Parametric Investigations on the Effect of Electrospinning Process Variables on the Macroscopic Properties of Hybrid Composites

Abstract

Electrospinning is regarded as an efficient process to form sub-micron and nano level fibers consistently in a simple laboratory scale setup. The process has excellent potential for scalability and for the structural applications of integrated electrospun fibers in polymer hybrid composites. In our on going work, the mechanical characterization of these hybrid composites with integrated electrospun fibers revealed significant variations based on the sintering temperature and the morphology of the formed electrospun fibers. The morphology (in particular, the fiber diameter) depends on the process parameters of the electrospinning process. This paper investigates the influence of two electrospinning parameters namely: Distance between spinneret and collector plate and voltage. Four voltage levels were selected varying from 15KV to 18 KV in the increments of 1KV. The spinneret to the collector plate distance was varied from 70 mm to 100 mm in 10 mm increments. Thus, a total 16 combinations of these parameters were studied keeping other parameters constant. The objective is to find the optimal voltage and distance combinations that produce smallest electrospun nano fiber diameters consistently. From each voltage-distance combination, the diameter of the deposited fibers was sampled at 50 different points using the morphological image data obtained with a scanning electron microscope (SEM). The analysis of experimental data indicated four favorable voltage-distance combinations that give smallest diameter size of electrospun nano fibers consistently. These four set of parameters were, 15KV and 70 mm; 15KV and 100 mm; 18 KV and 70 mm; and 18KV and 100 mm. The least diameter of fiber was observed and measured for a voltage distance combination of 18KV and 70 mm. The least diameter observed for these parameters can be attributed to the higher applied voltage resulting into higher bending instability causing the reduction in diameter of fibers. Another reason for reduction in fiber diameter is, when the distance between spinneret and collector is increased there is more space for elongation of fibers. With more increase in length of fiber, there is higher reduction in diameter of electrospun fibers. To correlate these process variations of electrospinning to the morphological properties of electrospun fibers, design of experiments study was carried out. It has been attempted here to investigate if there is any correlationship between the morphological property of electrospun fibers and properties of two phase composite. These investigations will provide an insight on the relationship between the process parameters — morphology — and the associated characterized macroscopic properties of the formed composites. Results from the stochastic modeling for variations in the fiber diameter due to the variations in the voltage and the distance correlate well to the ARMA (6,5) stochastic model. Greens functions for the model were derived and showed the stability of the electrospinning process.