An electrically conducting adhesive paste based on adhesive exopolysaccharide of Priestia aryabhattai KAG -18

Conventionally, lead/tin alloy-based solders, lead-free (Sn/Ag, Sn/Ag/Cu) solders, and metal-based ECAs are used for fabrication of electronic circuits. However, they have limitations such as low strength of joints, toxic flux materials, higher processing temperature, and fatigue. Although, recently metal-free ECAs based on graphite/carbon black/carbon nanotubes have drawn attention, the research on such ECA pastes is mainly focused on electrical conductivity, neglecting their binding strength. In the present study, the adhesive exopolysaccharide of Priestia aryabhattai KAG-18 (EPS/KAG-18) (5.0 % w/v) showed highest tensile strength of 1.5 ± 0.153 MPa using paper as substrate. EPS/KAG-18 was a heteropolysaccharide containing glucose, 11.0 %; galactose, 71.0 % and glucuronic acid, 18.0 %. Three ECA pastes i.e. KAG-18/C1, KAG-18/C2, and KAG-18/C3 were prepared by blending activated charcoal (20 %, w/w) with EPS/KAG-18. Upon TGA/DSC profile indicated ECA pastes were stable up to 250 °C, without glass transition. The XRD curves of ECAs, suggested amorphous nature of ECAs. The films of ECA on PCB exposed to different temperatures showed no deformation at −80, 30 and 150 °C. Overall, films prepared using KAG-18/C3 paste was uniform as indicated by surface roughness of the films. With increase in the shear rate, the viscosity of the three ECAs was found to decrease indicating their shear thinning or pseudo plastic behavior. The ECA pastes showed higher G′ than G″, in the order KAG-18/C2<KAG-18/C1< KAG-18/C3 which indicated their gel-like behavior. The tensile strength of the paper specimens bonded using ECAs were found to be in the order: KAG-18/C1<KAG-18/C2<KAG-18/C3 i.e.0.19 ± 0.021 MPa, 0.541 ± 0.069 MPa and 1.09 ± 0.099 MPa, respectively. As the content of adhesive biopolymer EPS/KAG-18 was increased from 10.0 % (w/w) to 15.0 (w/w) in KAG-18/C1and KAG-18/C2 pastes, respectively, the conductivity of these pastes also increased. The KAG-18/C2 paste could be used also as solder paste for fabrication of electric circuit on PCB board and cellulose paper.