Payal Polyplast Dioctyl Adipate (DOA)

Payal Polyplast Dioctyl Adipate (DOA) is supplied as a single standard-grade monomeric ester plasticizer derived from adipic acid and 2-ethylhexanol, CAS 103-23-1. The manufacturer does not currently publish subgrade model designations; the batch certificate references the generic material description and lot number. Typical release parameters are determined as follows: ester content ≥99.0% by gas chromatography, acid value ≤0.02 mg KOH/g (ASTM D1045-14), water content ≤0.10% (ASTM E203-16), Pt-Co color ≤30 (ASTM D1209-05), density 0.925 g/cm³ at 20°C (ASTM D4052-18), refractive index 1.446–1.448 (ASTM D1218-12), kinematic viscosity 13–14 mm²/s at 20°C (ASTM D445-19), and Cleveland open-cup flash point ≥196°C (ASTM D92-18). Batch-specific values from the Payal Polyplast certificate supersede these screening values for release decisions.

The ester is incorporated as a primary or secondary plasticizer in flexible poly(vinyl chloride), nitrile rubber seals, low-temperature cable sheathing, calendered film, and plastisol systems. In nitrile rubber compounds, DOA at 5–15 phr reduces Mooney viscosity without participating chemically in sulfur vulcanization; cure behavior should be confirmed by moving-die rheometer (ISO 6502-2:2018) because the ester acts as a diluent rather than a cure modifier.

What Distinguishes Dioctyl Adipate from Phthalate and Trimellitate Plasticizers?

The adipate backbone is a linear six-carbon dicarboxylic acid ester, whereas phthalate esters contain an aromatic benzene ring and trimellitates contain a trifunctional aromatic core. This structural distinction lowers DOA viscosity and plasticizer fusion torque but raises volatility and extraction loss. At equal plasticizer loading in suspension PVC, DOA reduces the temperature at which the compound exhibits a torsional modulus of 135 MPa in ASTM D1043-16 testing more than DOP and DINP. The aliphatic structure also contributes to lower Shore A hardness and higher elongation retention at -30°C. In contrast, DOP and DINP provide lower volatility and lower aqueous extraction because their higher molecular weight and aromatic content reduce diffusion rates in the PVC matrix. Compared with trimellitate esters, DOA is more volatile and less permanent, but produces a lower plastisol viscosity. Table 1 lists representative comparative data for formulation screening.

Values are representative published industrial data used for pre-formulation screening; batch-specific certificates from Payal Polyplast supersede these values for release decisions. The lower viscosity of DOA is a direct consequence of the absence of aromatic ring π-π interactions and the shorter adipate chain length relative to sebacate and azelate esters. In polymer matrices, this produces lower solvation viscosity and permits plasticizer uptake at reduced processing temperature, but lateral diffusion coefficients increase. Molded articles therefore show faster plasticizer evaporation at elevated service temperatures.

Plastisol viscosity response to DOA is influenced by resin particle size distribution, residual emulsifier level, and plasticizer solvation rate. In a typical 100 phr PVC plastisol based on a K 70 suspension resin, replacing DINP with DOA reduces Brookfield viscosity at 20 rpm and 23°C by approximately 20–35%, with the largest reduction observed in the first 24 h after mixing. Severs efflux viscosity at 0.14 MPa and 23°C decreases by 25–40% for DOA plastisols compared with DINP at equal plasticizer index. This can be exploited to raise filler loading by 5–10 phr in floor coating systems without exceeding the target application viscosity. High-shear dispersion in a dissolver with tip speed 5–8 m/s must be controlled below 30°C because early solvation can raise viscosity during extended mixing. Fusion behavior measured in a Brabender torque rheometer with a 60 cm³ mixing chamber at 90°C and 50 rpm shows an earlier fusion torque inflection and slightly lower maximum torque compared with DOP. The same wetting effect reduces dry-up time in dry-blend extrusion but can cause screw slippage when liquid plasticizer is injected into the first barrel zone. Batch-to-batch ester-viscosity variance can shift plastisol initial Brookfield viscosity by approximately ±5%; downstream coating lines without viscosity compensation therefore require tightened plasticizer lot-viscosity limits.

Low-Temperature Mechanical Property Trade-Offs in Extruded and Calendered PVC

Flexible PVC compounds produced with 50 phr DOA and 2 phr calcium-zinc stabilizer display a measurable depression of the brittleness temperature under ASTM D746-14 relative to the same compound plasticized with DOP. Clash-Berg torsional stiffness testing per ASTM D1043-16 shows that DOA-plasticized sheet retains a lower stiffness plateau at -30°C than DOP. Shore A hardness measured according to ASTM D2240-15 is generally 2–4 points lower for DOA at equal loading, reflecting lower solvation density and reduced internal viscosity. Tensile elongation at break per ISO 527-2:2012 remains comparable to DOP at 23°C, but low-temperature elongation is improved. On a production-scale intermeshing co-rotating twin-screw extruder with L/D 30:1 and barrel temperatures of 160–175°C, DOA reduces melt pressure ahead of the strand die, but vent-port condensate rises above the level observed with DINP. A narrow processing window exists because DOA volatilization accelerates above 180°C while incomplete fusion may occur below 160°C for high-molecular-weight PVC. Qualified barrel set points are often held to ±5°C around the established profile to prevent vent-port condensation and surface defects. Calendering at roll temperatures 145–155°C produces a dry film with lower roll-release force; plate-out on chrome rolls is observed when static heat stabilizer dose is below 2 phr.

Migration and extraction boundaries make DOA less suitable than high-molecular-weight phthalates or polymeric adipates for oily-food-contact films and long-term outdoor sheathing. Under ASTM D1239-13 soapy-water extraction and under n-hexane immersion, DOA-containing PVC exhibits higher mass loss than DOP-containing controls because the low molecular weight and aliphatic structure increase plasticizer migration kinetics through the PVC matrix. Volatility loss measured by ASTM D2288-01 at 130°C for 24 h is also higher for DOA; this restricts its use in high-temperature wire insulation unless the insulation is cross-linked or the plasticizer is blended with a permanent polymeric secondary plasticizer. Regulatory acceptance is application-specific rather than product-specific. The following compliance matrix summarizes designations that must be confirmed against the manufacturer’s current certification package.

When Dioctyl Adipate Replaces DINP in Automotive Interior Skin and Roofing Applications

In automotive interior skin formulations, replacing DINP with DOA lowers compound melt viscosity and improves cold flex, but the lower molecular weight increases volatile condensate. Gravimetric fogging measured by ISO 6452-1:2020 typically increases relative to DINP-plasticized skins; the magnitude depends on activation temperature, skin thickness, and topcoat coverage. For this reason, DOA is often restricted to the foam or backing layer rather than the exposed skin, or it is blended with a trimellitate or polyester plasticizer to reduce volatile release. In rotational slush molding, the processing window narrows because mold surface temperatures are held at 200–220°C while DOA volatility becomes measurable above 170°C. Production-scale slush lines running DOA-containing powder compounds require closed-loop venting and periodic condensate removal from the mold chamber. Published data for Payal Polyplast DOA in a specific OEM instrument panel skin formulation is limited; gravimetric fogging and tensile cold-flex screening should be run on each new compound. In PVC roofing applications, DOA contributes to low-temperature crack resistance but increases volatile loss during open-flame welding at temperatures above 230°C.

Before bulk transfer or drum thawing, the handling sequence should account for the -68°C pour point, which permits low-temperature liquid transfer but increases viscosity in cold-weather conditions. Bulk storage in 304L or 316L stainless steel is specified; unlined carbon steel may raise iron content above 0.5 ppm during extended residence and accelerate acid value drift. A dry nitrogen pad of 0.2 bar is specified to exclude moisture; partially filled containers may absorb atmospheric moisture and shift water content above 0.10%, altering plastisol rheology. Filled PVC compound should be pre-dried when ambient relative humidity exceeds 60%. Plastisol dispersions containing DOA are deaerated under 0.08 MPa vacuum for 15 min before casting to reduce air entrapment that causes pinhole defects in spread-coated film. Because DOA has a lower flash point than DINP, hot-oil temperature control units and electrostatic discharge paths must be verified in compounding plants converting from high-molecular-weight plasticizers. Final selection should be based on a plant-scale extrusion or calendering trial and not solely on the plasticizer viscosity specification.