Tailoring strategies of polyalkylene glycol ester for varied lube applications

Three biodegradable/ecofriendly polyalkylene glycol esters 1,4-PTHC₃, 1,4-PTHC₆ and 1,4-PTHC₈ [polyglycol containing 1:4 mol fraction of propylene oxide (PO) and tetrahydrofuran (THF)] esterified with propionic acid (C₃ fatty acid), hexanoic acid (C₆ fatty acid) and octanoic acid (C₈ fatty acid) were synthesized via two-step reaction mechanism. Initially, propylene oxide and tetrahydrofuran were polymerized in 1,2 dichloroethane to obtain a polymer 1,4-PTH (polyglycol containing 1:4 mol fraction of PO and THF) with molecular weight (\(\overline{{M_{n}}}\)) 1070.7. Finally, esterification of 1,4-PTH was done with varied fatty acids, i.e., C₃, C₆ and C₈ fatty acid catalyzed by p-toluenesulfonic acid and toluene as solvent to obtain final products 1,4-PTHC₃, 1,4-PTHC₆ and 1,4-PTHC₈ having the molecular weights (\(\overline{{M_{n}}}\)) 1154.78, (\(\overline{{M_{n}}}\)) 1192.86 and (\(\overline{{M_{n}}}\)) 1220.91, respectively. The molecular structure and crystallinity of the synthesized poly(propyleneoxide-co-tetrahydrofuran) ester was studied by FT-IR, X-ray diffraction and DSC. The physicochemical properties like; pour point (ASTM 97), kinematic viscosity (ASTM 445), viscosity index (ASTM 2270), refractive index, density, thermal stability, autoignition temperature (IS 7895), corrosion stability and oxidation stability (IP 48) were determined. The extreme pressure (IP 239) and antiwear properties (ASTM D 4172) were also evaluated in terms of weld load and average wear scar diameter, respectively. Hence all the properties so determined were compared with the specifications of lube oils and it was revealed that these poly(propyleneoxide-co-tetrahydrofuran) esters, i.e., 1,4-PTHC₃, 1,4-PTHC₆ and 1,4-PTHC₈ had suitable physical and tribological properties to be used as base stock for compressor lubricant, metal working fluid and fire-resistant hydraulic fluid.