Technology and Application of Advanced Thermoplastic Composites

For many years, aircraft manufacturers have benefited from thermoplastic composites in the form of strong and durable structural materials, and aerospace designs allow databases for commercial and military applications.

  While there are different reasons for choosing thermoplastic composites, there are several key reasons that have driven Original Equipment Manufacturers (OEMs) interest in thermoplastics. First, very low void thermoplastic unit tape development and automation solutions eliminate the need for autoclaves to produce very low void content thermoplastic structures. The second is the ability to weld thermoplastics via induction or resistance welding techniques, offering a viable way to reduce weight and cost without the use of fasteners. Migration to composite airframes then requires removal of metallic structural supports and associated galvanic corrosion effects.

   In addition to excellent flame retardancy and structural properties, thermoplastic composites offer cost-effective processes such as thermoforming and compression molding to fabricate multiple metal stents. Very high consistency, low void content thermoplastic prepregs have become essential in several emerging automation solutions.

  Polymer Technology

   Thermoplastic polymers are divided into amorphous and semi-crystalline types. In contrast to semi-crystalline polymers, amorphous thermoplastics do not form a crystalline structure and can be molded at temperatures close to their glass transition temperature (Tg). One problem with amorphous thermoplastics, however, is their poor resistance to certain solvents.

  Semicrystalline polymers have amorphous regions and regions that are tightly packed in a crystal lattice. The crystallinity of a particular fraction is based on the type of polymer and the cooling rate used to form the fraction. Semi-crystalline polymers have Tg and melting temperature Tm, and also have points where the crystalline structure breaks.

  Key thermoplastics used in composites include

   Polyetherimide (PEI) - Amorphous

  Nylon - Amorphous or Semi-Crystalline

  Polyetherketoneketone (PEKK) - semi-crystalline

   Polyetheretherketone (PEEK) - semi-crystalline

   Polyphenylene Sulfide (PPS) - Semi-Crystalline