Synergistic effect of additives on electrical resistivity, fire and smoke suppression of silicone rubber for high voltage insulation

This paper reports the fire and smoke behaviour along with the DC electrical volume resistivity of silicone rubber filled with alumina trihydrate (ATH), milled glass fibre rods (GFRs) and graphene nanosheets (GNs). Results show that there is a significant de-escalation in the fire and smoke parameters of filled composites. As seen in SRE, adding a small amount (1 wt%) of GNs in PDMS filled with 30 wt%-ATH and 5 wt%-GFRs can remarkably reduce the THR to 38.36 MJ/m2 from 58.83 MJ/m2 in SRA and 47.24 MJ/m2 in SRB. Moreover, TSR is declined to 332.74 m2/m2 in SRE whilst it is measured at 1301.29 m2/m2 and 864.32 m2/m2 in SRA and SRB, respectively. Besides, it is noticed that the inner layer of char residue in filled composites is found significantly rigid and compact which provides a shielding effect against heat transfer. Moreover, DC volume resistivity of silicone rubber is improved with ATH and GFRs additives, but it tends to reduce with GNs. A reduction in volume resistivity is measured about -1.5%, -4.5% and -21% in SRD, SRE and SRF as compared to SRA. SRE is found to be the most promising filled silicone rubber composite with excellent fire retardancy and superb electrical volume resistivity which makes it suitable for electrical insulation applications.