Dioctyl Phthalate (DOP) is a colorless, oily liquid that makes hard plastics flexible and soft. You’ve likely touched products containing DOP today – it’s in everything from shower curtains to electrical cables, working behind the scenes to give plastic products their bendable, durable qualities.
Think of DOP like water added to clay. Just as water transforms brittle clay into something you can shape and mold, DOP transforms rigid plastic into flexible material that won’t crack when you bend it.
Synonyms and Trade Names
DOP goes by several different names in the industry. The most common alternative name is Di(2-ethylhexyl) phthalate, often abbreviated as DEHP.
You might also see it listed as:
- Bis(2-ethylhexyl) phthalate
- BEHP
- Octyl phthalate
- Plasticizer DOP
Common trade names include Palatinol DH, Vestinol AH, and Flexol DOP. Different manufacturers use different brand names, but they’re all referring to the same chemical compound.
Basic Chemical Properties of DOP
Chemical Structure
DOP consists of a phthalic acid core connected to two octyl alcohol chains, giving it the molecular formula C₂₄H₃₈O₄. These long carbon chains act like flexible arms that slip between plastic molecules, pushing them apart and allowing them to slide past each other more easily.
The molecule weighs about 390.6 grams per mole, making it relatively heavy compared to water.
Physical Appearance
DOP appears as a clear, colorless to pale yellow liquid with an oily consistency similar to cooking oil. It has virtually no odor, which makes it ideal for use in consumer products.
The liquid flows easily at room temperature but becomes thicker when cold, much like honey behaves in your refrigerator versus on your countertop.
Volatility and Boiling Point
DOP has an extremely high boiling point of 385°C (725°F), which means it stays put in plastic products rather than evaporating into the air. This low volatility ensures that plasticized products maintain their flexibility for years.
For comparison, water boils at 100°C – DOP needs nearly four times that temperature to turn into vapor.
Solubility
DOP doesn’t mix with water at all – less than 0.01% will dissolve. However, it dissolves readily in organic solvents like alcohol, benzene, and mineral oils.
This property is why DOP-containing plastics can sometimes feel oily after contact with certain chemicals but remain stable when exposed to water.
Melting Point
DOP has a melting point of -50°C (-58°F), meaning it stays liquid even in extremely cold conditions. This ensures that plastic products containing DOP remain flexible in winter weather rather than becoming brittle and cracking.
Stability
DOP remains stable under normal conditions and resists breaking down from heat, light, or oxygen exposure. This chemical stability means products containing DOP maintain their properties for decades without significant degradation.
The compound only breaks down under extreme conditions, such as prolonged exposure to temperatures above 200°C or strong acids and bases.
Common Applications of DOP Plasticizer
DOP serves as a plasticizer in countless everyday products:
- Medical devices – IV bags, blood bags, and medical tubing rely on DOP for flexibility while maintaining sterility
- Construction materials – Vinyl flooring, wall coverings, and roofing membranes use DOP to withstand years of wear
- Electrical products – Wire and cable insulation contains DOP to prevent cracking and maintain flexibility
- Automotive parts – Dashboard covers, door panels, and underbody coatings use DOP for durability
- Footwear – Shoe soles, especially in rain boots and sandals, contain DOP for comfort and flexibility
- Adhesives and sealants – DOP improves spreadability and prevents brittleness over time
What Is the Difference Between DOP and DOTP Plasticizers
The main difference between DOP and DOTP lies in their chemical structure and safety profile. DOTP (Dioctyl Terephthalate) uses terephthalic acid as its base instead of phthalic acid, making it a non-phthalate plasticizer.
DOTP offers similar flexibility and durability to DOP but with significantly lower health concerns. While DOP has been linked to potential endocrine disruption and is restricted in many children’s products, DOTP is considered much safer for human contact.
Performance-wise, DOTP actually outperforms DOP in several areas. It has lower volatility, meaning it stays in the plastic longer, and provides better resistance to high temperatures.
The cost difference is the main drawback – DOTP typically costs 10-20% more than DOP. However, many manufacturers consider this worth it for the improved safety profile, especially for products that come into contact with food or children.
Migration rates also differ significantly. DOP tends to migrate out of plastics more readily than DOTP, which is why older vinyl products sometimes feel sticky or oily – that’s the DOP coming to the surface.
FAQs
Is DOP dangerous to human health?
DOP has been classified as a potential endocrine disruptor and is restricted in children’s toys in many countries. While normal adult exposure is generally considered low-risk, prolonged or high-level exposure may pose health concerns.
Can DOP be replaced in all applications?
Yes, alternatives like DOTP, DINP, and bio-based plasticizers can replace DOP in most applications. The main barriers are cost and the need to reformulate products for optimal performance with new plasticizers.
How can I tell if a product contains DOP?
Check product labels for phthalate-free certification or look for recycling code 3 (PVC), which often contains DOP. Many manufacturers now advertise products as “phthalate-free” if they use alternative plasticizers.
Does DOP break down in the environment?
DOP biodegrades slowly in the environment, taking months to years depending on conditions. Microorganisms can break it down, but it tends to accumulate in sediments and fatty tissues before complete degradation occurs.
How much DOP is typically added to plastic products?
Most flexible PVC products contain 20-40% DOP by weight. The exact amount depends on how soft the final product needs to be – more DOP creates softer, more flexible plastic.
Can DOP leak out of plastic products over time?
Yes, DOP can slowly migrate to the surface of plastics over time, especially when exposed to heat or oils. This process, called plasticizer migration, is why old vinyl sometimes feels sticky or leaves residue.