Abstract
The impact of polypropylene and high-density polyethylene backbone binders on the structure of organic matrix, feedstock, and ceramic parts is investigated in terms of morphology in this paper. The miscibility of wax with polyethylene and polypropylene is investigated in the molten state via a rheological study, revealing wax full miscibility with high-density polyethylene and restricted miscibility with polypropylene. Mercury porosimetry measurements realized after wax extraction allow the characterization of wax dispersion in both neat organic blends and zirconia filled feedstocks. Miscibility differences in the molten state highly impact wax dispersion in backbone polymers after cooling: wax is preferentially located in polyethylene phase, while it is easily segregated from polypropylene phase, leading to the creation of large cracks during solvent debinding. The use of a polyethylene/polypropylene ratio higher than 70/30 hinders wax segregation and favors its homogeneous dispersion in organic binder. As zirconia is added to organic blends containing polyethylene, polypropylene, and wax, the pore size distribution created by wax extraction is shifted towards smaller pores. Above zirconia percolation at 40 vol%, the pore size distribution becomes sharp attesting of wax homogeneous dispersion. As the PP content in the organic binder decreases from 100% to 0%, the pore size distribution is reduced of 30%, leading to higher densification ability. In order to ensure a maximal densification of the final ceramic, polyethylene/polypropylene ratios with a minimum content of 70% of high-density polyethylene should be employed.
Highlights
Backbone binders currently used in Ceramic injection molding (CIM) process are polyolefins (i.e., polypropylene (PP), low-density polyethylene (LDPE), and high-density polyethylene (HDPE)), polyethylene glycol (PEG), polystyrene (PS), ethylene-vinyl acetate (EVA), or poly(methyl methacrylate) (PMMA) [1,2]
This result is consistent with Scanning Electron Microscopy (SEM) observations, where wax seems mainly absorbed by HDPE phase (Figure 8a)
The results showed that the highest HDPE contents lead to the highest sintered density, 6.065, corresponding to 99.7% of the maximal theoretical density of zirconia powder
Summary
Using mercury porosimetry during wick-debinding, theytheir highlighted modification of employed EVA, PP, LDPE, HDPE, and blends asa significant backbone binders in porosity evolution The latter could beas relative to a modification in binderelectron affinity;microscopy the behavior feedstocks containing paraffin wax plasticizer [33]. LDPE/HDPE or PP/HDPE, present the more homogenous mixing,binders leading in to feedstocks the et al employed EVA, PP, LDPE, HDPE, and their structure blends asafter backbone highest densification ability They supposed resulted from synergistic effects of multi-polymer containing paraffin wax as plasticizer [33]. Density, they concluded that feedstocks composed of multiple backbone binders, such as LDPE/HDPE or PP/HDPE, present the more homogenous structure after mixing, leading to the highest densification ability They supposed it resulted from synergistic effects of multi-polymer blends; the behavior of neat polymer binders was not studied. Final ceramic quality is reviewed to deeply understand the link between backbone binder selection, organic matrix morphology, feedstock structure, and final product densification ability
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