Dielectric Strength of the Blends of Virgin and Recycled HDPE S. A. Cruz, M. Zanin Department of Materials Engineering—DEMa/Universidade Federal de Sa ˜o Carlos—UFSCar, Rodovia Washington Luı ´s, Km 235/Sa ˜o Carlos, SP, Brazil, CEP 13565-905 Received 8 November 2002; accepted 9 June 2003 ABSTRACT: This work evaluated the incorporation of re- cycled high-density polyethylene (HPDE) in the virgin poly- mer by measuring its dielectric strength. Post-consumer con- tainers of HDPE were collected and passed through the basic processes of plastics recovery: washing, grinding, and drying. Formulations were elaborated containing 0, 25, 50, 75, and 100% of recycled material incorporated to the virgin resin by extrusion and injection processes, stabilized with 0.2% Irganox B215. Samples of these materials were submit- ted to dielectric breakdown analysis by using an electrode- type sphere—plane and ramp of positive electric tension. The data were treated and analyzed by using the statistical distribution of Weibull, and the Maximum Likelihood method. The degree of crystallinity was measured by X-ray diffraction. Atomic absorption spectrophotometry was em- ployed to identify metallic residues present in the samples. The results showed that there is a 17% decrease in the values of the dielectric strength when we compare the virgin HDPE with the 100% recycled. Therefore, formulations containing up to 50% of recycled material may be taken into consider- ation in the development of products in electric insulating systems. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1730 –1735, 2004 Key words: recycling; post consumer; polyethylene; dielec- tric properties; dielectric strength INTRODUCTION The applications of recycled high-density polyethyl- ene (HDPE) are becoming more and more frequent and its use includes paving (recycled HDPE mixed with asphalt), plastic wood, building sites (conduits, etc.), plastics culture (canvases), automobile industry, production of containers for industrial chemical prod- ucts, bags (plastic carrier bags, etc.), blends with virgin resin for the packaging of cleaning, and plastic crates. Although the polymeric materials are commonly used as dielectric by the industries of the electric section and there is still a diversity of studies on the electric behavior of those materials, the survey in several data bases did not show any reference related to the char- acterization and application of recycled HDPE for sys- tems of electric insulation, with the exception of con- duits, in which the most relevant property is the me- chanic one. Among the various types of polymeric materials that are dielectric, HDPE stands out as a raw material for the production of insulators, spacers, and connec- tors for low tension and also as coating for cable conductors used in electrical power distribution net- works. For polymeric insulators, the dielectric strength is one of the properties that must be taken into account to check the ability to withstand high electric fields. Dielectric strength is defined as a ratio between the breakdown voltage and the dielectric thickness, representing the maximum field that the material can support for a specific experimental setup. 1–5 Even if variables such as morphology, additives or impurities, and test conditions are under control, scat- tering in the dielectric breakdown results is inevitable. Thus, it is necessary to use statistical models to treat and obtain the values of the dielectric strength and still evaluate its significance to guarantee the reliabil- ity of the data. Among current statistical models, the Weibull model is regarded as the most appropriate for data analysis obtained from breakdown tests. 2,5–7 Ueki and Zanin 5 used the distribution of Weibull to corre- late the form parameter  of this model with the distribution and dispersion of the carbon black parti- cles in the HDPE. They concluded that the larger the value of , the more homogeneous the system is. Therefore, this work intends to study the viability of recycling the HDPE from containers discarded in mu- nicipal solid waste to be employed in electric insula- tion systems. To this end, five blends were developed containing 0, 25, 50, 75, and 100% of recycled material incorporated in the virgin HDPE and its insulating properties evaluated through the dielectric break- down test. The statistical model of Weibull was used to treat the dielectric strength data, because they could show a wide dispersal. Also, atomic absorption spec- Correspondence to: M. Zanin (dmza@power.ufscar.br). Contract grant sponsors: CNPq and FAPESP. Journal of Applied Polymer Science, Vol. 91, 1730 –1735 (2004) © 2003 Wiley Periodicals, Inc.