Upcycling Waste Toothpaste Packaging into a Flexible Triboelectric Sensor for Motion Recognition and Human–Machine Interaction

The multilayer composite structure of waste toothpaste packaging hinders its effective recovery through conventional sorting and recycling processes. In this study, a flexible single-electrode triboelectric sensor based on waste toothpaste tubes (WTT sensor) was fabricated by functionally repurposing and integrating different components of toothpaste packaging waste. The aluminum–plastic composite film and aluminum foil recovered from discarded toothpaste tubes constituted the core triboelectric functional unit, with the aluminum foil also serving as the conductive electrode, while cardboard from the outer toothpaste box was used to construct an elastic spacer. At an excitation frequency of 1 Hz, increasing the applied force from 10 to 300 N raised the open-circuit voltage from approximately 15 to 40 V and the short-circuit current from approximately 0.1 to 0.3 μA. The output voltage exhibited a piecewise linear relationship with the applied force, with sensitivities of 0.391 VN−1 below 50 N and 0.024 VN−1 above 50 N. The output signal remained relatively stable over 1000 consecutive contact–separation cycles. The WTT sensor was attached to the heel region of an athletic shoe to acquire distinct electrical signals corresponding to five types of human motion: tiptoe standing, jumping, squatting, walking, and running. Subsequently, 15 features encompassing time-domain, peak-related, and frequency-domain characteristics were extracted and used in conjunction with an optimized ExtraTrees model for motion pattern recognition. To minimize the risk of data leakage, Complete motion recordings were first assigned exclusively to either the training or test set at a ratio of 7:3; all action samples segmented from a given recording were kept in the same subset to avoid data leakage. The optimized model achieved an overall classification accuracy of 96.18% on the independent test set. In addition, the WTT sensor was used as a self-powered input unit to wirelessly control multiple movements of a remote-controlled car. This work provides a simple and feasible upcycling strategy for converting difficult-to-recycle toothpaste packaging waste into value-added flexible smart sensing devices.