Structure and superstructure of carbon fibres

The structure of carbon fibres consists of stacks of carbon layers oriented parallel to the fibre axis. From X-ray wide-angle scattering studies (WAXS) one obtains various structural parameters characterizing the perfection of the stacking and the orientation of the layers. The latter is quantitatively related to the tensile modulus of the fibres. Small-angle scattering studies (SAXS) are used to determine size, shape and orientation of microvoids. For carbon fibres with high heat treatment temperatures (HTT), a correlation between microvoid content and elongation at break is observed which indicates an optimum value for the microvoid content. Electrochemical intercalation is used to obtain information on the accessibility of the carbon layer structure.     

Production and characterization of C and SiC layers on C fibres

Summary The construction, testing and operation of a semi-technical system for the multi-stage coating of endless fibres by means of thermally-activated CVD is described. One objective of this is to apply layer systems under conditions similar to those used in production with long-term reproducibility. Rovings coated in this way, for example, are made of high-tensile carbon fibres, and used as reinforcing components in the manufacture of modern composite materials. Research programs and laboratory test batches are characterized extensively by methods of surface and solid state analysis such as SEM, TEM, AES, XPS and RAMAN. Analytical investigations are supplemented by strength measurements made at several sites on the fibre coating and on the later application.     

Continuous Atmospheric Plasma Oxidation of Carbon Fibres: Influence on the Fibre Surface and Bulk Properties and Adhesion to Polyamide 12

Continuous atmospheric plasma oxidation (APO) was used to introduce oxygen functionalities to the surface of carbon fibres in an attempt to enhance interfacial adhesion between carbon fibres and polyamide-12 (PA-12). APO only affects the surface properties of the fibres while their bulk properties remained unchanged. Contact angle and ζ-potential measurements demonstrated that APO-treated fibres became significantly more hydrophilic due to the introduction of polar oxygen-containing groups on the fibre surface, which also resulted in an increase of surface energy on the carbon fibres. The interfacial shear strength of single carbon fibre/PA-12 model composites, determined by single fibre fragmentation tests, showed an increase from 40 to 83 MPa with up to 4 min of APO treatment time which confirms that the fibre/matrix interfacial adhesion was enhanced. This highlights that the incorporation of APO into composite manufacturing will allow tailoring of the fibre/matrix interface.     

Polymer blends based on epoxy resin and polyphenylene ether as a matrix material for high-performance composites

The application of poly(2,6-dimethyl-1,4-phenylene ether), PPE, as a matrix material for continuous carbon fibre reinforced composites has been studied. Due to the intractable nature of PPE melt impregnation is not feasible and a novel impregnation route, using epoxy resin as a reactive solvent, was developed. The introduction of epoxy resin results in enhanced flow and a reduced processing temperature, enabling the processing of PPE and the preparation of high quality composites. Upon curing, phase separation is initiated and epoxy resin is converted into a second phase. In composites, epoxy resin preferentially accumulates at the polar fibre surface, resulting in an epoxy layer around the fibres, providing a high level of interfacial adhesion. For a high fibre volume fraction (> 50%) this results in the ultimate morphology of epoxy coated fibres in a neat PPE matrix. Due to this unique morphology the composite materials reveal outstanding mechanical properties in terms of interlaminar toughness and impact performance.     

Raman spectroscopy of C-, BN-, SiC-layers deposited on multifilament substrates

The analytic characterisation of various layers and layer systems on fibrous materials are presented. The layers, deposited by an isothermal CVD process, consisting mainly of pyrolytic carbon, hexagonal boron nitride and silicon carbide were characterised by different analytical methods, especially by Raman spectroscopy [1]. The surface enhanced Raman spectroscopy (SERS) was used first time for the investigation of boron nitride (BN) coatings on fibres.     

Comfortable, flexible upholstery fire barriers on base of bast, wool and thermostable fibres

The paper presents elastic barrier materials developed at the INF which play a role of filling and fire barrier material at the same time in upholstery furniture, reducing the development and spread of fire on flammable materials. The presented results of flammability and biophysical tests confirm the comfort of products.The developed barrier materials use natural fibres (wool, flax FR) characterized by good air permeability, hygroscopicity, moisture transport, elimination of electrostatic charges and have effect on climate of interiors also when blended with thermostable fibres such as Polyacrylate. These flexible structures based on blend of natural fibres and thermostable fibres with at least two barrier effects i.e. durable resistance to fire, thermal insulation, control of electrostatic phenomena.     

On the chemical durability of a metal-metalloid glass from the alloy (Fe,Cr)80(P,C,Si)20 in hardened Portland cement investigated by FT-IRRS,ESCA, and SEM/EDX

Composites of metal-metalloid glass fibres FIB-RAFLEX^TM (Fe,Cr)₈₀(P,C,Si)₂₀ with ordinary Portland cement (OPC) were prepared and used for an accelerated ageing procedure to study the cement paste-fibre interfaces which affect the mechanical behaviour of concrete composites. The role of the interface on the global behaviour of the concrete composite as a basis for the development of high-performance cementitious materials was studied on pulled out fibres by EDX, ESCA and by FTIR/RAMAN microspectroscopy. A Ca(OH)₂ rich layer is predominant for the surface of the reinforced cementitious material and represents the interface between aggregate and matrix. The interaction between aggregate and matrix is the reason for the strength of composites with this fibre in the highly alkaline environment of hydrating cements.     

On the chemical durability of a metal-metalloid glass from the alloy (Fe,Cr)80(P,C,Si)20 in hardened Portland cement investigated by FT-IRRS, ESCA, and SEM/EDX

Composites of metal-metalloid glass fibres FIB-RAFLEX^TM (Fe,Cr)₈₀(P,C,Si)₂₀ with ordinary Portland cement (OPC) were prepared and used for an accelerated ageing procedure to study the cement paste-fibre interfaces which affect the mechanical behaviour of concrete composites. The role of the interface on the global behaviour of the concrete composite as a basis for the development of high-performance cementitious materials was studied on pulled out fibres by EDX, ESCA and by FTIR/RAMAN microspectroscopy. A Ca(OH)₂ rich layer is predominant for the surface of the reinforced cementitious material and represents the interface between aggregate and matrix. The interaction between aggregate and matrix is the reason for the strength of composites with this fibre in the highly alkaline environment of hydrating cements.     

Improvement of Fibre-Matrix-Adhesion of Natural Fibres by Chemical Treatment

Plastics, also called synthetic polymers, are playing an important role in daily living. To raise more applications it is necessary to modify known polymeric systems to reach improved materials/material systems. A possibility to create new optimised materials out of neat polymers is offered by compounding them with different filling material. Besides chemical modification of polymers, mixing, combining or use of different fillers, one possibility is given by the composite technique, whereas the combination of the polymeric matrix and the embedded reinforcement (e.g. fibre) are yielding in optimised materials adjusted to the required properties. Concerning the polymeric matrix, either thermoplastic or thermoset material can be used. In case of the reinforcement, either synthetic (carbon-, glass- or polymeric fibres) or natural fibres are introduced to composites. To obtain an appropriate adhesion of the matrix to the reinforcement system, synthetic fibres are equipped with an avivage. For natural fibres, there are no such materials available and the hydrophilic property of this system surface prevents an adhesion to hydrophobic polymers, as well as to sizings. In this paper, ways are shown to modify the natural fibres via chemical treatment to yield higher physical properties at better adhesion. Also we will explain activities on the use of natural fibres as reaction systems and processing tools as well as the attempt to isolate the different compounds of the neat fibre via selective work-up.     

Development of methods for testing barriers in food packaging materials

In some countries recycled materials are not allowed to come into contact with food without a protective layer such as plastic or virgin fiber. The purpose of this kind of barrier is to reduce migration of substances form beyond the barrier to the food. Two methods for studying a functional barrier are described. Both utilize migration cells in which one surface of the test specimen (for example a paper plate) is exposed to the food simulant. The first method involves the addition of indidcatsor substances to the non-food contact layer. The second method is to measure the migration of substances originally present in the layers beyond the functional barrier layer. Several kinds of barrier used in commercial papaer plates were studied and differences between them were found.     

Dye diffusion in anisotropic polyamide fibres

Radioactive tracer techniques have been used to study the diffusion of three dyes in polyamide fibres produced under different conditions. It has been shown that drawn nylon fibres have a surface barrier layer which limits diffusion. The permeability of the layer is reduced by drawing, and varies with drawing conditions. The dependence of dye diffusion on concentration, ionic size and draw ratio is less in the surface than in the bulk of the fibre, but variations in dyeing behaviour have been shown to follow surface rather than bulk diffusion characteristics.     

Heat transfer through a textile layer composed of hollow fibres

Textiles are used as thermal isolating materials for technical and clothing applications. The paper generally deals with heat transfer through textile layers by conduction, convection, radiation and evaporation of humidity. This experiment evaluates heat transfer by conduction and radiation through textile layers containing hollow polyethylene terephthalate (PET) fibres. The environment created by a composite textile layer containing hollow PET fibres and air is not identical for every method of heat transfer. During heat transfer through a textile layer, we evaluate of the importance of macromorphological structure of the elementary fibres and textile layer, taking into account the thermo-physiological properties.     

Atomistic computer simulation of mechanical properties of composites

An atomistic computer simulation is performed in order to investigate structure and mechanical behaviour of materials composed of fibres embedded in a polymer matrix. A graphite-poly(propylene) system is used as a model, the energy of which has been minimized. Unlike the models of other authors the bond angles of the polymer chains are assumed as flexible. The properties found were compared with those of the bulk polymer. The results show that the presence of the graphite surface affects the structure of the polymer as well as the values of the elastic constants within a layer of 7 Å thickness. In this layer the density has a maximum and the chain segments are oriented parallel by the graphite plane. A long range order, however, cannot be observed.     

Influence of plasma treatment on the adhesion between a polymeric matrix and natural fibres

The aim of this work is to study the influence of low-pressure plasma treatment on cellulose fibres to improve the adhesion between a polymeric matrix and natural fibres used as reinforcement. To evaluate fibre wettability, contact angle measurements were carried out on flax fibres after treatment with plasma under several conditions. Similarly, contact angle measurements were performed without plasma treatment. A comparison between all the samples led to the definition of the optimal plasma treatment conditions. Once the latter were determined, composite materials were prepared with treated and untreated flax fibres and a low-density polyethylene matrix. Composites, with different fibre contents (5 and 40%) and different fibre lengths (1 and 10 mm), were manufactured using a mixer and a hot plate press. The tensile strengths of the composites were assessed to determine optimal fibre content and length, and the plasma treatment effect was also quantified. It was found that the higher the fibre content, the higher the tensile strength, and the higher the Young’s modulus; however, fibre length did not affect tensile strength. Regarding plasma treatment, composites with treated fibres exhibited a considerably improved tensile strength and Young’s modulus. Plasma treatment effects were also studied by X-ray photoelectron spectroscopy and by differential scanning calorimetric. Finally, an analysis of the fibre surface and an interaction study between the matrix and the fibres was conducted with scanning electron microscopy.     

Effect of surface chemistry and topography of sulphite fibres on the transcrystallinity of polypropylene

In the present study the effect of chemically and mechanically treated cellulose materials on the degree of polypropylene transcrystallisation was investigated. The cellulose materials which were sulphite fibres, microcrystalline cellulose (MCC) and knife milled sulphite fibre, were either chemically treated by esterification or mechanically treated by beating. The esterified cellulose materials did not induce a transcrystalline layer, however, all unesterified cellulose materials clearly induced a transcrystalline layer. The fibres which were mechanically treated by beating gave a higher degree of transcrystallisation than the untreated ones. Our results show the importance of the surface chemistry of the added fibres on the growth of transcrystallisation in polypropylene composite materials.     

The Impact of Filler Geometry on Polylactic Acid-Based Sustainable Polymer Composites

Recently, biocomposites have emerged as materials of great interest to the scientists and industry around the globe. Among various polymers, polylactic acid (PLA) is a popular matrix material with high potential for advanced applications. Various particulate materials and nanoparticles have been used as the filler in PLA based matrix. One of the extensively studied filler is cellulose. However, cellulose fibres, due to their hydrophilic nature, are difficult to blend with a hydrophobic polymer matrix. This leads to agglomeration and creates voids, reducing the mechanical strength of the resulting composite. Moreover, the role of the various forms of pure cellulose and its particle shape factors has not been analyzed in most of the current literature. Therefore, in this work, materials of various shapes and shape factors were selected as fillers for the production of polymer composites using Polylactic acid as a matrix to fill this knowledge gap. In particular, pure cellulose fibres (three types with different elongation coefficient) and two mineral nanocomponents: precipitated calcium carbonate and montmorillonite were used. The composites were prepared by a melt blending process using two different levels of fillers: 5% and 30%. Then, the analysis of their thermomechanical and physico-chemical properties was carried out. The obtained results were presented graphically and discussed in terms of their shape and degree of filling.     

Cellulose/iron oxide hybrids as multifunctional pigments in thermoplastic starch based materials

Cellulose/iron oxide hybrids were prepared by the controlled hydrolysis of FeC₂O₄ in the presence of vegetable and bacterial cellulose fibres as substrates. By varying the relative amount of FeC₂O₄ and NaOH, either hematite or magnetic iron oxides were grown at the cellulose fibres surfaces. This chemical strategy was used for the production of a number of materials, whose coloristic properties associated to their reinforcement role allowed their use as new hybrid pigments for thermoplastic starch (TPS) based products. The TPS reinforced materials were characterized by several techniques in order to evaluate: the morphology and the compatibility between the matrix and the fillers; the mechanical reinforcement effect of the cellulose/iron oxide pigments on TPS and the coloristic properties of the composites. All materials showed good dispersion and strong adhesion for the cellulose/iron oxide nanocomposites in the TPS matrix thus resulting in improved mechanical properties.     

An Introduction to the Combustion of Carbon Materials

Combustion is arguably as old as homo sapiens ability to observe and use fire. Despite the long tradition of using carbon combustion for energy production, this reaction is still not fully understood. This can be related to several facts that are intertwined and complicate the investigation, such as the large variety of possible carbon structures, the actual surface structure, porosity, the solid-gas nature of this reaction, diffusion limitation and fundamental reaction steps. In this review, a brief history of carbon combustion science is given, followed by a detailed discussion of the most important aspects of carbon combustion. Special attention is given to limitations for example diffusion. In carbon combustion, kinetic control can rarely be observed. The literature of the fundamental reaction steps actually occurring on the carbon framework is reviewed and it becomes apparent that the reaction is occurring primarily on defects on the basal plane. Thus, the reaction between oxygen and carbon may be used as an analytical tool to provide further insights into novel materials, for example synthetic carbon materials, fibres and graphene type materials. Mastering the combustion reaction in all its complexity may prove to be very valuable in the future.     

Pattern formation and non-linear phenomena in stretched discotic liquid crystal fibres

This paper presents a non-linear numerical and bifurcation analysis of pattern formation phenomena in a discotic nematic liquid crystal confined to annular cylindrical cavities and subjected to extensional deformations. The results are of direct relevance to understanding the industrial melt spinning of mesophase carbon fibres, using discotic nematic liquid crystals precursor materials. Three types of orientation patterns are identified in this study: spatially constant (radial), monotonic (pinwheel), and oscillatory (zigzag). Numerical and closed form analytical results predicting continuous transformations between the radial, pinwheel, zigzag radial orientation modes are presented. The bifurcation analysis provides a direct characterization of the parametric dependence and the transitions between these three basic patterns, and provides a complete understanding of the multistability phenomena that is present in the oscillatory orientation patterns. In general it is found that small fibres of nearly elastically isotropic discotic nematic liquid crystals tend to adopt the classical ideal radial texture, while larger fibres with anisotropic elastic moduli tend to yield the zigzag texture. Fixed arbitrary surface orientation of intermediate size and anisotropy tend to adopt the pinwheel texture. The theoretical results are able to explain the main features and mechanisms that lead to the commonly observed cross-section textures of industrially spun mesophase carbon fibres.     

Fibrous chromium and molybdenum fabricated by cold working Cu-Cr and Cu-Mo binary alloys

Fibrous chromium and molybdenum were fabricated by cold working two-phase alloy ingots of Cu-Cr and Cu-Mo. Since the chromium and molybdenum are precipitated and grow as monocrystals in the copper matrix, there are no problems with grain boundaries which are responsible for the brittleness of polycrystalline group VIa metals. The chromium and molybdenum fibres can easily be removed from the composite by selectively etching away the copper matrix. Chromium fibres can be obtained almost irrespective of the purity of the starting materials. The composite of copper reinforced with chromium fibres exhibits high mechanical strength and electrical conductivity.