Gelling foams

In the Talalay process, the froth is produced by chemical rather than mechanical means. Hydrogen peroxide and an enzyme decomposition catalyst are mixed iato the latex and the mixture placed ia the mold. Decomposition of the peroxide by the added enzyme results ia the Hberation of oxygen which causes the latex mix to foam and fill the mold. The foam is then rapidly chilled and CO2 is iatroduced to gel the latex. The gelled foam is then handled ia a manner similar to that used ia the Dunlop process. 

A method of manufacturing latex foam. Compounded latex is foamed and gelling agent added the mould is filled and the gelled foam vulcanised by steam at 100 °C the product is stripped from the mould, washed and dried. See Talalay Process. 

Concentrated emulsions can exhibit viscoelasticity, as can gelled foams and some suspensions. Compared with the previous equations presented, additional coefficients (including primary and secondary normal stress coefficients) are needed to characterize the rheology of viscoelastic fluids [376,382]. 

Where the vapours to be controlled are flammable, many of these foams are quite similar to the protein, fluoroprotein, and aqueous-film-forming foams used in firefighting [590,594,598] (see also Section 12.9). Where longer-term odour and toxicity control are more important many of these foams are polymer-thickened and gelling foams [592-594]. Other applications of foam blankets are discussed in Sections 10.5 and 13. 

Figure 11.7 Photomicrograph of gelled-foam lamellae (see arrow) stretching across a pore in Berea sandstone rock, showing films, rods, and intermediate structures. From Schramm and Kutay [71] Copyright 2004, The Petroleum Society.

The casein retentate, when used as cheese milk, can almost be fully depleted of all whey proteins through a sufficient number of diafiltration volume turnovers. In contrast to conventional cheese technology, it is then possible to UHT treat the cheese milk in order to destruct spore formers. The whey proteins can be used as a WPG or WPI product or treated further in order to fractionate the whey proteins in their main components. Alternatively the whey proteins can particulated to form WPP see Section 19.5.1. Both approaches are options to build a platform for novel product matrices with specific properties such as gelling, foaming or emulsification. 

Figure 12. A plot that shows the effect of quality and shear rate on a gelled foam system. (Reproduced with permission from reference 11. Copyright 1983 Society of Petroleum Engineers.)...

Examples of surfactants for foaming include sodium dodecyl sulfate, cleaning compositions, lecithins, as well as pertinent derivatives of cellulose and other polysaccharides (33,34). For physical applications such as wound healing dressings, when a surfactant is included in the dried gelled foam, non-ionic surfactants, such as the ethoxylates of sorbitan esters, are preferred (34). 

Polymer thickened foams to which time-delayed cross-linking agents have been added, gelling foams, can be used to improve the efficiency of... 

Figure 9. Photomicrographs of gelled-foam lamellae in a Berea sandstone core, taken using a low energy scanning electron microscope (SEM). Image (a) shows a view down a pore surrounded hy rock grains. Image (b) is a magnification of the upper centre region.

Polyurethane is pulverized to iacrease its bulk density, mixed with 30—80% of a thermoplastic mol ding material, gelled, and then granulated to give coated urethane foam particles 0.1 to 0.15 mm in size (48). The particle bulk density is three times that of the polyurethane, while the volume is 15% less. This material may be injection molded or extmsion molded into products (49). Other technologies for recycling polyurethanes have also been reported. 

Catalysis of the flexible polyurethane foaming operation is accompHshed through the use of tertiary amine compounds, often using two different amines to balance the blowing and gelling reactions. OrganometalHc compounds, usually staimous salts, are also used to faciHtate gelling and promote final cure. 

Box Foa.ms. A measured quantity of the reaction mixture can be placed ia an open-topped crate or box and allowed to foam ia a free rise mode. The block is removed after gelling and is cut iato end use pieces after curiag. 

After the compound is prepared, it is whipped either on a batch or continuous basis. The Oakes continuous mixer is the standard piece of equipment ia the iadustry. Then the gelling agents, ie, Na2SiFg and ZnO, are added, the foam poured iato molds and cured, and the product stripped from the mold for further cure. 

Carrageenan is a gelling agent that forms a complex with the milk proteins, adding bulk and strength. A small amount will make a large difference in the ability to hold air in the foam. 

Gelatin has long been used as a food ingredient (e.g., gelling and foaming agent), in the preparation of pharmaceutical products (e.g., soft and hard capsule, microspheres), in the... 

In the case of aerated protein icings, however, stabilizers are essential. Where hot water is used, gelling-type stabilizers work best (agar, gelatin, Irish moss extract). In cold foams, prepared with cold water, cellulose-type gums are used to contain water in the foams colloidal precipitates, such as are formed through the reaction of carrageenin and protein, are very helpful. 

Certainly the optimal techniques depend on the type of reservoir. Reports that compare the techniques in a related environment are available. In the Kansas Hugoton field (Mesa Limited Partnership), several hydraulic fracturing methods were tested [403]. A method in which a complexed gelled water fracture was applied was the most successful when compared with a foam technique and with older and simpler techniques. The study covers some 56 wells where such techniques were applied. 

Incomplete texturization or partial denaturation at temperatures below 60 °C significantly increased gel strength, but at 75 °C or above, complete loss of the gelling property resulted. Foam volume remained high up to 50 °C but decreased significantly (p < 0.05) above 75 °C. Foam stability followed the same pattern as foam volume, being very stable for an hour below 50 °C. On the contrary, Phillips et al. (1990) reported that WPI heated to 80 °C had little effect on foam stability. 

Carico(139-140) has published comparative information about the various gelling agents. Xanthan has been adapted to foam fracturing gels. Xanthan gels can be broken by the addition of lithium hypochlorite(141). 

Distinctly different approaches to avoid these problems and still achieve high viscosities were conceived and applied. The different approaches can be categorized as 1) preparation of emulsions or foams and 2) addition of crosslinkers to the polymer. Two separate processes which utilized crosslinking of polymer gelling agents were pursued. These are the use of secondary (or delayed) gelling agents and the use of metallic crosslinkers added on-site. 

Emulsions. Emulsion fluids and foams came into routine use in competition with crosslinked fluids during 1970-80. Simple, barely stable emulsions had been used early in fracturing. These were mainly emulsified acids that "broke" when the acid spent on the formation surfaces. In the late 1960 s Kiel became a proponent of very high viscosity oil fluids as a method to place exceptional (at the time) amounts of proppant(337,338). To avoid the frictional resistance typical of gelled oils he advanced the concept of preparing a very viscous oil-external emulsion with one part fresh water, 0.1% sodium tallate surfactant, and two parts oil. The viscous emulsion had to be pumped simultaneously with a water stream to minimize frictional pressure. This process was clumsy and still... 

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