Solubility and diffusion coefficient of antioxidants in polyethylene

Abstract

SynopsisAs an aid in assessing the ability of antioxidant additives to persist in polymers and thus remain effective in protecting against oxidation, the solubility and diffusion COefficient of two antioxidants in branched polyethylene have been determined in this work. A method was developed for this purpose by which the diffusion coefficient and solubility could be determined simultaneously. The method consists of analyzing the concentration profile across a stack of polyethylene sheets through which the antioxidant was allowed to diffuse. The concentration of antioxidants in polyethylene was determined by a thermogravimetric technique which relies directly on the ability of the additives to suppress oxidation reaction. The diffusion coefficients determined showed excellent agreement with values in the literature which were obtained by a radiotracer method. The solubility of the antioxidants in three normal hydrocarbon solvents of varying molecular sizes was also determined by a conventional technique at various temperatures and found to correlate well with their solubility in polyethylene determined by the diffusion method. In particular, the dependence of the solubility on the size of solvent molecules and on temperature agrees well with an equation derived on the basis of the regular solution theory of liquid mixtures.

Study of the effects influencing additive migration in polymers

“…As the additives are relatively large molecules, concentration profiling and sorption are the most widely used techniques with different detection methods. In our laboratories the diffusion in semicrystalline polymers is investigated by a profiling technique -introduced by Roe et al 28) -using a stack of additive-free polymer films laid between two additive sources 19) . The additive concentration in the film layers is determined by UV or IR spectroscopy, depending on the chemical nature of the material investigated.…”

Kinetic modelling of phenols consumption during polyethylene thermal oxidation

“… Stabilizer is partially soluble [9,10,11,12]. In previous papers [13,14], we successfully simulated the behavior of phosphites and sulfurs by supposing that stabilizer soluble part disappear by reaction and evaporation, and insoluble one works as a reservoir maintaining the amorphous phase at the saturation limit as long as it is not totally consumed:…”

Comparison of stabilization by Vitamin E and 2,6-di-tert-butylphenols during polyethylene radio-thermal-oxidation

“…After irradiation, vitamin E residual concentration actually displays a maximum in the subsurface layers (Oral et al, 2007). This is an encouraging argument in favor of the model even if a most complete set of simulations is needed together with more accurate data on crystallinity profile, vitamin E and oxygen diffusivity etc... -D AH = 9.2×10 -10 cm 2 s -1 for AO1 from Roe et al (1974), Moisan (1980), Limm and Hollifield (1996) -D AH = 2.3×10 -8 cm 2 s -1 for AO2 from Moisan (1980). Using rates constants recalled in Table 1, the model simulates the depletion of each sort of phenols using vitamin E rate constants differing with the 2,6-di-tert-butyl phenols set expressing by the presence of constants expressing the stabilization reaction by P°, and a higher rate constant k S1 for stabilization by POO° trapping.…”