Effect of Carbon Black on the Strain Sensing Property of 3D Printed Conductive Polymer Composites

In this work, carbon nanotubes (CNTs) and carbon black (CB) filled thermoplastic polyurethane (TPU) composites (CNT/TPU and CB/CNT/TPU) were used to prepare the flexible piezoresistive strain sensors by fused filament fabrication (FFF) 3D printing, and the effect of CB addition on the sensing properties was studied. The results showed that all the sensors exhibited a typical positive piezoresistive response during the stretching process. Compared with 3 wt% CNT/TPU composite, the conductivity of 10-CB/CNT/TPU (CB:CNT = 1:10), 20-CB/CNT/TPU (CB:CNT = 2:10) and 30-CB/CNT/TPU (CB:CNT = 3:10) with 3 wt% CNTs and various CB contents increased by 30%, 124% and 500% from 1.64 × 10–4 S.m−1, respectively. The addition of CB also significantly improved the sensitivity of the sensors. The gauge factor (GF) of the CNT/TPU sensor was 10.3, while the GF of 10-CB/CNT/TPU, 20-CB/CNT/TPU, and 30-CB/CNT/TPU sensors increased to 14.2, 23.8, and 35.9 at 60–150% strain, respectively. The printed sensors detected strains of different magnitudes and frequencies, and CB addition enhanced the stability during 1500 loading cycles. The printed sensor was also applied to monitor human activities such as mouth opening and joints bending. This study provides valuable guidance for the customized fabrication and property tuning of flexible strain sensors.