Thermoplastic Additives

Various kinds of engineering thermoplastics such as polyether sulfone, polyether imide, polyaryl ether ketone, and polyphenylene oxide have been studied as toughening agents for 

TABLE 8.6 Formulas for Two-Part CTBN Modified Epoxy Adhesive System Cured Two Week at 25°C18 

TABLE 8.8 Typical Two-Part CTBN and ATBN Toughened Epoxy Adhesives22 

CTBN modified epoxy ATBN modified epoxy 

The thermoplastic resins are usually blended with the epoxy resin in a solvent solution. Early researchers realized that to make this approach effective, it was necessary to increase the compatibility and interfacial adhesion of the thermoplastic modifier and the epoxy resins. The problem of poor miscibility of the thermoplastic resins and poor processabihty of the final product are the main reasons that these materials have not achieved commercial success. 

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H,W. Voigt, Use of Thermoplastic Additives to Control Cracking and Exudation of Cast Explosives Containing TNT , PATR 3829 (1970)... 

Thermoplastic xylan derivatives have been prepared by in-hne modification with propylene oxide of the xylan present in the alkaline extract of barley husks [424,425]. Following peracetylation of the hydroxypropylated xylan in formamide solution yielded the water-insoluble acetoxypropyl xylan. The thermal properties of the derivative quahfy this material as a potential biodegradable and thermoplastic additive to melt-processed plastics. Xylan from oat spelts was oxidized to 2,3-dicarboxyhc derivatives in a two-step procedure using HI04/NaC102 as oxidants [426]. 

Polybrominated Diphenyl Ethers. PBDEs are used as additive flame retardants in thermoplastics. Additive flame retardants are physically combined with the polymer material being treated rather than chemically combined (as in reactive flame retardants). This means that there is a possibility that the flame retardant may diffuse out of the treated material to some extent. 

The development of low profile polyester resin adds an additional dimension to SMC and BMC. The post-molding finishing steps with FRP have been a strong deterrent in high appearance requirement applications. The low profile resins utilize thermoplastic additives to obtain... 

Ebdon, J. R., Hunt, B. J., Joseph, P., and Konkel, C. S., Flame-retarding thermoplastics Additive versus reactive approach, in Speciality Polymer Additives Principles and Applications, Al-Malaika, S., Golvoy, A., and Wilkie, C. A. (Eds.), 2001, Blackwell Science, Oxford, U.K., pp. 231-257. 

Four thermoplastic addition polymers—polyethylene, poly(vinyl chloride), polypropylene, and polystyrene—comprise the majority of the total amount of polymers manufactured in the United States. In 2002 a total of 33.6 million metric tons of these plastics was produced, distributed as shown in Table 24.1. 

Compared to the carboxylated nitrile elastomer additives, the use of thermoplastics has primarily been focused on the aerospace industry. On a cost per pound basis, the two-phase nitrile additives offer the best combination of property improvement without negative impact. The thermoplastic additives, however, may offer better high-temperature performance, but they are more difficult to formulate and to process as adhesives. As a result, the cost of these adhesives is generally much higher than that of other toughened epoxy mechanisms. 

Within the past several years, improvements in the toughening of high-temperature epoxies and other reactive thermosets, such as cyanate esters and bismaleimides, have been accomplished through the incorporation of engineering thermoplastics. Additions of poly(arylene ether ketone) or PEK and poly(aryl ether sulfone) or PES have been found to improve fracture toughness. Direct addition of these thermoplastics generally improves fracture toughness but results in decreased tensile properties and reduced chemical resistance. 

While thermoplastic additives bring about improvement in toughness, it is usually at the expense of increased dielectric properties which is undesirable for certain critical applications as described earlier. A method to introduce toughness and reduce Dk is based on microporous cyanurates prepared via chemically induced phase separation using a solvent such as cyclohexane. The solvent is removed to generate microvoids by heating the matrix in the vicinity of its Tg. Polycyanurates with significantly less density and Dk were thus prepared [279, 280]. 

Furthermore, with PES5003P, xcp 0.40 and the particles are also smaller than with NFBN. We also see an effect of the viscosity and of the reactive chain ends of the thermoplastic. But because is 180 °C, which is lower than the Tg of the thermoplastic, one important effect is certainly also the vitrification of the dispersed particles when phase separation occurs. The consequence is that only with thermoplastic additives is an evolution of the morphology observed between precuring and postcuring processes. 

Polyvinylacetate (PVAc) and vinyl acetate-acryUc copolymers (VAc-A), thermoplastic polyurethanes, polyethylene, polystyrene and polycap-rolactone are some of the candidates for low-profile shrinkage additives to SMC and BMC. PVAc and VAc copolymers are the most widely used thermoplastic additives. Typically a low-profile SMC recipe contains about 15% unsaturated polyester resin, 8% thermoplastic additive, 50% calcium carbonate and 27% glass fiber. 

Thermoplastic additives in SMC and BMC accounted for nearly 8 kton/y consumption in the USA [Skeist, 1992]. A primary requirement for the polymer additive is that it must be amorphous with a low to moderate T and fairly soluble or dispersible in the resin matrix initially, but capable of phase separation during the polymerization. 

J A Hough and F R Jones, Effect of thermoplastic additives and carbon fibres on the thermally enhanced moisture absorption by epoxy resins , in Eleventh... 

The semifinished goods used for this purpose are resin materials in the form of doughy, weakly crosslinked masses, mixed from the required components (UP resins, thermoplastic additives, styrene, fillers. E-glass, hardeners, initiators, dyestuffs, catalytic agents, separators, stabilizers, thickeners, and dispersants) before they are pressed or injection molded. 

Matrix ductiUty thermoplastic additives have been foimd to toughen... 

Homogenous blends of a thermoplast and an elastomer, or two thermoplasts, are produced to plasticize the matrix. On the other hand, heterogenous blends of elastomer particles in a continuous thermplast phase may produce high-impact-strength thermoplasts. Addition of fibers to thermoplasts increases rigidity. Blends can, however, be produced for a variety of other reasons to make polymers more flameproof with additive materials, to make processing easier, etc. 

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