Fiber-reinforced thermoplastics (TP) offer a number of advantages compared to thermosets (TS): For example, they can be melted, thus enabling forming and welding processes as well as recycling. The processing by thermoforming – which is common for continuously reinforced TP – is suitable for large-scale production, but the high investment costs represent a hurdle to entry. In-situ polymerizing thermoplastics provide a potential link that can be used for entry into TP technologies or within the context of prototype construction and series ramp-up. In this process, equivalent to thermosetting process chains, the low-viscosity monomers or oligomers are injected into a mold containing the fiber preform. Only there, they polymerize into the finished thermoplastic (Figure 1). In this context, intensive research is being carried out on polyamide 6, for example, which is formed from the monomer ε-caprolactam by anionic polymerization [1].

As part of a project supported by the European Regional Development Fund, the Leibniz-Institut für Verbundwerkstoffe is currently building up expertise in the field of in-situ polymerizing TP. In this context, a novel injection plant for the resin transfer molding (RTM) process has been developed, which is suitable for processing ε-caprolactam and other in-situ polymerizing thermoplastics. In contrast to commercially available equipment, the use for research is focused here. The system is therefore modular in design and can thus be adapted to other process parameters or material compositions with little effort if required. In addition, the system has a large number of sensors and configuration options. Other key aspects in the plant development were the special challenges of processing ε-caprolactam: corrosiveness, very low processing viscosity and a high sensitivity of the polymerization reaction to moisture and oxygen. Complementary to the plant, an injection tool was developed, which is also modular in design and can continuously measure and record all relevant process parameters for process control.

In this presentation, the relevant development steps and use cases are discussed.

Referenzen

[1] T. Ageyeva, I. Sibikin, J. Karger-Kocsis, Polymers, 2018, 10, 357