Development of Porous Metallized Polyamide Filaments as Sensors for Strain Monitoring Applications

In this research work, a metallization strategy for the fabrication of core-shell polymer-metal composite filaments has been presented for the development of strain sensors. The polyamide filaments were etched by carefully controlling the etching parameters and observing the surface functionality which allowed metallization of the filaments. The Differential Scanning Calorimetry (DSC) analysis revealed that the etching treatment did not result in substantial loss in crystallinity. The Attenuated Total Reflectance - Fourier Transformation Infrared (ATR-FTIR) Spectroscopy showed intensification of amide peaks. This was accompanied by the preservation of methyl peaks indicating an absence of chain scission. Etching of the filaments was followed by surface activation and acceleration prior to plating. The metallization of etched filaments comprised of electroless plating followed by electroplating with copper which resulted in the formation of a porous spongy metal network on the substrate filaments as revealed by the morphological analysis carried out using optical and electronic microscopes. The spongy network of copper gave the sensors high sensitivity to strain due to the presence of metallic percolation network at low initial resistance. The metallized polyamide filaments with strain sensing ability showed bilinear behavior under monotonic static tensile loading with an initial gauge factor of 7.6 increasing to a value of just over 31 in the 2
^nd
linear region. The hysteresis error also settled to a low value of ~0.01 after a few initial cycles during cyclic loading tests. The metallized polyamide filaments hold promise for structural health monitoring, proprioceptive testing, soft robotics and smart textiles etc.