Recent Advances in Polyolefin Additive Analysis

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Abstract
The extraction and quantitation of polymer additives continues to be a very important procedure in polymer deformulation. We have previously shown ultrasonic and microwave oven techniques to extract out antioxidants and slip agents from polyolefins in much less time than conventional methods such as Soxhlet extraction. The ability to reproducibly extract these materials out of polymer matrices at a high level (> 90%) is desirable to ensure that the correct amount of material is in the formulation to afford the necessary protection during processing and end use. This paper will emphasize the ultrasonic bath extraction and recovery of the phosphite ester, Irgafos 168, using various extraction solvents in high density polyethylene (HDPE). The phosphite esters will hydrolyze in extraction solvents containing alcohols (such as isopropanol, a common polyolefin extraction solvent), and also will undergo hydrolysis during the reverse phase gradient LC run if exposed to water for too long a period. The hydrolysis products will result in multiple peaks eluting in the chromatogram, which make the precision of the integration (by adding the multiple peak areas) quite poor. Also, the presence of these multiple peaks will co-elute with other antioxidants, such as Irganox 1076. The use of solvents such as cyclohexane and methylene chloride with an ultrasonic bath provides for a fast, reproducible method to extract these phosphite esters out without risking hydrolysis breakdown. Conventional acetonitrile/water reverse phase gradient techniques are discussed, as well as the use of normal phase, isocratic separations in under seven minutes. Also, flow programming is demonstrated to illustrate the use of this technique in further optimizing the LC analysis to improve selectivity and resolution.