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Noninvasive High-Frequency Acoustic Microscopy for 3D Visualization and Estimation of Hydrolytic Degradation of Lactide and ε-Caprolactone Polymers

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Document pages: 30 pages

Abstract: Monitoring of kinetics of degradation process in polymers is one of the attractive possibilities of applying ultrasound techniques that provide non-destructive imaging of internal microstructure and measurements of elastics properties. In this work biodegradable polymers and copolymers based on L,L-lactide, D,L-lactide and ε-caprolactone were studied at different stages of hydrolysis at 37°C by high-frequency (100 and 200 MHz) ultrasound. Acoustic microscopy technique was developed to reveal changes in internal microstructure and bulk speed of sound in the polymer samples over a hydrolysis period of 25 weeks. Ultrasound imaging provided visualization of amorphous and crystalline phases, internal imperfections, packing density variation and other microstructure features. The acoustic images demonstrate nucleation, growth and changes of internal inhomogeneities in the polymers during the degradation accompanied by the decrease in molecular weight of the polymers. We associate changes of elastic properties (speed of longitudinal and transverse wave) with polymer crystallinity which varies over the hydrolysis process. The results of ultrasound investigations are supplemented by gel permeation chromatography, differential scanning calorimetry and wide-angle X-ray spectroscopy.

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