Foam effectiveness

The foam effect is achieved by the dispersion of inert gas throughout the molten resin directly before moulding. Introduction of the gas is usually carried out by pre-blending the resin with a chemical blowing agent which releases gas when heated, or by direct injection of the gas (usually nitrogen). When the compressed gas/resin mixture is rapidly injected into the mould cavity, the gas expands explosively and forces the material into all parts of the mould. An internal cellular structure is thus formed within a solid skin. 

The foam properties of ether carboxylates are dependent on the fatty chain and ethoxylation degree. High foaming effect can be achieved with a longer fatty chain, with an optimal effect using C12-C14 chain, and a relatively short EO degree, with an optimum at about 4.5 EO [10,51,57] (Table 8). 

Nontoxic effect on the skin flora was found by Schafer, which means that these amidether carboxylates can be well used in products which remain on the skin for a longer period [80]. A laurylamidether carboxylate based on digly-colamine has been described for the use in syndet soap with high mildness and good foaming effect [36]. 

The foam-water sprinkler system is basically the same as a sprinkler system except foam concentrate is proportioned into the water causing foam to be discharged. These systems can flow either water or foam effectively. 

Diisocyanites have two reacting groups and they can form chains or even networks. The two most commonly used diisocyanites are toluenediisocyanites (TDI) and diphenylmethane diisocyanates (MDI) (Fig. 12.17). With each bond formed one molecule of gaseous carbon dioxide is released. This is responsible for the foaming effect. 

Chemical Defoamers The addition of chemical foam breakers is the most elegant way to break a foam. Effective defoamers cause very rapid disintegration of the foam and frequently need be present only in parts per million. The great diversity of compounds used for defoamers and the many different systems in which they are applied make a brief and orderly discussion of their selection difficult. Compounds needed to break aqueous foams may be different from those needed for aqueous-free systems. The majority of defoamers are insoluble or nonmiscible in the foam continuous phase, but some work best because of their ready solubility. Lichtman (Defoamers, 3d ed., Wiley, New York, 1979) has presented a concise summary of the application and use of defoamers. Rubel (Antifoaming and Defoaming... 

Bubbles are retained in the foam, effectively contributing to its expansion. 

Journal of Vinyl and Additive Technology 4, No.l, March 1998, p.26-9 VINYL FOAM EFFECT OF DENSITY ON PHYSICAL PROPERTIES... 

Work previously reported has shown very significant reductions in gas mobility when in situ generated foam was used in laboratory core tests. Using unconsolidated core models, investigators measured ten to several hundredfold decreases in gas mobilityThe effectiveness of foam for mobility control is vitally dependent on the choice of the surfactant used. Early tests using 1% ammonium lauryl sulfate were not totally successful in demonstrating foam effectiveness. ... 

V3 wave propagation velocities wave propagation velocity in gas phase wave propagation velocity in polymer phase packed volume cell volume volume of dry foam effective cell volume volume of gas phase... 

Klett, J., Hardy, R., Romine, E., et al. (2000). High-thermal-conductivity, mesophase-pitch-derived carbon foams effect of precursor on structure and properties. Carbon, 38, 953—73. 

Calcium ions used in the initial process were found not to be essential for stereoselectivity or the reaction rate but they had a welcome anti-foaming effect. Nevertheless, the original 20 mM calcium hydroxide solution (upper solubility limit for calcium hydroxide) was replaced by more concentrated sodium hydroxide solutions. 

Table 7-2 lists the foaming effectiveness of some surfactants in aqueous solutions, as well as some data on their (short-term) stability. 

TABLE 7-2 Foaming Effectiveness of Aqueous Surfactant Solutions (Ross-... 

Another little-studied aspect concerns the effect of the amount of oil present in the porous media. Friedmann and Jensen (41) interpreted their foam-flood results in terms of an apparent maximum residual oil saturation above which their foams were not stable. Isaacs et al. (42) tested a number of steam-foam floods in sand packs saturated with heavy crude oil and also found that foam effectiveness depended on residual oil saturation. Their foams were effective at saturations below about 10% and were not effective at oil saturations above about 15%. This finding has been incorporated into reservoir foam-flood simulations (14) using the concept of... 

The same conclusions have been reached on the basis of core-flood experiments. Suffridge et al. (35) studied foam effectiveness in Berea sandstone cores, both untreated (water-wetted) and treated with the Quilon C chrome complex described previously. The treated cores became intermediate to oil-wetted at waterflood residual oil saturation. They found that the foams were more effective (stable) in the water-wet cores than in the oil-wet cores. Holt and Kristiansen (27, 56) studied foams flowing in cores under North Sea reservoir conditions that were either partially or completely oil-wetted. They found that foam effectiveness was favored by water-wet conditions any degree of oil-wet character reduced the effectiveness of the flowing foam. 

A single model of foam-oil interaction cannot account for all situations. Certain foam—oil sensitivity models can be reconciled with both microvisual studies and core-flood foam effectiveness measurements, all for a wide variety of foams, oils, porous media, and other experimental conditions. However, exceptions are readily found. In an earlier section, the models of emulsification—imbibition, pseudoemulsion film thinning, entering, and spreading were introduced. Cases in favor of, and exceptions to, the applicability of each of these can be found in the literature. Although this situation prompts some inclination to search for additional mechanisms, the truth may be that all the models presented have some validity and that one or another valid mechanism is most significant in a given situation. 

Foam Effectiveness in Porous Media. No generally accepted correlations exist between foam characteristics measured outside the porous medium and foam effectiveness as a gas mobility-reducing agent in porous media. The performance of the nine surfactants that passed the solubility criteria was therefore evaluated in porous media under typical reservoir conditions. The results of such an evaluation can be expressed in several ways. One of the simplest measures of foam effectiveness, and arguably the most straightforward one, is the mobility-reduction factor (MRF). The MRF is defined as the ratio of pressure gradients across a... 

Blends should be avoided, unless they are properly examined and found not to cause foaming (blends of long-chain fatty with short-chain FA oils are known for their foaming effect). 

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