Polymer matrix material

Curing primarily refers to the process of solidification of polymer matrix materials. Metal matrix materials are simply heated and cooled around fibers to solidify. Ceramic matrix and carbon matrix materials are either vapor deposited, mixed with fibers in a slurry and hardened, or, in the case of carbon, subjected to repeated liquid infiltration followed by carbonization. Thus, we concentrate here on curing of polymers. 

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. 

Polymer-matrix materials include a wide range of specific materials. Perhaps the most commonly used polymer is epoxy. Other polymers include vinyl ester and polyester. Polymers can be either of the thermoset type, where cross-linking of polymer chains is irreversible, or of the thermoplastic type, where cross-linking does not take place but the matrix only hardens and can be softened and hardened repeatedly. For example, thermoplastics can be heated and reheated, as is essential to any injection-molding process. In contrast, thermosets do not melt upon reheating, so they cannot be injection molded. Polyimides have a higher temperature limit than epoxies (650°F versus 250°F or 350°F) (343°C versus 121°C or 177°C), but are much more brittle and considerably harder to process. 

Figure 15.1 Schematic picture ofa polymer-clay nanocomposite material with completely exfoliated (molecular dispersed) clay sheets within the polymer matrix material.

Although a majority of these composite thermistors are based upon carbon black as the conductive filler, it is difficult to control in terms of particle size, distribution, and morphology. One alternative is to use transition metal oxides such as TiO, VO2, and V2O3 as the filler. An advantage of using a ceramic material is that it is possible to easily control critical parameters such as particle size and shape. Typical polymer matrix materials include poly(methyl methacrylate) PMMA, epoxy, silicone elastomer, polyurethane, polycarbonate, and polystyrene. 

Spent resins are generally compatible with the polymer matrix material. Generally, the polymer and the resin do not interact chemically. The immobilization of spent ion-exchange resins in polymers is a common application all over the world. Epoxy resins, polyesters, polyethylene, polystyrene and copolymers, polyurethane, phenol-formaldehyde, and polystyrene are among the polymers used (IAEA, 1988). Inorganic materials are generally not immobilized using polymers because they are more acceptable to other immobilization matrices such as cement. 

Polymer matrix materials are categorized into thermoplastics and thermosets. Thermoplastics soften and melt above a specific temperature and become solid when cooled. They can be formed by repeated heating and cooling. In contrast, thermosets normally cure by irreversible chemical reaction (between two components, a resin and a hardener, for example, for epoxy (EP)) and chemical bonds are formed during the curing process. This means that a thermoset material cannot be melted and reshaped once it is cured. Thermosets are the most common matrix materials used for FRP composites in construction nowadays. The most common thermosets are unsaturated polyester (UP), EP, and vinylester (VE) [9]. Because of their organic material nature, aU of these matrix materials are sensitive to elevated temperatures and fire. 

Improvements in the properties and performance of fiber-reinforced polymer matrix materials from the addition of nano- and microscale particles have been reported in the literature [8], The availabiHty of different types of nanoparticles offered the possibiHty to tailor fiber/matrix interactions at a nanoscale level. Recently, it has been proven that nanoparticles homogeneously dispersed in a polymer matrix are able to play a beneficial role on the fiber/matrix interfacial adhesion in different types of structural composites [ 11 ], as it will be shown later. Hence, regarding structural properties, nanocomposites appear particularly appropriate as means of enhancing the mechanical properties of conventional composites rather than their use as nanocomposites by themselves, except in some particular cases. 

The term FRP describes a group of materials composed of organic or inorganic fibres embedded in a polymer matrix. Material with high... 

Table 1 Polymer matrix materials described and quantified for use in polymer nanocomposites...

Short name Polymer matrix materials described in [46]... 

Fine scaled composites can be prepared starting with molded and sintered ceramic arrays made by the soft mold process. Once the piezoceramic pillars have been formed, the remaining spaces are filled with a polymer matrix material. Next the base is removed by grinding. Metal electrodes are then bonded to the ends of the fibers and first used to polarize the piezoceramic at an elevated temperamre and then to apply an electric field or collect developed charges from the material. At this point, the active elements are ready to be used as piezoelectric transducer element. Experiments have shown that high-performance composites can be prepared . 

The performance of CNT-based polymer composites include the extent to which the CNTs can be wetted by a given polymer and the resultant adhesion between the nanotube and the surrounding polymer matrix material. Therefore, the interface between the polymer matrix and the reinforcement plays a crucial role in the physical properties of the composites. Several techniques like physical processing and melt compounding methods (ultrasonication, milling, or grinding) are known [130] to be efficient at dispersing CNTs into polymer matrices (Table 9). 

FRP composites are a laminate structure such that each lamina contains an arrangement of unidirectional fibres embedded in a thin layer of polymer matrix material. The fibres provide the strength and stiffness and the matrix binds and protects the fibres and transfers the stresses between them. Fibres used in FRP composites for civil engineering applications are continuous or long fibres, which are approximately 5-20 [xm in diameter. Continuous... 

As a result of their high aspect ratio and electrical conductivity it has been established that carbon nanotubes can form electrically conductive networks in epoxy adhesives and polymer matrix materials and ultimately make them electrically conductive which triggers the opportunity to develop in-situ SUM method. Another important factor is that the addition of carbon nanotubes served to increase the bonding strength and durability of epoxy joints [18]. 

Rohacell ) is one of the widely used core materials for an in situ process. Although its heat resistance is about 200°C, it enables only the production of sandwich structures using polymer matrix materials with a melting temperature in the same range (e.g., PE, PP, PA12). 

The first method is to introduce gas into the composite material while the material is solidifying or curing. In case of the starting polymer matrix material being a thermoset, one should be able to control the degree of cure, while in the case of a thermoplastic there must be careful control of the temperature during the foaming process. 

The actual contribution of this microfailure mechanisms to the interlaminar fracture energy of the composites tested under particular conditions are a function of the number of events taking place, the real area of fracture surface formed, and the size (length and width) of the damage zone (DZS) around the main crack. The larger the latter becomes the more side cracks have to be expected, and the more energy is consumed by plastic deformation of the polymer matrix material. 

The thermophysical properties of multiphase systems are affected by matrix and filler characteristics. In the case of the polymer phase, the microstructure is the most important feature that influences thermal conduction ability. When discussing the filler, one must take into consideration filler physicochanical properties but also several microstructural parameters, such as the diameter, length, shape, distribution, volume fraction, the alignment, and the packing arrangement. Fillers may be in the form of fibers or particles uniformly or randomly placed in the polymer matrix material. Therefore, thermal conduction of particle-filled polymers is isotropic, although... 

The nanoparticles provide ultrahigh specific surfaces and permit strong interactions with the polymer matrix. As a consequence, the amount of modified polymer interphase relative to the total volume will be significantly increased (transition from a polymer matrix material to a polymer interface material). 

Filling modification of polymer is the addition of solid additives with different composition and structure to the polymer matrix material to reduce costs or obviously change the performance of polymer products, which will improve the desired performance at the expense of other kinds of performance at the same time. Such an additive is known as a filler. Because these fillers are mostly inorganic powder, filling modification relates to performance difference and complementation of organic polymer and inorganic matter. This provides diverse areas of research and broad fields of application for filling modification. 

Another well-known case is when only chemical interactions exist between the dispersed phase, the polymer or polymer matrix material and the compatibiliser. One of the criteria of chemical compatibilisation is the existence of free functional groups, which can react with each other during compatibilisation. It is important to note that the presence of free functional groups is not often associated with the development of chemical interactions due to steric hindrance reasons the compatibilising functional groups, matrix and functional groups of the dispersed phase cannot react with each other, i.e., the interactions occur at the boundaries. One typical example of chemical compatibilisation is the so-called in situ functionalisation. In this case, surface modification of the matrix and dispersed phase occur first, and then the modified surfaces are linked via in situ connections [51-53, 75, 76]. 

Multiple layers of piezoelectric composites consisting of polymer matrix material and piezoceramic fibers form the walls of the considered beams. The properties of typical materials are given in Tables A.2 and A.3, respectively. For the calculations which are presented later in this chapter, the data of Epon... 

It is interesting to compare the efficiency of the reinforcement for AS4 fibre in PPS and PEEK. In the former case the values are 92% and 63% for modulus and strength respectively and in the latter 99% and 87% respectively. Modulus uptake is excellent in both cases and strength in the second. The poorer strength result for PPS may be due to reduced compatibility between the fibre surface and matrix. This is supported by the lower ILSS value for PPS carbon fibre composite. Compressive properties are notably lower than tensile ones, while transverse tensile properties are similar to those of thermosetting polymer matrix materials. 

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