A novel semi-automated apparatus to concentrate aqueous polymer solutions with a thermosensitive hydrogel

Construction and use of a novel, semi-automated apparatus for concentrating aqueous polymer solutions by means of a reversibly thermosensitive hydroge l are described. The gel was chemically crosslinked poly(N-isopropylacrylam ide-co-acrylic acid), which has a lower critical swelling temperature (T-c) of 37 degreesC, and the solute in the test solution was Dextran Blue (mole cular weight 2 x 10(6) g mol(-1)). The hydrogel is placed in a double-walle d cell, which is maintained at a temperature below or above T-c by passage of water from external baths. Switching between the two temperatures is eff ected by solenoid valves. Test solution is transferred from a reservoir int o the cell, the how rate and hence mass of test solution being controlled b y another solenoid valve. After swelling of hydrogel at the lower temperatu re the resultant, more concentrated test solution ('raffinate') is removed via a drainage stopcock and its concentration measured by VIS spectroscopy. The hydrogel is then deswollen by switching to the higher temperature mode , the water thereby expelled being removed via the drainage stopcock. A con siderable level of automation of the apparatus is achieved by use of indivi dual timers for each of the five solenoid valves. Separation factors and ef ficiencies of separation were evaluated and found to be dependent on (a) ti me of swelling; in some cases times were deliberately kept short and final equilibrium swelling was not reached, (b) concentration of test solution an d (c) mass of test solution relative to that of the initial gel. (C) 2001 E lsevier Science Ltd. All rights reserved.