United States Patent Office Patented Aug
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3,202,556 United States Patent Office Patented Aug. 24, 1965 2 mannan. As a consequence, crosslinking agents are used METHOD FOR GELiNGWATER-BEARNG3,282,555 EX to hasten the formation of gels, or they may be employed PLGSIVE COMPOSTIONS CONTAINNG GAYLAC to form gels which have desired physical properties at rel TOMANNAN (GUAS atively low gum concentrations, or even have properties Joseph D. Chrisp, Caymorf, Dai, assig or to E. I. du not obtainable by the use of the gum alone. An effective Poit de Neno Ers and Company, Wilmington, De., a and Well known crosslinking agent for the hydrated galac corporation of Delaware tomannans, especially for guar gum, is the borate ion No iPrawing. Fied July 23, 1963, Ser. No. 296,932 which acts as a crosslinking agent with hydrated guar gum 14 (Claims. (C. 49-20) to form cohesive structural gels. The process of cross 10 linking guar-containing compositions by adding borate This invention relates to a process for gelling aqueous ions has been employed in the manufacture of ammonium solutions of water-dispersible, non-ionic hydroxyl poly nitrate-based blasting agent compositions, as disclosed and mers. More particularly, this invention relates to a proc claimed in U.S. Patent No. 3,072,509. Such blasting ess for making water-bearing gels containing galactoman agents have a desirable body which resists dispersion of nans and to certain products obtained thereby including 5 the compositions by water and facilitates their handling explosives. and loading. Also, such crosslinked blasting agents are Water-soluble gums have been articles of commerce economical and safe to use, and have better storage prop for hundreds of years. These gums constitute a class of erties, that is, they retain their favorable physical proper Substances, organic in nature and related to the sugars ties for a considerably longer period of time, than do simi and carbohydrates. They have the characteristic prop 20 lar compositions which are made thicker simply by in erty of forming viscous solutions or mucilages either by creasing the concentration of gum without addition of a dissolving, i.e., dispersing uniformly, in water or by ab crosslinking agent. sorbing many times their own volume of water. In water, Experience in the use of the borate-crosslinked gels has colloidal solutions, or sols, are formed. The physical shown, however, that the gels will degrade under adverse properties of such solutions usually are characteristic of conditions of storage, for example at 100 F., even when one or a small group of related gums, so that a wide range protected from loss of water by evaporation. Deteriora of properties can be obtained by use of different guns un tion in storage is even more apparent in the gels contain der a variety of conditions. The properties of water ing high concentrations of electrolytes such as the am soluble gums, especially in solutions, make them extreme monium nitrate-containing blasting agent compositions re ly valuable in manufacturing processes. The textile, cos 30 ferred to hereinbefore. metic, pharmaceutical, and food industries, and to a This invention provides a unique process for forming lesser extent other industries, have found a wide applica stable gels of galactomannan gums having, for example, tion for the gums. These materials can increase the vis many times the stability of borate-crosslinked galactoman cosity of solutions very remarkably, and often can give nan gum gels. Also, this invention provides a process for gel structures at increased, but relatively low concenrta 3 5 readily controlling the rate of gelation of galactomannan tions of gum. The viscosity-building, or thickening, ac gums and the consistency of the gels obtained thereby and, tion of the guns in aqueous systems may be all that is thus, provides gels having a wide spectrum of utility. desired at times, whereas in other circumstances a sub The process of this invention for gelling aqueous solu stantial immobilization of the water-bearing composition tions of galactomannan gum comprises mixing water, is desired by formation of a gel. Gel formation is de 40 galactomannan gum, about from 0.05 to 20%, calculated sired especially if undissolved solids are present in the as metal (i.e., Sb or Bi) and based on the weight of galac system and must be maintained in a relatively uniform tomannan, of at least one crosslinking agent selected from state of dispersion therein even after removal from the the group consisting of compounds of the metals antimony mixer or other dispersing device. and bismuth soluble in the System, and a base, said gela As used herein, a gel is a mixture, one component of tion being carried out at a pH of about from 6 to 13, and which is water, homogeneous down to substantially col 45 preferably 7 to 11. In general, it is desirable to apprecia loidal dimensions and capable of resisting a finite shear bly hydrate the galactomannan prior to the addition of ing force. This resistance to shearing is evidence of some base since at higher pH's, for example, above 10, hydra sort of continuous mechanical network or structure, tion is materially retarded. Hydration is evidenced by an which, however, can consist of a relatively small frac appreciable increase in the viscosity, that is, thickening, of tion of the total mass. Thus, the gel forms a matrix in aqueous galactomannan gum solutions, for example, at which both dissolved and undissolved components may be least a ten-and usually at least a 1000-or more fold distributed. Simply cooling a gum solution prepared at increase in viscosity. Although the antimony and bis elevated temperatures, or increasing the concentration of muth crosslinking agents can be added to the galactoman the dissolved or dispersed gum may lead to gel forma nan-containing mixture after the pH thereof has been ad tion. Such gels, however, often have relatively low prac 5 5 justed by the addition of base, usually it is preferred to add tical utility because they are physically weak and tend to the base after the cross-linking agent is added to the galac rupture and crumble, or because gel formation is reversi tomannan and water. Thus, it is preferred to add the ble with increases in temperature, or because the gel crosslinking agent either with the galactomannan or to a structure collapses in the presence of other components preformed galactomannan solution, then add base. Al in the mixture, especially in the presence of dissolved 60 ternately, however, if a crosslinking agent such as anti electrolytes. Further, the increased concentration of rela mony oxide and a slowly reacting base such as magnesium tively expensive gum which is required to obtain a greater oxide are used, the galactornannan, crosslinking agent and degree of immobility of the aqueous system often imposes base can be added to water simultaneously. Efficient a substantial economic penalty on the resulting composi crosslinking of the galactomannan then begins after the tion. - addition of the base. As described more fully hereinafter, One of the industrially important classes of gums is the the extent and speed of crosslinking and gelation varies galactomannans of which locust bean and guar gums are with the particular antimony or bismuth compound se most important. These useful gums have a high tolerance lected, the strength of the base employed and concentra for dissolved electrolytes and produce high viscosity solu tion of the crosslinking agent and base. In general, for a tions in water and in salt solutions, but said solutions or 70 given galactomannan concentration, the speed of cross sols gel only at relatively high concentrations of galacto linking and, to a lesser degree, the extent thereof increase 3,202,556 4. with the solubility of the crosslinking agent and the centrations substantially greater than the concentration strength of the base employed. Similarly, all other things normally present in water. Examples of bases which can being held constant, the apparent rate and degree of cross be used in this invention are strong bases such as sodium linking increase with galactomannan concentration. hydroxide, potassium hydroxide, and other alkali metal The process of the instant invention is effective in cross hydroxides, as well as weaker bases such as ammonium linking galactomannan gums such as locust bean gum hydroxide and dimethylamine; alkaline salts such as and guar gum, and also other galactomannan gums which Na2CO3, Na3PO4, and complex alkaline salts containing include those from endosperms of seeds of leguminous antimony and bismuth such as potassium antimony tar plants such as the Sennas, brazilwood, tara, honey locust, trate which supply both crosslinking agent and a source of paloverde, and rattlebox, alfalfa gum, clover gum, and O hydroxyl ions; alkaline earth hydroxides, such as mag fenugreek gum. In commerce, however, the most im nesium, calcium and barium hydroxides; and the corre portant galactomannan gums are locust bean gun and sponding oxides, MgO, CaO and BaC). As to the amount guar burn. Locust bean gum also is marketed under of base added, in the broad aspect of this invention the other names which include Carob gum, gum Gatto, gum critical requirement is that enough hydroxyl ion be sup Hevo, Jandagum, Lakoegum, Rubigum, Lupogum, Lu plied to the reaction mixture either initially or during posol, gum Tragon, Tragarab, and Tragasol. Guar gum, the process to initiate gelation and to produce a gel of on the other hand, generally is identified as such. It is the desired consistency. Enough hydroxyl ion must be made by milling endosperm from seeds of the guar plant, supplied to raise the pH value to about 6.0, but not higher Cyanopsis tetragonolobus, family Leguminosa, an annual than 13. At the higher pH values in this range, cross crop.