Foams cell structural phenolic foam

Table 7.20 Properties of Cell structural phenolic foam ...

Hence, one of the most probable reasons for the formation of open cells, including microcells, due to water vapor is given in The mechanism described there, however, does not explain the formation of closed microcells which we observed in the structure of rigid phenolic foams The formation of these microcells is apparently connected with specific features of foaming and hardening kinetics in oligomeric compositions. 

According to Thomas elastic polymers often produce open-cell foamed plastics, whereas rigid polymers generally form closed-cell materials. However, there are many exceptions to this rule, owing to the variety of blowing techniques. Closed-cell structures are more likely to be produced from polyurethanes, epoxy resins, silicones, poly(vinyl chloride), polystyrene, etc., whereas open-cell materials mainly result from phenolic and carbamide foamed plastics. 

Rigid foams tend to be closed cell in nature, and this characteristic is necessary for some of the typical application areas such as thermal insulation and floatation aids. Some rigid foams do exist however with an open cell structure such as the phenol-fonnaldehyde-based horticultural and floral foams. 

Surfactants are added to a thermoset resin system to promote the dispersion of fillers in the resin matrix. Recently, surfactants have been used to disperse carbon nanotubes in polymer matrices [48-50]. Surfactants are of two types neutral and ionic. Surfactants have many applications in coating industries for the development of a water-based resin system [51]. Surfactants are added to phenolic or polyurethane foam formulation in which they facilitate formation of small bubbles. The size and uniformity of bubble formation results in a fine cell structure. A surfactant reduces the surface tension of resin formulations and provides an interface between the highly polar resin and the non-polar blowing agent. The surfactant for a particular resin system must be selected carefully so that it is compatible with the resin and resistant... 

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