Elastic Modulus and Stress-Transfer Properties of Tunicate Cellulose Whiskers

Abstract

Experimental deformation micromechanics of natural cellulose fibers using Raman spectroscopy and X-ray diffraction have been widely reported. However, little has been published on the direct measurements of the mechanical properties, and in particular the elastic modulus, of the highly crystalline material in the native state. Here we report on measurements of the elastic modulus of tunicate cellulose using a Raman spectroscopic technique. A dispersed sample of the material is deformed using a four-point bending test, and a shift in a characteristic Raman band (located at 1095 cm(-1)) is used as an indication of the stress in the material. Relatively little intensity change of the Raman band located at 1095 cm(-1) is shown to occur for samples oriented parallel and perpendicular to the polarization direction of the laser, as compared to a highly oriented flax sample. This indicates that the tunicate sample is a two-dimensional in-plane random network of fibers. By use of this result, the Raman shift, and calibrations with strain from other materials, it is shown that the modulus of the material is very high, at about 143 GPa, and a lack of Raman band broadening is thought to be due to the fact that there is pure crystalline deformation occurring without the effect of crystalline/amorphous fractions. A strain sensitivity of the shift in the 1095-cm(-1) Raman peak for this specimen is shown to be -2.4 +/- 0.2 cm(-1)/%. A molecular mechanics approach, using computer simulation and an empirical force field, was used to predict the modulus of a highly oriented chain of the material, and this is found to be 145 GPa, which is in agreement with the experimental data. However, by use of a normal-mode analysis, it is found that a number of modes have positions close to the central positions of the experimental Raman band. One in particular is found to shift at a rate of 2.5 cm(-1)/%, but due to the complex nature of the structure, it is not entirely conclusive that this band is representative of the experimental findings.

Preparation and Characterization of Polyvinyl Alcohol-Based Composite Reinforced with Nanocellulose and Nanosilica

“…However, the tensile strength exhibited very little tendency to increase when the incorporation of nanocellulose exceeded 5 wt%. The same observation has been reported by previous researchers (Bhatnagar and Sain 2005;Sturcova et al 2005;Qua et al 2009;Ibrahim et al 2010). This behavior could be explained by the fact that small amounts of nanofillers allowed the creation of strong hydrogen bonds between nanocellulose and PVA, which contributed to good dispersion of nanofillers in the PVA matrix and resulted in superior load transfer from the matrix to the nanocellulose and nanosilica reinforcements.…”

Stress-Transfer in Anisotropic and Environmentally Adaptive Cellulose Whisker Nanocomposites

“…18 The observed rate shift (with respect to % strain) of the Raman band located initially at 1095 cm -1 was -2.4 cm -1 % -1 . 18 This value, through comparison to the rate shifts of other cellulose fibers, was interpreted to indicate efficient stress-transfer between whiskers and whiskers and the glassy matrix material. 18 By interpolation of this shift rate, the modulus of the tunicate whiskers was estimated to be about 143 GPa.…”

“…18 This value, through comparison to the rate shifts of other cellulose fibers, was interpreted to indicate efficient stress-transfer between whiskers and whiskers and the glassy matrix material. 18 By interpolation of this shift rate, the modulus of the tunicate whiskers was estimated to be about 143 GPa. 18 This value is in close agreement with a recent measurement of the bending stiffness of tunicate cellulose whiskers, obtained using an AFM (atomic force microscope) technique.…”

“…18 By interpolation of this shift rate, the modulus of the tunicate whiskers was estimated to be about 143 GPa. 18 This value is in close agreement with a recent measurement of the bending stiffness of tunicate cellulose whiskers, obtained using an AFM (atomic force microscope) technique. 19 Values of 145 ( 31 and 151 ( 29 GPa were determined for tunicate whiskers whose surface was modified by oxidation with 2,2,6,6-tetramethylpiperiditie-1-oxyl radical (TEMPO) and acid-hydrolyzed tunicate whiskers, respectively.…”

Cellulose Nanocrystals as Advanced "Green" Materials for Biological and Biomedical Engineering

“…Tunicate cellulose microfibrils are similar to what is found in plant cell walls, and predominantly contain I β allomorph. Tunicates cellulose displays an ultra-fine fibrous network with a very large aspect ratio, ranging from 3 to 67, (Peng et al, 2011), highly specific surface area fluctuating between 150 to 170 m 2 /g, high crystallinity (95%), low density, and high mechanical strength and reactive surfaces (Sturcova et al, 2005;. The vastness of our marine ecosystem gives us promising reservoir for various kinds and amount of Tunicates CNCs, making them promising candidates for the production of cellulose nanocrystals for several innovative applications.…”