An investigation into plasticiser compatibility and the development of novel bio-based plasticisers for Polyvinyl Chloride

Burns, Katharine (2024) An investigation into plasticiser compatibility and the development of novel bio-based plasticisers for Polyvinyl Chloride. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Polyvinyl Chloride (PVC) is the world’s third most commonly used polymer and accounts for 80% of all plasticiser usage worldwide. Plasticisers, such as phthalate esters, are added to PVC to increase flexibility and softness. A number of phthalate esters exhibit toxic and environmentally harmful properties, leading to rapid growth in the development of non-phthalate plasticisers. Compatibility between plasticiser and polymer is crucial for successful formulation of PVC compounds. Compatible plasticisers show permanence in the PVC compound, whereas incompatible plasticisers often exude from the surface. The ASTM D3291 Loop compatibility test is the primary industrial method for testing compatibility, but this relies on a subjective observation of plasticiser exudation which may be unreliable. Analytical techniques were evaluated to develop an improved method for testing plasticiser compatibility. GC-MS analysis was found to be specific and sensitive enough to determine the quantity and composition of plasticiser exudation at levels that were undetectable by the standard method. Quantification of exudation through GC-MS was compared to other methods of testing plasticiser compatibility such as glass transition by TGA, giving minimal correlation between the results. This demonstrates the importance of considering both plasticising ability and permanence in the PVC compound when describing plasticiser compatibility. Epoxidised soybean oil (ESBO) is widely used as a bio-based non-toxic plasticiser for PVC but does not show the same plasticising ability as phthalates and so cannot fully replace these plasticisers. To improve the compatibility of ESBO with PVC, a selection of bio-based molecules were reacted with ESBO by epoxide ring-opening to introduce different functional groups to the plasticiser through ether linkages. Four derivatives of ESBO were prepared and evaluated as bio-based plasticisers for PVC. ESBO functionalised with methoxy-terminated poly(ethylene glycol) (mPEG) showed excellent plasticising ability, with tensile strength increased by 3% and elongation at break by 6.9%, as well as almost 2 °C lower glass transition temperature compared to ESBO. The novel plasticiser mPEG-ESBO offers for the first time a bio-based ESBO derivative which could be used as a true replacement for phthalate plasticisers, giving comparable mechanical performance and compatibility with PVC.