A Review and Further Exploration of the Usefulness of the HLD Equation to Predict Detergency

The hydrophilic–lipophilic difference (HLD) equation has been explored as a guide to help formulate for maximum cleaning in commercial laundry detergents. A short review shows that, with anionic surfactants, there is a range roughly between HLD = 0 and HLD = −3 where detergency is maximum. New work occurred using three different soils: sebum, meat gravy, and coconut oil. One anionic (alcohol ether sulfate, AES) and three nonionic surfactants (alcohol ethoxylates, AEs) were included on two different substrates: cotton and a 65/35 polyester/cotton mix. To our knowledge, a correlation between HLD and detergency for nonionic surfactants has never been explored. For the AES and two of the soils, sebum and coconut oil, a range between HLD = 0 and −5 and HLD = 0 and −2 for optimal cleaning was found respectively for the soils, while the HLD did not affect cleaning efficiency for meat gravy. Our work with nonionic surfactants is not inconsistent with an optimal range, but neither does the data clearly support an optimal range either. Much of the reason is due to the limited HLD range available with nonionic surfactants because the equation for nonionics has a linear salt term while that for ionics has a logarithmic salt term.