Eric David’s research while affiliated with École de Technologie Supérieure and other places

This work describes the thermal aging behavior of three industrial elastomeric compounds based on styrene–butadiene rubber (SBR) reinforced with carbon black. Samples were exposed to thermo‐oxidative aging at temperatures ranging from 70 to 120°C for durations between 14 and 365 days. The tensile and hardness tests were performed on the samples to determine changes in their mechanical properties. Upon aging, hardness and 100% modulus increased, while elongation at break decreased for all three samples. The results showed a significant decrease in elongation at break and an increase in hardness and modulus with prolonged aging time and higher temperatures. For instance, the elongation at break of the three types of samples decreased by approximately 50% in less than 90 days at 70°C, whereas at 120°C, this same level of degradation occurred in less than 2 days. These significant changes were correlated with increased brittleness and reduced flexibility of SBR composites. Swelling tests confirmed an increase in crosslink density due to aging. Laser scanning confocal microscopy revealed surface roughness and defects, attributed to oxidation, crosslinking, and the evaporation of low molecular weight components. Lifetime prediction methods, including the Arrhenius equation and time–temperature superposition (TTS), were applied to estimate the service life of the materials. The Ahagon plot was utilized to understand the aging mechanisms, revealing a transition from crosslinking‐dominated degradation to chain scission processes at higher temperatures and longer aging times. Highlights Thermal aging makes SBR compounds more brittle and less flexible over time. The hardness and stiffness of SBR compounds increase with aging temperature and time. Aging increases crosslink density, confirmed by swelling tests. Increased surface roughness and defects due to oxidation and crosslinking. The aging mechanism shifts from crosslinking to chain scission at higher temperatures.

Dielectric performance of post‐consumer recycled HDPE blended with virgin HDPE was investigated to evaluate the possibility of using these materials for the insulation of electrical wires and cables. The presence of organic and inorganic impurities was investigated using thermal and chemical methods (TGA, DSC, and EDX). The characterization of impurities revealed different amount of inorganic impurities in recycled material that was depending on the execution of melt filtration by the recycler to prepare the recycled material. Higher values of both dielectric losses and dielectric constant were observed for post‐consumer recycled PE, with the dielectric loss of recycled material almost 17 times higher than the one of virgin PE at power frequency (60 Hz). The short‐term breakdown strength of post‐consumer recycled HDPE was observed to be slightly lower than that of virgin PE. The experimental result showed that blending the recycled stream with virgin materials was effective in order to enhance dielectric properties of recycled material. In this regards, dielectric losses decreased by almost 50% when 50% of virgin HDPE was added to the recycled material. In addition, breakdown strength was improved when virgin HDPE was added.

This paper investigates the filler barrier effect on suppressing the erosion of silicone rubber composites during the DC dry-band arcing, by supplementing main micro fillers in silicon rubber, i.e. ground silica and micro-sized alumina tri-hydrate, with fumed silica and nano-sized alumina tri-hydrate fillers. A study framework employing simultaneous thermogravimetric-differential thermal analyses, the inclined plane tracking and erosion test and the dry-arc test is employed. Fumed silica in silicone rubber increases the amount of the crosslinked residue and suppresses silicone rubber depolymerization; whereas nano-sized alumina tri-hydrate releasing water of hydration may adversely impact the residue coherence and promote combustion. The viability of the filler barrier effect is synergistically achieved by adding fumed silica to the main ground silica filler, thereby maintaining the residue integrity. The inclined plane-tracking erosion test confirms the importance of the filler barrier effect of fumed silica in supplementing the volume effect of ground silica in the suppression of the DC dry-band arcing. These filler effects appear to mainly govern the erosion resistance, with insignificant effect shown for thermal conductivity under DC. The dry-arc resistance test is shown as a useful method to simulate a stable dry-band arcing and obtain reproducible surface erosion patterns that correlates with the outcomes of the DC inclined plane tracking and erosion test.

This paper investigates the effect of ground and fumed silica fillers on suppressing DC erosion in silicone rubber. Fumed silica and ground silica fillers are incorporated in silicone rubber at different loading levels and comparatively analyzed in this study. Outcomes of the +DC inclined plane tracking erosion test indicate a better erosion performance for the fumed silica filled composite despite having a lower thermal conductivity compared to the ground silica composite. Results of the simultaneous thermogravimetric and thermal differential analyses are correlated with inclined plane tracking erosion test outcomes suggesting that fumed silica suppresses depolymerization and promotes radical based crosslinking in silicone rubber. This finding is evident as higher residue is obtained with the fumed silica filler despite being filled at a significantly lower loading level compared to ground silica. The surface residue morphology obtained, and the roughness determined for the tested samples of the composites in the dry-arc resistance test indicate the formation of a coherent residue with the fumed silica filled composite. Such coherent residue could act as a barrier to shield the unaffected material underneath the damaged surface during dry-band arcing, thereby preventing progressive erosion. The outcomes of this study suggest a significant role for fumed silica promoting more interactions with silicone rubber to suppress DC erosion compared to ground silica fillers.

This study investigates the role of filler interface on suppressing the erosion of room temperature vulcanized silicone rubber composites filled with fumed silica, nano alumina trihydrate and sub-micron hexagonal boron nitride fillers during DC dry-band arcing. Simultaneous thermogravimetric-differential thermal analyses indicate a superior effect for fumed silica in suppressing the depolymerization of silicone rubber and promoting radical based crosslinking. This can be attributed to favorable interactions at the fumed silica-silicone interface tethering the siloxane chains. At low filler loading of alumina trlhydrate, water of hydration has insignificant effects on suppressing depolymerization compared to that influenced by fumed silica's interface at equal filler loading. Similarly, incorporating thermally conductive boron nitride filler in silicone rubber does not show improvement in the depolymerization rate compared to that influenced by fumed silica. These findings correlate with the +DC inclined plane tracking and erosion test outcomes indicating superior erosion performance for the fumed silica filled composite. This accordingly supports the influential role of the filler interface over the water of hydration and thermal conductivity enhancement in suppressing the DC erosion of silicone rubber composites under the test conditions of this study. A statistical boxplot analysis technique is introduced to elucidate the inception of the stable dry-band arc in terms of the change in leakage current randomness during the +DC inclined plane tracking and erosion test. The boxplots reveal a slow inception of the stable dry-band arc with the fumed silica filled composite delaying the erosion of silicone rubber during the test. This finding confirms the influence of the filler interface over composite thermal conductivity in suppressing erosion of silicone rubber under DC dry-band arcing.