Typical diffusion behaviour in packaging polymers – application to functional barriers

Evaluation of new safety decontamination approaches at lab scale for recycled highdensity polyethylene (rHDPE) intended for food contact

BACKGROUND

The increasing use of plastic packaging materials generates concerns related to the environmental problem generated by their waste. As a result, the search for new recycling methodologies to extend the lifecycle of plastic packaging is becoming more important, without forgetting to ensure the safety of these materials. Currently, the use of recycled polyolefins as food contact materials is not widespread yet. This is because the decontamination processes currently available are insufficient to produce clean, safe materials suitable for such applications. This work is focused on the evaluation of the safety of recycled high-density polyethylene (rHDPE), and the search for strategies to achieve its decontamination.

RESULTS

To this end, three batches of flakes and three batches of pellets of rHDPE coming from the mechanical recycling of post-consumer milk bottles were analyzed. The analysis of the volatile and semi-volatile compounds present in the samples was carried out using gas chromatography-mass spectrometry (GC-MS), finding a total of 67 compounds. The strategy to achieve the decontamination of flakes and pellets of this material has been based on the application of high temperature and vacuum at lab scale, obtaining a clear decrease in volatile compounds, below 50% of the initial value in most cases when applying 120 °C during 5 h. The migration test performed in the samples (treated and untreated) to different food simulants (10 % ethanol and 3 % acetic acid, 95 % ethanol) revealed also a clear decrease of concentrations of volatiles.

SIGNIFICANCE

The findings are highly encouraging, demonstrating substantial progress toward the safe and effective use of rHDPE in specific food packaging applications. This indicates a significant step forward in the potential uses of rHDPE. Nevertheless, the lack of toxicity data for many migrants necessitates additional toxicological testing to obtain a more precise risk assessment.

One-dimensional and comprehensive two-dimensional gas chromatographic approaches for the characterization of post-consumer recycled plastic materials

In September 2022, the European Commission published its new regulation on recycled plastic materials for food contact. It allows newly developed, non-authorized technologies and approaches, or so-called novel technologies, to be deployed in the field to generate the data needed for establishing regulatory and/or fit for purpose processes. The data shall be generated by using suitable methods, but the regulation does not give a more detailed description on those. In this study, commercially purchased buckets made of post-consumer recycled polypropylene were screened, using a number of different analytical approaches. Sample preparation methods, analysis techniques, and the data and information generated were compared. The results clearly demonstrate the need for a detailed characterization of such materials and the advantages and disadvantages of the analysis using conventional gas chromatography with flame ionization detection and mass spectrometery as well as two-dimensional comprehensive gas chromatography with time of flight mass spectrometry.

Mechanical recyclability of biodegradable polymers used for food packaging: case study of polyhydroxybutyrate-co-valerate (PHBV) plastic

For the purpose of mechanical recycling for food contact applications, decontamination of polyhydroxybutyrate-co-valerate (PHBV) plastic was performed under different temperatures and time conditions. As expected, increasing the decontamination temperature and duration increased the decontamination efficiency, but also the degradation of the polymer. The combination 160 °C/6 h was selected as the optimal conditions that maximize contaminants removal while minimizing polymer degradation. Then the safety of the recycled PHBV under these conditions was assessed, in accordance with EFSA regulation based on bottle-to-bottle PET recycling. Decontamination of low molecular weight molecules such as toluene, chlorobenzene, and methyl salicylate was nearly complete with residual concentrations below the modeled concentrations allowed in the polymer when the adult scenario is considered. However, the higher molecular weight and lower volatility molecules exhibited acceptable decontamination efficiencies, but their residual concentrations in the polymer exceeded the maximum concentrations of no concern. The presence of these molecules allows the use of nearly 21% recycled PHBV in the new materials to meet safety criteria. It is important to keep in mind that this work, never done before, is a preliminary work on mechanical recycling of PHBV, mainly based on extrapolation of PET conditions and regulations. Much more research needs to be done to improve the decontamination process, the barrier properties of PHBV or to think about a short recycling line for PHBV.

Effect of Ultrasound Treatment on Barrier Changes of Polymers before and after Exposure to Food Simulants

In this study, we investigated the impact of ultrasound treatment on barrier properties of linear low-density polyethylene (LLDPE) and acrylic/poly(vinylidene chloride) polypropylene (PPAcPVDC)-coated pouches intended for food packaging before and after exposure to food simulants. Packaging pouches were filled with two food simulants, namely ethanol (10% (v/v)) and acetic acid (3% (w/v)), in order to simulate food−packaging interaction and possible compound migration from packaging materials. Samples were subjected to an ultrasound water bath treatment for 5 min, 15 min, and 30 min at 60 °C (±2 °C) and with an amplitude of 100% as an equivalent to the heat-treatment conditions combined with an ultrasound effect. Furthermore, the effect of temperature on the polymer barrier (water vapour and oxygen permeability) properties was tested at 20 °C, 40 °C, and 60 °C. Results showed that PPAcPVDC possessed better properties of water vapour permeability and oxygen permeability properties to LLDPE. Statistical analyses showed a significant (p < 0.001) impact of ultrasound treatment on the overall migration value, regardless of the food simulant used.

How to make the use of recycled paperboard fit for food contact? A contribution to the discussion

Recycled paperboard contains hundreds of non-evaluated or even unidentified substances that could endanger human health if they turn out to be highly toxic. It seems as unrealistic to evaluate each of them as it is to phase out the use of the problematic ones or sort out the papers and boards introducing them into the recyclate. Therefore, measures should be taken that generally reduce migration into food, such as functional barriers or functional sorbents. A general approach is used for the recycling of plastics, particularly poly(ethylene terephthalate), PET: as not every potential contaminant can be regulated, a pragmatic approach is applied, for PET mainly on the required decontamination efficiency. Criteria are required on the required efficacy of the measures to be taken. Recycled paperboard is used for various types of food contact: mostly contact is through the gas phase (evaporation and recondensation), often indirect through other layers (e.g. internal bags or for transport boxes), seldom in wetting contact. Numerous factors have to be considered. For typical folding boxes and at least strongly dominating gas phase contact, it was proposed that no more than 1% of each contaminant in the recycled paperboard should enter the food. The efficiency of the measures required to comply with this criterion depends on the application. The three main measures are reviewed with regard to this criterion: (i) internal bags with an incorporated functional barrier (successfully used for some time), (ii) a barrier layer on the internal wall of the box (for which the design of the closures might be most critical) and (iii) functional sorbents added to the paperboard (for which the sorbent capacity is critical). For transport boxes, commonly of corrugated board (quantitatively the most important use of recycled paperboard in food contact), an adjusted or different criterion is needed.

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.

Effect of high pressure processing on migration characteristics of polypropylene used in food contact materials

The migration of small molecular mass organic compounds from polypropylene (PP) copolymer films into food simulants during and after high pressure processing (HPP) was studied. An overlapping temperature profile was developed to isolate the pressure effect of HPP (700 MPa, 71°C, 5 min) from equivalent thermal processing (TP) at atmospheric pressure (0.1 MPa). Chloroform, toluene, methyl salicylate, and phenylcyclohexane were chosen as surrogate compounds, and were spiked into test polymer films at concentrations of 762-1152 mg kg^-1 by a solvent soaking technique. Migration (w/w) of surrogate compounds from loaded PP films into Miglyol 812 (a medium-chain triglyceride mixture) and 10% ethanol was quantified by headspace GC/MS during HPP and TP, and subsequent storage at 25°C for up to 10 days. HPP significantly delayed migration of the surrogates from PP into both food simulants relative to TP. The average migrations into Miglyol after TP and HPP were 92.2-109% and 16-60.6%, respectively. Diffusion coefficients estimated by migration modelling showed a reduction of more than two orders of magnitude for all surrogate compounds under high pressure at 700 MPa (AP' = 8.0) relative to equivalent TP at 0.1 MPa (AP' = 13.1). The relative T_g increase of PP copolymer under compression at 700 MPa was estimated as T_g+94°C. For 10% ethanol, average migrations after TP and HPP were 9.3-50.9% and 8.6-22.8%, respectively. During extended storage, migration into both simulants from HPP-treated samples was initially slower than that from untreated or TP-treated films. However, after 8-24 hours of storage, the differences in percent migration of selected surrogates were not significant (p > .05) among the treated PP films. Therefore, the physical changes of PP films that occur during HPP appear to be reversible with a return to their original dimensions and diffusion properties after decompression.

Recyclable Multilayer Packaging by Means of Thermoreversibly Crosslinking Adhesive in the Context of Food Law

Lacking recyclability of multilayer packaging can be overcome by using a thermoreversible crosslinking adhesive consisting of maleimide- and furan-functionalized polyurethane-(PU-)prepolymers, reacting in a Diels–Alder-reaction. Here, the furan-functionalized PU-prepolymer carries furan-side-chains to avoid the usage of an additional crosslinking agent. Thus, N‑(2‑hydroxyethyl)maleimide and furfurylamine are the only two chemicals contained in the adhesive that are not listed in the appendix of EU Regulation 10/2011. Using migration modelling, it could be shown that, at 23 °C, both chemicals have lag-times of only a few minutes if 45 µm PE is used as a barrier. However, if the residual content is below 30 mg/kg, the legally specified maximum amount of 0.01 mg/kg food is not reached. After determining the diffusion coefficients and the activation energy of diffusion through ethylene-vinyl alcohol copolymer (EVOH), it could be determined that the lag-time of the migrants can be extended to at least 9 years by the use of 3 µm EVOH. From a food law point of view, the use of the described adhesive is possible if the above‑mentioned measures are complied.

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.

Total Life Cycle of Polypropylene Products: Reducing Environmental Impacts in the Manufacturing Phase

This paper assesses the environmental burdens of a polypropylene product throughout the product’s life cycle, especially focusing on the injection-moulding stage. The complete life cycle model of the polypropylene product has been developed from the raw material extraction and production phase through its usage to the end-of-life stage with the help of the life cycle assessment method. To find the answers to the posed problems, different impacts were analysed by GaBi 8.0 software. The analysis lasted from the cradle to the grave, expanding the analysis of the looping method. The aim of the research was to determine the energy and material resources, emissions, and environmental impact indicators. Basically, the article tried to answer three questions: (1) How can we optimize the production phase for the looping method? (2) Which materials and streams are recyclable in the design of the production process? (3) What is the relationship between life cycle stages and total life cycle of the product? As we inspect the life cycle of the product, the load on the environment was distributed as follows: 91% in the production phase, 3% in the use phase, and 6% in the end-of-life phase. The results of the research can be used to develop technologies, especially the injection-moulding process, with a lower environmental impact.

Sorption properties of hydrophobic organic chemicals to micro-sized polystyrene particles

It has been reported that microplastics (MPs) have strong affinity for hydrophobic organic chemicals (HOCs) and can be ingested accidentally by aquatic organisms, posing a potential threat to the environment. To date, the sorption data used in modelling to clarify the mechanism were mostly obtained in varied sampling durations and regions from different works, which might cause inevitable deviation in modelling results. The current study aimed to illustrate the sorption properties of HOCs to the micro-sized polystyrene (PS). The sorption behaviors of HOCs to the PS were investigated at a certain pre-equilibrium status, and the theoretical analysis was taken into consideration. A bottle-shaped passive dosing system was designed to measure the concentration ratio of HOCs in different phases of the exposure suspension at a certain time (loga_MP), including polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) with logK_ow ranging from 3.17 to 10.20, between water and PS MPs with different dimensions (diameters of 100 nm, 1 μm and 2 μm, respectively). The calculated loga_MP ranged from 3.73 to 8.34, and a positive correlation was found between loga_MP and log1r₀ (r₀ is the MP radius). The results indicated that HOCs would diffuse into the PS particles, but the mass transfers inside the particles were slow and would be negligible in some environmental cases. Under theoretical considerations, the diffusion through the boundary layer of the particle was considered as the dominating process because it was fast, and the contributions of absorbed amounts on the particle surface were larger for smaller PS particles (i.e. 100-nm PS). This study could provide applicable data for further exploring the effects of micro-sized plastics on the HOCs in environmental samples.

Radiation-Induced Fluorescence from Doped Polyolefins on a Nanosecond Time Scale: Kinetics of the Processes Involving Geminate Radical Ions

The delayed radiation-induced fluorescence from polyethylene and its alkyl- and fluorine-substituted analogues doped with aromatic luminophores was studied in the time range of 1-1000 ns. Qualitative analysis of the effects of a magnetic field on the fluorescence decay indicated that, in all polyolefins studied, the main portion of the fluorescence observed arose from the recombination of geminate spin-correlated radical ion pairs (RIPs). In the case of polyethylene, this conclusion was supported by observing the effect of an external electric field on the fluorescence decay. It was shown by comparison with the computer simulation of intratrack recombination that the tunneling character of the RIP recombination, which had an asymptotic time dependence of the geminate recombination rate close to t^-1, was typical of most studied polyolefins at temperatures below 273 K in the time range studied. The increase to room temperature and above caused a gradual transition to a regime where the geminate recombination rate was mainly determined by the migration of RIP partners with time dependence close to t^-3/2. The low estimate of the electron transfer distance upon the ion recombination in this regime was about 2 nm. In polyethylenes, exposed to an irradiation of 0.3-0.4 MGy, the role of charge carrier diffusion became hardly noticeable because of the cross-linking of polyethylene chains and the increase in polymer matrix stiffness. Oxygen, dissolved in a polymer doped with aromatic molecules, caused quenching of the recombination luminescence due to electron transfer from the dopant radical anion to the oxygen molecules. At room temperature, typical distances for such electron transfer were estimated to be ∼1.5 nm.

Potential of Incorporation of Antimicrobial Plant Phenolics Into Polyolefin-Based Food Contact Materials to Produce Active Packaging by Melt-Blending: Proof of Concept With Isobutyl-4-Hydroxybenzoate

There is an increasing interest for active food packaging incorporated with natural antimicrobial agents rather than synthetic preservatives. However, most of plastics for direct contact with food are made of polyolefins, usually processed by extrusion, injection, or blow-molding methods while most of natural antimicrobial molecules are thermolabile compounds (e.g., essential oils). Therefore, addition of plant phenolics (with low volatility) to different polyolefins might be promising to design active controlled release packaging processed by usual plastic compounding and used for direct contact with food products. Therefore, up to 2% (wt/wt) of isobutyl-4-hydroxybenzoate (IBHB) was mixed with 3 polyolefins: EVA poly(ethylene-co-vinyl acetate), LLDPE (Linear Low Density Polyethylene), and PP (PolyPropylene) by melt-blending from 75 to 170°C and then pelletized in order to prepare heat-pressed films. IBHB was chosen as an antibacterial phenolic active model molecule against Staphylococcus aureus to challenge the entire processing. Antibacterial activity of films against S. aureus (procedure adapted from ISO 22196 standard) were 4, 6, and 1 decimal reductions in 24 h for EVA, LLDPE, and PP films, respectively, demonstrating the preservation of the antibacterial activity after melt processing. For food contact materials, the efficacy of antimicrobial packaging depends on the release of the antimicrobial molecules. Therefore, the three types of films were placed at 23°C in 95% (v/v) ethanol and the release rates of IBHB were monitored: 101 ± 1%, 32 ± 7%, and 72 ± 9% at apparent equilibrium for EVA, LLDPE, and PP films, respectively. The apparent diffusion coefficients of IBHB in EVA and PP films were 2.8 ± 0.3 × 10⁻¹² and 4.0 ± 1.0 × 10⁻¹⁶ m²s⁻¹. For LLDPE films, IBHB crystals were observed on the surface of films by SEM (Scanning Electron Microscopy): this blooming effect was due the partial incompatibility of IBHB in LLDPE and its fast diffusion out of the polymer matrix onto the film surface. In conclusion, none of these three materials was suitable for a relevant controlled release packaging targeting the preservation of fresh food, but a combination of two of them is promising by the design of a multilayer packaging: the release could result from permeation through an inner PE layer combined with an EVA one acting as a reservoir.

Fireproofing of domestic upholstered furniture: Migration of flame retardants and potential risks

Flame retardants (FRs) are widely incorporated in polyurethane foams to decrease their fire reaction. Currently, the risks associated with the use of FRs in domestic upholstered furniture (UF) are evaluated according to FRs volatility and potency to be emitted into the atmosphere. However, exposure via contact and dermal penetration, mediated by sweat, has not been considered so far. Our study provides an identification of the latest-generation of FRs most commonly used in UF, and an evaluation of their potency to migrate into artificial sweat. First of all, an extensive literature search, along with surveys with professionals, led to the identification of twenty-two FRs and synergists commonly used in France and Europe. Then, migration into artificial sweat of various FRs embedded into synthetic or commercially available polymer matrix was studied and evidenced. These results were analysed in the light of their potential effects on human health and the environment. Based on the migration's data, it is not possible to clearly rule out potential effects of FRs on human and environment health. Therefore, the authors consider that the use of FRs in domestic upholstery does not seem to be justified due to potential risks and a lack of clear benefits.

Application of Experimental Polystyrene Partition Constants and Diffusion Coefficients to Predict the Sorption of Neutral Organic Chemicals to Multiwell Plates in in Vivo and in Vitro Bioassays

Sorption to the polystyrene (PS) of multiwell plates can affect the exposure to organic chemicals over time in in vitro and in vivo bioassays. Experimentally determined diffusion coefficients in PS ( D_PS) were in a narrow range of 1.25 to 8.0 · 10^-16 m² s^-1 and PS-water partition constants ( K_PS/w) ranged from 0.04 to 5.10 log-units for 22 neutral organic chemicals. A kinetic model, which explicitly accounts for diffusion in the plastic, was applied to predict the depletion of neutral organic chemicals from different bioassay media by sorption to various multiwell plate formats. For chemicals with log K_ow > 3, the medium concentrations decreased rapidly and considerably in the fish embryo toxicity assay but medium concentrations remained relatively constant in the cell-based bioassays with medium containing 10% fetal bovine serum (FBS), emphasizing the ability of the protein- and lipid-rich medium to compensate for losses by multiwell plate sorption. The PS sorption data may serve not only for exposure assessment in bioassays but also to model the contaminant uptake by and release from plastic packaging material and the chemical transport by PS particles in the environment.

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.

Designed cellulose nanocrystal surface properties for improving barrier properties in polylactide nanocomposites

Nanocomposites are an opportunity to increase the performance of polymer membranes by fine-tuning their morphology. In particular, the understanding of the contribution of the polymer matrix/nanofiller interface to the overall transport properties is key to design membranes with tailored selective and adsorptive properties. In that aim, cellulose nanocrystals (CNC)/polylactide (PLA) nanocomposites were fabricated with chemically designed interfaces, which were ensuring the compatibility between the constituents and impacting the mass transport mechanism. A detailed analysis of the mass transport behaviour of different permeants in CNC/PLA nanocomposites was carried out as a function of their chemical affinity to grafted CNC surfaces. Penetrants (O₂ and cyclohexane), which were found to slightly interact with the constituents of the nanocomposites, provided information on the small tortuosity effect of CNC on diffusive mass transport. The mass transport of water (highly interacting with CNC) and anisole (interacting only with designed CNC surfaces) exhibited non-Fickian, Case II behaviour. The water vapour caused significant swelling of the CNC, which created a preferential pathway for mass transport. CNC surface grafting could attenuate this phenomenon and decrease the water transport rate. Anisole, an aromatic organic vapour, became reversibly trapped at the specifically designed CNC/PLA interface, but without any swelling or creation of an accelerated pathway. This caused the decrease of the overall mass transport rate. The latter finding could open a way to the creation of materials with specifically designed barrier properties by designing nanocomposites interfaces with specific interactions towards permeants.

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.

Absorption behavior of poly(methyl methacrylate)-multiwalled carbon nanotube composites: effects of UV irradiation

Understanding the effects of carbon nanotubes (CNTs) and ultraviolet (UV) irradiation on solvent transport in polymers is of practical importance for the applications of polymer-CNT composites in electronics and photonics. The transport behavior of methanol in poly(methyl methacrylate)-multiwalled carbon nanotube (PMMA-MWCNT) composites with and without UV light irradiation has been studied. The anomalous transport has been investigated as a function of the weight percentage of MWCNTs and UV dose in the temperature range of 30-50 °C. The anomalous transport consists of Case I (controlled by concentration gradient) and Case II (controlled by stress relaxation) transport; both UV irradiation and the addition of MWCNTs in PMMA enhance the transport of methanol. The activation energies for Case I and Case II transport decrease with the increase of UV dose for the PMMA-MWCNT plates with the same weight percentage of MWCNTs. Without UV irradiation, the activation energy for Case I transport of methanol decreases with the increase of the weight percentage of MWCNTs, and the activation energy for Case II transport increases with the increase of the weight percentage of MWCNTs.

Predicting diffusion coefficients of chemicals in and through packaging materials

Most of the physicochemical properties in polymers such as activity and partition coefficients, diffusion coefficients, and their activation with temperature are accessible to direct calculations from first principles. Such predictions are particularly relevant for food packaging as they can be used (1) to demonstrate the compliance or safety of numerous polymer materials and of their constitutive substances (e.g. additives, residues…), when they are used: as containers, coatings, sealants, gaskets, printing inks, etc. (2) or to predict the indirect contamination of food by pollutants (e.g. from recycled polymers, storage ambiance…) (3) or to assess the plasticization of materials in contact by food constituents (e.g. fat matter, aroma…). This review article summarizes the classical and last mechanistic descriptions of diffusion in polymers and discusses the reliability of semi-empirical approaches used for compliance testing both in EU and US. It is concluded that simulation of diffusion in or through polymers is not limited to worst-case assumptions but could also be applied to real cases for risk assessment, designing packaging with low leaching risk or to synthesize plastic additives with low diffusion rates.

Nano selenium as antioxidant agent in a multilayer food packaging material

Selenium nanoparticles (SeNPs) were incorporated in a flexible multilayer plastic material using a water-base adhesive as vehicle for SeNPs. The antioxidant performance of the original solutions containing spherical SeNPs of 50-60 nm diameter, the adhesive containing these SeNPs, and the final multilayer plastic material to be used as food packaging were quantitatively measured. The radical scavenging capacity due to SeNPs was quantified by a free radical assay developed in the laboratory and by the diphenyl-1-picrylhydrazyl (DPPH) method. DPPH was not efficient to measure the scavenging capacity in the multilayer when the free radical scavenger is not in the surface in contact with it. Several multilayer laminated structures composed by [PET (20 m)-adhesive-LDPE (with variable thickness from 35 to 90 μm)] were prepared and measured, demonstrating for the first time that free radicals derived from oxygen (OH·, O2·, and O2H) cross the PE layer and arrive at the adhesive. SeNPs remain as such after manufacture and the final laminate is stable after 3 months of storage. The antioxidant multilayer is a non-migrating efficient free radical scavenger, able to protect the packaged product versus oxidation and extending the shelf life without being in direct contact with the product. Migration tests of both Se and SeNPs to simulants and hazelnuts demonstrated the non-migrating performance of this new active packaging. Graphical abstract ᅟ.

Required barrier efficiency of internal bags against the migration from recycled paperboard packaging into food: a benchmark

The use of recycled paperboard and corrugated board for food packaging is in the interest of the sustainability of resources, but in most applications the food must be protected against contamination from these materials, such as by an internal bag with a functional barrier. Producers of packaging need a specification to find the most suitable and economical barrier for a given application, and the customer needs the confidence that a solution offered to him is adequate. An accurate determination of the barrier efficiency is not possible due to the large number of migrants, most of which have not been evaluated or not even identified. Hence the specification must be based on assumptions and verifiable by a simple test. The proposed benchmark presumes that the migration of all non-evaluated or even unknown substances in recycled paperboard will remain below 0.01 mg kg(-1) food, the conventional detection limit, if their transfer does not exceed 1% of the content in the paperboard. Some substances, such as mineral oil or fatty acids, will exceed the 0.01 mg kg(-1) limit, but they are known, evaluated and of no concern at the reduced migration. Since the critical substances must be assumed to be unknown, the criterion of the 1% migration is tested with three surrogate substances of similar volatility and covering a broad range of polarity. The cornerstones of the method are specified.

A generic emission model to predict release of organic substances from materials in consumer goods

Organic chemicals may be released when consumer goods are used, contributing to environmental and human levels of potentially hazardous chemicals. A generic model was developed to predict emissions of organic chemicals from various materials in consumer products. The model involved three modules, which each predict a key parameter needed to calculate the mass of individual chemicals emitted. Partition coefficients between a material and the surrounding air were predicted using Abraham solvation parameters, diffusion coefficients in materials were calculated using the Piringer equation, and convective mass transfer coefficients were evaluated by applying the Chilton-Colburn analogy. The calculated emission rates from predicted parameters were evaluated and agreed well with literature data. The release of plasticizers from vinyl flooring used in Sweden was calculated to demonstrate the utility of the generic model. The estimated emitted masses of di(2-ethylhexyl)phthalate (DEHP), di-iso-nonylphthalate (DINP), and 1,2-cyclohexanedicarboxylic acid di-iso-nonyl ester (DINCH) in 2012 were 210 kg, 40 kg, and 3.6 kg respectively. Emissions from vinyl flooring were estimated for the period 1990 to 2035 and it was shown that the recent substitution of DEHP with DINP will help to reduce plasticizer emissions. Model calculations for alternative plasticizers revealed that DINCH would yield similar emissions to DINP, whereas use of diethyl hexyl-iso-sorbide or diethyl hexyl adipate would result in higher emissions.

Effect of migrant size on diffusion in dry and hydrated polyamide 6

Food safety authorities have already allowed the use of mathematical models to predict diffusion from plastic food contact materials. These models use the molecular weight of the migrant as a cornerstone parameter that describes the contribution of the migrant to the diffusion process. In this work, the dependence of the diffusion coefficient on the migrant size was examined through fluorescence recovery after photobleaching (FRAP). A model migrant series of fluorescent probes was used, covering a wide molecular weight range. The advantage and originality of the tested migrant series are associated with the fact that the same shape and chemical functionality are maintained regardless of the molecular weight of the migrants. In this way the dependence of the acquired data on parameters other than size is excluded. The same experiments were carried out in dry and hydrated polyamide 6 to evaluate the effect of polymer matrix mobility in the "diffusion-migrant size" relationship. The experimental data were compared to well-known mathematical or semiempirical approaches, verifying that there is a relationship between the diffusion coefficient and the size of the migrant. However, it is demonstrated that this relationship is also affected by the mobility of the polymer matrix, becoming more pronounced as the mobility of the matrix decreases.

Development of decision tools to assess migration from plastic materials in contact with food

Testing the specific migration limits of all substances intentionally added to polymer material according to European Union (EU) regulation is a time-consuming and expensive task. Although mathematical modeling offers an interesting alternative, it can significantly overestimate the migration in situations which are strongly conservative due to significant uncertainty in transport properties. In addition, its application is of little use for end-users or enforcement laboratories, which do not have access to the formulation. This paper revises the paradigm of migration modeling by combining modeling with deformulation experiments and iterative modeling in the framework of decision theory. The complete approach is illustrated for polyolefins in contact with 50% ethanol for eight typical migrants, including hindered phenolic antioxidants and low molecular weight surrogates. Results from a French ACTIA project on the identification of formulation fingerprints and on the prediction of partition coefficients with alcoholic and aqueous stimulants is described. When the true migration was close but still lower than the limit of concern, the proposed compact decision tree, including up to four sources of uncertainty, showed that the chance of demonstrating compliance was about 3 : 4 in the presence of one source of uncertainty, whereas it fell below 2 : 4 and 1 : 4 with two and three sources of uncertainty, respectively. The recommendations for further food packaging safety surveys and future developments are discussed.