Chitosan and chitosan composites reinforced with carbon nanostructures

Chitosan is a naturally-occurring polymer that can be derived from chitin through a deacetylation process from shells of crustaceans. Chitosan is abundant, easily collected as waste and repurposed for industrial and biomedical applications. This work demonstrates that the mechanical properties of chitosan can be improved by thermomechanical processing (milling and sintering) and through reinforcement with carbon nanostructures (CNS) to form mechanically tunable composites. Thermal analysis was used to optimize the sintering conditions for chitosan and chitosan-CNS preventing unwelcome degradation. The crystallinity index (CI%) ratio among crystalline (beta) and amorphous (alpha) phases, decreases from 57 to 18 depending on milling and sintering conditions. Although, the crystalline structure is affected during processing, Raman results demonstrated that the chitosan bonding is preserved and the added CNS percolate the chitosan. Pressing chitosan at room temperature does not guarantee consolidation, while chitosan sintered at 180 degrees C can reach a hardness of up to 15 +/- 0.7 mu HV. Addition of CNS and sintering at 220 degrees C demonstrate further benefits on hardness (26.1 +/- 0.1 mu HV) this hardness improvement is attributed to a grain boundary reduction and improved cohesion among chitosan and CNS. The nanohardness testing shows a unique elastic phenomenon resulting from the presence of graphene or graphitic carbon in the CNS. Published by Elsevier B.V.