TWI Industrial Member Report Summary 994/2011
By C Vacogne
There is currently considerable interest in the manufacture of components and products from composite materials including thermoplastic composites, in particular when based on Polyetheretherketone (PEEK), a high performance thermoplastic with excellent mechanical and chemical resistance properties. More generally, thermoplastic composites have excellent strength and stiffness to weight ratios and can be recycled by virtue of their melt processability, which makes them extremely attractive for industries such as Aerospace and Automotive. However, manufacturing thermoplastic composites remains nowadays costly and challenging.
One of the most popular methods to manufacture components using these materials is by (automated) tape laying. Tape laying involves the deposition and consolidation of a tape composed of pre-impregnated continuous fibres, in sufficient layers to make a component. This technology has certain intrinsic advantages over other composite manufacturing technologies, such as the ability to make very varied shapes and structures; including very large parts such as wind turbine blades and helicopter blades. It also allows the incorporation of sensors within the part and the ability to vary lay-up.
This project focused on PEEK impregnated continuous carbon fibre tapes (eg APC-2). Once processed by automated tape laying (ATL) or automated tape/tow placement (ATP) (Lamontia et al, 2009), a high performance and structural thermoplastic composite material is obtained. Its excellent chemical and mechanical properties make APC-2 components high-quality products, of growing interest for transport industries where light-weight, mechanical and chemical resistance are essential qualities.
The high melt viscosity of PEEK is considered as the principal cause for its slow and demanding weldability in terms of pressure and temperature; this is particularly relevant when APC-2 is processed by tape laying. It was therefore proposed to investigate ways of reducing the viscosity of PEEK and increasing the mobility of its polymer chains. The approach proposed to address this problem was to identify and assess 'welding agents' in the form of plasticisers for PEEK as well as in the form of low molecular weight or even amorphous PEEK. In other words, these welding agents are welding additives which can be described as chemical(s) that are introduced at the welding interface in order to 'facilitate' the welding process.
- To assess the feasibility of using welding agents for PEEK composite tape laying.
- To identify the preferred welding agent(s) amongst the list of potential candidates.