• We are experiencing a pungent foul smell in the polypropylene product pellets. The source of the same has remained untraceable having attempted various changes in the process, as required. Can someone please share a similar experience and the possible troubleshooting options?



  • Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br

    The literature presents some case studies related to this issue in plastics production, especially when recycled material is applied in the production process. In this case, the smell is attributed to VOCs (Volatile Organic Compounds) which are generated by the degradation of high molecular substances that were absorbed to the plastics during the use and these molecules that potentially cause odours are not removed during the wash step. For recycled plastics an alternative to minimize this issue is to include a degassing and filtration steps in order to avoid the odour production.

    Generally, the plastics production even without recycled materials can face the odour issue in the granulation step which is normally associated with three factors:

    1 - Decomposition of small molecules
    2 - Use of miscellaneous materials
    3 - Degradation of the material due to the multiple processing

    The literature quotes that it's possible to deal with odour issues through the use of gas adsorbent and antibacterial agents in the plastics aiming to reduce the as well as exhaust system to eliminate residual odours from bacterial agents.
    Another critical factor to control the odour in the granulated plastic is the quality of the applied resin, poor quality resins have higher concentration of residual monomer which will lead to odours in the final polymer.

    The other strategies to control the odour in the plastics is the use of adsorbent like zeolite material, use of an antibacterial agent, a desorption agent like activated carbon or simply add a fragrance to reduce the impact of the unpleasant odours.