Characterization and exploration of polyurethane nanofiber webs coated with graphene as a strain gauge

Abstract

The objectives of this study were as follows: (a) to compare two coating methods (i.e., brush painting and doctor blade coating) for applying graphene onto polyurethane nanofiber webs (PU NWs) for developing e-textiles; (b) to investigate the surface characteristics and chemical and mechanical properties of the specimens based on the coating conditions; (c) to find the relationship between the electrical resistances of the specimen and the amounts of graphene in the PU NWs; and (d) to evaluate electrical resistance changes when specimens are physically strained to calculate the gauge factors. The linear resistances of the graphene-coated PU NWs were less than 600 Ω/cm on all specimens. The PU NW linear resistances are about 1–500 Ω/cm when coated with silver nanowires and about 1000–7000 Ω/cm when coated with polypyrrole. The graphene-coated specimen linear resistances are lower than those of the polypyrrole-coated specimens and higher than those of the silver nanowire-coated specimens. As has been demonstrated in other studies, brush painting is a simple fabrication process, but the field emission scanning electron microscopy image showed that it did not produce uniform coatings compared to the doctor blade method. However, it was found that it is possible to fabricate e-textiles with linear resistances of less than 100 Ω/cm by merely using repetitive brush painting. Fourier transform infrared spectroscopy analysis confirmed the peak bands of urethane and the -NH- bending peak to investigate the graphene coating conditions. The tensile strength of the graphene-coated specimen was much lower than that of the untreated, but the elongation/strain at rupture was higher than that of the untreated specimen. This result shows that the graphene-coated specimens are strained to a smaller force than the untreated one. Furthermore, this indicates that graphene coating induced the changes of the tensile properties of the specimens. The electrical resistances are varied depending on the graphene coating uniformity. Using the doctor blade method, the electrical resistance values of the specimens were slightly lower than those for the brush painted specimens. The gauge factor values of the specimens were examined by the stretch and release test. The highest gauge factor was 97.24 (D2.6) and the lowest was 20.54 (D2.2).