Mechanical and morphological properties of cellulose nanocrystals extracted from industrial hemp agro-waste

Cellulose nanocrystals (CNCs) were produced directly from hemp agro-waste (HAW) using ammonium persulfate (APS) oxidation. Industrial hemp growth in the US has been accompanied with HAW production. While hemp has previously been shown as a source for CNCs, studies on CNCs from HAW (specifically hemp hurd) have not been reported on. Furthermore, studies on the mechanical characteristics of individual CNCs extracted using APS are lacking. Herein, the one-step oxidation treatment was followed by a purification step to remove impurities and hence to colloidally stabilize CNCs in aqueous suspensions, then analysis of the morphological and mechanical properties was performed. Purified and unpurified CNC samples were compared for potential differences in morphological and mechanical properties. Morphological analysis was performed using atomic force microscopy (AFM): purified CNCs had an average length of 183.1 ± 73.9 nm, unpurified CNCs had an average length of 202.0 ± 79.2, and both samples had an average diameter of 4 ± 2 nm. Mechanical analysis of individual CNCs using force-distance spectroscopy (FDS) suggested both samples had little differences with average values of Young’s modulus 2.19 ± 0.15 GPa, maximum loading force of 6.29 ± 0.09 nN, and adhesion energy of 1.57 ± 1.12e-16 J. No statistical differences between purified and unpurified CNCs were found in Young’s modulus and maximum loading forces measurements, suggesting the impurities had minimum impact on mechanical strength. These results highlight the potential for mechanical assessment of individual CNCs extracted using APS from HAW via FDS and the need for further exploration into the methodology of this type of mechanical analysis.