Morphology Of Cellulose Fibers Research Articles

Isolation of cellulose fibers from wetland reed grass through an integrated subcritical water hydrolysis-pulping-bleaching process

Cellulose fibers were isolated from wetland reed grass (Phragmites karka) by consolidated subcritical water hydrolysis, pulping and bleaching process. Phragmites biomass was treated with subcritical water at variable temperatures of 130–210 °C at constant pressure, reaction time and the biomass-to-water ratio of 3.5 MPa, 30 min and 1:50, respectively. The optimized temperature was found to be 170 °C with a total reducing sugars yield of 15.5 wt% and minimal charring of biomass. The treated biomass was carried out through pulping and bleaching process to isolate cellulose fibers. The highest cellulose yield was found to be 35.1 wt% with a residual lignin content of 0.4 wt% at 0.5 M NaOH. In a comparative study, the untreated biomass, subcritical water hydrolyzed biomass and cellulose were characterized by several physicochemical characterization tools such as proximate, ultimate and compositional analysis, thermogravimetric analysis, Fourier-transmission infrared, Fourier-transmission near-infrared and Raman spectroscopy, X-ray diffraction, solid-state nuclear magnetic resonance spectroscopy, scanning electron microscopy, transmission electron microscopy and atomic force microscopy to estimate the crystallinity index, carbon content, delignification, cellulose recovery as well as thermal stability and morphology of cellulose fibers. With the inclusion of subcritical water hydrolysis, a higher yield of cellulose was obtained from Phragmites with a crystallinity index of 65.3%. Due to the effective hydrolysis process, subsequent processes such as pulping and bleaching required less severe conditions.

Wood delignification with aqueous solutions of deep eutectic solvents

The development of a sustainable wood fractionation has been a goal for the pulp and paper industries to develop a bioeconomy. The use of green solvents, in particular deep eutectic solvents (DES) has been explored to accomplish such goal. This work unveils the potential of DES aqueous solutions (at 50 wt% water content) as green solvents for the Eucalyptus globulus Labill. wood delignification. Aqueous solutions of propionic acid:urea - PA:U (2:1), urea:choline chloride - U:Ch[Cl] (2:1), lactic acid:choline chloride - LA:Ch[Cl] (10:1) and p-toluenesulfonic acid:choline chloride - PTSA:Ch[Cl] (1:1) were investigated. The delignification process was assisted by the addition of mineral (H2SO4 and HCl) or organic (PTSA) acids to efficiently promote wood matrix disruption and further lignin extraction. This process enabled solid pulp and lignin as separated fractions, which were characterized by analytical, optical and spectrometric methods. The influence of each DES on the morphology of cellulose fibers in solid pulp and the chemical structure of isolated lignin fractions was evaluated. The best system allowing delignification while preserving the cellulose fibers (comparable to Kraft cellulose pulp) and lignin structure was PA:U (2:1) aqueous solution with 25 wt% PTSA. A mild wood delignification process (363.15 K for 8 h) using this DES allowed to obtain a cellulose pulp yielding 59.50 ± 0.51 wt% of the initial wood mass and containing only 3.86 ± 0.10 wt% residual Klason lignin content. This innovative approach led to 80.64 wt% lignin extraction from E. globulus wood at mild conditions showing its potential for industrial application. Furthermore, 40.73 wt% of the initial lignin was recovered from DES liquor by a simple precipitation with water.

Microstructure, morphology and strength of cotton yarns sized by collagen solution

For sizing cotton yarn before weaving, a new composition based on a biodegradable polymer—collagen, has been proposed. The detected changes in the FT-IR spectra of the yarn coated with a collagen solution indicate the obvious formation of new intermolecular hydrogen bonds between the primary and secondary amino groups of the collagen and the cellulose hydroxyl groups. The formation of such bonds contributed to the strengthening of the collagen film on the surface of cotton threads. SEM studies have shown a significant improvement in the microstructure of threads and the morphology of fibers compared with threads not sized and sized with starch. When sizing with a collagen solution, the diameter of the threads decreases by 14%, when sizing with a starch solution—by 18%. In cases of collagen sizing, along with bonding, compaction, a longitudinal orientation of the fibers is observed. The diameter of the cellulose fibers sized with collagen is in the range of 12–15 microns. Unlike starch, which fills the interfiber spaces and even penetrates into individual tubular fibers, collagen is evenly located only on the surface of the fibers. Improving the microstructure and morphology of cellulose fibers and threads when sizing with a collagen-based composition leads to a reduction in the consumption of sizing agent, an increase in the linear density of threads by 15–20%, an increase in breaking load by 25–35%, and a decrease in elongation at break by 15–20%.

Structure and morphology of cellulose fibers in garlic skin

The knowledge of the texture and morphology of cellulose is essential for reliable modelling of cell growth and mechanical resistance of vegetal systems. Microscopic observations on thin layers of the skin of Allium sativum have shown elongated structures (i.e. cellulose fibers) imbedded in a matrix of more or less rounded cells. Examination by an optical polarizing microscope (OPM) has shown an intermittent high and low birefringence along fibers. Transversal regions with a reduced brightness along fibers are expected to contain a higher amount of amorphous lignin, hemicelluloses and waxes, some of which might also be birefringent, but at a much lower degree than cellulose. Scanning electron microscopy (SEM) has also evidenced an alternating growth of the fibers. Moreover, the negative sign of birefringence suggests a parallel orientation of cellulose nanofibrils transversally to the fiber axis. The characteristic modulation of intensity along lignocellulosic fibers can be due to variation of the cellulose concentration or orientation, perhaps caused by circadian cycles of temperature and light during growth. Indeed, imperfect orthogonal light can be totally reflected at the interface between regions with different values of the refractive index, contributing to the optical effect of banding.

Cyclic loading of a cellulose/hydrogel composite increases its fracture strength

The fracture properties of hydrogels which present similar characteristics to the Mullins effect is expected to decrease under repeated cyclic loading. Therefore, we assessed how cyclic loading affects the fracture behavior, the distribution of strain fields and the microstructure of hydrogel composites reinforced with nano-fibrillated cellulose fibers. Surprisingly, we observed that preloading before the creation of a crack in the hydrogel composite increased the fracture strength of pre-notched samples, while the corresponding fracture energy decreased. To understand this behavior, a digital image correlation analysis at the macro- and microscopic scale was performed to obtain local information on the strain field. In addition, the morphology of cellulose fibers was directly observed through fluorescence confocal microscopy before and after cyclic loading at different maximal applied strains. Microscopy results show that cyclic loading re-arrange the fiber network and relax local residual stresses in the hydrogel composite. The re-arrangement of the fiber network decreases the overall elastic modulus and correspondingly the fracture energy. However, this phenomenon helps the hydrogel composite to accommodate larger strains before the crack starts to propagate, which subsequently improves the fracture strength of pre-notched samples.

TEMPO-mediated oxidation of cellulose in carbonate buffer solution

The reaction stability is a challenge in the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-mediated oxidation of cellulose. Carbonate buffer solution (Na2CO3/NaHCO3) was used to study pH effects on stability of the oxidation reaction in this work. The structure and morphology of cellulose fibers were characterized by XRD and SEM techniques, respectively. It was found that the carboxyl content of oxidized cellulose was changed with different composition ratio of buffer solutions. The highest carboxyl content was obtained at the molar ratio of 7:3. The NaClO addition, as well as reaction temperature, affected the process of the oxidation reaction. The carboxylate content of the oxidized cellulose was increased as the temperature and NaClO consumption increased. However, both temperature and NaClO consumption have negative effect on yield. SEM results showed that the morphology of oxidized cellulose fibers was significantly changed at high reaction temperature. XRD showed that the oxidized cellulose fibers maintained the crystal structure of cellulose I. However, the crystallinity was decreased from 56.4 to 40.8 % with increasing oxidation temperature from 25 to 40 °C.

Morphological investigation of nanoparticles obtained from combined mechanical shearing, and enzymatic and acid hydrolysis of sisal fibers

The goal of this work was to prepare cellulosic nanoparticles using different processing routes, viz. a combination of mechanical shearing, acid and enzymatic hydrolysis. It was shown that the enzymatic hydrolysis pretreatment of bleached sisal pulp helps the preparation of well individualized rod-like nanocrystals. The morphology of cellulose fibers and nanoparticles was determined by scanning and transmission electron microscopies, respectively. The main outcome of this study indicated the usefulness of the enzymatic treatment for cellulose nanocrystals production. The enzymatic treatment allowed production of a broad range of cellulosic nanoparticles. This investigation proved that the distinction between MFC and whiskers to describe such cellulose nanoparticles is not sufficient. Indeed, it appears essential to indicate the pretreatment performed.

Effects of Ultra-sonification Assisting Polyethylene Glycol Pre-treatment on the Crystallinity and Accessibility of Cellulose Fiber

In order to prepare the advanced cellulosic super-absorbent polymer with high grafting level, we tried the novel ultrasound wave assisting polyethylene glycol (PEG) pre-treatment method to decrease the crystallinity and increase the accessibility of cellulose fiber. The effects of ultrasonification assisting PEG method on the crystallinity and swelling capacity of cellulose fiber were investigated. To optimize the experimental condition, the Taguchi method was employed in the treatment process. The influence factors such as ultrasonic wave power, ultrasonic wave time and PEG molecular weight relative to the crystallinity of cellulose fiber were studied systematically. The degree of crystallinity of cellulose fiber was measured by wide-angle X-ray diffraction (WAXD). The morphology of cellulose fiber was observed by environment scanning electron microscopy (ESEM). The effects of pre-treatment variables on the water absorbency and water retention values of cellulose fiber were also investigated. The research results revealed that, under the optimal experimental condition (ultrasonic powder, 500 W; ultrasonic time, 150 s; PEG molecular weight, 600 g/mol), the crystallinity of cellulose fiber decreased from 72.16 to 42.95%. Accordingly, the absorbency of cellulose fiber increased from 1.436 to 2.063 g/g, and the water retention value increased from 47.21 to 113.4%. However, the morphology of cellulose fiber did not change thoroughly compared with the original cellulose fiber. It can be hypothesized that the original inter- and intra-macromolecular hydrogen bonds in cellulose network were weakened, resulting from the high level dispersion of PEG within cellulose network without breaking the surface morphology of fiber.

Surface methacrylation and graft copolymerization of ultrafine cellulose fibers

AbstractUltrafine fibrous (ϕ from 100 to 450 nm) cellulose membranes were generated by electrospinning of cellulose acetate [degree of substitution (DS): 2.45, weight‐average molecular weight: 30,000 Da], followed by alkaline deacetylation. Reaction of these ultrahigh surface‐area cellulose fibers with methacrylate chloride (MACl) produced activated surfaces without altering the fiber morphology. Surface methacrylation of these fibers was confirmed by the acquired hydrophobicity (θwater = 84°) as compared to the originally hydrophilic (θwater = 56°) cellulose. Changing the MACl:OH molar ratios could vary the overall DS of methacrylation. The very low overall DS values indicate the surface nature of the methacrylation reaction. At a DS of 0.17, the thermal properties of the surface methacrylated cellulose resemble those of cellulose derivatives at much higher DS values, an unusual behavior of the ultrafine fibers. The methacrylated cellulose could be further copolymerized with vinyl monomers (methyl methacrylate, acrylamide, and N‐isopropylacrylamide) as linear grafts or three‐dimensional (3D) networks. The morphology of cellulose fibers and the interfiber pore structure were not altered at 15–33% graft levels. This study demonstrates that either linear or 3D networks of vinyl polymers could be efficiently supported on ultrafine cellulose fibrous membranes via surface methacrylation. Through these surface reactions the chemical, thermal, and liquid wetting and absorbent properties of these ultrafine fibrous membranes were significantly altered with no change to the fiber dimensions or interfiber pore morphology. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 953–964, 2003

Modified cellulose adsorption method for the synthesis of conducting perovskite powders for membrane application

A modified cellulose adsorption method, i.e., pyrolysis of cellulose–(organic acid)–salt solid composite was applied for the synthesis of conducting perovskite-type La 1− x Sr x BO 3− δ (B=Co, Fe, Mn; x=0.0, 0.1, 0.2) functional oxides. Citric acid is mainly selected as the organic acid. Infrared (IR), scanning electron microscopy–electron diffusion spectroscopy (SEM–EDS) and X-ray diffraction (XRD) results indicated that the citric acid modified cellulose adsorption method could preserve the homogeneity of the solution system to the solid precursor more efficiently than the unmodified one, due to the change of interaction between metal salts and organic substance from weak chemical adsorption to chemical chelation and fixation. Thermal gravimetry and differential thermal analysis (TG–DTA) and IR results demonstrated that the citric acid's addition also changed the pyrolysis behavior of the precursor. Perovskite oxides could be obtained at low temperatures (≤600 °C) without development of other phases; the as-prepared powders had the morphology of cellulose fiber and relatively high Brunauer–Emmet–Teller (BET) surface areas (8–30 m 2/g). The resulted oxide powders also demonstrated excellent sinterability, it is suitable for fabrication of dense membranes.