Self-reinforcing composite

The macroscopic orientation of their extended-chain crystals depends on the orientation imparted by flow during mol ding. Because of the fibrous nature of the extended-chain crystals, these materials behave as self-reinforcing composites, with excellent mechanical properties. 

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. 

Gilbert, J. L., Ney, D. S. Lautenschlager, E. P. (1995) Self-reinforced composite poly(methyl methacrylate) — static and fatigue properties. Biomaterials, 16, 1043— 1055. 

Y. Fang, F. Yu, K.W. White, Microstructural influence on the R-curve behavior ofa 70% Si3N4-30% barium aluminum silicate self-reinforced composite, /. Mater. Sci., 35 2695-99 (2000)... 

In a previous work, the same authors also observed that the composite peel strength was significantly increased by introducing interleaved films of the same polymer between the layers of woven oriented tapes [30]. They continued working on PP self-reinforced composites enhanced with the addition of CNT, trying to improve properties by the use of interleaved films [28]. Samples of single-polymer polypropylene composites were produced with and without interleaved films, and with and without carbon nanofibers, located either in the oriented polypropylene tapes, in the interleaved film or in both. Maximum peel strength was observed... 

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]. 

Akhtar, S. and Isayev, A.I. (1993) Self reinforced composites of two thermotropic liquid crystalline polymers. Pdlym. Eng. Sd., 33, 32. 

Tormala, P., Biodegradable self reinforced composite materials, manufacturing structures and mechanical properties. Clinical Materials 10, 29-34 (1992). 

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. 

Self-Reinforced Composites Involving Liquid-Crystalline Polymers Overview of Development and Applications... 

ISAYEV Self-Reinforced Composites Involving LCPs... 

The second section is devoted to self-reinforced composites prepared through the melt processing of thermoplastics and thermotropic LCPs. The individual chapters address various aspects of rheology, processing compatibilization, and performance characteristics of in situ composites. Attention is directed to preparation of fibers and molded products, with the special objective of optimal performance properties through processing. 

Self-Reinforcing Composites—Molecular Reinforcement. The idea... 

Isayev A I and Subramanian P R (1991) Self-reinforced composite of thermotropic liquid crystalline polymers and process for preparing same, U.S. Patent 5,070,157, Austr Patent 645,154 (1994), Eur Patent EP 0543 953 (1997), Can Patent 2,086,931 (1993), Jap Patent 2 841 246, French Patent 0543953, Ger Patent 69125493.1, Great Brit Patent 0543953, Int Patent WO 92/03506 (1992). Isayev A I (1991) Wholly aromatic polyester fiber-reinforced polyphenylene oxide and process for preparing same, U.S. Patent 5,006,403. 

Isayev A I (1993) Self-reinforced composites and process for preparing same, U.S. Patent 5,260,380, Eur Patent EP 0 623 156, Austr Patent 661,123, Int Appl WO 93/15144, Jap Patent Appl... 

Song C H and Isayev A I (2001) LCP droplet deformation in fiber spinning self-reinforced composites, Polymer 42 2611-2619. 

However, common to all these composites is that they consist of a matrix and reinforcement that differ in their mechanical properties and a synergistic combination of the latter characterizes the final product. If this definition is used, the term single (or one) polymer composites would then refer to a subset of homocomposites, self-reinforced composites, or homogeneous composites, which is not restricted to polymers but can be adapted to any material, for example, wood. 

Bdrdny T, Izer A and Menyhard A (2010) Reprocessability and melting behavior of self-reinforced composites based on PP homo and copolymers, J Therm Anal Calorim 101 255-263. 

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. 

The first step in the production of self-reinforced composites is the primary shaping of films and tapes directly from the melt. While doing so, a mono-, and also a co-extrusion of the said products, can be targeted. In contrast to coextrudates, mono-extruded films and fibers require extremely precise temperature control during later hot-compaction and molding processes. However, they can be purchased for a lower price. 

Figure 22.2. Production of self-reinforced composite via selective melting of the outer surface of the oriented PP-tapes during hot-compaction under temperature and pressure according to [7,43]...

Figure 22.4. Schematic pressure and temperature dependent processing window for the hot-compaction of self-reinforced composites [22]...

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