Structure and characteristics of milled silk particles

• First analysis of the structure of nano size silk particles made by milling.
• Amorphous content of silk particles reduces during particle size reduction.
• 200 nm silk particles have dominant β sheet structures similar to silk fibre.

This study examined the structure, thermal property, and ion adsorption of silk particles. The particles were prepared by attritor–bead mill combination, using alkaline (pH 10) charge repulsion and surfactant steric repulsion methods. Both methods produced particles with a dominant β-sheet structure, similar to the silk fibre. There was no significant difference in the decomposition temperatures for either the silk fibre or the micro/nano silk particles. An important finding from this study is clear evidence of reduction of amorphous content during the final stage of powdering using the bead mill. As a result, despite reduction in β-sheet crystallites with the progressive milling, the relative β-sheet content actually increased during this process. However, intermolecular forces between the β-sheets reduced significantly and hence the XRD results showed significant reduction in crystallinity in nano silk particles but crystal forming segments remained with β-sheet conformations after milling. The structural change influenced the ion-adsorption property where particle-size reduction resulted in a significant increase in both the rate and volume of HCrO4− adsorption.

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