A wet method for pure particulate soiling of test cloths for detergency screening tests

A procedure is presented for soiling detergency test cloths with particulate soil. These cloths offer advantages over most commercial soiled cloths and laboratory soiling procedures in that there is no oily material necessary for dispersion and thereby the testor obtains results which are specific to particulate soil alone. The procedure involves a wet soiling technique, followed by drying and sorting for subsequent detergency evaluation. The soil composition includes Bandybalck clay, iron silicate, and iron oxide. Detergency results are discussed.     

Soil removal as a rate process

The rate of soil removal during multiple cycle washing has been studied for three artificially soiled cotton test cloths. Results are considered in relation to a soil removal rate concept proposed some years ago by Vaughn, Vittone, and Smith. It is shown that the rate of removal for these soils, when washed in the Terg-O-Tometer with a built, anionic, synthetic detergent, does not correspond to a simple first order rate process as proposed by Vaughn et al. Rather, it was found that under a variety of washing situations the percentage soil removal increased linearly with the log of cumulative wash time. Further, it was shown that for those experiments involving detergent concentration or level of mechanical action, the slopes of these log time relationships, which reflect the rate of soil removal, vary in the expected manner.     

Detergency study of the synergism between oily and particulate soil on polyester/cotton fabric

The removal of multiphase, multicomponent soils from fibrous substrates depends upon the nature of the soil mixture, the order of application, wash temperature, and type of detergent formulation. By studying these factors, we investigated the synergism between residual oil (triolein) and particulate soil (clay) on a durable press polyester/cotton fabric after laundering with four different detergents at wash temperatures of 27 and 49 C. To probe the interaction between clay and oil, fabric specimens were soiled with clay only, triolein only, clay followed by an application of triolein, and triolein followed by an application of clay. Four detergent formulations were used to launder the soiled fabrics, including one unbuilt liquid and three powdered detergents with different builder systems. The amount of residual oil (triolein) was determined by radiotracer technique, and the quantities of clay were determined by measuring aluminum by neutron activation. Reflectance measurements were used to calculate fabric whiteness. The soil distributions on and within the textile structure were obtained by scanning electron microscopy using backscattered electron images, secondary electron images and X-ray mapping. Osmium tetroxide was used to tag the oil, while silicon was the elemental tag for clay in the microscopic analysis. Results of the four factors studied can be summarized as follows. (i) In agreement with observations by previous researchers, a mixture of clay and oil is more difficult to remove than either the oil or the clay applied singly. It appears that oil acts as a matrix to bind clay, forming a composite soil. (ii) The specimens that were soiled first with oil and then clay had more soil removed by laundering than the specimens soiled with clay and then oil. Detergency was limited by the encapsulation of clay by the oil and adsorbtion of oil by the clay. (iii) The built powdered detergents were temperature sensitive, while the unbuilt liquid detergent was not. (iv) The built powdered detergents removed more soil (oily and clay) than the unbuilt liquid detergent.     

Nonbuilt heavy duty liquids: Detergency and formulating parameters

The detergency of nonbuilt heavy duty liquids containing linear alkylate sulfonate and/or linear alcohol ethoxylate nonionic active is discussed. Single cycle detergency on a broad range of linear alkylate sulfonate-nonionic compositions was evaluated on cloths soiled in the laboratory with a mixture of synthetic sebum and dust and a commercially available soiled cloth, ACH #120A. The effects of multiple cycle wash testing also were covered. Formulating parameters to produce usable nonbuilt heavy duty liquids are discussed. The nonionic of choice for maximum detergency in nonbuilt heavy duty liquids should be derived from ca. a 14 carbon chain length alcohol with ca. 70% ethylene oxide. For optimum solubility, linear alkylate sulfonate should be the sodium salt derived from a linear alkylbenzene of ca. 235–240 mol wt, a product like that currently used in light duty liquids. The presence of linear alkylate sulfonate in nonbuilt heavy duty liquids helped reduce product clear point. Nonionics were found to give the best performance on cotton cloth. Linear alkylate sulfonates were most effective on synthetics. Multiple cycle testing with Spangler soil on nonbuilt heavy duty liquids was shown to be unnecessary. Mixed active systems gave the best overall product on the basis of performance and physical properties.     

Lipid distribution on textiles in relation to washing with lipases

Effectiveness of lipase in detergency was studied using three test soils (lard, artificial sebum, and olive oil) on a woven cotton fabric. Distribution of oily soil on fabrics was determined for three different treatments (unwashed, washed with detergent without lipase, and washed with detergent plus lipase). Osmium tetroxide was used to label lipid soil for analysis in the scanning electron microscope. Both longitudinal and cross-sectional backscattered electron images for unwashed samples showed that soil was present on surfaces of the cotton fibers and in interfiber spaces of the yarn bundle. Lard soiled samples had large deposits on the fabric surfaces, while artificial sebum and olive oil appeared more uniformly distributed throughout the textile. Oil was deposited in the interfiber capillaries of the yarn bundle and in the crenulation, secondary walls, and lumen of the fibers. Energy dispersive X-ray microanalysis was used to determine relative concentrations of oil at selected morphological locations within the fiber structure and at the fiber surface. Soil distributions within the fibrous structures differed with type of soil and laundry treatment. Backscattered electron images dramatically demonstrated the effect of lipase on cleaning. After washing with detergent plus lipase, yarn surfaces had much less residual soil; residual soil that remained was in the irregularities of the cotton fiber surfaces. Concentrations of oil in the secondary walls, crenulations, lumen, and the fiber surfaces were lower after lipase treatment for all three soils. While washing with detergent removed soil from the yarn and fiber surfaces and the crenulation of the cotton fiber, only the samples washed with detergent plus lipase had lower concentrations of soils within the secondary wall and lumen of the cotton fibers. Fabrics soiled with olive oil and washed with detergent plus lipase had the lowest concentrations of residual soil across the textile structure; the residual soil observed was mainly in the irregularities on the fiber surfaces.     

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.     

Mechanistic Studies of Particulate Soil Detergency: II: Hydrophilic Soil Removal

In this work, the removal mechanism of kaolinite and ferric oxide (model hydrophilic particulate soils) from hydrophilic (cotton) and hydrophobic (polyester) fabrics was studied using three surfactant types: sodium dodecyl sulfate (SDS), octylphenol ethoxylate (OP(EO)10), and cetyltrimethylammonium bromide (CTAB). This work investigated the relations between zeta potential, surfactant adsorption, contact angle, solid/liquid spreading pressure, and dispersion stability in washing solutions as compared to detergency performance and antiredeposition as a function of surfactant concentration and pH level. The SDS showed the best detergency for both particulate soils, followed by OP(EO)10, with CTAB being the least effective surfactant. For SDS, the electrostatic repulsion between fabric and soil was found to be the dominant force for hydrophilic particulate soil removal. For the nonionic surfactant OP(EO)10, electrostatics are also important and steric effects aid particulate soil detergency. Electrostatic forces and solid/liquid interfacial tension reduction aids CTAB detergency. These same detergency mechanisms have previously been found for the case of hydrophobic soil removal from fabrics. Dispersion stability did not prove to be a dominant mechanism governing particulate soil detergency. From the SEM photos of soiled fabric, ferric oxide attaches to the fabric surface with no entrapment between fabric yarns; moreover, ferric oxide tends to form larger aggregates on cotton compared to polyester fabric. The adhesion of larger particles is hypothesized to be weaker than the smaller ones. Therefore ferric oxide can be more easily removed from cotton fabric than polyester. The SEM photos for kaolinite show little visual difference in particle agglomeration on polyester compared to cotton. Removal of kaolinite from cotton was found to be higher than from polyester, but there is less difference than for ferric oxide.     

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.     

An intelligent washing machine for the evaluation of laundry detergents

A computer-controlled washer can be programmed to evaluate automatically a large number of washing compositions for soil removal. Variable amounts of as many as six different detergent components are added with metering pumps. A continuous roll of soiled cloth passes through a washer and past a reflectance meter onto a take-up reel. Washing action is provided by a vertical reciprocating shaft attached to a plate which rubs on the fabric while tension is maintained by a spring-loaded roller. The length of the wash, number of rinses and addition of components is controlled by the computer program. Upon completion of the wash and rinse cycle, the fabric is advanced about 10 cm. Washed areas appear as lighter colored bands on the fabric. In one mode of operation a large factorial experiment is programmed in advance. After an initial calibration of metering pumps the apparatus runs unattended. In another mode, the computer receives feedback from the reflectance meter and a simplex procedure is used to determine the direction of maximum cleaning. Following the execution of a small number of initially programmed washes, the computer selects the succeeding wash compositions. Presented at the 73rd AOCS annual meeting, Toronto, 1982.     

Soap-based detergent formulations: X. Nature of detergent deposits

The cumulative deposition of detergent residue on unsoiled cotton and polyester-cotton permanent press finish cloth was determined for a variety of detergent formulations after washing 25 consecutive times in 300 ppm hard water in a laboratory Tergotometer. Included in this study were: a phosphate-built laundry detergent, two carbonate-built detergents, tallow soap and various tallow soap formulations with anionic and amphoteric lime soap dispersing agents, and a glassy sodium silicate. Sample swatches washed with each formulation were analyzed for calcium, magnesium, and organic acid content. Fabric washed with the carbonate detergents showed the highest calcium and magnesium content, while those washed with the phosphate detergent and the soap-lime soap dispersant-builder formulations had the lowest. Fabric washed with soap alone had a much higher fatty acid residue than those washed with the other detergent formulations. However, the amount of organic acids left on the fabric after washing with a soap-lime soap dispersing agent formulation was no greater than that produced by phosphate- and carbonate-built detergents. The presence or absence of deposits also was verified visually with a scanning electron microscope. Each formulation also was tested for detergency by measuring the soil buildup in a multiwash procedure. Generally, the buildup of soil paralleled the deposit of detergent residue on the unsoiled cloths.     

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.     

Mechanism for the anti-redeposition action of sodium carboxy-methyl cellulose with cotton. IV. Practical-scale tests

A variety of cotton articles—such as tea towels, hand towels, and sheets—and test cloths, both cambric and sheeting, have been washed in a ‘Hotpoint’ Empress washing machine in a heavy-duty detergent product containing radioactive sodium carboxy-methyl cellulose (SCMC). There was good agreement between the results of laboratory tests using small discs of fabric and results of the practical test. Even when the cotton fabrics had been pre-washed up to 25 times in a product containing SCMC, some SCMC was still adsorbed (up to 40 μg/g of fabric) in each wash. It is suggested that in each wash some SCMC desorbs from the fabric and is replaced by SCMC adsorbed from solution.     

Improvement of cotton cloth soil removal by inclusion of alkaline cellulase from Bacillus sp. KSM-635 in detergents

Alkaline cellulase from Bacillus sp. KSM-635 (EC 3.2.1.4) had reproducible detergent effects on cotton cloth that was artificially or naturally soiled with oily and/or particulate matter, under European washing conditions. The detergent effects of the cellulase, in combination with surfactants, apparently were the result of enzymatic action on amorphous regions of cotton fibers in which soil was trapped. The contribution of cellulase to soil removal increased as (i) the amount of soil in the amorphous regions of fibers in test fabrics was increased and (ii) the inhibition, by soil that adhered to the fibers' surfaces, of the action of the cellulase on fibers was reduced. Alkaline cellulase had the potential to replace, in part, both surfactants and zeolite in detergents, and it reduced washing time and allowed washing at lower temperatures under European washing conditions. The marked detergent effect of cellulase on naturally soiled cotton fabric was visually apparent, and it inhibited the accumulation of ash, calcium, and other inorganic components on cotton fibers during wash-and-wear cycles. These contributions of cellulase to the cleanliness of cotton fabrics were clearly increased by repeated wash-and-wear cycles. Cotton fabrics were not degraded by washing with the cellulase because effective hydrolysis by the cellulase occurred only in the amorphous regions of cotton fibers.     

A natural soil and mechanism of removal

Nitrogen compounds in natural soils are studied in relation to their effect on the soil removal mechanism in detergency. Nitrogen compounds in various forms and in fairly large amts are found in natural soils, and more than 24% of these nitrogen compounds are presumed to be high mol wt nitrogen compounds or proteins. These high mol wt nitrogen compounds which cannot be removed by water can be removed by the detergent action of sodium dodecyl benzene sulfonate (DBS). When the detergency of DBS was compared with nonyl phenol-polyoxyethylene adduct, the detergency for artificial soil cloths did not coincide with results obtained with naturally soiled cloths. These data suggest that some interaction between DBS and nitrogen compounds might have contributed to the detergent action. If proteins were added to the present artificial soil formulation, better correlation might be expected between artificial and natural soil detergency results in DBS evaluation.     

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.     

A double label radiotracer approach to detergency studies

The comparative detergency of a series of built detergents of commercial interest has been measured via the use of a doubly labeled multicomponent synthetic soil. Four test fabrics: cotton, nylon, Dacron, and Dacron/cotton were soiled with the seven-component soil, which was in turn almost completely and then individually labeled. The fabrics were washed in a conventional Tergotometer under cold-water and hot-water conditions. Analyses of the fabrics before and after washing were made by liquid scintillation counting. Two sets of experiments were run, the first based on cold-water detergent formulation (heavy-duty liquid), the second based on hot-water detergent formulation (heavy-duty powder). A number of nonionic surfactants were compared with linear alkyl aryl sulfonate in the first set, and two anionics were compared with two nonionics in the second set. Expressing results as total detergency, i.e., amount of soil removed from all four fabrics, it was found that, under cold-water conditions, LAS (average side chain C₁₃) is significantly less effective than the nonionics investigated. The linear primary alcohol (C₁₂-C₁₅ and C₁₄-C₁₅) ethoxylates removed slightly more soil than the ethoxylates of a Ziegler alcohol (C₁₄, C₁₆, C₁₈) and random secondary alcohols (C₁₁-C₁₅). The same tabulation for the heavy-duty powder formulations under hot-water conditions showed LAS to be least effective over-all, sulfated linear primary alcohol somewhat more effective, and ethoxylated linear, primary alcohol slightly more effective still. Redeposition of the various soil components onto unsoiled cotton was found to be slight, ranging from 0.2% to 1.7% of the amount in the wash water. Presented at the AOCS Meeting, Philadelphia, October 1966. US Testing Service, Hoboken, N. J.     

Studies on replacement of phosphate builders in laundry detergents using radiolabeled soils

The fabric detergency performance of systems containing different types of surfactants and several builders of reduced phosphate content has been compared using a radiolabeled sebum-clay soil. Use of this soil allows quantitative measurement of both sebum and clay removal from soiled swatches, generally cotton and permanent press Dacron-cotton. One study compared alkylbenzene sulfonate (LAS), alcohol sulfate (AS), alcohol ethoxysulfate (AEOS) and alcohol ethoxylate (AEO) as surfactants in formulations containing from 0–45% sodium tripolyphosphate (STPP). Especially under hard water conditions, the AEO and AEOS considerably out-perform the LAS and AS at equal use concentrations and are less sensitive to phosphate reduction. Tests with cotton swatches soiled with five different carbon black-oil mixtures generally rank the surfactants in the same order, although individual responses of the cloths vary considerably. A further study compares the effect of replacing STPP with sodium nitrilotriacetate (NTA) in formulations containing varying amounts of AEO or LAS. Detergency improves significantly with increasing surfactant concentration, particularly with AEO, and declines as builder strength is reduced. AEO exceeds LAS considerably in performance under the test conditions even at relatively high concentrations of LAS. Another study compares the performance of AEO and LAS at equal concentrations in formulations containing a variety of builders. AEO is generally superior to LAS in removing both sebum and clay soils and is less sensitive to builders and water hardness. The builders generally rank in this order: STPP > NTA = citrate > carbonate > sulfate. Presented at the AOCS Short Course, “Update on Detergents and Raw Materials,” Lake Placid, N.Y., June 1971.     

New detergent mechanism using cellulase revealed by change in physicochemical properties of cellulose

Sebum in naturally soiled cotton undershirt and oleic acid in artificially soiled cotton cloth, which entered interfiber space in the interior of cotton fibers were easily removed by alkaline cellulase fromBacillus sp., but only with difficulty by commonly used detergent ingredients such as surfactant and protease. Adsorption isotherms and the rate of hydrolysis of alkaline cellulase against insoluble cellulose powders revealed that the lower the relative crystallinity of cellulose powder, the more adsorptive alkaline cellulase became and the more hydrolysis was promoted. With alkaline cellulase, cotton having the highest relative crystallinity was adsorbed at pH 9 and 5°C, liberated a negligible small amount of reducing sugar at pH 9 and 40°C, and produced no changes in the degree of polymerization of cotton cellulose and in the tensile strength of cotton fabric at pH 9 and 30°C. On the other hand, differential scanning calorimetric studies revealed that under similar conditions even a small quantity of alkaline cellulase drastically reduced the amount of water bound to cellulose in cotton. Because water was bound only with hydroxy groups of cellulose molecules in the amorphous region of cotton fibers, it can be understood that soil entering the interfiber space of amorphous interlamellae in the interior of cotton fibers, was easily removed as the hydrated cellulose in the interlamellae was slightly hydrolyzed by alkaline cellulase. A new detergent mechanism is proposed.     

Cold water detergency studies using radiolabeled soils

The effects of single and multiple washing and of resoiling-rewashing of cotton and synthetic fabrics have been studied in Tergotometer tests at various levels of temperature, detergent concentration and water hardness. The soiling mixture consisted of a seven component sebum tagged with tritium and carbon-14; in some tests gammaray emitting Kaolinite clay was also used. Linear primary alcohol ethoxylate (LAEO) and linear alkylbenzene sulfonate (LAS) were used for surfactant type comparisons. In single wash tests in both hot and cold water, LAEO was generally more effective than LAS in removing sebum. This was particularly noticeable at low product concentration where insufficient sodium tripolyphosphate was present to sequester the water hardness. A 1/1 blend of the two surfactants approached LAEO in performance. The nonpolar sebum fraction was more readily removed from Dacron or nylon in cold water; otherwise, detergency was generally better at high temperatures. In rewash tests, using labeled lube oil, cholesterol and clay, a progressive increase in soil removal was found during five wash cycles. The nonpolar lube oil component was the most difficult to remove from permanent press Dacron-cotton (PP), but was more readily removed from cotton. The more polar cholesterol and especially the clay were more easily removed from PP. LAEO gave better detergency both hot and cold than LAS, especially in hard water. On cotton swatches resoiled with sebum after each wash the residual sebum content was still increasing after five cycles. With PP in soft water, a steady state was reached after three to five cycles. Soil buildup was greater as hardness increased and as wash temperature and active matter concentration decreased, and was generally greater on cotton than on PP. LAEO allowed appreciably less soil buildup than did LAS especially at low concentration in hard water, indicating a reduced requirement for sodium tripolyphosphate. Presented before the AOCS Meeting, New Orleans, April 1970.