With excellent reinforcing performance and many remarkable inherent properties, such as renewability and high strength-per-unit-mass, chitin nanofibers (ChNFs) are attractive resources for polymer composite applications. However, significant challenges resulting from chitin's insolubility have hindered efforts to incorporate it effectively into polymer matrices. Here, ChNFs extracted from crab shells were used as fillers to reinforce polyethylene oxide (PEO). The dispersion of ChNFs in the polymer matrix and the interactions between fiber and matrix were studied by utilizing solvent-etching of the polymer matrix, FTIR spectroscopy and AFM colloidal probe adhesion measurements. The results show that the ChNFs were dispersed well and formed a fine interconnected network structure in the PEO matrix. ChNFs also exhibited strong adhesion with PEO, resulting from hydrogen bond and van der Waals forces. The ChNF interconnected network greatly enhanced the mechanical properties of PEO, with a 3-fold increase in both the tensile strength and elastic modulus of the nanocomposites at 20% ChNF loading. Processing ChNFs in suspensions with slight acidity and water-soluble polymers appears to support the formation of highly interconnected networks that makes ChNF-polymer composites excellent candidates for reinforced, light-weight, renewable materials. (C) 2016 Elsevier Ltd. All rights reserved.