Phenolic foams resol type

A comparison between theoretical predictions and experimental results is illustrated for the foaming of a phenolic resin of the resol type (Vazquez and Williams, 1986). 

Classification. Phenolic foam is divided broadly into two categories. One is the novolac type and the other is the resol type (see Figure 55). In the novolac type, phenol and formaldehyde react in the presence of an acid catalyst and link the linear condensation product by a methylene bond. The basic curable crosslinking agent, such as hexamethylene tetramine and blowing agent are added to the linear condensation product and the resultant product is molded at elevated temperatures and high pressure. 

In the resol type, phenol and formaldehyde react in the presence of a basic catalyst and provide a liquid type resol to which an acid catalyst and blowing agent are added and the foam is then molded. In forming the resol a method is available for obtaining a benzylic ether-type liquid oligomer by reacting phenol and formaldehyde in nonaqueous phase. 

Resol-Type Foam Chemistry. Resol is obtained as a result of the reaction between phenols (P) and formaldehyde (F) in the presence of basic catalyst. Generally, the reaction is made at a temperature below... 

In manufacturing phenolic foams, a blowing agent such as R-113 (trichlorotrifluoroethane) is evaporated by using an exothermic reaction (Equation 7), and the blowing agent is included in the polymer. The reaction involved in forming the benzylic ether-type foam is shown below. Similarly, this foam will finally form a network polymer as do resol-type foams. 

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. 

Materials for Resol-Type Foams. Resol (Resin). As described above, resol is formed as a result of the reaction of phenol (P) with aldehyde (F) in the presence of a basic catalyst. A representative preparation process is shown in Figure 56. Representative manufacturing conditions and the properties of resol are shown in Table 57 (5). 

Madders. Phenolic polymers are known to have high rigidity, and this property extends to phenolic foams, which are highly friable. In order to reduce friabUity and permit some flexibUity and toughness, various kinds of modifiers are sometimes used. Reactive modifiers are used in the course of resol-resin preparation, and they become integral parts of the polymer structure. Examples include PVA (polyvinyl alcohol), PVA-PVC (polyvinyl alcohol-polyvinyl chloride-copolymer), resorcinol, o-cresol, furfuryl alcohol, and other various types of polyols. 

Other types of resin modifiers compatible with resols may also be used. Examples include UF (urea-aldehyde condensation product) and epoxide. Japanese workers have found that the most effective and economical ingredients as modifiers for phenolic foam are resorcinol, o-cresol, and fulfuryl alcohol. 

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. 

Thermal Coefficients. The thermal coefficients of phenolic foams are almost the same as those of resol- and novolac-type foams. Examples are as follows specific heat, 0.38 to 0.42 cal/g°Q flash point, 520 to 540 Q ignition point, 570° to 580°C softening point, do not soften. 

Examples of thermal gravimetric analysis (TGA) for phenolic foam are shown in Figure 63. The phenolic foam in this figure is the resol-type foam. In the case of novolac-type foams the values are almost the same (3). 

Chemical Resistance. Both resol- and novolac-type phenolic foams have excellent chemical resistance against inorganic and organic chemicals. However, phenolic foams are unable to resist against highly concentrated inorganic acids and alkalies. Chemical resistance data are shown in Table 70. 

Floral Foam. In the U.S. and Western European countries the most popular use of phenol foam for floral applications is a water-soaked foam using a resol-type composition. It is important to maximize the open-cell content in order to inq)rove its water penetration. Floral foam is produced as laige block or slab by a batch process. The foam is easily cut and packaged with a minimum of loss due to waste. Floral foam is commonly used for living flowers, but is not used for dried and artificial flowers. 

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. 

Phenol-formaldehyde (PF) resins were synthesized to manufacture non-flammable insulating foam. When alkali catalyst, for example, barium hydroxide (Ba(OH)2), was present, lesol resins are produced[l]. In the analj s of molecular species of resol, capillary GC-MS had been used to separate hemiformal-type compoimds(acetylated hydroxybenzylhaniformals)... 

Several other types of multicomponent ol otiKric foams have been proposed Foams based on mixtures of resol phenolic oligomers with novolac oligomers with urea oligomers 2—44) polycarboxamides with polyacrylonitrile with polystyrene ... 

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