Heat-resistant adhesives thermal properties

Epoxy Coreactants. One of the most successful epoxy coreactant systems developed thus far is an epoxy-phenolic alloy. The excellent thermal stability of the phenolic resins is coupled with the valuable adhesion properties of epoxies to provide an adhesive capable of 371°C short-term operation and continuous use at 175°C. The heat resistance and thermal-aging properties of an epoxy phenolic adhesive are compared with those of other high-temperature adhesives in Fig. 15.5. Epoxy-phenolic adhesives are generally preferred over other high-temperature adhesives, such as the polyimides and polybenzimidazoles, because of their lower cost and ease of processing. 

Epoxy or polyepoxide is a thermosetting polymer formed from reaction of an epoxide resin with polyamine hardener. Epoxy is used in coatings, adhesives and composite materials. They have excellent adhesion, chemical and heat resistance, good mechanical properties and electrical insulating properties. Epoxies with high thermal insulation, thermal conductivity combined with high electrical resistance are used for electronics applications. There are a few studies conducted on OPE-epoxy composites. 

Chemical vapor deposition (CVD) is an atomistic surface modification process where a thin solid coating is deposited on an underlying heated substrate via a chemical reaction from the vapor or gas phase. The occurrence of this chemical reaction is an essential characteristic of the CVD method. The chemical reaction is generally activated thermally by resistance heat, RF, plasma and laser. Furthermore, the effects of the process variables such as temperature, pressure, flow rates, and input concentrations on these reactions must be understood. With proper selection of process parameters, the coating structure/properties such as hardness, toughness, elastic modulus, adhesion, thermal shock resistance and corrosion, wear and oxidation resistance can be controlled or tailored for a variety of applications. The optimum experimental parameters and the level to which... 

Fillers are often useful in epoxy-polyamide adhesives (41). Fillers aid flow control—particularly at elevated temperatures. Other properties contributed by fillers are exhibited in the cured system. For example, they can increase the modulus of elasticity, modify the coefficient of thermal expansion, increase heat resistance, and even affect bond strength. Of course, the excellent wetting properties of polyamides Increase the dispersion efficiency of these fillers. The type of filler selected and the amount used also have a pronounced effect on adhesive quality. A few of these effects are illustrated in Tables VI and VII (37). (See also Table VIII.)... 

Chem. Descrip. Phenol-based epoxy novolac acrylate blended with tri-methylolpropane triacrylate (50%) with MEFIQ inhibitor (500 ppm) Uses Epoxy-acrylic for free radical-cured formulations and composites, metal/paper/wood coatings, electronics, inks Features High reactivity high thermal resist. good chem. resist., adhesion, hardness, heat resist., abrasion resist., impact str., water resist. Properties Gardner 11 max. clear liq. vise. 15,000-20,000 mPa s acid no. 3 max. 

PPQ films discolor on heating, but retain their transparency and the major parts of their mechanical properties. To date, PPQs have been tested for application as high-temperature-resistant adhesives and as matrices for bonding materials. In such high-temperature applications, a postcuring must be applied whereby cross-linking occurs as a result of thermal or thermo-oxidative decomposition. 

Fillers are relatively neutral substances added to the adhesive to improve its working properties, strength, permanence, or other qualities. Fillers are also intended to reduce materials costs. Considerable changes can be made in the properties of an adhesive by selective use of fillers. Fillers are used to modify adhesives to govern such properties as thermal expansion, electrical and thermal conductivity, shrinkage, and heat resistance. 

The selection of a particular adhesive type is for reasons other than modulus and associated stress distrihution. This might be for example, specific adhesion, chemical resistance, setting speed, gap fill capability, durability, heat resistance, fire performance, electrical properties, thermal conductivity, colour, toxicity or price. Low modulus adhesives are used very successfully in low stress applications to accommodate differential thermal expansion in applications like bonding glass to aluminium in double glazing assembly. 

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