Nuclear magnetic resonance investigation of water accessibility in cellulose of pretreated sugarcane bagasse

Biotechnology for Biofuels

Tito José Bonagamba³  Igor Polikarpov³  Marcel Nogueira d’Eurydice¹  Marisa Aparecida Lima³  Rodrigo de Oliveira-Silva³  Camila Alves Rezende³  Jefferson Esquina Tsuchida² 

[1]Current Address: School of Petroleum Engineering, University of New South Wales, Building H6, Tyree Energy Technologies Building, Sydney 2052, NSW, Australia

[2]Current Address: Departamento de Engenharia de Materiais, Universidade Federal de São Carlos, Laboratório de Materiais Vítreos, Rod. Washington Luis, km 235, São Carlos, SP, Brazil

[3]Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, CEP 13560-970, SP, Brazil

关键词: Scanning electron microscopy;    Solid-state NMR;    Chemical composition;    Alkali pretreatment;    Acid pretreatment;    Bioethanol;    Sugarcane bagasse;   

Others  :  1084546
DOI  :  10.1186/s13068-014-0127-5

 received in 2014-03-17, accepted in 2014-08-19,  发布年份 2014

【 摘 要 】

Background

Enzymatic hydrolysis is a crucial step of biomass conversion into biofuels and different pretreatments have been proposed to improve the process efficiency. Amongst the various factors affecting hydrolysis yields of biomass samples, porosity and water accessibility stand out due to their intimate relation with enzymes accessibility to the cellulose and hemicellulose fractions of the biomass. In this work, sugarcane bagasse was subjected to acid and alkali pretreatments. The changes in the total surface area, hydrophilicity, porosity and water accessibility of cellulose were investigated by scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR).

Results

Changes in chemical and physical properties of the samples, caused by the partial removal of hemicellulose and lignin, led to the increase in porosity of the cell walls and unwinding of the cellulose bundles, as observed by SEM. ¹H NMR relaxation data revealed the existence of water molecules occupying the cores of wide and narrow vessels as well as the cell wall internal structure. Upon drying, the water molecules associated with the structure of the cell wall did not undergo significant dynamical and partial moisture changes, while those located in the cores of wide and narrow vessels kept continuously evaporating until reaching approximately 20% of relative humidity. This indicates that water is first removed from the cores of lumens and, in the dry sample, the only remaining water molecules are those bound to the cell walls. The stronger interaction of water with pretreated bagasse is consistent with better enzymes accessibility to cellulose and higher efficiency of the enzymatic hydrolysis.

Conclusions

We were able to identify that sugarcane bagasse modification under acid and basic pretreatments change the water accessibility to different sites of the sample, associated with both bagasse structure (lumens and cell walls) and hydrophilicity (lignin removal). Furthermore, we show that the substrates with increased water accessibility correspond to those with higher hydrolysis yields and that there is a correlation between experimentally NMR-measured transverse relaxation times and the efficiency of enzymatic hydrolysis. This might allow for semiquantitative estimates of the enzymatic hydrolysis efficiency of biomass samples using inexpensive and non-destructive low-field ¹H NMR relaxometry methods.

【 授权许可】

   
2014 Tsuchida et al.; licensee BioMed Central Ltd.

【 图 表 】

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