Recycling packaging materials R. Franz and f. welle, fraunhofer Institute for process engineering and Packaging, Germany 23.1 Introduction Food packaging is a still growing market. As a consequence, the demand to re-use post-consumer packaging materials grows as well. Recycling of packaging materials plays an increasing role in packaging, and numerous applications can already be found on the market. Ten or twenty years ago most post-consumer packaging waste was going into landfill sites or to incineration. Traditionally, only glass and paper/board were recycled into new applications. In the case of packaging plastics the situation is quite different. Only uncontaminated in-house production waste was collected, ground and recycled into the feedstream of the packaging production line without further decontamination. With increasing environmental demands, however, post-consumer plastics packaging materials have also been considered more and more for recycling into new packaging A closed-loop recycling for packaging plastics is also supported by public pressure. The packaging and filling companies have to take responsibility for their packaging materials and environmental concerns. In many countries the consumer, government and the packaging companies want to have packaging materials with a more favourable ecobalance in the supermarkets. A more favourable ecobalance can be achieved with different approaches. One of these approaches is the re-use of recycled material in packaging. This development is driven by the recent strong increase in polyethylene terephthalate(PET) bottles used for soft drinks, water and other foodstuffs. Today, many filling companies have decided to start using recycled plastics into their PET bottles in the near future But recycling of packing plastics is also a question of recycling technology and collection of packaging waste. Today many countries have established
23.1 Introduction Food packaging is a still growing market. As a consequence, the demand to re-use post-consumer packaging materials grows as well. Recycling of packaging materials plays an increasing role in packaging, and numerous applications can already be found on the market. Ten or twenty years ago most post-consumer packaging waste was going into landfill sites or to incineration. Traditionally, only glass and paper/board were recycled into new applications. In the case of packaging plastics the situation is quite different. Only uncontaminated in-house production waste was collected, ground and recycled into the feedstream of the packaging production line without further decontamination. With increasing environmental demands, however, post-consumer plastics packaging materials have also been considered more and more for recycling into new packaging. A closed-loop recycling for packaging plastics is also supported by public pressure. The packaging and filling companies have to take responsibility for their packaging materials and environmental concerns. In many countries the consumer, government and the packaging companies want to have packaging materials with a more favourable ecobalance in the supermarkets. A more favourable ecobalance can be achieved with different approaches. One of these approaches is the re-use of recycled material in packaging. This development is driven by the recent strong increase in polyethylene terephthalate (PET) bottles used for soft drinks, water and other foodstuffs.1 Today, many filling companies have decided to start using recycled plastics into their PET bottles in the near future. But recycling of packing plastics is also a question of recycling technology and collection of packaging waste. Today many countries have established 23 Recycling packaging materials R. Franz and F. Welle, Fraunhofer Institute for Process Engineering and Packaging, Germany
498 Novel food packaging techniques collection systems for post-consumer packaging waste, like the green dot systems. Such country-wide collecting systems guarantee increasing recovery rates. Together with new developments of recycling systems and with increasing recycling capacity the way is open for some plastics for a high value recycling of packaging waste. Due to health concerns most of the recycled post-consumer plastics are going into less critical non-food applications, but in recent years there have also been efforts to recycle post-consumer plastics like PET into new food packaging applications. This changes the situation for some packaging plastics from an open-loop recycling of packaging plastics into a closed-loop consumer plastics into direct food contact application needs much more knowledge about contamination and migration than for non-food applications, order to assess the risk to consumers' health. Additionally a quality assurance system for post-consumer plastics should be established 23.2 The recyclability of packaging plastics It is generally known that food contact materials are not completely inert and can interact with the filled product. In particular, interactions between packaging plastics and organic chemicals deserve the highest interest in this context. Such interactions start with the time point of filling and continue during the regular usage phase of a package and even longer, in case a consumer misuses' the empty packaging by filling it with chemical formulations such as household cleaners, pesticide solutions, mineral oil or others. The extent of these interactions depends on the sorption properties and the diffusion behaviour which is specific to certain polymer types or individual plastics. These physical properties together with the contact conditions ultimately determine the potential risk of food contamination from recycled packaging plastics. In other words, taking only the polymer itself into consideration and not possible recycling technologies with their special cleaning efficiencies, etc, under given conditions the inertness of the polymer is the basic parameter which determines the possibility for closed-loop recycling of packaging plastics. The inertness of common packaging polymers decreases in the following sequence Poly(ethylene naphthalate)(PEN), poly(ethylene terephthalate)(PET), rigid poly (vinyl chloride)(Pvc)> polystyrene(PS)> high density polyethylene(HDPE), polypropylene(PP)> low density polyethylene In relation to this aspect, PEN, PET or rigid Pvc do possess much more favourable material properties in comparison to other packaging plastics, such as polyolefins or polystyrene and are, therefore, from a migration related point of view much better suited for being reused in packaging applications. Polymers
collection systems for post-consumer packaging waste, like the green dot systems. Such country-wide collecting systems guarantee increasing recovery rates. Together with new developments of recycling systems and with increasing recycling capacity the way is open for some plastics for a high value recycling of packaging waste. Due to health concerns most of the recycled post-consumer plastics are going into less critical non-food applications, but in recent years there have also been efforts to recycle post-consumer plastics like PET into new food packaging applications. This changes the situation for some packaging plastics from an open-loop recycling of packaging plastics into a closed-loop recycling into new packaging materials. However, the recycling of postconsumer plastics into direct food contact application needs much more knowledge about contamination and migration than for non-food applications, in order to assess the risk to consumers’ health. Additionally a quality assurance system for post-consumer plastics should be established. 23.2 The recyclability of packaging plastics It is generally known that food contact materials are not completely inert and can interact with the filled product. 2 In particular, interactions between packaging plastics and organic chemicals deserve the highest interest in this context. Such interactions start with the time point of filling and continue during the regular usage phase of a package and even longer, in case a consumer ‘misuses’ the empty packaging by filling it with chemical formulations such as household cleaners, pesticide solutions, mineral oil or others. The extent of these interactions depends on the sorption properties and the diffusion behaviour which is specific to certain polymer types or individual plastics. These physical properties together with the contact conditions ultimately determine the potential risk of food contamination from recycled packaging plastics. In other words, taking only the polymer itself into consideration and not possible recycling technologies with their special cleaning efficiencies, etc., under given conditions the inertness of the polymer is the basic parameter which determines the possibility for closed-loop recycling of packaging plastics. The inertness of common packaging polymers decreases in the following sequence: Poly(ethylene naphthalate) (PEN), poly(ethylene terephthalate) (PET), rigid poly(vinyl chloride) (PVC) > polystyrene (PS) > high density polyethylene (HDPE), polypropylene (PP) > low density polyethylene (LDPE) In relation to this aspect, PEN, PET or rigid PVC do possess much more favourable material properties in comparison to other packaging plastics, such as polyolefins or polystyrene and are, therefore, from a migration related point of view much better suited for being reused in packaging applications. Polymers 498 Novel food packaging techniques
Recycling packaging materials 499 like polystyrene and HDPE may also be introduced into closed loop recycling if the cleaning efficiency of the recycling process is high enough regarding the input concentrations of post-consumer substances. However, regarding consumers' safety, the composition and concentration of typical substances in post-consumer plastics and the ability of the applied recycling process to remove all post-consumer substances to concentrations similar to virgin materials is of interest. The incoming concentration of post-consumer contaminants can be controlled off-line with laboratory equipment like gas chromatography or HPLC or online with detecting or sniffing devices. With help of online devices nearly a 100% control of the input materials can be established. Therefore the post consumer material is much more under control and packaging materials with high concentrations of migratable substances, or misused bottles, can be rejected and the requirements on the cleaning efficiency of the recycling process are lower. The source control is therefore the crucial point regarding of the worst casescenario of the so-called challenge test (see Section 23. 4.1) Recovery of packaging plastics into new packaging applications requires blending of recycled with virgin materials. In praxis today, the recyclate content of packaging materials varies from only a few per cent up to 50% recycled material in some packaging applications. Numerous studies have been carried out on the determination the material properties and the blending behaviour of recycled plastics. However, it is not the focus of this chapter to deal with blending of polymers but it needs to be stressed that the recycled material should be suitable for blending with virgin materials. Additionally, the mechanical properties of the recyclate should be not influenced in a negative way, so as to avoid potential consequences for the additive status of the recycled plastics The average number of cycles is a function of the blend ratio and the number of recycling steps carried out. In practice the average number of cycles ranges from one to three. Therefore, the material is not recycled many times and the problem of accumulation of degradation products is in most cases of no concern An inherent problem of recycling, however, is the inhomogeneity of the recovered materials. Normally various polymer additives, lubricants, etc. are used by the different polymer manufacturers or converters in order to establish the desired properties of the packaging materials, and all different polymer additives are found as a mixture in the recyclate containing packages. Modern sorting technologies are able to provide input materials for recycling which are nearly 100% of one polymer type. Taking, in addition, the additive status into account will be a sophisticated challenge of future developments. Together with the inertness of the polymers this is one reason why recent closed-loop recycling efforts are focused on polymers which have low amounts of additives e.g. PET However, as mentioned above, the question of recyclability is mainly influenced by the source control of the input material going into the recycling process. If the recovery system considers the manufacturer or the origin of the packaging materials, usually the additive status of the input feedstock is known. An example for this will be HDPE milk bottles collected by a deposit system(see Section 23.5.2)
like polystyrene and HDPE may also be introduced into closed loop recycling if the cleaning efficiency of the recycling process is high enough regarding the input concentrations of post-consumer substances. However, regarding consumers’ safety, the composition and concentration of typical substances in post-consumer plastics and the ability of the applied recycling process to remove all post-consumer substances to concentrations similar to virgin materials is of interest. The incoming concentration of post-consumer contaminants can be controlled off-line with laboratory equipment like gas chromatography or HPLC or online with detecting or sniffing devices. With help of online devices nearly a 100% control of the input materials can be established. Therefore the postconsumer material is much more under control and packaging materials with high concentrations of migratable substances, or misused bottles, can be rejected and the requirements on the cleaning efficiency of the recycling process are lower. The source control is therefore the crucial point regarding of the ‘worstcase’ scenario of the so-called challenge test (see Section 23.4.1). Recovery of packaging plastics into new packaging applications requires blending of recycled with virgin materials. In praxis today, the recyclate content of packaging materials varies from only a few per cent up to 50% recycled material in some packaging applications. Numerous studies have been carried out on the determination the material properties and the blending behaviour of recycled plastics. However, it is not the focus of this chapter to deal with blending of polymers but it needs to be stressed that the recycled material should be suitable for blending with virgin materials. Additionally, the mechanical properties of the recyclate should be not influenced in a negative way, so as to avoid potential consequences for the additive status of the recycled plastics. The average number of cycles is a function of the blend ratio and the number of recycling steps carried out. In practice the average number of cycles ranges from one to three.3 Therefore, the material is not recycled many times and the problem of accumulation of degradation products is in most cases of no concern. An inherent problem of recycling, however, is the inhomogeneity of the recovered materials. Normally various polymer additives, lubricants, etc. are used by the different polymer manufacturers or converters in order to establish the desired properties of the packaging materials, and all different polymer additives are found as a mixture in the recyclate containing packages. Modern sorting technologies are able to provide input materials for recycling which are nearly 100% of one polymer type. Taking, in addition, the additive status into account will be a sophisticated challenge of future developments. Together with the inertness of the polymers this is one reason why recent closed-loop recycling efforts are focused on polymers which have low amounts of additives e.g. PET. However, as mentioned above, the question of recyclability is mainly influenced by the source control of the input material going into the recycling process. If the recovery system considers the manufacturer or the origin of the packaging materials, usually the additive status of the input feedstock is known. An example for this will be HDPE milk bottles collected by a deposit system (see Section 23.5.2). Recycling packaging materials 499
00 Novel food packaging techniques 23.3 Improving the recyclability of plastic packaging 23.3.1 Souree control The source control is the first and most important step of packaging plastics. There must be efficient recovery or sorting processes which are able to control the input fraction going into a closed-loop recycling process. The feedstream material should have a minimum polymer type purity of 99%. Other polymers, which may interfere, have to be sorted out of the recycling stream. Also the first life of the packaging material is of interest. In general only packages previously filled with foodstuffs should be used as an input fraction for a closed-loop recycling process. However there are exceptions, e.g. for Pet due to its high inertness the first packaging application is not so important. Two studies were undertaken",to determine the impact of PET materials formerly used for non-food applications. Both studies came to the same result, that due to the low diffusivity of PET packages from non-food applications could also be used as input material for bottle-to-bottle recycling This underlines the favourite position of PeT bottles for a closed loop recycling It could be shown that deposit systems and recovery systems like curbside ackaging collections with efficient sorting processes, are able to support input materials for high value recycling. However, as mentioned above, the higher the diffusivity of the polymer and, therefore, higher sorption of post-consumer substances the more important is the source control in order to reduce contamination with post-consumer substances or misused packages. The source control can be supplied by modern detecting or sniffing devices which are able to reduce the intake of undesired post-consumer substances into the recycling 3.3.2 Contamination levels and frequency of misuse of recycled plastics Regarding the typical contamination of post-consumer plastics most published data are available for PET bottles and corresponding recyclates. Most of them have quantified or identified substances in post-consumer PET by using different methods. Sadler et al. b, published two studies containing data of contaminants in recycled PET. In the first study he pointed out that most compounds found in recycled PET come from PET starting materials oligomers, flavour bases, label materials and compounds originating in base cups. Contaminants which do not fall into one of these categories are rare. In samples with high levels of contaminants the sum of all compounds was detected to be approximately 25 ppm. No single contaminant appears to be present in post-consumer PET above I ppm and all non-usual compounds in post-consumer PET were present below 0. 1 ppm. In a second study the identity and origin of contaminants in food grade virgin and commercially washed post consumer PET flakes were determined. A total of 18 samples of post-consumer recycled PET flakes was examined. In most cases, positive identification was possible, however, in few cases ambiguity resulted from the similarities in mass
23.3 Improving the recyclability of plastic packaging 23.3.1 Source control The source control is the first and most important step in closed-loop recycling of packaging plastics. There must be efficient recovery or sorting processes which are able to control the input fraction going into a closed-loop recycling process. The feedstream material should have a minimum polymer type purity of 99%. Other polymers, which may interfere, have to be sorted out of the recycling stream. Also the first life of the packaging material is of interest. In general only packages previously filled with foodstuffs should be used as an input fraction for a closed-loop recycling process. However there are exceptions, e.g. for PET due to its high inertness the first packaging application is not so important. Two studies were undertaken4,5 to determine the impact of PET materials formerly used for non-food applications. Both studies came to the same result, that due to the low diffusivity of PET packages from non-food applications could also be used as input material for bottle-to-bottle recycling. This underlines the favourite position of PET bottles for a closed loop recycling. It could be shown that deposit systems and recovery systems like curbside packaging collections with efficient sorting processes, are able to support input materials for high value recycling. However, as mentioned above, the higher the diffusivity of the polymer and, therefore, higher sorption of post-consumer substances the more important is the source control in order to reduce contamination with post-consumer substances or misused packages. The source control can be supplied by modern detecting or sniffing devices which are able to reduce the intake of undesired post-consumer substances into the recycling stream. 23.3.2 Contamination levels and frequency of misuse of recycled plastics Regarding the typical contamination of post-consumer plastics most published data are available for PET bottles and corresponding recyclates. Most of them have quantified or identified substances in post-consumer PET by using different methods. Sadler et al.6,7, published two studies containing data of contaminants in recycled PET. In the first study he pointed out that most compounds found in recycled PET come from PET starting materials, oligomers, flavour bases, label materials and compounds originating in base cups. Contaminants which do not fall into one of these categories are rare. In samples with high levels of contaminants the sum of all compounds was detected to be approximately 25 ppm. No single contaminant appears to be present in post-consumer PET above 1 ppm and all non-usual compounds in post-consumer PET were present below 0.1 ppm. In a second study the identity and origin of contaminants in food grade virgin and commercially washed postconsumer PET flakes were determined. A total of 18 samples of post-consumer recycled PET flakes was examined. In most cases, positive identification was possible, however, in few cases ambiguity resulted from the similarities in mass 500 Novel food packaging techniques
Recycling packaging materials 501 spectra of closely related compounds. Compounds identified were classified into categories associated with their chemical nature or presumed origins, e.g small and ethylene glycol related compounds (methanol, formic acid acetaldehyde, acetic acid), flavour compounds (limonene), benzoic acid or related benzene dicarboxylic acid substances(benzoic and terephthalic acid and corresponding esters, benzaldehyde, phthalates), aliphatic hydrocarbons and acids as well as unexpected and miscellaneous compounds(Tinuvin, nicotine) Bayer has analysed samples from five different recovery systems including PET containers from non-food applications. In these samples he identified 121 substances. The total concentration of all substances found in deposit material was 28.5 ppm. The corresponding concentrations of PET flakes coming from non-food applications were found to be 39 ppm. The key compounds identified were hexanal, benzaldehyde, limonene, methyl salicylate and 5-iso-propyl-2 methylphenol(the flavour compound carvacrol). In conventional washed flakes a maximum concentration of 18 ppm for limonene was determined. For PET flakes from non-food applications the major compound methyl salicy late was determined in a maximum concentration of 15.3 ppm. Additionally the material was analysed after a super-clean process. No peak could be detected in concentrations above the FDA threshold of regulation limit of 0.22 ppm All three published studies mentioned above found no hints for misuse of post-consumer PET bottles e.g. for storage of household cleaners etc. This is most probably due to the fact that these studies are based only on very small amounts of different flake samples. From a statistical point of view flakes from misused bottles should be extremely rare due to high dilution with non-misused PET bottles. Therefore, these published studies are not able to detect the frequency of misuse in typical post-consumer PET flakes In 2002 an EU project under the co-ordination of Fraunhofer IVV was finished.8,%, 10 Within this study 689 post-consumer PET flake samples from commercial washing plants were collected between 1997 and 2001. The samples are conventionally recycled deposit and curbside fractions collected in twelve European countries. In addition, 38 reprocessed pellet samples and 142 samples from super-clean recycling processes were collected. All samples were screened for post-consumer substances, and for hints of possible misuse of the PET bottles by the consumer, in order to get an overview of the quality of commercially recycled post-consumer PET. As a result the average concentrations in 689 PET flake samples for typical post-consumer compounds like limonene and acetaldehyde are 2.9 ppm and 18.6 ppm, respectively. A maximum concentration of approximately 20 ppm of limonene and 86 ppm for acetaldehyde could be determined, which is in close agreement with the above mentioned studies. The impact of the recovery system and the country, where st-consumer pet bottles were collected. on the nature and extent of adventitious contaminants was found not to be significant. However in three bottle flakes hints for a possible misuse of PET bottles e.g. for storage of household chemicals or fuels were found. From a statistical evaluation 0.03 to 0.04% of the pet bottles might be misused. Under consideration of the dilution
spectra of closely related compounds. Compounds identified were classified into categories associated with their chemical nature or presumed origins, e.g. small and ethylene glycol related compounds (methanol, formic acid, acetaldehyde, acetic acid), flavour compounds (limonene), benzoic acid or related benzene dicarboxylic acid substances (benzoic and terephthalic acid and corresponding esters, benzaldehyde, phthalates), aliphatic hydrocarbons and acids as well as unexpected and miscellaneous compounds (Tinuvin, nicotine). Bayer4 has analysed samples from five different recovery systems including PET containers from non-food applications. In these samples he identified 121 substances. The total concentration of all substances found in deposit material was 28.5 ppm. The corresponding concentrations of PET flakes coming from non-food applications were found to be 39 ppm. The key compounds identified were hexanal, benzaldehyde, limonene, methyl salicylate and 5-iso-propyl-2- methylphenol (the flavour compound carvacrol). In conventional washed flakes a maximum concentration of 18 ppm for limonene was determined. For PET flakes from non-food applications the major compound methyl salicylate was determined in a maximum concentration of 15.3 ppm. Additionally the material was analysed after a super-clean process. No peak could be detected in concentrations above the FDA threshold of regulation limit of 0.22 ppm. All three published studies mentioned above found no hints for misuse of post-consumer PET bottles e.g. for storage of household cleaners etc. This is most probably due to the fact that these studies are based only on very small amounts of different flake samples. From a statistical point of view flakes from misused bottles should be extremely rare due to high dilution with non-misused PET bottles. Therefore, these published studies are not able to detect the frequency of misuse in typical post-consumer PET flakes. In 2002 an EU project under the co-ordination of Fraunhofer IVV was finished.8,9,10 Within this study 689 post-consumer PET flake samples from commercial washing plants were collected between 1997 and 2001. The samples are conventionally recycled deposit and curbside fractions collected in twelve European countries. In addition, 38 reprocessed pellet samples and 142 samples from super-clean recycling processes were collected. All samples were screened for post-consumer substances, and for hints of possible misuse of the PET bottles by the consumer, in order to get an overview of the quality of commercially recycled post-consumer PET. As a result the average concentrations in 689 PET flake samples for typical post-consumer compounds like limonene and acetaldehyde are 2.9 ppm and 18.6 ppm, respectively. A maximum concentration of approximately 20 ppm of limonene and 86 ppm for acetaldehyde could be determined, which is in close agreement with the abovementioned studies. The impact of the recovery system and the country, where the post-consumer PET bottles were collected, on the nature and extent of adventitious contaminants was found not to be significant. However in three bottle flakes hints for a possible misuse of PET bottles e.g. for storage of household chemicals or fuels were found. From a statistical evaluation 0.03 to 0.04% of the PET bottles might be misused. Under consideration of the dilution Recycling packaging materials 501