Statistical optimization of polysilazane-derived ceramic: Electrospinning with and without organic polymer as a spinning aid for manufacturing thinner fibers

The manufacturing of electrospun mats from preceramic polymers is complex due to low and disperse molecular chain entanglements and a large number of operating parameters. Here, the electrospinning of polysilazane and polysilazane/polyacrylonitrile (PAN) solutions was evaluated and optimized. The reduction in Berry's number from 94 to 22 indicated the positive effect of adding organic polymer on the polysilazane chains to obtain homogeneous fibers. A fractional factorial design was first implemented to screen out the three most significant factors affecting the fiber diameter. Then, a response surface model was developed using the Box-Behnken design to obtain a quantitative relationship between operating parameters and fiber diameter. Finally, the models were used to find the optimal conditions that yield the thinnest fiber. For polysilazane, the feed rate showed a positive effect, while for polysilazane/PAN an interaction between the feed rate and the tip-to-collector-distance was the most significant factor, with a positive effect. The verification of the models was accomplished through model validation. The addition of PAN to polysilazane reduced fiber diameter from 1.79 +/- 0.26 mu m to 0.57 +/- 0.04 mu m. The polysilazane/PAN pyrolyzed at 1000 degrees C (SiCN_PAN) could shield more than 50% of electromagnetic energy from 100 MHz to 4.5 GHz. In addition to the presence of carbon-rich regions derived from PAN, thinner diameters caused an increase of interfaces between the voids and electrospun fibers, which intensified multireflection for dissipating electromagnetic energy. Owing to the optimized design, the SiCN_PAN fibers with satisfying electromagnetic shielding properties could meet advanced requirements of lightweight hybrid materials from aerospace to defense applications.