Surface active compounds may act as effective additives modifying water lubricity. Their action mechanism consists in the formation of a lubricating film enriched with an active compound. The reasons for the choice of polyvinylpyrrolidones as additives were their physiological inertness and a lack of harmful environmental effects. The tests were carried out on the solutions of two polyvinylpyrrolidones with degrees of polymerization of 450 (PVP 450) and 14400 (PVP 14400). A significant effect of the polymer chain length on physicochemical (viscosity, surface tension, wettability of steel) and tribological properties (resistance to motion, wear, scuffing) has been found. PVP 14400 showed a considerably greater ability to thicken solutions. Over 10 times higher coefficients of viscosity relative to an analogous PVP 450 solution were observed already at a concentration of 5%. A slightly higher ability of PVP 14400 to reduce surface tension was observed. In the case of wettability of steel, a more effective decrease in the wetting angle was observed for PVP 450. However, the differences obtained were not large and usually did not exceed 20%. The measurements of resistance to motion and wear at three constant loads (2000, 3000, 4000 N) as well as tests on antiseizure abilities under a constant velocity increment of load (409 N/s) were carried out using a four-ball tester (T-02 tester). All friction pairs were made of bearing steel. Introducing additives to water significantly affects a decrease in resistance to motion and wear as well as an increase in the ability of a tribological system to prevent seizure. The system did not undergo seizure even at a load of 4 kN. A 2-fold decrease in the coefficient of friction (μ) and an over 30% decrease in the value of wear scar diameters (d) relative to water were observed for PVP 450 and PVP 14400 solutions at 2.0 kN. The use of water as a lubricant led to seizure of the tribological system already at above 2 kN. Addition of the polymers to water also results in a significant improvement in its antiseizure properties. The values of scuffing load (P t) and limiting pressure of seizure (p oz) for individual solutions were even 5 and 15 times higher, respectively, than the values for water. Seizure load (P oz) was also relatively high, and its level was almost two times higher than that for water. The results obtained indicate that polyvinylpyrrolidone used as an additive considerably improves the tribological characteristics of water as a lubricant base.

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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 60% solutions of maracuja oil ethoxylated with 60 mol of ethylene oxide containing hexagonal mesophases were proposed as model biocompatible safe-to-use lubricants. Tests were carried out at steady loads using a four-ball tester (Tester T-02) (1−6 kN) and a ball-on-disk tribometer (Tester T-11) (10−50 N) in order to verify tribological properties of the solutions. At high loads (Tester T-02) a significant, almost 4.5-fold reduction in the coefficients of friction (μ) and about 2.5-fold decrease in wear scar diameter (d) were found relative to water as a base. Tester T-11 was used to study the suitability of the lubricant tested for lubrication of the following friction pairs: steel ball−steel disk, different types of ceramics, and polymers at lower loads. The ethoxylate solutions are excellent lubricants also for those pairs of materials. The interpretation of the results obtained was based on the proposed adsorptive-structural mechanism.