X-ray Tomographic Characterization of Natural Polymer Composites and Correlation of Bulk Mechanical Properties
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1219-AA04-06
X-ray Tomographic Characterization of Natural Polymer Composites and Correlation of Bulk Mechanical Properties Anahita Pakzad1, Paul Mainwaring2, Patricia A. Heiden3, Reza Shahbazian Yassar1 1
Mechanical Engineering- Engineering Mechanics, Michigan Technological University, Houghton, MI 49931, USA 2 Gatan Inc, Pleasanton, CA 94588, USA 3 Chemistry Department, Michigan Technological University, Houghton, MI 49931, USA ABSTRACT In this research, cellulose micro-crystals (CMC) were used to reinforce a bio-polymer, polycaprolactone (PCL). Mechanical properties were tested using nanoindentation. Electron microscopy imaging and a new technique called X-ray ultra microscopy and microtomography (XuM) were used to investigate the distribution of the filler in the matrix. We could demonstrate a clear correlation between the 3D spatial distribution of CMC-PCL composites and their nanomechanical properties. INTRODUCTION Cellulose is the most abundant natural polymer on earth, and is produced and recycled at a rate of 1010 tons/year [1]. It is mostly found as a structural material in plants, but some animals and bacteria also make use of this biopolymer. Because the cellulose chain possesses a large number of hydroxyl groups, it tends to hydrogen bond. This makes it difficult to achieve high quality dispersions, especially in non-polar thermoplastics. This dispersion (the spatial arrangement of the filler and the matrix), along with the properties of individual phases in the composite and their volume ratio, are the main factors that dictate the mechanical properties of the final product. Recently a technique called X-ray ultra microscopy and microtomography (XuM) has been developed [2, 3]. It offers the capability of observing the internal structure of opaque materials at sub-micron scales. In this method, which is hosted in a standard scanning electron microscope (SEM), two dimensional (2D) X-ray images are acquired as the sample is rotated in small angular increments. These projections are computationally combined and a three dimensional (3D) reconstruction of the object is obtained with the possibility of surface rendering and virtual slicing through the volume. In this project, commercially available cellulose microcrystals were dispersed in polycaprolactone (PCL). Mechanical properties such as elastic modulus and hardness of these natural composites were studied using nanoindentation. The surface morphology of these composites were imaged using SEM. Moreover, for the first time their internal distributions were observed using XuM, allowing the 3D structure to be visualized and the dispersion quality of the filler to be correlated to their mechanical properties. EXPERIMENTAL Cellulose composite film preparation: Commercially available cellulose microcrystal (CMC) was used as filler (Sigma Aldrich microcrystalline cellulose, batch #07422A5, with less
than 10 µm diameter). Polycaprolactone (PCL) was used as the matrix to prepare the composite films. All materials were used as bought and four different filler
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