Thomas Michael Köhler

One Step Production of Bicomponent Yarns with Glass Fibre Core and Thermoplastic Sheath for Composite Applications

The film stacking method is the industrial standard for the manufacturing of fibre reinforced thermoplastic composites (FRTCs). An alternative to this is commingling thermoplastic fibres with reinforcement fibres, e. g. glass fibres, into hybrid yarns. However, the composites produced by the use of film-stacking or hybrid yarns cannot achieve an optimal impregnation of reinforcement fibres with the matrix polymer. This stens from the high melt viscosity of thermoplastics, which prevents a uniform wetting of the reinforcement fibres. Leaving some fibers is unconnected to the matrix. This leads to composite lower strength than theoretically possible. The aim of the research is the coating of a single glass filament in the glass fibre nozzle drawing process to achive a homogenous distribution of glass fibres and matrix in the final composite. The approach uses particles with a diameter from 5 to 25 μm of polyamide 12 (PA 12) which are electrostatically charged and blown at an Eglass filament in the nozzle drawing process as seen in. The particles adhering to the filament are melted by infrared heating and winded afterwards. This development will allow the homogenous distribution of fibres and the matrix in a thermoplastic composite allowing a higher fibre volume content leading to improved mechanical properties. Even though the glass filaments could be coated with PA 12, a homogenous sheath could not be achieved in this investigation. Therefore, further research will focus on an improved homogeneity by reducing the agglomeration of PA 12, using dried PA12 and enhancing the coating setup.

Development of Bio-Based Self-Reinforced PLA Composites

Self-reinforced polymer composites (SRPCs) are receiving increasing attention by the industry for lightweight applications. The polymers used for SRPCs today are derived from fossil resources. However, due to a limitation of resources, interest is growing regarding the use of new alternatives for petrol based polymers in form of bio-based ones. SRPCs combine high stiffness, high impact and high durability with impairing recyclability. In SRPCs the same polymer is used for the reinforcing and matrix phases. SRPCs can be manufactured by commingling reinforcing and matrix fibres with different melting temperatures. The use of commingled yarns allows the combination of a large variety of fibres and therefore a wide range of material properties.

Development of Thermoplastic Composites for Visible Parts in Automotive

In order to reduce CO2 emissions, for the automotive industry, the most promising area of research is lightweight construction. Next to weight reduction, lightweight materials like fiber reinforced thermoplastic composites (FRTC) may also improve mechanical properties of vehicle body parts. FRTCs, so-called organic sheets, have the potential for large scale series production and they can be back moulded due to the thermoplastic matrix. On the other hand high production cycle times and a poor surface quality are limiting their potential. Therefore, ITA’s current research approaches these problems in two ways. Nanomodified materials and a new tool concept for heat pressing are going hand in hand and may lead to the technology’s breakthrough.To reduce the cycle times of the production of FRTCs innovative and modified matrix systems are investigated. The goal of the public founded project “VarioOrgano” is to analyze the potential of these modified yarns and the tool system during the FRTC production. Moreover, the capability of these composites in visible parts in automotive applications is investigated. Therefore, the whole process chain from compounding, to melt spinning, commingling and consolidation with a heat press is investigated.This paper shows the production steps along the process chain to produce these FRTCs with focus on hybrid yarn development and production.

An Overview of Impregnation Methods for Carbon Fibre Reinforced Thermoplastics

Carbon fibre reinforced plastics (CFRPs) can be classified according to whether the matrix is a thermoset or a thermoplastic. Thermoset-matrix composites are by tradition far more common, but thermoplastic-matrix composites are gaining in importance. There are several techniques for combining carbon fibres with a thermoplastic-matrix system. The composite’s characteristics as well as its manufacturing costs are dependent on the impregnation technique of the carbon fibre and the textile structure respectively. Carbon fibre reinforced thermoplastics (CFRTPs) are suitable for fast and economic production of high-performance components. Despite the higher material costs thermoplastic-matrix systems show cost benefits in comparison to thermoset-matrix due to substantial time savings in the production process. Moreover CFRTPs can be manufactured in large production runs. The commingling of reinforcement fibres with matrix fibres is a well-established process. Another approach is the coating of the carbon fibre with a thermoplastic subsequent to the carbon fibre production (carbonization, activation and deposition of sizing). The latter point is currently subject of research and is a promising method for further increasing the production speed. This paper presents the different possibilities of impregnating carbon fibres with a thermoplastic matrix. Diverse technologies along the process chain of the CFRTP production will be discussed.

Development of PLA hybrid yarns for biobased self-reinforced polymer composites

Lightweight materials are a necessity in various industries. Lightweight design is in the key interest of the mobility sector, e.g. the automotive and aerospace industry. This trend applies also for the consumer industries, e.g. sporting goods. In addition, the worldwide demand for replacing fossil-based materials has led to a significant growth of bioplastics. Due to their low mechanical performance and durability, their use is still limited. Therefore, it is necessary to develop biobased, sustainable polymeric materials with high stiffness, high impact and high durability without impairing recyclability at a similar price level of non-biobased solutions. Biobased self-reinforced polymer composites offer these unique properties.

Development of glass fibre reinforced composites using microwave heating technology

Fibre reinforced composites are differentiated by the used matrix material (thermoplastic versus duroplastic matrix) and the level of impregnation. Thermoplastic matrix systems get more important due to their suitability for mass production, their good shapeability and their high impact resistance. A challenge in the processing of these materials is the reduction of the melt flow paths of the thermoplastic matrix. The viscosity of molten thermoplastic material is distinctly higher than the viscosity of duroplastic material. An approach to reduce the flow paths of the thermoplastic melt is given by a commingling process. Composites made from commingling hybrid yarns consist of thermoplastic and reinforcing fibres. Fabrics made from these hybrid yarns are heated and consolidated by the use of heat pressing to form so called organic sheets. An innovative heating system is given by microwaves. The advantage of microwave heating is the volumetric heating of the material, where the energy of the electromagnetic radiation is converted into thermal energy inside the material. In this research project microwave active hybrid yarns are produced and examined at the Institute for Textile Technology of RWTH Aachen University (ITA). The industrial research partner Fricke und Mallah Microwave Technology GmbH, Peine, Germany develops an innovative pressing systems based on a microwave heating system. By implementing the designed microwave heating technology into an existing heat pressing process, FRTCs are being manufactured from glass and nanomodified polypropylene fibre woven fabrics. In this paper the composites are investigated for their mechanical and optical properties.

High strength and low weight hollow carbon fibres

Carbon fibres have strengths of 2.5 to 5 GPa in the fibre direction and an elastic modulus of 200 to 500 GPa. Carbon fibres have equal mechanical properties as steel but 20% of the weight. But the material is more expensive than steel. Therefore, they are only used in industry sectors where the benefits legitimate the high costs. The use of hollow rather than solid fibres allows an even lower weight of the components. At the same time, similar mechanical properties are achieved by the circular cross section. Carbon fibres are obtained from polyacrylonitrile fibers (PAN). These can be produced as hollow fibres. As a first step stabilization and carbonization of hollow PAN precursors is investigated to produce hollow carbon fibres.

Optimization of process parameters during carbonization for improved carbon fibre strength

Based on their extraordinary properties, carbon fibres nowadays play a significant role in modern industries. In the last years carbon fibres are increasingly used for lightweight constructions in the energy or the transportation industry. However, a bigger market penetration of carbon fibres is still hindered by high prices (~ 22

Production and characterisation of self-reinforced polymer composites made from biobased hybrid yarns

/kg) [3]. One crucial step in carbon fibre production is the process of carbonization of stabilized fibres. However, the cause effect relationships of carbonization are nowadays not fully understood. Therefore, the main goal of this research work is the quantification of the cause-effect relationships of process parameters like temperature and residence time on carbon fibre strength.