Carbon black filled electrospun fiberweb: Electrical and mechanical properties

The development of flexible and compliant conductive polymer composites with "textile" like characteristics remains an important endeavor in light of the recent activity in polymer/textile based electronics. In the present work, electrospinning is used to prepare a composite fiber containing carbon black (CB) and polyurethane (PU). The effects of introducing CB into the PU-matrix in the form of fiberweb have been investigated in terms of mechanical, electrical, and thermal properties. A percolation behavior of the CB filled fibers has been investigated using simulation. Theoretical percolation threshold was determined at CB volume fraction of 9.3. The highest conductivity of the fiberweb was experimentally determined to be ∼10-2 S/cm for 8.03 vol% of CB filler content, which is deemed useful for a number of applications including electrodes in polymer actuators. However percolation threshold of the conductivity of the PU-CB electrospun fiberweb was experimentally determined to be between 4.6-5.0 vol% of CB. The discrepancy may be due to the idealized structure assumed in the simulation. The critical exponent of percolation (t) was calculated as 2.165, when the percolation threshold was assumed to be at 4.6 vol%.; Electrical and mechanical properties of the fiberwebs have been compared with films with same constituents. The current-voltage (I-V) relationship of both spin-cast films and electrospun fiberweb was studied to understand the mechanism of electrical conduction. In both cases, at high absolute values of voltage the current increased linearly, while for low voltages the current values are substantially lower, as a result the behavior resembled like diodes. On subsequent voltage sweeps, lower resistance values were recorded and the relationship became more linear over the whole voltage range. The data suggests alteration of the initial percolation network on application of high voltage. This non-Ohmic behavior is attributed to quantum tunneling conduction mechanism. The results seem to confirm the tunneling-percolation behavior of the CB-PU composite fiberweb investigated in this research. Generally, fiberwebs show better electrical and mechanical properties than the films. Electrical conductivity of the fiberwebs is generally higher than the films.; As expected, elastic modulus of fiberwebs is found to be much lower than the films. The increase in bond density and the overall area of the bonds for higher CB content as well as the reinforcement effect of high modulus CB particles are likely to improve the modulus of the fiberweb. Both films and fiberwebs show similar piezoresistive behavior, however gauge factor of fiberwebs are slightly higher than equivalent films. To demonstrate a potential use, the CB-PU nanocomposite fiberweb was applied in the form of flexible electrodes on a circular dielectric elastomer actuator. The maximum mean areal actuation strain of 12.74% was recorded with 5.58 vol% carbon black filled fiberweb as electrodes applied on and VHB-4910 acrylic films.