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Friday, April 13, 2007

Nonionic Detergent

What is a nonionic detergent? How can a nonionic detergent like Alcojet have ionic sodium salts in it? What does it mean when a mil spec requires the use of a nonionic detergent?

Surfactants are surface active agents that are classified according to the charge on the organic part of the molecule. The surfactants are either: negatively charged which are anionic; positively charged which are cationic; neutrally charged which are nonionic; change charge with change in pH which are amphoteric; or in unusual cases the surfactant has both anionic and nonionic charges present on two parts of the molecule at once which are zwitterionic. So surfactants can be anionic, cationic, nonionic, amphoteric, or zwitterionic. In some cases, people somewhat ambiguously use the word detergent interchangeably with the word surfactant, so by the same logic when you are using the word detergent to mean surfactant, you can also say that there are anionic, cationic, nonionic, amphoteric and zwitterionic detergents. A less ambiguous definition for the word detergent is to use it to mean a blended product that contains a surfactant(s) plus other ingredients (typically called builders) to make a formulated detergent. By naming convention in the detergent industry, a formulated detergent is classified by the charge on the surfactant that is present in the detergent. You can also have formulated detergents that are anionic, cationic, nonionic, amphoteric and zwitterionic. These formulated detergents can contain builders such as sodium phosphates, sodium silicates, sodium carbonates, potassium hydroxide, citric acid and many other ionic salts or acids. So as you can see, it is perfectly possible to have a formulated detergent that is nonionic, yet contains many ions: both anionic and cationic. Understanding this possibility can be very important for electronic component cleaning where in some cases the use of nonionic detergents is specified. In many cases the intent of this nonionic specification is intended to assure that the detergent does not contain any metal ions that could deposit and leave a conductive residue. Many anionic surfactants have sodium or potassium metal ions present in their salt form when found in the detergent. For this reason, it is reasonable to consider not using anionic surfactants and anionic formulated detergents to avoid the possibility of depositing any sodium or potassium conductive metal salts in the event that the detergent evaporates on to the surface. In an effort to achieve this specification, it is often written as “the use of nonionic detergents”. Unfortunately, this can lead to the use of nonionic formulated detergents that contain many sodium and potassium metal ions that come from the builders in the formulated detergent. If these metal ion containing nonionic formulated detergents evaporate on to the surface during cleaning, they can result in conductive residue, even though a nonionic formulated detergent was used. To avoid this problem, when cleaning an electrical substrate where the cleaning specification calls for the use of a nonionic detergent, it is best to use a nonionic detergent that is ion-free. In this way you can assure that there are no metal ions coming from the builders in the nonionic formulated detergent. Alconox, Inc. supplies Detergent 8 which is both a nonionic detergent and an ion-free detergent.

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