A multitechnique approach to assess the effect of ball milling on cellulose

This paper presents a detailed analysis of effect induced by a dry ball milling process on cellulose structure, morphology and properties. The partial amorphization of cellulose was qualitatively estimated by ATR-FTIR analysis. Through WAXD analysis the crystallinity index and the mean size of the cellulose crystallite domains were calculated, both these parameters showing a progressive decrease as a function of the milling time. In particular, crystallinity index decreased from 0.53 to 0.15 after 60min ball milling, whereas the mean size of the cellulose crystallite domains showed a reduction from the original value of about 4.0nm up to about 3.4nm after 30min. These quantitative results were confirmed by ¹³C CP-MAS NMR analysis and measurements of the proton spin-lattice relaxation time in the rotating frame (T_1ρ^1H). Moreover, the increasing of the amount of water absorbed by cellulose samples (from 7.3wt% for untreated cellulose up to 11.6wt% for the cellulose sample ball milled for 60min) and the reduction of the thermal stability were evaluated by TGA. Finally, SEM analysis revealed that the original fibrous structure almost disappeared and was modified to a quasi-circular shape.