Foaming mechanism

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. 

The second function of the surfactant is to lower the surface tension of the system, thereby forming finer bubbles. The third function is to prevent the cell wall from becoming thin and unstable during the period of growth. This is called the Marangoni effect (3, 4). 

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The mechanical piopeities of stmctuial foams and thek variation with polymer composition and density has been reviewed (103). The variation of stmctural foam mechanical properties with density as a function of polymer properties is extracted from stress—strain curves and, owkig to possible anisotropy of the foam, must be considered apparent data. These relations can provide valuable guidance toward arriving at an optimum stmctural foam, however. 

Although glycol—water solutions are not inherently prone to foaming, mechanical and chemical conditions may cause foam to form in the system. 

C.F. Cullis, Combustion of Flexible Polyurethane Foams. Mechanism and Evaluation of Flame Retardance , Combust Flame 24 (2), 217-30 (1975) CA 83, 82287 (1975)... 

Although glycol-water formulations are not prone to foaming, mechanical and chemical factors may cause foaming in the system. The use of corrosion inhibitors and the presence of contaminants may enhance the tendency to form foams. For these reasons, antifoaming agents, such as silicones, polyglycols, or oils, are sometimes added. 

The applicability of the Gibson and Ashby approach to structure-property relationships, particularly deformation mechanisms, is discussed in relation to a series of thermoplastic foams. The foams examined were based on LDPE, EVA, and a propylene copolymer. A full range of foam mechanical properties is discussed. 8 refs. EUROPEAN COMMUNITY UK WESTERN EUROPE... 

Properties of Poly butene Sulfone Foam. Many properties of polybutene sulfone foam are similar to those of polystyrene foam. Mechanical properties are a little lower for the same foam density, but the bulk density of polybutene sulfone is 1.37 compared with 1.05 for polystyrene. Figure 6 shows that mechanical properties vary in the same ratio as density The insulating properties of polybutene sulfone foam are very good, somewhat better than polystyrene foam (Figure 7). Polybutene sulfone has a good solvent resistance as shown in Table I. In particular, styrene, benzene, and toluene do not attack polybutene sulfone but attack polystyrene. 

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. 

The effect of the gas on mechanical properties depends on the paradox of closed- versus open-cell construction. In a closed-cell foam, mechanical deformation compresses the gas, so the gas contributes to rigidity and strength of the plastic product. In an open-cell foam, on the other hand, the fluidity of air permits it to rush out when the foam is deformed and to rush back when the deformation is released therefore, the foam contributes to the softness, flexibility, and resilience of the plastic product. 

S.T. Lee, N.S. Ramesh, Polymeric Foams, Mechanism and Materials (CRC Press, Taylor and Francis Group, 2004)... 

Nano- and microporous structures obtained by gas foaming of nanostructured polymer blends characterization and evidences of the foaming mechanisms... 

Figure 9.31 Possible schemes of the heterogeneous nucleation foaming mechanism and pore growth in poly(methyl methacrylate) (PMMA)/MAM nanostructured blends.

In summary, it was found that hybrid 5 wt% RBI-201 in Tigerfoam is thermally superior over reference constituent materials, which seems to be due to a synergistic effect. Also, addition of the RBI-201 up to 5 wt% in the Tigerfoam did not result in significant deterioration of foam mechanical properties. Finally, foam samples contain 20-23 wt% volatiles. 

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