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Humidity Sensors on Flexible Substrate
Published in Ghenadii Korotcenkov, Handbook of Humidity Measurement, 2019
A brief analysis showed that no polymer meets all requirements. Right now, the most suitable for the widest number of applications appears to be polyethylene terephthalate (PET), offering curing advantages, or polyethylene naphthalate (PEN), offering thermal and dimensional stability. However, the experiments and results presented in Table 22.2 show that polyimide (PI) offers more options in terms of processing, as long as transparency isn’t necessary. For example, Briand et al. (2006) have shown that PI-based flexible micro-hotplates on PI sheets and on silicon for gas-sensing and thermal actuating applications can be realized. Moreover, platinum and aluminium microheating elements on PI exhibited promising characteristics for their integration in the low-power gas sensors and thermal actuators. In particular, a high operating temperature (up to 400°C–500°C) was obtained at a relatively low-power (100–150 mW), and the thermal stability of the structure allowed the annealing of a metal–oxide film to realize metal–oxide gas sensors. Compared to micro-hotplates on silicon with their membranes made of dielectric layers, the fabrication of micro-hotplates with PI-based membranes brings the advantages of simplified processing and an improved robustness and flexibility. Meanwhile, Briand et al. (2011) believe that PI will only be used for applications with specific requirements regarding temperature and the robustness of the substrate: Most devices will be produced on PET and PEN substrates.
Medical textiles
Published in Textile Progress, 2020
PET for medical applications involving implanting needs to be improved compared with the commodity product suitable for apparel, particularly in regard to it needing to possess high tenacity, high modulus and low elongation [131]. Whilst PET can show enhanced properties when higher molecular weight polymer is used to improve strength and the extruded filaments are subjected to hot drawing treatments similar to those used in the production of tyre cord to fully orient the polymer, there is a higher-performance polyester, polyethylene naphthalate (PEN) coming into use. Although PEN is more expensive, it is inherently stiffer and shows better thermal performance and barrier properties to chemical agents than PET [132].