Choosing the right strategy: cryogrinding vs. ball milling – comparing apples to apples

Abstract

Despite many reports on ball milling (BM) of chitin, the effect of cryomilling of chitin has not yet been reported, even though it is a solventless and environmentally-friendly method for the processing of chitin polymer. In this work, commercially available chitin has been cryoground for up to 96 min and the resulting morphological and chemical changes after cryomilling were monitored and compared with those induced by BM. FE-SEM analysis (1000×) revealed that cryogrinding resulted in size reduction of chitin particles and the size reduction was proportional to cryogrinding time. FTIR followed by PCA analysis revealed the breaking of intra- and intermolecular hydrogen bonds, partial amorphization, and insignificant breaking of glycosidic bonds after up to 48 min of cryogrinding, whereas an increase of cryogrinding time to 96 min resulted in a slightly higher number of broken bonds and highly amorphous material. The crystalline structure analysis demonstrated a decrease of crystallinity from 68 to 58% after 48 min of cryogrinding, and to 51% after 96 min of cryogrinding. No change in the crystallite size was found in the (110) plane, while a ∼15% decrease in crystallite size was determined in plane (020). No changes in the molecular weight were detected, although deacetylation to some extent was determined, contrarily to BM. The thermal stability of the polymer was higher than that of the starting material. Overall, the study highlighted similarities and differences between BM at room temperature and cryomilling, and set a foundation for co-processing of chitin with temperature-labile compounds.