Soil redeposition versus deposition tests in evaluation of laundry detergents

Whiteness retention results obtained with a soil “deposition” type test, in which soil material as such is added to the detergent bath, are found to be in contradiction to those obtained with soil “redeposition” tests, in which clean and soiled cloth are washed together. A carbon soil deposition test shows polyvinyl alcohol (PVA) and polyvinylpyrrolidone (PVP) to be superior to sodium carboxymethyl cellulose (CMC), and a polyethylene glycol (PEG) equal to CMC in improving whiteness retention results with a built anionic detergent, with pronounced synergistic effects for PVA-CMC and PEG-CMC combination. In contrast, the redeposition tests, employing either carbon black or tagged clay soil, show only the CMC to be effective, the nonionic polymers being ineffective alone and in combinations with CMC. Further, in evaluating the effect of tripolyphosphate builder with an alkylbenzene sulfonate, the deposition and redeposition tests give quite contradictory results. The observed contradictions cast considerable doubt on the validity of the usual carbon soil deposition tests, and emphasize the need for further study of whiteness retention test methods.     

Principles of performance testing of laundry detergents

Summary Laboratory performance tests for laundry detergents can fill important needs in laboratory development programs and in control testing, in which cases full scale practical testing is inapplicable. It has been found to be unnecessary and undesirable to attempt close simulation of practice conditions. In order to be most useful to the experimental investigator or the manufacturer of detergents the soil removal and whiteness retention properties should be measured by separate tests. A soil removal test has been devised in which the soil, which consists essentially of carbon black, is applied to the test fabric from aqueous medium. Soiling from aqueous medium has advantages with respect to reproducibility in tenacity and in variation and susceptibility to removal by detergents having different degrees of effectiveness. The quantity of soil removed is measured directly by means of light transmission measurements on the soiled detergent solution. This eliminates uncertainties and limitations inherent in the reflectance method and permits the use of high soil loads in the test cloth, which minimizes redeposition effects. Multiple wash tests are not required. The whiteness retention property is determined by agitating unsoiled swatches in the detergent solution containing carbon black dispersion and measuring the reflectance change of the swatches. The results of both tests are expressed in relative terms, reference detergents being used as controls. The precision of the soil removal tests is approximately ±3.4% in terms of mean deviation and that of the whiteness retention test approximately ±5.1%. Both tests have been used over a period of several years for research and control purposes and have been successfully correlated with actual results in commercial laundries. Presented at the fall meeting of the American Oil Chemists' Society, Chicago, Oct. 31-Nov. 2, 1949.     

Evaluation of detergents for washing fabrics

Various methods are used today to check the washing effect of detergents. They differ mainly in whether the cleaning assessment is determined by the use of artificially soiled test fabrics, anonymous naturally soiled laundry in a single wash test, or new family bundles in multiple use and wash test series. Correlation of the information based on the actual field behavior of the different methods is discussed. Applicability of the different systems will depend on the special conditions which call for abbreviated procedures. Multiple use and wash tests are very close to practical use, give information about cumulative effects and thereby allow the detection of small differences. Their disadvantages are high costs and length of time for the test. For a realistic evaluation from a consumer viewpoint, they are of little significance without a ranking scale correlating to consumers’ appraisal. Classification of tested products depends on the kinds of textiles in the family bundles which are used in the detergency evaluation. This factor is important in the detection of correlations between the two methods. For product evaluation and especially for overall quality ratings, the use of test fabrics is satisfactory if a carefully selected combination of these is chosen. Taking into consideration empirical data obtained with standard formulations, one can obtain satisfactory results corresponding to consumers’ appraisals. Stain removal and soil redeposition have to be given the same weight as soil removal. An overall investigation of possible correlations is lacking so that some uncertainties still remain.     

Detergency measurement using artificially-soiled cloths

Summary and Conclusions Four types of artificially-soiled cloths are compared in their ability to evaluate cleaning of representative detergent products. Three of these cloths are commercially available while the fourth is from a private laboratory. These are compared in their ability to rate detergents in the same order as naturally-soiled clothes rate detergents. Sensitivity and reproducibility of the various soiled cloths in measurement of soil removal and whiteness retention are studied. Results show that artificially-soiled cloths must be used advisedly. There is no substitute for actual performance tests of detergent products under practical conditions. At best, artificially-soiled cloths are useful for “screening” purposes where positive test results are confirmed by practical tests. Presented at the 25th annual fall meeting, American Oil Chemists’ Society, Chicago, Ill., October 8–10, 1951.     

Detergency evaluation. III. Adjustment of Terg-O-Tometer and launderometer wash test methods to produce comparable soil removal data

Conclusions It was demonstrated that the average soil removal values for the four 10-minute wash Launderometer method could probably be essentially duplicated by a single 3-minute Terg-O-Tometer wash and one 2-minute rinse. The 3-minute Terg-O-Tometer method did not result in the same comparative rating of four detergents, but a series of tests with several other detergents using a 5-minute wash and a 5-minute rinse (using for comparison purposes a standard detergent) resulted in quite effective ratings. Of 13 detergents tested over a period of time, the two test methods provided soil removal values identical within a 95% confidence limit. These data indicate that a satisfactory technique can be developed using the Terg-O-Tometer, which would provide soil removal values and ratings of detergents closely paralleling the results obtained by the Launderometer multiple-wash method.     

A laboratory method for testing laundry products for detergency

A laboratory screening test for fabric detergency has been developed, which closely parallels practical laundry operations. Natural airborne particulate is used so that the argument for and against carbon soil is eliminated. The oily soil consists of synthetic sebum, thereby simulating the surface film that covers the human integument. The particulate and fatty matter are combined into an aqueous suspension and padded onto the fabric. Variables can be measured in a minimum of time because the entire procedure is carried out in the laboratory and is not dependent on a panel of subjects as is the case in most practical testing. The procedure for this test as generally employed consists of multiple washes and measures brightener build up and redeposition in addition to detergency. Precision of the method is ± 0.4% at the 95% confidence level. Evaluations are made both visually and instrumentally.     

A realistic soil cloth and test procedure for detergent evaluation

The preparation of a uniformly soiled cloth for detergency studies is described. The soil, chosen for its realistic nature, consists of a colored clay as the particulate portion and triolein as the fatty or oily portion. The particulate portion of the soil is applied by tumbling the fabric in a horizontal axis washing machine containing a suspension of clay. The fatty portion is then applied by allowing the fabric to adsorb a known quantity of solvent-dissolved triolein with subsequent evaporation of the solvent. An evaluation test procedure for measuring the relative efficiencies of proprietary detergents is also described. Using this procedure, soil removal, soil redeposition and optical brightener effectiveness of a detergent are determined simultaneously. Detergents can thus be given a numerical rating according to their over-all performance. This rating is calculated from the equation: Overall Performance=Soil Removal−Soil Redeposition + Optical Brightener. Typical detergent evaluation data obtained with this soil cloth and test procedure are given, along with a statistical treatment of the data.     

The development of a particulate radioactive soil for detergency studies

A sample of kaolinite clay has been tagged by neutron irradiation. After an extended cooling period (18 months) to allow the short lived nuclides to decay, the clay is still sufficiently radioactive to use it in detergency studies. Extraction tests show that about 25% of the radioactivity is labile, i.e., removed by sodium tripolyphosphate but that the remainder is strongly fixed in the clay matrix, resisting extraction by built detergents. The clay has a number of nuclides emitting both beta and gamma radiation. Analytical methods for both types of radiation have been developed for use with fabrics and wash waters. The clay has been combined with the doubly labeled fatty soil (³H and¹⁴C) to make a triply labeled particulate soil. Tergotometer runs with three test fabrics show good precision for all three labeled components of the soil. Redeposition measurements were also made and showed that a considerable fraction of the residual clay on a washed swatch may in fact be due to redeposition rather than retention. Some problems remain in the application of this synthetic soil: the padding step must be modified so that the clay is more tenaciously bound to the fabric; a more automatic method of padding is required to handle large numbers of samples; the specific activity of the clay should be increased so that liquid scintillation analysis for all three tagged components can be made on a single sample of wash water. Presented at the AACC-AOCS Joint Meeting, 1968, Washington, D.C.     

A natural soil and mechanism of removal: Part II

Based on the findings of interaction between dodecyl benzene sulfonate (DBS) and high molecular weight nitrogen compounds in natural soil in the first report of this series, artificially soiled clothes containing protein were prepared and a washing test was carried out with a use of DBS or nonyl phenol-polyoxyethylene adduct (NPEO). Cattle serum globulin, cod sperm protamine and feather keratin of wild duck were used as protein. The built DBS detergent showed better detergency on the artificially soiled clothes than the built NPEO detergent at a same surfactant concentration of 0.05%, although no difference was observed in the redeposition test between these detergents. A significant dissolving action of DBS was observed. Results indicate that when discussing the mechanism of dissolution of natural soil or in the course of modifying the artificially soiled clothes, a chemical reaction between DBS and protein had to be considered in addition to the well known physico-chemical surface activity of the surfactant for removal of soil.     

Novel Route of Producing Zeolite A Resin for Quality‐Improved Detergents

Most of the commercial manufacturers of soap and detergents are still using sodium tripolyphosphate and trisodium phosphate as the builder material which results into eutrophication through laundry. Phosphate mainly originates from detergents and affects the aquatic ecosystem severely. This may increase decomposer organisms that require oxygen, which can deplete the amount of oxygen dissolved in the water. To remedy this, many leading detergent manufacturers currently use zeolite A as the builder material which has proven to be a better substitute for phosphatic additives. Zeolite A is a three‐dimensional crystalline aluminosilicate resin having a high exchange capacity towards ions that cause water hardness. In spite of this tremendous potential, the high cost of zeolite A has limited its effective use in detergents. The specific objectives of this study were to synthesize zeolite A resin in a more economically viable fashion using waste material, a composite ash, which is the post‐combustion residue of rice husk blended with coal, and to formulate an eco‐friendly phosphate‐free detergent powder using the same. The studies also focused on evaluating its detergency action by analyzing moisture content, foam height, surface tension, tea/coffee stain test along, and alcohol solubility. The results show that the synthesized detergent has comparable detergency to two known commercial brands of detergent. This economical synthesis combined with the exceptional parameters of zeolite A resin, such as fine particle size, high exchange capacity, inert nature, and anti‐redeposition properties, makes this detergent an elite and cost‐effective product.     

Consumer testing liquid syndets. II. Biodegradable formulations

The results of experiments investigating the interrelated effects of biologically degradable nonionic and anionic synthetic detergents in a light duty liquid detergent are presented. The formulations studied explore the performance of various biodegradable nonionic candidates in the presence of a fatty based alkylolamide foam stabilizer and biologically “soft” alkyl aryl sulfonate at two levels of nonionic concentration. The nonionic detergents evaluated are all polyoxyalkylated, including products of natural and synthetic origin. Products based on unsaturated and secondary alcohols are included. Consumer and laboratory test data show that biologically degradable detergents cannot be directly substituted in formulations without first testing their effect on the formulation itself. The data also show that small differences in molecular weight or in saturation of the materials being used can be reflected materially by technical differences in the finished product. These differences are manifested by analytical determination, by consumer panel evaluation using a duplicated balanced incomplete block design, and by standard dishwashing evaluation. The consumer panel data relate to dermatological properties, general performance and suds stability. It is obvious that the big switch to biologically degradable surface active agents is not as smooth a changeover as had been hoped, this being especially true for smaller producers of chemical specialties who do not have extensive facilities for formulation testing. These data do, however, indicate that with a careful experimental approach and judicious experimentation that formulations having a performance superior to their nonbiodegradable counterparts can be prepared. It is also stressed that judiciously designed consumer panel evaluations can yield data that is just as precise and valid as can be obtained through some of the more sophisticated testing procedures that require investment in equipment and in training of test panels. Presented at AOCS Meeting, New Orleans, April 1964.     

Establishment of a standardized detergency evaluation method

This paper describes a standardized laboratory procedure for determining the fabric soil-removal efficiency of heavy-duty detergents. A careful analysis of machines, standard soil fabrics, operating times, and water hardness had led to the standardization of technique. The precision of the method has been presented for tests carried out in hard and soft water on two anionic heavy-duty detergents at a concentration of 0.2%. Standard deviations of 0.74% for a water hardness of 50 p.p.m. and 1.03% for a water hardness of 135 or 300 p.p.m. have been obtained. Paper I in a series entitled: “Detergency Evaluations.” Presented at spring meeting, American Oil Chemists' Society, St. Louis, Mo., May 1–3, 1961.     

A kinetic study of fabric detergency

The kinetics of soil removal were investigated under domestic laundry conditions by incorporating small swatches of four artificially soiled test fabrics into a standard load of clean cotton goods. This prevented soil redeposition from affecting the soil removal rate. Two runs were analyzed, one with an anionic and the other with a nonionic detergent. Assessment of the amount of soil remaining on the fabric was made by reflectivity measurements interpreted according to the Kubelka-Munk equation. First-order kinetics were found to prevail for periods ranging from the first 6 min of the wash cycle to the entire 20 min, depending upon test fabric and detergent. For these lengths of time, the rate of soil removal was directly proportional to the amount of soil remaining on the fabric. The 8 first-order rate constants had rather similar values, varying at most by a factor of 2.3. The average value, 0.109 min⁻¹, corresponds to a 6.4-min wash period for removing one-half of the soil and to a 21-min period for removing 90% of the soil from the soiled fabric. The magnitude of the response of the four artificially soiled test fabrics to the two detergents is compared and discussed in terms of the soiling materials. The nonionic detergent was more effective in cleaning a fabric soiled mainly with kaolin and wool fat, while the anionic detergent was more effective with a fabric containing large amounts of liquid oily soil plus carbon black and oleophilic bentonite.     

Consumers are the final product judges

Consumers repurchase detergent products based upon satisfactory performance in their homes. While laboratory tests are essential tools to help develop detergents to meet consumer needs, they cannot totally reflect the real world of in-home experiences with its multitude of variables. The need to update laboratory test methods continually to account for changing lifestyles, consumer practices, and trends in related industries will be discussed, as will the pitfalls of relying solely on laboratory tests to try to predict whether product performance answers consumer’s needs.     

Lipid distribution on cotton textiles in relation to washing with cellulase

Enzymes are used widely as effective additives to laundry detergents for improved detergency on soiled fabric. They have potential for cleaning of “dingy” soils in addition to the stain removal benefits. Cellulases contribute to the overall whiteness of cotton-containing textiles when worn and washed several times, meaning that their cleaning is not associated solely with the regions characterized by high amounts of fatty material, e.g., collars/cuffs. The focus of this research was to study further the performance of cellulases for whiteness maintenance of cotton textiles. Cotton garments soiled by multiple wearings and washed using a cellulase treatment were evaluated using scanning electron microscopy and X-ray microanalysis. Washing with cellulase significantly reduced residual soil concentrations at all morphological locations on the cotton fibers for each set of matched garments. The relative concentrations of residual soil on the fabrics agreed well with the color differences measured at 440 nm. Cellulase affected removal of oily soil from within the cotton fiber secondary wall, resulting in residual oil concentrations similar to those at morphological locations that were more accessible for detergency such as the fiber surface and crenulations. Since cellulase hydrolyzes cellulose, it was expected that the effect would be within the structure of the fiber, i.e., secondary wall. The cellulase effect on redeposition garments was similar to garments worn and washed. As with lipase, the enhanced removal of soil from the interior bulk structure of the cotton fiber with use of cellulase is unique, since most other detergent components have higher functionality at fabric, yarn, and fiber surfaces. We think that cellulase is functioning by hydrolyzing cellulose from the internal surfaces of fibrils within the secondary wall, opening up the pore structure for enhanced detergency and forming a new surface with each washing.     

The safety of household products

When detergents were essentially soap, it was easy to assume that they were perfectly innocuous in use. Even later, when synthetic actives and phosphate builders appeared, it wasn’t necessary to carry out extensive testing to confirm their safety. However, nowadays one has to say with certainty that a detergent product is not only safe to use but also to manufacture and release into the environ-ment. This is a big, often long and expensive, job. A battery of tests have had to be developed and every likelihood covered as far as pos-sible. The kinds of tests used will be briefly discussed and examples given of the lengths to which manufacturers go to ensure the safety of our products.     

How do soil P tests,plant yield and P acquisition by <Emphasis Type="Italic">Lotus tenuis</Emphasis> plants reflect the availability of added P from different phosphate sources

The relative effectiveness (RE) of each one of three different sources of P—P in solution (Psol), triple superphosphate (TSP) and phosphate rock (PR)—for reflecting the availability of P in a P-deficient soil were assessed by measuring in Lotus tenuis variables associated with growth, organ morphology, and plant tissue P-content together with the amounts of P extracts from soil by two of the currently used soil-P tests—Bray I and Olsen. A hyperbolic equation was used to fit the response curves of each one of those plant variables to added-P. The ratio between the shapes of paired response curves of any P-sources was used to compute the RE and substitution rate (K) of one source relative to the other. More P was needed from TSP and PR compared to Psol-100% soluble P-source. On the average P applications as TSP relative to Psol and PR relative to TSP were only 68 and 63% effective respectively for plant growth. Plant roots were more sensitive than soil-P tests to detect shifts in P-availability from different P-sources. Because soil tests are commonly used to estimate the current P status in soil in order to calculate the optimum application levels of fertilizer P for a crop or pasture, these results would have practical agronomical consequences if reproduced in other cultivated species because they show that the response curve of a plant species as a function of added P and soil test might differ among fertilizer types, measured plant variables, and the test used to measure P availability in the soil.     

New accelerated test for rapid measurement of detergent biodegradability

A new accelerated biodegradation test has been developed in order to determine rapidly the biodegradability of detergents. Natural river water is fortified with additional microorganisms isolated from sewage effluent by continuous centrifugation to remove residual detergent. This increases the reproducibility between different samples of river water and decreases seasonal effects. Using detergents of different chemical structures, this accelerated procedure gave the same biodegradable results as obtained with the usual river die-away test. However, such data can now be obtained in as little as ten days or less. Multiple test results are presented showing the rate and degree of biodegradation of representative test detergents and the reproducibility between different series of tests with the same compound. Examples are given showing that the extent and completeness of biodegradability of the test compounds depends on the degree of branching.     

Change‐point detection in panel data

We consider N panels and each panel is based on T observations. We are interested to test if the means of the panels remain the same during the observation period against the alternative that the means change at an unknown time. We provide tests which are derived from a likelihood argument and they are based on the adaptation of the CUSUM method to panel data. Asymptotic distributions are derived under the no change null hypothesis and the consistency of the tests are proven under the alternative. The asymptotic results are shown to work in case of small and moderate sample sizes via Monte Carlo simulations.     

Assessing detergent safety: A comparison of a nonphosphate laundry detergent with phosphate detergents

The potential hazard of a carbonate-based, phosphate-free detergent was compared with that of a variety of granular and liquid phosphate detergents. Evaluations were made using methods prescribed by the Federal Hazardous Substances Act (FHSA) and others designed to more closely approximate exposure in actual use. Some phosphate products produced esophageal and gastric mucosal irritation similar to that produced by the nonphosphate detergent, while others caused varying, lesser degrees of injury. The nonphosphate detergent, as well as several phosphate products, was seriously irritating to the unwashed eye at required FHSA test levels. Under more realistic conditions, eye irritation was reduced significantly. Skin irritation by the nonphosphate product was comparable to that by phosphate detergents, and in some cases was lower. In skin irritation tests with human subjects, results with the carbonate detergent were equal to or lower than those obtained with phosphate detergents. The carbonate detergent was found not to be phototoxic, nor a contact- nor photo-sensitizer. Total alkalinity was shown not to correlate with the severity of tissue injury in either test animals or in man. Presented at the AOCS Short Course, “Update on Detergents and Raw Materials,” Lake Placid, New York, June 1971.