Abstract:
A composition for forming an essentially biodegradable foam for application to a substrate to provide a barrier between the substrate and the atmosphere formulated from a mixture in water of specified materials in certain proportional relationships. Its use in preparing such a foam barrier is also provided.

Description:
The present invention relates to a novel composition especially adapted to generate an improved foam barrier layer between a substrate and the atmosphere and to the method of using the composition More particularly, the present invention relates to such a composition that may be manufactured, transported, stored and handled as a concentrate and which, upon dilution with water, can be converted to a foam of exceptional thickness and persistence. 
     BACKGROUND OF THE INVENTION 
     In my prior U.S. Letters Pat. No. 4,874,641 are disclosed compositions for generating foam adapted to form an inexpensive, temporary barrier layer between a substrate, such as a layer of waste deposited in a landfill, and the atmosphere. As pointed out in the patent, such a barrier layer might serve to protect the atmosphere from deleterious materials which would escape from the substrate, such as odors and blowing trash from landfills, dust or noxious fumes from spills, and the like. As also pointed out in the patent, such a barrier layer might also serve to protect the substrate from adverse conditions in the atmosphere, as in protecting growing fruit, vegetables and plants from unseasonal frost. It might be added, in connection with the latter situation, that such a foam, particularly one prepared according to the present invention, might be used in the control of mine fires, specifically abandoned mine fires, where the foam can be pressure injected underground. In this application, the foam would serve four fundamental functions: (1) displacement of combustion air and gases which are products of combustion; (2) extinguishment of the actively burning zones; (3) heat removal from the surrounding strata; and (4) deposition of known chemical fire fighting ingredients (urea for instance) in order to minimize problems associated with reignition. 
     U.S. Pat. Nos. 4,421,788 and 4,519,338 relate to using a hardenable plastic foam to replace the daily compacted earth cover on a landfill. The foam employed according to these patents is prepared using a foaming agent and a liquid synthetic resin, such as a precondensate of urea and formaldehyde. U.S. Pat. No. 4,421,788 describes covering successive layers of refuse with foamed polyurethane, polyether or polyester-based resins. 
     Since the development of the foam composition of my prior patent, certain state governmental agencies have promulgated regulations governing sanitary landfills and the like with more stringent requirements. For example, there is a requirement that the sanitary landfill daily cover foam be six inches thick in addition to satisfying all other conventional requirements. Among the latter are the requirement that the cover be effective in sealing off of odors from, and in preventing insects from gaining access to, the waste, while being innocuous to the environment. The foam generated from the composition as disclosed in my prior patent was not stiff enough to &#34;stack&#34; six inches thick, especially on a slope and at low temperatures. 
     The foam-generating composition must be capable of being produced, transported, stored and handled as a concentrate in order to avoid the handling of large volumes of liquid which is mostly water. The concentrate, of course, is subjected to widely different atmospheric temperature conditions, including very low temperatures. Attempts at modifications of the prior foaming composition to meet the new technical and regulatory requirements led to other problems. 
     There are conflicts between soluble/insoluble characteristics of combinations of components in a foam-generating composition. Potassium soaps are generally much more soluble in water than sodium soaps, and higher molecular weight fatty acids, like palmitic and stearic, give more dense, more stable foams than lower molecular weight homologs. Yet, in order to obtain the stiffness and drain time performance (foam persistence), it is desirable to have the foam in the &#34;insoluble&#34; mode, while, on the other hand, in order to provide a foaming composition in the form of a concentrate, the materials should be in a &#34;soluble&#34; mode so that active ingredients are not precipitated and lost to the system. Solubility is also important to the ultimate foaming performance. It is generally accepted that soaps foam well in hot water, foam moderately in room temperature water and do not foam in cold water. Yet foams of the type to which the present invention is directed are generally applied under ambient temperature conditions ranging from below freezing, at the low end, to 90°-100° F. at the high end. 
     OBJECTS OF THE INVENTION 
     It is, therefore, the principal object of the present invention to provide new and improved foam-producing compositions for forming a barrier between a substrate and the atmosphere. 
     It is another object of the present invention to provide a novel foam-producing composition adapted to be produced, transported, stored and handled as a concentrate, even at very low ambient atmospheric temperatures, while being capable, upon dilution with water, of generating a foam meeting the technical and regulatory criteria. 
     It is a further object of the present invention to provide a novel method of producing a foam barrier layer between a substrate and the atmosphere utilizing the novel composition. 
     These and other objects will become apparent from a consideration of the following specification and claims. 
     SUMMARY OF THE INVENTION 
     The composition of the present invention, for forming a biodegradable foam for application to a substrate to provide a barrier between the substrate and the atmosphere, is formulated from a mixture in water of: 
     (A) a sodium sulfonate having the formula ##STR1## where R is an alkyl, alkylene or alkaryl group containing from 10 to 20 carbon atoms; (B) a carboxylic acid R 1  COOH where R 1  is an alkyl group containing 8 to 30 carbon atoms; (C) potassium hydroxide; (D) potassium silicate, the proportion of C plus D to B being sufficient for substantially complete neutralization to form the potassium salt of B and the proportion of B to A providing a mol ratio of B to A greater than 1:1 and up to about 2:1; (E) a non-ionic, solid, organic, water-soluble material such as sucrose or urea, and (F) a hydroxylic solvent for the potassium salt of B. Where hard water is encountered, a water conditioner (G) such as potassium tripolyphosphate can be included. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the above-described composition, each of the components plays an important role in providing the overall characteristics of the final foam as well as the concentrated and diluted forms of the composition. These roles will be referred to below in connection with the discussion of each of the components. In addition, the composition is the result of mixing components (A) through (F) in water so that, in the resulting composition, the identity of certain of the components as such may be lost through, for example, ion interchange and neutralization. 
     Component A is a sodium sulfonate having the defined formula. It is the surfactant foaming agent. Preferably, A is a sodium alphaolefin sulfonate containing from 10 to 20 carbon atoms, especially a mixture containing principally 14 and 16 carbon atoms. 
     Carboxylic acid (component B) provides, upon neutralization to its potassium salt, the soap foaming agent. Preferably, R 1  is a straight chain alkyl group containing from 8 to 20 carbon atoms, especially stearic and palmitic acids. In such a mixture, the relative proportions of stearic acid to palmitic acid may be between about 45 and about 55%, by weight, of the former to between about 55 and about 45%, by weight, of the latter, preferably about 50:50. 
     To form the desired potassium ion content, two sources are employed: component C, potassium hydroxide, and component D, potassium silicate. For example, silicate is required for minimization of carboxylic acid salt precipitation. However, if potassium silicate is used as a source of neutralizing potassium ion, precipitation of a complex silicate occurs. As stated above, the proportion of C plus D to carboxylic acid (B) is sufficient for substantially complete neutralization to form the potassium salt of B. However, the proportion of C to D will be such as to provide between about 50% to 90% of the potassium base from the potassium hydroxide (C) and about 50% to 10% of the potassium base from the potassium silicate (D). The preferred mole ratio is 4 moles of potassium base from the potassium hydroxide (C) to 1 mole of potassium base from the potassium silicate (D). 
     To enhance the stiffness of the resulting foam by increasing the solids content without upsetting the ionic equilibrium of the composition, a solid, non-ionic water soluble material, such as sucrose or urea (component E) is included. Sucrose is preferred on the basis of drain time, concentrate physical properties and foam stiffness. 
     At very low temperatures, the viscosity of the composition comprising components A through E may still present problems. The viscosity of the concentrate even at 30°-40° C. is higher than desired for ease in production, transportation, storage and handling, and the risk of solidification upon further decline in temperature is high. The viscosity of the concentrate is preferably about 200-300 cps at 30° C. so that it can be handled easily in a bulk storage/dilution system. Hence, there is included component F, a solvent for the potassium salt of carboxylic acid (B). This will generally be a hydroxylic solvent such as methanol, isopropanol, ethylene glycol, propylene glycol, glycol ethers and the like. Of these, the glycol ethers are preferred, especially ethylene glycol monobutyl ether and diethylene glycol monobutyl ether, particularly the latter. 
     The degree of hardness of the water used to produce the composition, both concentrate and diluted form, can have and effect on the persistence and quality of the resulting foam. Hence, in order to accommodate water of various degrees of hardness from differing sources available, a hardness control agent, component G, can be included. Hardness control agents such as ethylene diamine tetraacetic acid or potassium phosphates can be used, but potassium tripolyphosphate, a known dispersing agent, is preferred because it improves the physical characteristics of the concentrate. In the preparation of the concentrate, the hardness control agent (G) is preferably added to the water immediately following the addition of the sodium alphaolefin sulfonate (A). 
     Reference has been made above to proportional relationships among certain of the components. In general the proportions of the components, on a water-free basis and in terms of percent by weight based on the combined weight of components A through F are: (A) from about 15 to about 20%, preferably about 18-19%; (B) from about 25 to about 35%, preferably about 30-32%; (C) from about 2 to about 8%, preferably about 5-6%; (D) from about 2 to about 5%, preferably about 3-4%; (E) from about 15 to about 30%, preferably about 23-24%, and (F) from about 10 to about 15%, preferably about 13-14%. 
     In the preferred concentrate, potassium tripolyphosphate (G) is also included in an amount between about 3 and 7%, preferably about 5-6%, based on the combined weight of the components A-G. 
     Reference has also been made to preparation of the composition as a concentrate with subsequent dilution with water, usually at the site of use, for foam generation. The concentrate may have a concentration of components A through F by weight on a water-free basis of between about 10 and about 40%, preferably about 23 to 31%, based on the total weight of the concentrate. For generation of foam such concentrate may be diluted with about 7 to about 9 volumes of water per volume of concentrate to provide a concentration of components A through F by weight on a water-free basis of between about 1 and about 6%, preferably about 3 to 4%, based on the total weight of the diluted composition. 
     Foam is generated from the diluted composition by agitation in the presence of air. One apparatus for this purpose forces the foamable mixture through a restricted passage at a high pressure and injects air into the composition downstream of the restriction. The foam may then be sprayed onto the substrate through a nozzle. 
     The invention may be more readily understood from a consideration of the following specific example which is given for the purpose of illustration only and is not intended to limit the scope of the invention in any way. 
    
    
     EXAMPLE 
     To room temperature water are added in sequence: (1) sodium alphaolefin sulfonate (a commercial grade containing principally 14 and 16 carbon atoms); (2) sugar (sucrose), and (3) diethylene glycol monobutyl ether. The mixture is heated to 45° C. and the remaining materials are added in sequence: (4) potassium hydroxide; (5) potassium silicate (a commercial grade, &#34;Kasil #1&#34; manufactured by PQ Corporation of Valley Forge, Pa.), and (6) a commercial mixture (about 50:50) of stearic and palmitic acids (&#34;Hystrene 5016&#34; manufactured by Witco, Humko Division). Heating is continued until solution is complete. The amounts are shown in the following table. 
     
         ______________________________________           PARTS BY WEIGHT           ASSOCIATEDMATERIAL          SOLIDS   WATER    TOTAL______________________________________1.  sodium alpha olefin sulfonate                 1426      2138  35642.  sugar (sucrose)   1782            17823.  diethylene glycol monobutyl                  990            990    ether4.  potassium hydroxide                  396      484   8805.  potassium silicate                  287      703   9906.  stearic/palmitic acids                 2376            2376    water                      11418  11418    TOTAL             7257     14743  22000______________________________________ 
    
     This concentrate may be transported, stored and handled at temperatures above about 25° C. For generation of foam, it is diluted with eight volumes of water per volume of concentrate. 
     The diluted concentrate can be foamed using a pneumatic foam unit of the kind described in U.S. Pat. No. 4,474,680, dated Oct. 2, 1984. The foam is discharged from the foam unit onto the working face of a sanitary landfill at a thickness preferably exceeding six inches. This is believed to be the maximum foam layer thickness required in the United States. The foam exhibits no cold flow, and only very slight contraction overnight. If deposited in the late afternoon or early evening at a thickness in the range of 6 to 7 inches, the foam layer will normally have a thickness of around 5 to 6 inches in the morning. The foam is very stiff, but does not dry to a dust as do typical more ionic foams, including fire-fighting foams. Foam performance is best where warm water (&gt;30° C.) is used for dilution, but declines only slightly as the temperature of the diluent water approaches freezing. 
     Various modifications can be made to the composition described herein. For example additional ingredients can be included in the composition, such as small quantities of carbon black (up to 2% of the weight of the concentrate). The composition and can be modified in various other respects without departing from the scope cf the invention as defined in the following claims.