Thermoplastic prepreg sheet (CFRTP) continues to show potential in the field of aerospace composite materials

Aerospace, aviation, urban air transportation (UAM) and military research work has been going all out to realize the next generation of aircraft-composite materials, especially thermoplastic prepreg sheets (CFRTP), which is the key to many of these efforts. Compared with thermosetting prepreg sheets, thermoplastic composites have advantages such as higher toughness, easier recycling, ability to be processed outside the autoclave (OOA), and storage at room temperature. The most striking is its multiple formatting functions, including cutting the thermoset and thermoplastic prepregs provided by the supplier into different shapes and formats to meet specific customer requirements. For example, format high-performance polyetheretherketone (PEEK), polyetherketoneketone (PEKK), and polyaryletherketone (PAEK) thermoplastic prepreg sheets, are most commonly used in the aerospace industry.

1. TP prepreg sheets for secondary aerospace structures-and challenges from primary structures

At present, most of the aviation structural activities in thermoplastic prepregs are concentrated on secondary structures, such as clips, inspection panels or substructures, while the main flight-critical structures such as wings and fuselages are made of thermosetting composite materials or metal.

Thermoplastic prepregs (UD sheet) can be formatted for various automated manufacturing technologies, including wire-wound prepreg sheet for AFP, mat-wound prepreg sheet for ATL, and wire-wound for additive manufacturing  

Many challenges are related to risk management, and part of the problem has always been the growing pain of thermoplastic prepregs provided by suppliers. Thermoplastic materials are not as mature as thermosetting sheets. Although thermosetting sheet has decades of mass production scale and perfect experience, the use of thermoplastic materials in the automated process of mass production is still in its infancy. However, in the past few years, the consistency and scale of the overall material have been greatly improved. The width, length, thickness, fiber tension, and resin uniformity of materials are now more consistent and of higher quality. Another obstacle to making larger thermoplastic primary structures is that thermoplastic materials tend to be more expensive than thermoset materials. If there is no overall cost advantage, it will not be more widely adopted. Collaboration and technical assistance are essential to help reduce process costs.

2. Process flexibility and material customization

In general, thermoplastic sheet (UD sheet) has great potential and increasing actions now and in the future, and flexibility is one of the main turning points for customers. At present, thermosetting prepreg sheets are mainly limited to automatic fiber placement (AFP), which is limited by autoclave curing and storage temperature requirements. Thermoplastic composites enable more flexible process methods and OOA processing, including sheet formats for automatic sheet laying (ATL) and filaments for additive manufacturing.

Commercial-scale formatting and supply chain solutions are essential to provide aerospace structural manufacturers with the thermoplastic cut prepreg sheet needed to support the projected industry's construction speed. Thermoplastic prepregs can also be customized for specific applications. The end user wants to match the material to each application. Because thermoplastics are highly adaptable, specific formats can be developed for specific parts, thereby maximizing material usage and reducing customers' downstream costs. Formatting thermoplastic materials for specific applications can also help reduce waste. In the aerospace industry, the purchase-to-flight ratio, that is, the ratio of the quality of raw materials to finished product, is a key issue. The goal is to make the ratio of purchase to flight as close as possible to 1:1, which means there is almost no waste. Providing the right materials in the right format for the right application can greatly reduce waste. In the aerospace industry, 30% waste is very common. To make the waste below this level requires the cooperation of all parties. Combining materials and processes is essential, and thermoplastic prepreg sheets are becoming a viable solution for aerospace structural manufacturers.