Interfacial properties of polyelectrolyte–cellulose systems. III. Theoretical model for the electrokinetic behavior of cellulose fibers with adsorbed monolayers of cationic polyelectrolyte

A theoretical model is proposed to account for the experimental results in part II. The basic assumption is that the total surface charge of the monolayer-formed DP fibers stems from (i) fixed ionized groups on the surface and (ii) adsorbed ions on the surface from surrounding solutions. The fixed ionized groups are the carboxyl groups of the fibers and quaternary ammonium groups of the polymer. The proposed model correlates the amount of adsorbed polymer with the zeta potential of the monolayer-formed DP fibers. Calculations made on the proposed model using the experimental data in part II suggest that a comparison of the charge calculated from zeta potential with that from the amount of adsorbed polymer yields ca. 0.04% of the fixed ionizable groups as effective charged sites, i.e., electrokinetically detectable. This finding is due to the binding of counterions to the fixed ionized sites on the surface. Zeta potentials of the DP with adsorbed monolayers largely stem from the fixed ionized groups with only a minor contribution from the adsorbed ions. The zeta potentials are nearly proportional to the difference between the number of cationic and anionic groups on the surface.     

Interfacial properties of polyelectrolyte-cellulose systems. IV. Electrokinetic properties of carboxymethylcellulose fibers with adsorbed multilayers of cationic polyelectrolyte

Zeta potential measurements by the streaming current method were performed on carboxymethylcellulose (CMC) with and without irreversibly adsorbed multilayers of cationic polyelectrolyte. Factors affecting the electrokinetic properties such as the amount of adsorbed polymer, polymer molecular weights (M_n 50,000 and 200,000), ionic strength (10^?5 ～ 10^?2M KCl), and pH of the streaming medium (KCl solutions) were examined. The negative zeta potential of CMC decreased to the point of monolayer formation and increased from that point to the saturated multilayer formation. The polarity of the zeta potential was negative throughout every adsorption stage. The negative zeta potential increase was attributed to: (a) binding of anions (Cl^? and OH^?) to the outermost layer of the multilayer from KCl solutions and (b) change in chemical potentials of counterions in a diffuse double layer due to expansion of the double layer in the presence of the adsorbed multilayer on CMC. The results suggest that the carboxyl groups under the monolayer are undetectable electrokinetically; however, the negative charge, due to unneutralized carboxyl groups under the monolayer, appears to cause further adsorption forming a saturated multilayer. When the effect of unneutralized carboxyls of CMC are shielded at higher levels of adsorption, the outermost layer of the multilayer becomes a potential-determining layer.     

Grafting of polypropylene fibers. II. Electrokinetic properties of grafted polypropylene fibers

Electrokinetic properties of methacrylic acid- and acrylonitrile-grafted polypropylene fibers measured in the presence of cationic dyes are reported. The zeta potential of polypropylene fibers decreases, and the surface charge density along with surface conductivity increases as the concentration of the dyes in the streaming solution increases. The zeta potential at pH 7 decreases as the amount of graft increases in case of both acrylonitrile- and methacrylic acid grafted fibers. Both surface charge density and surface conductivity increase with the increase in dye concentration for both acrylonitrile- and methacrylic acid-grafted fibers. The results are explained on the basis of the cationic dye adsorption on the grafted fiber in the case of methacrylic acid graft. In the case of acrylonitrile-grafted fibers, this could be due to the strong attraction of cationic dye to the nitrile group of the grafted fibers.     

High-strength–high-modulus polyimide fibers II. Spinning and properties of fibers

The polyimides based on 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) described in Part I of this series were dissolved in p-chlorophenol and spun into fibers using a coagulating bath of ethanol. The fibers as spun had in general low tenacities and low moduli, but a heat treatment at 300–500°C under tension produced a remarkable increase in strength and modulus, and fibers with a tensile strength of 26 g/den (3.1 GPa) and an initial modulus higher than 1,000 g/den (120 GPa) could be obtained. Thus, the annealed fibers of polyimides are comparable to aramid fibers in mechanical properties. To heating in air and in the saturated steam, the polyimide fibers showed higher resistance than the aramid fibers. The polyimide fibers surpassed the aramid fibers in resistance to acid treatment and ultraviolet (UV) irradiation, but were inferior in resistance to alkali treatment. The annealed fibers of polyimides displayed distinct X-ray diffraction patterns. The chain repeat distance of 20.5 Å determined on the fibers of polyimide prepared from BPDA and o-tolidine, and 20.6 Å determined on the fibers of polyimide derived from BPDA and 3,4′-diaminodiphenyl ether are reasonable when the dimensions of monomeric units and the shapes of the molecular chains are considered. The X-ray reflections of both polyimide fibers were indexed satisfactorily on the basis of postulated unit cells.     

Interfacial properties of regenerated cellulose fiber and thermoplastic systems

In dry-formed polymer-bonded networks of cellulose fibers and in other types of nonwovens, the fiber-polymer joint is considered to be the primary factor determining the ultimate properties of the network structure. In an attempt to develop a model describing the joint failure, the well-known fiber pullout test has been applied to a system consisting of regenerated cellulose fibers and three different polymer matrices: a styrene–acrylate copolymer, poly(vinyl alcohol), and high density polyethylene. For each system, the interfacial bond strength was evaluated. The results are, to some extent, discussed in relation to the mechanical behavior of dry-formed networks bonded with similar polymeric materials. It is suggested that both the interfacial properties and the cohesive strength of the polymer binder are of importance for the mechanical strength of the bonded network.     

Grafting onto polyester fibers. III. Electrokinetic properties of acrylic acid and acrylonitrile-grafted polyester fibers in the presence of cationic dyes

The electrokinetic properties such as zeta potential, surface charge density, and surface conductivity of polyester fibers grafted with acrylic acid and acrylonitrile were measured when cationic dye solutions were streamed through. The presence of the cationic dyes on the surface of the fibers and their specific adsorption at the carboxylic groups in the acrylic acid graft copolymer produce lowering of zeta potential. The decrease in surface charge density as the percent graft increases is due to the decrease in surface area of the fibers due to the adsorption of the cationic dyes. The same trend is observed with acrylonitrile-grafted fibers. The surface conductivity of the acrylonitrile-grafted polyester fibers increases with increase in dye concentration of the streaming solution. The results for the 27.4% grafted sample differed from those of the 7.32% and 12.1% grafts, which is indicative of the formation of a three-dimensional network causing change in both the physical structure as well as the chemical nature of the surface of the substrate.     

Electrokinetic properties of polypropylene‐layered silicate nanocomposite fibers

Nanocomposite fibers based on polypropylene (PP) polymer were prepared with different content of nanofiller. Filaments were spun from an isotactic iPP homopolymer. Montmorillonite modified by N,N‐dimethyl‐N,N dioctadecylammonium cations was used for preparation of PP nanocomposite fibers. A PP grafted with acrylic acid was added as a coupling agent. Nanocomposite fibers were characterized, i.e., the surface morphology of PP nanocomposite fibers was observed and surface properties were defined by electrokinetic properties determination by zeta potential measurements. For particle distribution observation the plasma etching was involved as a method for sample preparation. The addition of nanoparticles has an impact on ZP value of nanofilled fibers, however, isoelectric point IEP is not significantly influenced by different concentrations of nanofiller. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Surface modification of cellulose fibers. II. The effect of cellulose fiber treatment on the performance of cellulose–polyester composites

Cellulose fibers treated with different coupling agents based on trichloro-s-triazine have been evaluated in terms of their reinforcement effect on unsaturated polyesters. The treatment with coupling agents containing double bonds resulted in what we believe to be the formation of covalent bonds between fiber and matrix. This has been compared with a treatment, which can only lead to formation of close interfacial molecular contact by wetting. The tensile properties of composites prepared from treated and untreated fibers were studied before and after exposure to water. It was found that all types of fiber treatment decreased water absorption and the reduction of mechanical properties in wet conditions, but that the degradation at the fiber/matrix interface which occurs from immersion in water and drying could only be avoided through the development of covalent bonds between fiber and matrix. Scanning electron microscopy was used to study the adhesion between fiber and matrix. An explanation of the reduction of mechanical properties of cellulose-fiber reinforced polymers in wet conditions is proposed.     

Infrared–deuteration study of regenerated cellulose fibers

This paper describes a study by infrared, deuteration, and other techniques of the fine structure of three regenerated cellulose fibers (Fortisan, a super tire yarn, and a fiber of high wet modulus). The infrared and deuteration measurement provide information on the amount and perfection of the hydrogen-bond ordered material in these celluloses. The three fibers are markedly different in structure: the Fortisan contains about 40% ordered cellulose of a high average degree of perfection, whereas the super tire yarn contains a smaller amount (about 20%) of ordered cellulose of a lower average degree of perfection: the yarn of high wet modulus contains about as much ordered material as the Fortisan, but of an average degree of perfection more similar to that of the super tire yarn. Infrared-dichroism measurements on the fibers are described. The infrared and dichroism studies are discussed in relation to the results of x-ray, moisture regain, acid hydrolysis, and birefringence measurements on the fibers. The infrared-deuteration behavior of acid hydrolysis residues prepared from the three fibers is described; these residues are more highly ordered than the patent fibers, but yield no information of any value in characterizing the structures of the parent fibers.     

Mercerization of cellulose. II. Alkali–cellulose intermediates and a possible mercerization mechanism

Continued study of the five crystalline Na–celluloses, previously shown to occur as intermediates during the mercerization of cellulose and exhibiting two types of crystallographic fiber repeats, further indicates that they fall into three classes based on their unit cells and NaOH contents. In one class are Na–celluloses I and III, both containing up to 34% NaOH; in the second class are Na–celluloses IIA and IIB, marked by ca.15 Å fiber repeat and containing up to 65% NaOH; and in the third class is Na–cellulose IV which is likely to be a hydrated form of cellulose II. Na–cellulose I was found to be the common first alkali–cellulose structure produced in the NaOH treatment of both cellulose I and cellulose II. Further study of this conversion step suggested a mercerization mechanism in which the alkali begins the conversion of cellulose to Na–cellulose I in the amorphous parts of the fiber. The conversion of the parallel-chain cellulose I structure to an antiparallel one is likely to occur already in this first step.     

Preparation of grafted cationic polymer/silver chloride modified cellulose fibers and their antibacterial properties

In this article, we present a simple method for synthesizing antibacterial cellulose fibers that were modified with a cationic polymer and immobilized silver chloride (AgCl) particles. Relatively simple techniques of graft polymerization and onsite precipitation were used to fabricate the composites. Scanning electron microscopy images, Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, and energy‐dispersive X‐ray spectroscopy confirmed the immobilization of the AgCl particles. The observed inhibition zone of the immobilized AgCl particle composites indicated that the biocidal silver ions were released from the composites in aqueous solution. Compared with cationic‐polymer‐grafted cellulose fibers or AgCl alone, the cationic polymer/AgCl composites showed excellent antibacterial activity against Gram‐negative Escherichia coli and Gram‐positive Staphylococcus aureus. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42092.     

Heterogeneous polymer–polymer composites. II. Preparation and properties of model systems

A two-stage emulsion polymerization procedure has been developed and used to prepare relatively uniform populations of heterogeneous acrylic latex particles (HLP). One class of particles (HLP1) can be described as composite materials comprising a glassy continuous phase and a rubbery discrete phase. Another class (HLP2) can be described (at high rubber content) as composite materials comprising a rubbery continuous phase and a glassy discrete phase. The phase structure of the HLP1 is sufficiently stable to allow fabrication of composites having a uniform spatial distribution of inclusions by direct compression molding. Although the observed particle structure of the HLP2 does not depend markedly on crosslinking, the phase structure and mechanical properties of compression moldings do. Crosslinking of the glassy stage appears to stabilize HLP2 phase structure during molding, while crosslinking of the rubbery stage favors phase inversion. The observed HLP2 particle structures and the morphology of molded HLP1 specimens are consistent with a shell-core model. It is found that the modulus and thermal expansion coefficient of many of these materials can be adequately described in terms of a simple theoretical model for the elastic and thermoelastic properties of particulate composites, provided that an interaction parameter interpreted as a maximum packing fraction is introduced.     

Poly(methyl methacrylate)–cellulose nitrate copolymers. II. Physical and mechanical properties

Poly(methyl methacrylate)–cellulose nitrate copolymers were prepared by bulk polymerization using benzoyl peroxide as initiator. Cellulose nitrates of two different nitrogen contents (11.4 and 12.2%) were used. The prepared copolymers were γ-irradiated for specified periods of up to 11.83 Mrad. Their physical and mechanical properties were measured before and after irradiation. The title copolymers showed lower modulus, tensile strength, and elongation at break than poly(methyl methacrylate) itself, but they showed better hardness and abrasion. Irradiation to up to 6.57 Mrad improved the modulus of the copolymers. Hardness and abrasion were improved by increasing cellulose nitrate content. The prepared copolymers that contained cellulose nitrate of 11.4% nitrogen showed secondary transition points. The increase of cellulose nitrate concentration shifted both first and second transition points to relatively higher values.     

Cellulose graft copolymers. II. Graft copolymerization of ethyl acrylate with γ-irradiated cellulose from acetone–water systems

Ethyl acrylate was graft-copolymerized from acetone–water systems with γ-irradiated, purified cotton cellulose. The scavenging of the free radicals in the irradiated cellulose by water, acetone, and water–acetone systems was determined by electron spin resonance spectroscopy. The ESR spectra of free radicals, scavenged by water and acetone, were recorded by the use of a time-averaging computer attached to the ESR spectrometer, in which the ESR spectrum of the irradiated cellulose, which had been immersed in water and/or acetone, was electronically subtracted from the ESR spectrum of the irradiated cellulose control. For both water and acetone, the ESR spectra of the scavenged free radicals were singlets. This indicated that free radical sites formed on carbon C₁ or C₄ on radiation-initiated depolymerization, which would generate singlet ESR spectra, were readily accessible to these solvents. The maximum scavenging of the radicals was observed when irradiated cellulose was immersed in acetone–water solution which had a composition of 25/75 vol-%. The scavenging of the free radicals in irradiated cellulose when immersed in acetone–water solutions was less than when immersed in methanol–water solutions. Also, the extent of graft copolymerization of ethyl acrylate from acetone solutions with irradiated cellulose was less than that of ethyl acrylate from methanol solutions. These differences were probably due to differences in the diffusion rates of acetone and methanol into the cellulosie structure. The Trommsdorff-type effect in the acetone solutions would be less than in the methanol solutions, since acetone is a better solvent for poly(ethyl acrylate) than methanol.     

Interfacial interaction and mechanical properties of chitin whisker–poly(vinyl alcohol) gel‐spun nanocomposite fibers

Nanocomposite fibers were prepared from chitin whiskers (ChWs) as the reinforcing phase and poly(vinyl alcohol) (PVA) as the matrix. Colloidal suspensions of ChWs, obtained by acid hydrolysis of chitin from crab shell, were thoroughly mixed with aqueous PVA. The homogeneous PVA–ChW suspensions were gel‐spun into a methanol coagulating bath. Wide‐angle X‐ray diffraction patterns evidenced the orientation of ChWs along the fiber axis. From differential scanning calorimetry, the crystallinity of the PVA component was found to increase with ChW loading due to the possible dragging of PVA chains adhering to ChWs during vertical extrusion. The non‐isothermal crystallization peak of PVA was observed to shift to lower temperature with ChW loading indicating interfacial interactions between PVA and ChW. Further interaction between PVA and ChW was evidenced by the shifting of the Fourier transform infrared bands of PVA to lower wavenumber and the dynamic tan δ peak, corresponding to α‐relaxation of PVA, shifting to higher temperature. The interaction of ChWs with the matrix PVA yielded a significant enhancement in the mechanical properties of the nanocomposites. Copyright © 2012 Society of Chemical Industry     

Copper (II) ions and copper nanoparticles‐loaded chemically modified cotton cellulose fibers with fair antibacterial properties

This work describes the release of copper(II) ions from cellulose fibers, which have been chemically modified by periodate‐induced oxidation of cellulose, followed by covalent attachment of biopolymer chitosan. The release of copper(II) ions has been investigated in physiological fluid (PF) and protein solution (PS) both at 37°C. Fibers have demonstrated excellent antibacterial activity against E. coli. Finally, their borohydride‐induced reduction has yielded copper nanoparticle‐loaded fibers, with average diameter of particles, nearly 28.94 nm. The formation of copper nanoparticles has been established by surface plasmon resonance and FTIR spectroscopy. These fibers also show fair biocidal action against E. coli. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

含硼非均相体系中纤维素阳离子化反应的优化

在含有硼化合物（BC）的异丙醇（iPA）-H₂O非均相体系中,以3-氯-2-羟丙基三甲基氯化铵（CTA）为醚化剂,对棉短绒纤维素（Cel.）进行阳离子化反应。采用正交实验确定了影响阳离子纤维素取代度（DS）的因素,并对反应进行了优化,并采用¹H-NMR对产物的结构进行了确认。结果表明,按m(Cel.)∶m(iPAⅠ)∶m(iPAⅡ)∶m(30% NaOH)∶m(50% CTA)∶m(BC)= 100∶1000∶400∶296∶696∶20的配比,室温25 ℃活化处理60 min,50 ℃恒温反应4 h,产物取代度DS达到0.54。     

Polylactide. II. Discontinuous dry spinning–hot drawing preparation of fibers

The mechanical properties and morphology of poly(L-lactide) fibers, prepared by the dry spinning–hot drawing process using different nonsolvent/chloroform spinning solutions, were studied in relation to fiber in vitro degradability. Acetone, methanol, ethanol, and cyclohexane were used as nonsolvents in the spinning mixture with as-polymerized PLLA, i.e., PLLA containing 10% of residual L-lactide. The tensile strength, structure, and degradability of obtained fibers were mainly governed by the nonsolvent volatility. Generally, the higher the volatility, the higher the strength, and the faster the degradation. The acetone/chloroform spinning system produced fiber with an increased degradation rate in comparison to the pure chloroform spinning system. © 1994 John Wiley & Sons, Inc.