Search

Developing green and simple methods for the preparation of cellulose nanofibrils (CNFs) is of great significance. Herein, a green deep eutectic solvent (DES) system based on choline chloride (ChCl) and citric acid (CA) is employed to pretreat cellulose fibers for the preparation of CNFs. The effect of the pretreatment temperature on the chemo-physical properties of the CNFs is comprehensively investigated. A high CNFs yield of up to 84.19% can be achieved under optimized conditions. The optimal CNFs show a narrow diameter distribution and length up to several microns, high crystallinity and thermal stability, as well as excellent dispersibility in water. Furthermore, semi-transparent and flexible cellulose nanopaper (CNP) was fabricated through a facile vacuum filtration process. The optimal CNP shows high tensile strength (175.15 MPa) and toughness (7.51 MJ/m 3 ). Therefore, this work provides a sustainable and facile approach to fabricate CNFs and CNP, which can be potentially used for various high-tech applications., (Copyright © 2021. Published by Elsevier Ltd.)

Composite films of xylan and polyvinyl alcohol were produced with citric acid as a new plasticizer or a cross-linking agent. The effects of citric acid content and polyvinyl alcohol/xylan weight ratio on the mechanical properties, thermal stability, solubility, degree of swelling and water vapor permeability of the composite films were investigated. The intermolecular interactions and morphology of composite films were characterized by FTIR spectroscopy and SEM. The results indicated that polyvinyl alcohol/xylan composite films had good compatibility. With an increase in citric acid content from 10% to 50%, the tensile strength reduced from 35.1 to 11.6 MPa. However, the elongation at break increased sharply from 15.1% to 249.5%. The values of water vapor permeability ranged from 2.35 to 2.95 × 10(-7)g/(mm(2)h). Interactions between xylan and polyvinyl alcohol in the presence of citric acid become stronger, which were caused by hydrogen bond and ester bond formation among the components during film forming., (Copyright © 2013. Published by Elsevier Ltd.)

Many plant species excrete organic acids into the rhizosphere in response to aluminum stress to protect sensitive cells from aluminum rhizotoxicity. When the roots of Eucalyptus camaldulensis, a major source of pulp production, were incubated in aluminum-toxic medium, citrate released into the solution increased as a function of time. Citrate excretion was inducible by aluminum, but not by copper or sodium chloride stresses. This indicated that citrate is the major responsive organic acid released from the roots of this plant species to protect the root tips from aluminum damage. Four genes highly homologs to known citrate-transporting multidrugs and toxic compounds exclusion proteins, named EcMATE1-4, were isolated using polymerase chain reaction-based cloning techniques. Their predicted proteins included 12 membrane spanning domains, a common structural feature of citrate-transporting MATE proteins, and consisted of 502-579 amino acids with >60 % homology to orthologous genes in other plant species. One of the homologs, designated EcMATE1, was expressed in the roots more abundantly than in the shoots and in response to both Al and low pH stresses. Ectopic expression of EcMATE1 and 3 in tobacco hairy roots enhanced Al-responsive citrate excretion. Pharmacological characterization indicated that Al-responsive citrate excretion involved a protein phosphorylation/dephosphorylation process. These results indicate that citrate excretion through citrate-transporting multidrugs and toxic compounds exclusion proteins is one of the important aluminum-tolerance mechanisms in Eucalyptus camaldulensis.