The aim of this study is to investigate the impact of mechanical recycling on the physical and mechanical properties of recycled polyamide 6 (PA6) and polyamide 66 (PA66) in relation to their microstructures. Both PA6 and PA66 raw materials were reprocessed six times, and the changes in their properties were investigated as a function of recycling number. Until the sixth round of recycling, slight changes in the mechanical properties were detected, except for the percentage of elongation. For the physical properties, the change in both flexural strength and Young’s modulus followed a decreasing trend, while the trend in terms of elongation showed an increase. Microscopic analysis was performed on virgin and recycled specimens, showing that imperfections in the crystalline regions of polyamide 6 increased as the number of cycles increased.

Industrial brake lining materials are composite with complex formulations consisting of multiple constituents. Resulting from the fabrication process, the morphology and distribution of the constituents have significant influences on the future properties and braking performance. In this study, an in-depth analysis ranging from the microscale to the macroscale was performed to assess the relationships between the microstructure, the mechanical properties and the braking performance of an industrial brake lining material formulated for heavy vehicles. It was observed that the manufacturing process had different effects on the morphology and size of constituents and on their distribution in the phenolic binder. The morphologies of large organic particles such as rubber and graphite were affected by the mixing procedure, contrary to those of fibres and mineral particles. A transverse anisotropy consistent with fibre orientation due to cold preforming and hot moulding was observed. The microstructure displayed a strong local heterogeneity right up to the mesoscopic scale at which friction and wear mechanisms typically occur. The mechanical properties were analysed with regard to the heterogeneity of the microstructure to determine the scale at which these properties could be considered to be associated with a homogenised behaviour. The rubbing surface after braking showed that load-bearing localisation depends on the nature, morphology and orientation of constituents but that this heterogeneity can be of interest with regard to the braking ability.

Following the ban of its use in brake linings, asbestos has been replaced by various materials based on industrial feedback and trial and error, but without any real understanding of how it affects contact during braking. As copper too will be prohibited in a few years' time, we set out to study the influence of one of its alloys, namely brass. A simplified brass-containing material was developed for this purpose. This material has an anisotropic microstructure and consequently exhibits anisotropic mechanical behavior and increased thermal diffusivity. It displays good tribological behavior at moderate and high temperatures. A surface analysis shows that the contact area is very effective at trapping third bodies and developing secondary plateaus, which provide good conditions for stabilizing friction to a high degree, even at high temperatures.