A simple solvent selection method for accelerated solvent extraction of additives from polymers
A simple solvent selection procedure for accelerated solvent extraction (ASE®) of polymers is described using Hildebrand solubility parameters. A series of extractions with a solvent with a solubility parameter several Hildebrand units (MPa1/2 ) different from the polymer are carried out at increasing temperatures until maximum extraction is reached. A second solvent with a solubility parameter close to that of the polymer is then added incrementally at the optimum temperature found from the initial experiments, until a maximum in the extraction rate is reached. This method is used to determine optimum conditions for ASE® of additives from ground polypropylene (PP), poly(vinyl chloride) (PVC) and nylon. Complete extractions were possible of Irganox 1010 (pentaerythrityl tetrakis (3,5-di-tert-butyl-4-hydroxyphenyl) propionate) from freeze ground PP in 18 min (propan-2-ol–cyclohexane (97.5∶2.5) at 140 °C), and dioctyl phthalate (DOP) from PVC in 13 min (hexane–ethyl acetate (60∶40) at 170 °C). ASE® extraction from PVC pellets was possible in reasonable time (1 h) without grinding or cutting the polymer. The results were not significantly different from those obtained by conventional solvent extraction methods. From nylon, 96% extraction of the dimer in 19 min (hexane–ethanol (60∶40) at 170 °C) was possible, compared to the total amount extracted by exhaustive ASE®. The behaviour of poly(ethylene terephthalate) (PET) and poly(methyl methacrylate) (PMMA) was observed with different solvents at high temperature to determine likely optimum extraction conditions. These were ethyl acetate at 190 °C for PET and hexane–ethyl acetate (70∶30) at 150 °C for PMMA.