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Table 2. Initial OIT of Polyethylene Sample.Minutes (OIT at 200°C)Unexposed Control Sample104Table 3. OIT of Polyethylene Samples Immersed inWater With 5 ppm Free Chlorine.Three Weeks at 85°C, 5 ppm Free Chlorine Minutes (OIT at 200°C)Control Sample42Additive Compound A100Additive Compound B37Additive Compound C15The OIT of the unexposed sample was 104 minutes. Afterthree weeks in 5 ppm free-chlorine water at 85°C, the sam-ple OIT dropped to 42 minutes (60% decrease from originalvalue). However, with the incorporation of a specialty addi-tive, Compound A, the OIT was measured and recorded at100 minutes (less than 4% decrease from original value).New Compounds B and C did not show a positive effect.Color stability can be important in certain applications.See the pictures of the plaques below.It was generally notedthat with prolonged exposure to free chlorine, samples yel-lowed and then darkened.After being immersed for six weeks in 5 ppm free-chlo-rine water at 60°C, the control plaque increased 20.4units in yellowness index (YI), while the Compound Aplaque increased only 12.9 YI units.ConclusionIn this study, the degradation of commercial-grade poly-ethylene pipe accelerated under exposure to free chlorine.Accelerated degradation was observed with a significantdecrease in OIT versus samples that did not contain freechlorine. Compared with a sample exposed to "wateronly," early carbonyl formation was observed at the sur-face of the pipe sample exposed to free chlorine.Premature formation of microcracks was observed at thesurface of the pipe exposed to free chlorine.Several additive compounds were evaluated in order toincrease the pipe's resistance to free-chlorine oxidativedegradation. Compound A was found to maintain thepipe's original OIT even under exposure to 5 ppm of freechlorine after three weeks at 85°C. Further studies areplanned to optimize and enhance the performance ofpolyethylene pipe under exposure to free chlorine.AcknowledgmentsThe authors extend their gratitude to Jeff Jenkins,Kimberly Fallo, Jerome O'Keefe, and Chermeine Rivera,who performed the work that generated most of the testresults. Special thanks also go to Brent Sanders and SariSamuels for their valuable insight. The authors' apprecia-tion also goes to the management of Cytec Industries Inc.for the support and permission to publish this paper.References1. Water Chlorination,Chlorine Chemistry Council,Arlington, Virginia (February 2003).4.S. Chung, K. Oliphant, et al., An Examination of the RelativeImpact of Common Potable Water Disinfectants on Plastic PipingSystem Components,Jana Laboratory. 5. W. McGlynn, Guidelines for the Use of Chlorine Bleach as aSanitizer in Food Processing Operations,Oklahoma StateUniversity, FAPC-116-2.6.L.P. Candeias, M.R. Stratford, and P. Wardman, Free Radic Res,1994 Apr. 20(4):241-9. "Formation of hydroxyl radicals on reac-tion of hypochlorous acid with ferrocyanide, a model iron(II)complex."7. Fontana, Minisci, et al., Free Radicals in Synthesis and Biology,Chlorination of Hypochlorous Acid. Free Radical Versus ElectrophilicReactions,pp. 269-82.8. ASTM Designation D3895-98, Standard Test Method forOxidative Induction Time of Polyolefins by Differential ScanningCalorimetry.The authors first presented a version of this paper at SPE'sPolyolefins 2009 Conference.24| PLASTICS ENGINEERING | OCTOBER 2011| ControlCompound ACompound BCompound CImmersed in DI WaterImmersed in 5ppm of free chlorine solution60oC, 6 Weeks!YI =17.9!YI =20.4!YI =9.9!YI =20.4!YI =13.4!YI =12.9!YI =24.6!YI =29.3 85oC, 6 WeeksControlCompound AImmersed in 5ppm of free chlorine solutionControlCompound