What Are Phthalate Esters?

American Chemistry Council
Phthalate Esters Panel

Phthalate esters are liquid plasticizers -- similar in appearence to vegetable oils -- added to a hard plastic called polyvinyl chloride (PVC or vinyl). The liquid phthalate esters act as softeners causing the plastic to become flexible. For example, rigid PVC with no plasticizer could be a pipe under a sink or the vinyl siding on a house. When plasticizers are added, a wide range of flexible vinyl products can be created such as toys, flooring, wire and cable sheathing and shower curtains. Vinyl is actually the second most popular plastic in the world as a result of its durability, low cost and versatility.

Making The Difference

Flexible vinyl is different from other plastics due to its fabrication process. Other plastics are single grade materials which don't vary appreciably in flexibility, hardness or other properties. The plastic as supplied to the processor can be molded or shaped, but the material's characteristics cannot be changed. In contrast, vinyl may start as a rigid plastic, but adding phthalate esters during product manufacture will actually soften the material. This process can achieve a desired level of flexibility or softness.

Quite simply, phthalate esters are unique products that can transform rigid plastic into soft and pliable plastic. As a result, the compounds provide incredible versatility.

How Plasticizers Do Their Job

PVC consists of long chain polymers with large (high molecular weight) strands of molecules. Plasticizers, such as phthalate esters, are liquids. The processing conditions -- involving heat and sometimes pressure -- force the polymers and the liquids together. In the new state, the liquid acts as an internal lubricant and allows the polymer chains to move relative to each other, i.e., provides flexibility. This material then can be molded or shaped into a variety of useful products.

Because of their extensive use in a variety of applications, phthalate esters have been subjected to extensive health and safety scrutiny. In fact, these are among the most studied and best understood compounds from a health and environmental viewpoint. No other class of plasticizer has ever been subject to toxicity and safety testing to the same degree. Phthalates have been used for over 40 years in flexible vinyl products without any evidence of adverse human health effects.

Phthalate esters provide an excellent combination of performance and safety and are used more widely than any other known class of plasticizers.