Fracture and thermal aging of resin‐filled silicone elastomers

Abstract

The role of nano-sized resin fillers on the fracture and viscoelastic behavior of silicones was examined in the context of thermal aging. Systems with different resin volume fractions and resin glass transition temperatures were compared. X-ray scattering patterns were collected over a wide range of q-values in order to provide insight into the physical structure of the silicone elastomers. Additionally, tensile, dynamic mechanical, and fracture tests were performed. Temperature shift factors obtained from the dynamic mechanical data were used to obtain master plots of the fracture toughness as a function of reduced crack velocity. The elastic modulus for each of the materials increased as a function of thermal aging time, and the high-temperature fracture behavior for each of the systems was reduced to values characteristic of unfilled systems after 14 days of aging at 200 8C. In order to obtain an accurate representation of the viscoelastic response of the materials in the megahertz frequency regime, quartz crystal resonators were used to measure mass changes and rheological properties after thermal aging. The results are consistent with a simple picture of dynamic heterogeneity, where high toughness requires that regions with different dynamic properties exist within the sample.

Quantitative characterization of alkyd cure kinetics with the quartz crystal microbalance

“…The dynamic mechanical data was collected at a maximum of 10 Hz, while the QCM data was at 15 MHz. A similar difference between dynamic mechanical and QCM moduli and phase angles has previously been observed for systems that were heterogeneous on a nanometer length scale [44].…”

Effects of zinc oxide filler on the curing and mechanical response of alkyd coatings

“…First, the van Gurp-Palmen curves from the DMA measurements at frequencies from 0.1 to 10 Hz overlap with one another in the glassy regime, indicating that these glassy systems share some features that are independent of the filler content. Second, the QCM data obtained at a frequency of 15 MHz are shifted to higher moduli by a factor of about 2 in comparison to the DMA data, reminiscent of the behavior observed in filled silicone systems consisting of nanoscale regions with different dynamic properties [39]. These results are an excellent starting point for further detailed investigations of the mechanics of these systems, ideally including model systems that are more fully understood than the commercial alkyd system used in our experiments.…”

RTV Silicone Rubber Degradation Induced by Temperature Cycling

“…Studies performed by Schneider et al [16] also showed similar results. In their experiments, two commercially-available silicones, namely RTV 615 and Sylgard 184, were exposed to temperature cycles ranging from −40 • C to 150 • C. Higher elastic moduli of aged samples compared with unaged samples was observed, and the crosslinking aging mechanisms leading to tighter polymer networks was emphasized [17]. These results presented in this study may be attributed to the reaction of RTV silicone rubber with moisture in the air, which is controlled by the temperature.…”

“…All of these studies concentrated on the degradation of RTV silicone rubbers at constant temperatures. However, so far few studies have explored the degradation of RTV silicone rubbers under temperature cycling, which has proven to be a major cause of the aging and failure of materials [15][16][17].…”

“…Wu et al [14] reported that the side chain reaction and the crosslinking reaction are the main reactions during the thermal oxidation aging of silicone rubbers in the temperature range from 120 • C to 250 • C. All of these studies concentrated on the degradation of RTV silicone rubbers at constant temperatures. However, so far few studies have explored the degradation of RTV silicone rubbers under temperature cycling, which has proven to be a major cause of the aging and failure of materials [15][16][17].…”