Polyurethane Resole

Finally, various Mannich bases used as catalysts in the crosslinking of oligomers (see also Chap. V, A.2.), are worth mentioning. Their basic properties are applied in the curing of epoxy oligomers- as well as in the production of polyurethanes and, less frequently, in the crosslinking of resols. - Compounds of types 426 and 427 are employed mostly for the above purposes. 

Foaming Mechanism. The process for producing resol-type phenolic foams is simUar to that of polyurethane foam. The foaming process in phenolic foam may be divided into five steps. This process does not progress by step-by-step, but the several phenomena progress spontaneously. 

Foaming Process of Resol-Type Foam. The foaming processes for phenolic foam of both the resol type and benzylic-ether type are the same as those for rigid polyurethane foams. The block-foaming process (slab foaming), pouring process, continuous-laminate process, and spray process are used. See Figure 57. 

Examples of foaming characteristics of resol-type phenolic foams (free-rise) are shown in Table 64 in comparison with rigid urethane foam (3). Rise-profile curves, foaming-pressure curves and temperature curves for phenolic and polyurethane foams are shown in Figure 61. 

The cost of raw materials for use in phenolic foams is low, but since this foam has the weak points listed above, it cannot exceed polyurethane foam in cost performance. Resol-type foams and benzylic ether-type foams use chlorofluorocarbon (CFC) as a foamimg agent. It is necessary to develop a new foaming agent which does not destroy the ozone layer in the atmosphere. When these problems are solved phenolic foam applications will make further rapid progress. 

Water-based dispersions or emulsions such as polyvinyl acetate, acrylics, polyvinyl chloride and polyvinyl alcohol with plasticizers and tackifiers. In addition, this range can include urea formaldehyde and phenolic adhesives, resins, natural adhesives produced from starch, dextrin, casein, animal glues (see Polyvinyl alcohol in adhesives, Phenolic adhesives single-stage resoles. Phenolic adhesives two-stage novolacs. Animal glues and technical gelatins) and rubber latex (see Emulsion and dispersion adhesives). Solvent-free 100% solids such as polyurethane. Hot melt adhesives include Ethylene-vinyl acetate copolymers, polyolefins, polyamides, polyesters with tackifiers and waxes. More recent additions include cross-linkable systems. 

The best approach has been to react (Step polymerization) the resoles, during cure, with suitable high-molecular weight polymers such as polyvinyl acetals, epoxies, acrylonitrile butadiene rubbers (NBR) or, better, their carboxylated variants, polyurethanes and polyamides. The methylol groups on the phenolic react with the active hydrogen groups (hydroxyls or secondary amines) on the polymer. 

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