Effect of Zeolite Morphology and Loading on Local Segmental Dynamics and Crystallisation Behaviour of PDMS-Zeolite Composites

The tiny movements of parts of the polymer chains in polydimethylsiloxane (PDMS) affect how the material behaves. When zeolite particles are added, they change these movements. This change is important because it affects the overall performance of the final composite material, which can be useful in many industrial applications. The aim of this study was to investigate the influence of the addition of zeolites on the local dynamic behaviour of PDMS chain segments in PDMS-zeolite composites. Three types of zeolites were used: Zeolite A with cubic morphology, Zeolite A with spherical morphology, and Zeolite X, each incorporated into the PDMS matrix at 20, 30, and 40 wt%. Local segmental dynamics was investigated using the powerful electron spin resonance (ESR) - spin probe method, while the thermal behaviour was analysed using differential scanning calorimetry (DSC). ESR results showed that the presence of zeolites increases the isothermal crystallisation rate, which significantly affects the segmental mobility in the amorphous phase below the crystallisation temperature. This effect was found to depend more strongly on zeolite morphology than on filler content. DSC measurements showed no change in glass transition temperature with the addition of zeolite but shifts in cold crystallisation and melting behaviour were observed, indicating changes in crystal structure and its perfection. These results indicate that zeolites act as heterogeneous nucleation agents and that their structural properties critically influence the crystallisation behaviour of PDMS.