Light Stabilizer Tinuvin 622 in Polyethylene

This study presents an inexpensive and reagentless turbidimetric technique for the determination of Tinuvin 622 in polyethylene matrix. Tinuvin is dissolved in acetone, and water is added to it. The solubility of the analyte is reduced in the water/acetone mixture and it precipitates in the form of small particles. Different parameters affecting the analysis were studied, and it was found that in a 50:50 mixture of water and acetone high turbidity was obtained. Turbidity increases to 30 min and remains constant for at least 1 h. Stirring speed and ionic strength are no effective factors in this method. The linear dynamic range is relatively large (10–250 mg L⁻¹) with a limit of detection of 3 mg L⁻¹. The repeatability of the method is good, and the relative standard deviation for six repeated experiments performed on solutions containing 100 mg L⁻¹ is 1.5%. To analyze real samples (polyethylene polymer), the matter is dissolved in hot xylenes, and methanol is added while the solution is being stirred. The precipitated polymer is filtered and the solution evaporated into the rotary. The remaining solids are dissolved in acetone and analyzed as standards. The obtained results were compared with those obtained by gas chromatography (after saponification) and no significant differences were observed.