A multi-functional ammonia gas and strain sensor with 3D-printed thermoplastic polyurethane-polypyrrole composites

Fabrication methods for 3D soft and flexible gas/strain sensing materials are of great interest in various sensing fields. This study investigated electrically modifying 3D-printed soft thermoplastic polyurethane (TPU) as an ammonia gas/strain sensing material due to its tunable mechanical and stretchable properties and ease of fabrication. 3D-printed soft TPU were electrically modified with polypyrrole (PPy) using a sequential procedure of vapor phase polymerization (VPP). VPP can make two-phase composites with a high degree of homogeneity. PPy polymerized via VPP was distributed into a TPU matrix. Tunable mechanical properties were realized by changing the infill density (porosity) of 3D printed TPU. Moreover, TPU-PPy composites showed excellent electrical strain sensing behavior, stability, and durability during 5000 bending/releasing cycle loading. TPU-PPy composites were further evaluated for selectivity and sensitivity to investigate gas sensing behavior towards other reducing gases such as ammonia, triethylamine, ethanol, and methanol. 3D-printed and electrically modified soft TPU showed great potential as an ammonia gas sensor and as a strain sensing material with high performance.