Tough laminates

The vinyl esters have better impact resistance and greater tolerance to cyclic temperatures, pressure fluctuations, and mechanical shock than the chlorendic and bisphenol polyester resins. This results in a tough laminate that is resistant to cracking and crazing. 

Nylon fabrics are used with phenolic resins to produce tough laminates with good electrical properties. They are listed as Grade N-1 in NEMA Standard LI-1. Creep or cold flow limits their application. 

Nicholson, P.S., Nature s ceramic laminates as models for strong, tough laminates. Can. Ceram. Q., 24-30 (Feb. 1995). 

As a tme thermoplastic, FEP copolymer can be melt-processed by extmsion and compression, injection, and blow molding. Films can be heat-bonded and sealed, vacuum-formed, and laminated to various substrates. Chemical inertness and corrosion resistance make FEP highly suitable for chemical services its dielectric and insulating properties favor it for electrical and electronic service and its low frictional properties, mechanical toughness, thermal stabiUty, and nonstick quaUty make it highly suitable for bearings and seals, high temperature components, and nonstick surfaces. 

Poly(phenylene sulfide) (PPS) is another semicrystalline polymer used in the composites industry. PPS-based composites are generally processed at 330°C and subsequently cooled rapidly in order to avoid excessive crystallisation and reduced toughness. The superior fire-retardant characteristics of PPS-based composites result in appHcations where fire resistance is an important design consideration. Laminated composites based on this material have shown poor resistance to transverse impact as a result of the poor adhesion of the fibers to the semicrystalline matrix. A PPS material more recently developed by Phillips Petroleum, AVTEL, has improved fiber—matrix interfacial properties, and promises, therefore, an enhanced resistance to transverse impact (see PoLYAffiRS containing sulfur). 

The synthesis of his[3-(2-a11y1phenoxy)phtha1imides] and their copolymer properties with BMI have been reported (43). These allylphenoxyimide—BMI copolymers provide toughness and temperature resistance when used in carbon fiber laminates (44). 

The markets for polyetherimides arise to an extent from stricter regulations concerning flammability and smoke evolution coupled with such features as high strength, toughness and heat resistance. Application areas include car under-the-bonnet uses, microwave equipment, printed circuit boards and aerospace (including carbon-fibre-reinforced laminated materials). The polymer is also of interest in flim, fibre and wire insulation form. 

These effects have been found by Creton et al. [79] who laminated sheets of incompatible polymers, PMMA and PPO, and studied the adhesion using a double cantilever beam test to evaluate fracture toughness Fc. For the original laminate Fc was only 2 J/m, but when interface reinforced with increasing amounts of a symmetrical P.M.M.A.-P.S. diblock copolymer of high degree of polymerisation (A > A e), the fracture toughness increased to around 170 J/m, and then fell to a steady value of 70 J/m (Fig. 9). 

Williams, J.G., Davies, P. and Brunner, A.J. (1995). Standard tests for the toughness of composite laminates-some bones of contention. In Proceedings of Intern. Conf. on Composite Materials (ICCM-10), Whistler, Canada. Vol. I, pp. 71-75. 

Fig. 6.25. Maximum fracture toughness, ATr, as a function of relative crack length, 2a/W, for carbon fiber-epoxy matrix [0°/ 45°/0°]j and (0°/90°]2 laminates. After Ochiai and Peters (1982).

Bathias, C., Esnault, R. and Bellas, J. (1983). On the increasing fracture toughness at increasing notch length of 0/90 and 0/ 45/0 graphite/epoxy laminates. Composites 14, 365-369. 

Caprino, G. Halpin, J.C. and Nicolais, L. (1980). Fracture toughness of graphite/epoxy laminates. Composites 11, 105-107. 

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