Enhancement of fracture toughness of hybrid organic-inorganic polyurethane composites

The mechanical robustness and damage tolerance of a lightweight covalently linked polyurethane-clinoptilolite (PUC) composite comprising polyol, diisocyanate, and naturally occurring aluminosilicate (clinoptilolite) microparticles have been investigated. The PUC composite is shown to possess superior flexural properties (strength and strain capacity) and fracture toughness as compared to ordinary Portland cement (OPC), which is conventionally employed in structural materials. Interestingly, these enhancements in the composite performance were observed despite the higher volume fraction and larger aspect ratio of voids in the PUC composite compared to OPC. Furthermore, microstructural analysis of the fractured surfaces revealed distinct differences between the failure patterns of the PUC composite and OPC; while the composite exhibited intricate flow patterns and irregular fracture surfaces, OPC exhibited particle-like features and secondary cracks. These distinctions in void features and failure patterns, combined with the covalent linkages between the organic and inorganic components in the PUC composite, are proposed to contribute to improvements in its mechanical performance.