Physico-chemical properties of flax microcrystalline cellulose

Mechanical activation is a simple, fast, cost-effective green technology that has been used for the upgrading and modification of microcrystalline cellulose (MCC). However, there is no information on the effect of short-term grinding on its physicochemical properties, as it is widely used for obtaining MCC powder or smaller particle with a size below 50 µm. Thus, the aim of our work was the investigation of physico-chemical properties of the flax unground and short-term ground MCC. In that study MCC was derived from air-dry flax in the medium ‘‘acetic acid–hydrogen peroxide–water’’ in the presence of 2 wt% sulfuric acid catalyst and then in the dry state it was ground in the laboratory mill for 1, 2 and 5 min. The morphology and composition of mechanically unground and ground MCC samples were analysed by different methods: XRD, XRF, FTIR-ATR, AFM, TGA and DSC. According to the XRD patterns of MCC samples, mechanical activation did not change the crystalline form of cellulose, but obviously, it destroyed the crystal structure of ground MCC, resulting in the increase of amorphization and the decrease of crystallinity index (from 86.2 to 78.2%). The FT-IR spectra also showed that the band corresponded to symmetric CH2 bendings at 1435–1429 cm−1, known as the crystallinity band, decreased with MCC samples grinding. AFM indicated that relief of the surface of original MCC changed by mechanical grinding (from the relief with large and small aggregates to the relief consisted of long-chain cellulose molecules parallel layers).