Interfacial Micromechanics of All-Cellulose Nanocomposites Using Raman Spectroscopy

Abstract

All-cellulose nanocomposites, in which both the matrix and the reinforcing fillers are cellulose, were successfully prepared using different solvents (LiCl/DMAc and NaOH/urea) and different sources of cellulose whiskers (cotton and tunicate whiskers) as control parameters. The volume fraction of cellulose whiskers was varied from 5 to 20%. The mechanical properties and crystallinity of the nanocomposites were characterised using tensile testing and X-ray diffraction. The tensile properties and crystallinity of nanocomposite samples are associated with the stiffness and crystallinity of the cellulose whiskers. Using Raman spectroscopic technique, the stiffnesses of single cotton and tunicate whiskers are found to be approximately 56-105 and 118-221 GPa respectively, assuming two dimensional (2D) and three dimensional (3D) arrangements. A comparison between two different solvent systems showed that the stress transfer of nanocomposites prepared using NaOH/urea is lower than samples prepared using LiCl/DMAc due to the thermal sensitivity of NaOH/urea solvent system. In this study, the N,N-dimethyl acetamide (DMAc) containing LiCl was used as the main solvent system due to the dissolution process is well controllable. Raman band located at 1095 cm-1 and 895 cm-1 related to the reinforcing phase and matrix material have been monitored during deformation. It is shown that Raman spectroscopy can be used to discriminate the matrix-fibre interactions in all-cellulose nanocomposites. By wetting the nanocomposite samples, it was shown that three interactions can be "switched off"; namely whisker-matrix interfaces, interactions between whiskers and interactions within the cellulose matrix. Disabling these interactions leads to the lack of stress-transfer within the composite. By drawing in wet conditions and subsequent drying, preferred orientation was introduced into the all-cellulose nanocomposite films. The effect of a 1.2 T magnetic field on the orientation of cellulose whiskers was also investigated. The presence of a magnetic field during the curing process of the nanocomposites has been shown to induce partial orientation of the whiskers.

Date of Award	1 Aug 2013
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Stephen Eichhorn (Supervisor)