Two-step debinding and co-extrusion of ceramic-filled PEBA and EVA blends

Abstract

The objective of this study is to investigate the choice of thermoplastic binders in a two-step debinding process involving solvent extraction (SE) and thermal debinding (TD) of samples produced using polymer (co-)extrusion. Two-step debinding uses a binder system combining soluble binders and thermoplastic binders, which are removed by SE and TD, respectively. In prior work, it was demonstrated that the two-step protocol eliminates debinding defects that are commonly observed in TD (Sharmin and Schoegl, 2014 [1]). The primary goal of this follow-up study is to establish that two-step debinding eliminates debinding defects irrespective of the choice of thermoplastic binders; a secondary goal is to investigate how the binder choice affects the co-extrusion process. In total, five batches using alumina powder and a binder system with a 1:1 ratio of thermoplastic binder and polyethylene glycol (PEG) as water soluble binder were tested. Three grades of polyethylene butyl acrylate (PEBA) and two grades of polyethylene vinyl acetate (EVA) with different melt flow indices were investigated. In all cases, extraction tests resulted in 80wt% removal of the original PEG content. However, PEBA samples showed a significantly faster PEG removal compared to EVA samples, which is attributed to a better dispersion of PEG within EVA. Tests with 4h extracted PEBA and 6h extracted EVA samples resulted in 60wt% removal of PEG and a defect-free specimen after TD and sintering. Also, microstructures of sintered PEBA and EVA samples are comparable, which confirms that the choice of thermoplastic binders has no effect on the two-step debinding process. Co-extrusion tests were performed for selected EVA and PEBA blends, where results showed better performance for co-extrusion of EVA blends.