Purpose – Modern cutting fluids often are real aqueous solutions of chemical compounds. That form of cutting fluid is simpler in preparation, as compared to emulsions and microemulsions. The water base is a good cooling medium of high-ecological value. The purpose of this paper is to discover water-soluble additives that could improve the lubricity of water. Design/methodology/approach – Three cationic surfactants were chosen to be analyzed. Their tribological properties were verified using two testers: T0-2 (four-ball machine) and T-11 (ball-on-disk). The results of the tests performed using friction couples made of steel (T0-2, T-11) and steel-ceramics (T-11) were satisfactory. Findings – The friction coefficients and wear scar diameters are even a few times smaller, as compared to the ones measured in a water environment. Originality/value – The paper demonstrates that the crucial role in improvement of the tribological properties is played by the surface activity of the additives (confirmed by the measurements of the surface tension and wetting angle). As the cationic surfactants are bactericidal and anti-corrosive, they can be classified as multi-purpose additives modifying water lubricity.

This study deals with metalworking fluids (MWFs). According to DIN 51385, depending on their base, the fluids are divided into oil and water fluids. The oil bases include, among others, mineral, synthetic, vegetable and paraffin oils. This division does not comprise surfactant solutions which can be successfully used in metalworking. Due to the fact that this type of fluid was not qualified, a new type of lubricant based on the aqueous solutions of surfactants has been proposed. Two new notions have been introduced: surfactant working fluids (SWFs) for working fluids and surfactant lubricants (SLs) for all kinds of lubricants as a broader term. The effect of the physicochemical properties of aqueous solutions of sodium lauroyl sarcosinate (SLS), also known as sodium N-dodecanoyl-N-methyl glycinate, on tribological properties determined using a four-ball machine (Tester T-02) (Łukasiewicz Research Network—The Institute for Sustainable Technologies, Radom, Poland) was analyzed. On the basis of aqueous SLS solutions a composition of working fluids was developed and their functional properties were verified by means of tribological and stand tests as well as during operation. The test results obtained clearly indicate that functional properties of 2% solutions of sodium lauroyl sarcosinate with a foam inhibitor (0.05%) and a biocide (0.1%) are comparable to those of a quality commercial hydraulic fluid.

Aqueous solutions of sodium alkyl sulphate (surfactant) and polyvinylpyrrolidone (polymer) whose physicochemical properties, including complexing ability, have been widely described in the literature were proposed as a model lubricant. It has been assumed that aqueous solutions of these compounds will favourably modify lubricating properties of water under high load conditions. For this purpose, measurements were made on a four-ball apparatus (T-02 Tester) for aqueous solutions of these compounds. Two kinds of tests were carried out: at constant loads (2, 3, and 4 kN) and variable loads within the range of 0 to 7.2 kN. Unexpectedly, high decreases in motion resistance and wear as well as an increase in antiseizure properties were found in relation to water as a base. The results obtained are so promising that solutions with an optimized composition can find practical applications. The surprisingly high effectiveness of the additives used results from the formation of surfactant/polymer complexes. These adducts adsorb at the interface, and, under friction conditions, they form a lubricant film capable of carrying high loads.

From the large group of surfactants with branched chains, sulfosuccinate derivatives obtained based on 2-ethylhexyl alcohol were selected. The surfactant of reference was ethoxylated sulfosuccinate with an alkyl chain (C12-C14). Tests regarding foam-forming ability (V0) and foam stability (V10) for selected solutions of the three surfactants were performed. Foam stability of the solutions of sterically specific surfactants (P13, P14) decreased by up to a factor of ten as compared with the equivalent linear alkyl chain (P19). This was achieved with the high surface activity of the solutions of these compounds as represented by surface tension and wettability of the surface of the bearing steel. The consequence of the high surface activity of the compounds were low friction and wear in tribological tests at constant load and excellent anti-seizure properties. On the cooperating friction pairs, adsorption layers were formed, effectively separating the two materials and able to transfer the high loads [L. 3]. Summing up, there is the possibility of using solutions of sterically specific surfactants as model cutting fluids with low foaming ability.

Based on the analysis of published results of studies on the complexes of polymers with surfactants in aqueous solutions, shampoo formulations containing sodium dodecyl sulfate (SDS) and polyvinylpyrrolidone (PVP), which are mild to the skin, were developed. The measurements of surface tension, foamability and zein number confirmed that the aqueous solutions of PVP and SDS may be used as bases for shampoo with low irritation potential. The most favorable evaluation of physicochemical and sensory tests was obtained for a shampoo containing PVP90 (termed the original shampoo). A comparison of selected functional properties of the original product with the commercial product was performed. Both shampoos were of comparable quality, but the zein number (ZN), which is a measure of irritation potential, was reduced by more than 30 % compared to the commercial shampoo.