Characterization of cellulose and TEMPO-oxidized celluloses prepared from Eucalyptus globulus

Eucalyptus (Eucalyptus globulus) cellulose was isolated from wood powder by dewaxing, delignification, and subsequent 4% NaOH extraction. 2,2,6,6-Tetramethyl-piperidine-1-oxyl (TEMPO)-oxidized eucalyptus celluloses were prepared from never-dried eucalyptus cellulose (EC) in yields of 96% and 72% (based on the dry weight of EC) when oxidized with NaOCl of 5 and 10 mmol/g-EC, respectively. Their carboxy contents were 1.4 and 1.8 mmol/g, respectively, when determined by conductivity titration. The crystallinity of cellulose I for EC decreased by TEMPO-mediated oxidation, showing that the originally crystalline region in EC was partly converted to disordered regions by TEMPO-mediated oxidation. Correspondingly, the relative signal area of C6‒OH/C1 with the trans-gauche (tg) conformation attributed to crystalline cellulose I in the solid-state 13C NMR spectrum of EC decreased from 0.42 to 0.34 by TEMPO-mediated oxidation with NaOCl of 10 mmol/g-EC. TEMPO-oxidized EC prepared with NaOCl of 10 mmol/g-EC was almost completely converted into individual TEMPO-oxidized EC nanofibrils (TEMPO-ECNFs) of homogeneous widths of ∼3 nm widths and lengths of >1 μm by mechanical disintegration in water. However, the TEMPO-ECNFs contained many kinks and had uneven surfaces, probably owing to significant damage occurring on the surface cellulose molecules of crystalline cellulose microfibrils during TEMPO-mediated oxidation.

Mechanism and Conformation Changes for the Whole Regeneration Process of Cellulose in Pyridinium-Based Ionic Liquids

In this work, mechanism and conformation changes of cellulose regenerated from ionic liquid by anti-solvents (water, ethanol and acetone) were investigated by molecular simulations. Cellulose model consists of seven glucose single chains were constructed. In order to depict the regeneration mechanism, both the dissolution and regeneration processes of cellulose in [Bpy][OAc] IL were simulated. The methyl hydroxyl group of cellulose will change its conformation during dissolution and regeneration. The conformation of initial cellulose crystal is mainly the tg conformation. After dissolved in ILs, the cellulose conformation changes into the gt conformation and the gg conformation. After regenerated by anti-solvent, the proportion of the gg and gt conformation changes, and the gg conformation increased and the gt conformation decreased. Based on energy analysis, it is concluded that the energy for tg is the lowest, and the tg widely exists in cellulose I. After cellulose is dissolved in ILs, the conformation changes into two higher energy conformations, the gt and gg. In the subsequent regeneration process, with the completion of regeneration, the gg conformation increases and the gt conformation decreases.

Crystalline structure analysis of all-cellulose nanocomposite films based on corn and wheat straws

Cellulose solution and nanocellulose were prepared from corn straw and wheat straw and then used to fabricate an all-cellulose nanocomposites film (ANF). The crystal structure (CS) of ANFs was analyzed by X-ray diffraction (XRD) and Fourier transform infrared spectrometry (FTIR). Cellulose-I and cellulose-II were found to coexist within regenerated cellulose films (RCF) and ANFs. With the change of nanocellulose content, the proportions of cellulose-I and cellulose-II changed. Cellulose transformation was found to depend on the raw material and the preparation method. When cellulose solution was prepared from corn straw that had been extracted, the cellulose type tended to be transformed from cellulose-I to cellulose-II; the proportion of cellulose-I showed a tendency to increase when nanocellulose content exceeded 1.5%. When the dissolved cellulose had been treated by an acid-alkali method, the results did not follow a clear pattern. However, when cellulose solution was prepared from wheat straw, under extraction method, the cellulose type tended to transform from cellulose-I to cellulose-II; under acid-alkali method, cellulose-I did not follow a clear pattern with nanocellulose content. Though the small amount of nanocellulose can’t dominate the content of cellulose-I, it could cause an increase in disorder of the cellulose matrix.

Highly Insulative PEG-Grafted Cellulose Polyurethane Foams—From Synthesis to Application Properties

In this paper, native cellulose I was subjected to alkaline treatment. As a result, cellulose I was transformed to cellulose II and some nanometric particles were formed. Both polymorphic forms of cellulose were modified with poly(ethylene glycol) (PEG) and then used as fillers for polyurethane. Composites were prepared in a one-step process. Cellulosic fillers were characterized in terms of their chemical (Fourier transformation infrared spectroscopy) and supermolecular structure (X-ray diffraction), as well as their particle size. Investigation of composite polyurethane included measurements of density, characteristic processing times of foam formation, compression strength, dimensional stability, water absorption, and thermal conductivity. Much focus was put on the application aspect of the produced insulation polyurethane foams. It was shown that modification of cellulosic filler with poly(ethylene glycol) has a positive influence on formation of polyurethane composites—if modified filler was used, the values of compression strength and density increased, while water sorption and thermal conductivity decreased. Moreover, it was proven that the introduction of cellulosic fillers into the polyurethane matrix does not deteriorate the strength or thermal properties of the foams, and that composites with such fillers have good application potential.

CELLULOSE NANOMATERIALS IN TEXTILE APPLICATIONS

Nanocellulose (NCC) has attracted increasing attention for use in several applications owing to its impressive strength-to-weight ratio, ease of functionalization, and apparent biocompatibility. In the nanocomposite textile field, NCC has exhibited outstanding potential for reinforced fibers, especially fibers processed by solution spinning. Continuous NCC fibers with high modulus and strength can be obtained, while preserving the cellulose I crystal structure. Owing to the various possibilities of surface modification, NCC is an efficient adsorbent of cationic and anionic textile dyes, as it reaches maximum removal capacities comparable to those of commercial adsorbents. In dyeing, NCC contributes in improving dye fixation and reducing the consumption of chemicals and water. In this review, recent studies on the applications of NCC in the textile field are discussed. The main methods, advances and limitations, regarding the NCC applications for fiber reinforcement of water-soluble and insoluble materials, dye removal and textile finishing, are presented.

Terahertz Time-domain Spectroscopy as a Novel Tool for Crystallographic Analysis in Cellulose: Cellulose I to Cellulose Ii, Tracing the Structural Changes Under Chemical Treatment

Terahertz time-domain spectroscopy (THz-TDS) has expanded possibilities in cellulose crystallography research, as THz radiation detects most intermolecular vibrations and responds to the phonons of crystalline lattices. In this study, we traced the transformation of the cellulose crystalline lattice from cellulose I to cellulose II by THz-TDS and X-ray powder diffraction. Cellulose II was obtained by treating cellulose I with NaOH of different concentrations (0 wt%–20 wt%, at 2 wt% intervals). The THz absorption coefficient spectra of cellulose II showed three characteristic peaks (at 1.32 THz, 1.76 THz, and 2.77 THz). The THz absorption coefficient spectra of cellulose II treated with 20-wt% NaOH and cellulose I without NaOH treatment were fitted by a seventh-order Fourier series. Thus, the THz absorption coefficient spectra of samples treated with NaOH of other concentrations could be considered a combination of these two fitted profiles of cellulose I and cellulose II, multiplied by different coefficients. Furthermore, the coefficients could reflect the relative contents of cellulose I and cellulose II in the samples.

Cellulose Nanocrystals Obtained From Microcrystalline Cellulose by p-toluene Sulfonic Acid Hydrolysis, NaOH and Ethylenediamine Treatment

Cellulose nanocrystals (CNC) were first isolated from microcrystalline cellulose (MCC) by p-toluene sulfonic acid (p-TsOH) hydrolysis. Cellulose II nanocrystal (CNC II) and cellulose III nanocrystal (CNC III) were then formed by swelling the obtained cellulose I nanocrystal (CNC I) in concentrated sodium hydroxide solutions and ethylenediamine (EDA) respectively. The properties of CNC I, CNC II and CNC III were subjected to comprehensive characterization by Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The results indicated that CNC I, CNC II and CNC III obtained in this research had high crystallinity index and good thermal stability. The degradation temperatures of the resulted CNC I, CNC II and CNC III were 300 ℃, 275 ℃ and 242 ℃, respectively. No ester bonds were found in the resulted CNC. CNC prepared in this research also had large aspect ratio and high negative zeta potential.

Extraction and Characterization of Cellulose Nanowhiskers from TEMPO Oxidized Sisal Fibers

Cellulose nanowhiskers as one kind of renewable and biocompatible nanomaterials evoke much interest because of its versatility in various applications. Herein, the sisal cellulose nanowhiskers with length of 100–500 nm, ultrathin diameter of 6–61 nm, high crystallinity of 74.74 % and C6 carboxylate groups converted from C6 primary hydroxyls were prepared via a 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)/NaBr/NaClO system selective oxidization combined with mechanical homogenization. The effects of sodium hydroxide concentration in alkali pretreatment on the final sisal cellulose nanowhiskers were explored. It was found that with the increase of sodium hydroxide concentration, the sisal fiber crystalline type would change from cellulose I to cellulose II. The versatile sisal cellulose nanowhiskers would be particularly useful for applications in the nanocomposites as reinforcing phase, as well as in tissue engineering, filtration, pharmaceutical and optical industries as additives.