Critical length reinforcement in core-shell electrospun fibers using composite strategies

An understanding of the reinforcement mechanism in composites is crucial for the development of novel materials where the application is limited by their mechanical properties. One of the methods used to obtain high performance composites is reinforcement with short fibers. Polymeric materials, such as electrospun polymethyl methacrylate (PMMA) fibers, have a very high tendency to fragment into regular short fibers after applying very low stress. This phenomenon was used to reinforce a polycarbonate (PC) core-shell structure (PMMA-PC) by using fragmented short PMMA fibers for reinforcement in the critical length limits. Mechanical testing revealed an increase of maximum stress and Young's modulus of almost 260% and 630%, respectively, for PMMA-PC fiber meshes. The observation of core-shell fibers after mechanical testing was confirmed by using confocal microscopy, showing very regular short fragments of PMMA fibers inside the PC shell. This work demonstrates a hierarchical approach that can be taken for reinforcement of a single fiber on the nanoscale and a composite on the macroscale.