EPDM-based thermoplastic vulcanisates: crosslinking chemistry and dynamic vulcanisation along the extruder axis
Martin van Duin, DSM Research, The Netherlands
This paper will consist of two parts: 1) A general overview on TPVs will be given, dealing with positioning of TPVs as thermoplastic elastomers, commercial production and suppliers, composition, morphology, properties and applications. The relationships between composition/morphology/properties/applications will be explained. 2) Results of recent experimental studies will be presented. The chemical mechanism of resol crosslinking of EPDM has been elucidated using low-molecular-weight model studies and via 13C NMR of resol-crosslinked 13C-labeled EPDM. The proposed cationic mechanism explains the reactivity of different EPDM grades. Increasing the number of substituents on the residual EPDM unsaturation results in enhanced reactivtiy for resol crosslinking. The dynamic vulcanisation process of EPDM/HDPE blends has been studied by taking samples along the extruder axis and determining the morphology and degree of crosslinking. Crosslinking of the elastomer phase already starts before melting of the thermoplastic phase. Upon melting the morphology is more or less immediately established, while crosslinking of the elastomer phase continues. For a 50/50 blend phase inversion from an EPDM matrix via a co-continuous EPDM phase to an EPDM dispersion is observed. Finally, the melt and solid state properties of the resulting TPVs will be correlated with the morphology and composition.