(384e) Direct Ink Writing of Modified Cellulose Nanocrystals

Cellulose nanocrystals (CNCs) are stiff, lightweight rod-shaped nanoscale materials that have a tensile strength eight times that of steel (7.5 GPa). In addition to their outstanding mechanical properties, CNCs are low cost, low density (~1.6 g/cm³), renewable in nature, and are easily processed. These nanoparticles have attracted the attention of researchers and there has been an exponentially increasing number of works devoted to understanding such materials and their applications. The addition of CNCs into a polymer matrix has been shown to enhance the mechanical properties of the resulting composite, however, the utilization of CNCs in more common non-polar polymers, such as epoxy resins, is still limited to their hydrophilicity and poor dispersibility. Surface modification is hence needed to aid in dispersion. With the proper modification, dispersion of these CNCs into common non-polar polymers, such as epoxy resins, polypropylene, or polystyrene, can allow for the development of robust, durable, lightweight, and transparent materials to be used in structural composites, adhesives, energy storage devices, actuators, and sensors. Understanding the dispersibility, structure of CNC’s in the matrix and its resultant effect on macroscopic properties such as rheology and hence printing performance is of utmost importance before these composites are put to use.

In this work we characterize the effects of a functionalized CNC on the rheological properties and printing behavior (Direct Ink Writing (DIW)) of an epoxy resin. CNC functionalization is achieved by grafting an activated medium chain fatty acid to substitute the hydroxyl functional groups. The level of CNC modification is evaluated using Fourier Transform Infrared (FTIR), thermo-gravimetric analysis (TGA), X-ray diffraction (XRD), and solvent dispersibility studies. Functionalized CNCs are dispersed into the epoxy resin (EPON 828) at loadings up to 20 wt%. Initially, rheological studies are used in this study to assess the printability of the inks. The rheological percolation threshold is the critical concentration at which there is a transition from liquid-like to solid-like behavior. For this system, this value was found to be at ~10wt%. We found that for the final printed structure to exhibit structural integrity, it is necessary to print at loadings slightly above this value. Future work will include microscopy (SEM and polarized light) of both printed and cast samples to observe the dispersion and alignment of the CNCs within the polymer matrix. Finally, the mechanical properties of all samples will be measured to show the effect of the reinforcement in the matrix.