Aging resistant TiO2/silicone rubber composites

Significance 

Recent research has proven that the in-service aging of silicone rubber (SIR) sheds and sealants of non-ceramic insulators (NCI), which are widely used in high voltage transmission lines, can result from various environmental and electrical factors. In particular, salt, UV, acid, leakage currents and corona discharge – among other factors – can degrade NCIs. Such insulators are mainly built from polydimethylsiloxane (PDMS): a silicon-based polymer with hydrophobic methyl groups. At present, the existing plethora of literature has highlighted that polymer aging results in alterations of the room temperature vulcanized (RTV) SIR surface hydrophobicity. Consequently, catastrophic mechanical and electrical failures of the transmission lines employing NCIs can occur in service. Even worse, in coastal environments, salt accelerates the deterioration of SIRs in NCIs by decreasing their hydrophobicity. Therefore, it is imperative that the resistance of the SIRs to extreme environmental aging be improved so as to avert catastrophic failures of NCIs and minimize maintenance costs.

To this effect, University of Denver scientists: Dr. Monika Bleszynski and Professor Maciej Kumosa from the NSF I/UCRCenter for Novel High Voltage/Temperature Materials and Structures (HVT Center) demonstrated a new and highly transformative approach to improve the resistance of SIRs to extreme environmental aging by embedding titanium dioxide micro-particles. In particular, they addressed the ultra-aggressive aging environments, such as hypochlorous acid or electrolyzed aqueous salts, among which the aforementioned rubbers insulating systems may be exposed to. Their work is currently published in the research journal, Composites Science and Technology.

In brief, the research method employed entailed conducting molecular dynamics simulations so as to determine the combined effects of a titanium dioxide and different concentrations of hydrophobic PDMS methyl groups on surface hydrophobicity of a titanium dioxide/RTV composite. Next, they predicted the effects of both titanium dioxide and silica on the diffusivities of low voltage aqueous salt components in the PDMS and related them to unique interfacial interactions between the particles and the methyl groups of the PDMS. Lastly, titanium dioxide/RTV SIR was subjected independently to hypochlorous acid and electrolyzed low voltage aqueous salt.

The authors observed that the rutile titanium dioxide reoriented methyl groups away from the particles reducing the diffusivities of water and hypochlorous acid. This effect was seen to shield the PDMS network against environmental chain scissions. Conversely, silica was seen to attract the groups and thereby accelerating acid and water migrations and thus enhancing damage to the network. All in all, the titanium dioxide micro-particles were observed to greatly increase the contact angle, reduce the surface energy and most importantly, improve the hydrophobicity of the composite.

In summary, the Bleszynski-Kumosa study demonstrated the application of titanium dioxide microparticles to enhance the hydrophobicity of RTV SIRs. Specifically, the titanium dioxide was noted to have the capability to offset the negative effect of the reduced concentrations of methyl groups thereby improving the hydrophobicity of the titanium dioxide/RTV composite as a whole. Altogether, using this technique, aging of the rubber was effectively reduced by about 50% in highly oxidative environments.

Aging resistant TiO2/silicone rubber composites - Advances in Engineering
Fig. 1. a-b. PDMS and TiO2 surface; a) (top) before and b) (bottom) after molecular dynamics interfacial close contacts modeling
Aging resistant TiO2/silicone rubber composites - Advances in Engineering
Fig. 2. a-c. SEM cross sections of a RTV-1 (a) virgin, (b) subjected to 0.046% HOCl for five weeks at RT, (c) with 3% embedded TiO2 subjected to 0.046% HOCl for five weeks at room temperature

About the author

Dr. Monika Bleszynski is a Research Scientist and DU Program Director of the National Science Foundation Industry/University Cooperative Research Center for Novel High Voltage/Temperature Materials and Structures (HVT Center) at the University of Denver (DU). She holds a bachelor’s degree in Biology from Saint Louis University, and obtained her PhD in Materials Science at DU in 2018 which focused on extreme aging of polymeric materials and computational modeling.

Her research interests include biomimetic engineering, environmental aging of polymers and polymer composites, and developing molecular dynamics simulations to create novel materials for extreme applications.

About the author

Dr. Maciej S. Kumosa received his Masters and Ph.D. degrees in Applied Mechanics and Materials Science in 1978 and 1982 from the Technical University of Wroclaw in Poland. Between 1984 and 1990, he was a Senior Research Associate at the University of Cambridge in the UK. He is currently a John Evans Professor of Mechanical Engineering at DU and the Director of the National Science Foundation Industry/University Cooperative Research Center for Novel High Voltage/Temperature Materials and Structures .

Dr. Kumosa’s research interests include the experimental and numerical multiscale analysis of advanced materials for electrical, aerospace and other applications subjected to extreme in-service conditions. Dr. Kumosa has completed more than 250 publications in numerous composites, materials science, applied physics, applied mechanics, general science and IEEE international journals (120) conference proceedings (70), and national research reports (60). He also graduated 19 PhD and 19 MS students. Dr. Kumosa is on the Editorial Board of the Journal of Composites Science and Technology.

Reference

Monika Bleszynski, Maciej Kumosa. Aging resistant TiO2/silicone rubber composites. Composites Science and Technology, volume 164 (2018) page 74–81.

Go To Composites Science and Technology

Check Also

Featured Video Play Icon

Atomistic simulation of the formation and fracture of oxide bifilms in cast aluminum