Effects of antioxidants and their interactions on HDPE

Abstract

This research aims to investigate the effects of primary, secondary antioxidantsm an optical brightener and their interactions on high densitly polyethylene (HDPE). Five commercially available antioxidants. An optical brightener and an hindered amine light stabilizer (HALS) were compounded with the HDPE. Designing quality formulation compounds generally requires numerous experimental samples and runs which are costly and time-consuming. To minimize the number of experiments, an experimental design had been applied so that the results, obtained from a minimal number of experiments, would still be statistically conclusive. The present study had chosen the technique of Central Composite Rotatable (CCR) for the experimental design. Empirical models depicting relationships between the concentration of additives and their corresponding response will be analyzed by the technique of Response Surface Methodology (RSM). After each compounding formula was designed, the selected, the selected additives of the designed amount were compounded by mixing with the unstabilized HDPE. The compounding was conducted by using a sigle screw extruder, Extrusion was repeatedly performed up to five passes. Physical properties and the thermal stability of the compounded HDPE were investigated. It was found that increasing the concentration of the primary antoxidant enhances the Oxidative Induction Time (OIT) but it also generates considerable discoloration to the appearance of the compounded HDPE. The problem of yellowness can be remedied by adding a secondary antioxidant and an optical brightener. Moreover, the combination of and the ratio of additives used had significant effects on the properties of the HDPE. In this work the combination of the blended antioxident and the optical brightener gave the strongest synergistic effects on the OIT. The combined use of Octadecyl 3-(3,5-di-tert.bulyl-4-hydroxy phenyl)-propionate primary antioxidant by 0.06%, 0.02% Distearyl thiodipropionate secondary antioxidant and 0.00072% of 2,5-thiophenediyibis(5-tert-butyl-1,3-benzoxazole) optical brightener was found to give the best OIT. Further analysis yielded empirical equation showing the relationship between the properties of compounded HDPE and the additives studied.