Cold sintering with functionalized polymers for ductile ceramic matrix composites with controllable mechanical performance

Structuring ceramics with polymers in hierarchical morphologies provide mechanisms for substantial toughening. Bi-continuous composites are generated in a single processing step through cold sintering of ceramic and polymer particles, which consolidates the inorganic phase at temperatures compatible with polymer processing. Here, we demonstrate that limited maleation (∼1 %) of polypropylene (PP) provides a chemical handle to alter the interaction between the polymer and inorganic phases that leads to a more homogeneous composite morphology at multiple length scales, as evidenced by X-ray microcomputed tomography (µ-CT) and elemental mapping during electron microscopy for a wide range of composite compositions from from 14.5 vol% to 68.2 vol% polymer. The extensibility of the composite and the ultimate tensile stress (UTS) of the hybrid composites are increased substantially in comparison to unfunctionalized PP at the same composition. Quantitative analysis of µ-CT data identifies an interphase in polymer-ceramic composites where there is significant mixing of inorganic and polymer phases that is associated with the generation of a hierarchical morphology. We find that the impact of the interphase is primarily in the reduction of the thickness of the pure ceramic domain. This domain size is inversely correlated with the UTS with universal behavior irrespective of the functionality of the PP. This observation underscores the pivotal role of functional groups on polymers to enhance composite homogeneity, reduce ceramic domain size, and consequently augment the mechanical response of cold sintered ceramic matrix composites that provides a route to sustainable composite materials.