Polymer Resin Matrices

The most common matrix materials of carbon-fiber composites are the polymers, also called resins or plastics. Carbon-reinforced polymers are low-density, high-strength, and high-modulus composites with extensive applications, especially in aerospace as mentioned above. Their cost is still high but is gradually decreasing as the fabrication techniques are becoming less labor-intensive. 

A number of polymers are suitable as matrix material, each with its own advantages and disadvantages, with wide differences in properties, and the selection of a given carbon fiber-polymer system must be made after a thorough analysis of its suitability for the application. 

The polymers are usually processed in a preliminary step in the form of prepreg , that is pre-coated and partially cured (polymerized) on the fiber. This prepreging provides uniform impregnation of the fiber bundle and uniform resin-to-fiber ratio. The following polymers are presently available commercially 

High-Temperature Polymers. Several polymers with higher-temperature capability than epoxies are now avaiiabie in the form of prepreg. Their maximum-use temperature is shown in Table 9.2. 

Thermoplastic Polymers. Thermoplastic polymers do not require a cure cycle but need only to be melted during processing (usually injection molding). The most common are nylon, polypropylene, and polyethylene which are usually molded with 10-25 vol.% discrete (chopped) carbon fibers. The addition of fibers substantially increases the modulus and, to a lesser degree, the strength. Electrical conductivity is also considerably increased and many applications of these composites are found in electromagnetic-interference (EMI) shielding. 

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Multi-walled CNTs (MWCNTs) are produced by arc discharge between graphite electrodes but other carbonaceous materials are always formed simultaneously. The main by-product, nanoparticles, can be removed utilizing the difference in oxidation reaction rates between CNTs and nanoparticles [9]. Then, it was reported that CNTs can be aligned by dispersion in a polymer resin matrix [10]. However, the parameters of CNTs are uncontrollable, such as the diameter, length, chirality and so on, at present. Furthermore, although the CNTs are observed like cylinders by transmission electron microscopy (TEM), some reports have pointed out the possibility of non-cylindrical structures and the existence of defects [11-14]. 

Fiber-reinforced polymer structures are typically laid up by hand, consolidated (compressed together) with the polymer resin matrix material, and cured with heat and pressure. This method is capable of producing uniquely shaped, strong, and lightweight structural pieces. Fiber-reinforced polymers can also be used in mass-production methods thermoplastic materials can be employed to produce many relatively simple shapes that do not call for high strength. Variations on these methods, such as extrusion and pultrnsion, represent combinations of these methodologies. 

FE A continuous and aligned hybrid composite O consists of aramid and glass fibers embedded within a polymer resin matrix. Compute the longitudinal modulus of elasticity of this material if the respective volume fractions are 0.24 and 0.28, given the following data ... 

Piezocomposite transducers are an advancement of piezoelectric ceramics. Instead of the classic piezoceramic material, a compound of polymer and piezoceramic is used for the composite element to improve specific properties. The 1-3 structure, which is nowadays mostly used as transducer material, refers to parallel ceramic rods incorporated in an epoxy-resin matrix (see Fig. 1). 

Fig. 5. Chemistry of cyclized mbbei—bis-a2ide negative acting resist, (a) Preparation of cyclized mbber resin from polyisoprene (b) photochemistry of aromatic bis-a2ide sensiti2ers. The primary photoproduct is a highly reactive nitrene which may combine with molecular oxygen to form oxygenated products, or may react with the resin matrix by addition or insertion to form polymer—polymer linkages.

The thermoplastic or thermoset nature of the resin in the colorant—resin matrix is also important. For thermoplastics, the polymerisation reaction is completed, the materials are processed at or close to their melting points, and scrap may be reground and remolded, eg, polyethylene, propjiene, poly(vinyl chloride), acetal resins (qv), acryhcs, ABS, nylons, ceUulosics, and polystyrene (see Olefin polymers Vinyl polymers Acrylic ester polymers Polyamides Cellulose ESTERS Styrene polymers). In the case of thermoset resins, the chemical reaction is only partially complete when the colorants are added and is concluded when the resin is molded. The result is a nonmeltable cross-linked resin that caimot be reworked, eg, epoxy resins (qv), urea—formaldehyde, melamine—formaldehyde, phenoHcs, and thermoset polyesters (qv) (see Amino resins and plastics Phenolic resins). 

Mechanical and Chemical Properties. Colorants, especially pigments, can affect the tensile, compressive, elongation, stress, and impact properties of a polymer (5). The colorants can act as an interstitial medium and cause microcracks to form in the polymer colorant matrix. This then leads to degradation of the physical properties of the system. Certain chemicals can attack colorants and there can be a loss of physical properties as well as a loss of the chromatic attributes of the colorant. Colorants should always be evaluated in the resin in which they will be used to check for loss of properties that ate needed for the particular appHcations. 

Other applications are based on the use of solutions of reversed micelles as templates. For example, solutions of reversed micelles have been employed as a matrix to control the porosity of cross-linked polymer resins. The pore size of the polymers was controlled by varying the amounts of water in the AOT-reversed micelles [67]. 

Cement and Concrete Concrete is an aggregate of inert reinforcing particles in an amorphous matrix of hardened cement paste. Concrete made of portland cement has limited resistance to acids and bases and will fail mechanically following absorption of crystal-forming solutions such as brines and various organics. Concretes made of corrosion-resistant cements (such as calcium aluminate) or polymer resins can be selected for specific chemical exposures. 

Thus the quantum yield for acid production from triphenylsulfonium salts is 0.8 in solution and about 0.3 in the polymer 2 matrix. The difference between acid generating efficiencies in solution and film may be due in part to the large component of resin absorption. Resin excited state energy may not be efficiently transferred to the sulfonium salt. Furthermore a reduction in quantum yield is generally expected for a radical process carried out in a polymer matrix due to cage effects which prevent the escape of initially formed radicals and result in recombination (IS). However there are cases where little or no difference in quantum efficiency is noted for radical reactions in various media. Photodissociation of diacylperoxides is nearly as efficient in polystyrene below the glass transition point as in fluid solution (12). This case is similar to that of the present study since the dissociation involves a small molecule dispersed in a glassy polymer. 

Dripping is a complex behavior that depends on the resin matrix, viscosity and part design. However, over the years, it has been found that very low levels of some fluorinated polymers, notably polytetrafluoroethylene (PTFE), can significantly reduce dripping. 

The subject of silane chemistry and its interaction with both glass surface and polymer resins have been studied extensively. Since the silane coupling agent for improving the bond quality has first appeared in the literature (Rochow, 1951), a wide variety of organofunctional silanes has been developed, prominently by Plueddemann and coworkers. An early compilation of this subject for epoxy and polyester matrix composites (Plueddemann et al., 1962, Clark and Plueddemann, 1963 Plueddemann, 1974), and more recent reviews on the use of silane agents and... 

Most structural PMCs consist of a relatively soft matrix, such as a thermosetting plastic of polyester, phenolic, or epoxy, sometimes referred to as resin-matrix composites. Some typical polymers used as matrices in PMCs are listed in Table 1.28. The list of metals used in MMCs is much shorter. Aluminum, magnesium, titanium, and iron- and nickel-based alloys are the most common (see Table 1.29). These metals are typically utilized due to their combination of low density and good mechanical properties. Matrix materials for CMCs generally fall into fonr categories glass ceramics like lithium aluminosilicate oxide ceramics like aluminnm oxide (alnmina) and mullite nitride ceramics such as silicon nitride and carbide ceramics such as silicon carbide. 

The high strength of polymer composites is dependent on a transfer of external stress from the resin matrix to the fiber or filler. The efficiency of this transfer is dependent on the strength of the interfacial bond between the... 

In recent work by Arkles el al. [4, 5], it has been proposed that, in comparison with monomeric silanes, polymeric silanes may react with substrates more efficiently. A typical polymeric silane is shown in Fig. la, in which pendant chains of siloxanes are attached through methylene chain spacers to a polyethyleneimine backbone. The film-forming polymeric silane thus provides a more continuous reactive surface to the polymer matrix in the composite. In this case, the recurring amino groups on the polymeric silane backbone can react with an epoxy resin matrix through chemical bond formation. 

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