Polyamides Thermal expansion coefficient

When the epoxy adhesive cannot be made flexible enough, the thermal conductivity and thermal expansion coefficient are controlled by appropriate fillers. General-purpose room temperature cured epoxy-polyamide adhesive systems can be made serviceable at low temperatures by the addition of appropriate fillers to control thermal expansion. 

Most micromechanical theories treat composites where the thermoelastic properties of the matrix and of each filler particle are assumed to be homogeneous and isotropic within each phase domain. Under this simplifying assumption, the elastic properties of the matrix phase and of the filler particles are each described by two independent quantities, usually the Young s modulus E and Poisson s ratio v. The thermal expansion behavior of each constituent of the composite is described by its linear thermal expansion coefficient (3. It is far more complicated to treat composites where the properties of some of the individual components (such as high-modulus aromatic polyamide fibers) are themselves inhomogeneous and/or anisotropic within the individual phase domains, at a level of theory that accounts for the internal inhomogeneities and/or anisotropies of these phase domains. Consequently, there are very few analytical models that can treat such very complicated but not uncommon systems truly adequately. 

Montmorillonite platelets are particularly effective for reducing thermal expansion coefficients of plastics, as shown in Figure 4.2 for used exfoliated polyamide 6 nanocomposites. 

FIGURE 4.2 Coefficient of thermal expansion coefficient of montmorillonite-filled polyamide nanocomposites. 

In Figure 9.33 the dependence a p(D ) for the considered epoxy polymers is adduced, which has an expected character. The growth in the thermal expansion linear coefficient with an increase in molecular mobility level is observed. In Figure 9.33 a solid straight line shows the similar dependence oc(D p) for amorphous aromatic polyamide (phenylone S-2). As one can see, this straight line corresponds well to the data for the considered epoxy polymers. This means that irrespective of the class of polymers, their thermal expansion coefficient is defined by the molecular mobility level, which in paper [62] is characterised by the dimension... 

Shrinkage, coefficient of thermal expansion and creep are rather low, the more so as semiaromatic polyamides are very often reinforced. The absorption and swelling by exposure to moisture are slow and low (see Figure 4.66). 

FIGURE 3.8 Journal bearing application. Outer cylinder (stainless steel) is bonded to inner cylinder (polyamide-imide) with an epoxy adhesive. Exposure to low temperatures causes significant stress on bond due to differences in coefficient of thermal expansion. 

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.)... 

Metal aircraft parts are easily converted to parts composed of polyamide-imide, because of the metal-like coefficient of thermal expansion of the filled compounds. The high modulus and low creep of polyamide-imides provide outstanding thread-holding ability for nonmetallic and thermally-isolating aerospace fastener mounts [20]. 

Torlon 4435 polyamide-imide resin is specifically designed to provide exceptionally low-wear performance in nonlubricated applications even at high pressure and velocity (PV) conditions greater than 50,000 ft lb/(min in). The low coefficient of thermal expansion provides the ability to meet close tolerances over a wide temperature range. Due to its electrically dissipative property, this grade may also be considered for antistatic functions. 

Table 3.3-18 Polyamide 6, PA6 polyamide 66, PA66 polyamide 610, PA610 heat capacity, thermal conductivity, and coefficient of thermal expansion...

Nylon family These are polyamides resulting fi-om the condensation reaction of an amine funetion and an acid function. As a family, they are tough and hard. They are resistant to many liquids and have low coefficients of thermal expansion. They ean be reinforced with glass fibers, carbon, and minerals. Applications include molded parts for electrieal power transmission, molded parts for a wide range of automotive functions, pulleys, bearings and items which need good abrasion resistance and toughness. 

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