Polyether based foams

Foams prepared from phenol—formaldehyde and urea—formaldehyde resins are the only commercial foams that are significantly affected by water (22). Polyurethane foams exhibit a deterioration of properties when subjected to a combination of light, moisture, and heat aging polyester-based foam shows much less hydrolytic stabUity than polyether-based foam (50,199). 

Polyether-based foams account for more than 90% of all flexible polyurethane foams. The properties of foams are controlled by the molecular structure of the precursors and the reaction conditions. In general, density decreases as the amount of water increases, which increases the evolution of carbon dioxide. However, the level of water that can be used is limited by the highly exothermic nature of its reaction with isocyanate, which carries with it the risk of self-ignition of the foamed product. If very low density foams are desired, additional blowing agents, such as butane, are incorporated within the mixing head. 

Another major use for semi-rigid polyurethane foams is as shoe soles. In this application, their light weight, abrasion resistance, and shock absorbing properties are important. In safety shoes, chemical and oil resistance are important. Polyether-based foams are used in applications where microbial attack is common, such as shoes intended primarily for use on soil or grass. 

An ingeniously simple screening method was used by Britain and Gemeinhardt [146] to evaluate catalysts for the isocyanate/hydroxyl reaction. To approximate as closely as possible actual polymerization conditions, the 80 20 ratio of 2,4- and 2,6-tolylene diisocyanate (80 20 TDI) isomers and a polyether triol of 3000 molecular weight were mixed at NCO OH ratio of 1.0. A 10% solution of catalyst in dry dioxane was added, the final catalyst concentration being 1% of the weight of polyether. The time for the mixture to gel at 70°C was noted as an indication of catalytic strength. This technique used the same reactants employed in one-shot flexible polyether-based foam systems, almost completely eliminated solvent, and was used to screen quickly hundreds of possible catalysts. 

There are two main types of flexible foam slabstock polyester-based foams, used for technical and high elongation grade laminates or textiles and polyether-based foams used for upholstery, HR, and flame retardance. By varying the type of polyester or polyether, the length of the polyol chain, the structure and size of the hard segment, and the amount of blowing, the foam can be tailored to meet the required specifications. ... 

The basic reaction involved in the formulation of PU is between hydroxy compounds and isocyanates. The first record of this reaction was made by Wurtz and Hoffmann in 1848. Commercially significant advances did not occur until 1937, when 0. Bayer of Germany developed diisocyanate. Bayer and co-workers continued the development of polyester-based urethane polymers as nylon substitutes in the 1940-45 time period. Polyester toluene-diisocyanate (TDI) foams became commercially available in the United States in 1952-53. Two further developments occurred that allowed the use of PU foam to reach the present level. The first of these was the development of polyether polyol and the subsequent "one-shot" foaming process. Rigid polyether-based foams were available in 1957. The second development was the incorporation of halocarbons as blowing agents in 1958. 

Airborne noise applications include acoustically transparent open-cell polyurethane foam (148) for use as a microphone windscreen, and acoustically absorbing polyurethane foam (149) for noise abatement. Polyester-based foam has superior mechanical properties and acoustical absorption, but poor humid aging. Polyether-based foam has better humidity resistance and is inexpensive, but has less absorption. 

The majority of hydroxy groups in the polyesters used for foam making are primary groups and are comparatively reactive towards isocyanates. It is therefore sufficient to include only simple tertiary amine catalysts in the formulation to obtain a satisfactory foam. The reactions which occur during the foaming process are the same as those described for polyether-based foams. 

Table 2. Typical properties of polyether based foams.

Most flexible foams produced are based on polyether polyols ca 8—10% (15—20% in Europe) of the total production is based on polyester polyols. Elexible polyether foams have excellent cushioning properties, are flexible over a wide range of temperatures, and can resist fatigue, aging, chemicals, and mold growth. Polyester-based foams are superior in resistance to dry cleaning and can be flame-bonded to textiles. 

Our laboratory, in conjunction with the Maine Medical Center Research Institute, conducted a series of experiments to study the incorporation of cell binding components. A composite was produced by grafting an MDI-based hydrophilic polyurethane to a 30-pore-per-inch polyether reticulated foam using no surfactants. A flbronectant solution was added to discs of the composite foam. The discs were then inoculated with endothelial cells and cultured. 

Polyurethane is also used as a foam, mostly in sheet form as an underlay or middle layer for example in fruit bins. The following starting materials for polyurethane foam can be used polyester with hydroxyl end groups made from adipic acid, diethylene glycol, trimethylol propane as well as polyether based on ethylene oxide and/or propylene oxide with free hydroxyl groups in combination with 2,4-toluene diisocyanate and 2,6-toluene diisocyanate. Stabilizers, dispersants and amines (as catalysts in amounts up to 1.2 %) can be used. 

M. Ravey and E. M. Pearce, Elexible polyurethane foam. 1. Thermal decomposition of a polyether-based, water-blown commercial type of flexible polyurethane foam, J. Appl. Polym. Sci., 63, 47-74 (1997). 

Polyester- and polyether-based rigid urethane foams generally require a surfactant, whether expanded with COj from the water-isocyanate reaction, or with an inert blowing agent such as fluorocarbon. Without surfactant the foam may collapse or have a coarse cell structure. Castor-oil-based systems generally do not require surfactants, but better results will be obtained if they are used (20). 

The superior characteristics of polyester polyol based polyurethanes are explained by a better crystalline structure [1, 7] in the urethane segment, compared to the majority of poly ether polyols which are amorphous [except polytetrahydrofuran (PTHF)], due to the superior secondary forces between the polyester chains [8] and also due to a superior thermal and fire resistance, compared to polyether polyol based polyurethanes. Polyester-based polyurethanes (flexible foams, coatings), have a superior solvent resistance compared to the polyether-based polyurethanes [8]. 

An interesting aminolysis process based on the reaction of ground polyether-based rigid PU foam wastes with an alkanolamine, in the presence of an alkaly hydroxyde as catalyst was developed [36, 40, 41], The ratio between PU waste and alkanolamine could be around 15 1 to 50 1 (one cubic meter of foam can be chemically destroyed by one litre of alkanolamine) [34, 41]. 

Uses PU intermediate for flexible, water-resist, fabric coatings, microcellular foams which are resist, to HC soivs., polyether-based molded foam formulations to improve adhesion between the foam and vinyl mold skins Features Polyester polyol... 

Not taking cyclic molecules into account, the general structures of industrial silicone surfactants for flexible slabstock foam production can be seen in Figure 2.13. The main building blocks of these materials are a PDMS backbone and attached polyethers based on ethylene oxide and propylene oxide addition products. The siloxane backbones can either be linear or branched and can have their polyether substituents attached in an either pendant or terminal location. These four general structures are outlined in Figure 2.13). 

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