Novolac-Type Foam

Novolac (Resin). The raw materials used for novolac-type resins are phenols and aldehydes just as for resol-type resins. These materials 

Blowing Agents. In novolac-type foam decomposing-type materials are used. Typical organic compounds can be used as described in the section on blowing agents. Dinitroso-compoimds, especially di-N-nitrosopentamethylenetetramine, is commonly used. 

Auxiliary Materials. Glass fibers, polypropylene fibers and simUar fibers may sometimes be used as reinforcing materials for phenolic foams. Mechanical properties and heat resistance are improved by reinforcing phenolic foams with these fibers. 

It is easy to use these reinforcing materials for novolic-type foams, but they are difficult to use for resol-type foams because the viscosity of the latter foams is high and it is hard to distribute the reinforcing fibers evenly in the foam. However, if even distribution becomes technically possible, a bright futine is expected for these reinforcing materials in such applications. 

Facing materials for use on the laminate board and sandwich panel, etc. include metal plates (steel, iron, and aluminum), metal foils, non-woven cloth and various kinds of paper (glass-fiber, ceramic-fiber, and flame-retardant), and the complex of these materials. Because the adhesive strength of phenolic foam is weak, special measures must be taken on the side of the facing material. 

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Novolac-Type Foam Chemistry. In this type excess P reacts with F in the presence of acid catalyst and forms a linear-condensation product to which the basic crosslinking agent, such as hexamethylene tetramine, is added to form the foamed product. 

Table 63 Topical Formulation of Novolac Type Foam (15)...

After thorough mixing of the prescribed components, grind well (to 100 mesh) with a ball mUl, add other fUlers if required, and make up into a compound. FUl up the metal mold with this compound or put this compound on the hot press and heat it in steps from 100° to 200° C and foam, then cure it after the foam is formed. Hot presses commonly used in the compression-molding process can be used in the manufacturing facUity for novolac-type foams. 

The general properties of novolac-type foams are shown in Table 68 (13). 

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). 

Ingredients (%) Resol Type Foam Novolac-Type Foam... 

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. 

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. 

Epoxy syntactic foams are the best known representatives of this type of material. The brands manufactured in the USSR are EDS (with glass microspheres), EDM (with phenol microspheres). Dienic, novolac, bisphenolic, and esteric structured epoxy resins are used... 

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 ... 

Novoiac Foam. Novolac foam is molded in die manufacturing facOities in a fixed form. The demand for this type of foam has been stabilized. The foam is used as a thermal insulating material for chemical plants, stcMrage tanks, piping for LNG and LPG, oil storage tanks, etc. It is important to note Uiat the acid catalyst does not remain in novolac foam, and for this reason, diere is no fear of metal conosion. Thus novolac foam is an essential thermal-insulating material for chemical dants. 

The early technique for PF manufacturing was based on the expansion of novolac-hexamethylenetetramine (FiMTA) mixtures. Now, the manufacturing is based on acid catalysed process of a resole type PF with added foaming agent and surfactant [43]. 

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