An Investigation of Dielectric Thermoplastic Elastomers for Civil Infrastructural and Energy Harvesting Applications

Poly(styrene-ethylene/butylene-styrene) [SEBS] and poly(styrene-ethylene/butylene-styrene)-grafted-maleic anhydride [SEBS-g-MA] triblocks have been shown to have superior mechanical performance relative to conventional dielectric elastomers with better morphology. However, historically their use in capacitive energy harvesting, and stress/strain sensing have been constrained by (i) the dearth of knowledge about thermal, mechanical, thermo-mechanical and thermo-electrical properties of elastomers and their nanocomposites, (ii) low dielectric constant of elastomers, and (iii) poor dispersion of high dielectric materials in elastomers.\ud Dielectric filler (barium titanate [BT]) and conductive fillers (carbon black [CB]) based elastomeric composites were successfully manufactured using twin screw extrusion process with/without supercritical fluid carbon-dioxide (scCO2). Thermal, mechanical, morphological, dielectric and conducting properties of dielectric thermoplastic composites (DTC) were studied.\ud Dielectric analysis and dynamic mechanical analysis showed CB composites (below the percolation threshold) manufactured using scCO2 assisted twin screw extrusion were found to have low dielectric loss at low frequency (0.0001 Vs 0.006 dielectric loss at 1Hz for SEBS/CB 1 wt.%), low mechanical losses (0.034 and 0.043 Vs 0.046 and 0.051 value of tan delta in transverse and parallel direction to extrusion respectively at 30 ̊C of SEBS/CB 1 wt %) and improved dielectric permittivity (30% Vs 15% increase upon addition of 1% CB on SEBS) compared to those composites manufactured without scCO2. Similar results were obtained for BT filler based composites. In addition, the composites manufactured with an assistance of scCO2 showed highly conductive behaviour and low mechanical losses at 5 wt. % of CB in SEBS making them sensitive under strain conditions. This result is far superior compared to conventional processing for similar materials. Similarly, chemical, thermal and morphological analysis showed improved interaction and dispersion of both CB and BT in all phases of elastomers when elastomers were extruded with scCO2. Thermoelectric analysis confirms the BT fillers based composites manufactured using scCO2 have highly stable dielectric permittivity over a range of temperatures (40-120 ̊C) and frequencies (1kHz-1MHz) compared to composites manufactured without scCO2. TEM images showed that composites manufactured usingscCO2 have uniformly dispersed additives (CB as well as BT) in elastomers compared to composites manufactured without scCO2.\ud Finally, dielectric measurement of CB and BT composites manufactured with scCO2 presented high sensitivity to uniaxial strain making them highly suitable for stress/strain sensing and energy harvesting application