Effect of Grinding Conditions on Radical Formation Following Structural Change of Amino Acid Particles

Functional materials have been applied in various fields such as pharmaceutical, cosmetics and foods. Mechanochemical process via grinding has been used as a promising method to create functional materials. However, the mechanism of mechanochemistry is too complex to comprehend completely despite utilizing in a practical way, because mechanochemical reaction comes concurrently with fine particle, amorphization and radical formation. It is necessary to understand the effect of milling process on both the structural change and radical formation to design the composite functional materials. The characteristics such as size reduction and structural change of alanine particles by dry-grinding process were examined from the relationship between degree of activation and operating conditions. Morphology of alanine particles were evaluated using scanning electron microscope. Crystallinity of alanine particles were determined by X-Ray Diffraction and differential scanning calorimeter. Change of radical strength was investigated by means of electron spin resonance. Size reduction of alanine particles was affected significantly by the rotation speed ; values over 400 rpm produced agglomerated particles. The amorphization of alanine particles progressed with increasing the rotation speed. The radicals of alanine particles dry-milled by grinding were formed in the low speed range.