Homogeneous foams

As previously mentioned, the homogeneity of foamed materials and the proportion of open and closed cells can be influenced by additives such as emulsifiers and stabilizers. Emulsifiers (e.g., sodium, potassium, or zinc salts of long-chain fatty acids) cause a uniform distribution of water in the reaction mixture, ensuring homogeneous foaming, while stabilizers (certain silicone oils) prevent a breakdown of the cell structure at the beginning of the reaction and also act as pore regulators. 

Another variant of this technique involves measuring the electrical resistance of a cylindrical column of a homogenous foam closed between two porous plates. The external sides of both plates are in contact with the foaming solution. Equal reduction of pressure Ap is created in the spaces above the upper and below the lower porous plates. If pressure is not strongly reduced and foam column is not very high, the capillary pressure in the whole foam volume is constant. 

We will first discuss homogeneous foams in detail and then consider pneumatic foams. Before we proceed further, it must be mentioned that several assumptions were involved in obtaining most of the results that will be presented in the following sections ... 

As mentioned earlier, homogeneous foams are characterized by a uniform initial liquid fraction [36]. The initial condition for homogeneous foams therefore is ... 

The other distinguishing property of homogeneous foams is that they do not start draining immediately. Some time usually elapses before some continu-... 

Thus, for a homogeneous foam, there are two critical conditions one for the separation of the dispersed phase (xp = xpc) and the other for the sepa-... 

Flexible, semirigid PUR foam products with a cross section of homogeneous foam structure are produced in relatively lightweight molds. These products are usually very bulky. Typically, the PUR volume (and the volume of the mold) of a cushion for an upholstered furniture, with a weight of 15 kg and a density of 45 k m, has a volume of 300 1. Similar or even larger dimensions are common with products made from PUR foam, such as sandwich panels or freezer cabinets. 

Features Leads to medium-fine homogeneous foams and an open cell stmeture hydrolysis-resistant has low volatility and Is especially suitable for achieving low VOC and fogging values... 

Features Leads to very-fine homogeneous foams has no negative influence on the color or the odor of the foam esp. suitable for achieving low VOC and fogging values hydrolysis-resistant... 

Features Leads to f ne homogeneous foams with a high content of closed cells and a regular distribution of the foam density chemically stable in the polyethers commonly used for rigid foam suitable for formulations with a high water content Properties Lt, brn, liq, completely misc, with water dens. 1.05 g/ml vise. 500 mPa S vapor pressure < 1 hPa flash pt, > 94C ref. index 1.449 95% NV Use Level 0,5-2,0%... 

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