MATERIALS | THERMOPLASTIC COMPOSITES


Right: Starting with individual tapes through to functionalisation in injection moulding, Engel integrates all processing steps for the manufacture of fibre composite components in a highly efficient, automated production process


up, visually checked, placed in a controlled position and spot-welded together. Engel and its partner FILL of Gurten, Austria have developed a production unit based on the heating/cooling principle for the consolidation process which follows immediately downstream. In a fully automated process, this system consoli- dates the fibre stacks into a solid panel, while retaining thickness variations introduced in a targeted manner.


Engel has also used lightweight Duroplast design to demonstrate that production efficiency can still be improved – even for long-established technologies. The rear seat panel of the Audi A8 has a complex carbon fibre structure and local reinforcements. Series production is by a supplier from Germany using an Engel V-duo 1700 machine with the fully automated HP-RTM process. The interdisciplinary Engel Lightweight Engineering team covers a broad development spectrum from the processing of thermoplastic preforms and Duroplast moulding compounds to reactive technologies. At its Center for Lightweight Com- posite Technologies in Austria, the company works on particularly economical composite solutions for the automotive industry. Aimplas, the Technological Institute of Plastics


Below: Examples of UD tapes produced on the Aimplas pilot plant line


in Spain, is a major developer of long-fibre-rein- forced thermoplastic (LFT) composite technolo- gies. The organisation has recently installed a new pilot line to produce LFT pellets and unidirectional tapes using a small amount of material (1-3 kg per sample) to enable companies to analyse the properties of different materials as efficiently as possible. The pultrusion line is attached to a co-rotating twin-screw extruder. The line produces unidirectional tapes for depositing fibres (AFP and ATL) and long-fibre pellets


for injection and compression moulding. The matrix can be modified to enhance these materials with new functionalities, such as flame resistance, electrical and thermal conductivity, and electromagnetic shielding. The pilot plant line at Aimplas is


INJECTION WORLD | January/February 2021


designed to investigate new technologies and applications for thermoplastic alternatives for thermoset composites, offering advantages of light weight, processability and recyclability. “The development of thermoplastic composites began in the aeronautical industry with the use of technical polymers with superior mechanical properties and high-temperature resistance,” says Begoña Galindo,


Sustainable and Future Mobility Group Leader. “These


include polyether ether ketone (PEEK), poly- etherimide (PEI), polyimide (PI), polyphenylene sulphide (PPS) and polyaryletherketone (PAEK) reinforced with carbon fibres. In the automotive industry, the most commonly used polymers are polypropylene (PP) and polyamide (PA), usually reinforced with glass fibre to create a more inexpensive composite with better properties than traditional short-fibre thermoplastic composites. An even more inexpensive alternative can be made using recycled polymers. Long-fibre reinforcement increases composite properties, which may be a suitable strategy for the recovery of plastic waste. Thermoplastic composites can also be very useful in other industries, such as railway, navigation, aerospace and defence.” Galindo continues: “The production process of


long-fibre pellets and tapes is based on the pultrusion of thermoset composites, in which reinforcing fibres are guided into a resin impregna- tion bath and then pass through a die to give them their profile shape. In the case of thermoplastic composites, the process is a bit more complicated because the impregnation bath is fed with an extruder to ensure that the polymer is melted, and the fibre is thoroughly impregnated. The choice of matrix polymer is crucial because the polymer’s rheological properties play an important role in ensuring the fibre is properly impregnated. If the fibre is not impregnated properly, the interface between the matrix and the reinforcement will not meet quality standards. Voids may be generated between the two phases and begin a cracking process that accelerates mechanical failure of the material. Chemical compatibility between the fibre and matrix is another factor that should be consid- ered. Fibre coupling and the incorporation of compatibilising additives into the matrix can help improve compatibility and balance the polarity and surface stress in both materials. However, additives should be incorporated into the matrix while


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IMAGE: ENGEL


IMAGE: AIMPLAS


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