The Mass Transfer of 3, 5-Di-Tertiary-Butyl-4-Hydroxy Toluene and α-Tocopherol from Coextrusion Film Structures

The antioxidants, 3, 5-di-tertiary-butyl-4-hydroxy toluene (BHT) and α-tocopherol were incorporated into multilayer coextrusions consisting of a heat-seal layer, a core layer of high-density polyethylene (HDPE) impregnated with antioxidant (either BHT or α-tocopherol), and an outer HDPE layer. The rates of loss of the antioxidants from the respective films were determined as a function of time and temperature, using ultraviolet spectrophotometric and high-pressure liquid chromatographic procedures. Graphical analysis indicated that antioxidant loss from the coextrusion structures was well described by a first-order or pseudo-first-order rate expression. 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 lost from the coextrusion within 36 h at 40°C, within 5 days at 30°C, and within 16 days at 23°C. In comparison, it is estimated that to achieve similar levels of loss of α-tocopherol from the coextrusion, it would require nearly 54 days at 30°C and 20 days at 40°C. At 23°C, 85% of α-tocopherol was lost from the coextrusion after 195 days of storage. Assuming a first-order rate expression, the rate-loss constants for BHT were 4.3 × 10 3 , 29 × 10 3 , and 65 × 10 3 h −1 at 23°C, 30°C, and 40°C, respectively. For α-tocopherol, the rate-loss constants were 0.4 × 10 3 , 2.0 × 10 3 , 6.8 × 10 3 , and 28.4 × 10 3 h −1 at 23°C, 30°C, 40°C, and 50°C, respectively.