Determination of the activation energies of diffusion of organic molecules in poly(ethylene terephthalate)

Migration Testing of GPPS and HIPS Polymers: Swelling Effect Caused by Food Simulants Compared to Real Foods

Migration kinetic data from general purpose polystyrene (GPPS) and high impact polystyrene (HIPS) were generated for a set of model substances as well as styrene monomer and oligomers at different temperatures (20 °C, 40 °C, 60 °C) using food simulants stipulated in the European Regulation (EU) 10/2011 and real foods like milk, cream and olive oil (20 °C, 40 °C). The extent of polymer swelling was characterized gravimetrically and visual changes of the test specimens after migration contact were recorded. Isooctane and 95% ethanol caused strong swelling and visual changes of HIPS, overestimating real migration into foods especially at high temperatures; GPPS was affected by isooctane only at 60 °C. With 50% ethanol, after 10 days contact at 60 °C or 40 °C both polymers were slightly swollen. Contrary, most of the real foods analyzed caused no detectable swelling or visual changes of the investigated polymers. This study demonstrates that the recommendations provided by EU regulations are not always in agreement with the physicochemical properties of styrenic polymers. The critical point remains the selection of adequate food simulants/testing conditions, since the high overestimation of aggressive media can lead to non-compliance of polystyrene materials even if the migration into real food would be of no concern.

Diffusion Coefficients and Activation Energies of Diffusion of Organic Molecules in Polystyrene below and above Glass Transition Temperature

General Purpose Polystyrene (GPPS) and High Impact Polystyrene (HIPS) is used in packaging food as well as for technical products. Knowledge of the diffusion behavior of organic molecules in polystyrene (PS) is important for the evaluation of the diffusion and migration process. Within this study, diffusion coefficients were determined in GPPS and HIPS below and above the glass transition temperature. Diffusion coefficients were determined from desorption kinetics into the gas phase using spiked GPPS and HIPS sheets as well as from permeation kinetics through a thin GPPS film. Overall, 187 diffusion coefficients were determined in GPPS and HIPS at temperatures between 0 °C and 115 °C. From the temperature dependency of the diffusion coefficients 45 activation energies of diffusion E_A and the pre-exponential factor D₀ were determined. As expected, the activation energies of diffusion E_A show a strong dependency from the molecular volume of the investigated substances. At the glass transition temperature, only a slight change of the diffusion behavior were observed. Based on E_A and D₀, prediction parameters for diffusion coefficients were established.

Litsea cubeba fruit essential oil and its major constituent citral as volatile agents in an antimicrobial packaging material

Food packaging films were coated with polyvinyl acetate (PVA) containing different concentrations of citral or Litsea (L.) cubeba essential oil (EO). Antimicrobial contact trials in style of ISO22916 were performed. Citral coatings achieved bactericidal effects against Escherichia coli (2.1 log) and Staphylococcus aureus (4.3 log) at concentrations of 20%_DM. L. cubeba inactivated more than 4 log cycles of both bacteria at a concentration of 20%_DM. To determine the antimicrobial activity across the gas phase, a unique method for volatile agents was developed, adapting ISO22196. GC/MS measurements were performed to supplement microbiological tests in a model packaging system with a defined 220 ml headspace (HS). HS-equilibrium concentrations of 1.8 μg/ml_Air were found for 20%_{DM '}citral-coatings, resulting in antimicrobial effects of 3.8 log against of E. coli. Saccharomyces cerevisiae (4.74 log) and Aspergillus niger (4.29 log) were more effectively inactivated by 3%_DM and 5%_DM coatings. In an application trial with strawberries, simulating a headspace packaging, growth inhibitory effects on the yeast and mold microbiota were found for the 20%_DM coatings.

Contamination Levels in Recollected PET Bottles from Non-Food Applications and their Impact on the Safety of Recycled PET for Food Contact

PET beverage bottles have been recycled and safely reprocessed into new food contact packaging applications for over two decades. During recollection of post-consumer PET beverage bottles, PET containers from non-food products are inevitably co-collected and thereby enter the PET recycling feed stream. To explore the impact of this mixing on the safety-in-use of recycled PET (rPET) bottles, we determined the concentrations of post-consumer substances in PET containers used for a range of non-food product applications taken from the market. Based on the chemical nature and amounts of these post-consumer substances, we evaluated their potential carry-over into beverages filled in rPET bottles starting from different fractions of non-food PET in the recollection systems and taking worst-case cleaning efficiencies of super-clean recycling processes into account. On the basis of the Threshold of Toxicological Concern (TTC) concept and Cramer classification tools, we present a risk assessment for potential exposure of the consumer to the identified contaminants as well as unidentified, potentially genotoxic substances in beverages. As a result, a fraction of 5% non-food PET in the recycling feed stream, which is very likely to occur in the usual recollection systems, does not pose any risk to the consumer. Our data show that fractions of up to 20%, which may sporadically be contained in certain, local recollection systems, would also not raise a safety concern.

A blob model to parameterize polymer hole free volumes and solute diffusion

Solute diffusion in solid polymers has tremendous applications in packaging, reservoir, and biomedical technologies but remains poorly understood. Diffusion of non-entangled linear solutes with chemically identical patterns (blobs) deviates dramatically in polymers in the solid-state (α_lin > 1, Macromolecules 2013, 46, 874) from their behaviors in the molten state (α_lin = 1, Macromolecules, 2007, 40, 3970). This work uses the scale invariance of the diffusivities, D, of linear probes D(N·M_blob + M_anchor,T,T_g) = N^{-α_lin(T,T_g)}D(M_blob + M_anchor,T,T_g) comprising N identical blobs of mass M_blob and possibly one different terminal pattern (anchor of mass M_anchor) to evaluate the amounts of hole-free volume in seven polymers (aliphatic, semi-aromatic and aromatic) over a broad range of temperatures (-70 K ≤T-T_g≤ 160 K). The new parameterization of the concept of hole-free volumes opens the application of the free-volume theory (FVT) developed by Vrentas and Duda to practically any polymer, regardless of the availability of free-volume parameters. The quality of the estimations was tested with various probes including n-alkanes, 1-alcohols, n-alkyl acetates, and n-alkylbenzene. The effects of enthalpic and entropic effects of the blobs and the anchor were analyzed and quantified. Blind validation of the reformulated FVT was tested successfully by predicting from first principles the diffusivities of water and toluene in amorphous polyethylene terephthalate from 4 °C to 180 °C and in various other polymers. The new blob model would open the rational design of additives with controlled diffusivities in thermoplastics.

Diffusion Coefficients of n-Alkanes and 1-Alcohols in Polyethylene Naphthalate (PEN)

Polyethylene naphthalate (PEN) is a polyester polymer with well-known good barrier properties. PEN had been used in the food packaging area till 2012 especially as refillable bottles for soft drinks, juices, and beer. Now, PEN is mainly used in technical applications, e.g., for data storage tapes and organic light-emitting diode (OLED) applications. The aim of the study was the determination of the diffusion coefficients of organic molecules (n-alkanes, 1-alcohols) in PEN. Diffusion and partition coefficients were determined from the lag times of the permeation process of the permeants through a commercial 12 μm biaxial-oriented PEN film. In addition, activation energies of diffusion EA were calculated according to the Arrhenius approach. The activation energy of diffusion EA follows a correlation with the molecular volume V of the investigated permeants. In addition, the preexponential factor D0 follows a correlation with the activation energy of diffusion EA. The results of this study for PEN (e.g., EA, DP) were compared to literature data on PET.

Migration of Bisphenol A from Can Coatings into Beverages at the End of Shelf Life Compared to Regulated Test Conditions

Beverage cans are used for energy drinks, soft-drinks, sparkling waters, and beer. Bisphenol A is still part of the formulation of epoxy coatings of beverage cans. Due to concerns that bisphenol A acts as an endocrine-active substance, the migration of bisphenol A is restricted. Typically, the migration from beverage cans is tested at elevated temperatures into food simulants, like 20% ethanol in water. However, comparison tests of the migration of bisphenol A at the end of shelf life, with the migration into ethanolic food simulants, are not available in the scientific literature. The aim of the study was to determine the migration of the migration of bisphenol A into real beverages, compared to routine migration tests into the European official food simulant of 20% ethanol at 40 °C and 60 °C after storage for 10 days. As a result, bisphenol A-containing coatings show a considerably higher migration when tested at 60 °C in comparison to 40 °C. On the other hand, migration into energy drinks and coke, from the same coatings at the end of shelf life when stored at room temperature, was below the detection limit in either case. As expected, migration values of bisphenol A below the analytical detection limits were observed for any test conditions from the coating labeled bisphenol A-free. Spiking tests show that bisphenol A is stable in real beverages. Therefore, it can be concluded that the accelerated migration tests with 20% ethanol at the test conditions 10 d at 40 °C and 10 d at 60 °C significantly overestimate the real migration into beverages at the end of shelf life. This overestimation of the migration of bisphenol A is due to swelling of the epoxy can coating by the ethanolic food simulant. These findings were supported by migration modeling based on diffusion coefficients predicted for polyethylene terephthalate.

Factors affecting migration kinetics from a generic epoxy-phenolic food can coating system

This study investigated how the properties of a polymeric can coating film, such as thickness and crosslink density as well as the type of migrant, influence the migration kinetics of model migrants in an attempt to better understand, model and control the migration process. Four model migrants were used BADGE (bisphenol A diglycidyl ether), BADGE·H₂O, cyclo-diBADGE and Uvitex OB, that differ in size and polarity. Fatty and aqueous food simulants were used at high temperatures (70-130°C). The apparent diffusion coefficients were found to decrease with increasing crosslink density, while they increased with increasing film thickness. The apparent activation energy of BADGE and BADGE-related compounds was calculated from the diffusion data and were high, in the range of 250-264kJmol^-1. The polarity of the simulant and the polarity of the migrant were found to influence migration. The results can be used to improve existing migration models, and thereby help to reduce migration from packaging into food by using safety-by-design approaches in new product development.

Worst case prediction of additives migration from polystyrene for food safety purposes: a model update

A reliable prediction of migration levels of plastic additives into food requires a robust estimation of diffusivity. Predictive modelling of diffusivity as recommended by the EU commission is carried out using a semi-empirical equation that relies on two polymer-dependent parameters. These parameters were determined for the polymers most used by packaging industry (LLDPE, HDPE, PP, PET, PS, HIPS) from the diffusivity data available at that time. In the specific case of general purpose polystyrene, the diffusivity data published since then shows that the use of the equation with the original parameters results in systematic underestimation of diffusivity. The goal of this study was therefore, to propose an update of the aforementioned parameters for PS on the basis of up to date diffusivity data, so the equation can be used for a reasoned overestimation of diffusivity.

A quantitative property-property relationship for the internal diffusion coefficients of organic compounds in solid materials

Indoor releases of organic chemicals encapsulated in solid materials are major contributors to human exposures and are directly related to the internal diffusion coefficient in solid materials. Existing correlations to estimate the diffusion coefficient are only valid for a limited number of chemical-material combinations. This paper develops and evaluates a quantitative property-property relationship (QPPR) to predict diffusion coefficients for a wide range of organic chemicals and materials. We first compiled a training dataset of 1103 measured diffusion coefficients for 158 chemicals in 32 consolidated material types. Following a detailed analysis of the temperature influence, we developed a multiple linear regression model to predict diffusion coefficients as a function of chemical molecular weight (MW), temperature, and material type (adjusted R² of .93). The internal validations showed the model to be robust, stable and not a result of chance correlation. The external validation against two separate prediction datasets demonstrated the model has good predicting ability within its applicability domain (Rext2>.8), namely MW between 30 and 1178 g/mol and temperature between 4 and 180°C. By covering a much wider range of organic chemicals and materials, this QPPR facilitates high-throughput estimates of human exposures for chemicals encapsulated in solid materials.