twin-screw extruder with an L/D ratio of 36:1 to 44:1, using a barrel profile from 240 °C to 260 °C. The resulting compound typically shows a tensile strength of 90–120 MPa and a flexural modulus of 6000–8000 MPa according to ISO 527-2:2012. The limiting operational boundary is hydrolytic degradation: polybutylene terephthalate in hot-water environments above 85 °C loses measurable tensile strength after 1000 h, and unreinforced polybutylene terephthalate is not recommended for continuous service in ethylene glycol cooling fluids without hydrolysis-stabilized grades.

What Limits Rewetting and Tack in PTA-Based Powder Coating Resins?

Powder coating polyester resins based on PTA and neopentyl glycol are formulated to acid values of 30–70 mg KOH/g for crosslinking with β-hydroxyalkylamide or triglycidyl isocyanurate. PTA raises the glass transition temperature of the resin to 55–65 °C and reduces melt viscosity compared with phthalic anhydride-based polyesters. The resin is melt-mixed with pigment, flow control agent, and hardener in a twin-screw extruder with a barrel temperature of 90–110 °C and a screw speed below 300 min⁻¹ to avoid premature gelation. The extrudate is cooled on a chilled flaker, ground to a median particle size of 30–40 µm, and sieved. Curing is conducted at 160–180 °C for 15 min; gel time at 180 °C is typically in the range 100–250 s.

The operational boundary for PTA-based powder coating resins is moisture sensitivity during storage and application. Powders exposed to relative humidity above 70 % at 25 °C can sinter and form lumps; the glass transition temperature of the resin must exceed storage temperatures by at least 10 °C. Coating film hardness is evaluated by pencil hardness according to ISO 15184:2020, and rapid deformation resistance is tested by ISO 6272-1:2011. Higher PTA content in the polyester backbone can increase hardness and chemical resistance, but it also narrows the cure window and increases the tendency to orange peel if the melt viscosity rises too early in the bake cycle.

Esterification of PTA with 2-ethylhexanol yields dioctyl terephthalate, a non-phthalate plasticizer for flexible PVC. The reaction is carried out at 180–230 °C with an alcohol/PTA molar ratio of 2.2:1 to 2.6:1 and a titanium-based catalyst at 0.05–0.15 wt % of total batch mass. Water removal controls conversion; residual acidity is neutralized with an aqueous alkali wash, and the crude ester is steam-stripped under vacuum below 10 mbar to remove unreacted 2-ethylhexanol and light esters. Finished dioctyl terephthalate has an ester content above 99.5 %, an acid value below 0.1 mg KOH/g, and a water content below 100 mg/kg. The product is filtered through a 5 µm filter before loading into lined steel drums or flexitanks.

Flexible PVC compounds plasticized with 40–60 phr dioctyl terephthalate are used in wire and cable insulation, sheet flooring, and automotive interior skins. Dioctyl terephthalate has lower volatility than dioctyl phthalate at 150 °C and does not require phthalate labelling under REACH Annex XVII entry 51. The processing viscosity of a PVC plastisol containing dioctyl terephthalate is higher than a dioctyl phthalate-based plastisol, so viscosity depressants or higher shear mixing are needed in slush-moulding lines. In dynamic stability testing at 180 °C, dioctyl terephthalate-filled PVC exhibits lower weight loss but can show increased early discoloration unless epoxidized soybean oil is added at 3–7 phr.

Polyester Polyol Intermediates and the Viscosity Threshold in Rigid Foam Formulation

Aromatic polyester polyols are produced by condensation of PTA with diethylene glycol or a mixed glycol stream; the resulting oligomers contain hydroxyl end groups and are used as B-side polyols in polyisocyanurate rigid foams for insulation panels. PTA-based polyester polyols are supplied at hydroxyl numbers of 200–350 mg KOH/g and acid values below 3 mg KOH/g; dynamic viscosity at 25 °C ranges from 3000 mPa·s to 30000 mPa·s when measured by ISO 3219:2021. The high aromatic content improves dimensional stability and char formation but increases polyol viscosity and can reduce compatibility with pentane blowing agents. Formulators blend PTA-based polyols with aliphatic polyester polyols or low-viscosity polyether polyols to maintain an overall formulated polyol viscosity below 1500 mPa·s at 25 °C for high-pressure dispensing equipment.

The process boundary in PTA-based polyol synthesis is the control of free PTA and insoluble species. Unreacted PTA particles above 20 µm can plug dispenser filters and create surface defects in rigid foam laminates. Esterification is therefore run to a clear point before vacuum stripping; a small excess of diethylene glycol is used, and the final acid value is titrated to below 3 mg KOH/g. In polyisocyanurate formulations, the hydroxyl number and aromaticity directly affect the trimerization exotherm; closed-cell rigid foam made with PTA-based polyols typically achieves a compressive strength above 150 kPa when tested by ISO 844:2021 and a thermal conductivity below 0.024 W/(m·K) at 10 °C. Published data for Lotte-specific polyester polyol applications is limited, but these limits are observed across commercial PTA-based aromatic polyol production.

In high-speed melt spinning of polyester filament yarn from PTA-based PET, the polymer is dried to below 50 mg/kg and extruded at 285–295 °C through spinnerets with 36–144 capillaries. The extruded filaments are quenched in a cross-flow air chamber at 0.3–0.6 m/s and wound at speeds of 2500–3500 m/min for partially oriented yarn. The resulting partially oriented yarn is drawn at draw ratios of 1.5–1.8 to produce fully drawn yarn with an elongation at break of 20–35 % and a tenacity of 350–550 mN/tex when tested by ISO 5079:2020. Uniformity of PTA particle size and low p-toluic acid content influence melt viscosity stability; fluctuations greater than ±2 °C in the spin pack cause denier variability above ±1 % and package breaks.

Textile filament yarn made from PTA is further processed through texturing with a draw-texturing machine at a heater temperature of 190–220 °C. Yarn lubricant is applied at 0.3–0.6 % by mass to control fibre-to-guide friction; insufficient lubrication leads to broken filaments and higher fuzz in weaving. Dye uptake of PTA-based PET filament is evaluated with disperse dyes at 130 °C under 0.2–0.3 MPa in package dyeing machines; carboxyl end group concentration above 35 mmol/kg causes uneven dye uptake at low dye concentrations. This filament route is distinguished from staple fibre by higher winding speed and tighter online quality monitoring, not by fundamental changes in monomer chemistry.