A new life for silicone waste: Cryo-milling and reuse as soft/elastic filler in silicone formulations for pressure sensors

Several types of silicone rubbers based on different formulations, for specific fields of use, were selected to evaluate their suitability for mechanical recycling, a more economical and ecological option, especially due to the simplicity of the process, low energy consumption and the absence of harmful by-products. The materials were cryo-milled under different regimes, depending on their nature and behavior under such treatment. Subsequently, without any further processing, they were incorporated as soft fillers at concentrations of 10 and 20 wt% into a virgin silicone matrix consisting of a polydimethylsiloxane-α,ω-diol with a number-average molecular weight (Mn) of 36,000 g/mol, without the use of any solvent. The homogenized mixtures were processed into films, which were stabilized by dibutyltin dilaurate-catalyzed condensation crosslinking with tetraethyl orthosilicate. Morphological analysis revealed the presence of large, non-uniform aggregates. While the thermal behavior of the silicone was not affected by these aggregates, a slight decrease in tensile strength and elongation at break was observed. However, the modulus increases, indicating the suitability of these composite materials for applications where thermal stability and rigidity are critical. Compressive mechanical data reveal in certain cases a stable response under repeated loading, while the capacitive behavior under pressure exhibits good linearity, suggesting potential for integration into soft robotics or compression-based medical devices.