Lytic Polysaccharide Monooxygenase-Assisted Preparation of Oxidized-Cellulose Nanocrystals with a High Carboxyl Content from the Tunic of Marine Invertebrate Ciona intestinalis

Anthi Karnaouri,Wolfgang Maus-Friedrichs,Leonidas Matsakas,Blanca Jalvo,Paul Christakopoulos,Oliver Höfft,Ulrika Rova,Georgia Sourkouni,Aji P. Mathew,Philipp Moritz

doi:10.1021/acssuschemeng.0c05036

Abstract

The tunicate species Ciona intestinalis is a fast-growing marine invertebrate animal that contains cellulose in its outer part—the tunic. The high crystallinity and microfibril aspect ratio of tunicate cellulose make it an excellent starting material for the isolation of nanocellulose. In the present work, tunic from C. intestinalis was subjected to organosolv pretreatment followed by bleaching and acid-hydrolysis steps for the isolation of nanocrystals. Applying an intermediate enzymatic treatment step with a lytic polysaccharide monooxygenase (LPMO) from the thermophilic fungus Thermothelomyces thermophila was proved to facilitate the isolation of nanocellulose and to improve the overall process yield, even when the bleaching step was omitted. LPMOs are able to oxidatively cleave the glycosidic bonds of a polysaccharide substrate, either at the C1 and/or C4 position, with the former leading to introduction of carboxylate moieties. X-ray photoelectron spectroscopy analysis showed a significant increase in the atomic percentage of the C═O/O–C–O and O–C═O bonds upon the addition of LPMO, while the obtained nanocrystals exhibited higher thermal stability compared to the untreated ones. Moreover, an enzymatic post-treatment with LPMOs was performed to additionally functionalize the cellulose nanocrystals. Our results demonstrate that LPMOs are promising candidates for the enzymatic modification of cellulose fibers, including the preparation of oxidized-nanocellulose, and offer great perspectives for the production of novel biobased nanomaterials.

Highlights

The decrease of oil-based resources prompts the use of biomass as a feedstock to produce renewable materials, which are expected to be environmentally friendly and offer improved properties, such as biodegradability and enhanced biocompatibility
These methods included: (i) an initial OS pretreatment method, by employing a low-toxic aqueous ethanol solution, which has been previously reported to be very efficient for the fractionation of tunic and the removal of proteins and lipids[33] and (ii) an additional enzymatic treatment with lytic polysaccharide monooxygenase (LPMO) that has been demonstrated to promote fibrillation and facilitate the isolation of cellulose nanofibrils from other feedstocks, such as cotton linters,[34] birchwood Kraft pulp,[27] and spruce biomass.[28]
The results show selective recovery of cellulose in the solids and solubilization of protein and ash, which underline the suitability of this process as an initial step for the isolation of Tunicin nanocrystals (TNCs)

Summary

Introduction

The decrease of oil-based resources prompts the use of biomass as a feedstock to produce renewable materials, which are expected to be environmentally friendly and offer improved properties, such as biodegradability and enhanced biocompatibility. Cellulose is a natural renewable, biodegradable, and biocompatible polymer with abundant availability, which makes it a very promising substrate for numerous applications. Cellulose nanofibrils and cellulose nanocrystals (CNCs), each one with distinct properties regarding their shape, size, and morphology.[1] Both these nanoparticles have found application in various fields, including polymer reinforcement, production of antimicrobial and medical materials, biosensors, hydrogels, drilling fluids, and drug delivery systems.[2−4] Cellulose nanofibrils are processed by mechanical treatment, including homogenization or grinding with or without other pretreatment steps that provide lateral cleavage of cellulose fibers into nanofibrils with diameters less than 10 nm and lengths in the micron scale.[5] The isolation of cellulose into highly crystalline nanoscale materials, namely, CNCs, requires chemical treatments such as acid hydrolysis to remove the amorphous regions in the cellulose chains and yield fibrils that typically have diameter < 10 nm and lengths in the nanometer range, for example, 150−300 nm for wood-based nanocrystals.[6]. The isolation of cellulose into CNCs has become a major research focus because of their attractive combinations of physicochemical characteristics, such as high crystallinity and good processability, as well as high specific strength and modulus, biocompatibility, and biodegradability, among others.[5,7] The dimensions and the crystallinity of these nanocrystals depend on the origin of the cellulose fibers as well as the procedure employed to obtain them because variations in the CNC extraction process lead mainly to Received: July 9, 2020 Revised: November 11, 2020 Published: December 8, 2020

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Conclusion