Thermoplastic matrix materials

Advantages The major advantages of the thermoplastic-based disposal systems are by dispiosin of the waste in a dry condition, the overall volume of the waste is greatly reduced most thermoplastic matrix materials are resistant to attack by aqueous solutions microbial degradation is minimal most matrices adhere well to incorporated materials, therefore, the final product has good strength and materials embedded in a thermoplastic matrix can be reclaimed if needed. 

Describe and discuss thermoset-matrix and thermoplastic-matrix materials. Contrast their production times if you were to build a composite structure with both materials. 

The prepreg winding technique offers better control of fiber volume fraction, but at a cost. Material costs are 1.5 to 2 times higher, and there are additional costs associated with storing the preimpregnated (thermosetting matrix) tows. Preimpregnated tows are used almost exclusively for thermoplastic matrix materials, where there are no shelf-life restrictions. 

Process models allow composite case manufacturers to determine the affects of process variable settings on final cylinder quality. Because the cost of a composite cylinder can be as great as 500,000, the ability to simulate filament winding can significantly reduce cost and improve quality. Several computer models of the filament-winding process for both thermoset and thermoplastic matrix materials have been developed. These models are based on engineering principles such as conservation of mass and energy. As such, numerous resin systems and fiber materials can be modeled. 

Figure 13.8 Flow chart showing interrelationship of submodels for filament winding with thermoplastic matrix materials...

Consolidation and development of interlaminar bond strength for thermoplastic matrix composites have been modeled by two mechanisms intimate contact and autohesion. Intimate contact describes the process by which two irregular ply surfaces become smooth (Fig. 13.10). In areas in which the ply surfaces are in contact, autohesion occurs, and the long thermoplastic polymer chains diffuse across the ply boundaries. Filament winding with thermoplastic matrix materials is considered an on-line consolidation process in that local... 

Most high performance applications in aircraft use epoxy-based resin systems. Silicones, phenolics and polyimides are limited to special high temperature or electrical applications. Although thermosetting resins such as epoxy are commonly used in filament winding, there has been recent research into using thermoplastic matrix materials [9]. 

The mechanical properties of molecular composites have also been artalyzed theoretically. A theory by Halpin and Tsai relates the composite modulus to the individual moduli of the compmrents (Halpin and Tsai 1973 Halpin and Kardos 1976). hr the limiting case where the reinforcing fiber aspect ratio approaches infinity, the composite modulus and tensile strength are predicted to follow a finear rule of mixtures. That is, the composite properties are a finear functimt of the fiber and the matrix properties and volume fraction. This ultimate rule of mixture reinforcement behavior was achieved for composites of PBT in arcHnatic, heterocycUc matrix polymers (Krause et al. 1986,1988 Hwang et al. 1983) and work was also dmte to achieve that same effect with thermoplastic matrix materials (WickcUffe 1986 Tsai and Arnold 1982). 

In principle, all the fiber ty pes described above can be used advantageously for reinforcing thermoplastic matrix materials to improve their mechanical and thermomechanical properties. This has been demonstrated for PP as matrix material [7]. In what follows, however, the focus is put on rayon tire cord yam, as it has favorable properties (cf. Table 18.1) and is commercially available as a technical (endless) filament yam with suitable yam titre. 

Pultrusion. Another method by which thermoplastic fiber-reinforced polymers are produced is pultrusion. In pultrusion, an appropriately designed bundle of continuous fiber strands is drawn through a die along with a molten thermoplastic matrix material. The die serves to consolidate the material combination, and as the matrix material solidifies on exiting the die, a continuous fiber-reinforced structure is produced. Examples of pultruded products include fiberglass rods and reinforced water hoses. 

The selection of a suitable thermoplastic matrix material mostly depends on the desired mechanical properties and the desired long-term service temperature. Depending on the application area, there are other decision criteria known from thermoset matrix materials, which can be of major interest, for example the chemical resistance or the water absorption properties. In contrast, thermoplastic composites are normally featured with an improved toughness compared to their thermoset competitors. Table 8.2 gives an overview on properties of different common polymers which are used for the pultrusion process. 

Viscosity of reactive and non-reactive thermoplastic matrix materials. (From reference 17.)... 

Like the pultrusion process, the selection of a suitable thermoplastic matrix material mainly depends on the desired mechanical properties and the desired long-term service temperature. The range of usable matrix materials starts with standard polymers such as polyethylene (PE) or polypropylene (PP) and ends with high performance polymers such as polyetherimide (PEI) or poyletheretherketone (PEEK). Recent developments have shown that the processing of reactive thermoplastic materials is possible as well (CBT). For some physical properties of common matrix materials see Table 8.2. °... 

Table 19.2. Comparison of processing temperatures for melt- and reactive processing of some common thermoplastic matrix materials [38,43,46,47] ...

As a general rule, self-reinforced composites consist either of layers of highly-oriented thermoplastic textiles [4-7] or of a combination of self-reinforced textiles and a similar thermoplastic matrix material, which is added in the form of a film, powder or melt [1]. These are then hot-compacted to structurally consolidated mono-composites under pressure and temperature in a pressing process. For the most part, the fiber composite concept relies upon the embedding of stretched endless fibers or tapes made of PP into a chemically identical matrix. 

In order to obtain good composite properties (interlaminary adhesion), a balanced relation between the selective melting of the textiles for the generation of a sufficient melt amount and the preservation of high macromolecular orientations must be taken into account. By adding an identical thermoplastic matrix material while the material is in a film, powder or melt state, the melt flow and the associated fiber impregnation can be supported and partly improved [6,53,54]. 

Depending on the application, different matrix materials are used. Among the duromers, most common are polyester and epoxy resins. Thermoplastic matrix materials are polyethylene (pe) and polypropylene (pp), but the use of thermoplastics with aromatic rings on the chain and thus with increased temperature stability also grows. One example is polyetheretherketone (peek), characterised by high toughness and a glass temperature of about 150°C. 

Thermoplastic matrices may also be used with the microdrop method [58,61] A method to form thermoplastic matrix material microdrops in various fiber-thermoplastic systems has been reported by Gaur et al. [58]. They measured the interfacial shear strength of carbon and aramid fibers embedded in four thermoplastic resins polyetheretherketone (PEEK), polyphenylene sulfide (PPS),... 

Usually, carbon fibers have a diameter of 3-15 n- Carbon fibers may have graphene ribbons parallel to ihe fiber axis. Carbon fibers are produced commercially by pyrolysis of organic precursors such as phenolics, poly(acrylonitrile), or pitch. In general, carbon fibers are chopped, having an initial length of about 0.05-5 cm. Sized fibers are conventionally coated on at least a portion of their surfaces with a sizing composition. The sizing composition effects increased compatibility with the polymeric thermoplastic matrix material (7). 

Adams M E, Campbell G A and Cohen A, Thermal-stress induced damage in thermoplastic matrix materials for advanced composites , Polym. Eng. Sci., 1991, 31 (18) 1337-1343. 

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