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

Abstract

BackgroundEnzymatic 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).ResultsChanges 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.ConclusionsWe 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.

Sugarcane Bagasse as an Efficient Biosorbent for Methylene Blue Removal: Kinetics, Isotherms and Thermodynamics

“…Parenchyma cells, which form a soft filling tissue, are roughly separated from the conducting vessels and from the sclerenchyma during the sugarcane milling process. After milling, conducting bundles reinforced by sclerenchyma result in more lignified and resistant sugarcane fibers, while the more fragile tissues constitute the pith residual component [15]. Thus, when observing the SEM micrograph sample of SCB ( Figure 1) it is easy to notice two distinct groups: larger particles, called fibers, and smaller particles, called pith.…”

Multimodal analysis of pretreated biomass species highlights generic markers of lignocellulose recalcitrance

“…Electron tomography can be used to directly assess pores size but requires drying the samples which might induce possible collapsing of the pores [ 13 ]. Low-field nuclear magnetic resonance (NMR) spectroscopy was recently used to study the interactions and retention of water molecules by the plant cell wall constituents in pretreated spruce [ 14 , 15 ] and bagasse samples [ 16 ] showing positive correlation between water accessibility and biomass hydrolysis. The analysis of water molecules microenvironment can also be used to assess biomass porosity in conditions similar to that of saccharification.…”

Biomass‐water interactions correlate to recalcitrance and are intensified by pretreatment: An investigation of water constraint and retention in pretreated spruce using low field NMR and water retention value techniques

“…Time domain spin‐spin ( T 2 ) LFNMR relaxometry techniques have been found useful to characterize water present in biomass. This technique classifies water in various sample types, and relates to both chemical and physical properties of biomass and cellulose . Using LFNMR relaxometry a relationship between water constraint, as expressed by T 2 relaxation times of the solvent, and enzymatic hydrolysis yields of cellulose was found for soluble monosaccharides and for various insoluble cell wall polymers .…”

“…This technique classifies water in various sample types, and relates to both chemical and physical properties of biomass and cellulose. [30][31][32][33][34][35] Using LFNMR relaxometry a relationship between water constraint, as expressed by T 2 relaxation times of the solvent, and enzymatic hydrolysis yields of cellulose was found for soluble monosaccharides 36 and for various insoluble cell wall polymers. 37,38 Based on the research published so far on the interrelations between plant biomass digestibility and water availability, quantification and characterization of the interaction between biomass and water could be a feasible path toward a better understanding of the generic mechanisms underlying biomass recalcitrance.…”