Molecular Mechanisms of Disperse Dyeing of Polyester and Nylon Fibres

The kinetics of the dyeing of polyester fibres with disperse dyes have previously been discussed in terms of a model in which the only forces of interaction between dye and polymer are those that give rise to mutual solubility. The rate and extent of dyeing depend on the size and shape of the dye molecules and the detailed structure of the fibre. The concentration profiles of dye within single filaments of polyesters and nylons have now been determined by a new method termed ‘optical sectioning’, in which an image of a filament is scanned by a narrow slit. The dye distributions are found by comparing experimental transmission values with those calculated by a computer for a model system in which various parameters can be adjusted. For the polyester-dye systems the rate constant of transfer of dye from dyebath to fibre (k₁) was the same as the rate constant of diffusion away from the interface (k₂). Some nylon-dye systems, on the other hand, behaved as if k₂ = k₁, whereas others behaved initially as if k₁ = k₂ but later as if k₂ > k₁. Apparent diffusion coefficients were also derived from sorption measurements and were found to fall as the dye concentration in the fibre increased. Measurement of the orientation of the dye molecules by optical dichroism showed that the dye molecules entering the filaments late in the dyeing process were more highly orientated than the earlier ones. The decrease in diffusion coefficient has been interpreted in terms of the observed higher orientation, as resulting from a greater entropy of activation in the diffusion process.     

A significant approach to dye cotton in supercritical carbon dioxide with fluorotriazine reactive dyes

A series of fluorotriazine reactive dyes have been synthesized and applied to dye cotton in supercritical carbon dioxide (scCO₂) with good dyeing results. The pieces of cotton to be dyed were previously presoaked in a protic solvent and cosolvents were applied during dyeing. The colour strength of the dyeings was evaluated by K/S measurements. The K/S values achieved on cotton dyed were up to 35.8 ± 4.2. Even after the cotton was subjected to a Shoxlet extraction at 358 K for 1 h, a maximum K/S value of 20.2 ± 1.8 was measured. The percentage of dye molecules chemically fixed to the cotton was on average 85%. The excellent reactivity of fluorotriazines allowed a reduction of 3 h on the dyeing time. It is noticeable that a dye concentration of 10% on weight of the fibre (owf) can be applied to dye cotton with fluorotriazines, since no damage of the cotton fibres occurred, as observed for the chlorotriazines at this high dye concentration.Dyes with fluorotriazine as reactive group were found to be the most preferable dyes for dyeing cotton in scCO₂, as they were able to exceed the limitation of the reaction with the cotton.     

Pulsed n.m.r. studies of molecular motion in wet nylon-6,6 fibres

The influence of water molecules on molecular motion in commercial nylon-6,6 fibres has been investigated by pulsed n.m.r. techniques. Transient n.m.r. signals, T₂ and T₁ relaxation times for the fibre protons were measured as a function of temperature and moisture (D₂O) content. Above the glass transition temperature, T_g, of the fibre, separation of the signal into two components, a ‘rigid’ and ‘non-rigid’ fraction, was possible. For wet fibres, the temperature at which the ‘non-rigid’ or ‘mobile’ component appeared was reduced as the water content was increased and the ‘mobile fraction’ increased with temperature. This behaviour is explained in terms of the mobilization of amorphous chain segments above the T_g and their ability to be ‘plasticized’ by water molecules. The effect of D₂O molecules and paramagnetic Mn²⁺ ions on T₁ relaxation of rigid and mobile segments provided further information on the properties of accessible chain segments between and on the crystallite surfaces. A chain folded model of semi-crystalline morphology has been adopted throughout the discussion.     

Confocal Raman study of poly(ethylene terephthalate) fibres dyed in supercritical carbon dioxide: dye diffusion and polymer morphology

Confocal Raman microscopy (CRM) has been used to extract dye diffusion data from poly(ethylene terephthalate) (PET) fibres dyed with Disperse Yellow 23 under supercritical CO₂ conditions. Spectral information as a function of depth was measured in a non-destructive manner using dry and oil objectives in confocal Raman mode. Mapping along the radius of the fibre cross-section was performed and compared to the data from the confocal measurements. A significant dye concentration gradient has been observed along the line normal to the fibre surface which the data from the oil confocal measurements accurately describes to a depth of 45 μm. The effect of the supercritical CO₂ dyeing process on the fibre morphology has also been evaluated using CRM.     

Properties,morphology and structure of BPDA/PPD/ODA polyimide fibres

Abstract

A family of random co-poly(amic acid)s containing 4,4′-oxydianiline (ODA) moiety were synthesised in N,N′-dimethylacetamide. The co-poly(amic acid) solutions were used as spinning dope for dry jet wet spinning process into as spun poly(amic acid) (PAA) fibres. The polyimide (PI) fibres were obtained from PAA fibres after being imidised and drawn in furnace. The processability and mechanical properties of the fibres were notably improved by incorporating ODA into 3,3′,4,4′-biphenyltetracarboxylic dianhydride/p-phenylenediamine (BPDA/PPD) backbone. The best strength and modulus of BPDA/PPD/ODA PI fibre (diamine mole ratio of PPD/ODA?=?85∶15) attained 2·25 and 96·5 GPa respectively, which were approximately three times the tenacity of the BPDA/PPD PI fibre. The SEM image showed that the cross-section of each stage fibres was round and void free. In addition, ‘skin–core’ and microfibrillar structure were not observed. The thermal properties of PI fibres were also investigated. The results showed that the PI fibres have excellent thermal stability; moreover, the dimensional stability and structural homogeneity of the fibres were significantly improved by heat drawn stage. T_g was found to be ～290°C by thermomechanical and dynamic mechanical analyses. The X-ray (wide angle X-ray diffraction and small angle X-ray scattering) experiments indicated that the ordering degree of longitudinal and lateral stacks, as well as the molecular orientation of PI fibre, was improved in the preparation process of fibres. Furthermore, the mechanical properties of fibres are profoundly affected by the heat drawn conditions.     

Effect of metal salts on the dyeing of freshly spun polyacrylonitrile fibre with acid dyes

Conclusions The effect of the metal cations Al³⁺, Zn²⁺, and Cr³⁺ on the process of dyeing freshly spun PAN fibres with acid dyes has been studied. It has been found that the greatest amount of dye is fixed on the fibre when Al³⁺ ions are introduced into the dye bath.On the basis of analysis of the IR spectra of the dyed fibres, a mechanism has been proposed for the interaction of both the metal cations and also of the dye with PAN fibre. It has been found that the metal cation is bonded with the fibre both by an ionic bond with the—COOH groups and also by a coordination bond with >C=0 groups of the polymer substrate.Translated from Khimicheskie Volokna, No. 6, pp. 13–14, November–December, 1986.     

The coloration of polypropylene fibres with acid dyes

Modified polypropylene fibre has been prepared by incorporating a polymeric additive into the polypropylene, followed by melt spinning. Fibres with various additive concentrations were dyed with acid dyes, and the amount of dye adsorbed by the fibre was compared with the concentration of dye sites supplied to the fibre by the additive. A diffusion mechanism of dye molecules through interconnected additive particles to the fibre matrix is proposed. Colour yield was assessed by reflectance spectroscopy and photoacoustic spectroscopy. The latter was shown to be particularly suitable for measuring very dark colours. Photoacoustics can also used to detect ring dyeing of fibres at lower additive concentration.     

MODELLING AND CORRELATING THE PERMEABILITY OF PULP AND PAPER

ABSTRACT

A sheet of paper is modelled as a network of cellulose fibres, either cylindrical or band-shaped. The equations for creeping flow through such structures are solved, and The calculated permeabilities are compared with measured values. Flow through some paper structures such as pulp sheets and handsheets of unbeaten sulphate pulp is adequately described by the structural model involving band-shaped fibres when a fibre aspect ratio of 3.5 is used. For newsprint sheets the measured permeability is lower than that predicted by the models when physically realistic values of the aspect ratio are taken. A total of 19 different paper grades have been characterised by measurement of the total specific surface area and The fibre orientation ratio in addition to the measurements of effective diffusivity, permeability and porosity. Permeability and effective diffusivity correlate with each other and permeability correlates with fibre orientation, so that at constant porosity, permeability decreases with increasing fibre orientation.     

A Study of the Interphase Region in Carbon Fibre/Epoxy Composites using Dynamic Mechanical Thermal Analysis

We have examined the effect of fibre addition on the glass transition temperature (T _g ) of two epoxy resin systems (an amine cured and an anhydride cured epoxy system) using dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC). The presence of fibres changes the glass transition temperature (T _g ) of an anhydride cured epoxy resin but does not affect that of an amine cured epoxy. The data suggest that two counteracting mechanisms are responsible for these changes: firstly, the presence of fibres causes a restriction of the molecular motion in the resin system, and secondly, the presence of carboxyi and keto-enol groups on the fibre surface inhibit curing of the resin close to the fibre, i.e. in the interphase region. The former increases the T _g and is a long range effect whereas the latter decreases the T _g and is a localised phenomenon. Changes in the dynamic properties of the interphase region are only detected when the samples are loaded in the longitudinal direction and not in the transverse direction where bulk matrix properties dominate. Sizing the fibres before their incorporation into the epoxy resin eliminates the variation in interfacial properties arising from differences in fibre surface chemistry.     

Affinity of Direct Dyes for Cellulose Film

A fast spectrophotometric method of assessing the affinity of different substances for surfaces is proposed. The effect of the dyeing temperature and concentration of the dye bath components (electrolyte and dye) on the value of the affinity of direct dyes for cellulose fibres was investigated. The optimum values of the temperature and concentrations of dye and electrolyte with respect to the affinity of the dye for the fibre were found. A series of experiments to investigate the effect of enzymes and surfactant additives on the affinity of the dye for the fibre was conducted and the insignificant effect of these components on the dyeing process was demonstrated.__________Translated from Khimicheskie Volokna, No. 2, pp. 10–12, March–April, 2005.     

Compressive behaviour of rigid rod polymer fibres and their adhesion to composite matrixes

Abstract

The deformation behaviour of the new high performance polymer fibres, poly(p-phenylene benzobisoxazole) (PBO) and polypyridobisimidazole (PIPD) and their adhesion to an epoxy composite matrix have been investigated. Both fibres give well defined Raman spectra, and the deformation micromechanics of PBO and PIPD single fibres and composites were studied from stress induced Raman band shifts. Single fibre stress-strain curves were determined in both tension and compression, thus providing an estimate of the compressive strength of these fibres. It was found that the PIPD fibre has a higher compressive strength (~1 GPa) than PBO (~0·3 GPa) and other high performance polymer fibres, because hydrogen bond formation is possible between PIPD molecules. It has been shown that when PBO and PIPD fibres are incorporated into an epoxy resin matrix, the resulting composites show very different interfacial failure mechanisms. The fibre strain distribution in the PBO-epoxy composites follows that predicted by the full bonding, shear lag model at low matrix strains, but deviations occur at higher matrix strains due to debonding at the fibre/matrix interface. For PIPD-epoxy composites, however, no debonding was observed before fibre fragmentation, indicating better adhesion than for PBO as a result of reactive groups on the PIPD fibre surface.     

Dyeing of poly(lactic acid) fibres with synthesised novel heterocyclic disazo disperse dyes

Poly(lactic acid) (PLA) is the first melt‐processable, renewable, sustainable and biodegradable natural‐based synthetic fibre. It has a broad range of uses and combines ecological advantages with outstanding performance in textiles. PLA fibre, as an aliphatic polyester, can be dyed with disperse dyes. Apart from the limited number of commercial disperse dyes, disperse dye exhaustion on PLA is generally lower than that on  poly(ethylene terephthalate) (PET). In this study, new heterocyclic disazo disperse dyes, substituted with methyl, nitro and chloro groups at their ortho‐, meta‐ and para‐ positions, synthesised in our previous study, were applied to PLA and PET fibres to examine their dyeing performance, and colour fastness and dye exhaustion properties. Different shades of yellow, orange, reddish brown and brown were obtained. Most of the synthesised novel heterocyclic disazo disperse dyes exhibited good build‐up properties with high K/S levels on both fibres. Para‐ bonding substituent provided higher K/S values than meta‐ and ortho‐ positions for –NO₂ and –Cl substituents for both fibres. Overall, the most synthesised novel heterocyclic disazo disperse dyes in this study exhibited good build‐up properties with high K/S, exhaustion and wet fastness levels on both PLA and PET fibres.      

Opto-mechanical properties of fibres. Part 1. Optical properties and orientation of drawn polyethylene fibres

Changes in the structure of different drawn polyethylene (PE) fibres are studied by the Becke' line method and interferometrically. The Becke' line method is used to study the changes in the optical properties of the skin layer of PE undrawn fibres. A Pluta polarizing interference microscope is used to determine the mean refractive indices and mean birefringence of the drawn fibres. Some structural parameters, such as optical orientation function, electric polarizability difference and isotropic polarizability (Δα/3α₀), are determined. This last parameter is found to be constant and depends only on the fibre structure. The number of molecules per unit volume and the distribution of segments at an angle with respect to the draw ratio are also determined. The generalized Lorentz–Lorenz equation given by de Vries is used to determine PE fibre structural parameters. A comparison between the experimental and those obtained using the Lorentz–Lorenz equation is given. A refractive index profile can assist fibre characterization. An empirical formula is suggested to correlate the changes in A, Δn, f_θ and θ with the draw ratio, and its constants are determined. Microinterferograms and curves are given for illustration. © 1999 Society of Chemical Industry     

The Determination of Diffusion Coefficients as a Function of Concentration for Dyes in Fibres

A method of determining the dependence on dye concentration of the diffusion coefficient of dyes in fibrous substrates has been developed, based on an approximation method of Crank, in which the amount of dye adsorbed by the fibre is measured colorimetrically as a function of time. The method has been applied to two dyeing systems, the direct dye Chlorazol Sky Blue FF (C. I. Direct Blue 1) on rayon and the acid dye Naphthalene Scarlet 4R (C. I. Acid Red 18) on nylon 6. 6. The results are in good agreement with those of R. H. Peters et al. for the same dyes and substrates, although Peters used films and not fibres and determined diffusion coefficients by an experimentally more complex method that appears impractical for fibres, the film being sectioned and the dye concentration measured as a function of distance with a microdensitometer.     

Restricted diffusion of residual molecules in catalyst pores under reactive conditions

The restricted diffusion of residual molecules under catalytic conversion conditions was investigated using commercial catalysts. The effectiveness factor, η, and the effective diffusion coefficient, D_e, for residual molecules were evaluated and explicitly compared based on a pseudo-first-order reaction kinetic model and the Thiele modulus. The experimental results showed that the restrictive diffusion of heavy oil molecules is affected by the joint functions of several factors, such as the operating conditions, the size and configuration of the reactant molecules, and the average pore diameter of the catalyst. The reaction temperature has a greater influence on restrictive diffusion than the other operating factors, and the ratio of reactant molecular size to catalyst pore size is the most critical factor that determines the degree of restrictive diffusion. Moreover, a mathematical expression was derived for the restrictive factors in order to describe the relationship between the effective diffusivity and ratio of molecule-to-pore size.     

Pretreating poly(p‐phenylene benzobisoxazole) fibre with polyphosphoric acid and dyeing with disperse dyes

In recent years, many advanced composite materials based on poly(p‐phenylene‐2,6‐benzobisoxazole) fibres have become prominent in applications requiring high‐strength and flame‐retardance such as body armour, industrial reinforcement materials and military camouflage. However, the application of these fibres used as protective clothing is limited due to difficulties in dyeing and printing. In the present work, a process for pretreating poly(p‐phenylene benzobisoxazole) fibre with polyphosphoric acid was applied, and the pretreated fibre was then dyed with disperse dyes via dip dyeing. Effects of pretreatment temperature and time on structure and properties were investigated. Surface morphology, crystallinity, chemical structure and degree of orientation of fibres were characterised. The results indicated that the supramolecular structure of the fibre was relaxed or swelled by polyphosphoric acid in the pretreatment process, so that the dyeability of poly(p‐phenylene benzobisoxazole) fibre was improved, with satisfactory dye exhaustion, K/S values and dyeing fastness. Also, with the appropriate pretreatment process, the swelling effect of polyphosphoric acid on the structure of poly(p‐phenylene benzobisoxazole) fibre was limited, so as to control the decrease in tensile strength and limiting oxygen index of the dyed fibre.     

The roles of polymer relaxation phenomena,aqueous dye solubility and the physical properties of water in the mechanism of adsorption of a disperse dye on poly(ethylene terephthalate) fibres: part 5 analysis of polymer relaxation phenomena for different polymers

The temperature dependent uptake of a commercial disperse dye on cotton and polyamide 66 fabrics at dyeing temperatures between 30°C and 130°C adhered to the Williams–Landel–Ferry equation, insofar as, very good correspondence was observed between plots of experimentally determined colour strength data points (log1/f_k) and the respective structural relaxation times of the cellulose and nylon 66 polymers (loga_T data points), as a function of the parameter (T − T_g). Adsorption of the dye on both types of fibre therefore concurs with the fundamental precept of the free volume model of dye diffusion. Comparison of the adherence of the uptake of the commercial dye on cotton and polyamide 66 fabrics with that secured on polyester fabric revealed that despite the major chemical and physical differences between the three types of fibre, the same dyeing mechanism likely applies to each fibre type. The marked temperature dependent uptake of the commercial grade disperse dye each of the three types of substrate is the consequence of two, different, but inherently interconnected, thermally activated phenomena, namely the relaxation times of the molecular rearrangements occurring within the respective cellulose, nylon 66 or poly(ethylene terephthalate) macromolecule, in which polymer glass transition assumes the principal role, and the aqueous solubility of the commercial grade disperse dye.     

The Dyeing of Acrilan with Basic Dyes in the Presence of Benzyl Alcohol*

The dyeing of Acrilan with C.I. Basic Green 4 from water containing benzyl alcohol and benzyl alcohol containing water has been examined. Benzyl alcohol in water acts as a plasticizing agent for the fibre. The plasticizing action of small quantities of water in benzyl alcohol has also been detected and in both systems the rate of diffusion of dye into the fibre is related to the plasticizing action. The equilibrium absorption is a function of the difference between the dyeing temperature (T) and the glass transition temperature (T_g) of the fibre. The differences in the behaviour of the dye in the aqueous and benzyl alcohol dyebaths are related to the degree of dissociation of the dye and the mechanical properties of the fibres.     

Color removal from dye wastewaters by adsorption using powdered activated carbon: Mass transfer studies

Color removal from synthetic dye wastewater which typically emanates from the Taiwan textile industry has been studied using powdered activated carbon (PAC) as an adsorbent. The CIE colorimetric system has been used in the measurement of color for the treatment of disperse-red-60 dye wastewater. The effect of contact time, dye concentrations and PAC dosage on color and color removal has been investigated. A film-pore double resistance diffusion model for mass transfer has also been used in this study to determine the effective diffusivity, D_eff, for the adsorption of disperse-red-60 dye wastewater to PAC.     

Effect of N,N‐diethyl‐m‐toluamide on the structure and dyeing properties of meta‐aramid and para‐aramid fibre

N,N‐Diethyl‐m‐toluamide has been widely used in the mosquito‐repellent finishing of textiles over the past few decades, but the use of N,N‐diethyl‐m‐toluamide as a dye carrier for aramid dyeing with disperse dye has been seldom reported. Meanwhile, the application of aramid fibre in clothing is limited because it is difficult to dye. In this work, the effect of N,N‐diethyl‐m‐toluamide on the dyeing properties of aramid fibre was examined by measuring the percentage disperse dye exhaustion under different conditions. In order to understand the mechanism by which N,N‐diethyl‐m‐toluamide promotes the exhaustion of disperse dye on aramid fibre, the ultraviolet‐visible spectrum of the dye and N,N‐diethyl‐m‐toluamide solution, the glass transition temperature, the crystalline structure, and the degree of orientation of aramid fibre treated with N,N‐diethyl‐m‐toluamide were measured by ultraviolet‐visible spectrophotometry, differential scanning calorimetry, X‐ray diffraction analysis, and velocity‐oriented tests respectively. The results indicated that N,N‐diethyl‐m‐toluamide not only could reduce the glass transition temperature and degree of orientation of aramid fibre but could also improve the solubility of disperse dye in aqueous solution, and therefore could enhance the percentage disperse dye uptake on aramid fibre, whereas treatment with N,N‐diethyl‐m‐toluamide showed little effect on the crystalline structure of aramid fibre. The results implied that N,N‐diethyl‐m‐toluamide was beneficial to the diffusion of disperse dye molecules into the amorphous region of aramid fibre under the dyeing conditions, but seldom affected the mechanical properties of aramid fibre.