Considerable effort has been made to investigate the thermo-mechanical properties of epoxy/cellulose nanocomposites. Studies have focused on measuring final properties and correlating it to the underlying structure. However, sill there is a gap when it comes to understanding and tracking the macroscopic changes that occur during the formation of the three-dimensional (3D) network within the epoxy resin system. Understanding the process of structure formation during curing and its influence on resulting rheology will help in fine tuning the underlying microstructure to achieve desired properties for a certain application. In this study, we systematically evaluated the influence of surface modified cellulose nanocrystal (CNC) content on the curing behaviour of epoxy nanocomposites. The surface modification of CNC was carried out using lauroyl chloride (LCCNC) via esterification method. The formation of functional groups (ester bonds) on the surface of LCCNC were studied using Fourier-Transform Infrared spectroscopy (FTIR) and the resulting structure studied by X-ray diffraction (XRD). The effect of different loading levels of LCCNC (10, 15, 20 and 25 wt%) into the epoxy and the curing reaction kinetics of the formulated composites under isothermal conditions (120 and 177 oC) were studied systematically using rheology, differential scanning calorimetry (DSC) and FTIR methods. The curing rheology was used to observe time dependent rheological changes in storage (G’) and loss (G’’) modulus of LCCNC/epoxy composites during isothermal curing process. In order to compare against curing rheology measurements, the DSC and FTIR experiments were also performed to monitor the curing reaction. The DSC data reveals the curing reaction is completed at 177 oC, whereas at the same time the rheological measurements confirm the cured resin is still in a low viscoelastic state, favouring reactant diffusion. However, when the samples are held at 177 oC for a period of time, a crosslink network forms and the G' increases significantly (by a factor of 1000) due to network formation. This result suggests that even though FTIR and DSC results point to the fact that curing is almost complete, network formation to produce a solid takes more time as measured by rheology. Thus, a two-stage mechanism of buildup of mechanical properties is revealed with ring opening/curing int he first stage followed by network formation in the second stage. In summary, this study lays the groundwork for advancing the development of high-performance, sustainable, and multifunctional epoxy-based nanocomposites, with broad applications in materials science and polymer processing.
