Performance of straight-chain alkylbenzene sulfonates (LAS) in heavy-duty detergents

The foamability (dishwashing and washing machine) and detergency of LAS in heavy-duty detergents is directly compared with polypropylenė ABS (PPABS) at various mol wt, conen, water hardnesses and temp. In every case a peak in performance is obtained in the C₁₁ to C₁₇ side chain range. The peak is shifted to lower mol wt as water hardness is increased, especially at low detergent conen. LAS opt performance is generally equal to PPABS, except in dishwashing foam in soft water. The LAS peaks, however, are shifted to ca. one carbon lower mol wt than the PPABS. Therefore, best over-all performance is obtained for LAS whose average mol wt corresponds to a 12.5 carbon side chain, whereas PPABS is best with an average 13.5 carbon side chain. Dishwashing foamability is markedly different for the different isomers contained in LAS. When the phenyl group it attached to the middle of the alkyl chain, surprisingly high results are obtained. This dishwashing difference is great enough to be noticeable when the isomer distribution changes in whole products made using different alkylation catalysts. Detergency and washing machine foam are not affected enough to see differences between whole alkylates. LAS solubility is greater than PPABS and is influenced by isomer distribution. Present address: W. Reg. Res. Lab., USDA, Albany, Calif.