Palm oil based stretchable piezoresistive strain sensors

The advancement of wearable devices and soft robots requires soft and stretchable sensors to detect their movements. This article proposes palm oil as an organic solvent for a stretchable piezoresistive strain sensor made from a composite consisting of elastomer (Ecoflex 00-30) filled with carbon black. The high content of palmitic acid in the palm oil increases the dispersity of carbon black in the composite, hence effectively improving the conductivity of the sensors. Furthermore, using palm oil as a natural plasticizer can lower the degree of crosslinking of the matrix, reducing the modulus elasticity but still producing a stretchable sensor with 500 % elongation at break. The presence of palm oil in the sensor also increases the gauge factor, showing a value of 2.43-4.75 and better repeatability during loading. These gauge factors are associated with two linear strain regions of the sensors (R² > 0.99), which are 20-200 % and 0-20 % strain, respectively. The stretchable sensor also shows high durability that can withstand >1500 cycles at 60 % strain. The as-fabricated sensor can be deployed to detect the movement of the human body, such as for measuring a finger's joint angle and in soft robotics applications.