Preparation and performance of balsa wood-based carbon sponge/TPU composite pressure sensor
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摘要: 近年来,具有三维网状结构的柔性压力传感器展现出高度可逆压缩性和良好灵敏性等特点,其复杂的网络形态也有利于构建稳定的导电网络,广泛应用于人体健康监测、可穿戴设备、医疗诊断等领域。本文围绕构建稳定的三维导电网络和传感性能优化为目标,设计了一种基于天然轻木的具有三维层状结构的碳海绵(CWS)/热塑性聚氨酯弹性体(TPU)复合压力传感器,并对该传感器的催化处理、碳化工艺、传感性能及人体适用性进行表征。结果表明:通过催化处理和高温碳化得到的轻木基CWS/TPU复合压力传感器,其碳化得率达到20.15%,压缩应变可达60%,在0~4 kPa压力范围内,最高压力传感灵敏度达12.87 kPa−1,并且在超过5000次的压缩/释放周期后仍具有良好的传感稳定性和环境稳定性,表现出良好的传感性能。应用该传感器成功地对手部活动、行走和脉搏进行了实时监测,显示了该传感器在运动和健康监测方面潜在的应用价值。Abstract: In recent years, flexible pressure sensors with three-dimensional mesh structure show high reversible compressibility and good sensitivity, and their complex network shape is also conducive to the construction of stable conductive network, which is widely used in human health monitoring, wearable devices, medical diagnosis and other fields. In this study, a carbonized wood sponge (CWS)/thermoplastic polyurethane elastomers (TPU) composite pressure sensor with three-dimensional layered structure based on natural balsa wood was designed to construct a stable three-dimensional conductive network and optimize the sensing performance. The catalytic treatment, carbonization process, sensing performance and human applicability of the sensor were characterized. The results show that the carbon yield of the light wood-based CWS/TPU sensor by catalytic treatment and high temperature carbonization can reach 20.15%, the compressive strain can reach at 60%, and the maximum pressure sensing sensitivity can reach 12.87 kPa−1 in the pressure range of 0-4 kPa. Moreover, the sensor still has good sensing stability and environmental stability even after 5000 compression/release cycles, showing good sensing performance. The sensor is successfully used to monitor hand movement, walking and pulse in real time, which shows the potential application value of the sensor in motion and health monitoring.
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图 1 碳海绵(CWS)/热塑性聚氨酯弹性体(TPU)柔性压力传感器的制备:(a) 酸性催化CWS的制备过程;(b) 碳化工艺图;(c) 传感器结构示意图
Figure 1. Preparation of carbonized wood sponge (CWS)/thermoplastic polyurethane elastomers (TPU) flexible pressure sensor: (a) Preparation process of acidic catalytic CWS; (b) Carbonization program; (c) Schematic diagram of the sensor structure
图 6 CWS/TPU复合材料的力学性能:(a) 高度可逆压缩性示意图;(b) 不同碳化温度下、60%应变下的压缩应力-应变曲线;(c) 不同应变下的压缩应力-应变曲线(插图为0%~20%压缩范围内的放大图);(d) 在50%应变下循环5次的压缩应力-应变曲线
Figure 6. Mechanical properties of CWS/TPU composites: (a) Schematic diagram of highly reversible compressibility; (b) Compressive stress-strain curves under 60% strain at different carbonization temperatures; (c) Compressive stress-strain curves at different strains (Inset is enlarged image in the 0%-20% compression range); (d) Compressive stress-strain curves cycling 5 times at 50% strain
图 7 CWS/TPU柔性压力传感器的压阻传感性能:(a) 传感器结构示意图;(b) 传感器在不同压力下的电流响应;(c) 循环前后传感器在不同施加压力下电阻的相对变化(ΔR/R0);(d) 传感器在500 Pa的加载和卸载压力下的响应和恢复时间;(e) 传感器的最低检测限;(f) 本文制备的CWS/TPU压力传感器的灵敏度与其他文献中三维结构传感器进行对比[24, 26, 28-30]
Figure 7. Piezoresistive sensing performance of CWS/TPU flexible pressure sensor: (a) Schematic diagram of sensor structure; (b) Current response of the sensor at different pressures; (c) Relative change in the resistance (ΔR/R0) of the sensor under different applied pressures before and after cycle; (d) Response and recovery time of the sensor upon loading and unloading pressure of 500 Pa; (e) Minimum detection limit of the sensor; (f) Sensitivity of the CWS/TPU pressure sensor prepared in this paper compared with other three-dimensional structural sensors[24, 26, 28-30]
S—Sensitivity; R2—Correlation coefficient; GR—Graphene; CNTs—Carbon nanotbes; CNC—Cellulose nanocrystal composite; rGO—Reduced graphene oxide; CMC—Carboxymethyl cellulose; MC—Methyl cellulose; PDMS—Polydimethylsiloxane
图 8 CWS/TPU传感器的稳定性:(a) 传感器超过5000次循环的电阻变化(插图为5000次循环后的三维碳层结构SEM图像);(b) 循环后1 kPa压力下传感器在不同放置时间、温度、湿度的电阻相对变化
Figure 8. Stability of CWS/TPU sensor: (a) Resistance change of the sensor over 5000 cycles (Insert is SEM image of 3D carbon layer structure after 5000 cycles); (b) Relative change in the resistance of the sensor at different placement time, temperature and humidity with 1 kPa pressure after cycling
图 9 CWS/TPU传感器在人体健康监测方面的应用:(a) CWS/TPU传感器与LED灯连接的照片,以可视化压缩和释放CWS时的亮度变化;(b) 指关节弯曲;(c) 腕关节弯曲;(d) 模拟行走过程;(e) 脉搏跳动
Figure 9. Applications of CWS/TPU sensor in human health monitoring: (a) Photographs of the CWS/TPU sensor connected with an LED lamp to visualize the brightness change upon compressing and releasing the conductive sponge; (b) Knuckle bending; (c) Bending of the wrist joint; (d) Simulating the walking process; (e) Pulse beating
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