Micromechanical characterization of cellulose fibers

Abstract

The work presented here aims towards the characterization of micromechanical properties of individual cellulose fibers. In particular, our interest is in determining the elastic modulus, tensile strength and tensile elongation of cotton and wood based cellulose fibers. Testing is conducted at a microscale, on single fibers of a few millimeters in length and tens of microns in width, a scale so chosen because such fibers are commonly used as industrial raw materials. An in-house microtensile fiber tester was designed and fabricated. A fine resolution stepper motor (10 nm per step) provides the actuation for the microtensile load frame and load in the fibers is measured by a high sensitivity load cell (0.01 mN resolution). The entire assembly is placed below a zoom stereo microscope for the dual purpose of aiding in specimen mounting and visually recording the experiment. After calibration of the device, good results were obtained when testing both the cotton and wood based cellulose fibers. Average Young's moduli of 4 GPa and 2 GPa were found for the two fibers, respectively. However, a large variation in failure stress was found for the fibers of both kinds, necessitating a statistical analysis assuming a Weibull distribution of failure. Based on this, mean strengths of 496 MPa for cotton cellulose fibers and 164 MPa for wood cellulose fibers were obtained.