Layered silicates titration

Figure 6.3 Leaching of sensor layers M4, M1, M2 and M3 (from top) on exposure to a flow of buffer solution (left) and titration plots of AF in poly-TMOS (Ml), an organically modified silicate (M4), and covalently immobilized on ICPS (M2) and GOPS (M3) (right). (Reproduced from ref. 4, with permission.)...

The mixture is kept for 3 hours at 105°C after the oxide addition is complete. By this time, the pressure should become constant. The mixture is then cooled to 50°C and discharged into a nitrogen-filled botde. The catalyst is removed by absorbent (magnesium silicate) treatment followed by filtration or solvent extraction with hexane. In the laboratory, solvent extraction is convenient and effective, since polyethers with a molecular weight above about 700 are insoluble in water. Equal volumes of polyether, water, and hexane are combined and shaken in a separatory funnel. The top layer (polyether and hexane) is stripped free of hexane and residual water. The hydroxyl number, water, unsaturation value, and residual catalyst are determined by standard titration methods. 

The Biometer flask test procedure, partially modified for testing polymeric materials with low-to-moderate propensity to biodegradation was used. Biodegradation tests were carried out in glass vessels containing a multilayer substrate in which a mixture of mature compost with perlite, a chemically inert heat expanded aluminium-silicate rock, was sandwiched between two perlite layers (Figure 1). Test polymer samples were placed in the middle layer and the vessels were kept in the dark at 55 °C. The CO2 evolved from samples and blanks was trapped in beakers containing 40-50 ml of 0.05 N KOH solution placed inside the test vessels. Every few days, this solution was back titrated with 0.1 N HCl after addition of 4-5 ml of 0.25 N BaCb, and then replaced with fresh solution. 

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