Influence of Planetary Ball Milling Pretreatment on Lignocellulose Structure

Ball milling mechanochemical pretreatment stands out as it can be used for biomass processing without the use of chemicals. This pretreatment is recognized to alter the organization of the biomass components and to reduce the degree of crystallinity of cellulose structure. In this context, the study of characterization techniques that identify and quantify post-pretreatment alterations still deserves attention. In this study, the alterations caused by dry grinding in a planetary ball milling in sugarcane bagasse, Tectona grandis, and Eucalyptus saligna biomass were evaluated by C-13 solid-state nuclear magnetic resonance (ssNMR). The biomasses were pretreated for 60, 150, and 180 min and enzymatically hydrolyzed. Saccharification results, at optimal conditions, were correlated to the cellulose crystallinity reduction, which was assessed by examining the relative C4 and C6 crystalline and amorphous areas using C-13 CPMAS NMR. The cellulose crystallinity index (CI) measured through the C4 relative area in the NMR spectra decreased with the increase of glucose yield: CI from 33 to 15 (yield from 18 to 82%) for sugarcane bagasse, from 41 to 22 (yield from 4 to 87%) for Tectona, and from 41 to 26 (yield 2 to 80%) for Eucalyptus. The lignin phase, measured by the syringyl/guaiacyl ratio, and acetyl groups linked to the hemicellulose phase seem not to be affected by the pretreatment. This study reports the first-ever ball milling and saccharification and C-13 CPMAS spectrum of Tectona grandis. C-13 ssNMR proved to be a reference method for probing the deconstruction process promoted by mechanochemical pretreatment in plant biomass.

Automated summary

Ball milling mechanochemical pretreatment is a chemical-free method for biomass processing, which can alter the organization of biomass components and reduce cellulose crystallinity. This study evaluated the effects of ball milling on sugarcane bagasse, Tectona grandis, and Eucalyptus saligna biomass. The results showed that ball milling decreased cellulose crystallinity and increased glucose yield.