The most common industrial aqueous foam applications use the produced foam as a barrier, often between a substrate and the surrounding atmosphere. The most widely known barrier application is fire fighting where a foam barrier separates a burning substrate from oxygen. This application is described in Perri, J. M., “Fire Fighting Foams”, in Bikerman, J. J., “Foams: Theory and Industrial Applications,” Reinhold Publishing Corporation, New York, N.Y., 1953. Although, in the case of a fire fighting foam, the heat generated by the fire destroys the applied foam, extinguishment occurs because the foam application overwhelms the burning substrate.
There are many other barrier foams which are not related to fire extinguishing. For example, various barrier foams are described in United States patents. Alm U.S. Pat. No. 4,923,903, Chao U.S. Pat. No. 5,696,174, DiMaio U.S. Pat. No. 5,225,095, Fisher U.S. Pat. No. 1,985,491, Johnston U.S. Pat. No. 4,127,383, Kent U.S. Pat. No. 4,795,590, Kittle U.S. Pat. Nos. 4,874,641, 5,096,616, 5,215,786 and 5,853,050, Kramer U.S. Pat. Nos. 4,421,788 and 4,519,338, Nachtman U.S. Pat. Nos. 5,556,033, 5,849,364, 5,897,946 and 6,096,373, Present U.S. Pat. No. 3,466,873, Stern U.S. Pat. No. 5,026,735, Thach U.S. Pat. No. 5,434,192, describe the use of foams for landfill coverage or volatile emissions applications. Butler U.S. Pat. No. 3,669,898, Cole U.S. Pat. No. 3,563,461, Lambou U.S. Pat. No. 3,891,571, Lightcap U.S. Pat. No. 7,022,651, Neumann U.S. Pat. No. 4,086,331, and Thiegs U.S. Pat. No. 2,875,555 describe the use of foams for frost protection. In these examples, foam barriers separate a solid or liquid substrate from the atmosphere, thereby inhibiting mass or heat transfer.
With the exception of fire fighting foams, which are partially consumed during application, in general, barrier foams need to exhibit persistence after they have been applied. In each of the application areas mentioned above, landfills, volatile emissions, and frost protection, the applied foam should remain essentially unchanged for a relatively long time interval, e.g., 10-12 hours, or overnight, in order to minimize application costs. To satisfy this performance parameter, the “drain time,” which is usually expressed in terms of rate of drainage (% of sample per minute, rather that in terms of time), needs to be reduced, i.e., the drainage is slowed down, so that the amount of decomposition is only a small percentage of the total volume of the initially applied foam in the desired 10-12 hour interval. The general chemical approach used to reduce the drain time involves increasing the surface viscosity of the foam bubbles, in theory, but in practice, this is reduced to increasing the viscosity of the foamed material, most desirably, after the foaming operation has been completed.
There are three general methods to achieve this final viscosity result: (a) use a composition which crosslinks after foaming, as in the following United States patents: Alm U.S. Pat. No. 4,923,903, Chao U.S. Pat. No. 5,696,174, Kent U.S. Pat. No. 4,795,590, Kramer U.S. Pat. Nos. 4,421,788 and 4,519,338, Stern, or (2) use a composition which gels after foaming as in the following United States patents: DiMaio U.S. Pat. No. 5,225,095, Kittle U.S. Pat. No. 5,853,050, and Neumann U.S. Pat. No. 4,086,331, or (3) use a composition which provides a somewhat rigid and insoluble system after foaming, such as stearate salts, as in the following United States patents: Kittle U.S. Pat. Nos. 4,874,641, 5,096,616 and 5,215,786. It is notable that both the starch/gum systems and the stearate systems are similar in that both produce insoluble phases via the foaming process.
Another important application feature for many types of foam is “stiffness,” which relates to the ability of the applied foam to be stacked or piled, or for the applied foam to resist cold flow, or leveling, or exhibit a high value for its angle of repose. As a common example, for reference, lightly whipped cream will exhibit a low angle of repose and little resistance to cold flow or leveling, while good quality aerosol shaving cream can be piled easily and remain in place for hours.
When the requirement of stiffness is added to the slow drain time requirement, the list of viable foaming systems becomes quite short. The implementation of two component systems, i.e., the foaming system plus the catalyst for cross linking or curing, is particularly difficult in many industrial applications. Consequently, the useful systems are generally reduced to hydrolyzed protein foaming systems, such as those described in DiMaio U.S. Pat. No. 5,225,095 and Kittle U.S. Pat. No. 5,853,050. Each of these foaming concentrates uses ferrous ion stabilized hydrolyzed protein (from hoof and horn meal), some processing aids (lignosulfonate), and an ingredient to slow down the drain time. DiMaio uses natural gums, while Kittle uses amylopectin starch. In each of these cases, an unwanted result is that the concentrates exhibit excessive viscosity (20000 +cps). The fact that the concentrates are gels leads to other processing and application difficulties. Additionally, the stabilizing iron salts contribute to instability in the concentrate, especially when natural gums are used.
During the development of the technology described in Kittle U.S. Pat. No. 5,853,050, the utilization of common corn starch as the drain time-slowing ingredient was identified and characterized. In fact, ordinary common corn starch could have been used in the production process as the final foam product, after proper dilution, was very suitable in all respects. Unfortunately, common corn starch, generally a mixture of amylose (linear starch) and amylopectin (branched starch), exhibits a characteristic called “retrogradation,” which is essentially the precipitation or coagulation of poorly soluble linear dextrins present in starch solutions. Retrogradation is described in Whistler, R. L., Bemiller, J. N., and Paschall, E. F., “Starch: Chemistry and Technology,” Second Edition, Academic Press, New York, N.Y., 1984. The precipitation problem causes a second phase to form in the concentrate, thereby degrading the performance, and rendering the formulation useless. This usually occurs within a week or two, and consequently the composition is not commercially viable. The remedy for this ever present retrogradation in common corn starch was to substitute, for common corn starch, a unique starch containing essentially 100% branched material (amylopectin). This is a starch obtained from waxy maize corn and it is commonly available from major starch producers.
Making the raw material substitution allowed retrogradation to be circumvented, and thereby made the product concept commercially realistic. Negative effects associated with the stability advantage include not only the previously noted “gel-like” consistency of the final concentrate, but, in addition, an extremely high viscosity during one step of the formulation production sequence. This process nuisance required special pumping equipment as well as considerable patience on the part of the operator. Needless to say, avoiding these problems would be very much worthwhile, and, in addition, would allow preparation, in general, of higher level concentrates, which is always beneficial.
When preparing compositions using amylopectin, as in Kittle U.S. Pat. No. 5,853,050), the process scheme required the use of hot water in the initial step. As the amylopectin was added to the formulation, its viscosity increased to more than 30000 cps. In order to finish the formulation, special progressive cavity pumps were required. By the time the final ingredients had been added, the viscosity was acceptable, although still very high. This processing limitation effectively restricted the available and usable final concentration.