The development and popularity of wearable electronics increase demand for wearable energy harvesters that can scavenge energy from environment or human body movements. In this paper, we present a novel yarn as a wearable piezoelectric nanogenerator (PNG) consisting of a layer of electrospun poly(vinylidene fluoride) (PVDF) nanofibers integrated with PVDF film around a silver deposited nylon filament acting as an inner electrode. Electrospun PVDF nanofiber was wrapped around core yarn using a customized electrospinning device followed by coating of PVDF solution. The mesh of PVDF electrospun layer ensured uniform coating of PVDF solution, and the after coated PVDF film improved interfacial properties with inner electrode as well as strengthened the abrasion resistance of the piezoelectric polymer layer. The resultant unique yarn produced an average peak voltage of 0.52 V, peak current of 18.76 nA, and power density of 5.54 μW cm−3 under a cyclic compression of 0.02 MPa at 1.85 Hz, which is significantly higher than the energy output of a yarn with only a PVDF electrospun nanofibrous layer. More importantly, the high-performance was retained after 50 000 cycles of compression. The flexible yarn-based PNG device with good energy output and durability demonstrated its great promise to be used as a wearable energy harvester.
The goal of this research was to understand how firefighter protective suits perform in different operational environments. This study used a sweating guarded hotplate to examine the effect of environmental temperature (20–45°C) and relative humidity (25–85% RH) on evaporative heat loss through firefighter turnout materials. Four firefighter turnout composites containing three different bi-component (semi-permeable) and one microporous moisture barriers were selected. The results showed that the evaporative resistance of microporous moisture barrier systems was independent of environmental testing conditions. However, absorbed moisture strongly affected evaporative heat loss through semi-permeable moisture barriers coated with a layer of nonporous hydrophilic polymer. Moisture absorption in mild environment (20–25°C) tests, or when testing at high humidity (>85% RH), significantly increased water vapor transmission in semi-permeable turnout systems. It was also found that environmental conditions used in the total heat loss (THL) test (25°C and 65% RH) produced moisture condensation in bi-component barrier systems, making them appear more breathable than could be expected when worn in hotter environments. Regression models successfully qualified the relationships between moisture uptake levels in semi-permeable barrier systems and evaporative resistance and THL. These findings reveal the limitations in relying on THL, the heat strain index currently called for by the NFPA 1971 Standard for Structural Firefighter personal protective equipment, and supports the need to measure turnout evaporative resistance at 35°C (Ret), in addition to THL at 25°C.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.