Performance of sulfoxylated fatty acid methyl esters - Springer Link

Performance of Sulfoxylated Fatty Acid Methyl Esters Leon Cohen* and Francisco Trujillo Escuela Politecnica Superior de Algeciras, Universidad de Cadiz, 11202 Algeciras, Spain

ABSTRACT: Sulfoxidation of fatty acid methyl esters with SO2, O2, and ultraviolet light of appropriate wavelength has led to the synthesis of methyl esters sulfonates or sulfoxylates known as Φ-MES because of the possible random position of SO3 group in the alkyl chain. This work describes experimental measurements of physical properties such as solubility and viscosity of sodium Φ-MES water solutions. Amphipathic properties such as surface tension, critical micelle concentration, wetting and foaming powers were measured as well and compared to linear alkylbenzene sodium sulfonate (LAS). Finally, stability to water hardness, dishwashing test, and detergency performance were evaluated. Expectedly, these products may be used as LAS partners either in heavy-duty powders or in hand dishwashing liquids. Experimental results on Φ-MES of varying carbon number indicate that C16 is the optimal carbon chain length. Paper no. S1113 in JSD 2, 363–365 (July 1999). KEY WORDS: Detergency, dishwashing test, foaming power, Φ-MES, performance, viscosity.

Sulfoxylated methyl esters (Φ-MES) are obtained via sulfoxidation of fatty acid methyl esters with SO2 , O2, and ultraviolet light of appropriate wavelength. In a previous paper (1) the synthesis and characterization of Φ-MES were described. Due to the mechanism of their synthesis via radicals, which may allow the introduction of the SO3 group in a random position along the hydrophobic chain (this needs to be demonstrated by further analysis research), Φ-MES can be viewed as new anionic surfactants with potential application in formulations for hand dishwashing liquids or for heavy-duty liquids. For the above-mentioned reasons, it was judged worthwhile to study the properties and performance of these products and to compare them with αMES and LAS (linear alkylbenzene sulfonate). This work refers to Φ-MES obtained through the preparation and purification methods depicted in Reference 1.

FIG. 1. Viscosity of sulfoxylated methyl esters (Φ-MES) at 20°C.

that Φ-MES are more efficient and effective than α-MES and LAS and that Φ-MES have a significantly lower CMC than LAS (made from linear alkylbenzene with an average molecular weight of 240) (1). (i) Viscosity. Determination of this property was done in a Haake RV-100 rotoviscosimeter (Haake Co., Karlsruhe, Germany) at 20°C. Results are shown in Figure 1. Viscosity values for Φ-MES samples are within 10 and 200 cen-

RESULTS AND DISCUSSION Physicochemical and surface properties. Surface tension and critical micelle concentration (CMC) measurements show *To whom correspondence should be addressed at Escuela Politecnica Superior, Avda Ramón Puyol, 11202 Algeciras, Spain. E-mail: [email protected] Copyright © 1999 by AOCS Press

FIG. 2. Solubility of Φ-MES prior to purification. See Figure 1 for abbreviation.

Journal of Surfactants and Detergents, Vol. 2, No. 3 (July 1999)

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L. COHEN AND F. TRUJILLO

FIG. 3. Solubility of Φ-MES after sulfates removal. See Figure 1 for abbreviation.

FIG. 5. Foaming power of Φ-MES and LAS. Anionic concentration 1 g/L. Temperature 49°C. See Figures 1 and 4 for abbreviations.

FIG. 4. Solubility of linear alkybenzene sulfonate (LAS). See Figure 1 for other abbreviation.

FIG. 6. Wetting power of Φ-MES. Anionic concentration 1.2 g/L. Temperature 20°C. See Figure 1 for abbreviation.

tipoises, thus meaning that they are low viscous liquids compared to LAS, 9500 cps at 30% active ingredient. (ii) Solubility. Krafft points, defined as the temperature at which a water solution of surfactant becomes turbid on cooling, were measured for different surfactant concentrations. As seen in Figures 2 and 3, the values are significantly different before and after the extraction of soap and inorganic salts such as sodium sulfates. In Figure 4, the Krafft point of two sodium LAS with 335 and 343 average molecular weights are shown for the sake of comparison.

(iii) Stability to water hardness. The method used to measure calcium ion tolerance was the UNE-55-507-72 Spanish standard equivalent to ISO-1063/79 (2). It consists of preparing five solutions with anionic concentrations given in Table 1. The solutions are prepared at different calcium ion concentrations expressed as calcium carbonate. According to the standard, a maximal value of 5 is given to a totally clear solution by visual observation, and a minimal value of 1 is given to a solution where abundant precipitate forms. Results for Φ-MESC16, represented in Table 1, indicate a very high tolerance to calcium hardness. (iv) Foaming power. The Ross-Miles test was conducted, and results are shown in Figure 5. Φ-MESC16 has the highest values among all Φ-MES and just slightly below LAS. (v) Wetting power. The Draves test was used (equivalent to ASTM-D2281/68) (3). According to the results shown in Figure 6, wetting power of Φ-MES increases with an increase in both molecular weight and water hardness. Detergency evaluation. (i) Dishwashing. The method gives a stability index for foam generated using a certain type of

TABLE 1 Stability of Φ-MESC16 to Water Hardnessa Φ-MESC16 Concentration of Ca2+ (g CaCO3/L) 5.00 2.50 1.25 0.62 a

Φ-MES, sulfoxylated methyl esters.

Hardness (°F) 20

30

45

60

5 5 5 5

5 5 5 5

5 5 5 5

5 5 5 5


PERFORMANCE OF SULFOXYLATED FATTY ACID METHYL ESTERS

FIG. 7. Dishwashing test of Φ-MES. Anionic concentration: 0.5 g/L, temperature: 49°C, soil: pig fat and olive oil. See Figure 1 for abbreviation.

365

FIG. 9. Detergency of Φ-MES. EMPA-104. Anionic concentration: 1.2 g/L, temperature: 30°C. See Figure 1 for abbreviation.

30°C for 20 min. Once concluded, the swatches were rinsed for 10 min in distilled water. Finally, the fabrics were dried with hot air. Detergency performance was then determined by measuring the reflectance of soiled fabrics on each swatch before and after washing. As shown in Figures 8 and 9, Φ-MESC16 gives the best results with EMPA-101; however, no significant differences appear with EMPA-104 between the three MES tested except at 300 ppm of CaCO3. Conclusively, the optimal MES is C16 as far as detergency is concerned.

REFERENCES

FIG. 8. Detergency of Φ-MES. EMPA-101. Anionic concentration: 1.2 g/L, temperature: 30°C. See Figure 1 for abbreviation.

soil at a definite anionic surfactant concentration (4). A correlation exists between the stability index and a hypothetical number of dishes washed according to the typical dishwashing manual test. Test conditions are shown in Figure 7. The conclusions that can be drawn indicate that the optimal chain length is C16–C18 for low and medium water hardness and C16 for higher hardness. (ii) Detergency performance. Detergency performance was done according to the ASTM-D-3080/75 (5) method with the following equipment and materials: Soiled fabrics were prepared by soiling EMPA-101 (cotton) and EMPA-104 (polyester and cotton) with carbon black and olive oil (10 × 10 swatches; EMPA, St. Gallen. Switzerland). A Terg-oTometer (U.S. Testing Co., Hoboken, NJ) was used for washing experiment. The test was conducted with six swatches of fabric per pot, containing a liter of washing liquor formed by water of a given hardness and a predetermined detergent concentration. Washing was done at

1. Cohen, L., and F. Trujillo, Synthesis, Characterization, and Surface Properties of Sulfoxylated Methyl Esters (Φ-MES), J. Surf. Deterg. 1:335 (1998). 2. International Standards Organization, ISO Standard 1063/79, Geneva, 1979. 3. American Society for Testing and Materials, Arlington, Method ASTM-D-2281/68, 1968. 4. Soler, J., Proceedings of the XV Jornadas del Comité Español de la Detergencia, Barcelona, 1984, p. 139. 5. American Society for Testing and Materials, Arlington, Method ASTM-D-3080/75, 1975. [Received October 27, 1998; accepted April 15, 1999]

Dr. Leon Cohen received his Ph.D. in chemistry at Sevilla University. In 1994, he earned the EURCHEM designation. He worked for Petresa from 1970 to 1996. He is currently a professor of chemical engineering at the University of Cadiz, where he is leading the research group entitled "Surface Activity and Detergency." He is the author of more than 25 papers related to detergency. Dr. Francisco Trujillo received his Ph.D. in chemical engineering at Cadiz University, where since 1980, he has been a professor of chemical engineering. He is currently the Director of the Escuela Politecnica Superior in Algeciras.
