DPHP (Di(2-propylheptyl) phthalate) is a high-performance plasticizer that makes rigid plastics like PVC flexible, durable, and heat-resistant. It’s essentially a clear, oily liquid chemical additive that manufacturers mix into plastics at levels of 30-60% by weight to transform hard, brittle materials into soft, pliable products you use every day.
The plasticizer works by embedding itself between polymer chains, creating space that allows them to slide past each other more easily. This molecular-level change is what gives your car’s dashboard its soft touch or allows electrical cables to bend without cracking.
Chemical Identity and Molecular Structure
DPHP stands for Di(2-propylheptyl) phthalate, also known as bis(2-propylheptyl) benzene-1,2-dicarboxylate. Its molecular formula is C₂₈H₄₆O₄, with a molecular weight of 446.68 g/mol.
The structure consists of a central phthalate core (a benzene ring with two ester groups) connected to two identical branched 2-propylheptyl chains. These branched C₁₀ alcohol chains make DPHP a high molecular weight phthalate, essentially a specific isomer of diisodecyl phthalate (DIDP).
Physical and Chemical Properties
DPHP appears as a clear, colorless oily liquid at room temperature with an extremely faint odor. Here are its key properties:
| Property | Value |
|---|---|
| Chemical formula | C₂₈H₄₆O₄ |
| Molecular weight | 446.7 g/mol |
| Appearance (20°C) | Clear, oily liquid with faint odor |
| Density (20°C) | 0.960–0.968 g/cm³ |
| Melting point | –48°C |
| Boiling point | 254°C (at reduced pressure) |
| Vapor pressure (20°C) | 3.7×10⁻⁹ kPa (extremely low) |
| Water solubility (20°C) | 0.0002 mg/L (practically insoluble) |
| Log Kow | >6 (very hydrophobic) |
| Flash point | 238°C (closed cup) |
| Viscosity (20°C) | 120-130 mPas |
Manufacturing Process of DPHP Plasticizer
The production of DPHP follows a straightforward chemical process with several key steps:
- Raw material preparation: Manufacturers start with two main ingredients – phthalic anhydride (derived from oxidizing o-xylene) and 2-propylheptanol (a branched C₁₀ alcohol produced via oxo synthesis from C₇ olefins).
- Esterification reaction: Two moles of 2-propylheptanol react with one mole of phthalic anhydride in a closed reactor system with an acid catalyst like para-toluenesulfonic acid.
- Water removal: The reaction produces DPHP and water as a byproduct. Manufacturers continuously remove water under reflux conditions to drive the reaction to completion.
- Purification: The crude DPHP undergoes vacuum distillation to remove unreacted alcohol and impurities, achieving purity levels of 99% or higher.
- Recovery and recycling: Any unreacted 2-propylheptanol gets recovered and recycled back into the process, minimizing waste.
- Stabilization: Producers add stabilizers like 0.3-0.5% bisphenol A or 0.1% Topanol CA (a hindered phenolic antioxidant) to prevent discoloration and oxidation during storage.
- Quality control: The final product undergoes testing to ensure it meets specifications – clear appearance, less than 0.1% moisture content, and minimal trace impurities.
Applications of DPHP Plasticizer
DPHP serves as a versatile plasticizer across numerous industries, with typical loading levels of 30-60% by weight in PVC compounds:
- Wire and cable insulation: DPHP provides the flexibility and heat resistance needed for electrical cables that meet UL and VDE standards up to 80°C service temperature.
- Automotive interiors: Car manufacturers use DPHP in dashboards, door panels, and synthetic leather seats because it reduces windshield fogging and doesn’t produce that “new car smell” from off-gassing.
- Building materials: You’ll find DPHP in vinyl flooring, wall coverings, roofing membranes, cable ducts, and weather seals where durability and UV resistance matter.
- Outdoor products: Tarpaulins, awnings, billboards, and coated fabrics rely on DPHP’s excellent weathering resistance to maintain flexibility in sun, rain, and temperature extremes.
- Food contact applications: The FDA has approved DPHP for food packaging uses like jar lid gaskets, conveyor belts, and food-handling gloves.
- Consumer goods: Footwear soles, luggage, sporting equipment, and synthetic leather goods use DPHP where flexibility meets durability requirements.
- Adhesives and sealants: DPHP improves the workability and flexibility of PVC-based caulks, sealants, and certain rubber formulations.
Is DPHP Plasticizer Toxic
DPHP has a significantly safer toxicological profile compared to older phthalates like DEHP, which is why regulators haven’t restricted its use. The oral LD₅₀ in rats exceeds 5,000 mg/kg, classifying it as practically non-toxic by ingestion.
Unlike DEHP, which is classified as a reproductive toxicant and endocrine disruptor, DPHP shows no evidence of reproductive or developmental toxicity at typical exposure levels. Studies using doses up to 1,000 mg/kg/day found only minor effects like slight decreases in body weight gain and minimal liver changes at these extremely high doses.
The key safety advantages of DPHP include no classification as carcinogenic, mutagenic, or toxic to reproduction under GHS standards. It doesn’t require the H360 warning labels that DEHP, DBP, and BBP carry in Europe.
Comparison with Other Common Plasticizers (DEHP, DINP, DOTP)
| Characteristic | DEHP | DINP | DPHP | DOTP |
|---|---|---|---|---|
| Chemical Type | C₈ ortho-phthalate | C₉ ortho-phthalate | C₁₀ ortho-phthalate | C₈ terephthalate (non-ortho) |
| Molecular Weight | 390.6 g/mol | ~419 g/mol | 446.7 g/mol | 390.4 g/mol |
| Volatility | Higher (6×10⁻⁵ Pa) | Low (1×10⁻⁶ Pa) | Very low (3.7×10⁻⁶ Pa) | Low (similar to DINP) |
| Plasticizing Efficiency | High efficiency but migrates easily | Slightly less efficient than DEHP | Comparable to DINP/DEHP | Similar to DEHP |
| Best Applications | Indoor controlled use only | Toys, cables, flooring | Automotive, outdoor, high-heat | Medical, toys, food wrap |
| Health Classification | Reproductive toxicant 1B, endocrine disruptor | Not classified as CMR, lower toxicity | No CMR classification, low toxicity | Non-phthalate, very safe profile |
| Regulatory Status | Heavily restricted, SVHC in EU, banned in toys | Banned in mouthable toys only | No restrictions, FDA approved | No restrictions anywhere |
| Relative Cost | Lower | Moderate | Slightly higher than DINP | Moderate to higher |
| Temperature Stability | Good | Better than DEHP | Excellent | Good with better low-temp flex |
FAQs
Is DPHP biodegradable?
Yes, DPHP undergoes biodegradation through microbial ester bond hydrolysis, breaking down into CO₂ and water under aerobic conditions, though more slowly than shorter-chain phthalates.
Is DPHP restricted in any countries?
As of 2025, DPHP faces no specific restrictions globally and isn’t on regulatory concern lists like the EU SVHC or California Prop 65.
Can DPHP replace DEHP directly in formulations?
Yes, DPHP typically works as a 1:1 drop-in replacement for DEHP in most PVC formulations without significant reformulation needed.