The use of nonionic detergents has drawn increased attention in laboratory settings due to their ability to more effectively remove certain types of soils. There is some confusion, however, as to the nature of these cleaners why one type of cleaner is referred to as being anonionic' and another, aionic', and when to use each of them for effective results in laboratory cleaning.
By industry standard, a detergent's charge (nonionic, anionic, cationic, zwitterionic or amphoteric) is determined by the charge of the emulsifier or surfactant in the cleaner. Thus a nonionic detergent is made up of a nonionic emulsifier and other ingredients. If a blend of anionic and nonionic surfactants is used, the detergent is referred to as being anionic.
Use of the term nonionic, however, does not necessarily mean that the detergent is ion-free. For example, Alcojet is a nonionic detergent, but most of its other ingredients are sodium salts. As a result, Alcojet is a nonionic, highly ionic detergent.
Furthermore, while the type of charge determines the detergent's ionic type, by itself, it does not provide a basis on which to select a cleaner. In clarifying this issue, it is important to first look at how nonionic surfactants are used in formulating detergents. These surfactants are generally employed in three main types of formulations, based on their intended application: u Manual and immersion cleaning mechanisms. These are nonionic detergents (high-emulsifying nonionic detergents) that enhance the ability to remove oily residues. Typically they provide optimum oil-removing performance in a synergistic combination with anionic surfactants. These nonionic cleaners typically contain surfactants of the alcohol ethoxylate class. Examples: Liqui-nox and Citranox. u High agitation machine or pressure spray-in-air cleaning. These nonionic surfactants are more dispersing in nature with low-foaming and defoaming properties that enhance wetting, rinsing and particle removal while not interfering with mechanical cleaning action. These types of nonionic cleaners typically have nonionic surfactants of the block copolymer class. Examples: Alcojet and Det-o-jet. u Ion-free, non-conductive-residue leaving. Nonionic detergents can also be part of ion-free formulations designed so they are unable to leave ionic or conductive residues. These types of nonionic cleaners can contain either type of nonionic surfactant depending on whether they more are intended for soak emulsifying cleaning or high agitation cleaning. Example: Detergent 8.
The chart on the left is designed to make it easy to select nonionic cleaners based on the intended application.
Additional factors in detergent selection
Machine cleaning detergents need to work very quickly because a droplet of detergent sprayed onto a surface has only a very short time to perform any chemical cleaning before the next droplet sweeps it away. For this reason, these types of formulations tend to be very chemically aggressive, having extremes of pH either highly alkaline (high pH) or highly acidic (low pH), along with other chemically aggressive ingredients such as oxidising agents (bleach). In unique soaking applications where the soils being removed are labile to these cleaning mechanisms, these cleaners expressly designed for machine use can be very effective.
In general, a good choice for soak cleaning of oily residues on glassware is Liqui-nox (a synergistic blend of anionic and nonionic surfactants) or Citranox (the same blend with additional ingredients optimised for trace metal and inorganic complex removal with some loss of capability in removing oily soils).
If, however, an ion-free cleaner is absolutely essential for soak cleaning, Detergent 8 is an excellent choice.
Enquiry No 79
Malcolm McLaughlin is vice-president, Alconox Inc, White Plains, NY, USA. www.alconox.com He is co-author of The Aqueous Cleaning Handbook.