Analysis of Phthalate Ester Content in PVC Plastics by means of FT-Raman Spectroscopy

Polyvinyl chloride, PVC or [CH2-CHCl]n , is a common polymer used extensively for a wide range of industrial and household products. To achieve the proper material characteristics (e.g. softness, ductility), plasticizers such as phthalates are usually added to the otherwise hard and brittle PVC, sometimes in very large (10-60 w%) concentrations.

Phthalates are not chemically bonded to the PVC and will with time escape by evaporation or by extraction when in contact with liquids. There is serious concern that fat-soluble phthalates such as di(2-ethylhexyl) phthalate, or DEPH, in e.g. vinyl food film, medical devices and toys may harm the e.g. reproductive organs of exposed infants.

PVC is readily distinguished from other common polymers (e.g. polyethylene, polypropylene, polystyrene) by the use of Raman spectroscopy. By far the most commonly used phthalate plasticizer in PVC is di(2-ethylhexyl) phthalate, DEHP (also referred to as dioctyl phthalate - DOP) and many products containing this phthalate are in common use.

We measured the Raman spectra of 21 different phthalate esters and found six common Raman bands, present for all. These bands are accordingly assigned to the dicarbonyl ortho-phenyl group, and as the relative intensities of the six bands vary only slightly from one phthalate ester to the next one we have obtained an identifiable, characteristic fingerprint of the phthalate ester group as a whole.

By use of the set of six bands, which are common to all the measured Raman spectra, we thus foresee an easy way to identify the presence of phthalates in a range of different products.