Effect of Chitosan Loading on the Morphological, Thermal, and Mechanical Properties of Diglycidyl Ether of Bisphenol A/Hexamethylenediamine Epoxy System

The effect of chitosan filled diglycidyl ether of bisphenol A (DGEBA) epoxy system were investigated using the thermal, mechanical, and morphological properties. The mixing ratio of resin/hardener was kept constant while the chitosan of 1.0, 2.5, 5.0, 7.5, and 10 weight percentage (wt%) was incorporated into the system. The thermal stability and the transition behaviour of the chitosan filled epoxy system were analysed through a differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR) while atomic force microscope (AFM) and scanning electron microscopy (SEM) were used to investigate the morphology. It was observed that the additive tends to agglomerate, with the formation of clear phase separation, when the chitosan content increases above 5？wt%. At lower chitosan loading (2.5？wt% and below), relatively uniform dispersion of the additive can be achieved. The thermal stability of the system increases with chitosan loading while the mechanical tensile strength is compromised. 1. Introduction Epoxy resins are molecules containing one or more α- or 1, 2-epoxide groups, which can be crosslinked to form three-dimensional (3D) thermoset network structure. The degree of crosslinking and hence the material properties can be controlled by varying the amount of the resin hardener system, controlled curing over a wide range of temperatures and introduction of additives or fillers. Epoxy has been extensively used in a wide range of industrial applications owing to its excellent adhesiveness, resistance to heat and common chemical, mechanical strength, and electrical insulating properties. However, the material remains excessively brittle once cured and suffers from low impact strength, poor fracture toughness, and resistance to crack propagation. Du？ek et al. [1] pointed out that alternating mechanism of network formation in DGEBA amine hardener system does not offer the potential of partial segregation for the formation of inhomogeneous crosslinking. On the other hand, more pronounced inhomogeneity may be promoted through thermodynamic incompatibility or nonalternating curing mechanisms in more complicated thermosetting systems. Over the past decade, various attempts to enhance the toughness of epoxy system have been carried out by incorporating fillers into epoxidesto produce a variant form of epoxy resin coupled with different chemical compositions. Review of the literature shows that majority of the previous work employed thermoplastic, rubber, and elastomer compounds as toughening agents in