Development, improvement, and application of new eco-sustainable friction materials: from laboratory development to the finished green product

The disc brake is an essential safety system in vehicles. The main component is the pad friction material, which consists of a mixture of 15-20 components bonded by an in-situ polymerised binder. Each component imparts specific properties that ensure adequate friction and wear performance under different braking conditions. According to their function, the components are classified into binders, reinforcements, abrasives, solid lubricants and functionalised fillers. The PhD project was carried out in collaboration with ITT Italia S.r.l., a leading company in the production of brake pads, to optimise the production process to reduce the energy costs related to the baking of the pads. The current process is energy-consuming as it involves two heat treatments: the first in a press at about 150°C for 3-10 minutes to pre-form the pad and start the cross-linking of the resin; the second in an oven at about 210°C for 150 minutes to complete polymerisation and guarantee the required mechanical performance. The PhD project was carried out in two phases. In the first, the main chemical-physical properties of certain friction material components (such as solid lubricants, fillers and binders) were analysed using spectroscopic and diffractometric techniques. In the second step, the polymerisation process of phenolic resins, which is responsible for the formation of the three-dimensional polymer network that binds the other components, was studied. This process was analysed using thermal (DSC and rheology) and spectroscopic (FT-ATR) techniques, obtaining information on the kinetic parameters and the evolution of the cross-linking reaction. Finally, it was possible to reduce the curing time from 150 to 30 minutes without compromising the performance of the tablets for some of the resins analysed. This result, which appears to be of great technological interest, will lead ITT to improve the production process.