Self-reinforcing polymers

Advanced all-polymer prepregs or self-reinforced polymers... 

Other self-reinforced polymers are being developed. For example, PURE is based on highly oriented co-extruded tapes of polypropylene and a consolidation binder. Properties vary according to the form (see Table 6.27) - sheets, tapes or fabrics. 

Subclass All obtains the so-called self-reinforcing polymers viz. the polymeric liquid crystals (reinforcement by orientation in the mesophase followed by quenching below the solidification temperature). Subgroup A12 contains the thermoplastic elastomers, block copolymers in which the segments have very different Tg values, giving the possibility of intermolecular segregation and formation of physical networks. 

This chapter provides an overview of current researches on liquid crystalline polymers (LCPs). Topics include syntheses of main-chain and side-chain LCFs, structured characterization of LCFs and LCP networks and rheology and processing. Applications of LCP/polymer blends as self-reinforced polymers and electro-optical meterials are also discussed. 

C3 + D3) Molding of self-reinforced polymers — No (unsolved process for molecular composites) ... 

Vectra LCPs consist of parallel, closely packed, fibrous chains in injection molded parts which give the polymer a wood-like appearance at fracture surfaces and also give it seU-reinforcing properties that are at least as good as those of conventional fiher-reinforced thermoplastics. ICI supphes LCPs (self-reinforcing polymers) under the trade name Victrex SRP. Excellent physical properties, low comhnstihility and smoke generation, resistance to chemicals and solvents, and stahihty towards radiation are some of the important properties of LCPs. 

Although composites are a very important class of polymeric materials they form a separate subject in their own right, in which it is necessary to assume an understanding of the properties both of the polymer matrix and of the reinforcing material. They are not discussed further in this book, but it is interesting to note that in some ways semi-crystalline polymers can be considered as self-reinforcing polymers, because the mechanical properties of the crystalline parts are different from those of the non-crystalline parts, which often effectively form a matrix in which the crystals are embedded. 

Another rod like TP is self-reinforcing polymers (SRPs) that has exceptional high performance properties but very difficult to process. Unlike LCPs they are amorphous, isotropic, and transparent. Research on SRPs was sponsored during the 1960s by Wright-Patterson Air Force Base, Dayton, OH. 

The use of nanocomposite fibers as reinforcement of self-reinforced polymers also seems appealing to enhance not only interfacial adhesion and the subsequent processing window, but also to improve fiber properties and therefore the final material s mechanical performance. 

Before going any further, let us adopt the terminology introduced by Samulski [5]. We have already used above the abbreviation PLCs. Samulski contrasted PLCs to MLCs, and defined the latter as low molecular mass LCs— irrespective of the fact whether they can or cannot polymerize. His terminology is unequivocal and succinct. People unfamiliar with it use long and not necessarily well-defined terms, such as liquid-crystalline substances with low molecular weights —when they presumably mean MLCs. Other names such as liquid crystalline polymers (LCPs) for PLCs or LMMLCs for MLCs are also in use. The abbreviation SRPs for self-reinforcing polymers and the name in situ— composites [6] are used as weU. Moreover, PLCs are sometimes also called molecular composites. 

PEI with 35-95 wt% LCP, self-reinforced polymer compositions LCP fibers, tensile strength, modulus, elongation, impact strength, HDT Isayev and Swaminathan 1989... 

From a survey of the recent development in the field of self reinforcing polymers it appears clearly that the unique properties of the LCP make them primary candidates as reinforcing agent, added to engineering thermoplastic in the form of second phase. In the design of the blend several parameters have to be considered, but first let consider in close details the major features of liquid-crystalline compounds. 

All-cellulosic based composite films can be prepared from either isotropic or anisotropic cellulosic derivatives solutions. However, these composites cannot compete with mechanical properties of cellulose nanofiber reinforced composites. Pioneering studies reported by Favier et al. [35, 36], showed that small amounts of cellulose tunicate whiskers resulted in dramatic improvements in modulus above the glass transititMi temperature of an amorphous polymer matrix, due to the percolation of the cellulose nanofibers. Also recently, a completely new route to cellulose-based composites was proposed by Nishino and Arimoto [37], Soy-keabkaew et al. [38—40], They focused on approaches following self-reinforcing polymer concepts [41, 42] to create composites that often outperform traditional nanofiber reinforced composites [38,40],... 

As can be seen from Fig. 11.2, many fibrils are observed in the cross section of tensile fractured as-spun fiber LCP. These fibrils are acting as if they are reinforcements, and therefore LCP is often referred to as self-reinforced polymer. However, this anisotropy is a big practical problem when LCPs are used in injection-molded parts because LCPs produce oriented moldings with anisotropic mechanical and thermal properties. Properties along the flow direction tend to be superior to those across the flow direction. Fillers represented as glass fiber are often added to LCPs to reduce the anisotropy because the addition of any filler disrupts the alignment of the LCP molecules. This is just the reverse of what is experienced with... 

The increasing environmental awareness requires that the used material have a high or full recyclability. Self-reinforced polymers are one of these... 

Hare C (Ed.) (2010) Self reinforced polymer composites with impact Technical bulletin, www.espritproject.eu... 

Rein D M, Vaykhansky L, Khalfin R L and Cohen Y (2002) Controlling the properties of singlepolymer composites by surface melting of the reinforcing fibers, Polym Adv Technol 13 1046-1054. Hine P J, Ey R H and Ward I M (2008) The use of interleaved films for optimising the production and properties of hot compacted, self reinforced polymer composites, Compos Sci Technol 68 1413-1421. 

By using these techniques, a series of self-reinforced polymers based on semicrystalline thermoplastics are produced [18-30]. They have the following advantages over conventional particulates or fibers reinforced polymers ... 

Light weight density of the reinforcement in a self-reinforced polymer is obviously lower than that of the composites containing inorganic particles and fibers consequently, not only the end products are lightened, but also their specific strength and modulus are increased ... 

Recyclability all the components in a self-reinforced polymer belong to the same species, which are melt-processable after serving their original purpose, they can be remanufactured into additional products. 

Nevertheless, self-reinforced polymers possess evident shortcomings arising from their thermoplastics nature. Temperature sensitivity, for example, limits the application at elevated temperature environment. With a rise in temperature, contraction and disorientation of the reinforcing component take place [31,32], and the material s properties have to be deteriorated. 

Hine P J, OUey R H and Ward 1M (2008) The use of interleaved films for optimising the production and properties of hot-compacted, self reinforced polymer composites. Compos Sci Technol 68 1413-1421. 

Alternative routes, due to environmental awareness and increasing interest in sustainable material concepts, have led to the development of bio- and green composites for structural composite applications, the so-called all-polymer composites or self-reinforced polymer composites . These new materials promise to overcome the critical problem of fiber-matrix adhesion in biocomposites by using chemically similar or identical cellulose materials for both matrix and reinforcement and are designated as all-cellulose composites [39, 40]. 

MG rubbers show the hybrid qualities of the blend. When compounded, MG rubbers are self-reinforcing polymers with high hardness, impact resistance, and good elongation. Compatible with natural rubber in all proportions they can be molded into such items as cutting blocks. They also find use in adhesives permitting bonds to be made between natural or synthetic rubbers and PVC, synthetic fibers, leather, etc. 

Gao C, Yu L, Liu H, Chen L (2012) Development of self-reinforced polymer composites. Prog Polym Sci 37 767-780... 

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