Isononyl Alcohol (INA): Primary Alcohol for Low-Volatility Plasticizers

Isononyl alcohol (INA; CAS 27458-94-2) is a branched C9 primary alcohol manufactured by hydroformylation of C8 olefins followed by hydrogenation. The resulting product is a mixture of branched C9 isomers with a primary hydroxyl content generally above 99.5 mol%, a feature that permits quantitative esterification to phthalate, adipate, trimellitate, and cyclohexanoate esters. The dominant INA-derived plasticizer is diisononyl phthalate (DINP); other high-volume esters include diisononyl adipate (DINA), triisononyl trimellitate (TINTM), and diisononyl cyclohexane-1,2-dicarboxylate (DINCH), which is produced by complete hydrogenation of DINP. These esters are used in flexible poly(vinyl chloride) (PVC) where low volatility, low fogging, and adequate migration resistance are required.

Does Branching in Isononyl Alcohol Reduce Plasticizer Volatility More than Chain Length?

Volatility of a plasticizer ester is controlled primarily by molecular weight, vapor pressure, and the diffusion coefficient of the plasticizer in the polymer matrix. Esterification of INA with phthalic anhydride yields DINP with a molecular weight near 419 g/mol, compared with 391 g/mol for di-2-ethylhexyl phthalate (DOP) from 2-ethylhexanol. This molecular weight increase lowers the vapor pressure of the neat ester and reduces volatile loss under ASTM D1203 activated-carbon exposure. The branched C9 chain also raises plasticizer viscosity and reduces plasticizing efficiency by 2–5 Shore A points at 50 phr in suspension PVC when measured by ASTM D2240. Low-temperature flexibility of DINP-plasticized PVC is less than that of DOP but remains sufficient for most building and automotive interior uses. The branching of INA prevents the side-chain crystallization that can occur in linear C9 or C10 phthalate esters at sub-ambient temperatures. Automotive fogging performance measured by ISO 6452 or SAE J1756 is generally better for DINP than for DOP at equal plasticizer loading because of the lower concentration of low-molecular-weight volatile fractions and lower plasticizer vapor pressure.

Representative commercial specification for isononyl alcohol

Property	Typical range or limit	Test method
Total C9 alcohol content	≥99.0% by gas chromatography area	internal GC based on DIN 51405
Density at 20°C	0.832–0.836 g/cm³	ASTM D4052 /ISO 12185
Boiling range (5–95 vol%)	194–205°C	ASTM D86 /ISO 3405
Flash point (closed cup)	76–82°C	ASTM D93 /ISO 2719
Water content	≤0.05 wt%	ASTM E203
Color	≤10 Pt-Co	ASTM D1209 /ISO 6271
Hydroxyl value	385–395 mg KOH/g	ASTM E222

The narrow boiling range and low water content are critical. Residual water above 0.05 wt% in the alcohol feed can suppress esterification conversion, increase acid value, and generate haze due to catalyst hydrolysis. The hydroxyl value range corresponds to an equivalent molecular weight of 142–146 g/mol; deviations indicate the presence of nonanol isomers, ethers, or esters, all of which reduce plasticizer quality.

Esterification Process Conditions and Catalyst Selection

Industrial esterification of INA with phthalic anhydride is performed in batch or continuous reactors at 180–230°C. Water of reaction is removed by azeotropic distillation with a hydrocarbon entrainer, by nitrogen sparging, or by vacuum-assisted evaporation. Titanium tetraalkoxide catalysts, such as tetrabutyl titanate, are typically used at 0.05–0.2 wt% relative to phthalic anhydride. Sulfonic acid catalysts, including p-toluenesulfonic acid, provide faster conversion but require more aggressive neutralization and can increase Pt-Co color. The reaction is operated with excess INA of 10–30 mol% to drive conversion. Endpoint control is based on acid value; the reaction is stopped when acid value falls below 0.5 mg KOH/g before neutralization. After esterification, residual acidity is neutralized with dilute sodium carbonate, and the crude ester is washed, dried, and filtered to remove catalyst residues.

Excess INA is recovered by flash evaporation and vacuum stripping. Final stripping in a thin-film or wiped-film evaporator at 180–210°C and 10–30 mbar reduces free alcohol to ≤0.1 wt%. Over-stripping or prolonged residence time above 210°C can dehydrate the branched alcohol to nonenes or generate ether by-products, increasing color and reducing plasticizer purity. The recovered alcohol is dried and returned to the esterification reactor; water in recycled INA must be below 0.05 wt% to avoid poisoning the titanate catalyst. Finished DINP is controlled for acid value ≤0.05 mg KOH/g by ASTM D1045, water content ≤0.1 wt% by ASTM E203, and color ≤20 Pt-Co. Free alcohol at ≤0.1 wt% is a critical specification for plastisol applications because free INA can lower flash point and increase volatile organic compound emissions during gelation.

Continuous esterification lines often use two or three stirred reactors in series with overhead columns for water and entrainer recovery. The first reactor operates at 180–200°C and near atmospheric pressure; the final reactor is vacuum-assisted at 200–230°C. Titanate catalyst is injected as a diluted solution in INA to avoid localized hydrolysis. Reaction sampling for acid value and color is conducted every 2–4 h; batch propagation is adjusted when acid value reduction slows below 0.02 mg KOH/g per hour. The crude ester is neutralized and then passed through a filtration loop to remove titanium dioxide hydrolysis products. Final steam stripping or wiped-film evaporation reduces free alcohol and light ends, and the overheads are condensed for alcohol recovery.

Compliance of INA-derived plasticizers is governed by the finished article rather than the alcohol itself. DINP is restricted under EU REACH Annex XVII entry 52 in toys and childcare articles that can be placed in the mouth, with a limit of 0.1% by weight of the plasticized material. This restriction does not apply to general-purpose PVC flooring, cables, or building profiles. In food-contact applications, migration testing must be conducted according to EN 1186 and EU Regulation (EU) 10/2011; the specific migration limit for DINP must be verified against the current positive list. In the case of DINCH, which is produced from INA via DINP hydrogenation, several food-contact and medical applications have been cleared in specific regulatory jurisdictions, but regional positive-list verification is required. Published data for niche food-contact configurations is limited, and formulators should obtain individual batch compliance documentation from the plasticizer producer.

Compliance and test method checklist for INA-derived plasticizer applications

Regulation or standard	Application scope	Relevant requirement
EU REACH Annex XVII entry 52	Toys and childcare articles that can be placed in mouth	DINP ≤ 0.1% by weight of plasticized material
EU Regulation (EU) 10/2011	Plastic food-contact materials	Migration testing by EN 1186; specific migration limits from positive list
ASTM D1203	Flexible PVC plasticizer volatility	Activated-carbon weight loss method
ISO 6427	Extractable matter from plastics	Organic solvent extraction resistance
SAE J1756	Automotive interior fogging	Gravimetric condensate measurement

For automotive interior specifications, low-volatility and low-fogging performance is commonly evaluated by SAE J1756 after compound conditioning. Plasticizer-formulated PVC compounds for instrument panel skins and door trim typically use DINP or DINCH to reduce windshield fouling while maintaining Shore A hardness in the range 60–85. In heavy-metal-free stabilizer systems, the low volatility of INA-derived esters complements calcium-zinc stabilizers, provided processing temperatures remain below 200°C to avoid stabilizer depletion.

When Low-Volatility Requirements Intersect with Thermal Aging in Wire and Cable Compounds

Wire and cable insulation compounds rated for 105–125°C service often use TINTM produced from INA and trimellitic anhydride. The trifunctional ester has higher molecular weight than DINP and lower plasticizer volatility under ASTM D1203 exposure. Thermal aging in circulating-air ovens at 121°C for 168 h is specified in many cable standards, including IEC 60811-1-2; tensile retention and elongation retention must generally remain above 80% and 65%, respectively. Because plasticizer volatility contributes to loss of elongation during aging, TINTM and DINP are preferred over DOP in high-temperature insulation compounds. The exact retention values depend on the polymer K-value, filler loading, antioxidant package, and crosslinking co-agent.

Production of these compounds uses high-speed mixers that heat PVC dry blend to 70–120°C before liquid plasticizer is sprayed onto the resin. The dry blend is then processed in a twin-screw extruder with L/D ratios of 25:1 to 40:1. Barrel temperatures are usually set between 160°C and 190°C, and vacuum venting is applied to remove residual moisture and volatile fractions. Free INA in the plasticizer above 0.05 wt% can reduce melt torque, generate oxygenated volatiles, and cause porosity in the insulation wall; users are advised to monitor free alcohol certificates for every batch. Pre-drying of PVC resin is required when storage humidity exceeds 60% RH; moisture above 0.2 wt% in the dry blend leads to surface defects and reduced plasticizer uptake.

Thermogravimetric analysis of a plasticized PVC compound under nitrogen per ISO 11358-1 shows two mass-loss regions: first plasticizer volatilization and second polymer dehydrochlorination. For TINTM compounds, the first mass-loss region shifts to higher temperature and shows lower total mass loss than DOP compounds; onset of 5% mass loss for 50 phr TINTM compounds can occur near 240–260°C, depending on stabilizer and resin. Published data for this specific configuration is limited.

The migration behaviour of INA-derived plasticizers in flexible PVC is diffusion-controlled and accelerates with temperature. At 23°C, apparent diffusion coefficients for DINP in plasticized PVC are generally reported in the range 10⁻¹³ to 10⁻¹² cm²/s; at 60°C, diffusion can rise by one to two orders of magnitude. This increase raises extraction by organic solvents and food simulants under ISO 6427 and EN 1186. In comparative solvent extraction tests, DINP shows lower extractability than DOP because of higher molecular weight and lower concentration gradient at the polymer surface. However, the branched alcohol-derived plasticizer is not extraction-proof; in applications involving repeated contact with non-polar solvents or aggressive cleaning agents, surface tack and hardening can develop after plasticizer loss. Formulations above 70 phr DINP in suspension PVC can exceed the compatibility limit, leading to exudation under compression per ASTM D3291. Calcium carbonate and calcined clay fillers reduce free plasticizer migration by adsorbing exuded ester and lowering the effective diffusion area, but they also raise compound density and reduce elongation.

Benchmarking Isononyl Alcohol against Linear C9 and C10 Plasticizer Alcohols

Comparisons with linear nonanol and isodecyl alcohol show that INA balances fusion speed, plasticizer viscosity, and low-temperature behaviour. Linear C9 phthalate gives slightly lower Shore A hardness than DINP at equal loading, but the linear chain can increase the plasticizer tendency to exude at low temperatures and may produce a stiffer plastisol at low shear. Isodecyl alcohol produces a C10 phthalate with even lower volatility but higher plasticizer viscosity and slower dry-blend fusion; it is typically used when low volatility is more important than processing speed. DINP from INA occupies an intermediate position, with faster fusion than C10 phthalates and lower volatile loss than DOP.

Plastisol rheology is a key control in rotary casting and dip coating. Brookfield viscosity of DINP plastisols is higher than DOP plastisols at low shear, but the material is shear-thinning under ISO 3219 rotating-spindle or cone-and-plate conditions. Low-temperature brittleness is measured by ASTM D746; DINP-plasticized PVC at 50 phr typically has brittleness temperatures in the range −30°C to −40°C, while DOP may reach −40°C to −45°C. The choice of INA over linear or higher-carbon plasticizer alcohols is therefore based on the specific balance of processing, low-temperature performance, and emission limits required by the final part. Published data for high-filler content and crosslinked PVC configurations is limited; screening trials are required.

Storage and handling of INA require moisture exclusion and temperature control. The alcohol is stored in stainless steel or internally lined carbon steel tanks under nitrogen blanketing at 15–35°C. Prolonged storage above 50°C can increase peroxide concentration and Pt-Co color. Loading and unloading lines should be equipped with desiccant breathers to maintain water content below 0.05 wt%. Because the flash point of INA is 76–82°C, the material is combustible but not classified as highly flammable at ambient temperature. DINP and TINTM have flash points generally above 220°C and 250°C, respectively, which reduces fire risk in high-temperature compounding. INA-derived plasticizers should not be combined with strong oxidizing agents or exposed to open flame. In compounded PVC, amine-based additives can interfere with acid scavengers and stabilizer systems; compatibility trials are required before production.