Thin compressive layers within a laminar ceramic arrest large cracks (surface and internal) and produce a threshold strength. This phenomenon increases the damage tolerance of ceramics and will allow engineers to design reliable ceramic components for structural applications. The stress intensity factor derived for a crack sandwiched between two compressive layers suggests that the threshold strength is proportional to the residual compressive stress and the thickness of the compressive layer and is inversely proportional to the distance between the compressive layers. Laminates composed of thick alumina layers (605 ± 11 micrometers) and thin mullite/alumina compressive layers (37 ± 1.4 micrometers) fabricated for this study had a threshold strength of 482 ± 20 megapascals, in fair agreement with the theory.

Titanium oxide-based photocatalytic filters were produced by Fused Deposition Modelling (FDM) using biopolymers obtained from renewable biomass resources. The thermoplastic route allows shaping composites through the immobilization of photoactive TiO₂ nanoparticles in an environmentally friendly bioplastic such as the polylactic acid (PLA). Composites with an inorganic charge of 30 wt% of TiO₂ nanoparticles (NPs) exhibit a 100% methyl orange (MO) degradation after 24 h of light exposition due to the extremely uniform dispersion of the nanophase within the polymer matrix in the FDM feedstock. Surface modification of TiO₂ NPs allows the optimization of the colloidal dispersion and stabilization of the inorganic charge in a PLA solution and hence, the optimal distribution of nano-photoactive points in the TiO₂/PLA filaments and scaffolds. The proposed new route of processing improves the dispersion of nano-charges comparing with the traditional thermo-pressing routes used for mixing thermoplastics based composites, avoiding the thermal degradation of the polymer and providing a customised product. In this manuscript the evolution of photodegradation with the increase of TiO₂ content in the composite and the variation of the filter geometry was evaluated.