Cellulose Nanocrystals as Ultrastrong Bio/Nano Materials: New Insights from Nanomechanical Studies

Reza Shahbazian-Yassar

Department of Mechanical Engineering, Michigan Technological University, USA

Abstract
Cellulose nanocrystals are new emerging biomaterials that are considered to posses extremely high mechanical properties. However, the effects of resources on the mechanical properties of cellulose nanocrystals are rarely studied. Differences in hydrogen bonding patterns result in two allomorphs in native cellulose (Iα and Iβ). In turn, Iα and Iβ have distinct crystallographic structures and are composed of one chain triclinic and two chain monoclinic unit cells, respectively. The objective of this study is to quantify the transverse mechanical properties of cellulose I nanocrystals (CNCs) prepared from tunicate (Iα-rich) and cotton (Iβ-rich) using acid hydrolysis. Atomic force microscopy (AFM) were performed under peak force mode on individual CNCs. The transverse elastic modulus (ET) was also calculated by comparing the experimental AFM indentation results with 3-dimensional FEA analysis of CNC indentations. We observed that tunicate and cotton CNCs have different nanomechanical (ET and adhesion) properties. These properties are dictated by the localization of Iα and Iβ and Iα/ Iβ ratio along their chains, and the single crystal morphology (aspect ratio and diameter).