Water-blown foam process

Whether the one-shot process or prepolymer technique is used, the development of a foam involves the juxtaposition of gas generation and the development of tensile strength within the developing foam. The evolution of gas can be via the use of blowing agents or the in situ generation of CO2 from the reaction of water with an isocyanate to produce a water-blown foam. In any case, the gas evolution creates an internal pressure that must be resisted by the development of a gel structure via polymerization reactions as shown in Figure 3.13. 

One of the early consequences of not using CFCs has been some scorching and discoloration in fire-retarded water-blown foams, because of the exothermic isocyanate hydrolysis reaction (CFC blowing agents tended to act as heat removers). It has been suggested that the scorch process is accentuated by certain flame retardants. 

Types of extruders manufactured by Berstorff for the processing of thermoplastic elastomers are reviewed. These include extmsion compounding lines and machineiy for the extmsion and coextrusion of water blown foam profiles. 

In the Toray process, the foamable sheet is expanded as it floats on the surface of molten salts and is heated from the top by infrared lamps. The mol-fen salt mixture consists of potassium nitrate, sodium nitrate, and sodium nitrite. The salt residues from the surface of the foam are blown off by hot air and stripped in water. The Toray process is suitable to produce cross-linked PP foam sheet as well as polyethylene foam sheet. In fact, Toray was the first one to produce commercial PP foam. ... 

In this paper, instrumental means are used to obtain a physical description of the rise of urethane foam and cell opening. Infrared analysis is used to identify the chemical species present in reacting foam and to determine the order and relative rates of reaction of these species. From these data, a reaction sequence model is deduced for the process of making stable, water-blown urethane foam. 

The same PU foam was also treated with a mixture of glycerine and water (up to 40%) to investigate the effective decomposition through the combined mechanisms of hydrolysis and glycolysis. The presence of water slowed down the process to 10 min at 160 °C, while working at higher temperatures resulted in undesired trans-esterification and pyrolysis products. However, this hydroglycolysis approach did dramatically reduce the amount of solvent required. In addition, due to the presence of water, the resultant polyols formed could be easily used in new formulations of water-blown PU foams. 

Handmix rate of rise comparison tests were performed using the same equipment and process as described for TDI and MDI hand mix foam. The formulations used are listed in Table 1.42 and the rate of rise data reported in Table 1.43. Dabco BLV with Dabco T-9 was used as the industry standard catalyst control for the water blown flexible slabstock foam formulations. The silicone surfactant used in the reported flexible slabstock formulations was DC5160. All water blown formulations were made at densities of 23 kg/m. ... 

The following description is clearly an oversimplification, and more detailed descriptions can be foimd in the literature (20, 23, 36, 39). The rections and reaction sequence taking place during the process of making water-blown polyurethane foam can be described as follows. 

Skim the floating debris from two liters of water, and add it to the flotation tube. The tubing is disconnected from the water saturator bottle and the air is turned on. Any water in the line between the water saturator and the dispersion tube is blown out and the line then reattached to the saturator. A sample of this water is taken to serve as the original. The quaternary amine solution is added to the addition tube, and 20 mL are added to the water. The system is allowed to run for a few minutes to see if foaming occurs. If not then further additions are made until foaming occurs. The foam is collected, and after about 15 minutes, or until the foaming has subsided, another sample is taken from the tube. More quaternary amine is added, and the process repeated two more times. The absorbance of the water is measured by a spectrophotometer set at 400 nm. The goal is to get water below 0.015 absorbance units. 

One of the most important foam materials is flexible polyurethane, which is customarily blown by using the carbon dioxide formed as a result of the chemical reaction between di-isocyanates and water. The process is accompanied by the evolution of carbon dioxide, as a product of the reaction between water or acids and isocyanate groups ... 

The crystal structure and three-dimensional network prevent cellulose from behaving as a polyol for PU syntheses. To overcome this problem a liquefaction process in the presence of organic solvents was developed and resulted in products suitable for PU synthesis. Yan and co-workers (2008) liquefied corn stalk, an agricultural by-product, and tested it for the synthesis of PU foams blown by water. The report revealed that such polyurethane foams had excellent mechanical and thermal properties and could be used as heat insulating materials. 

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