PEDOT:PSS Films for Paper-Based Humidity and Moisture Sensing in Fiber-Reinforced Polymers

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a flexible, organic polymer with high humidity sensitivity. Printed on paper substrates, the resin of fiber-laminate structures can completely penetrate the substrate. This allows the sensors to be embedded into fiber laminates without weakening the composite or generating an acoustic impedance mismatch. Here, we show that based on a frame-casting approach, well-defined, residue-free PEDOT:PSS layers can be realized on paper that show high sensitivity toward relative humidity and material moisture. An increase in resistance by 480% is reached when increasing relative humidity at room temperature from 20% to 80% on relatively small areas (12 mm2). The low-cost printing process achieved a good sensitivity, comparable to other resistive humidity sensors. Most importantly, we show that our organic sensors can withstand the embedding process at high pressures and elevated temperatures of 140 °C without noticeable degradation. This allows for a continuous monitoring of the structural health of fiber-based materials, which is a key enabler in establishing them as an ecofriendly alternative to concrete, providing a pathway toward carbon-neutral construction. This sensor technology enables the detection of water penetration into natural fiber-based construction materials at an early stage, enabling close monitoring of structural elements to avoid any risk due to weakening of the material by increased water content.