Revealing the 3D internal structure of natural polymer microcomposites using X-ray ultra microtomography.

Properties of composite materials are directly affected by the spatial arrangement of reinforcement and matrix. In this research, partially hydrolysed cellulose microcrystals were used to fabricate polycaprolactone microcomposites. The spatial distribution of cellulose microcrystals was characterized by a newly developed technique of X-ray ultra microscopy and microtomography. The phase and absorption contrast imaging of X-ray ultra microscopy revealed two-dimensional and three-dimensional information on CMC distribution in polymer matrices. The highest contrast and flux (signal-to-noise ratio) were obtained using vanadium foil targets with the accelerating voltage of 30 keV and beam current of >200 nA. The spatial distribution of cellulose microcrystals was correlated to the mechanical properties of the microcomposites. It was observed that heterogeneous distribution and clustering of cellulose microcrystals resulted in degradation of tensile strength and elastic modulus of composites. The utilization of X-ray ultra microscopy can open up new opportunities for composite researchers to explore the internal structure of microcomposites. X-ray ultra microscopy sample preparation is relatively simple in comparison to transmission electron microscopy and the spatial information is gathered at much larger scale.