Langhui Dioctyl Terephthalate LF-30 (DOTP)

Langhui Dioctyl Terephthalate LF-30 (DOTP) is a non-phthalate ester plasticizer identified chemically as bis(2-ethylhexyl) benzene-1,4-dicarboxylate, CAS 6422-86-2, with a molecular weight of 390.56 g/mol. The product is manufactured by direct esterification of purified terephthalic acid or recovered dimethyl terephthalate with 2-ethylhexanol under metal-catalysed conditions, followed by neutralisation, washing and vacuum stripping of unreacted alcohol and low-boiling esters. The LF-30 designation denotes a controlled-volatility DOTP grade intended for flexible PVC calendering, extrusion, injection moulding and plastisol processing where non-phthalate regulatory positioning and low fogging are required. Because the ester is based on a para-terephthalate backbone rather than an ortho-phthalate backbone, REACH Annex XVII Entry 51 restrictions for DEHP, DBP, BBP and DIBP do not apply to this substance. RoHS Directive 2015/863 similarly excludes DOTP from its restricted phthalate list. The material is supplied as a clear, low-colour liquid with ester content typically not less than 99.5% by gas chromatographic area normalisation. It is not a drop-in replacement for every application; solvation speed, nitrile rubber compatibility, and end-use food-contact or medical clearance require application-specific validation.

Bulk storage of LF-30 in carbon steel tanks at 25°C to 35°C with nitrogen blanketing at 0.02 MPa to 0.05 MPa prevents moisture ingress and colour drift. Transfer lines should be heat-traced if ambient temperature falls below 18°C because viscosity increases and gravimetric meter calibration shifts. Incoming QC should compare acid value, moisture and APHA colour against the certificate of analysis; an acid value increase above 0.02 mg KOH/g during storage indicates exposure to water or oxidative ageing. Published certificate-of-analysis data for LF-30-specific batch-to-batch variation is not set out in public literature; the following data describe the DOTP plasticizer class and the supplier-controlled parameters commonly associated with this grade.

How Does LF-30 Differ from General-Purpose DOTP and Ortho-Phthalate Esters?

Table 1 summarises structural and regulatory differences between LF-30 DOTP, DOP/DEHP and DINP. In melt compounding, the principal difference between LF-30 DOTP and DOP is not molecular weight but ester geometry. DOP is bis(2-ethylhexyl) benzene-1,2-dicarboxylate; DOTP is the para isomer. The para arrangement alters the spatial distribution of the carbonyl groups and changes the solubility parameter contribution of the ester, which is observed in PVC dry blend as a slower solvation front. Comparative gelation data from torque rheometers typically place DOTP fusion time several minutes beyond DOP at equivalent plasticizer loading; processors often raise the hot mixer discharge temperature by 3°C to 5°C or increase compounding residence time. Published data for LF-30-specific fusion time is limited, but the trend is documented for DOTP in flexible PVC compounds.

In wire and cable compounds rated 105°C, DOTP retention of elongation after air oven ageing at 100°C for 168 h per ISO 188 and tensile testing per ISO 527-2 is better than DOP because volatile loss is lower. DOP is restricted under REACH Annex XVII Entry 51 at 0.1% by weight in toys and childcare articles; DINP is restricted under Entry 52 in mouthable articles. DOTP is not captured by either entry. This does not automatically confer food-contact or medical clearances; it only removes the ortho-phthalate restriction status from the plasticizer chemistry.

In high-speed dry-blend mixing for flexible PVC, LF-30 is introduced after the resin reaches approximately 80°C to 90°C in a turbo mixer. The hot mixer discharge is maintained at 105°C to 120°C; the cold mixer discharge is held below 45°C to arrest plasticizer absorption and prevent PVC grain agglomeration. On counter-rotating twin-screw extruders with L/D 40:1, typical barrel zone setpoints range from 145°C to 175°C for a 50 phr DOTP-filled compound. Zone 3 and zone 4 deviations beyond ±5°C from the validated profile produce yellowness index drift and die lip plate-out in long runs. Vacuum venting at −0.08 MPa to −0.09 MPa is used to remove residual moisture and trace 2-ethylhexanol; without adequate venting, moisture levels above 0.05 wt% in the ester cause micro-foaming and surface roughness in profile extrusion. LF-30 should not be processed for extended residence times above 220°C in the presence of strong acid or alkali residues because ester hydrolysis accelerates and liberates 2-ethylhexanol. Published production-scale data for LF-30-specific extrusion throughput is limited; the equipment settings described here represent common DOTP practice in PVC profile and sheet lines.

Plastisol processors using LF-30 encounter a longer maturing period than DOP-based plastisols at 23°C because the para ester solvates PVC more slowly. Apparent viscosity measured by ASTM D1824 at 20 rpm and 25°C can remain elevated in the first 24 h compared with DOP, then stabilise. Spread coating and rotational casting lines should avoid accelerating maturation above 35°C because viscosity overshoot increases the risk of trapped air and gel particles. Published data for LF-30-specific plastisol ageing curves is limited.

When Low Volatility and Fogging Resistance Are Required in Automotive Interior PVC

Automotive instrument panel skins and door trim made from PVC or PVC/ABS skin compounds are evaluated for fogging by ISO 6452 or DIN 75201-B. The test quantifies volatile condensate on a glass plate after heating a specimen for 3 h at 100°C. DOTP is used in this application because its lower saturated vapour pressure relative to DOP reduces the condensable fraction without sacrificing Shore A hardness or low-temperature flexibility when compounded at equivalent plasticizer loading. OEM fogging requirements frequently set a condensate limit of ≤2 mg under ISO 6452-A; however, each formulation must be validated because fillers, stabilizers and PVC K-value shift the result. In thermoformed PVC skins, the plasticizer must also resist extraction by polyurethane foam amine catalysts. DOTP is less prone to exudation at the PVC/polyurethane interface than DOP, but the interface remains a critical quality point. Published comparative fogging data for LF-30 in specific automotive PVC skin formulations is limited; qualification testing should use DIN 75201-B and ISO 6452 with the actual compound.

For PVC/ABS skins thermoformed on nickel shell tooling at 180°C to 220°C, the lower volatility of DOTP reduces mould staining during extended production campaigns. Mould release agents containing amine-based silicones can interact with ester at the interface and should be evaluated by trial before full production. Published production-scale data for LF-30 in PVC/ABS slush skin tooling is limited.

Viscosity, Density, and Acid Value Specification Range

Table 2 lists representative specification controls used for incoming inspection of DOTP plasticizer grades in the LF-30 class. Acid value is a direct indicator of residual terephthalic acid or monoester. Elevated acid value above 0.02 mg KOH/g can increase viscosity drift in plastisols and reduce long-term electrical volume resistivity in cable insulation. Moisture above 0.05 wt% is critical for calendered sheet because steam bubbles form at nip temperatures above 150°C. The density range permits rapid incoming QC by digital density meter per ASTM D4052. Viscosity at 25°C is monitored by ASTM D445 and affects gravimetric dosing pump accuracy; higher-viscosity material increases suction line pressure drop in unheated storage tanks.

For plastisol viscosity stability, acid value and moisture are more important than ester content alone. A low-acid DOTP grade reduces the potential for acid-catalysed PVC chain scission during storage and lowers the amount of tin or calcium-zinc stabilizer consumed during early gelation. In calendered clear sheet, APHA colour is monitored because colour bodies from incomplete ester purification become visible as yellowing after 180°C roll-bank residence.

Migration Kinetics in Flexible PVC Depend on Ester Branching and Molecular Volume

DOTP has a branched C8 alcohol moiety identical to DOP, so migration is not suppressed solely by molecular weight. The terephthalate geometry reduces extraction into non-polar alkanes when tested by ISO 177 with n-hexane or isooctane because the para carbonyl spacing alters polymer chain packing and free volume distribution in the PVC matrix. In ASTM D3291 compatibility testing under compression, DOTP can exhibit slightly higher exudation than DIDP but lower than DOP at high addition levels above 70 phr. The implication for compounders is that DOTP is generally suitable for indoor flexible articles where contact with fatty foods, mineral oil, or aggressive solvents is limited; it should not be specified for oil-resistant technical parts without extraction testing. LF-30 is not self-certified for USP Class VI, ISO 10993, or 21 CFR food-contact status; regulatory validation is supplied through the converter and end-article assessment under specific conditions.

When LF-30 is used in NBR/PVC rubber-plastic blends, the ester can migrate into the nitrile phase and reduce vulcanizate plateau torque. Published data for LF-30-specific NBR blend torque curves is limited, so mill mixing trials should measure cure rheology by ISO 6502. The interaction is concentration-dependent and is more evident in compounds with high nitrile content and low crosslink density. For extruded gaskets and automotive weatherstrip based on NBR/PVC, this behaviour requires rebalancing the cure system rather than rejecting the plasticizer chemistry.