Waste-to-energy: Repurposing flexible polyurethane waste for triboelectric nanogenerator applications

Triboelectric Nanogenerators (TENG) is a promising approach for clean energy harvesting. Light weight, flexible, cheap and environmentally-friendly materials are being explored as potential components in the TENG device in order to increase its efficiency. This paper reports the first effort to successfully utilize rebonded flexible polyurethane (RFPU) waste as a tribopositive material in a TENG device. A batch moulding technique was used to create two different densities (60 and 70 kg/m³) of flexible polyurethane (FPU) scraps, including customer waste and slabstock foam production waste. The current study investigates the effect of density on the compression strengths of the RFPU materials, as well as the impact on the output voltage of the TENG. Additionally, the effect of various RFPU sheet thicknesses (2, 4, 6, and 8 mm) as well as the effect of different applied forces and frequencies on the TENG's output voltage were investigated. The findings showed that the compressive strength increases with higher RFPU density. The output voltage values of the TENG device were recorded both with and without pre-charging. The results, without pre-charging, revealed that the highest output voltage of the TENG was obtained using an RFPU sheet with a density of 60 kg/m³. Furthermore, output voltage was shown to decrease with increasing RFPU sheet thickness and to increase with applied frequency. Pre-charging showed a similar trend, but yielded better results compared to the RFPU samples that were not pre-charged. The power density peaked at 0.085 mW/cm², at a load resistance of 5 MΩ and a force of 4.7 N. The RFPU-based TENG successfully powered four white LEDs connected in series. Analysis of the embodied energy associated with using PU foam waste instead of virgin PU foam was conducted and demonstrated that utilizing PU foam waste provides environmental benefits due to the significant contribution of raw materials to the overall embodied energy in PU foam that is saved when reusing foam waste. Additionally, assessing the embodied energy of the components of the TENG device was also conducted and shows that the generated energy can partially offset the embodied energy of the TENG device. As a result, the prepared RFPU material not only helps to safeguard the environment but also shows great promise for use in developing more efficient and affordable TENGs in the future.