Other Thermoset-Based Composites

PU-based green composites have already shown promise in the automotive industry, using fibers such as jute and ramie to manufacture parts such as door Hnings. However, PUs, one of the most versatile thermosetting materials, have been used as a biocomposite matrix in only a limited number of research reports Bledzki et al. [34], for instance, have come up with an experiment-based approximation model relating the static mechanical properties of jute and flax fabric-reinforced PU microfoams with microvoid content The mechanical performance and properties of other thermoset biocomposites, such as coir fiber-reinforced ethylene glycol dimethacrylate (EGDMA) [35] and oil palm fiber-reinforced poly(allyl methacrylate) 

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At the outset of the composites industry, the matrices were unsaturated polyesters. Then other thermosets were developed but some years ago the manufacture of thermoplastic composites began and their development is now faster than that of thermoset-based composites. 

The other difference [21] is fhaf fhermosef composife shows higher balanced sfrength and toughness compared to thermoplastic composite, with a little brittleness. Thus, thermoset composite plates can be fabricated relatively thinner and have more applications. On the other hand, as mentioned before, a well developed injection molding process has been applied as the fabrication process of thermoplastic-based composite plates to assure high quality and low cost. 

Epoxy/cyanate ester thermoset blend-based composites have low dielectric constant desirable for advanced radomes, microwave anteimas, and stealth aircraft composite applications. Other applications include its use in copper clad laminates, semiconductor devices, and fire-resistant aircraft structural composites. 

Commercial bismaleimide thermoset resins are based on aromatic bismaleimides such as 4,4 -bismaleimidodiphenylmethane (Compimid MDAB, Evraiik). Compimid MDAB, also known in literature as MDA-BMT is derived from the condensation reaction between 4,4 -methylene dianiline (MDA) and maleic anhydride, both relatively low-cost monomers. The MDA-BMI is often used as a eutectic mixture with other BMIs such as TDA-BMI, to reduce its melting point for improved impregnation and tackiness in the glass and carbon-fiber-based composite prepregs. 

Similar to all commercial plastics, the traditional and more commonly used thermosetting resins are considered as petrochemicals, having been manufactured from petroleum. Some of the primary distillation products of crude oil, which can be classified either as olefins or aromatics, serve as precursors for the synthesis of thermosets. For example, epoxy resins are manufactured by the reaction of epichlorohydrin, a chloro-oxirane, and a derivative of propylene, with bisphenol A, which is a derivative of cumene. Another example would be the unsaturated polyesters (UPs), which are derivatives ultimately originating from ethylene (ethylene glycol) and benzene (maleic acid) [6]. Epoxies and polyesters constitute more than 95% of the thermoset composite market of the two, polyester-based systems predominate in volume by about 10-fold [6, 7]. Other thermoset resins used in reinforced form are phenolics, vinyl esters, and polyimides. Details of the properties and applications of these thermoset systems will be further discussed in the following section. 

In more recent work, a composition which was claimed to be fusible and melt-extrudable was developed in a joint effort of UNIAX Corp., Santa Barbara, CA, USA, and Neste Oy, Porvoo, Finland, given the tradename PANIPOL [278]. In its typical preparation, a sulfonated P(ANi) salt, a plasticizer, and other "optional additives" are fed into a twin-screw extruder with a typical temperature profile along the screw of between 100 and 180 °C and residence time 5 to 10 mins. The resulting conductive strands are cooled, pelletized and packaged. The conductive pellets are then compounded for such end uses as injection molded articles or extruded films and fibers, or any other conductive thermoplastic products. The authors also claimed to have demonstrated conductive thermosets based on solution-processed PANIPOL. 

Composite Particles, Inc. reported the use of surface-modified rubber particles in formulations of thermoset systems, such as polyurethanes, polysulfides, and epoxies [95], The surface of the mbber was oxidized by a proprietary gas atmosphere, which leads to the formation of polar functional groups like —COOH and —OH, which in turn enhanced the dispersibility and bonding characteristics of mbber particles to other polar polymers. A composite containing 15% treated mbber particles per 85% polyurethane has physical properties similar to those of the pure polyurethane. Inclusion of surface-modified waste mbber in polyurethane matrix increases the coefficient of friction. This finds application in polyurethane tires and shoe soles. The treated mbber particles enhance the flexibility and impact resistance of polyester-based constmction materials [95]. Inclusion of treated waste mbber along with carboxyl terminated nitrile mbber (CTBN) in epoxy formulations increases the fracture toughness of the epoxy resins [96]. 

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