Phenolic foams foaming mechanism

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. 

Auad, M.L. Zhao, L.H. Shen, H.B. Flammability properties and mechanical performance of epoxy modified phenolic foams. J. Appl. Polym. Sci. 2007,104, 1399-1407. 

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. 

In order to elucidate the mechanism of moisture and water absorption by phenolic foams, Lowe et al." calculated the wall thickness of cells using three simplified models of cell packing 1) spheres with point contacts 2) den packing of cubes without distortion of faces 3) fused cubes with distorted faces. 

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. 

Flame Retardance. The most important reason for phenolic foam being an excellent flame retarder is that the phenolic polymer is easily carbonized and the char part formed as a result is highly stabilized. This mechanism of char-formation is considered that of a multi-aromatic ring with chemically stabilized strong bond formed through a dehydrogenation reaction by heating and oxidation. 

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Rigid foam PS, PU, and phenolic resin, and the semirigid foam of PE were examined with regard to their mechanical properties. The effects of preloading the foams on their mechanical properties are discussed. 

Syntactic foams manufactured from hollow glass or silica microspheres and an epoxide, phenolic or other matrix resin represent a class of lightweight structural materials used for buoyancy purposes, insulation and packaging. The effect of silanes on the mechanical properties of syntactic foams at a nominal density of 0.35 g/cm3 is shown in Tables 14-16. The Proportional Limit is defined as the greatest stress which the foam is capable of sustaining without any deviation from proportionality of stress to strain (Hooke s Law). 

Until recently, the materials made from epoxy binders and glass microspheres were believed to be the strongest syntactic foams. However, several papers 26,39) have shown that, when carbon microspheres replace those of glass, the material becomes stronger, more water resistant, and more capable to withstand hydrostatic pressure (for the same filler concentration) (Table 13). The smaller the carbon microspheres, the stronger are the resulting foams, 9 135). Carbon microspheres also improve the mechanical properties of phenolic and resol syntactic materials (Table 14) 38). 

Unsaturated polyester syntactic foams are cheaper than epoxy foams, although the latter are stronger, more water resistant, and shrink less if cured at room or high temperatures 83,136). One merit of polyester syntactic foams is the low apparent density that can be obtained. But the mechanical characteristics depend upon the apparent density e.g. for the Soviet polyester syntactic foams (SPB), using phenolic microspheres (BV-01)1 ... 

Polybenzimidazole foams with phenolic or glass microspheres also have good thermal properties. Since they are not combustible they retain good mechanical properties up to 350 °C, starting to lose mass at 600 °C 109). 

Dementyev and Tarakanov 8 160) used another approach by adopting a macrostructural model of syntactic foam morphology161 to calculate the strength properties of an epoxy foam with phenolic microspheres. They made two restrictive assumptions, i.e. that the mechanical properties of the microsphere walls and the binder are the same, and that the volume fraction of filler is substantially smaller than that of the matrix. The macrostructural parameters of the syntactic foam are then defined in terms of the dimensions of the microspheres, and their displacements have the same nature as the deformations of the nodes and edges of an imaginary latice. We then get ... 

The Mannich polyols described are aromatic aminic polyols, the aromatic rings have a real contribution in improving the physico-mechanical, thermal and fire proofing properties of the resulting rigid polyurethane (PU) foams. The Mannich bases, for example the Mannich base resulting from one mol of nonyl-phenol, 2 mols of formaldehyde and 2 mols of... 

Mannich polyols are aromatic polyols, which confer excellent physico-mechanical, thermal and fire proofing properties to rigid PU foams. Mannich polyols, especially those based on p-nonyl phenol, have a very good compatibility with pentanes used as blowing agents (for example sucrose polyether polyols have a poor compatibility with pentanes, giving emulsions at normal concentrations for foaming, but not real solutions). 

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