Developing porous and flexible capacitive pressure sensors from silver nanowire coated willow fibers

Willow fibers, harvested from willow genus trees of the Salicaceae family, possess characteristics that make them suitable for the production of flexible capacitive sensors. The aim of this study is to examine the physical properties of willow fiber in comparison with other prominent natural fibers including cotton, poplar, wool and kapok fibers. Due to their finer diameter and shorter length (<1 cm) compared to these commonly used natural fibers, willow fibers are often considered as ecological waste, limiting their use in textiles. To promote sustainable utilization of this waste, this study explores their potential in producing flexible capacitive sensors. Herein, round-shaped and porous nonwoven pads are fabricated by spraying a spandex/DMAc solution onto cleaned willow fibers. To impart electrical conductivity, a dip-coating method is employed, resulting in the formation of silver nanowire (AgNW) networks on the willow fibers. Electrochemical measurements demonstrate that the obtained willow fiber pads have low sheet resistance (1.09–2.42 Ω/sq), high sensitivity (0.255 kPa⁻¹ in the low pressure range) and excellent wash durability, maintaining performance after five washing cycles. The pads also retained conductivity after 10,000 bending cycles. These findings suggest willow fiber-based capacitive sensors as promising candidates for wearable electronics due to their high sensitivity, rapid response and durability.