POLYMER-MATRIX

The first reinforced plastics were all based on thermoset polymers. For many years the most popular have been the family of polymers known as thermoset polyesters (6.N. 1 ). These are versatile, inexpensive polymers, used extensively with glass-fibre reinforcement, often in substantial plastic components (such as 

Storage tanks, pipes, boat hulls, and seating for public places). Other thermosets are in competition with them, the foremost being the epoxies (6.N.2). These are preferred to polyesters in demanding applications, where their superior mechanical performance (especially greater toughness) justifies their higher cost. 

Thermoset polymers have some great virtues when used as matrices in reinforced plastics  

As the key degradation reaction is main chain scission in most polymers, the activation energies for degradation in a particular environment are strongly dependent on the strength of the weakest bonds in the polymer backbone. Thus polymers with simple 

As discussed in Section 10.2.3, PVP and DNA have been used to wrap and water-solublize SWNTs. For specific actuator, electrical and electro-optic applications, SWNTs have been wrapped by piezoelectric polyvinylidene fluoride and trifluor-oethylene copolymer [50] or with conjugated polymers [51, 52]. The conjugated polymer used to form a composite with MWNTs and an electron-transport layer in light-emitting diodes is poly(m-phenylene-vinylene-co-2,5-dioctyloxy-p-phenylene-vinylene) (PmPV) [53]. Wrapping coupled with electron doping has been achieved with polyethylene imine to form p-n junction devices ([40], see footnote 1). 

1) Zhang, Y., Grebel, H., and Iqbal, Z. Polyethylene-imine functionalization of single wall carbon nanotubes for air-stable n-type doped coatings, unpublished data. 

The main functions of the matrix in a fiber-reinforced composite are to bind the fibers and to transfer loads to and between them only a small amount of the applied load is supported by the matrix. Let us consider a bunch of unidirectionally aligned continuous fibers subjected to a tensile stress. If a fiber breaks down, it becomes useless but if the fibers are embedded in a polymer matrix (see Fig. 15.1a), the load distributes around the break point and the fiber remains useful. Furthermore, the matrix protects the fibers from self-abrasion and scratches on handling, keeps the reinforcement in 

Al-Zn-Mg alloy Quenched and tempered low alloy steel Carbon fiber-epoxy resin 7.85 207 2050-600 12-28 11 26.4 261-76 800 

Perpendicular to fibers Glass fiber-polyester resin 1.62 7 38 0.6 30  

One of the most important characteristics to consider in choosing a matrix is its adhesion with the fiber. The fiber/matrix interfacial adhesion plays a critical role in the mechanical properties of the composite. The loads are transferred from the matrix to the fiber through the interface, and the strength of the composite depends on the bond between fiber reinforcement and matrix. 

Organic matrices are divided into thermosets and thermoplastics. The main thermoset matrices are polyesters, epoxies, phenolics, and polyimides, polyesters being the most widely used in commercial applications (3,4). Epoxy and polyimide resins are applied in advanced composites for structural aerospace applications (1,5). Thermoplastics Uke polyolefins, nylons, and polyesters are reinforced with short fibers (3). They are known as traditional polymeric matrices. Advanced thermoplastic polymeric matrices like poly(ether ketones) and polysulfones have a higher service temperature than the traditional ones (1,6). They have service properties similar to those of thermoset matrices and are reinforced with continuous fibers. Of course, composites reinforced with discontinuous fibers have weaker mechanical properties than those with continuous fibers. Elastomers are generally reinforced by the addition of carbon black or silica. Although they are reinforced polymers, traditionally they are studied separately due to their singular properties (see Chap. 3). 

---

New PHB materials are composed of Zn-tetraben2oporphyrin—aromatic cyanide—poly (methyl methacrylate) (180) or of tetraphenylporphyrin derivatives dispersed in polymer matrices such as PMMA and polyethylene (181). A survey of such materials has been given (181). 

Nitro-substituted indolino spiroben2opyrans or indolino spironaphthopyrans are photochromic when dissolved in organic solvents or polymer matrices (27). Absorption of uv radiation results in the colorless spiro compound [1498-88-0], C22H2gN202, being transformed into the colored, ring-opened species. This colored species is often called a photomerocyanine because of its stmctural similarity to the merocyanine dyes (see Cyanine dyes). Removal of the ultraviolet light source results in thermal reversion to the spiro compound. 

Composites High E, CTy, k c but cost Stiff (E > 50 GPo) Strong a = 200 MPa) Tough (kic > 20 MPa m ") Fatigue resistant Corrosion resistant Low density Formobility Cost Creep (polymer matrices)... 

Those basic matrix selection factors are used as bases for comparing the four principal types of matrix materials, namely polymers, metals, carbons, and ceramics, listed in Table 7-1. Obviously, no single matrix material is best for all selection factors. However, if high temperatures and other extreme environmental conditions are not an issue, polymer-matrix materials are the most suitable constituents, and that is why so many current applications involve polymer matrices. In fact, those applications are the easiest and most straightforward for composite materials. Ceramic-matrix or carbon-matrix materials must be used in high-temperature applications or under severe environmental conditions. Metal-matrix materials are generally more suitable than polymers for moderately high-temperature applications or for modest environmental conditions other than elevated temperature. 

Methods for Estimating the Filler Effect on Polymer Matrices... 

The same is indicated by yield stress values (as the position of the whole flow curve) when we compare the properties of different polymer matrices with the same filler [11],... 

Noble metal nanoparticles dispersed in insulating matrices have attracted the interest of many researchers fromboth applied and theoretical points of view [34]. The incorporation of metallic nanoparticles into easily processable polymer matrices offers a pathway for better exploitation of their characteristic optical, electronic and catalytic properties. On the other hand, the host polymers can influence the growth and spatial arrangement of the nanoparticles during the in situ synthesis, which makes them convenient templates for the preparation of nanoparticles of different morphologies. Furthermore, by selecting the polymer with certain favorable properties such as biocompatibiHty [35], conductivity [36] or photoluminescence [37], it is possible to obtain the nanocomposite materials for various technological purposes. 

There are different mechanisms for explaining exfoliation of organically modihed clays in the polymer matrices. One such mechanism is the Lattice model proposed by Vaia and Giannelis [200]. The mechanism is explained as follows. 

Reinforcement of polymer matrices using various types of nanofillers is being extensively studied nowadays. The reinforcement mechanisms as well as enhancement of properties are different with different types of fillers. This field is quite green and many more developments are yet to come to enrich our science and technology in the near future. 

Polymer disposal in an inappropriate manner creates environmental problems such as dioxin formation, catastrophic fires, breeding of rats, and mosquitoes. Several methods have been explored to utilize plastics and mbber waste in an environment-friendly manner. Some of the recent advances in mbber recycling are reviewed in this chapter with special emphasis to waste mbber reutilization in plastics and mbbers. The utilization of waster mbber powder in polymer matrices provides an attractive strategy for polymer waste disposal. 

Chemical and electrochemical techniques have been applied for the dimensionally controlled fabrication of a wide variety of materials, such as metals, semiconductors, and conductive polymers, within glass, oxide, and polymer matrices (e.g., [135-137]). Topologically complex structures like zeolites have been used also as 3D matrices [138, 139]. Quantum dots/wires of metals and semiconductors can be grown electrochemically in matrices bound on an electrode surface or being modified electrodes themselves. In these processes, the chemical stability of the template in the working environment, its electronic properties, the uniformity and minimal diameter of the pores, and the pore density are critical factors. Typical templates used in electrochemical synthesis are as follows ... 

Selim, K., Tsimidou, M., and Biliaderis, C.G., Kinetic studies of degradation of saffron carotenoids encapsulated in amorphous polymer matrices, Food Chem., 71, 199, 2000. 

Unfortunately, extraction procedures are often elaborate and labour intensive since many of the polymer matrices are poorly soluble or insoluble. For this reason, substantial efforts have been directed towards additive analysis without prior separation from the polymer. Chapter 9 deals with direct methods in which such separation of polymer and additive can be omitted. Yet, this direct protocol still requires sample pretreatment (dissolution) of the polymer/additive system as before. 

While most polymer/additive analysis procedures are based on solvent or heat extraction, dissolution/precipita-tion, digestions or nondestructive techniques generally suitable for various additive classes and polymer matrices, a few class-selective procedures have been described which are based on specific chemical reactions. These wet chemical techniques are to be considered as isolated cases with great specificity. 

---