Effect of TiO2 on Microstructure and Mechanical Properties of Nacre-Mimetic Al2O3 - PMMA Composite

Abstract

The brick-and-mortar structure of abalone nacre imparts exceptional durability, compressive strength and superior fracture toughness, serving as inspiration for the fabrication of lightweight, robust structural materials with superior mechanical properties. Replicating the intricate microstructural arrangement of nacre in bulk has been a fabrication challenge. Our study presents a scalable, bottom-up approach to fabricate a natural nacre-like Al2O3 platelets-PMMA (Polymethylmethacrylate) composite. The inorganic phase of nacre is mimicked by using α-alumina platelets via forced sedimentation process. To achieve dense ceramic phase (i.e. bricks), TiO2 as a sintering aid was incorporated at varying concentrations of 0 to 6 wt% of alumina content, and subsequently sintered at 1350°C/4 hr to achieve optimal densification. The maximum ceramic fraction of 75% was achieved with 4wt% of TiO2. The sintered ceramic compacts were infiltrated with PMMA, polymerized via in-situ polymerization using 1wt% AIBN (Azobisisobutyronitrile), to achieve the final bioinspired composite having relative density of 98-99%. All compositions (with different TiO2 content) exhibited nacre-like large scale aligned brick-and mortar microstructure. Mechanical characterization involved flexural strength and single edge notched beam (SENB) tests, revealing significant enhancements in the fracture properties with increasing TiO2 content. The nacre-mimetic composite exhibited a flexural strength of 240 MPa and a fracture toughness of 8.4 MPa√m (with 4 wt% TiO₂). This work highlights the potential of the present scalable processing technique to produce high-dense, nacre-inspired composites with enhanced mechanical properties suitable for a wide range of structural applications.