Self-reinforced thermoplastic fiber composite materials

Self-reinforced thermoplastic fiber composite materials 

In contrast, the concept of self-reinforced thermoplastic single polymer composites (SPCs) is based upon macromolecular, highly oriented thermoplastic fibers or tapes, which are embedded in a chemically identical thermoplastic matrix [4-7]. Consequently, the use of foreign reinforcing materials is not necessary and the material systems can still be tailored for nearly any application just like conventional fiber composites, for example, by varying the fiber content, fiber orientation or number of fabric layers [8-10]. 

The aspect of self-reinforcement is of great importance for the performance of the single polymer composites. Apart from the stretching of the molecules, which occurs during the fiber and/or tape production, crystalline structures are also induced [11]. So-called shish kebab structures can be specifically developed by means of melt or solid phase deformation [12] and give the stretched thermoplastic tapes or fibers significantly higher mechanical properties than are possible for a comparable compact material that is not self-reinforced. 

It can be deduced that a manifold variety of self-reinforced fiber composite materials with exceptional properties exist. However, these hardly ever have a structural function in construction parts. The main reason is that thermoplastic fibers and the composites made from them have a very high temperature sensitivity during processing and application. Furthermore, adhesion problems can occur in composites with differing fiber and matrix polymers. And, finally, the cited studies [17-37] do not deal with SPCs but in the best case, with polymer-polymer composites. 

As a general rule, self-reinforced composites consist either of layers of highly-oriented thermoplastic textiles [4-7] or of a combination of self-reinforced textiles and a similar thermoplastic matrix material, which is added in the form of a film, powder or melt [1]. These are then hot-compacted to structurally consolidated mono-composites under pressure and temperature in a pressing process. For the most part, the fiber composite concept relies upon the embedding of stretched endless fibers or tapes made of PP into a chemically identical matrix. 

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Self-reinforced thermoplastic fiber composite materials... 

An exceptional advantage of self-reinforced thermoplastic composites is that they can be thermally recycled, but also reprocessed due to their polymer purity. This can be done by either returning the composite to a melted state or by simply re-granulating it. Thus, this process does without the complicated and expensive separation of the components, because an actual single-material system is on hand. Such a simple and useful recycling concept (in regard to material reuse) for the quantities currently in circulation has yet to be developed for the established foreign fiber reinforced thermoplastics. 

RPs that combine two different materials (plastic matrix and reinforcement) are a separate major and important segment in the plastic industry. They are also called plastic composites and composites. There are also self-reinforcing plastics such as liquid crystal polymers (Chapter 1) and others.301 It is a fact that RPs have not come near to realizing their great potential in a multitude of applications usually due to cost limitations that particularly involves the use of expensive fiber reinforcements (carbon, graphite, silica, etc.).1 Information on thermoplastic and thermoset plastic RPs are reviewed in Chapter 15. 

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