Investigating Two-dimensional Behavior of Antioxidant Additives and Migration Through Food Contact Polymers

Abstract

Research described in this thesis examines the surface and bulk behavior of analytes in food contact polymers. Irganox 1076 (IN1076) and Irganox 1010 (IN1010), phenol containing species often used as antioxidant additives in food packaging polymers, have both hydrophilic and hydrophobic functional groups. Consequently these additives are likely to absorb to surfaces where their free energy is minimized. Surface pressure isotherms show that repeated compression of films formed from IN1076 and IN10101 at the air/water interfaces leads to continued irreversible loss of molecules and that on a per molecule basis, this loss is more pronounced for IN1076 than for IN1010. Differences in the surface properties of these two antioxidant additives are interpreted based on differences in molecular structure. Surface specific vibrational measurements of these organic films show very little conformational order, implying that even when closely packed, both antioxidant species have little affinity for forming highly organized domains. A second study examined the temperature dependent permeation of different dichloroethylene (DCE) isomers through commercially available low density polyethylene (LDPE). Initial experiments measured migration rates of DCE isomers from neat liquids through the LDPE film into Miglyol. The isomers consisted of 1,1 dichloroethylene (1,1-DCE), cis-1,2-dichloroethylene (c1,2-DCE) and trans 1,2 dichloroethylene (t1,2-DCE). Despite having equivalent masses, the three isomers migrated through LDPE with rates that varied by up to a factor of three. Migration data were used to calculate permeation coefficients. Permeation coefficients did not correlate with calculated molecular sizes. The temperature dependence of the permeation coefficients was used to calculate effective permeation activation energies. Subsequent experiments examined DCE migration through LDPE from dilute solutions (1% v/v) of c1,2-DCE and t1,2-DCE isomers in Miglyol. The permeation rates slowed at lower concentrations with the permeation coefficient of c1,2-DCE decreasing by an order of magnitude. The permeation activation energy increased, by factors of ~3, for both isomers.