Effect of the platinum catalyst content on the tracking and erosion resistance of addition-cure liquid silicone rubber

An addition-cure liquid silicone rubber (ALSR) with ureido-containing MQ silicone resin (U-MTQ) was prepared by hydrosilylation with platinum catalyst (Pt). ALSR samples were characterized by thermogravimetric analysis (TGA) and thermogravimetry coupled with infrared spectroscopy (TG-FTIR), and the char layers of ALSR samples after inclined plate tracking and erosion test (IPT) were characterized by X-ray photoelectron spectroscopy (XPS). The effects of Pt content (5-100 ppm) on the curing characteristics, mechanical properties and tracking and erosion resistance of ALSR were investigated. It was found that the cure rate increased with increase of Pt content. When the Pt content was 10 ppm or 15 ppm, the ALSR had excellent tracking and erosion resistance, all specimens could pass the 4.5 kV level in IPT, and the erosion rate was only 0.13% and 0.15%, respectively. ALSR samples possessed optimum mechanical properties and thermal stability when the Pt content was 15 ppm. TG-FTIR results showed that ALSR generated less carbonyl compounds (CH2O) and cyclic oligomers but more methane (CH4) when the Pt content was 15 ppm. This demonstrated that there were lower levels of the oxidation of methyl groups and the main chain unzipping degradation of ALSR, and more homolysis of Si-CH3 during the degradation. The XPS results also showed that the macromolecular radicals would further cross-link to form a firm Si-C ceramic barrier to protect ALSR samples under Pt catalysis and high temperature, thus the tracking and erosion resistance of ALSR could be improved.