Moisture-Resilient and Temperature-Insensitive Graphene-Coated Thread-Based Strain Sensor With Waterborne Polyurethane Encapsulation

Recent advancements in graphene-coated flexible strain sensors have sparked significant interest due to their potential in wearable electronics. However, maintaining the robustness of these sensors is challenging, as graphene is highly sensitive to changes in temperature and humidity, and it disperses poorly in organic solvents. To address these issues, we have formulated a new recipe using waterborne polyurethane (WPU) as the primary solvent and encapsulating agent. This approach establishes strong hydrogen bonds between WPU and graphene, leading to uniform dispersion and isolating strain responses from environmental interferences, such as moisture and temperature fluctuations. Consequently, the stability and functionality of graphene-based strain sensors are significantly improved. Our sensor demonstrates outstanding linearity in strain sensing, with a gauge factor of 23.42 in the range from 0% to 20% and 110.31 from 20% to 28%. It maintains a consistent piezoresistive output within moisture levels from 50% to 95% relative humidity and performs robustly without failure at temperatures from 25 to 125 °C, with changes remaining below 1%. These findings enhance the reliability of sensor responses, particularly in outdoor environments.