Odors from synthetic material, including soft plastics and vinyl, rubber, polyester, rayon, and nylon can produce unpleasant odors and may also contain chemicals harmful to people. Solvents and other plasticizers may continue to outgas long after the plastic object has been formed. Often chemicals such as toluene, benzene, 1,1,1-trichloroethane, chloroform, styrene, formaldehyde, phenol, and alcohols are given off.

Here’s a technical paper that odor causing chemicals can now be quickly identified and remediation steps taken to improve the quality of plastic materials.