Abstract:

Using boric acid （BA） and polyethylene glycol （PEG） as raw materials, a series of polyethylene glycol borates （PEG-BAE） were prepared by solvent-free method. The products were characterized by FT-IR. Their thermal stability was tested by TGA, and their surface activity was tested on a static surface tensiometer. Their rust-inhibiting properties were evaluated using HT300 cast iron and Q235 steel sheets. The lubricating properties of their aqueous solutions were tested on an MS-800 four-ball tester. Through single-factor experiments, the optimized synthesis conditions for PEG-BAE were determined as follows: reaction temperature of 115 ℃, molar ratio of PEG-400 to BA of 3.1∶1, and reaction time of 100 min. Under these conditions, a series of products were prepared with different PEGs, with esterification rates all exceeding 89%. FT-IR results indicated the presence of a C-O-B stretching vibration peak at 1 107 cm^-1 for PEG-BAEs with different molecular weights, confirming the formation of target products. TGA results showed that PEG-BAE exhibited good thermal stability, with weight loss only occurring at temperatures above 200 ℃. The results of surface tension measurement for PEG-BAEs with different molecular weights revealed that PEG-BAEs exhibited good surface activity, among which PEG-600-BAE demonstrated the lowest static surface tension of 33.89 mN/m. At a mass concentration of merely 1.5 g/L, PEG-600-BAE could meet the rust-preventative requirements; in acidic environment, at the mass concentration of 2 g/L, its corrosion-inhibition efficiency reached 90%. At the load of 25 kg, the wear scar diameter was 0.29 mm when the mass concentration of PEG-200-BAE was 1.5 g/L. Therefore, polyethylene glycol borates showed promising application as rust-preventative lubricants in water-based metalworking fluids.

Key words: polyethylene glycol, borate, surface activity, antirust, lubrication