Extraction Methods for Hexavalent Chromium in Polymers

As a part of international inter-labs study aiming to draft the section of standard IEC62321 regarding the measurement of Cr(VI) in polymers, the influences of matrix materials, powder size and extraction duration on extraction efficiency of Cr( M) in alkaline solution have been investigated. Polymers including acrylonitrile buladiene slyrene (ABS), polyvinyl chloride (PVC) and elhylene vinyl acetate/polyethylene copolymer (EVA/FE) of three different sizes (< 125 mu m, 125-250 mu m, 250-500 mu m) have been selected as samples for this investigation. The samples were digested at 90-95 degrees C in the alkaline solution of mixture of 0.28 mol/L Na2CO3 and 0.5 mol/L NaOH, and extraction duration varies from one to six hours. The test results show that the extraction efficiency of Cr( VI) in polymers is dramatically influenced by matrix materials. The extraction efficiency is good for PVC, and tolerable for ABS. But it is almost impossible to extract Cr(VI) from EVA/PE. The maximum extraction efficiency can be achieved within the extraction duration of 3 hours for PVC and ABS. The powder size less than 250 mu m will obviously enhance the extraction efficiency.