Effects of different thermoplastic binders on the processability of feedstocks for ceramic co-extrusion process

The co-extrusion process involves the simultaneous extrusion of multiple materials, such as ceramic–thermoplastic feedstocks that can be used to manufacture fine-scaled piezocomposites, for both structural and functional applications. The primary step in the development of the feedstocks is the selection of the optimal thermoplastic binder with the function of providing plasticity as well as proper rheological behavior to the ceramic material during processing. The objective of the present work was to investigate the effects of different commercially available thermoplastic binders (polystyrene, low-density polyethylene, poly(ethylene-co-ethyl acrylate) and a blend of poly(ethylene-co-ethyl acrylate) and poly(isobutyl methacrylate)) on the processability of highly loaded lead zirconate titanate (PZT) feedstocks, suitable for the co-extrusion process. After characterizing the thermal behavior of the binders by means of TG and DSC analyses, the flow behavior of the unfilled polymers was analyzed and compared with the corresponding PZT-filled mixture (58 vol.% PZT) applying torque rheometry. Using an Arrhenius relation, the temperature dependency of viscosity was determined and the energy of activation for the viscous flow calculated. Due to the fact that the polyethylene presented a low viscosity with a high solid loading, no indication of degradation, a strong polymer–particle interaction as well as a comparatively low die swell, this thermoplastic binder was used in the formulation of PZT feedstocks to successfully produce thin solid (240 μm diameter) and hollow (800 μm diameter) PZT fibers by the co-extrusion technique.