Abstract
Sodium lauroyl isethionate is a popular, milder alternative to traditional soaps and surfactants in personal care formulations. Product performance, efficiency, color, and odor, however, can be compromised by thermal degradation at elevated manufacturing temperatures. Prediction of isothermal degradation rates in both air and N2 for a range of process conditions are determined using the Friedman isoconversional method. The thermal degradation levels in air are found to be 28 times higher than those in N2 over 5 h at 240 °C. Manufacturing under inert conditions, with maximum temperatures of 250 °C, is therefore necessary to avoid degradation levels significantly greater than 1 wt %. Using TGA-FTIR, the evolved gases from the degradation of sodium lauroyl isethionate are identified to be water, carbon dioxide, carbon disulfide, sulfur dioxide, as well as alkyl and carbonyl species. The ensuing temperature-dependent analysis can be used to minimize evolution of undesirable or hazardous gases in isethionate manufacturing processes.
Highlights
Surfactants are the primary ingredients in most personal care formulations
For ease of application and comparison, the current study focused on the KAS method for the integral acquisition of activation energy values
Mass loss (%) data was normalized in terms of the degree of degradation (α) where the end of the final degradation zone was designated as α = 1
Summary
Surfactants are the primary ingredients in most personal care formulations. They are present in shampoos, liquid cleansers, and soap bars to reduce the surface tension of water and aid in the solubilization of lipidic, sebaceous residues on the skin.[1]. The significant evolutions of alkyl species, carboxylic acids, CO2, and water vapor correspond with the gases produced from the thermal degradation of other long-chain organic molecules.[50,54,68,71] A decompositional study of SDS reported that the surfactant degraded to form primary alkenes, with characteristic C C vinyl stretches and general olefinic stretch reported to occur at 1640 and 1580 cm−1, respectively.[62] In the current study, the experimental spectra displayed very limited activity in these regions to confirm any substantial formation of volatile alkenes in the inert thermal degradation of SLI In reported evolved gas studies of long-chain organic materials, similar increases have been proposed to result from oxidative combustion, at the temperatures corresponding to the second and third degradation zones observed in the oxidative study of SLI (Figure 8).[68,73] due to the highly complex, interdependent nature of the radical reactions pertaining to all evolved gases observed in this study, further time-resolved analyses would be required to confirm the specific mechanisms most relevant to the thermal degradation of isethionate surfactants
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