Alkaline hydrogen peroxide bleaching of cellulose

A closed system bleaching apparatus was designed to determine the kinetics and effects of various factors on alkaline hydrogen peroxide bleaching of textile cellulose fabrics. It was confirmed that perhydroxyl anion is the primary bleaching moiety in alkaline hydrogen peroxide systems. The use of the apparatus in the measurement of fabric color, waste oxygen, and the subsequent calculation of hydroxyl ion, and molecular hydrogen peroxide confirmed that pH and titration of 'free' hydrogen peroxide in alkaline bleaching systems are not good indicators of bleaching mechanism. The role of the cellulose itself in the chemical bleaching system was determined. The rate of bleaching on cotton fabric was shown to be a first order reaction in concentration of perhydroxyl anion at 60 and 90°C. An activation energy of 17kcal/mole was estimated. Decomposition of H₂O₂ into waste oxygen was found to be second order kinetics.     

Microstructural order in cotton fibers by relative availability of O(3)H: Never-dried fibers

Availabilities of O(3)H relative to O(2)H (that is, [O(3)H]_a/[O(2)H]_a) on accessible surfaces of microstructural units of cotton fibers were measured by chemical microstructural analysis (CMA). CMA involves a mild chemical reaction with N,N-diethylaziridinium chloride, determination of substituent distribution for this product and a corresponding product from decrystallized cellulose, and simple computations. Measurements for fibers in commercial cotton fabric, for field-dried fibers, and for never-dried fibers are reported. The [O(3)H]_a/[O(2)H]_a, an inverse measure of intact O(3)H ·· O(5′) bonds, decreased in the stated order; thus, intact O(3)H ·· O(5′) hydrogen bonding increased in this same order. Results indicate a high degree of order in intramolecular bonding in the never-dried fiber and an increasing disruption of this bonding as the never-dried fiber is dried and processed.     

Activated peroxide bleaching of regenerated bamboo fiber using a butyrolactam-based cationic bleach activator

Regenerated bamboo fibers are potentially a valuable source of renewable fibers for use in a wide variety of applications. As with almost all natural fibers, inherent yellowness must be reduced or eliminated in order for the fibers to be used effectively in processes such as dyeing. Oxidative bleaching in the form of hot alkaline hydrogen peroxide is the most common method for bleaching cellulosic fibers. However, significant fiber damage results, especially in the case of regenerated bamboo. Recently, more benign oxidative bleaching methods have been developed using so-called bleach activators. Reported is an effective bleaching method using a novel bleach activator, N-[4-(triethylammoniomethyl)benzoyl]butyrolactam chloride (TBBC). The ratio of TBBC to hydrogen peroxide and pH were found to be critical to achieving effective bleaching at low temperature. Using equimolar amounts of TBBC and hydrogen peroxide at pH 7 and 50 °C, comparable whiteness and less fiber damage compared with conventional peroxide bleaching was obtained. However, at pH 11.5, TBBC had no effect on whiteness.     

Effect of pre‐treatment of sugarcane bagasse on the cellulose solution and application for the cellulose hydrogel films

Sugarcane bagasse was used as a cellulose resource, and the transparent cellulose hydrogel films were obtained from the purified cellulose by phase inversion process without chemical cross‐linking, when the dissolved cellulose in lithium chloride/N,N‐dimethyl acetamide was transformed into the solid film. On these processes, bagasse was pre‐treated by 10 wt% sodium hydroxide in the absence and presence of bleaching of 10 vol% sodium hypochlorite (NaOCl) solution in order to obtain cellulose fibers. Here, the bleaching temperature was varied from 40 to 50°C. The effect of pre‐treatment conditions on the resultant cellulose solution and hydrogel films was investigated. It was seen that strong bleaching removed most of lignin component from the bagasse. However, viscosity and size exclusion chromatogram of the cellulose indicated that this operation decreased average molecular weight of the cellulose fibers from 2.1 × 10⁶ to 4.8 × 10⁵. These property changes of fibers also caused increase of water content and weakening of mechanical strength of the resultant hydrogels. In addition, scanning probe microscopy in wet state revealed that the porous fiber network structure in the hydrogel was greatly influenced by bleaching with NaOCl. The average pore size of fiber network was decreased from 8.1 to 5.9 nm as the NaOCl treatment was at 50°C, because of expanded fibers in the swollen hydrogel. Copyright © 2016 John Wiley & Sons, Ltd.     

Electrokinetic properties of processed cellulose fibers

Natural cellulose fibers (cotton) comprise several noncellulose compounds (hemicellulose, wax and pectin substances) and cationic impurities which cause problems during different adsorption processes such as dying, or final fiber finishing and coating. Therefore the chemical purification (NaOH boiling, enzymatic purification, demineralization, extraction or oxidative bleaching) is the most important step in cellulose textile finishing. Alternative ways to describe the success of different processes in fiber purification which result in distinct surface charge and hydrophilicity are the determination of electrokinetic properties and the water uptake of textile fibers. The zeta-potential (ζ) was determined by streaming potential measurement as a function of the pH. From the ζ–pH functions the adsorption potential for all ionic species Φ_i (i.e. ( , in the case of potassium chloride solutions), the charge densities σ^k and the pK values are calculated according to the Börner and Jacobasch model.

The degradation and removal of hydrophobic noncellulose compounds which cover the primary hydroxyl and carboxyl groups of the cellulose polymer is clearly shown by an increase of the negative ζ of the plateau, which is in good agreement with the electrokinetic parameters of cotton samples determined by the Börner and Jacobasch model. The electrokinetic parameters determined by the Börner and Jacobasch model can be used to describe the adsorption/dissociation ability of textile fibers. The progress of the fiber processing (cleaning) is reflected by the surface charge as well as the hydrophilicity of the fiber.     

Decolourization of vat dyes on cotton fabric with infrared laser light

A method for the decolourization of coloured cotton fabric dyed with vat dyes, based on exposure to infrared laser light, has been tested. Pulsed CO₂ laser has been used for all experiments. To detect changes in colour shade, reflection data of original and dyed cotton irradiated at various fluency of infrared laser light were measured on a UV–VIS spectrophotometer, and then colour intensity was calculated for each vat dye. To observe changes in chemical composition and morphology of fiber surfaces, an analysis was performed by X-ray photoelectron spectroscopy and scanning electron microscopy due to thermal effects. Thermal stability of vat dyes and cotton fabric was determined with differential scanning calorimetry method to simulate the heating process during exposure of samples to the infrared laser irradiation.     

Bleaching cellulosic fibers via pre-sorption of N-[4-(triethylammoniomethyl)-benzoyl]-butyrolactam chloride

The sorption of a novel cationic bleach activator, N-[4-(Triethylammoniomethyl)benzoyl]-butyrolactam Chloride (TBBC), was measured on regenerated bamboo fiber. At 25 °C near neutral pH, the sorption rate of TBBC onto the fiber was initially rapid and equilibrium was reached within 20 min. Adsorption equilibria experiments followed a Freundlich isotherm. At the sorption equilibrium, bleaching was initiated by addition of sodium perborate to liberate hydrogen peroxide, which reacted with TBBC to generate a peracid that is a more kinetically active oxidant than peroxide. A sorption–activation model was developed that supports the enhanced bleaching of cellulosic fibers using cationic bleach activators under neutral to alkaline conditions.     

Thermodynamic interactions of natural and of man-made cellulose fibers with water

The vapor pressure of water was measured for binary mixtures with cellulose containing fabrics at 37 °C by means of two complementary methods. Different types of fabrics were studied: One consisting exclusively of cellulose fibers, either of natural origin (cotton) or regenerated from solutions in the mixed solvent NMMO/water (Lyocell fibers, CLY) and another kind of fabric containing polyethylene terephthalate (PET) fibers in addition to CLY fibers. The Flory-Huggins interaction parameters χ and their composition dependence calculated from these vapor pressure data are broadly similar for cotton and for CLY, apart from the fact that water interacts somewhat more favorably with CLY than with cotton. In both cases the χ values pass successively a maximum and a minimum as the concentration of water rises. The experiments performed with the fabrics containing two types of fibers demonstrate that the water uptake of PET is negligible as compared with that of cellulose. The results for the system water/cellulose fibers obtained at 37 °C differ fundamentally from corresponding data for 80 °C, reported for cellulose films prepared from solutions in dimethylacetamide + LiCl. The maximum water uptake of cellulose is determined by its degree of crystallinity. In all cases it is possible to model the Flory-Huggins interaction parameters as a function of composition quantitatively by means of an approach subdividing the dilution process conceptually into two separate steps: Contact formation between the dissimilar components (keeping their conformation constant) and subsequent relaxation of the system into the equilibrium state. Similarities and dissimilarities of the systems water/polysaccharide are being discussed in detail.     

Determination of the Nitrogen Content of Cationic Cellulose Fibers by Analytical Pyrolysis

Summary.  Analytical pyrolysis in combination with gas chromatography and mass spectrometry or a nitrogen-phosphorus detector, respectively, were used to characterize the quaternization reagent glycidyltrimethylammonium chloride and a cationic cotton fabric. Trimethylamine was shown to be the most abundant nitrogen-containing product in the pyrolysis of glycidyltrimethylammonium chloride and was thus used for the quantification of the nitrogen content of the cationic cotton fabric. The results were compared to those obtained by traditional methods such as Kjeldahl and elemental analysis. It could be shown that pyrolysis is well suited for monitoring the nitrogen content of cellulose fibers. Received July 11, 2001. Accepted (revised) August 2, 2001     

Comparative physical and chemical analyses of cotton fibers from two near isogenic upland lines differing in fiber wall thickness

The thickness of cotton fiber cell walls is an important property that partially determines the economic value of cotton. To better understand the physical and chemical manifestations of the genetic variations that regulate the degree of fiber wall thickness, we used a comprehensive set of methods to compare fiber properties of the immature fiber (im) mutant, called immature because it produces thin-walled fibers, and its isogenic wild type Texas Marker-1 (TM-1) that is a standard upland cotton variety producing normal fibers with thick walls. Comprehensive structural analyses showed that im and TM-1 fibers shared a common developmental process of cell wall thickening, contrary to the previous report that the phase in the im fiber development might be retarded. No significant differences were found in cellulose content, crystallinity index, crystal size, matrix polymer composition, or in ribbon width between the isogenic fibers. In contrast, significant differences were detected in their linear density, cross-section micrographs of fibers from opened bolls, and in the lateral order between their cellulose microfibrils (CMFs). The cellulose mass in a given fiber length was lower and the CMFs were less organized in the im fibers compared with the TM-1 fibers. The presented results imply that the disruption of CMF organization or assembly in the cell walls may be associated with the immature phenotype of the im fibers.     

Ultrasound-assisted ozone bleaching of cotton

In this study, the effects of ultrasound on ozone treatment processes for bleaching cotton fabrics were investigated and compared with the conventional hydrogen peroxide bleaching process (60 °C over 90 min). Two ultrasonic + ozone treatments of cotton fabric samples were carried out: (1) ozone in an ultrasonic homogenizer (UH) and (2) ozone in an ultrasonic bath. Ozone dosages, temperature and time variations were determined with both ozone-ultrasonic bleaching processes. Whiteness, yellowness, weight, tensile strength properties, FTIR (ATR) spectra and visual appearance, via scanning electron microscopy of treated cotton fabrics as well as chemical oxygen demand (COD) of bleaching effluents, were investigated. It was concluded that the ozone + UH process, conducted for 30 min at 30 °C, produced closely equivalent values of cotton fabric whiteness and yellowness to the classic peroxide bleaching process, with slightly less weight loss, dramatically less COD in the process effluent (29 mg/l for ozone-UH vs. 4,316 mg/l for classical peroxide treatment), and without causing any adverse and/or detrimental effects on loss of fabric strength or elongation of the cotton fabrics. The ozone-UH process also leads to time and energy savings with much less environmental impact. Consequently, the combination of ozonation plus UH carried out at 30 °C over 30 min can be used successfully for cotton bleaching instead of the classic hydrogen peroxide bleaching process.     

Hydrolytic stability of a series of lactam-based cationic bleach activators and their impact on cellulose peroxide bleaching

A series of five cationic bleach activators containing lactam-based leaving groups of varying ring size was synthesized and characterized. The hydrolytic stability of each activator was determined via HPLC-based analysis of hydrolysis products, titration of available oxygen, and whiteness assessment of cellulosic fibers using a peroxide-activator bleaching system following solution storage for various times under controlled conditions. Aqueous alkaline solutions of each activator hydrolysed at different rates with the slowest rates observed with the ω-octalactam ring system, the largest ring size investigated, and the most rapid hydrolysis was found with a six-membered lactam ring based activator. The whiteness of cotton bleached with stored bleach activator solutions inversely correlated with the hydrolysis rate for each activator. The hydrolysis rate followed pseudo first order kinetics.     

Determination of the Nitrogen Content of Cationic Cellulose Fibers by Analytical Pyrolysis

 Analytical pyrolysis in combination with gas chromatography and mass spectrometry or a nitrogen-phosphorus detector, respectively, were used to characterize the quaternization reagent glycidyltrimethylammonium chloride and a cationic cotton fabric. Trimethylamine was shown to be the most abundant nitrogen-containing product in the pyrolysis of glycidyltrimethylammonium chloride and was thus used for the quantification of the nitrogen content of the cationic cotton fabric. The results were compared to those obtained by traditional methods such as Kjeldahl and elemental analysis. It could be shown that pyrolysis is well suited for monitoring the nitrogen content of cellulose fibers.     

Immobilization of lysozyme-cellulose amide-linked conjugates on cellulose I and II cotton nanocrystalline preparations

Lysozyme was attached through an amide linkage between some of the protein’s aspartate and glutamate residues to amino-glycine-cellulose, which was prepared by esterification of glycine to preparations of cotton nanocrystals. The nanocrystalline preparations were produced through acid hydrolysis and mechanical breakage of the cotton fibers from a scoured and bleached cotton fabric and a scoured and bleached, mercerized fabric, which was shown to produce cellulose I (NCI) and cellulose II (NCII) crystals respectively. A carbodiimide-activation coupling reaction was used to create the lysozyme-amino-glycine-cellulose conjugates using both NCI and NCII in a polar solvent and gave yields of covalently linked lysozyme at 604 mg/gram of cotton nanocrystal. The incorporation of lysozyme conjugated to the NCI and NCII preparations gave very high activity (1,500 U/mg cotton) when assessed using a fluorescence tag assay to measure antimicrobial activity against Micrococcus lysodeikticus. Scanning electron micrographs demonstrated an aggregation of nanoparticles corresponding to lysozyme bound on the surface of larger cotton nanocrystalline sheets. The approach of producing high enzyme activity on cotton nanocrystals is discussed in the context of selectively presenting robust hydrolase activity on nanocrystalline surfaces.     

Preparation, characterization, and antimicrobial property of cotton cellulose fabric grafted with poly (propylene imine) dendrimer

Two generations of poly (propylene imine) dendrimer with amino terminated groups (G2- and G5-PPI-NH₂) were grafted on cotton cellulose fabric using cross linking agents (citric or glutaric acids). Fourier transform infrared (FTIR) spectroscopy identified ester groups which were formed between hydroxyl groups of the cotton fabric and carboxylic groups of the cross linking agents. Also, attenuated total reflectance-FTIR (ATR-FTIR) analysis confirmed formation of amide groups between the carboxylic groups of the cross linking agents and the amino end groups of the dendrimers. Nitrogen content (N-content) analysis revealed the presence of the dendrimers on the cotton fabric even after 5 washing cycles. In order to study the dispersion of the PPI dendrimers on the surface of the cotton fabric, field emission scanning electron microscopy (FE-SEM) was performed. The particle size distribution of the G2- and G5-PPI-NH₂ aqueous solutions was also determined by dynamic light scattering (DLS) analysis. Antimicrobial activity of the PPI dendrimer aqueous solutions and the cotton cellulose fabric grafted with the dendrimers was evaluated both quantitatively and qualitatively against Gram-positive bacterium (Staphylococcus aureus), Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli) and fungus (Candida albicans). The dendrimer grafted cotton cellulose fabric exhibited a 99 % reduction in bacterial counts against S. aureus, E. coli and C. albicans. The antimicrobial activities of the grafted cotton cellulose fabric with the PPI dendrimers were maintained even after 5 washing cycles.     

Effect of cationization on adsorption of silver nanoparticles on cotton surfaces and its antibacterial activity

Cotton was cationized by exhaustion method using 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHPTAC) as a cation-generating agent. Adsorption of silver nanoparticles on normal and cationized cotton was studied by exhaustion method at temperatures of 80°C and 100°C. Two exhaustion baths were used, containing nanosilver colloidal solutions stabilized by two different stabilizers and various concentrations of silver nanoparticles. Fourier-transform infrared (FT-IR) spectra of normal and cationized samples confirmed the existence of quaternary ammonium groups on cationized cellulose fibers. X-ray diffraction (XRD) patterns showed that crystallinity of the modified cellulose fibers was decreased. Scanning electron microscope (SEM) images revealed that the surface of the modified cotton was rougher than that of normal cotton. In addition, SEM images showed the presence of silver nanoparticles on the surface of treated fabric samples. The amount of silver particles adsorbed on the fabric samples was determined using inductively coupled plasma-optical emission spectrometer. Antibacterial tests were performed against Escherichia coli bacteria as an indication of antibacterial effect of samples. Cationized cotton samples adsorbed more silver nanoparticles and then had greater ability to inhibit bacteria.     

Preparation of durable superhydrophobic surface by sol–gel method with water glass and citric acid

Durable superhydrophobic surface on cotton fabrics has been successfully prepared by sol–gel method. Cellulose fabric was first coated with silica sol prepared with water glass and citric acid as the acidic catalyst. The silica coated fabric was then padded with hydrolyzed hexadecyltrimethoxysilane afterwards obtaining low surface energy. Water contact angle and hydrostatic pressure were used to characterize superhydrophobicity and washing durability. Scanning electron microscopy was used to characterize the surface morphology changes after certain washing times. All results showed good durable hydrophobicity on cellulose fabrics. In addition, the influence of citric acid and sodium hypophosphite (NaH₂PO₂) on the durability of hydrophobicity was also investigated. The durability of treated cotton improved with the increase of concentration of citric acid in the presence of NaH₂PO₂. It could be concluded that citric acid acted as multi-functional heterogeneous grafting chemicals to improve washing durability of hydrophobicity by forming the ester bonds between cotton fabric and silica sol and improved the durability of hydrophobicity.     

Reaction pathway to CZTSe formation in CdI2

The thermal decomposition of cotton and hemp fibers was studied after mild alkaline treatments with tetramethyl-, tetraethyl- and tetrabutylammonium hydroxides with the goal of modeling the chemical activation during carbonization of cellulosic fibers. The thermal decomposition was studied by thermogravimetry/mass spectrometry and pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS). The treated samples decomposed in two temperature ranges during heating in the thermobalance. At lower temperature, tetraalkylammonium hydroxides (TAAH) ionically bonded to the cellulose molecules were decomposed; moreover, the alkaline agents initiated the partial decomposition of cellulose. Those fiber segments, which were not accessible for TAAH, decomposed at similar temperatures as the original cotton and hemp samples. It is known that quaternary ammonium hydroxides swell the cellulosic fibers; however, the results of this study proved that there was a chemical interaction between the alkaline swelling agents and cotton or hemp fibers at rather low temperatures (200–300 °C). The evolved products indicated that the alkaline chemicals reacted with the cellulose molecules and alkylated compounds were formed. This observation was confirmed by thermochemolysis experiments carried out by Py–GC/MS using tetramethylammonium hydroxide reagent. The thermochemolysis experiments under mild conditions resulted in the methylation of the glucoside units and levoglucosan, and no peeling reactions of the sugar units were observed as during strong alkaline conditions described in the literature.

     

Isolation of cellulose fibers from kenaf using electron beam

Cellulose fibers were isolated from a kenaf bast fiber using a electron beam irradiation (EBI) treatment. The methods of isolation were based on a hot water treatment after EBI and two-step bleaching processes. FT-IR spectroscopy demonstrated that the content of lignin and hemicellulose in the bleached cellulose fibers treated with various EBI doses decreased with increasing doses of EBI. Specifically, the lignin in the bleached cellulose fibers treated at 300 kGy, was almost completely removed. Moreover, XRD analyses showed that the bleached cellulose fibers treated at 300 kGy presented the highest crystallinity of all the samples treated with EBI. Finally, the morphology of the bleached fiber was characterized by SEM imagery, and the studies showed that the separated degree of bleached cellulose fibers treated with various EBI doses increased with an increase of EBI dose, and the bleached cellulose fibers obtained by EBI treatment at 300 kGy was separated more uniformly than the bleached cellulose fiber obtained by alkali cooking with non-irradiated kenaf fiber.     

Statistical Experimental Design for Obtaining Nanocellulose from Curaua Fiber

Summary: This study focuses on the methodology to obtain nanocellulose from vegetal fibers. An experimental planning was carried out for the treatment of curaua fibers and parameters were estimated, having the concentration of H₂SO₄, hydrolysis time, reaction temperature and time of applied sonication as independent variables for further statistical analysis. According to the estimated parameters, the statistically significant effects were determined for the process of obtaining nanocellulose. With the results obtained from the thermogravimetric analysis (TGA) it was observed that certain conditions led to cellulose with degradation temperatures near or even above that of the untreated cellulose fibers. The crystallinity index (I_C) obtained after fiber treatment (by X-ray diffraction technique) was higher than that of the pure fiber. Treatments with high acid concentrations led to higher IC. After the statistical experimental design, mixtures of polypropylene with fibers prepared after different treatments were performed in a mini-extruder. It was possible to observe a sharp increase in the mechanical properties through the dynamic mechanical thermal analysis (DMTA).