Size Also Matters in Biodegradable Composite Microfiber Reinforced by Chitosan Nanofibers

Pioneer works on nanocomposites were focused in carbon nanofibers or nanotubes dispersed in epoxy matrix, a viscous liquid facilitating the compounding stage. The interest in developing new composites aimed for biomedical applications led us to design new nanocomposites based in biodegradable polymers with demonstrated biological performance. We report herein the development of micro-nano composites by extruding poly(butylene succinate) (PBS) microfibers with two different diameters, 200 and 500 m, reinforced with electrospun chitosan nanofibers. Analysis of the microfibers showed high levels of alignment of the reinforcing phase and excellent distribution of the nanofibers in the composite. Its geometry facilitates the development of orthotropy, maximizing the reinforcement in the axial fiber main axis. The biodegradable microfiber composites show an outstanding improvement of mechanical properties and of the kinetics of biodegradation, with very small fractions (0.05 and 0.1 wt.%) of electrospun chitosan nanofibers reinforcement. The high surface area-to-volume ratio of electrospun nanofibers combined with the increased water uptake capability of chitosan justify the accelerated kinetics of biodegradation of the composite as compared with the unfilled synthetic polymer. INTRODUCTION Nanocomposites are a class of advanced materials consisting in a reinforcing phase with some dimensions in the nanometer size range dispersed in a continuous matrix. Usually the nanometer dimension range is defined between 1 and 100 nm. This requirement is not consensually accepted, depending on the characteristics of the nanoentities of interest and on the field of application [1]. The nanocomposites may exhibit enhanced properties such as the elastic modulus, strength, heat resistance, barrier properties, transparency or biodegradability. The superior properties of nanocomposites have potential interest for many applications in electronic, automotive or biomedical industries [2]. Fibrous composites allow easier structuring of reinforcements being more effective than bulk materials. Its geometry facilitates the development of orthotropy, maximizing the reinforcement in the fiber main axis. The production of composite fibers by melt processing 6 1