Properties of Nitrogen-Based Surfactants

A surfactant comprises a hydrophobic tail and a hydrophilic head. The balance of hydrophobic and hydrophilic character is what defines the properties and performance of the surfactant. Hydrophobes from fatty acids consist of linear alkyl chains from C8-C22. Coconut oil provides a valuable source of the shorter C8-C14 acids while tallow, palm oil and soya bean oil are rich in C16-C18 acids. The longer C20-C22 chains are obtained from rapeseed. Natural fats and oils are triglycerides comprised of a distribution of different fatty acids and therefore, unless fractionated, the surfactants produced from them also comprise a mixture of chain lengths. While the chain length distribution of an oil or fat varies on a lot-to-lot basis, the differences in composition do not significantly impact the performance of the surfactant in most applications. 

A study of the effect of various quaternary ammonium salts in combination with sodium lauryl sulfate (SLS) and sodium lauryl ether sulfate (SLES-3) (where SLES-3 indicates that there are three EO groups in the molecular stmcture) found that in general the ether sulfate provided a broader mixing range than SLS and that alkylamldo quats were more compatible with anionics than alkyl quats [56]. Betaines were also examined and found to provide good synergies for foam and viscosity control [57]. 

Cationic surfactants are noted for their affinity for natural surfaces and their strong biocidal activity. Thus, they find use in applications such as fabric softening, mineral flotation, corrosion inhibition, cleaning and disinfecting. A few examples illustrating applications and benefits afforded by natural fat and oil-based cationic surfactants are given here. 

Fabric softeners represent the single largest application for cationic surfactants, about 250000 metric tonnes worldwide [58]. This market was for many years dominated by 

The voluntary withdrawal of chromated copper arsenate (CCA) as a wood preservative for domestic applications was driven by public concerns over its health and environmental profile. In its place have risen two competing systems, the amine copper quat (ACQ) system and the copper azole system. Both systems avoid using heavy metals such as chromium and arsenic and rely on the co-biocidal effects of copper and organic biocides. The elimination of CCA has created many opportunities for oleochemicals as preservative companies try to develop formulations that are not only environmentally friendly but can also match the preservative performance of CCA [66]. The ACQ system is based on didecyldimethyl ammonium bicarbonate and has produced a significant demand for ClO-based amine and quat. The azole systems use biocides such as tebuconazole and propiconazole in combination with copper ethanolamine complexes. Ethoxylated amines [67] and amine oxides [68] have been described as providing improved performance in azole-based systems. Other copper systems have employed ethoxylated diamines [69] and amine oxides [70] to enhance performance. 

---