Recent Advances in Self-Powered Piezoelectric and Triboelectric Sensors: From Material and Structure Design to Frontier Applications of Artificial Intelligence.

The development of artificial intelligence and the Internet of things has motivated extensive research on self-powered flexible sensors. The conventional sensor must be powered by a battery device, while innovative self-powered sensors can provide power for the sensing device. Self-powered flexible sensors can have higher mobility, wider distribution, and even wireless operation, while solving the problem of the limited life of the battery so that it can be continuously operated and widely utilized. In recent years, the studies on piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs) have mainly concentrated on self-powered flexible sensors. Self-powered flexible sensors based on PENGs and TENGs have been reported as sensing devices in many application fields, such as human health monitoring, environmental monitoring, wearable devices, electronic skin, human-machine interfaces, robots, and intelligent transportation and cities. This review summarizes the development process of the sensor in terms of material design and structural optimization, as well as introduces its frontier applications in related fields. We also look forward to the development prospects and future of self-powered flexible sensors.

The key role of unique crystalline property in the hydrolytic degradation process of microcrystalline cellulose-reinforced stereo-complexed poly(lactic acid) composites.

Stereo-complexed poly(lactic acid) (SC-PLA) has unique stereo-complexed crystallites (SC) and homogeneous crystallites (HC), but the effect of this special crystalline property on the hydrolytic degradation of SC-PLA has not been researched. In this study, the hygrothermal aging behaviour of injection-molded SC-PLA and SC-PLA/microcrystalline cellulose (MCC) composites at different temperatures (25 °C and 60 °C) was investigated from micro- and macroscopic perspectives. The results demonstrated that the hydrolysis of SC-PLA was sequentially dominated by the amorphous region, the homogeneous crystalline region, the stereo-complexed crystalline region (three stages). The hydrolytic degradation of SC-PLA only completed the first stage after 4 weeks aging at 25 °C, while it was in the third stage after 4 weeks aging at 60 °C. On this basis, the accelerating effect of 10 wt% MCC on the hydrolysis process of SC-PLA at different stages was investigated. It was found that MCC shortened the hydrolysis time in the stereo-complexed crystalline region by reducing the rearrangement of amorphous structure to form SC and causing cracks and interfacial deterioration by water absorption-swelling-degradation. In addition, the thermal properties and impact strength of SC-PLA and SC-PLA/MCC composites decreased dramatically due to rapid hydrolytic degradation at 60 °C. Overall, the results of this study can provide theoretical basis for the application of SC-PLA and SC-PLA/MCC composites in hygrothermal environment.

High-performance degradable films of poly(lactic acid)/thermochromic microcapsule composites with thermochromic and energy storage functions via blown film process.

In this study, the polylactic acid (PLA)/reversible thermochromic microcapsule (TCM) packaging application film was successfully synthesized by the blown film process. White mineral oil (WMO) was used as a dispersant to prepare PLA/TCM extruded materials with different mass fractions, in which the mass fraction of TCM was up to 20 wt% and the structural, thermal, mechanical, barrier, thermochromic, and heat storage-release properties were evaluated. It was found that WMO had a plasticizing effect, the elongation at break and water vapor transmission rate of the films with the addition of 7 wt% TCM were increased by 533 % and 31.38 %, respectively. For each thermochromic film, significant thermochromic and energy storage release phenomena were observed. For instance, 20 wt% TCM thermochromic film was most effective for prolonging the holding time and suspending the temperature drop rate. In general, thermochromic packaging films with optimized constitutes were successfully synthesized by the blown film process, which provides essential reference significance for the large-scale thermochromic film applications.