PRODUCT REVIEW
Polyelectrolyte Builders as Detergent Phosphate Replacements J. F. Schaffer and R. 1.Woodhams. &p,tment of Chemical Engineering and Apptied Chemistv, University of Toronto, Toronto, Canada M5S 1A4
J. F. Schaffer is Technical Sales Representative with the Pulp and Paper Chemicals Department ofHercules Canada Limited in Toronto, Canada. H e has a degree in Chemical Engineering from the University of Technical Sciences, Budapest, Hungary , and a n M.A.Sc. degree from the University of Toron to, Prior to his present
Raymond T. Woodhams is a professor a n d graduate secretary in the Department of Chemical Engineering and Applied Chemistry a t the Uniuersity of Toronto, Toronto, Canada. He received his BSc. a n d M S c . degrees from the University of Western Ontario and his Ph.D. from the Polymer Institute, Polytechnic Institute of Brooklyn in 1954. After 14years with the Dunlop Research Centre in Sheridan Park, Ontario, where h e became Manager of Chemical Research, he joined the University of Toronto where he is now located. His main interests are in the area ofplastics engineering related to high performance composites. This study is a n outgrowth of filler encapsulation studies involving polyelectrolytes.
Introduction Phosphates as a Pollution Problem. The realization in the 1960’s that phosphorus compounds were partly responsible for the eutrophication of the Great Lakes and many other important fresh water bodies prompted legislation to limit the phosphorus content of home laundry detergents in many parts of the United States and Canada. However, the limitation of phosphorus compounds such as pentasodium tripolypbosphate (STPP) in home laundry detergents represents only a 10% decrease in the total use of phosphates in all cleaning products (I 1. Furthermore, the continued growth i n t h e demand for phosphorus derivatives has almost regained the position lost in 1969 when sanctions were imposed to limit the use of phosphorus in home laundry detergents. Perhaps coincidentally,the water quality of the Great Lakes continues to decline. Despite extensive efforts by industry to develop suitable builder replacements for STPP, the situation, according to Richey, “is that on a cost-effective basis, no adequate suhstitute has been developed” ( I ) . Matzner e t al. have summarized the present state of the art and have detailed the difficulties inherent in finding a suitable substitute (2). The patent literature indicates that polymeric polycarhoxylates have already been recognized as possible alternatives to STPP hut only a few cursory examples have been cited. This paper attempts to relate polyelectrolyte builder activity and its relationship to polymer structure, perhaps thereby providing useful clues for more experienced workers in the detergent industrv who may still he attemuting . . to solve this serious problem. The word eutronhic describes a rather well nourished state of an aquatic biosystem whose natural equilibrium is upset hy the abundance of certain nutritive substances that canse algae, bacteria, and other flora and fauna to reproduce a t very rapid rates. Algae, growing a t an extremely rapid rate, produce enormous quantities of slime and microbial tissue exhausting the oxygen supply, through respiration and decay, both in the surface and bottom layers of water bodies. Phosphorus, nitrogen, and carbon are the major nutrients contrihuting to this unwanted algal bloom that often chokes water bodies rendering them uninhabitable for fish and unattractive for recreational use. Any of these elements may he the limiting nutrient under certain circumstances; however, in a great many cases the extent of algal growth can be reduced by controlling the amount of availahle phosphorus (3).Sources of the other two nutrients, nitrogen and carbon, are very difficult if not impossible to control because of their diffuse, ubiquitous nature. Waste water, containing domestic waste, urban storm sewer runoff, and agricultural runoff, is the source of phosphates lnd. Eng. Chem., Prod. Res. Dev., Val. 16. No. 1, 1977
3
that pollute rivers, lakes, estuaries, and coastal waters. Relative contributions from these sources vary widely depending on the season and location. However, the largest single source of phosphates is domestic waste water with 50-60% of its phosphorus content originating in detergents; the remainder is from human waste and agricultural runoff. In the United States, about 2 billion pounds of detergent phosphates are released into the environment yearly, while the Canadian contribution is 150 million pounds per year. Water analyses indicate that the phosphorus content of Lake Erie increased from 14 WgA. in 1942 to 40 pgA. in 1968, and that the rate of increase is greater for phosphorus than for any other polluting chemical. Removing phosphates from sewage in treatment plants could eliminate 80-95% of all phosphorus but the cost is considered too high to allow immediate and general application. Replacing phosphate builders in home detergent formulations offers only a partial reduction in the phosphorus concentration of effluents entering natural water bodies. Of the key elements essential to life, phosphorus is one of the more limited elements and the least efficiently recycled element in nature. If current trends continue, estimated reserves of phosphorus may be seriously depleted within 60 years ( 4 ) . New reserves may be discovered, but in the geological upper crust of the earth there is a limited amount, about 30 billion tons, of usable phosphorus. Without phosphate fertilizers world food production may sharply decline and thereby aggravate an already serious food problem. This investigation had as its main objective the partial evaluation of several carboxylic polyelectrolytes as detergent builders in the search for a practical substitute for the presently used phosphate compounds. Phosphate Replacements. Potential phosphate builder replacements must satisfy a large number of requirements including sequestering ability, alkalinity, buffer capacity, bleach compatibility, soil deflocculation, oral toxicity, skin absorption, eye irritation, effects on fish and other aquatic life, and economic practicability. Biodegradability is likely to be necessary if the compounds are likely to affect the quality of the environment particularly the long term effects on living organisms. These and other factors relating to organic builder salts have been adequately discussed by Matzner and coworkers (2).Several candidates for total or partial replacements of phosphates are currently under extensive testing while others such as sodium carbonate and sodium silicate are now used in several phosphate-free detergents. Sodium carbonate and sodium silicate-built detergents perform almost as well as the leading phosphate formulations but their high alkalinity can be hazardous, producing eye and skin irritations. Sodium citrate has also been used in commercial nonphosphate detergents. Its main disadvantages are higher cost and mediocre sequestering power. The use of nitrilotriacetic acid (NTA) was banned in the U.S.A. in 1970 (but not so far in Canada) because of a potential health hazard stemming from its high chelating power (increases the transmission of heavy metals across the placental barrier to the fetus, thereby contributing to birth defects). NTA, along with several experimental phosphate substitutes such as sodium acetamidonitrilodiacetate (SAND), sodium hydroxyethylimidodiacetate (SHIM), carboxymethylene oxysuccinate (CMOS), tetrasodium oxydisuccinate (TSODS), sodium oxydiacetate (SODA), tetrahydrofuran tetracarboxylic acid (THFTA), and benzene polycarboxylic acids (BPCA), are now under extensive testing and evaluation in order to establish safety records prior to commercialization. Another potential class of new builders is the polyelectrolytes, principally polycarboxylic acid derivatives. Their chelating ability varies according to the structure of the polymeric 4
Ind. Eng. Chern., Prod. Res. Dev., Vol. 16, No. 1, 1977
segments and the number and displacements of the carboxyl groups. Sizable research funds have been channelled into work on polyelectrolyte builders and numerous polymers were found to be good sequestrants possessing excellent deflocculating power. Their sodium salts provide sufficient alkalinity and buffer capacity, and they are compatible with bleaches. However, polyelectrolytes with good builder characteristics have poor biodegradability, a feature which has so far limited their acceptance. The building properties of water-soluble polymers based on a-halogen-substituted acrylic acids were discovered as early as 1940 ( 5 ) .Several other polyelectrolytes such as sodium salts of poly(ma1eic acid), poly( itaconic acid), poly(itaconic-aconitic acid), poly(itaconic-acrylic acid), poly(ma1eic acidethylene) were also claimed to be better detergent builders than sodium tripolyphosphate (6). Sulfonated poly(ma1eic anhydride) (7) and a unique copolymer of maleic anhydride and carbon monoxide (8) have been reported as effective b u i1ders. Starch-based polyelectrolyte builders form a distinguished class because of their somewhat improved biodegradability. Ether (9) and ester derivatives of starch (IO),dicarboxyl starches ( I I ) , and various other starch derivatives (12)have also been suggested for use as detergent builders. Of all the starch derivatives dicarboxyl starches are the most biodegradable (30%biodegradable). At the present state of polyelectrolyte research it is very tempting to come to a decision that would eliminate polyelectrolytes from the contest for replacing phosphates. However, poor biodegradation should not be a limiting factor in assessing the potential of polyelectrolytes as detergent builders since methods other than biological degradation are able to eliminate polyelectrolytes from waste waters, e.g., by adsorption or precipitation. Special types of polyelectrolytes are commonly employed in municipal sewage treatments for flocculation purposes. During the present work the precipitation of several polyelectrolytes (samples P E 13, 17,30,35, 43,47, and 49) was observed at pH 6-7 when they were titrated with 0.01 N CaClz solution. Lang et al. reported the water insolubility of Li and Ba salts of poly(ma1eic acid) (13). Bianchi et al. investigated the formation of insoluble complexes between anionic polyelectrolytes and polypeptides (14). Carboxylic polyelectrolytes also form insoluble precipitates with algae (15),viruses (It?), and heavy metals, a characteristic which may actually have a beneficial effect on water quality.
Experimental Section Acrylic acid, methacrylic acid, styrene, and vinyl acetate were freshly distilled before use. All other monomers, solvents, and initiators were reagent grade except aconitic acid, Nadic methyl anhydride and 2-sulfoethyl methacrylate which were used as received from the supplier. Polymerizations were carried out.in 12-02 or 28-02 soft drink bottles fastened into a rotating rack which was immersed in a constant-temperature water bath. In the solution polymerizations, the solvent and monomer(s) were mixed together to yield a 10%solution by weight, charged into a soft drink bottle, and purged with nitrogen for several minutes. Initiator (1 mol % based on monomer(s) content) was added and the bottle was sealed. Polymerizations were conducted at 65 "C and interrupted a t 15-20% conversion. Benzene was used as solvent for most of the polymerizations. In cases where the monomer was not soluble in benzene a more polar solvent such as dimethyl formamide or a 3:l mixture of benzene and glacial acetic acid was used. The polymeric products were generally insoluble precipitates. The soluble products were first precipitated by adding suitable nonsolvent to the reaction mix-
__._One of the few possible substitutes for phosphate builders in detergent formulations includes the family of carboxylic polyelectrolytes. Although the nature of these derivatives has been briefly described in the patent literature, this paper reveals some of the factors which influence the effectiveness of carboxylic polyelectrolytes as builders, particularly their ability to sequester calcium (and magnesium) ions and their ability to redissolve calcium soap precipitates. Carboxylic polyelectrolytes are generally nonbiodegradable, a factor which has been considered undesirable by some experts although this assumption is questionable. The sodium salts of carboxylic polyelectrolytes possess medium alkalinity similar to that of the widely used pentasodium tripolyphosphate. The most effective polyelectrolytes include the polymers and copolymers of maleic acid. The results of this study further confirm the superiority of carboxylic polyelectrolytes over phosphate builders in terms of chelating ability and ability to redissolve calcium soap precipitates at low alkalinities. Further studies would be required to fully establish the toxicological and long term ecological effects of these candidates, and to assess their economic viability. A sensitive high-frequency titration apparatus was constructed in order to characterize the neutralization behavior of the polyelectrolyte builders.
ture then the precipitate was filtered, washed, and dried under vacuum at 40 "C. In bulk polymerizations, the monomer(s) and initiator (5 mol %) were charged into the bottles, flushed with nitrogen, sealed, and placed in the constant-temperature polymerization bath a t 75 "C. Products were purified by extracting the residual monomer with a suitable solvent. For the determination of lime soap dispersing and redissolving power of the polyelectrolytes, a standard sol was prepared as follows. Standard 0.1 M CaC12 solution was obtained from the Fisher Scientific Co. along with oleic acid purum and reagent grade NaOH. The calcium oleate dispersion was prepared by mixing 2 1. of 3 X IO-" M CaClz solution (300 ppm of CaC03) and 400.0 ml of 0.1 N sodium oleate solution. The resulting dispersion contained a fine calcium oleate precipitate equivalent to 250 ppm of CaC03 at a sodium oleate/calcium oleate ratio of 4.67. This colloidal suspension was then aged for 24 h at 60 "C prior to use. The 0.5 N polyelectrolyte solutions were prepared by dissolving of the carboxyl gramequivalent weight of the purified polyacid in a solution of 2.00 g of NaOH in 75 ml of distilled water and then bringing the volume to 100.0 ml in a volumetric flask by adding more distilled water after the pH was adjusted to 10.0 with 0.1 N NaOH. The reference solution for transmittance measurements was prepared by diluting 100.0 rnl of 0.1 N sodium oleate solution with 500.0 ml of distilled water. The Fisher Electrophotometer I1 was used to measure the intensity of light transmitted by the sample (turbidity) relative to a reference solution. Absorption cells of 23 ml volume and of 23 mm path length were used at 650 mp wavelength; 50.0-ml aliquots of the calcium soap dispersion were titrated with 0.5 N solutions of several polyelectrolyte sodium salts at 60 "C. After each addition of polymer the sample was mixed for 5 min in a 60 "C water bath then part of it was quickly transferred into a preheated absorption cell and the transmittance was measured. The titration was carried on until either near 100% relative transmittance was restored or a maximum of 6.0 ml titrant was consumed. The calcium ion sequestering ability of each polyelectrolyte was measured directly using a specific ion meter. Standard 10-1 M CaClz of extreme purity was obtained from Fisher Scientific Co. (Orion Research Inc., code 92-20-06).By diluting the standard with deionized water, a stock sample solution of lo-? M CaClz concentration (100 ppm of CaC03 hardness) was prepared. This solution was then used to make up a series of calibration standards of lo-?, lo+, and 10+ M CaClJ concentration. Appropriate amounts of analytical grade NaCl were added to the latter three standards so that the composition of each standard-in regard to e a 2 + and Na+--approximates that of the sample a t corresponding Ca2+ levels. The ionic strength of samples and standards was further adjusted t o p = lo-* by adding reagent grade tetraethylammonium (TEA) chloride. The solutions of polyelectrolyte sodium J &
salts were prepared from their purified polycarboxylic acid forms with reagent grade 1 N NaOH and deionized water. A Model 407 Specific Ion Meter, Model 92-32 Divalent Cation Electrode, and Model 90-01 Single Junction Reference Electrode-all from Orion Research 1nc.-were used to follow the changes in the e a 2 +activity of the samples during the titrations; 100.0-mlaliquots of the lop3M CaClz solution-ionic strength adjusted to p = M with TEA chloride-were titrated with 0.1 N solutions of the different polyelectrolyte sodium salts at room temperature. Samples were agitated with a magnetic stirrer. After each addition of the titrant sufficient time-3 min-was allowed for equilibration and the Ca2+ activity was then recorded. When entering a new activity M, the Nernst slope factor of the inrange, e.g., lo-" to strument was changed according to values obtained from the calibration standards. The titrations were carried on until either a minimum in the amount of titrant vs. Ca2+ activity was observed or until 10.0 ml of 0.1 N sodium polyelectrolyte solution had been added. The following conditions were chosen for the Ca2+titrations performed with the Orion Divalent Cation Electrode: pH, 8-9; t = 25.0 f 1.0 "C; p = M (&lo%). The Na+ ion interference was compensated for by using calibrated standards containing various sodium ion concentrations. Since the ion electrode response changes with time, frequent calibration was necessary for accurate results. The depth of immersion of electrode was maintained at 25 mm and the rate of stirring was the same for all measurements. The Nernst slope factors are shown below for each calcium ion concentration range. The values show a spread due to the above mentioned aging effects: 94-98% for the 10V to lo-* M CaL+range; 90-95% for the to l o + M Ca2+ range; 8449% for the IO-' to M Ca2+range. Observing all these requirements, the reproducibility of measurements in the three concentration ranges was f 2 % , f 5 % , and &lo%, respectively. The alkalinity of the polyelectrolyte builders was determined as follows. In a 150-ml beaker 0.1 g of the polyelectrolyte was dissolved in 99.9 g of a solution containing the amount of NaOH in distilled water that is necessary for the complete neutralization of the 0.1 g of polyacid (calculated from the carboxyl equivalent weight of the sample). The pH of the obtained solution was then determined at 25 "C with a conventional pH meter.
Results and Discussion Two major classes of anionic polyelectrolytes, the strong acid type (e.g., poly(styrenesu1fonic acid)) and the weak acid type (e.g., poly(acry1ic acid)) can be distinguished. Strong acid polyelectrolytes tend to ionize completely with most counterions whereas weak acid polyelectrolytes dissociate to a much lower extent. Because of the anticipated benefits in sequestering calcium ions with weak acid polyelectrolytes, Ind. Eng. Chem., Prod. Res. Dev., Vol. 16, No. 1, 1977
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Table I. List of Monomers Employed for the Synthesis of Various Polyelectrolytes Acrylic acid (AA) Methacrylic acid (MAA) Maleic acid (MA) Mesaconic acid (MEA) Itaconic acid (IA) Aconitic acid (ACA) Nadic anhydride (NA) Nadic methyl anhydride (NMA) Styrene (ST) Vinyl acetate (VA) Thiophene (TH) Furan (FU) 2-Sulfoethyl methacrylate (SEM)
mainly carboxylic monomers were selected for this study. Owing to their commercial availability, most of the emphasis was placed on acrylic derivatives which provided a variety of building blocks for the syntheses of polyelectrolytes of different chemical structures and charge densities. Two unique dicarboxylic compounds, Nadic anhydride (3,6-endomethylene-1,2,3,6-tetrahydro-cis-phthalic anhydride) and its methyl derivative Nadic methyl anhydride were also included for the purpose of comparing the effect of rigid, cyclic carboxylic units on the calcium sequestering ability of polymeric segments. Relatively new advances in charge transfer polymerization prompted the use of furan (17) and thiophene (18) in copolymerizations with maleic anhydride thereby introducing heterocyclic segments into the polymer backbone. Only one monomer, 2-sulfoethylmethacrylate, was selected tu illustrate the behavior of strongly acidic substituents. Monomers with no ionic functional groups such as styrene, vinyl acetate, and vinyl methyl ether served to modify or “dilute” the charge densities of selected polyelectrolytes. All the monomers used in this study are listed in Table I. No detailed data on the reactivity ratios of these monomers were available. Therefore, in most cases a 1:l ratio of comonomers was used for copolymerization unless the low reactivity of one of the comonomers was obvious. Acrylic monomers were expected to homopolymerize and copolymerize readily whereas di- and trisubstituted double bonds were expected to polymerize reluctantly. The existence of interfering side reactions was reported by Braun and Aziz El Sayed (19)and also Tate et al. (20).These authors found that itaconic, maleic, fumaric, mesaconic, and citraconic acids yield carbon dioxide during polymerization. The loss of carboxyl groups interferes with the effectiveness of the polyelectrolyte as a detergent builder only if it is not compensated by the similar sequestering capacity of the newly formed groups. The decarboxylation phenomenon, however, is confined to polymers that have adjacent carboxyl groups such as the homopolymers of maleic acid, itaconic acid or their copolymers with small amounts of monocarboxylic monomers. Increasing amounts of monocarboxylic or noncarboxylic comonomers gradually eliminate such decarboxylation. The preparation of all homopolymers and the complete set of copolymers from the dual combination of the six carboxylic monomers (that is 6 homopolymers and 15 copolymers) was attempted. Owing to the reactivity limitations of some of these monomers only 4 homopolymers and 11copolymers could be prepared. Under the conditions described in the experimental part, mesaconic acid and aconitic acid did not homopolymerize and attempts to copolymerize the mesaconic acidmaleic acid, mesaconic acid-itaconic acid, mesaconic acidaconitic acid, and itaconic acid-aconitic acid monomer pairs were not successful. Copolymerization of the acrylic acid6
Ind. Eng. Chem., Prod. Res. Dev., Vol. 16, No. 1, 1977
aconitic acid, maleic acid-itaconic acid, and maleic acidaconitic acid monomer pairs yielded products that were thought to be low molecular weight oligomers (based on high frequency titration data). Two copolymer series, poly(acry1ic acid-co-maleic acid) and poly(methacry1ic acid-co-maleic acid) were prepared with different monomer ratios to provide polyelectrolytes of similar chemical structures but with different charge densities. The carboxylic monomers, acrylic acid and maleic anhydride, were used to prepare several polyelectrolytes with various compositions via copolymerization with other monomers such as Nadic methyl anhydride, Nadic anhydride, styrene, vinyl acetate, thiophene, furan, and 2-sulfoethyl methacrylate. Two commercial samples were also added to the group of synthesized polyectrolytes; Acrysol A5 (polyacrylic acid) was obtained from the Rohm and Haas Co. and Gantrez AN-119 was received from the GAF Corp. The complete list of all the polyelectrolytes is contained in Table 11. Characterization of Polycarboxylic Acid Polyelectrolytes. Standard acid-base titrations with the use of an indicator are unsuitable for determining carboxyl equivalent weights of carboxylic acid polymers. Phenolphthalein, for example, was observed (21)to change its color anywhere in the pH region from 6 to 11 in the case of itaconic acid copolymers. Potentiometric titration has been used with partial success from the determination of the composition of certain copolymers containing carboxylic segments (22). However, difficulties were encountered in trying to locate inflection points on the potentiometric curves. Drougas, Timmick, and Guile recommended the use of high-frequency titration for the characterization of polydicarboxylic acid copolymers, namely itaconic acid-styrene and maleic acid,styrene copolymers (21). Their method allows the identification and approximate resolution of two carboxylate species in the same polymer. A similar high-frequency titration method used in this work proved to be a convenient and sufficiently accurate way to determine the carboxyl equivalent weights of carboxylic polyelectrolytes. No attempt was made to compare this method with conductometric titration methods. Evaluation of Polyelectrolytes f o r Detergent Builder Use. Substantial efforts have been made for years to develop a realistic test procedure for detergent evaluation and the difficulties in doing so have already been reported by Matzner et al. (2). Many techniques t,hat are in use at present attempt to simulate the every day laundering under controlled laboratory conditions (23). Such procedures generally employ a laboratory washing device to artificially launder soiled swatches of various fabrics. Parameters such as washing solution/fabrics ratio, water hardness, detergent concentration, temperature, length and intensity of agitation, rinsing, and drying conditions are appropriately selected to represent industrial and/or household laundering conditions. Evaluation is based on reflectance measurements made of the original and washed soiled swatches and also of the unsoiled fabric. Results are expressed in terms of percentage of soil removal. The success in obtaining a meaningful test method strongly depends on the proper selection of artificial soiling materials and their application to the test fabric. In view of the very large number of possibilities it is readily understandable that the choice of artificial soiling to be employed has a major role in determining the effectiveness of a particular detergent formulation. Detergent builders may be evaluated by substituting the builder component in a detergent control formulation of known performance with various experimental builders while
Table 11. Polyelectrolytes Synthesized o r Received a s Commercial Samples ~
Code name PE13 14 15 16 11
18 19 20 21 22
PE23 24 25 26 21
28 29 20
a
Composition
Code name
poly(AA-co-MA) poly(AA-co-MA) poly(AA-co-MA) poly(AA-co-MA) poly(AA-co-MA) poly(AA-co-MA) poly (AA-co-MA) poly(AA-co-MA) poly (AA-co-MA) poly (AA-co-MA)
(1:80) (1:ZO)
poly(MAA-co-MA) poly (MAA-co-MA) poly(MAA-co-MA) poly(MAA-co-MA) poly(MAA-co-MA) poly(MAA-co-MA) poly(MAA-co-MA) poly(MAA-co-MA)
(5:l)" (3:l) (2:l)
PE32 33 34 35 16
poly(MA) poly(AA) poly(MAA) poly(MA) PoMIA)
PE50 51 52 53
poly(SEM) poly(SEM-Co-MA) poly (SEM-co- AA) poly(SEM-co-MAA)
(1:lO)
(1:4) (1:2)
(1:l) (2:l) (3:l) (4:l) (5:l)
PE42 43 44 45 46 41 49 82 84
poly(AA-co-NMA) poly(MA-co-NMA) poly(AA-co-NA) poly (MA-co-NA) poly(AA-co-ST) poly(MA-co-ST) poly(MA-co-VA) poly(MA-co-TH) poly(MA-co-FU)
PE55 56
poly(AA-co-MA) poly (AA-co-MAA) poly (AA-co-MSA) poly (AA-co-IA) poly (AA-co- ACA)
51
58 59
(1:l)
(1:2) (1:3) (15) (1:lO)
Composition
PE61 66 61 68
poly(MAA-co-MA) poly(MAA-co-MSA) poly(MAA-co- IA) poly(MAA-co- AC A)
PE63 64
poly(MA-co-IA) poly(MA-co- AC A)
Acrysol A5 Gantrez AN-1196
poly(MA-co-VME)
Numbers denote the ratio of comonomers in the initial reaction mixture. Commercial products.
all other components and conditions remain unchanged. Testing the builders this way is lengthy and cumbersome and although the results indicate the practical value of a builder no additional information can be obtained about the nature of the chemical or molecular factors that were responsible. Consequently, Tokiwa and Imamura (24, 25, 26,27) preferred to employ a testing method which evaluated characteristic builder properties in well defined physical-chemical terms in order to afford a more rapid screening procedure for the evaluation of polyelectrolyte builders. This approach has been adopted in the present investigation. Alkalinity of Polyelectrolyte Builders. I t has been customary for the detergent industry to determine alkalinity and buffer capacity by acid-base titration. Due to the lack of a precise end point during titration, this method was unsuitable for polyelectrolytes. Therefore, the pH of a standard builder solution was used as a basis for comparing the alkalinity and buffer capacity of the experimental polyelectrolyte builders. The concentration of each standard builder solution was adjusted to 0.1% by weight to approximate the conditions prevailing in an average washing solution. Fully neutralized polyelectrolytes readily hydrolyze in aqueous solution to yield alkaline solutions. The pH values in Table I11 clearly show that poly(Na-monocarboxylate) type polyelectrolytes (PE34, PE56, and Acrysol A5) possess the lowest alkalinity and are comparable to that of Na5P3010. All other neutralized polymers approach the alkalinity of NaZC03 which is near the optimum p H of 10. The highest alkalinity is obtained with the poly(Na-dicarboxylate) type polymers (PE35, PE43, PE45) which also possess the highest charge densities. Poly(Na-itaconate) (PE76) has the lowest alkalinity in its class. The rest of the examples include poly(Na-monocarboxylate-co-dicarboxylate) and poly(Na-dicarboxylateco-diluent) type polymers displaying moderate alkalinity.
Table 111. Relative Alkalinity of Various Detergent Builders and Polyelectrolytes Builder
pH of a 0.1% by wt solution
12.0 12.5" Na2Si03.5H20 10.9 11.4O Na2C03 9.3 9.5" NasP301o 9.4b PE13 9.4 PE30 9.9 PE35 9.1 PE42 PE43 9.8 9.2 PE44 9.9 PE45 PE41 9.6 9.5 PE49 9.0 PE56 9.2 PE58 9.1 PE16 9.0 PE34 Gantrez AN-119 9.6 Acrysol A-5 9.0 PE51 7.8 " Measured in 1.0% solution. All polyelectrolytes are fully neutralized with sodium hydroxide ( a = 1.0).
The data imply that these polyelectrolyte salts possess sufficient alkalinity and moderate buffer capacity for use in general purpose detergents. Highly alkaline formulations would require the additional use of NaOH, Na2C03, or sodium silicates. Lime Soap Redissolving P o w e r of Polyelectrolytes. Polymers are widely used as both dispersants and flocculants. Ind. Eng. Chem., Prod. Res. Dev., Vol. 16, No. 1, 1977
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Table IV. Lime Soap Dispersing and Redissolving Power of Various Polyelectrolyte and Phosphate Builders a
Polymer PE64 PE68 PE32 PE35 PE76 PE43 PE45 PE62 PE63 PE13 PE17 PE22 PE23 PE26 PE30 PE42 PE44 PE57 PE58 PE59 PE66 PE67 PE51 Gantrez AN-119 PE40 PE41 PE47 PE49 Acrysol A-5 PE33 PE34 PE56 PE50 PE46 SHMP STPP SPP
Amount added, equiv x lo4 (per acidic H+) 30.0 30.0 6.0
5.0 3.2 15.8 8.0 30.0
30.0 9.2 20.2 30.0 30.0 30.0 9.4 25.0 17.8 30.0 6.6 30.0 30.0 30.0 30.0 22.0
Transmittance
