Self-reinforcing composite system

Tm etc. for the mesophase transitions and by Ti for the transition to an isotropic melt. The presence of such a mesophase (for mainchain LCP systems usually a nematic one) offers the possibility to use these polymers as a reinforcing fibre phase in so-called self-reinforcing composite systems. 

All the above systems require a sequence of steps and the use of solvents to attain the final goal, which complicates the process both in toms of economical and ecological soundness. The direct transformation of cellulose fibres into self-reinforced composites by partial oxypropylation was considered a promising alternative to this working hypothesis since it eliminated the use of solvents and could be conducted in a straightforward one-step operation. The study of this system confirmed its viabOity and produced interesting composite materials [20]. 

Isayev, A. (1996) Self-reinforced composites involving liquid-crystalline polymers Overview of development and applications, in Liquid-Crystalline Polymer Systems Technological Advances, (eds A.I. Isayev, T. Kyu and S.Z.D. Cheng) ACS Symposium Series 632, American Chemical Society, Washington, DC, pp. 1-20. 

As with conventional composites, when creating self-reinforced composites by combining discrete fibres and matrices such as by film and fibre stacking, various authors have also reported the surface pretreatment of the fibres to improve the interfacial properties of the composites [48, 51, 52]. However, details such as fibre preparation treatments and failure modes that dominate during specimen failure will not be presented in detail here. Instead, the focus of this review is the performance of the composite systems, and the reader is encouraged to consult the referenced literature for more details on the failure modes that dominate. 

Possible structures which may arise dming the phase separation of binary mixtures have been discussed elsewhere. It is important that the microphase particles evolved in this process, which have different composition and size be considered as quasi-particles of polymeric filler and the system as a whole- as a self-reinforced composite material. Thus polymer-polymer systems with incomplete phase separation may be described as systems consisting of polymeric matrix and polymeric filler. The common feature for both such systems and polymers obtained by the introduction of polymeric filler consists of formation of an interphase zone between two separated coexisting phases. 

Self-reinforced PP is an intriguing avenue for creating a more recyclable, single-polymer, reinforced material. Such a composite system is reinforced by oriented, drawn PP fibers within a PP matrix, or as part of a laminated system. However, current cost disadvantages have limited their use [7-42]. 

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]. 

Figure 22.1. Production system of self-reinforced mono- and hybrid-composites [38,39]...

Compared to glass fiber and other foreign fiber reinforced polypropylenes, prominent characteristics are an exceptionally high impact strength and resistance to perforation [26,76]. These are caused by an efficient absorption of energy by self-reinforced fiber composite systems. 

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. 

As with the numerous groups who have applied fibre and film stacking techniques to produce self-reinforced polymer composites based on PE, the fibre and film stacking technique was also applied to PP-based systems, as reported by Kitayama et al. [59, 60]. The authors report the production of a unidirectional composite by consolidating PP multifilament yams between films of an ethylene-propylene random copolymer. This film was reported to have a broad melting behaviour with an endothermic melting peak at 130 °C, and so allowed for composite... 

The development of most composite materials is driven by the need to achieve a material with a combination of properties that cannot be readily obtained by using a homogenous material. In many cases, the development is driven by a need to improve mechanical properties, and this is so for many self-reinforced polymer composites. The following sections of this review present a summary of the mechanical properties of some of the self-reinforced polymer composites based on PE, PP, PET, PMMA and PA, with extra references to some other reported systems. 

The mechanical performance of any self-reinforced polymer composite system will also depend on the polymer used in that particular system, and this will now be discussed further. A review of the pubUcatimi dates for the literature collected in this review for self-reinforced polymer composites based on PE, PP, PET, PMMA and PA gives an indication of the trends cmiceming the materials used in... 

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