The morphological changes upon cryomilling of cellulose and concurrent generation of mechanoradicals

Abstract

With mechanical input, chemical bonds in polymers can be broken. Recently, it was shown that reactive ends formed by homolytic cleavage, so-called mechanoradicals, can be used in driving further chemical reactions or in making new composite materials. Cellulose, the most abundant polymer on earth, can also be subjected to mechanical input via ball-milling to produce mechanoradicals. Despite many reports on morphological changes in cellulose upon milling, there is only a limited understanding on how these changes affect the mechanoradical production, i.e., in which domains of cellulose the bonds are broken to produce the mechanoradicals. Here we show, the effect of the initial morphology of cellulose (cotton or microcrystalline cellulose) and the mode of grinding (dry or solvent-assisted) on the amount of generated cellulose mechanoradicals. The morphological and the chemical changes taking place upon milling of cellulose are monitored by SEM, XRD, and ATR, and the number of mechanoradicals is determined by a first-time quantitative analysis of cellulose mechanoradicals using radical scavenger DPPH. Our findings can help in efficient mechanofunctionalization of cellulose and to make useful mechanochemical reactions of cellulose using mechanoradicals, which stand as a promising economic and environment-friendly alternative to the conventional solvent-assisted chemistry of cellulose.