Ch. Cherif

Carbon and Glass Fibers Modified by Polysilazane Based Thermal Resistant Coating

Thermal resistant coatings of textile materials are required so that they can fulfill the high security demands in the case of resistance to fire. These coatings also improve the properties of textiles as composite materials. In this research work, a polysilazane based coating was applied on carbon filament (CF) and glass filament (GF) rovings by a padding method. Tensile testing under thermal stress was carried out to assess the thermomechanical properties of both coated and uncoated rovings. Scanning electron microscopy, energy dispersive X-ray analysis, contact angle measurements, and surface energy calculations were performed to evaluate the surface properties of coated and uncoated rovings. The amount of coating mass on rovings was also determined using different recipes. Thermo-gravimetric analysis and weight loss after thermal treatment of coated and uncoated CF rovings were carried out to observe the oxidation behavior, as well as the thermal stability. The obtained testing results were assessed to ascertain the coating performances on GF and CF rovings.

In-Situ Polymer Coating of Open Grid Warp Knitted Fabrics for Textile Reinforced Concrete Application

This article presents the research work done in the framework of the Collaborative Research Centre — Textile Reinforcement for Structural Strengthening and Retrofitting. Previous results of textile reinforced concrete (TRC) have shown that the mechanical properties of the applied open grid warp knitted fabrics made of alkali-resistant glass filament yarns or carbon filament yarns as reinforcement material have not been utilized to complete satisfaction in the composition with the mineral matrix system. Further we have noticed that the orientation and configuration of the reinforcing fiber material is quite influenced by the handling in the further processing steps, which leads to the need of a sustainable structural stabilization.Different technologies for a subsequent structural stabilization e.g., dip-or spray coating with water-based polymer dispersions, thermal bonding, and laminating have been investigated. The results of these preliminary investigations have been published [2] and in consequence a suitable technology for a structural strengthening process has been selected. The structural strengthening of open grid warp knitted fabrics by means of an in-situ polymer coating process, which is completely integrated, as a modular line concept, into a multi-axial warp knitting machine from Karl Mayer Malimo increases the utilization of mechanical performance in TRC applications. Further the developed structural strengthening process improves the handling properties of the textile fabric. The modular line concept consisting of coating and drying moduless will be described. The influence of process and structure parameters to the mechanical properties of polymer-modified textile fabrics will be explained and sets the basis for the development and manufacturing of textile fabrics with structural properties adjusted to the requirements of the intended application. The effect of polymer-modified fabrics to the load bearing capacity of TRC will be discussed. To demonstrate the application potential of the developed composite material the TRC has been applied to reinforce a hypar shell structure of a campus building at the University of Applied Sciences in Schweinfurt, Germany.

Application of carbon filament (CF) for structural health monitoring of textile reinforced thermoplastic composites

Abstract Textile reinforced composites are a leading trend in lightweight structure design. The demand for additional function integration for the online health monitoring of lightweight structures using multimaterial design is growing rapidly. Carbon filament (CF) seems to be the simplest, most cost effective and most durable functional element for use in textile reinforced composites as a strain sensor. This paper reports on the production of functional hybrid yarn made with DREF-2000 friction spinning using CF yarn as the core component and polypropylene fibres as the sheath component. A comparative study was performed on the suitability of friction spun hybrid yarn and as spun CF yarn (i.e. in the form received from the manufacturer). The differences in electromechanical characteristics were analysed specifically for glass/polypropylene thermoplastic composite applications. Moreover, various types of connectors of CFs were also investigated.

Surface modification of Twaron aramid fiber by the atmospheric air plasma technique

Twaron aramid fibers (AFs) were modified by atmospheric air dielectric barrier discharge plasma with various parameters. The wettability of plasma-treated AF was observed by means of contact angle and surface free energy measurement. Surface roughness was investigated with the help of scanning electron microscopy. Energy-dispersive X-ray analysis was used to measure the chemical composition of AF in volume with one micrometer dimension. The tensile test of AF roving was carried out to determine the effect of plasma surface treatments on the mechanical properties of the fibers. A pull-out force test was carried out to observe the adhesion effect with matrix material. Lower contact angles, increase of oxygen concentration at the fiber surface, surface roughness and increase of pull-out force with the rubber matrix were observed after the air plasma treatment.

Improvements in the warp-knitting process and new patterning techniques for stitch-bonded textiles

Stitch-bonding technology offers a highly effective process of manufacturing reinforcement textiles for composite materials. This innovative technology is based on joining layers of threads and fabric with a knitting thread to create a layered structure, a multi-ply. Thus far, the knitting thread has restricted the positioning of individual layers in the fabric. It has been impossible, until now, to position warp layers symmetrically in one step as the outer layers of the fabric. It has been accomplished as a multi-step process, which in turn compromises productivity and quality. With the needle shift technique as an extension of the stitch-bonding process, all previous restrictions on multi-plies are eliminated. Both outer warp layers can be secured in one procedure by incorporating a shift of the needle bar during the stitching process, creating endless possibilities for the arrangement and patterns in the stitch-bonding process. For the numerical description and diagramming of the new patterning techniques, we have reworked and expanded previous illustration models.

Carbon filament yarn-based hybrid yarn for the heating of textile-reinforced concrete

In this study, the application of carbon filament yarn (CFY)-based conductive hybrid yarn as the heating element in a textile-reinforced concrete structure is reported. For this purpose, a hybrid yarn having a core-sheath structure (the core is made of carbon filament yarn and the sheath consists of a mixture of short glass and polypropylene fibres) is manufactured by DREF-2000 spinning technique and integrated into textile structure by tailored fibre placement method. Heat can be generated in the concrete structure by passing electric current through the conductive carbon filament yarn core of the hybrid yarn using the principle of resistive heating, where the sheath acts as the protection and isolation layer. From the initial investigations made on a small concrete specimen, important information is gathered and a large concrete slab with integrated conductive hybrid yarn is manufactured. The heat ability and the comfort level of the manufactured concrete slab are measured. The investigations have revealed the potential of using such hybrid yarn for a pointwise heating of the concrete surface for possible appliance in outdoor furniture.

Novel fiber-based pure chitosan scaffold for tendon augmentation: biomechanical and cell biological evaluation

Abstract One possibility to improve the mechanical properties after tendon ruptures is augmentation with a scaffold. Based on wet spinning technology, chitosan fibres were processed to a novel pure high-grade multifilament yarn with reproducible quality. The fibres were braided to obtain a 3D tendon scaffold. The CS fibres and scaffolds were evaluated biomechanically and compared to human supraspinatus (SSP) tendons. For the cytobiological characterization, in vitro cell culture experiments with human mesenchymal stem cells (hMSC) were performed. Three types of 3D circular braided scaffolds were fabricated. Significantly, higher ultimate stress values were measured for scaffold with larger filament yarn, compared to scaffold with smaller filament yarn. During cultivation over 28 days, the cells showed in dependence of isolation method and/or donor a doubling or tripling of the cell number or even a six-fold increase on the CS scaffold, which was comparable to the control (polystyrene) or in the case of cells obtained from human biceps tendon even higher proliferation rates. After 14 days, the scaffold surface was covered homogeneously with a cell layer. In summary, the present work demonstrates that braided chitosan scaffolds constitute a straightforward approach for designing tendon analogues, maintaining important flexibility in scaffold design and providing favourable mechanical properties of the resulting construct.

Development of new hybrid yarn construction from recycled carbon fibers for high performance composites. Part-I: basic processing of hybrid carbon fiber/polyamide 6 yarn spinning from virgin carbon fiber staple fibers

The availability of a considerable amount of waste carbon fiber (CF) and the increased pressure to recycle/reuse materials at the end of their life cycle have put the utilization of recycled CF (rCF) under the spotlight. This article reports the successful manufacturing of hybrid yarns consisting of staple CF cut from virgin CF filament yarn and polyamide 6 fibers of defined lengths (40 and 60 mm). Carding and drawing are performed to prepare slivers with improved fiber orientation and mixing for the manufacturing of hybrid yarns. The slivers are then spun into hybrid yarns on a flyer machine. The investigations reveal the influence of fiber length and mixing ratio on the quality of the card web, slivers and on the strength of the hybrid yarns. The findings based on the results of this research work will help realize value-added products from rCF on an industrial scale in the near future.

Development of carbon fibre/polyamide 6,6 commingled hybrid yarn for textile-reinforced thermoplastic composites

With increased use of carbon fibre (CF)-based textile-reinforced thermoplastic composites, the demand of hybrid yarns consisting of carbon filament yarns (CFYs) and thermoplastic filament yarns with improved properties is also high. Hybrid yarn manufacturing using commingling process by means of compressed air shows some distinct advantages over other hybrid yarn manufacturing processes. However, the potential of commingling process for the production of CF-based thermoplastic hybrid yarns is not yet fully explored. In this article, extensive investigations have been carried out for the development of commingled hybrid yarns manufactured from CFY and polyamide 6,6 (PA 6,6) filament yarns with improved adhesion properties between CFY and matrix in composites. Hybrid yarns are manufactured by varying air pressure and keeping overfeeds and delivery speed constant. Moreover, an additional heat treatment on CFY is done online for a better opening of CFY prior to the mixing with PA 6,6 filament yarn. The tensile properties of hybrid yarns as well as different mechanical properties of unidirectional composite, such as tensile, flexural, impact and interlaminar shear strength are investigated. The results show good potential for the development of hybrid yarns produced from CFY and thermoplastic filament yarns with improved adhesion properties for their application in textile-reinforced thermoplastic composites.

Effect of thermal-resistant polymeric coatings on thermomechanical and topographical properties of glass fiber

Thermal-resistant coatings, based on polysilazane and polysiloxane polymers, were applied onto the glass fiber rovings with the dip-coating method. The coated glass fibers were characterized by performing different experiments to evaluate the effect of coatings on thermomechanical and topographical properties of glass fiber. The effect of temperature on the mechanical properties of the coated rovings were studied and compared with the uncoated rovings. Thermogravimetric analysis was carried out to investigate the thermal stability of coated samples. Scanning electron microscopy and energy-dispersive X-ray analyses were performed to evaluate the surface topographical characteristics of the glass fiber rovings. These analyses showed the changes in surface morphological properties due to modification of glass fiber by coating treatment. The results of tensile testing indicated that thermal-resistant coatings enhanced up to 60% tensile strength and 20% stiffness of uncoated glass fiber roving. Thermomechanical study up to 500℃ revealed that polysiloxane coating on glass fiber showed better performance than polysilazane polymeric coating.