Applications of FT Raman Spectroscopy and Micro Spectroscopy Characterizing Cellulose and Cellulosic Biomaterials

FT Raman spectroscopy and micro spectroscopy were used for the investigation of cellulose, cellulose derivatives and cellulosic plant fibres. Lattice structures of cellulose, polymorphic modifications I and II, as well as amorphous structure, were clearly identified by means of FT Raman vibrational spectra. Chemometric models were developed utilizing univariate calibration as well as methods of multivariate data analyses of FT Raman spectral data for the fast prediction of cellulose properties. Cellulose properties like the degree of crystallinity Xc_Raman, the degree of substitution DS_CMC, DS_AC and cellulose reactivity were determined. In situ/ in vivo FT Raman micro spectroscopy was used for the characterization of cellulose structures of flax and hemp fibres. Orientational and stress dependent FT Raman experiments were carried out.     

Some further observations on the systems cellulose/trifluoroacetic acid/CH2Cl2 and cellulose triacetate/TFA/CH2Cl2

There is little or no trifluoroacetylation of cellulose dissolved in TFA-CH₂Cl₂ admixtures. Both cellulose and cellulose triacetate (CTA)are slowly degraded in the solvent. Cellulose forms a mesophase as low as 4%(w/w)concentration, but CTA has a much higher critical concentration, 20% (w/w), in TFA-CH₂Cl₂. The cellulose behaves as a rigid rod in TFA-CH₂Cl₂ (70/30v/v) and its persistence length calculated using the lattice model approximates its chain length, presumably due to extensive interaction with the solvent. As expected, due to low polymer-solvent interactions, the persistence length of CTA in TFA-CH₂Cl₂ is only one-fourth the chain length.     

Unique structural characteristics of nematic ordered cellulose—Stability in water and its facile transformation

Nematic Ordered Cellulose (NOC) film that exhibits a noncrystalline yet highly ordered form was prepared by stretching a water‐swollen cellulose gel obtained in a unique manner with coagulation of cellulose molecules dissolved in the N,N‐dimethylacetamide/LiCl solvent system. In this article, structural characteristics of this unique film were investigated. Orientation of the molecular chains in the noncrystalline regions across the entire film were stable after immersing in water at room temperature, though conventional amorphous cellulose regions are in any forms believed fairly to be recrystallized under a humid atmosphere. Even 30 days after immersing in water at 50 °C, neither crystallization nor disordering of the chains occurred in the NOC film. On the contrary, the film was capable of being transformed into films composed of cellulose polymorphs domains where the molecular orientation was still maintained as the initial film under various mild conditions that both cotton and cellophane did not show any changes on their structure. These contradictory properties of the NOC film proved to be dependent on its unique supermolecular structure. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2850–2859, 2007     

An Efficient and Environmentally Friendly Method for the Synthesis of Cellulose Carbamate by Microwave Heating

An efficient, solvent‐free, and catalyst‐free microwave synthesis of cellulose carbamate from a mixture of native cellulose and urea is reported. The structure of the samples are characterized by elemental analysis, FT‐IR spectroscopy, X‐ray diffraction, and NMR spectrometry. Cellulose carbamates with a nitrogen content of 0.651–2.427% are obtained by microwave heating at 255 W for 2–5 min. With the introduction of carbamate groups, the hydrogen bonding and crystalline structure of the native cellulose are partially destroyed. The products retain the cellulose I crystalline form of the native cellulose, and display good solubility in NaOH solutions.

     

Phase transformations in microcrystalline cellulose due to partial dissolution

All-cellulose composites were prepared by partly dissolving microcrystalline cellulose (MCC) in an 8.0 wt% LiCl/DMAc solution, then regenerating the dissolved portion. Wide-angle X-ray scattering (WAXS) and solid-state ¹³C NMR spectra were used to characterize molecular packing. The MCC was transformed to relatively slender crystallites of cellulose I in a matrix of paracrystalline and amorphous cellulose. Paracrystalline cellulose was distinguished from amorphous cellulose by a displaced and relatively narrow WAXS peak, by a 4 ppm displacement of the C-4 ¹³C NMR peak, and by values of T₂(H) closer to those for crystalline cellulose than disordered polysaccharides. Cellulose II was not formed in any of the composites studied. The ratio of cellulose to solvent was varied, with greatest consequent transformation observed for c < 15%, where c is the weight of cellulose expressed as % of the total weight of cellulose, LiCl and DMAc. The dissolution time was varied between 1 h and 48 h, with only small additional changes achieved by extension beyond 4 h.     

Rheological Behaviors in the Regimes from Dilute to Concentrated in Cellulose Solutions Dissolved at Low Temperature

Cellulose was dissolved rapidly in 9.5 wt.‐% NaOH/4.5 wt.‐% thiourea aqueous solution pre‐cooled to ?5 °C to prepare cellulose solution with different concentrations. The rheological properties of the cellulose solutions in wide concentration regimes from dilute (0.008 wt.‐%) to concentrated (4.0 wt.‐%) at 25 °C were investigated. On the basis of data from the steady‐shear flow test, the critical overlap (c*), the entanglement (c_e) and the gel (c_g) concentrations of the cellulose solution at 25 °C were determined, respectively, to be 0.10 wt.‐%, 0.53 wt.‐% and 2.50 wt.‐%, in accordance with the results of storage modulus (G′) versus c by dynamic test. Moreover, the Cox‐Merz deviation at relatively low concentrations was in good agreement with the micro‐gel particles in dilute regime. As the cellulose concentration increased, a homogeneous 3‐dimensional network formed in the cellulose solution in the concentrated regime, and further increasing of the concentration led to micro‐phase separation as determined by the time‐temperature superposition (tTS). So far, this complex cellulose solution has been successfully described by the concentration regime theory for the first time, and the relatively molecular morphologies in each regime have been determined, providing useful information for the applications of the cellulose solution systems.

     

Dilute solution properties of cellulose in LiOH/urea aqueous system

Cellulose was dissolved rapidly in 4.6 wt % LiOH/15 wt % urea aqueous solution and precooled to –10 °C to create a colorless transparent solution. ¹³C‐NMR spectrum proved that it is a direct solvent for cellulose rather than a derivative aqueous solution system. The result from transmission electron microscope showed a good dispersion of the cellulose molecules in the dilute solution at molecular level. Weight‐average molecular weight (M_w), root mean square radius of gyration (〈s²〉_z^1/2), and intrinsic viscosity ([η]) of cellulose in LiOH/urea aqueous solution were examined with laser light scattering and viscometry. The Mark–Houwink equation for cellulose in 4.6 wt % LiOH/15 wt % urea aqueous solution was established to be [η] = 3.72 × 10^?2 M in the M_w region from 2.7 × 10⁴ to 4.12 × 10⁵. The persistence length (q), molar mass per unit contour length (M_L), and characteristic ratio (C_∞) of cellulose in the dilute solution were given as 6.1 nm, 358 nm^?1, and 20.8, respectively. The experimental data of the molecular parameters of cellulose agreed with the Yamakawa–Fujii theory of the worm‐like chain, indicating that the LiOH/urea aqueous solution was a desirable solvent system of cellulose. The results revealed that the cellulose exists as semistiff‐chains in the LiOH/urea aqueous solution. The cellulose solution was stable during measurement and storage stage. This work provided a new colorless, easy‐to‐prepare, and nontoxic solvent system that can be used with facilities to investigate the chain conformation and molecular weight of cellulose. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3093–3101, 2006     

Caracterisation par analyse thermique de la lignine,de la cellulose et de quelques uns de ses derives etherifies

Cellulose and its derivatives (methyl cellulose, sodium carboxymethyl cellulose, hydroxymethyl cellulose and hydroxypropyl cellulose) used as excipients in pharmaceutical industry can be characterised by simultaneous thermoanalytical (DTA and TG) methods, based on the temperatures of exothermic peaks. Lignine cellulose can be identified by taking into account the difference in temperature between the first exothermic DTA peak and the corresponding DTG peak.

     

Effect of Sulfation Route and Subsequent Oxidation on Derivatization Degree and Biocompatibility of Cellulose Sulfates

Sulfated cellulose (CS) represents an interesting biopolymer due to bioactivity comparable to heparin. However, use of CS for making surface coatings or hydrogels requires the presence of reactive groups for covalent reactions. Here, an approach is presented to oxidize cellulose sulfates for subsequent cross‐linking reactions with amino groups to form imine bonds. Cellulose is sulfated by direct sulfation or acetosulfation, followed by a M alaprade oxidation. The CS obtained is characterized by elemental analysis and ¹³C‐NMR spectroscopy. The resulting oxidized cellulose sulfates (oxCS) have different degrees of sulfation ranging from 0.79 to 1.13 and oxidation degrees from 0.18 to 0.34, but also different mass average molecular mass (M_W). Toxicity studies are carried out with mouse 3T3 fibroblasts exposed to aqueous solutions of oxCS. The results show that all oxCS are non‐toxic at lower concentrations (0.5 mg mL^?1), but with both increasing degree of oxidation and concentrations, toxic effects are observed particularly for acetosulfated and lesser for direct sulfated oxCS, which is related to a decrease in the M_W of the products. It is concluded that oxCS obtained by direct sulfation with M_W above 70 kDa may represent a biocompatible material for the applications suggested above.     

The Reductive Dehydration of Cellulose by Solid/Gas Reaction with TiCl4 at Low Temperature: A Cheap,Simple, and Green Process for Preparing Anatase Nanoplates and TiO2/C Composites

Metal oxides and metal oxide/carbon composites are entering the development of new technologies and should therefore to be prepared by sustainable chemistry processes. Therefore, a new aspect of the reactivity of cellulose is presented through its solid/gas reaction with vapour of titanium(IV) chloride in anhydrous conditions at low temperature (80 °C). This reaction leads to two transformations both for cellulose and titanium(IV) chloride. A reductive dehydration of cellulose is seen at the lowest temperature ever reported and results in the formation of a carbonaceous fibrous solid as the only carbon‐containing product. Simultaneously, the in situ generation of water leads to the formation of titanium dioxide with an unexpected nanoplate morphology (ca. 50 nm thickness) and a high photocatalytic activity. We present the evidence showing the evolution of the cellulose and the TiO₂ nanostructure formation, along with its photocatalytic activity. This low‐temperature process avoids any other reagents and is among the greenest processes for the preparation of anatase and also for TiO₂/carbon composites. The anisotropic morphology of TiO₂ questions the role of the cellulose on the growing process of these nanoparticles.     

The role of hydroxyl groups in interchain interactions in cellulose Iα and Iβ

Complex networks of hydrogen bonds within the cellulose I_α and I_β contribute greatly to cellulose's anisotropic physical properties such as material stiffness. The interchain hydrogen bonding interactions through hydroxyl groups are isolated in each of the three lattice planes of the adjacent chains within the unit cell of two allomorphs of natural cellulose. In our density function theory study with dispersion corrected Perdew–Burke–Ernzerhof (PBE‐D2) functional, these hydroxyl groups participate in strong hydrogen bonding interactions (?24.8 and ?24.8 kcal/mol for cellulose I_α and I_β, respectively) in the side‐to‐side lattice plane. Unexpectedly, the hydroxyl groups also participate significantly in hydrogen bonding interactions (?11.0 and ?12.4 kcal/mol for cellulose I_α and I_β, respectively) in one of the diagonal lattice planes in both cellulose I_α and I_β. Both PM7 and PBE‐D2 method predict that the overall interaction is asymmetric and stronger in the right diagonal lattice plane. While hydrogen bonding interactions are strongest in side‐to‐side lattice plane as expected, the role of hydrogen bonding interactions for keeping the sheet together is more significant than previously thought.     

Novel cellulose derivatives. V. Synthesis and thermal properties of esters with trifluoroethoxy acetic acid

Esters of cellulose with trifluoroethoxy acetic acid (TFAA) were prepared in homogeneous phase using a mixed anhydride with p‐toluenesulfonic acid. Esters with low degree of substitution (DS), and with DS rising from 0 to 3, had hydrophobic character that prevented the usual association with moisture, which is otherwise typical of cellulose esters with low DS. Cellulose trifluoroethoxy acetate (CT) had T_g's declining by about 40 °C per DS‐unit (from 160 to 41 °C) as DS rose from 1 to 3. Mixed esters, cellulose derivatives with acetate and trifluoroethoxy acetate substituents (CAT), exhibited glass‐to‐rubber and melting transitions by DSC. A linear relationship between both T_g and T_m with respect to DS was recorded with the T_g and T_m separated by 30° to 40 °C. This is consistent with cellulose esters described elsewhere. Surprisingly, the T_g's of CT and CAT were found to be identical when the DS was equivalent to the DS of the fluoro substituents (DS_F). © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 486–494, 2000     

纤维素及其衍生物的高压静电纺丝

高压静电纺丝作为一种制备纳米纤维的先进技术,近年来受到普遍关注。而纤维素和纤维素衍生物由于其优越的性质已应用于各个领域。运用高压静电纺丝技术对纤维素及其衍生物进行研究,开拓了新的研究领域和发展方向。本文介绍了高压静电纺丝技术的研究背景和原理,总结了近几年研究者们在纤维素以及纤维素衍生物高压静电纺丝方面的工作进展,尤其对不同溶剂体系溶解纤维素用于静电纺丝的优缺点进行了比较,评述了这方面的前沿性探索研究,并对未来的发展进行了展望。     

Preparation and Characterization of Nanocomposites of Carboxymethyl Cellulose Reinforced with Cellulose Nanocrystals

Summary: Cellulose nanocrystals (CNC) were extracted from Kraft pulp of Eucalyptus urograndis. The CNC were isolated by acid hydrolysis with H₂SO₄ 64% (w/w) solution, for 20 minutes at 45 °C. The morphology and crystallinity of the CNC were investigated by atomic force microscopy (AFM) and X-ray diffraction (XRD), respectively. The AFM image supports the evidence for the development of crystals of cellulose in nanometric scale. These nanoparticles were used as reinforcement material in carboxymethyl cellulose (CMC) matrix. Nanocomposites films were prepared by casting. The nanocomposites were characterized by thermal (TGA) and mechanical (DMA) analyses. A large reinforcing effect of the filler was observed. The tensile strength of nanocomposites was significantly improved by 107%, the elongation at break decreased by 48% and the thermal resistance increased slightly. The improvements in thermo-mechanical properties suggest a close association between filler and matrix.     

Dissolution capacity and rheology of cellulose in ionic liquids composed of imidazolium cation and phosphate anions

Cellulose is one of the most abundant natural polymer sources, but the applications of cellulose are limited due to difficulty in dissolving cellulose in water and common chemical solvents. In the past decades, ionic liquids have been studied to dissolve cellulose efficiently, sustainably, and in an eco‐friendly manner. In this study, a series of imidazolium‐based ionic liquids were synthesized to explore as solvents for cellulose, including 1,3‐dimethylimidazolium dimethylphosphate ([mmim]dmp), 1‐ethyl‐3‐methylimidazolium dimethylphosphate ([emim]dmp), 1‐butyl‐3‐methylimidazolium dimethylphosphate ([bmim]dmp), 1‐hexyl‐3‐methylimidazolium dimethylphosphate ([hmim]dmp), 1‐ethyl‐3‐methylimidazolium diethylphosphate ([emim]dep), 1,3‐diethylimidazolium diethylphosphate ([eeim]dep), and 1‐butyl‐3‐ethylimidazolium diethylphosphate ([beim]dep). Rheology experiments were conducted to study the flow behavior of cellulose in these ionic liquids and cosolvents. We found that the dissolution capacity of cellulose increases with decreasing viscosity of the solvent and that the rheological properties depend most strongly on the concentration of cellulose dissolved. Systems composed of cellulose in [mmim]dmp, [emim]dmp, and [emim]dep behave as viscoelastic gels, while formulations of cellulose in [bmim]dmp, [hmim]dmp, [eeim]dep, and [beim]dep show viscoelastic liquid behavior. These results will impact development of new solvents for processing of cellulose‐based polymeric materials.     

Behavior of cellulose in NaOH/Urea aqueous solution characterized by light scattering and viscometry

Cellulose was dissolved in 6 wt % NaOH/4 wt % urea aqueous solution, which was proven by a ¹³C NMR spectrum to be a direct solvent of cellulose rather than a derivative aqueous solution system. Dilute solution behavior of cellulose in a NaOH/urea aqueous solution system was examined by laser light scattering and viscometry. The Mark–Houwink equation for cellulose in 6 wt % NaOH/4 wt % urea aqueous solution at 25 °C was [η] = 2.45 × 10^?2 weight‐average molecular weight (M_w)^0.815 (mL g^?1) in the M_w region from 3.2 × 10⁴ to 12.9 × 10⁴. The persistence length (q), molar mass per unit contour length (M_L), and characteristic ratio (C_∞) of cellulose in the dilute solution were 6.0 nm, 350 nm^?1, and 20.9, respectively, which agreed with the Yamakawa–Fujii theory of the wormlike chain. The results indicated that the cellulose molecules exist as semiflexible chains in the aqueous solution and were more extended than in cadoxen. This work provided a novel, simple, and nonpollution solvent system that can be used to investigate the dilute solution properties and molecular weight of cellulose. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 347–353, 2004     

Regioselective sulfation of trimethylsilyl cellulose using different SO3-complexes

Trimethylsilyl cellulose (DS_Si = 2.9) dissolved in dry tetrahydrofurane was reacted with SO₃-complexes of N,N-dimethylformamide, triethylamine, pyridine and ethyldiisopropylamine. Under the given reaction conditions, i.e. 25 °C, 24 h, 2.2 mol equivalent SO₃-complex, the SO₃ attacks the trimethylsilyl ether groups followed by the formation of sodium sulfate cellulose under sodium hydroxide work-up conditions. The regioselectivity of the sulfation is controlled by the complex partner of SO₃. Cellulose sulfates with preferred O-6 sulfation were obtained using SO₃-N,N-dimethylformamide. In case of SO₃-triethylamine, cellulose-2-sulfates could be prepared with good regioselectivity. Small residual amounts of silicon in the cellulose sulfates (0.1–0.2% w/w) can be quantified using inductively coupled plasma-optical emission spectroscopy (ICP-OES), and can be decreased up to 80% by heating (70 °C, 24 h) the polymers in vacuum.     

Antibacterial cellulose acetate films incorporated with N‐halamine‐modified nano‐crystalline cellulose particles

Cellulose acetate (CA) membranes have been widely used as food packaging materials as well as reverse osmosis systems. This study presents the manufacturing of composite CA film with antibacterial properties which is essential for CA film applications in the industry. N‐Halamine precursor of polymethacrylamide‐modified nano‐crystalline cellulose particles (NCC‐PMAMs) were prepared and incorporated into CA film. The composite films with intercalated structure were formed via a solvent‐casting technique. After chlorination, the composite film CA/NCC‐PMAM‐Cl‐1.0 with 1.82 × 10¹⁶ atoms/cm² covalently bonded chlorine showed excellent antibacterial properties by inactivating 6.04 logs of Staphylococcus aureus and 6.27 logs of Escherichia coli within 10 and 5 min, respectively. According to X‐ray diffraction spectra, NCC‐PMAMs behaved as a facilitator for film crystallization. The mechanical strength of the composite film also increased compared with that of pure CA film. However, the composite film became brittle and the maximum decomposition temperature decreased slightly. Preliminary data of in vitro cytocompatibility evaluation indicate that the film is not toxic and has potential use in food packaging. Copyright © 2016 John Wiley & Sons, Ltd.     

Synthesis of Fluorescent 2,6‐Dicyano‐3,5‐Disubstituted Anilines Using Cellulose Sulfuric Acid in Aqueous Media

The synthesis of some fluorescent 2,6‐dicyano‐3,5‐disubstituted anilines using cellulose sulfuric acid (Cellulose‐SA) as an environmentally benign catalyst in H₂O is described. The one‐pot reaction of 1,3‐diketone and three equiv. of malononitrile was carried out in the presence of one equiv. of a secondary amine, Cellulose‐SA as catalyst, and H₂O as solvent. The photophysical properties (λ_Abs., λ_Flu.) of the synthesized compounds in CH₂Cl₂, MeCN, and MeOH have been measured. The emission spectra of the new compounds in the solid state are also reported.