The influence of pre-fibrillation via planetary ball milling on the extraction and properties of chitin nanofibers

A planetary ball milling was applied as a pretreatment of chitin powder to prepare precursors for chitin nanofiber (ChNF) production. The study aims to examine the effects of ball milling conditions (dry milling, and wet milling in neutral and acidic aqueous medium) on the degree of pre-fibrillation of the ChNF precursors and the characteristics of the resulting nanofibers. The results showed that no fibrous-morphology ChNFs were obtained using dry ball milling followed by high-pressure homogenization (HPH), but fibrous-morphology ChNFs were successfully prepared using wet ball milling as a pretreatment. Ball milling in a mildly acidic aqueous medium was found to most effectively pre-fibrillate chitin, thus facilitating fibrillation in the subsequent HPH treatment to generate the finest ChNFs with an average diameter of around 12 nm and the narrowest size distribution. The resultant chitin products from wet milling pretreatment exhibited much higher crystallinity and thermal stability than those from dry milling. The results suggest that pre-fibrillation of chitin via ball milling in this study plays a crucial role in the successful procuration of the ChNFs in a subsequent mechanical disintegration process, while wet ball milling, especially under mildly acidic conditions, is a promising green approach to produce efficient precursors for ChNF production.