Polyethylene terephthalate bottles (PRBs): a health and safety assessment

Recent Advances in Biological Recycling of Polyethylene Terephthalate (PET) Plastic Wastes

Polyethylene terephthalate (PET) is one of the most commonly used polyester plastics worldwide but is extremely difficult to be hydrolyzed in a natural environment. PET plastic is an inexpensive, lightweight, and durable material, which can readily be molded into an assortment of products that are used in a broad range of applications. Most PET is used for single-use packaging materials, such as disposable consumer items and packaging. Although PET plastics are a valuable resource in many aspects, the proliferation of plastic products in the last several decades have resulted in a negative environmental footprint. The long-term risk of released PET waste in the environment poses a serious threat to ecosystems, food safety, and even human health in modern society. Recycling is one of the most important actions currently available to reduce these impacts. Current clean-up strategies have attempted to alleviate the adverse impacts of PET pollution but are unable to compete with the increasing quantities of PET waste exposed to the environment. In this review paper, current PET recycling methods to improve life cycle and waste management are discussed, which can be further implemented to reduce plastics pollution and its impacts on health and environment. Compared with conventional mechanical and chemical recycling processes, the biotechnological recycling of PET involves enzymatic degradation of the waste PET and the followed bioconversion of degraded PET monomers into value-added chemicals. This approach creates a circular PET economy by recycling waste PET or upcycling it into more valuable products with minimal environmental footprint.

[Safety verification for reuse of PET and glass bottles]

In order to verify the safety associated with reusing PET and glass bottles, a challenge test was conducted with five surrogate contaminants: 1,1,1-trichloroethane, chlorobenzene, toluene, benzophenone and phenyl cyclohexane. Bottles were filled with a cocktail solution of these contaminants and stored at 50 °C for 7 days, then washed with water and alkaline solutions. Material and migration tests were conducted at each step. The material test results showed that 430-1,440 µg/g of the contaminants were retained after water washing, and that even after washing with a 3.5% NaOH solution, 225-925 µg/g of the contaminants were retained. The migration tests revealed that 0.095-7.35 µg/mL of the contaminants were eluted. Similar tests were conducted with a soft drink ingredient, limonene. The results revealed that 48 µg/g of limonene was retained even after washing with NaOH solution, and that 0.16 µg/mL of limonene was eluted. Conversely, no contaminants were eluted from glass bottles after washing with the NaOH solution. Thus, from the viewpoint of safety and the preservation of content quality, PET bottles are not considered suitable for reuse when compared with glass bottles.

Evaluation of sub-critical water as an extraction fluid for model contaminants from recycled PET for reuse as food packaging material

Recycling of plastics for food-contact packaging is an important issue and research into meaningful and cost-effective solutions is in progress. In this paper, the use of sub-critical water was evaluated as an alternative way of purifying poly(ethylene terephthalate) (PET) flakes for direct food contact applications. The effects of temperature, pressure and flow rate were assessed on the extraction efficiency of two of the most challenging classes of contaminants (toluene and benzophenone) from PET by sub-critical water using a first-order fractional experimental design. Extraction yield was quantified using GC/FID. The most important parameter was flow rate, indicating that the decrease in sub-critical water polarity with temperature was insufficient to eliminate partition effects. Temperature was also important, but only for the optimization of toluene extraction. These results may be explained by the poor solubility of higher molar mass compounds in sub-critical water compared to lower molar mass compounds under the same conditions, and the small decrease in dielectric constant with temperature under the experimental conditions evaluated. As cleaning efficiency is low and PET is very susceptible to hydrolysis, which limits the use of higher temperatures vis-à-vis physical recycling, the proposed extraction is unsuitable for a standalone super-clean process but may be a step in the process.

Identification of chemicals, possibly originating from misuse of refillable PET bottles, responsible for consumer complaints about off-odours in water and soft drinks

Mineral water and soft drinks with a perceptible off-odour were analysed to identify contaminants originating from previous misuse of the refillable polyethylene terephthalate (PET) bottle. Consumers detected the off-odour after opening the bottle and duly returned it with the remaining content to the producers. The contaminants in question had thus been undetected by the in-line detection devices (so-called 'sniffers') that are supposed to reject misused bottles. GC-MS analysis was carried out on the headspace of 31 returned products and their corresponding reference products, and chromatograms were compared to find the possible off-odour compounds. Substances believed to be responsible for the organoleptic change were 2-methoxynaphthalene (10 bottles), dimethyl disulfide (4), anethole (3), petroleum products (4), ethanol with isoamyl alcohol (1) and a series of ethers (1). The mouldy/musty odour (5 bottles) was caused by trichloroanisole in one instance. In some cases, the origins of the off-odours are believed to be previous consumer misuse of food products (liquorice-flavoured alcohol, home-made alcohol containing fusel oil) or non-food products (cleaning products, petroleum products, oral moist snuff and others). The results also apply to 1.5-litre recyclable PET bottles, since the nature and extent of consumer misuse can be expected to be similar for the two bottle types.

European survey on post-consumer poly(ethylene terephthalate) (PET) materials to determine contamination levels and maximum consumer exposure from food packages made from recycled PET

Typical contamination and the frequency of misuse of poly(ethylene terephthalate) (PET) bottles are crucial parameters in the risk assessment of post-consumer recycled (PCR) PET intended for bottle-to-bottle recycling for direct food contact applications. Owing to the fact that misuse of PET bottles is a rare event, sustainable knowledge about the average concentration of hazardous compounds in PCR PET is accessible only by the screening of large numbers of samples. In order to establish average levels of contaminants in PET source materials for recycling, PET flakes from commercial washing plants (689 samples), reprocessed pellets (38) and super-clean pellets (217) were collected from 12 European countries between 1997 and 2001. Analysis of these materials by headspace gas chromatography revealed average and maximum levels in PCR PET of 18.6 and 86.0 mg kg-1 for acetaldehyde and 2.9 and 20 mg kg-1 for limonene, respectively. Acetaldehyde and limonene are typical compounds derived from PET itself and from prior PET bottle contents (flavouring components), respectively. Maximum levels in PCR PET of real contaminants such as misuse chemicals like solvents ranged from 1.4 to 2.7 mg kg-1, and statistically were shown to result from 0.03 to 0.04% of recollected PET bottles that had been misused. Based on a principal component analysis of the experimental data, the impact of the recollecting system and the European Union Member State where the post-consumer PET bottles had been collected on the nature and extent of adventitious contaminants was not significant. Under consideration of the cleaning efficiency of super-clean processes as well as migration from the bottle wall into food, it can be concluded that the consumer will be exposed at maximum to levels < 50 ng total misuse chemicals day-1. Therefore, PCR PET materials and articles produced by modern superclean technologies can be considered to be safe in direct food applications in the same way as virgin food-grade PET.

Flavor threshold for acetaldehyde in milk, chocolate milk, and spring water using solid phase microextraction gas chromatography for quantification

The detection threshold of acetaldehyde was determined on whole, lowfat, and nonfat milks, chocolate-flavored milk, and spring water. Knowledge of the acetaldehyde threshold is important because acetaldehyde forms in milk during storage as a result of light oxidation. It is also a degradation product of poly(ethylene terephthalate) during melt processing, a relatively new packaging choice for milk and water. There was no significant difference in the acetaldehyde threshold in milk of various fat contents, with thresholds ranging from 3939 to 4040 ppb. Chocolate-flavored milk and spring water showed thresholds of 10048 and 167 ppb, respectively, which compares favorably with previous studies. Solid phase microextraction (SPME) was verified as an effective method for the recovery of acetaldehyde in all media with detection levels as low as 200 and 20 ppb in milk and water, respectively, when using a polydimethyl siloxane/Carboxen SPME fiber in static headspace at 45 degrees C for 15 min.

Desorption behavior of sorbed flavor compounds from packaging films with ethanol solution

Desorption behavior of sorbed flavor compounds such as ethyl esters, n-aldehydes, and n-alcohols from LDPE and PET films was investigated in 0 to 100% (v/v) ethanol solutions at 20 degrees C, 50 degrees C, and 60 degrees C. In both films, the desorption apparently increased with increasing ethanol concentration and treatment temperature, depending on the compatibility of the flavor compound with the solvent. Namely, the partition coefficient of ethyl esters, n-aldehydes, and n-alcohols in the LDPE film turned out to be approximately zero at >/=60%, >/=80%, and >/=40% (v/v) ethanol, respectively (for PET film, >/=80%, >/=80%, and >/=40% (v/v) ethanol concentrations were required for complete desorption, respectively). As for physical properties (heat of fusion, melting point, and tensile strength and elongation at break) of LDPE and PET films, there were no significant differences between intact film and the treated film with 60% (v/v) ethanol for 30 min at 60 degrees C. These results suggest that it is possible to apply a desorption solvent such as ethanol solution for desorption of sorbed flavor compounds from packaging films with no physical change in the film properties by this desorption treatment.

Quality and safety aspects of reusable plastic food packaging materials: a European study to underpin future legislation

The objective of this study was to develop a comprehensive package of quality assurance criteria for use by industry and regulatory authorities for ensuring the quality and safety-in-use (sensory, microbiological and chemical) of reused plastics for food packaging. The study included thermal degradation effects, flavour carry-over caused by flavour and off-flavour substances, the influence of washing processes on the materials, and the efficiency of washing processes in removing off-flavour substances and surrogate substances representing misuse chemicals as might be put in bottles by consumers. The microbial safety of the refillable plastic articles in relation to commercial washing processes and the industrial procedures applied has also been investigated. Lastly, the suitability of laboratory procedures using strips of bottle material for predicting the sorption and washing properties of refillable plastic bottles has been studied. In general it is concluded that reuse of the articles does not significantly influence any of the properties investigated. Neither the chemical, physical nor surface properties seem to be significantly influenced by repeated washing. It can be concluded, however, that it is very likely that most of the articles investigated will cause flavour carry-over to a new filling if they are contaminated with strongly flavoured products. Finally it can be concluded that the procedures evaluated can serve as a basis for future legislation on refillable articles, but for several procedures (like quick predictive testing with strips) more investigation is required to create a more solid basis.

Gel permeation chromatography (GPC) of repeatedly extruded polyethylene terephthalate (PET)

The paper deals with gel permeation chromatography (GPC) monitoring of the behaviour of PET (polyethylene terephthalate) after repeated extrusions. Virgin PET was submitted to three successive extrusion/drying cycles and then the samples were swelled with hexafluoroisopropanol and treated with chloroform. GPC analysis was carried out at room temperature on a B.C.S. Serial LC 2000 GPC system equipped with a series of four GPC columns with UV detection at 254 nm and chloroform as eluent. GPC results showed that after each extrusion step the molecular weight distribution of the PET was different and Mw, Mn and Mz decreased. These findings suggest that during each extrusion degradation occurs and that repeated extrusions, as in the case of the recycling PET, may cause an alteration of the molecular weight distribution of the original PET.

Evaluation of recycled HDPE milk bottles for food applications

The possibilities of recycling milk-contaminated HDPE were investigated. Bottles were blown of respectively untreated, caustic-washed and caustic-washed/steam-stripped/air-dried recycled material. The migration characteristics of the different bottles were compared using various food simulants, as well as their sensorial and mechanical properties. From the analytical and sensorial experiments, it was shown that the untreated and caustic-washed recycled material could not be considered as a food packaging material. A high number of compounds able to migrate were detected, causing an off-flavour which could easily be recognized. The steam-stripped recycled material however, seemed to perform almost as well as its corresponding virgin material. Only low amounts of compounds able to migrate could be detected, resulting in a packaging material characterized by excellent sensorial properties which could not be distinguished from its virgin material. Furthermore it was proved that the mechanical properties of the recycled material did not change during the recycling process.

Evaluation, modelling and optimization of the cleaning process of contaminated plastic food refillables

In this study several types of bottle materials (glass, PET (polyethylene terephthalate), PC (polycarbonate), HDPE (high density polyethylene), PP (polypropylene) and PVC (polyvinyl chloride)) were evaluated in order to be used as food refillables, comparing the residual chemical contamination after classical caustic washing. Bottles were contaminated with model chemicals (chloroxylenol and d-limonene) and caustic washed with varied process parameters using a simulated laboratory-scale washing procedure. After washing, the chemical-contaminated bottles were filled with water and stored for 28 days at 37 degrees C. The concentrations of the model chemicals in the water after storage were taken as a measure of chemical contamination. The influence of the cleaning parameters (temperature, caustic and commercial additive concentration) was studied using response surface methodology. Washing temperature showed a significant influence on the removal of absorbed chemicals from surfaces compared with the effect of the caustic and especially the additive concentration. Optimization of caustic cleaning for the cleaning process in question led to better cleaning effectiveness, although none of the different washing conditions were able to remove all absorbed chemicals out of the polymeric resins. Commercially available plastic refillables (PET and PC) showed the best chemical rinsability. Glass bottles, however, had in every case the best rinsing characteristics.

Validation studies of a quick test for predicting the sorption and washing properties of refillable plastic bottles

Quick tests are proposed in the literature as alternatives to the large scale contamination and washing studies performed to date to assess the acceptability of plastic beverage bottles for refilling. These tests use small plastic specimens ('strips') in place of bottles and use mixtures of surrogate contaminants to model the myriad of chemicals that could in principle contaminate returned bottles because of consumer mis-use. The work reported here has measured the sorption and wash performance using the quick test protocol with PET (polyethyleneterephthalate) strips and laboratory washing and compared the results with tests using actual bottles and a commercial washing process. The comparison indicates that the quick test satisfactorily simulated contamination and commercial washing of intact bottles. The results also show that repeated washing of PET bottles does not cause higher sorption of contaminants.

HACCP approach to ensure the safety and quality of food packaging

EC Directive 93/43/EEC of 14 June 1993 on the hygiene of foodstuffs has been implemented in the Netherlands through the Food and Commodity Act (Warenwet) of 14 December 1995. This Directive requires food companies to identify steps in their activities that are critical to ensuring food safety, and to ensure that adequate safety procedures are identified, implemented, maintained and reviewed based on the principles of the Hazard Analysis Critical Control Point (HACCP) system. HACCP is a tool used to assess hazards, estimate risks and establish specific control measures that emphasize prevention and control rather than reliance on end-product testing. Increasing public awareness of food safety, together with the introduction of this new legislation, has led producers and retailers of food to demand higher standards from their suppliers. Suppliers of raw materials, ingredients and also food packaging will be expected to bring their standards of hygiene in line with the expectations of the food industry. Food producers will need to obtain the guarantee from their suppliers that the packaging does not negatively influence their products. HACCP is a method that can also be applied to ensure the safety and other quality aspects of all kinds of food packaging materials such as films, foils, trays, cups, boxes and tubs made of paper, cardboard, polymers, metal and other materials (single use or disposable packagings as well as re-usable and recycled packagings). At the Netherlands Organization for Applied Scientific Research (TNO), the quality and safety aspects of re-use of food packaging, and refillable bottles in particular, have been the subject of extensive investigations in the project 'Quality monitoring of synthetic refillable bottles'. In this paper the set-up of the project and the Codes of Practice for refillable bottles are described. Moreover, the applicability of HACCP to food packagings and an example of a HACCP study for refillable PET bottles will be discussed.