The mass transfer of 3,5-di-tertiary-butyl-4-hydroxy toluene and alpha-tocopherol from coextrusion film structures

The antioxidants, 3,5-di-tertiary-butyl-4-hydroxy toluene (BHT) and alpha-t ocopherol were incorporated into multilayer coextrusions consisting of a he at-seal layer, a core layer of high-density polyethylene (HDPE) impregnated with antioxidant (either BHT or alpha-tocopherol), and an outer HDPE layer . The rates of loss of the antioxidants from the respective films were dete rmined as a function of time and temperature, using ultraviolet spectrophot ometric and high-pressure liquid chromatographic procedures. Graphical analysis indicated that antioxidant loss from the coextrusion str uctures was well described by a first-order or pseudo-first-order rate expr ession. Volatilization from the respective surface layers was assumed to be the rate-limiting parameter for mass transfer. The results showed that for BHT, greater than 95% of the antioxidant was lo st from the coextrusion within 36 h at 40 degrees C, within 5 days at 30 de grees C, and within 16 days at 23 degrees C. In comparison, it is estimated that to achieve similar levels of loss of ol-tocopherol from the coextrusi on, it would require nearly 54 days at 30 degrees C and 20 days at 40 degre es C. At 23 degrees C, 85% of alpha-tocopherol was lost from the coextrusio n after 195 days of storage. Assuming a first-order rate expression, the ra te-loss constants for BHT were 4.3 X 10(3), 29 X 10(3), and 65 X 10(3) h(-1 ) at 23 degrees C, 30 degrees C, and 40 degrees C, respectively. For cr-toc opherol, the rate-loss constants were 0.4 X 10(3), 2.0 X 10(3), 6.8 X 10(3) , and 28.4 X 10(3) h(-1) at 23 degrees C, 30 degrees C, 40 degrees C, and 5 0 degrees C, respectively.