Microstructure and surface properties of fibrous and ground cellulosic substrates

Cotton and linen fibers were ground in a ball-mill, and the effect of grinding on the microstructure and surface properties of the fibers was determined by combining a couple of simple tests with powerful techniques of surface and structure analysis. Results clearly proved that the effect of grinding on cotton fiber was much less severe than on linen. For both fibers, the degree of polymerization reduced (by 14.5% and 30.5% for cotton and linen, respectively) with a simultaneous increase in copper number. The increased water sorption capacity of the ground substrates was in good agreement with the X-ray results, which proved a less perfect crystalline structure in the ground samples. Data from XPS and SEM-EDS methods revealed that the concentration of oxygen atoms (bonded especially in acetal and/or carbonyl groups) on the ground surfaces increased significantly, resulting in an increase in oxygen/carbon atomic ratio (XPS data: from 0.11 to 0.14 and from 0.16 to 0.29 for cotton and linen, respectively). Although grinding created new surfaces rich in O atoms, the probable higher energy of the surface could not be measured by IGC, most likely due to the limited adsorption of the n-alkane probes on the less perfect crystalline surfaces.     

Recycling of Cellulosic Fibers by Enzymatic Process

In this research, enzymatic treatment as an environmental friendly process has been used for recycling process of old cellulosic wastes such as cotton, viscose, and lyocell. Cellulase hydrolyses cellulosic chains and shortens cellulosic fibers. This study investigates to detect the optimum enzyme concentration and time of treatments for suitable changes of length and weight loss. The main purposes of this article are shortening of cellulosic fibers and evaluating of enzymatic treatment in different kind of cellulosic fibers. According to the data of experiments, with the increase of enzyme concentration and the treatment time, the length and weight loss percentage of the cellulosic fibers has been decreased. The length and weight loss percentage of treated viscose is more than that of lyocell and cotton fibers. Optimized condition, reaction time, and enzyme concentration have been determined by mean length of treated cellulosic samples. Suitable longitudinal distribution of fiber for papermaking industries is in the range of 0 to 4 mm. Optimum enzyme concentration and treatment time for recycling cotton, lyocell, and viscose fibers are 2% and 48 h for cotton and lyocell and 0.5% and 48 h for viscose, respectively. According to the data of experiment, the length of treated fibers is appropriate for its usage as a raw material in papermaking industries.     

Determination of Surface Functional Groups in Lignocellulosic Materials by Chemical Derivatization and ESCA Analysis

Simple and convenient methods for determining surface chemical composition of lignocellulosic materials are described. The methods are based on vapor phase fluorine surface derivatization with either trifluoro acetic anhydride (TFAA), tri-fluoro ethanol (TFE) or pentafluorophenyl hydrazine (PFPH) and subsequent Electron Spectroscopy for Chemical Analysis (ESCA). Model cellulosic surfaces with well defined functionalities were used to optimize the derivatization reaction conditions. Detection and accessibility of surface hydroxyl functional groups were investigated in cotton and regenerated cellulose as models. Carboxymethyl cellulose (CMC) was used as a model surface for detection and quantification of carboxylic acid groups. Theoretical conversion curves for derivatization reactions were calculated and used to evaluate the extent of the reactions on the model surfaces. It was found that the conversion was higher for the regenerated cellulose and CMC than for cotton. The protocols developed using the model surfaces were applied to a case study on wood fibers with different degrees of complexity, namely dissolving and chemithermomechanical (CTMP) pulp. Untreated and oxygen-plasma modified pulps were compared with respect to the surface composition of functional groups. According to the derivatization reactions, functionalities containing oxygen were significantly increased on the plasma-treated samples. The effect of the treatment was found to be dependent on the type of pulp. Fluorine derivatization is shown to be an unambiguous method for clear assessment of the chemical functionalities of cellulosic surfaces.     

Adsorption and inactivation behavior of horseradish peroxidase on cellulosic fiber surfaces

The physical immobilization behavior of horseradish peroxidase (HRP) on cellulosic fiber surfaces was characterized using adsorption and inactivation isotherms measured by the depletion method followed by fitting of Langmuir’s and Freundlich’s models to the experimental data. The adsorption and inactivation behavior of simpler and relatively non-porous high and low crystalline cellulosic substrates (microcrystalline cellulose and regenerated cellulose) as well as more complex and porous cellulosic pulp fibers (bleached kraft softwood fibers) were investigated. The effect of the sorbent surface energy on HRP adsorption was demonstrated by increasing the hydrophobicity of the cellulosic fibers using an internal sizing agent. The influence of the fiber surface charge density on HRP adsorption was studied via modification of the cellulosic fibers using TEMPO (2,2,6,6-tetramethyl-1-piperidiniloxy radical)-mediated oxidation methods. Results showed that hydrophobic interactions had a much larger effect on HRP adsorption than electrostatic interactions. More hydrophobic fiber surfaces (lower polar surface energy) result in larger enzyme-fiber binding affinity constants and higher binding heterogeneity. It was also found that oxidation of the cellulosic fiber substrate reduces enzyme adsorption affinity but significantly increases the loading capacity per unit weight of the surface.     

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.

     

Anionic groups on cellulosic fiber surfaces investigated by XPS, FTIR-ATR, and different sorption methods

Anionic groups (AGs) on different cellulosic fiber surfaces were investigated by methylene blue (MB) and polyelectrolyte (PE) sorption, X-ray photoelectron spectroscopy (XPS), and total attenuated reflectance infrared spectrometry (FTIR-ATR). The MB sorption isotherms fitted well the Langmuir equation that gave consistent estimations of sorption capacities. FTIR-ATR showed that MB molecules had extensive accessibility to the fiber wall pores. Estimation of surface AGs by PE sorption gave much higher values than a new method combining MB sorption and XPS measurements (MB-XPS). The surface AGs in different cellulosic fibers accounted for 1-3% of the total AG content as revealed by MB-XPS. It was suggested that PE molecules can penetrate the fiber wall and form loops or unattached segments at external fiber surfaces that disrupt the PE sorption stoichiometry. The competition of MB and PE for the anionic sites in papermaking was assessed and it was shown that MB ions have a much stronger affinity to AGs than PE molecules.     

The fire-retarding effect of inorganic phosphorus compounds on the combustion of cellulosic materials

The pyrolysis and combustion of cellulosic substances treated with MAP and DAP have been studied using thermal analysis, flame spread tests and a specifically designed apparatus for smoldering combustion test. The samples used were: cotton string, cotton fabric and pure cellulose powder. Diammonium Phosphate (DAP) and Monoammonium Phosphate (MAP) can reduce the combustion and pyrolysis maximum mass loss temperature, decrease the initial pyrolysis temperature and considerably increase mass residue. Moreover, MAP and DAP reduce the flaming combustion rate of cellulosic materials and completely inhibit smoldering combustion. This study can facilitate a better understanding of the mechanism of pyrolysis and combustion of fire-retarded cellulosic materials.     

Use of Sucrose‐based Epoxy ­Formulations and Cellulosic Fibers in ­the Design,Preparation, and Screening ­of New Composite Insulation Materials

Non‐woven composite insulation materials were generated from cotton, kenaf, jute, polyester, polypropylene, sucrose‐based epoxy formulations, and aluminum foil. The needlepunched fiber batts were rendered flame resistant by use of inorganic reagents and urea. To discover suitable epoxy formulations to bind the cellulose fibers to themselves or to dissimilar surfaces and to make flexible composites, a comparison of the performance of the known epoxy allyl sucroses (EAS), epoxy crotyl sucroses (ECS), and diglycidyl ether of bisphenol‐A (DGEBA) was made. The epoxies were cured with commercial diethylenetriamine (DETA), and UNIREZs‐2142 and 2355®, to discover a formulation with the following characteristics: (a) low cure temperature; (b) low Young's moduli and glass transition temperatures of cured thermosets for flexible composites; (c) ample bond strength between the fabric and the bonded surfaces; and (d) non‐cytotoxicity and non‐mutagenicity of the epoxies. Based on results following these criteria, EAS was selected, and the formulation comprising EAS and UNIREZ‐2355® was deemed suitable to bind fiber batts to surfaces of any type and geometry. ASTM guidelines were used to construct a wooden frame cube (heat box) for the simultaneous rapid screening of cellulosic fiber batts and composites. The new materials were compared against R‐19 fiberglass insulation for their ability to resist heat flow (denoted by relative R‐values) and time taken to approach thermal equilibrium. Plain non‐woven cellulosic fiber batts showed relative R‐values of 4.0 °F ft² hr/Btu per inch thickness (0.27 K m²/W per cm), and took about 2 hr to establish equilibrium heat flow. Commercial fiberglass batts showed relative R‐values­of 2.2 per in (0.15 per cm) and took 1 hr to attain equilibrium heat flow. When 6.25 in (15.9 cm) thick batts of fiberglass were needle punched to a thickness of 1 in (2.54 cm), relative R‐values and equilibrium heat flow times were 4.0 per in (0.27 per cm) and 2 hr, respectively. This denoted that the densities and thermal resistances of non‐conducting materials are raised concurrently. Anisotropic heat flow behavior was observed in cellulosic fiber composites with aluminum foil (shiny side out) bonded on one side. It depended upon whether the aluminum foil side or the fibers side faced the heat source. In the latter orientation the aluminum acted as a heat sink, and in the former orientation the foil acted as a poor heat reflector. The poor performance of these insulation composites was related to the fact that aluminum was directly bonded to the fiber batts and was acting as a heat conductor. When cellulose fiber shims (spacers) were placed between the fiber batts and the aluminum foil, the R‐values of the composites were comparable to those of plain batts but the times taken to approach thermal equilibrium increased to >3 hr, denoting that the foil was acting more as a reflector and less as a conductor. Copyright © 2001 John Wiley & Sons, Ltd.     

Analysis of the topochemical effects of dielectric-barrier discharge on cellulosic fibers

This study investigates the fundamental topochemical effects of dielectric-barrier discharge treatment on bleached chemical pulp and unbleached mechanical pulp fiber surfaces. Fibers were treated with various levels of dielectric-barrier discharge treatment ranging from 0 to 9.27 kW/m²/min. Changes to the fiber surface topochemistry were investigated by atomic force microscopy (AFM). The AFM studies were complemented by inverse gas chromatography (IGC), contact angle evaluation, poly-electrolyte titration, viscosity testing and determination of water retention value (WRV). The static coefficient of friction and zero-span tensile index of sheets were also evaluated. Low dielectric-barrier discharge treatment levels resulted in increased surface energy and roughness. Fibers treated at high applied power levels showed surface energies and roughness levels near that of reference samples as well as evidence of degradation and decreased fiber swelling.     

Use of inverse gas chromatography to characterize cotton fabrics and their interactions with fragrance molecules at controlled relative humidity

The present work focused on the surface characterization and fragrance interactions of a common cotton towel at different relative humidities (RHs) using inverse gas chromatography (IGC) and dynamic vapour sorption. The sigmoidal water sorption isotherms showed a maximum of 16% (w/w) water uptake with limited swelling at 100% RH. This means that water interacts strongly with cotton and might change its initial physico-chemical properties. The same cotton towel was then packed in a glass column and characterized by IGC at different relative humidities, calculating the dispersive and specific surface energy components. The dispersive component of the surface energy decreases slightly as a function of relative humidity (42 mJ/m2 at 0% RH to 36 mJ/m2 at 80% RH) which would be expected from swelling of the humidified cotton. The Gutmann's donor constant Kd increased from 0.28 kJ/mol at 0% RH to 0.42 kJ/mol at 80% RH, indicating that a greater hydrophilic surface exists at 80% RH, which is also as expected. Water, undecane and four fragrance molecules (dimetol, benzyl acetate, decanal and phenylethanol) were used to investigate cotton-fragrance interactions between 0 and 80% RH. The adsorption enthalpies and the Henry's constants were calculated and are discussed. The higher values for the adsorption enthalpies of polar molecules such as dimetol and phenylethanol suggest the presence of hydrogen bonds as the main adsorption mechanism. The Henry's constant of dimetol was also determined by headspace gas chromatography measurements at 20% RH, giving a similar value (230 nmol/Pa g by IGC and 130 nmol/Pa g by headspace GC), supporting the usefulness of IGC for such determinations. This work confirms the usefulness of chromatographic methods to investigate biopolymers such as textiles, starches and hairs.     

Surface modification of high-performance polymeric fibers by an oxygen plasma. A comparative study of poly(p-phenylene terephthalamide) and poly(p-phenylene benzobisoxazole)

Poly(p-phenylene terephthalamide) (PPTA) and poly(p-phenylene benzobisoxazole) (PBO) fibers were exposed to an oxygen plasma under equivalent conditions. The resulting changes in the surface properties of PPTA and PBO were comparatively investigated using inverse gas chromatography (IGC) and atomic force microscopy (AFM). Both non-polar (n-alkanes) and polar probes of different acid-base characteristics were used in IGC adsorption experiments. Following plasma exposure, size-exclusion phenomena, probably associated to the formation of pores (nanoroughness), were detected with the largest n-alkanes (C(9) and C(10)). From the adsorption of polar probes, an increase in the number or strength of the acidic and basic sites present at the fiber surfaces following plasma treatment was detected. The effects of the oxygen plasma treatments were similar for PPTA and PBO. In both cases, oxygen plasma introduces polar groups onto the surfaces, involving an increase in the degree of surface nanoroughness. AFM measurements evidenced substantial changes in the surface morphology at the nanometer scale, especially after plasma exposure for a long time. For the PBO fibers, the outermost layer - contaminant substances - was removed thanks to the plasma treatment, which indicates that this agent had a surface cleaning effect.     

A study of the surface properties of cotton fibers by inverse gas chromatography

In the present study, the potential relationships between the microstructure and the surface properties of different cotton fibers are analyzed by inverse gas chromatography (IGC) at infinite dilution. By measuring the retention time of polar and nonpolar gaseous probes into a column containing the fibers, surface characteristics of these fibers, in particular the dispersive component of their surface energy and their surface morphological index, were determined. It is clearly shown that the presence of natural waxes on cotton fibers plays a major role on their thermodynamic surface properties, affecting the surface energy and the acid-base character as well as the morphological aspects of such fibers. Finally, it appeared that IGC is a well appropriate method for the evaluation of the surface characteristics of cotton fibers.     

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.     

Covalent attachment of lysozyme to cotton/cellulose materials: protein verses solid support activation

Covalent attachment of enzymes to cellulosic materials like cotton is of interest where either release or loss of enzyme activity over time needs to be avoided. The covalent attachment of an enzyme to a cellulosic substrate requires either activation of a protein side chain or an organic functional group on the cellulosic substrate. Use of a water soluble carbodiimide to create an amide linkage as the covalent attachment between the enzyme and substrate represents an aqueous-based alternative which may be preferred for textile processes. Here we describe an amide bond-mediated lysozyme immobilization applied to cotton where either the carboxylate side chains of the protein or pendant carboxylates in a citrate, cross-linked cotton support are activated as the O-acyl-isourea intermediate, and the reactive amino nucleophiles are derived from amino-silanized cotton and the protein’s amino side chains, respectively. A comparison is made of the two activation approaches to covalently link lysozyme to two different cotton fabrics using the water soluble carbodiimide 1-cyclohexyl-3-(2-morpholinoethyl)-carbodiimide-metho-p-toluene sulfonate. A comparison of the resulting enzyme activities of lysozyme on two different cotton supports showed that linking lysozyme to citrate crosslinked cotton gave higher activity than on aminosilanized cotton. The lysozyme-cellulose conjugate formed on the citrate crosslinked nonwoven cotton fabric gave the highest yield and antimicrobial activity.     

Hard to remove water in cellulose fibers characterized by high resolution thermogravimetric analysis - methods development

A new method is applied to classify water, termed ‘hard-to-remove (HR) water’, in a cellulosic fiber and water system from an isothermal thermogravimetric analysis (TGA). The hard-to-remove (HR) water content is defined as the moisture ratio (g of water / g of dry sample) of the fiber-water system at the transition between the constant rate zone and the falling rate zone of evaporative change in mass. Specific experimental conditions have been defined for an appropriate measurement of the HR water content. The HR water content was correlated with measurable characteristics of cellulosic fibers including water retention value and freeness. The new TGA protocol can be performed on extremely small samples as a convenient and insightful characterization technique for cellulosic fibers.     

The effective surface energy of heterogeneous solids measured by inverse gas chromatography at infinite dilution

Inverse gas chromatography (IGC) at infinite dilution has been widely used to access the nonspecific surface free energy of solid materials. Since most practical surfaces are heterogeneous, the effective surface energy given by IGC at infinite dilution is somehow averaged over the whole sample surface, but the rule of averaging has thus far not been established. To address this problem, infinite dilution IGC analysis was carried out on mixtures of known heterogeneity. These materials are obtained by mixing two types of solid particles with significantly different surface energies as characterized individually with IGC, and results are obtained for binary combinations in varying proportions. It is found that when all surface components have the same accessibility by probe molecules, the effective surface energy of such a heterogeneous surface is related to the surface energy distribution by a square root linear relationship, square root sigma(eff)(LW)= summation operator (i)phi(i) square root sigma(i)(LW), where sigma(i)(LW) refers to the nonspecific (Lifshitz-van der Waals) surface energy of patches i, and phi(i) to their area fraction.     

Antibacterial cotton fabric prepared by a “grafting to” strategy using a QAC copolymer

Quaternary ammonium compounds (QACs) have outstanding antimicrobial effect, but covalent immobilization of plentiful QAC onto cotton fiber surface to realize a durable function remains a challenge. Herein, a quaternary ammonium monomer, [2-(methacryloyloxy) ethyl] trimethylammonium chloride (DMC) was co-polymerized with methyl acrylate (MA) to prepare an antibacterial copolymer, poly(DMC-co-MA). To graft the copolymer with an improved grafting efficiency, cotton fabric was treated using carboxymethyl chitosan (CMC) to establish an amino-functionalized fiber surface first. This treatment allows the amidation reactions between the amino groups and the pendant ester groups in the poly(DMC-co-MA) to take place, achieving a durable anionic polymer coating onto the fiber surfaces with remarkably antibacterial effect. Characterization results indicated that when DMC/MA monomer ratio was 100:1, the resulting copolymer endows the modified cotton fabric with antibacterial capability that inactivates all Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Even after 50 laundering cycles, more than 98.0% of the antibacterial rate could still be retained. Moreover, the wearing comfort properties such as softness, water absorption and air permeability of the finishing cotton fabrics have been insignificantly changed by comparing to the untreated cotton fabric.

     

Nonequilibrium Phenomena Influencing the Wetting Behavior of Plant Fibers

It is examined whether useful information on plant fiber surfaces can be retrieved from wetting experiments such as dynamic contact angle (DCA) analysis by use of the Wilhelmy technique and the Lifshitz-van der Waals acid-base theory. It is argued from a theoretical point of view that plant fibers may give rise to various complex phenomena during wetting experiments, phenomena which are typically not found for synthetic fibers, and that these phenomena can be a source of invalidation of experimental techniques which are commonly thought to supply information on equilibrium (or quasi-equilibrium) properties of plant fiber surfaces or of surface-liquid interactions. The nonequilibrium phenomena are studied experimentally by DCA analysis of 10 sisal fibers, 10 coir fibers, and 5 polyacrylate-coated glass fibers. The fibers are immersed in deionized water at 10 different speeds ranging from 2 to 100 μm s(-1) and the relationship between immersion speed and contact angle is examined. In contrast to what is found for the coated glass fibers, the results indicate that the (aqueous) wetting behavior of sisal and coir fibers is qualitatively far from the behavior which should ensure the meaningful interpretation of the wetting data as (quasi-)equilibrium data. From both a theoretical and a practical basis it is hence concluded that nonequilibrium phenomena necessitate a more severe form of precaution toward surface energy component theories when these are used for interpreting plant fiber wetting than what is currently at issue. Copyright 2001 Academic Press.     

Acetylation of raw cotton for oil spill cleanup application: an FTIR and 13C MAS NMR spectroscopic investigation

Fourier transform infrared (FTIR) and 13C MAS NMR spectroscopy have been used to investigate the acetylation of raw cotton samples with acetic anhydride without solvents in the presence of different amounts of 4-dimethylaminopyridine (DMAP) catalyst. This is a continuation of our previous investigation of acetylation of commercial cotton in an effort to develop hydrophobic, biodegradable, cellulosic sorbent materials for cleaning up oil spills. The FTIR data have again provided a clear evidence for successful acetylation. The NMR results further confirm the successful acetylation. The extent of acetylation was quantitatively determined using the weight percent gain (WPG) due to acetylation and by calculating the ratio R between the intensity of the acetyl C=O stretching band at 1740-1745 cm(-1) and the intensity of C-O stretching vibration of the cellulose backbone at about 1020-1040 cm(-1). The FTIR technique was found to be highly sensitive and reliable for the determination of the extent of acetylation. The level of acetylation of the raw cotton samples was found to be much higher than that of cotton fabrics and the previously studied commercial cotton. The variation of the R and WPG with reaction time, amount of DMAP catalyst and different samples of raw cotton is discussed.     

Thermal analysis of aged hdpe based composites

HDPE based composites were produced with 10-20-30 and 40% composite mass of wood fiber. The coupling agents were epolene and silane. The thermal behavior of composite samples was analyzed as a function of the coupling agent content, the exposure time and the wood fibers content by means of differential scanning calorimetry. Calorimetric curves of all samples of first and second heating shows a similar behavior. Some significant relation has been observed between the exposure time and the degree of crystallinity for the same percentage of fiber samples. A linear relation between the melting enthalpy average vs. content in cellulosic fibers is detected. Nevertheless, the fibers non-pretreated with coupling agent show a lower loss of crystallinity of the HDPE matrix at low wood fiber content (10%). A slight diminution of the melting peak temperature is detected as increasing the exposure time. This revised version was published online in July 2006 with corrections to the Cover Date.