Sodium Metaphosphate in Mechanical Dishwashing CHARLES SCHWARTZ' AND BERNARD H. GILMORE,Mellon I n s t i t u t e of Industrial Research, Pittsburgh, Pa. P = precipitation factor, or" the H E critical examination The precipitation factor is an important amount of adherent inof detergent processes phase of detergent processes. Available water soluble substances has in recent years asformed by reaction besupplies usually contain appreciable quantities tween detergent, water, sumed a n a s p e c t of some imof calcium and magnesium salts which have and soil, and deposited portance, as evidenced by numero n t h e a r t i c l e s being the property of forming insoluble and adherent ous papers on metal cleaning, washed during the washlaundering, and textile scouring, precipitates of calcium and magnesium coming process but the field of d i s h w a s h i n g pounds f r o m the alkaline salts added as deterT h e following i n t e r r e l a t i o n has been almost entirely gents and the soaps resulting from the interexists among these variables: neglected. Upon superficial exaction qf' a n alkaline detergent with fatty soil. The greater E and S are the a m i n a t i o n t h e problems inI t has been shown that sodium hexametaphosgreater the detergent efficiency; volved in dishwasliing m i g h t while the greater P is, the less seem trivial; however, when one phate has the property of sequestering calcium the detergent efficiency. considers t h e tremendous and magnesium ions by the formation of soluble The emulsifying power of any amount of such activity in the complex molecules in which the concentration d e t e r g e n t w h i c h i s u s e d in bottling industries, pharmaceuof calcium and magnesium ions is considerably dishmashing is a rather vague tical manufacturing, hotel and diminished. The addition of sodium hexaand a m b i g u o u s t e r m unless restaurant operation, and in the certain definite limitations are home, where cleanliness is absometaphosphate to dishwashing compounds preestablished. For the p u r p o s e lutely e s s e n t i a l f o r both hyvents film formation, permits the full value of of this work the discussion may gienic and e s t h e t i c r e a s o n s , the detergent mixture to be obtained, and yields b e l i m i t e d , (1) to the type the issues involved become of results that are superior with respect io brightness of difficultly r e m o v a b l e soil major importance. and freedom f r o m film. which includes fats and solid This investigation was undermaterials commonly o c c u r taken t o d e t e r m i n e h o w t h e performance of established commercial detergents could be ring in food products, and (2) to detergents such that when improved and, if possible, to develop a composition which made up to a concentration in water of 0.25 to 0.5 per would have none of the shortcomings of present compounds. cent by weight, the pH will be between 10 and 12. With these two limits fixed, the effect of various alkalies in solution a t that pH upon soils of a greasy type may be conTHEORETICAL CONSIDERATIONS sidered. The detergent efficiency of any washing process depends Khile no alkali has a marked emulsifying effect upon soil upon the following factors: which is completely free from fatty acid, all alkalies have a marked emulsifying effect upon soil containing a small amount (1) The mechanical efficiency of the proces. of free fatty acid, owing to the formation of alkali soaps which (2) The temperature at which the mashing operation is have excellent emulsifying properties in the presence of alkali. carried out. If the amount of soap present is the same in each case, the (3) The amount and concentration of the detergent agent. (4) The amount and type of soil. emulsifying properties of the commonly used alkalies are of ( 5 ) The emulsifying power of the detergent-in other words, the same order of magnitude. Thus, it may be seen: (1) its power of suspending dirt, oil, and grease. In order for any alkali to be a rapid emulsifier, there must be (6) The saponification power of the detergent, or its ability to form soaps by interaction with fatty soil which may thus be free fatty acid present in soil to be removed, or the alkali must washed away. be compounded with a soap or a similar emulsifying agent; (7) The formation of adherent and insoluble substances (2) if this is true, the selection of the alkali to be used in a during the washing process. (8) The corrosive effect of the detergent upon the articles detergent must rest upon other considerations than the emulsifying power, as will be shown. t o be cleaned. The saponifying power of any substance depends in general For the sake of expediency let it be assumed that the first upon its pH in solution and the temperature. Thus, when four factors enumerated remain constant, and let the last any alkaline detergent is used a t relatively elevated temperaone be temporarily neglected. Then there might be formu- tures in the presence of fats, a greater or lesser amount of lated a speculative, but reasonable, mathematical expression saponification and neutralization takes place with the formafor the detergent efficiency of any substance: tion of soap. This soap in turn acts as a n emulsifying agent upon the soil to be removed. Thus, E and S are closely reD = f(E, S,P ) lated, and, if the alkali used is of such a nature as to cause the formation of enough soap during the washing process, the where D = detergent efficiency E = emulsification or soil-suspending power of the emulsifying power of the detergent mixture will be sufficient substance under investigation S = saponification or soap-forming polver of the sub- to clean off any soiled article, provided that the soil or the mash water is free from any substance which will form an adstance under investigation herent precipitate with any product of the saponification or with the detergent. 1 Present address. Hall Laboratories. Inc.
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The pc,"irtnry I? T h e following ex-
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rrinkr the wash water modcnrtely hiard (eqkvuieiit
l o 191) 1., p in. of m ~ l ~ i i i carbonate), m thrrehy iiicrensing the
eiit,s perfumed undcr less severe 'Sum macliines n i the domestic type, cquipped wit,Ii spray be;ub :rod n motor-driven propcllcr which agitated the det,ergent solution during t,he rvsshing process, were used. Both machines were conncctcd side hy side to the same nster supply. The rwsh water ranged hotween 128" and 140" I?., temperatures i.wonrmeniied by the manuSxct.urem of the machines. For oiw:it,ion. the mnchine is e q u i w e d with a single trinngular
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