A new approach to obtain cellulose nanocrystals and ethanol from eucalyptus cellulose pulp via the biochemical pathway

Abstract

The feasibility of integration of cellulosic ethanol production with the manufacture of cellulose nanofibers (CNF) and cellulose nanocrystals (CNC) was evaluated using eucalyptus cellulose pulp as feedstock and employing the biochemical route alone. For the enzymatic hydrolysis step, experimental central composite design (CCD) methodology was used as a tool to evaluate the effects of solids loading (SL) and enzymatic loading (EL) on glucose release and cellulose conversion. Glucose concentrations from 45 to 125 g/L were obtained after 24 h, with cellulose conversions from 35 to 96%. Validation of the statistical model was performed at SL of 20% and EL of 10 mg protein/g, which was defined by the desirability function as the optimum condition. The sugars released were used for the production of ethanol by Saccharomyces cerevisiae, resulting in 62.1 g/L ethanol after 8 h (yield of 95.5%). For all the CCD experimental conditions, the residual solids presented CNF characteristics. Moreover, the use of a new strategy with temperature reduction from 50 to 35°C after 24 h of enzymatic hydrolysis enabled CNC to be obtained after 144 h. The CNC showed a crystallinity index of 83%, length of 260 nm, diameter of 15 nm, and aspect ratio (L/D) of 15. These characteristics are suitable for many applications, such as reinforcement in polymeric materials and other lower volume higher value bio-based products. The findings indicate the viability of obtaining ethanol and CNC using the biochemical route exclusively, potentially contributing to the future implementation of forest biorefineries. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:1085-1095, 2017.

Nanocellulose Production: Exploring the Enzymatic Route and Residues of Pulp and Paper Industry

“…In the particular case of CNFs production, the enzymatic hydrolysis is commonly followed by a mechanical step of fibrillation, such as homogenization [ 38 , 44 ], microfluidization [ 49 , 50 ], extrusion [ 25 , 51 ], and sonication [ 27 , 52 ], among others. Few studies have also reported no mechanical treatment step after hydrolysis [ 12 , 53 , 54 , 55 ], hence totally relying on the enzymes to produce the nanofibers.…”

“…A final aspect to also consider is that enzymatic extraction does not modify the surface chemistry of cellulose since no additional charges are introduced [ 103 ], usually resulting in a material with higher thermal stability [ 47 , 54 , 121 ]. As compared to sulfuric acid hydrolysis, this represents a clear advantage since the presence of sulfur groups leads to a negative surface charge [ 122 ].…”

“…Thermal stability is an important property for NC since the processing temperatures of most composite materials are usually above 200 °C [ 43 , 54 ]. Cellulosic materials degrade below 400 °C (generally decomposition starts at 310 °C and persists until 400 °C) [ 53 ], with the degradation temperature dependent on the structure and chemical composition [ 126 ].…”

“…On the other hand, Chen et al [ 64 ] produced rod-like and spherical CNCs, according to the enzyme load, and reported similar thermal stability (Tonset at ~205 °C and Tmax at ~345 °C). Furthermore, Bondancia and co-authors [ 54 ] reported that CNFs and CNCs obtained by enzymatic hydrolysis presented superior thermal stability compared to materials obtained by means of chemical hydrolysis reactions. They reported degradation of cellulose pulp at 331 °C, CNFs (24 h) at 323 °C, and CNCs (144 h) at 325 °C.…”

Nanocellulose nanocomposite hydrogels: technological and environmental issues

“…43 To avoid these problems, many researchers have studied alternative processes to obtain CNCs. Among them, we can highlight enzymatic hydrolysis, 44,45 enzymatic hydrolysis followed by acid hydrolysis, 46 ultrasonically assisted hydrolysis without 47 and with weak organic acids, 48 hydrolysis with oxidizing agents, 49 hydrolysis in subcritical water 50 and hydrolysis mediated by ionic liquids. 51…”