EFRE-EasyEntry2TPC - Commissioning of an injection plant for processing ε-caprolactam

The production of thermoplastic components with directional fiber reinforcement is usually carried out in a thermoforming process whereby the component production is preceded by the production of a semi-finished product. In this process, textile semi-finished products are fully impregnated with a thermoplastic in powder form or in the shape of a thermoplastic film and provided as plate-shaped semi-finished products (organo sheets). These can then be given their final shape by pressing in a downstream thermoforming process. Although the process is suitable for large-scale production, the high melt viscosities of the thermoplastic matrices require high process pressures and temperatures in the production of the semi-finished products which entails corresponding investments in the plant technology. In addition, the process as a whole remains limited to shell-shaped components.

Fiber composite production based on the material group of reactive thermoplastics represents a far-reaching departure from this classic processing route for thermoplastic composites. Whereas in the conventional case, polymerization from monomer to long-chain polymer takes place under controlled process conditions in the reactors of chemical production and is completed with the production of thermoplastic pellets, reactive thermoplastics allow in-situ polymerization, i.e. transferring the polymerization reaction directly to component production. This method has a number of advantages but is particularly attractive because reactive thermoplastics feature very low processing viscosities, some of which are even below those of thermoset resin systems. They can therefore be used in resin injection processes normally restricted to thermosets. Furthermore, it is possible  to combine the processing advantages of thermosets with the material advantages of thermoplastics which include their subsequent formability and weldability as well as their large potential for material recycling. In addition to the much simpler impregnation of dry fiber structures, the significantly lower process pressures and process temperatures are particularly noteworthy. Furthermore, the lower investment costs in plant engineering also make smaller quantities economical.

This bridge building thus paves the way for shortening the process chain in the production of thermoplastic components with directional fiber reinforcement. The upstream organo sheet production can be omitted, and the forming process is replaced by an injection into a mold equipped with a textile preform.

However, all these potential advantages are offset by the fact that the processing of reactive thermoplastics is associated with significantly higher demands on process management and process control and requires both special plant technology and special expertise.

This acquisition of competence in handling the reactive processing of thermoplastics was the focus of "EasyEntry2TPC" project funded by European Regional Development Fund (ERDF), with the main objective of implementing the processing of ε-caprolactam to polyamide 6. In the course of the two-year project, the necessary plant technology and experience were built up at Leibniz-Institut für Verbundwerkstoffe in order to provide support in the application of this technology, especially for SMEs that were previously active in the field of thermosetting liquid impregnation processes. In addition to a resin injection system, a sensor-equipped injection tool has been developed for this purpose. Both can subsequently be used to investigate different plastic systems and additives as well as different process conditions.

The injection system is designed as a two-line system and can be fully temperature controlled, since the starting materials for the anionic chain polymerization to PA6 are present as solids at room temperature, which requires continuous heating of the entire plant equipment. In addition, the material system places high demands on corrosion resistance and the prevention of moisture ingress. In terms of design, these requirements were taken into account by the exclusive use of sufficiently corrosion-resistant materials and the possibility of applying vacuum or inert gas to all material-carrying strands. The discharge capacity of the system is up to 1 kg/min and control is via a built-in computer and LabVIEW programming. The dimensioning was deliberately chosen above the requirements of a pure laboratory operation and offers sufficient potential for modifications, not least due to a generous definition of the installation space.

The project "EasyEntry2TPC" was funded by European Regional Development Fund (ERDF) and Ministry of Economics, Transport, Agriculture and Viticulture (MWVLW) (grant number 84007039).

We thank the industrial user advisory board of EasyEntry2TPC project which accompanied the system and process development and enriched it with its user perspective. Furthermore, we thank L. Brüggemann GmbH & Co. KG for supporting the project providing test material.

Contact:

M.Sc. Alexander Faas
Scientific Employee Impregnation & Preform Technologies
E-Mail: alexander.faas@ivw.uni-kl.de
Telephone: +49 631 2017 434