Structure of carbon fibres

Conclusions -- Carbon fibres have been examined as carbon band oriented amorphous-crystalline polymers.-- Characteristic regions in the formation of the structure of carbon fibres have been established, plus the interconnection between structural parameters.-- The components of preferential orientation of carbon fibres have been marked out, and a systematization of orientation in the transverse section of fibres has been presented.-- The character of change in axial component of texture with change in treatment temperature has been given, plus the connection between it and the elasticity and strength of fibres.-- A characteristic has been proposed for evaluating the activity of the surface of carbon fibres.Combustible Minerals Institute. Translated from Khimicheskie Volokna, No. 3, pp. 26–29, May–June, 1991.     

Gel-casted porous Al<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramics by use of natural fibres as pore developers

An approach using ceramic shaping by gel-casting and addition of natural tropical fibres as burnable pore developers has been explored for development of porous alumina materials with predetermined pore structures. The fibres used have been characterized in terms of size, shape, water uptake and surface charge. The degree of fibres loading in slurry has been varied. It has been shown that the amount of added fibres correlates well with the measured porosity, the shape of the developed pores however deviating slightly with that of the introduced fibres. The ceramic bodies have been characterised in terms of porosity, shrinkage and flexural strength. It could be assumed that at fibres amount in slurry above 30% V, an open porosity appears which is accompanied by a sharp drop in strength. In order to explore the benefits of the gel-casting method for complex bodies development, two key issues need to be addressed: air evacuation prior to casting and lowering slurry viscosity at fibre loadings higher than the tested ones. For reaching the latter objective, surface modification of fibres has been undertaken.     

The modification of wild silk fibres with methacrylamide

Wild silk and cultivated mulberry silk fibres have been graft copolymerised with methacrylamide, and the changes in the dyeing behaviour when dyeing with the levelling acid and milling acid dyes investigated. The tensile properties of the fibres and their durability during laundering have also been examined. The amount of the levelling acid dye adsorbed by all the fibres decreased with increasing polymer add-on, while the amount of milling acid dye adsorbed by the mulberry silk fibres was almost unchanged by the graft treatment. The breaking loads of the fibres were almost unchanged whereas rigidity of the fibres increased following graft treatment. The tensile properties of the grafted silk fibres were not diminished by laundering at polymer add-on levels greater than 50%.     

Interfacial characterisation of flax fibre-thermoplastic polymer composites by the pull-out test

The interface between flax fibres and thermoplastic polymer matrices has been investigated. Two types of flax fibres have been used: dew retted and upgraded Duralin fibres. The latter fibres have been treated by a novel treatment process for improved moisture and rot sensitivity. The apparent shear strength of dew-retted and upgraded Duralin fibres embedded in high and low density polyethylene, polypropylene and maleic anhydride modified polypropylene, respectively, has been calculated from the maximum force measured from the pull-out test using the Kelly-Tyson equation. Higher apparent shear strength values have been measured in the case of high density polyethylene. An improvement in the interfacial shear strength by the use of upgraded flax fibres has not been clearly observed. The curves of pull-out force versus displacement for all samples are typical of a brittle fracture mixed mode interface behaviour. The pull-out test of flax fibre-polymer matrices exhibit similar characteristics with the pull-out test of synthetic fibre-polymer systems.     

Effects of plasma treatment on mechanical properties of rubber/cellulose fibre composites

Natural rubber materials reinforced with cellulose fibres have been studied with respect to crosslink density, tensile strength and stress relaxation. The fibres have been grafted with butadiene or divinylbenzene by plasma treatment. Chemiluminescence analysis was used to indicate the grafting on the surface of the cellulose fibres and also to estimate the effect of the plasma on the cellulose fibres. The results indicate the possibility of obtaining a surface layer on the fibres, which is a conceivable way of improving the mechanical properties of rubber composites.     

New Developments in Acrylic Carpet Fibres for Specific End–uses

There is considerable activity in the introduction of new acrylic fibres, and second–and third–generation fibres are being developed for specific end–uses. Bicomponent fibres have found considerable application in woven carpets because their increased bulk and cover offer advantages over traditionally used fibres. Improved flame–resistant fibres incorporating halogen compounds have been developed to meet flammability requirements for carpets. Modacrylic blends are used for shag and some ‘saxony’ (high–pile low–density) applications. Three acrylic fibres of different dyeability have been developed for continuous piece dyeing: reduced–affinity basic, regular or deep basic, and acidic. Rapid–dyeing fibres are being introduced for use on the Craw ford–Mohasco equipment with which the fixation time is limited to 3 min at 100°C Finally, highshrinkage fibres can be used to impart extra bulk and cover or alternatively to produce sculptured effects in woven or tufted carpets.     

Cellulose fibres, nanofibrils and microfibrils: The morphological sequence of MFC components from a plant physiology and fibre technology point of view

During the last decade, major efforts have been made to develop adequate and commercially viable processes for disintegrating cellulose fibres into their structural components. Homogenisation of cellulose fibres has been one of the principal applied procedures. Homogenisation has produced materials which may be inhomogeneous, containing fibres, fibres fragments, fibrillar fines and nanofibrils. The material has been denominated microfibrillated cellulose (MFC). In addition, terms relating to the nano-scale have been given to the MFC material. Several modern and high-tech nano-applications have been envisaged for MFC. However, is MFC a nano-structure? It is concluded that MFC materials may be composed of (1) nanofibrils, (2) fibrillar fines, (3) fibre fragments and (4) fibres. This implies that MFC is not necessarily synonymous with nanofibrils, microfibrils or any other cellulose nano-structure. However, properly produced MFC materials contain nano-structures as a main component, i.e. nanofibrils.     

Influence of various chemical treatments on the interactions between hemp fibres and a lime matrix

In this paper, results presented concern both the chemical and physical behaviours of hemp fibres in lime-based mineral matrix in order to better understand the role of chemical modifications of cellulosic fibres in the evolution of the macroscopic properties, essentially mechanical ones, of such composite materials. The role of fibres surface treatment has been also studied through various chemical treatments applied on hemp fibres. In a first step, the influence of such treatments on the fibre characteristics has been investigated by several means, such as scanning electron microscopy, thermal analysis, X-ray diffraction and FTIR spectroscopy, in order to evaluate their consequences on the fibre behaviour itself. Secondly, an attempt to characterise the influence of the various chemical treatments of fibres on the mechanical behaviour of hemp reinforced lime-based composites has been completed by a three points bending testing campaign. According to the results, it seems that the modifications induced by specific chemical treatments (EDTA, NaOH) on fibres play a major role in the strengthening of the lime/fibres interface but also in the improvement of the overall stiffness of the composite (with respect to the one reinforced by untreated fibres) most probably related to a specific stiffening process of the fibre itself.     

Surface topography and mechanical properties of carbon fibres

Surface topography of polyacrylonitrile based carbon fibres preoxidized under a variety of conditions has been studied in detail. Only those carbon fibres processed under optimum conditions are found to possess defect free surface topography. Changes in surface topography and the tensile strength of carbon fibres with processing conditions have been discussed.     

The effect of molecular orientation on the vapour sorption of cyclohexane in amorphous polyester fibres

The sorption and transport of cyclohexane in poly(ethylene terephthalate) (PETP) fibres with various molecular orientations below the glass transition have been studied. The results have been analyzed in terms of the dual sorption model which has been successfully employed for glassy polymers. It has been shown that the capacity of the Langmuir mode of sorption inherent to glassy polymers is connected with the molecular orientation in the fibres of PETP. The increase of molecular orientation in the fibres has caused the decrease of the Langmuir capacity of PETP. This postulates a decrease in the free volume as a consequence of gradually increasing molecular orientation. Observations on the diffusion coefficients and activation energies for cyclohexane-PETP fibres system have been discussed.     

Some features of moisture exchange by carbon fibres

Conclusions A mathematical model for the moisture exchange of carbon fibres in an atmospheric medium has been proposed.The kinetics of moisture exchange by carbon fibres has been studied. Depending on atmospheric humidity, the dynamics of moisture exchange by carbon fibres is determined by a mechanism of activated, Knudsen, or free diffusion or by a combination of these.Diffusion coefficients have been obtained for the moisture which make it possible to carry out a calculation of the drying process and to select optimum conditions for storing carbon fibres.Translated from Khimicheskie Volokna, No. 1, pp. 36–37, January–February, 1990.     

Experimental evaluation of man-made fibre brittleness

Conclusions The behavior of fibres which are different in degree of structure anisotropy and properties has been investigated in the case of joint action of stretching and bending.Low-modulus fibres are not brittle under normal conditions. High-modulus, highly-anisotropic fibres fail with lengthwise fibrillation.Critical values of brittleness in bending have been found for high-modulus, low-anisotropy and isotropic fibres.The procedure proposed for evaluating brittleness under conditions of joint action of bending and stretching can be used to predict the behavior of fibres and articles made from them in processing and use.Translated from Khimicheskie Volokna, No. 2, pp. 36–37, March–April, 1989.     

Storage stability and mechanism of polyvinyl pyrrolidone based alkoxide composite electrospun fibres

Abstract

Polyvinyl pyrrolidone (PVP) based titanium n-butoxide (TNBT) and zirconium n-propoxide (ZNP) composite fibres were prepared by electrospinning, and the corresponding fibres with the addition of acetic acid (HAc) were also prepared for comparison. The storage stabilities of four alkoxide composite fibres and PVP electrospun fibres under standard laboratory conditions (20°C, 65% relative humidity) were investigated. Some unexpected but interesting phenomena were discovered. Electrospun PVP fibres lose their fibrous shapes after they have been stored for only 24 h. The TNBT, ZNP and ZNP(HAc) composite fibres still remain their morphologies even though they have been stored for 15 days, exhibiting excellent chemical and morphological stability in the air, because the hydrolysis and condensation of alkoxide have completed during the electrospinning process, while TBNT(HAc) composite fibres hydrolyse and condense during the storage period. This investigation provides useful knowledge for preparing ceramic electrospun fibres, especially for large scale production or electrospinning over extended time.     

Evaluation of relative wettability of carbon fibres

A new mathematical approach to an existing wicking method has been presented to determine the relative wettability of carbon fibres. The wettability of carbon fibres is discussed in terms of the angle of contact of a test liquid against the fibres. The wettability of carbon fibres of a given quality is evaluated relative to that of those of a known quality. Thus if the angle of contact of the test liquid against fibres of the known quality is known, the same against fibres of the given quality can be readily determined.     

Proprietes electroniques et magnetiques de fibres de carbone evolution sous irradiation neutronique

Techniques developed for the measurement of the electrical resistivity and the diamagnetic anisotropy of carbon fibres, in the temperature range 77–300°K are described. Two types of fibres were studied: the Rigilor AC fibres treated at 1100°C and the Rigilor AG fibres treated at 2500°C. The measurements of electrical resistivity performed on single fibres show the presence of some correlation between this property and the cross-sectional area of the fibre. Measurements of diamagnetic susceptibility carried out on bundles of fibres demonstrate a large anisotropy of the fibres. The influence of small neutron irradiation doses on these properties has been studied at room temperature.     

Light-stability of Lavsan dyes in bulk with aroylene-benzimidazole derivatives

Conclusions Naphthoylenebenzimidazole derivatives have been found which are able to dye polyethylene terephthalate fibres in bulk.It has been shown that the dyes reduce the thermal degradation which takes place in melt-spinning polyethylene terephthalate fibres.The sorption properties of the fibres obtained have been evaluated.Translated from Khimicheskie Volokna, No. 3, pp. 38–39, May–June, 1988.     

Basic stages and threshold characteristics of the action of laser radiation on fibres

Conclusions The possibility of using the photo-acoustic method to study the process of laser radiation action on fibres has been demonstrated. For groups of synthetic, artificial, and natural fibres, basic stages and energy thresholds have been determined: for proportionality, structural rearrangements, radiation strength, and destruction under the action of radiation from a CO₂ laser.A classification of fibres with respect to resistance to the action of laser radiation has been made; these fibres have been characterized by energy thresholds of radiation resistance and destruction thresholds, and also by the type of processes taking place.Translated from Khimicheskie Volokna, No. 6, pp. 42–44, November–December, 1987.     

Microstructural characterisation of surfactant treated nylon fibres

Small-angle neutron scattering and differential scanning calorimetry have been used to probe for changes in the microstructure of nylon fibres following exposure to surfactant, acid and alkali solutions. SANS was also used to investigate fibres that had been subjected to intentional loading, environmental exposure, and natural ageing. A number of structural parameters have been derived. The data are capable of differentiating between untreated, treated, loaded, and used fibres. Mostly subtle effects are observed. Only exposure to concentrated acid solutions, or applied strain, imparted any significant structural perturbation. These findings, though relevant in a number of areas of application of nylon fibres, are discussed with particular reference to nylon ropes and the laundering of nylon textiles.     

Zeta-potential Studies in Cellulose Fibre–Aqueous Electrolyte Solution Systems

Zeta-potential studies of cotton and viscose rayon fibres in aqueous sodium and potassium chloride solutions of different concentrations have been carried out using the streaming-potential method. The Eversole and Boardman equation, which relates the measured zeta potential to the thickness of the electrical double layer, has been found to be valid in all cases. Using the surface-potential values calculated from this equation, the surface-charge densities in these fibres have been estimated. They are in good agreement with the theoretical surface-charge densities calculated from data on the carboxyl-group content of these fibres and the BET nitrogen surface areas for the water-swollen uncollapsed fibres. Two alternative explanations for the apparent increase in surface-charge density with decrease in the zeta potential have been given, without assuming that the anions are absorbed. The variation in zeta potential with increasing carboxyl-group content in samples of oxycellulose has been explained in terms of changes in the degree of dissociation of carboxyl groups with increasing carboxyl content, and an increase in the surface area of the cellulose fibre on oxidation. Studies of the zeta potentials in Form-W and Form-D formaldehyde-crosslinked cotton fibres have indicated that the zeta potential increases with increase in formaldehyde content with Form-D fibres. This result can be explained in terms of the decrease in the surface area of Form-D cottons with increase in the content of bound formaldehyde.     

Efficiency of flame-proofing action of flame-proofers for fibres of aromatic polyamides

Conclusions The possibility of raising the oxygen index of fibres of aromatic polyamides by use of organophosphorus or chlorinated organic compounds has been examined. It has been shown that, to obtain modified fibres whose fire-protected effect is resistant to wet treatment, it is necessary to introduce glycasine additionally into the fibre.As a result of investigating the physicomechanical properties of the original and flame-protected fibres, it has been found that the use of organophosphorus compounds for the modification of fibres from aromatic polyamides is more advisable.Translated from Khimicheskie Volokna, No. 6, pp. 18–20, November–December, 1983.