Diffusion of limonene in polyethylene.

Diffusion coefficients of limonene in various linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE) resins have been determined from sorption data using a thermogravimetric methodology. From these data, one can determine whether polymer synthesis parameters such as the choice of catalytic process or co-monomer result in substantial differences in how much food packaging additives might migrate to food. For example, LLDPE is currently manufactured using either one of two distinct catalytic processes: Ziegler-Natta (ZN) and metallocene, a single-site catalyst. ZN catalysis is a heterogeneous process that has dominated polyolefin synthesis over the last half-century. It involves a transition metal compound containing a metal-carbon bond that can handle repeated insertion of olefin units. In contrast, metallocene catalysis has fewer than 20 years of history, but has generated much interest due to its ability to produce highly stereospecific polymers at a very high yield. In addition to high stereospecificity, metallocene-catalysed polymers are significantly lower in polydispersity than traditional ZN counterparts. Absorption and desorption testing of heat-pressed films made from LLDPE and LDPE resins of varying processing parameters indicates that diffusion coefficients of limonene in these resins do not change substantially.

Evaluation of migration models that might be used in support of regulations for food-contact plastics.

Materials and articles intended to come into contact with food must be shown to be safe because they might interact with food during processing, storage and the transportation of foodstuffs. Framework Directive 89/109/EEC and its related specific Directives provide this safety basis for the protection of the consumer against inadmissible chemical contamination from food-contact materials. Recently, the European Commission charged an international group of experts to demonstrate that migration modelling can be regarded as a valid and reliable tool to calculate 'reasonable worst-case' migration rates from the most important food-contact plastics into the European Union official food simulants. The paper summarizes the main steps followed to build up and validate a migration estimation model that can be used, for a series of plastic food-contact materials and migrants, for regulatory purposes. Analytical solutions of the diffusion equation in conjunction with an 'upper limit' equation for the migrant diffusion coefficient, D(P), and the use of 'worst case' partitioning coefficients K(P,F) were used in the migration model. The results obtained were then validated, at a confidence level of 95%, by comparison with the available experimental evidence. The successful accomplishment of the goals of this project is reflected by the fact that in Directive 2002/72/EC, the European Commission included the mathematical modelling as an alternative tool to determine migration rates for compliance purposes.

The determination of the ability of polyurethane foam to release toluene diisocyanate into air.

A study was conducted to assess the ability of polyurethane foam to release toluene diisocyanate (TDI) into the air. The study was completed in two phases. In the first phase, three-day post-production foam samples were "extracted" using 37 degrees C, 30 percent relative humidity air for a total of three days. In the second phase, foam samples were "loaded" with TDI (approximately 1 ppm (w/w) in the foam) by passing air containing a controlled level of TDI vapor through the foam. The "loaded" foam was then aged for three days (to simulate minimum possible expected time between production and consumer contact) before being extracted for three days using 37 degrees C, 30 percent relative humidity air. In both phases of the study, the extracted TDI was quantified by trapping it from the air using glass-fiber filters coated with 1,(2-pyridyl)piperazine (PP) derivatizing agent (modified OSHA Method 42) then analyzing the TDI derivative formed using high-performance liquid chromatography with ultraviolet detection. Validation of the test system was conducted using diffusion-tube-generated TDI atmospheres. Results of the Phase 1 portion of the study showed no quantifiable TDI being extracted from the three-day post-production commercial foam samples at a limit of quantitation of approximately 0.1 ppb TDI in air. Results of the Phase 2 portion of the study showed no quantifiable TDI being extracted from the "loaded" foams at a limit of quantitation of 0.12 microgram TDI (less than 0.03% of the level of TDI loaded into the foams). In conclusion, the results from this study indicate that it is not likely that TDI would be released from three-day post-production polyurethane foams in amounts likely to produce air concentrations of concern.

Using a simple diffusion model to predict residual monomer migration--considerations and limitations.

A simple mathematical equation based on a diffusion model has been utilized recently to estimate migration of both acrylonitrile and styrene from polymers produced from these monomers which are used under a wide variety of food-contact applications. These calculated migration values have subsequently been used to estimate the US consumer's exposure to acrylonitrile and styrene from food stored in these materials. The basic assumptions integral to the model are discussed in relation to potential errors in migration estimates that could be experienced if the assumptions are not true. In addition to the discussion of the basic assumptions, factors affecting the migration predictions such as polymer 'ageing', temperature changes during the lifetime of the polymeric article, the effects of polymer-modifying materials (plasticizers, impact modifiers), and the physical form of the article or test sample are discussed.

A model for estimating the daily dietary intake of a substance from food-contact articles: styrene from polystyrene food-contact polymers.

An approach has been developed to estimate the exposure of consumers to styrene from polystyrene food-contact articles which incorporates published literature on the diffusion of styrene through polymeric materials and industry survey data on uses of polystyrene in food-contact applications. The approach has been shown to be quite practical and has yielded an exposure estimate of 3 ppb (9 micrograms/day) styrene, on average, in the daily diet of people in the United States. This value compares reasonably well with the value of 1-4 micrograms/day for residents of the United Kingdom in 1983. The value is also four orders of magnitude less than the acceptable daily intake calculated by the Styrene Information and Research Center.

Migration of styrene from polystyrene foam food-contact articles.

Polystyrene foam is used in many food-contact articles such as plates, cups, bowls, egg cartons, meat trays and hinged 'carryout' containers. In most of these applications the food is in contact with the article for a relatively short period of time at mild temperatures (up to 130 degrees F), or for longer periods of time at refrigerated temperatures (40 degrees F). The extent of migration of residual styrene from foam articles under these conditions is of interest in order to predict potential exposure of consumers to styrene from food-contact polymers. Studies of styrene migration from all polystyrene foam articles except egg cartons were completed using food oil as the simulant. Results showed that the amount of styrene migrating from the various food-contact articles made with thermoformed polystyrene sheet into food oil was proportional to the square root of time of exposure. The mean diffusion coefficients derived from these data, assuming the migration was Fickian in nature, showed a linear relationship between the log of the diffusion coefficient and the inverse of the absolute temperature of exposure from 70 to 150 degrees F (21-66 degrees C). The mean diffusion coefficients ranged from about 4.5E-11 cm2/s at 70 degrees F to 3.4E-9 cm2/s at 150 degrees F. Among the four thermoformed articles exposed to food oil, the diffusion coefficients varied by a factor of four or less at a given temperature. The migration of styrene from egg cartons was examined using conditions simulating 'typical' exposure temperature and time with 8% ethanol as the simulant (31 days at 40 degrees F (4 degrees C)). No migration of styrene was observed under this condition, with a detection limit of < 0.01 micrograms/cm2.

The 'vapour-phase' migration of styrene from general purpose polystyrene and high impact polystyrene into cooking oil.

General purpose and high impact polystyrene (GPPS and HIPS, respectively) are used in many food packaging applications. In some packaging configurations, where there is no direct contact of a liquid surface with the polymer, 'vapour-phase' migration of styrene monomer from the polymer with subsequent absorption into food is thought to be a significant mode of transfer. Correlation of residual styrene concentrations in polystyrene with vapour-phase styrene migration is of interest in order to predict potential consumer exposure to styrene from food-packaging applications of this configuration. Studies of the migration of styrene from GPPS and HIPS into air with subsequent absorption of the monomer into cooking oil, 'vapour-phase' migration, was determined in a sealed system. The results showed that for both polymers the amount of styrene migrating from the polystyrene and being absorbed by the oil was proportional to the square root of the time of exposure. The diffusion coefficients calculated for the vapour-phase migration of styrene from both polymers were found to be in good agreement with the diffusion coefficients previously determined for the 'liquid-phase' migration of styrene from similar polymers where the polymers were completely submerged in the cooking oil. These results indicate that the styrene concentrations measured in both experiments were attributable to the intrinsic diffusion of styrene from polystyrene, and that contact with cooking oil did not accelerate migration in previous experiments.

Styrene migration from general-purpose and high-impact polystyrene into food-simulating solvents.

General-purpose and high-impact polystyrenes (GPPS and HIPS, respectively) are used in many food-contact applications for the packaging of aqueous-based, fatty and dry foods. The correlation of residual styrene concentrations in polystyrene with styrene migration into food-stimulating solvents is of interest in order to predict the potential exposure of consumers to styrene from food-packaging applications. Studies of the migration of styrene into 8% ethanol and cooking oil from a GPPS and a HIPS polymer, each containing three different residual styrene levels, have been completed at temperatures ranging from 70 to 180 degrees F (21 to 82 degrees C). The results showed that the amount of styrene migrating from both polymers into cooking oil was proportional to the square root of the time of exposure, and the total amount of styrene migrating was proportional to the residual levels of styrene in the polymers. The calculated diffusion coefficients were found to be independent of the residual levels of styrene in a given polymer at a given temperature. While the partition equilibrium was not approached when the polymers were exposed to cooking oil, it was observed in the 8%-ethanol exposure studies. The calculated partition coefficients between the polymers and 8% ethanol appeared to be independent of the residual levels of styrene in the polymers at a given temperature. Linear relationships were observed between the logs of the diffusion and partition coefficients and the inverse of the absolute temperature of exposure.

The migration of acrylonitrile from acrylonitrile/butadiene/styrene polymers into food-simulating liquids.

The correlation of residual acrylonitrile (AN) monomer concentration in AN-containing polymers with AN migration into food simulants is of interest because the US FDA regulates the use of these polymers on the basis of the amount of AN that may migrate into food simulants. Studies of the migration of AN into water from seven acrylonitrile/butadiene/styrene polymers with varying composition and residual AN levels showed that a linear relationship exists between the concentration of AN in the polymer and the amount of AN migrating, for a given set of exposure conditions. A linear relationship was also observed between the diffusion coefficients generated from the experimental data using a simple Fickian diffusion model and the inverse of the absolute temperature of exposure.

The migration of Irganox 1010 antioxidant from high-density polyethylene and polypropylene into a series of potential fatty-food simulants.

Alternatives to highly-volatile ethanol or analytically complex cooking oil were examined as potential fatty-food simulants which would undergo high-temperature exposures to food-packaging polymers in food-packaging evaluation studies. The alternatives consisted of alcohols containing four to eight carbons. As test cases, the migration of Irganox 1010 antioxidant from high-density polyethylene and polypropylene into the higher alcohols was compared to the migration of Irganox 1010 into aqueous ethanol solutions and cooking oil, the US Food and Drug Administration's currently recommended fatty-food simulants. The data obtained showed slightly greater migration of the antioxidant into 95% ethanol than into cooking oil, and slightly less migration into 50% ethanol than into cooking oil. The migration of the antioxidant into the alcohols consisting of four or more carbons was much greater than the migration observed in cooking oil. In many experiments the polymers became depleted of the antioxidant prior to the end of the short, high-temperature exposure period (i.e. 2 h at 250 degrees F) to the higher alcohols. Also, for all experiments run under the same time/temperature/simulant conditions, migration of the antioxidant was greater from polypropylene than from high-density polyethylene. Diffusion coefficients generated for 95% ethanol and corn oil from these data compare closely with data from the literature.