Determination of the concentration profile and homogeneity of antioxidants and degradation products in a cross-linked polyethylene type A (PEXa) pipe

A solvent extraction technique has been developed to determine the concentration profile of two antioxidants and five degradation products of antioxidants in cross-linked polyethylene (PEX) materials. Irganox (R) 1076 and two degradation products in a PEX pipe type A (PEXa) were detected after extraction in chloroform.

Fick's second law of diffusion was used to verify that 24 h of extraction at room temperature was sufficient to extract Irganox (R) 1076 and the degradation products from PEX materials with a thickness of 5 pm. With the use of gas chromatography and mass spectrometry, the concentration profile was measured at four different places on a 100 m PEXa pipe.

A two-way ANOVA analysis showed that the composition of Irganox (R) 1076 was homogenous in the radial direction and heterogeneous in the longitudinal direction. Two degradation products of antioxidants were detected, 2,6-di-tert-butyl-p-benzoquinone and 2,4-di-tert-butyl phenol. The composition of 2,6-di-tert-butyl-p-benzoquinone was found to be homogeneous in the radial and longitudinal direction. 2,4-Di-tert-butyl phenol was homogeneous in the radial direction but heterogeneous in the longitudinal direction.