Resources, Conservation and Recycling 78 (2013) 74– 80
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Resources, Conservation and Recycling
journa l h om epa ge: www.elsevier.com/locate/resconrec
Review
Polymer film packaging for food: An environmental assessment
C.Y. Barlow∗, D.C. Morgan
Institute for Manufacturing, University of Cambridge, 17 Charles Babbage Road, Cambridge CB3 0FS, UK
a r t i c l e i n f o
Article history:
Received 16 March 2013
Received in revised form 7 July 2013
Accepted 8 July 2013
Keywords:
Packaging
Multi-layer plastics
Barrier
Recycling
a b s t r a c t
Plastics packaging is ubiquitous in the food industry, fulfilling a range of functions including a significant
role in reducing food waste. The public perception of packaging, however, is dominated by end-of-life
aspects, when the packaging becomes waste often found littering urban, rural and marine environments.
A balanced analysis of the role of packaging demands that the whole lifecycle is examined, looking not
only at the packaging itself but also at the product being packaged. This paper focuses on packaging in the
meat and cheese industry, analysing the impact of films and bags. The functions of packaging are defined
and the environmental impact of delivering these functions is assessed. The influence of packaging on
levels of waste and energy consumption elsewhere in the system is examined, including the contentious
issue of end-of-life for packaging.
Strategies for minimizing the environmental impact of the packaging itself involve reduction in the
amount of material used (thinner packaging), rather than emphasizing end-of-life issues. Currently, with
polymer recycling not at a high level, evidence suggests that this strategy is justifiable. Biodegradable
polymers may have some potential for improving environmental performance, but are still problematic.
The conclusion is that although current packaging is in some ways wasteful and inefficient, the
alternatives are even less desirable.
© 2013 Elsevier B.V. All rights reserved.
Contents1. Packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .741.1. The role of packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .741.2. Polymer film packaging in the meat and cheese industry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .751.3. Multi-layer or mono-layer polymer films? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .762. Polymer recycling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .772.1. General issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .772.2. Recycling of mixed or post-consumer polymers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .782.3. Recycling of films . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .793. Biodegradable polymers for food packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .794. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79Funding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .801. Packaging1.1. The role of packagingPackaging of different sorts is found in the food and drink supplychain. Primary or sales packaging (e.g. packets for biscuits, bottlesfor milk) is the most familiar to the general public, and is defined as“a sales unit to the final user or consumer at the point of purchase”∗Corresponding author. Tel.: +44 1223332627.E-mail address: cyb@eng.cam.ac.uk (C.Y. Barlow).(European Parliament and Council Directive, 1994). The function ofsecondary packaging is to group items together for sale to the cus-tomer or to replenish the shelves at the point of sale e.g. trays, boxesor films. Finally tertiary packaging is used to group goods for trans-port, for example pallets and film are used to facilitate transportin trucks (Incpen, 2010). We will here focus on primary packaging,which tends to be the most visible aspect of packaging. Secondaryand tertiary packaging is mostly removed by retailers, and so formspart of the commercial rather than the domestic waste stream.End-of-life disposal of polymers from industrial and commercialsources is handled differently from products which have enteredthe consumer market. In some ways the problems are less difficult
0921-3449/$ – see front matter © 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.resconrec.2013.07.003
C.Y. Barlow, D.C. Morgan / Resources, Conservation and Recycling 78 (2013) 74– 80 75
Table 1
Functions of primary packaging.
Function Achieved by Example
Product handling Containers for loose goods and liquids; clustering of
small items.
Bottle, box, bag (liquids, powders) Tray, bag (meat,
cheese, loose foods and other products)
Barrier; hygiene Prevents contact between atmosphere/environment
and product; selective passage of gases; protect from
light; prevent odours escaping.
Plastic bag for foods multi-layer packaging for cheese
Protection Fragile items: impact-resistant packaging; surface
damage for other items
Egg box; blister pack
Increased product life Barrier function; inert atmosphere; reduce handling Foods in protective atmosphere or in vacuo
Tamper-evidence Sealed container Tamper-evident tabs; removable metal can lids
Information; advertising Writing and pictures on packaging Labels stuck on; printing directly on to packaging
to tackle: contamination may be lower, and the range of materialsis smaller, but economic pressures mean that effective recyclingrates may be very low (e.g. Hopewell et al., 2009; Shonfield, 2008).The functions of primary packaging are summarized in Table 1.The packaging industry is huge: the UK industry is estimatedat £10 billion, with 85,000 employees, making up 3% of the UKworkforce (Packaging Federation, 2013). The industry is subjectto pressure from disparate stakeholders: producers, retailers andcustomers have different priorities, and packaging is not alwaysperceived as adding value to the product. Packaging is by its naturetransient; most packaging has a short lifetime and is discarded afteruse, entering the municipal waste stream after a lifetime of typicallyless than a year (Hopewell et al., 2009). Public attitudes towardspackaging are generally negative, when the matter is considered atall. Reporting on a survey of over 1000 consumers (Incpen, 2008),79% believed products to be over-packaged, about 35% believedpackaging is difficult to dispose of and is bad for the environment.The industry invests time and energy in defending the benefits ofpackaging in reducing waste across the whole supply chain (e.g.Incpen, 2010, reporting that packaging typically protects food andgoods which have more than ten times the energy and resourcesembodied in the packaging).As is evident from Table 1, packaging does have many functions.80% of customer purchasing decisions for foodstuffs are madebased on the packaging (Mortensen, 2008).It is estimated (Packaging Federation, 2013) that 50% of foodmay be wasted in developing countries before it reaches retailers,compared with 3% in developed countries; packaging is thought toplay a large part in this. The wastage reduction comes mainly fromthe physical protection against damage afforded by the packaging,and by the increased usable product life provided by the barrierfunction. For example, the Packaging Federation cites a cucumbergrowers association study that claims unwrapped cucumbers areunsaleable after 3 days because of loss of water, but 1.5 g packagingreduces water loss to the extent that the shelf-life can be increasedto 14 days.It is estimated that 50% of food produced globally never reachesconsumers and that a significant proportion of this could bereduced by increased packaging (Incpen, 2010; Love Food HateWaste, 2013) The industry (Packaging Federation, 2013) points outthat packaging reduces damage in the supply chain and increasesthe shelf-life of products.Through tamper-proofing, packaging enables a high standard ofproduct quality assurance, which is not possible with loose goods.The energy consumed by packaging must be viewed in relation tothe whole supply chain. Looking at a typical food supply chain,50% of the energy is used in food production, 10% in commercialtransport to shops and retailing, 10% for packaging and 30% by con-sumers transport to shops, storing and cooking food (Incpen, 2010).Looking at the specific example of meat packaging using LDPE film,some estimates are given in Table 2. A bag weighing about 20 gis sufficient for between 0.5 and 1 kg of meat. The emissions fromproduction of 1 kg of LDPE in the form of film are about 3 kg CO2e(Plastics Europe, 2008), so that 0.05 kg CO2e is emitted to providepackaging for 1 kg meat.Packaging is subject to legislation to try to minimize environ-mental impact. UK legislation introduced in 2003 specifies that“. . .packaging volume and weight be limited to the minimum ade-quate amount to maintain the necessary level of safety, hygieneand acceptance for the packaged product and for the consumer”(Packaging Legislation, 2003). It is a further requirement that pack-aging “shall be designed, produced and commercialized in sucha way as to permit its reuse or recovery, including recycling. . .”These two requirements are not compatible: as demonstrated inthe current work, minimum weight packaging comes at the costof sacrificing recyclability. Reference is also made to minimizingthe presence of noxious and hazardous materials in end-of-lifeprocessing. Other countries have comparable aspirations to try toachieve these aims. For example, the US Environmental ProtectionAgency supports the Sustainable Packaging Coalition (SPC). A crossindustry working group founded in 2005, the SPC proposes criteriafor sustainable packaging which include minimizing the amount ofmaterial used, and avoiding materials which could be harmful atany stage in their lifecycle (Sustainable Packaging Coalition).The aims of such initiatives are admirable, but the implementa-tion is more problematic. Some of the technical issues are exploredfurther in Section 2, but there are also social and economic factors.Widespread adoption of sustainable practices requires strong andcoherent policy, at national and international levels. Some of thedifficulties relating to policy and plastics are discussed by Shaxson(2009).1.2. Polymer film packaging in the meat and cheese industryThe preservation of meat and cheese as it passes throughnational and international distribution networks requires anextended shelf life so that the product remains saleable. The pack-aging is typically designed to fulfil a range of functions, as shownin Table 3. The function of the barrier layer is not always simply toact as an impermeable membrane isolating the contents from itssurroundings. The requirements for cheese are particularly exact-ing, varying with cheese type (e.g. Robertson, 2013). For example,Emmental cheese emits carbon dioxide and propionic acid as itripens inside the packaging. The CO2needs to be able to escape bydiffusing out through the packaging, whilst water must be retainedinside the package and oxygen must be prevented from entering(Mortensen, 2008). By contrast, soft cheeses such as camembert
Table 2
Comparison of packaging and food production energies.
Beef Chicken Pork
Meat production CO2 equivalent/kg (Fiala, 2008) 14.8 1.1 3.8
% emissions contributed by LDPE packaging 0.5% 7% 2%
76 C.Y. Barlow, D.C. Morgan / Resources, Conservation and Recycling 78 (2013) 74– 80
Table 3
Functions of polymer film packaging (Morgan, 2010).
Function Achieved by Typical Material
Fits closely around product Shrink-wrap; flexible
film
LLDPE
Packaging closure Heat seal LDPE
Mechanical strength Toughness PE, PP
Attractiveness High gloss surface PE
Barrier Impermeable or
semi-permeable film:
keep inert atmospheres
in; controlled passage
or barrier to range of
chemicals including
odours, oxygen, water,
CO2
PVDC, EVOH, PA
Bonding layers together Thin tie-layer EVA
need to lose water at a rate varying between 0.5% and 12% at differ-ent stages in the ripening process. Different polymers have differentpermeabilities for each of these chemicals (Brent Strong, 2005),so the packaging barrier properties can be tailored to the prod-uct by choice of materials and the film thicknesses. For soft cheesesit is common to tailor barrier properties by introducing carefullycontrolled perforations.The most common polymer barrier materials are EVOH, PVDCand PA, and these may be blended to modify their functional-ity. Additional barrier properties can be provided by the use ofaluminium, either in the form of foil (about 12 m in thickness),or as a metalized layer (typically about 30 nm) on a polymerfilm, often PP or PET. Food packaging films vary in thicknessbetween about 10 m and 250 m depending on the combina-tion of strength, durability and barrier function demanded by theapplication. Cheese packaging is usually between 100 and 200 m;the barrier layer typically comprises 20–30% of the total thickness.Mechanical properties, and in particular the toughness which pro-vides resistance to piercing and splitting, are commonly suppliedby PE or PP in thicknesses which can be at least 70% of the total filmthickness.An obvious way of minimizing the amount of material in thepackaging is to use different materials optimized for each of thesefunctions, combined into a single multi-layer film. Three, five andseven layer films are commonly manufactured; more layers aresometimes required. Producing multi-layer blown film of suchcomplexity has been standard practice in the industry for manyyears, and does not add significantly to the cost of the process. Thenumber of failure modes and hence likely amount of waste mate-rial associated with the production of multi-layer films is typically,however, somewhat increased (Morgan, 2010). Furthermore, a filmof this type suffers the disadvantage that it is formed of polymerswhich are immiscible or otherwise incompatible, and so it is noteasily recycled.The alternative to multi-layer films is to use polymers thatare not optimized for these different functions, which means thatgreater thicknesses are required to achieve the barrier proper-ties and the mechanical strength in particular. These optimizationaspects are explored further in Section 1.3.1.3. Multi-layer or mono-layer polymer films?Polymer films are immediately attractive as lightweight pack-aging because of their high strength-to-weight ratio, and usingcombinations of films optimized for the different required func-tions leads to further light-weighting. However, this is achieved atthe cost of recyclability: multi-layer films are at best difficult, andtypically essentially impossible to recycle to a high-value product(e.g. Pilz et al., 2010). In this section we will explore the advantagesFig. 1. Permeability of plastics relative to PVDC. Data from CES, 2008.and disadvantages of multi-layer packaging as opposed to simplerfilms which might more easily be recycled.Looking first at the barrier function of the film, which is its mostdistinctive feature, we can compare the performance of differentpolymers by looking at the thickness of the film which would berequired to achieve the same function, shown in Fig. 1 (Morgan,2010). PVDC, commonly used as the barrier layer, is used as thebaseline comparator. Noting that the chart uses a logarithmic scale,it is immediately apparent that EVOH and PVDC appear to presentbest opportunities for minimization of material. The industry isfiercely competitive on cost, so Fig. 2 shows the cost of achievingequivalent barrier function, again normalized to PVDC. Once again,EVOH and PVDC are the most attractive: the greater material costsper unit weight are more than outweighed by the reduction in theamount of material required, because of the reduction in thicknessof the film.Minimizing the film thickness carries environmental advan-tages which extend beyond simply reducing the amount of materialconsumed in fulfilling the function of the film. Factors relevant tothis analysis are summarized in Table 4.Attempting to quantify all of these effects is difficult. However,the most important environmental factor is the thickness of mate-rial required to fulfil a particular function, and this is determinedby the choice of material. The results are shown in Table 5.Fig. 2. Relative cost of plastic films to achieve equivalent barrier functions. Datafrom CES, 2008.
C.Y. Barlow, D.C. Morgan / Resources, Conservation and Recycling 78 (2013) 74– 80 77
Table 4
Environmental consequences of optimizing packaging parameters.
Feature Achieved by Positive consequences Negative consequences
Reduced weight of packaging Reduce film
thickness by using
multi-layer film
Less material required; material production
energy saved
Reduced transport costs
Increased complexity of manufacture means
higher failure rates so more wastage
Recyclability impaired or prevented
Reduced volume of packaging Polymer bags
rather than trays
Volume of packaged item reduced: better
packing density enabled. Transport used more
efficiently (e.g. fuller lorries: fewer needed)
Refrigeration costs reduced
Reduced pressure on end-of life facilities
(landfill)
Less material required; material production
energy saved
Trays potentially easier to recycle than bags
The relative film thicknesses have been calculated assuming thatflux of molecules through the film is determined by Fick’s first law,so that it is inversely proportional to film thickness. Environmen-tal impact is indicated by a single factor, energy, which includescontributions both from the energy required to manufacture thepolymer (the embodied energy) and the energy required to makethe film (which is a much smaller factor, typically 10% of the embod-ied energy).For the oxygen barrier function, EVOH requires a slightly thin-ner film to maintain the same oxygen barrier properties as a PVDCfilm. The other materials require films very significantly thicker,by a factor of between one and two orders of magnitude, and thesethicker films carry proportionately greater environmental burdens.The spread of thicknesses required to achieve the same moisturebarrier function as PVDC is much smaller; HDPE provides a signifi-cant advantage for this function, whilst EVOH is the least effective.It is clear from this analysis that using a single material for pack-aging which needs to achieve low permeability to both moistureand oxygen, requires a compromise on properties. The analysishas been normalized for PVDC, which is not the optimum mate-rial on all metrics, but is a popular material in the industry. Noneof these materials scores highly on all factors. The case for a multi-layer film seems to be strong, allowing the film to be optimized forthickness, energy footprint and cost. Consideration of other filmattributes (see Table 2) will indicate other materials which shouldbe incorporated into an optimized multi-layer film.This analysis is incomplete without discussion of end-of-life fac-tors, which is the subject of the next section.2. Polymer recycling2.1. General issuesWith increasing pressure to reduce waste going to landfill,recycling of materials in general is moving up the political agenda.Polymers typically comprise about 14% of the UK municipal wastestream by weight (WRAP, 2009), but the proportion by volumeis greater by a factor of about 2.5 (ACRR, 2002) and volumes arethe limiting factor. Recycling of polymers is therefore an area ofparticular interest. Recent rapid increases in raw material pricesare also helping to promote development of recycling (e.g. BritishPolythene and Industries, 2013). The problems, however, aresubstantial. With a few exceptions, polymer waste streams areregarded as low-value waste, and economic considerations providea deterrent to performing costly processes to return the material tothe use cycle. However, polymers are energy-intensive to manufac-ture (in the region of 70–100 MJ per kg, comparable to metals) andmost are derived from fossil fuels, so their environmental impact issubstantial. If recycling can be achieved without excessive energyexpenditure then there should be environmental benefits. Mostimportantly, if recycled material can substitute for some virginpolymer, pressures to increase virgin polymer production mightbe relieved. Of secondary significance in terms of environmentalimpact is the reduction in the amount of waste going to landfill, orother non-value-adding end-of-life routes such as litter, althoughthis is the aspect which attracts the most attention from the mediaand the general public.The choices for what to do with polymers at end of life aresummarized in Table 6. Broadly, mechanical recycling involves thelowest input of energy and resources, and is most suitable forthe higher purity waste-streams of thermoplastic polymers. Feed-stock recycling, including pyrolysis, hydrogenation and gasification(Scheirs, 1998) and depolymerisation, partial oxidation or crack-ing (Garforth et al., 2004) is more tolerant of impurity, but is amuch more energy-intensive process which appears to operateeffectively only for high throughput volumes. Thermal recycling,burning, recaptures a fraction of the intrinsic energy of the oil-based polymer, but is not normally regarded as recycling. It ismost suitable for contaminated and mixed plastics. Other recyclingapplications typically involve grinding polymer and using it as afiller for a range of materials – mainly polymers and rubbers ormixed composites (e.g. polymer and paper). The recyclate here isgenerally substituting for a rather low-grade alternative material,so the environmental benefits are mainly concerned with avoidinglandfill, regarded as the least environmentally desirable option. Thelifetime of conventional polymers in landfill sites is essentially infi-nite – they do not degrade under anaerobic conditions. This doesraise the intriguing possibility of gaining revenue from combustion
Table 5
Comparison of thickness, embodied energy and cost for equivalent barrier functions delivered by single material films.
PVDC film alone EVOH film alone HDPE film alone LDPE film alone PET film alone
Relative energy for polymer film
manufacture per unit volume
1 0.6 0.3 0.3 0.6
Relative cost per unit volume 1 0.6 0.004 0.004 0.005
Oxygen barrier function only Relative thickness 1 0.7 425 1250 14
Relative CO2 footprint 1 0.4 140 400 8.7
Relative cost 1 0.4 1.8 5.1 0.07
Moisture barrier function only Relative thickness 1 7.8 0.3 2.9 5.3
Relative CO2 footprint 1 4.8 0.1 0.9 3.2
Relative cost 1 4.8 0.001 0.012 0.027
78 C.Y. Barlow, D.C. Morgan / Resources, Conservation and Recycling 78 (2013) 74– 80
Table 6
End-of-life options for polymers.
Suitable waste
streams
Energy and
resource usage
Comments
Mechanical,
primary or
closed-loop
recycling
Clean, wellcharacterised
industrial or
post-consumer
thermoplastics.
Low Post-consumer
recycling
normally
limited to
bottles (HDPE,
PET or PVC)
Chemical or
feedstock
recycling
(depolymerisation;
partial
oxidation;
cracking)
More mixed and
impure polymer
streams.
Specialist
polymers.
High High volumes
needed to be
economic
Energy recovery Most; chlorinecontaining
polymers
excluded
Negative Legislation
limits some
waste streams.
Public
opposition.
Other material
re-use (e.g. as
fillers)
High-volume
examples include
electronics
thermosets;
rubbers
Variable;
generally low
Potential for
increasing
amounts, but
material is
low-value
Landfill Any Low
of polymers if landfill sites are mined in the future (Van der Zeeet al., 2004).Estimates for Europe in 2009 were that 22.5% of post-consumerplastic is recycled, with a further 31.5% being used for energy recov-ery (Plastics Europe, 2010). Mechanical recycling dominates therecycling industry; chemical recycling reached a fairly steady levelof about 350kt in Western Europe between 1997 and 2003. Thiswas around 4% of the recovered total in 2003 but represented asteadily decreasing fraction as mechanical recycling ramped up(Plastics Europe, 2004). The commonest other waste treatment pro-cesses which are regarded as environmentally responsible and areincreasing in popularity are Energy from Waste, Mechanical andBiological Treatment Plants, and Gasification (RECOUP, 2009).2.2. Recycling of mixed or post-consumer polymersBecause of the difficulty of purifying polymers, the nature ofthe output of a recycling process is crucially dependent on thepurity of the input material. This is one of the critical factorswhich distinguishes polymer processing from that of metals, wherepurification is routinely an intrinsic part of both manufacture andrecycling. High-value polymer recycling therefore requires high-purity input, and the potential for this varies between differentpolymers and between different waste streams. For example, poly-olefins are amongst the more easily recyclable polymers, but evenhere there are many obstacles to a profitable recycling operation.A highly specialized waste stream such as HDPE milk bottles con-tains uncoloured polymer with few or no additives which has beenoptimized for blow moulding by having a high molecular weight(Scheirs, 1998). This can yield high-value material which can berecycled to food-grade polymer and so substitute directly for virginpolymer. However, a waste stream comprised of different gradesof HDPE is likely to contain coloured plastic, different molecularweights, and a range of additives to improve processing or aspectsof the lifetime phase (e.g. UV protection). In addition, the contami-nants from the use phase will be varied, and so cleaning processesare more costly. There may also be labels. Historically these weremade from paper, which was difficult to separate completely fromthe polymer stream and so was a barrier to recycling. Labels nowa-days are usually made from a range of polymers (e.g. polypropylene,PET, LDPE), most of which are not compatible with HDPE recyclingso still need to be removed together with any adhesive used toattach them to the bottles.Generating a high-value waste stream from mixed plas-tics normally requires sophisticated separation techniques (e.g.Wastewatch (2008)) or extensive manual handling, which remainsthe dominant method of separation (at the component level) inthe UK (RECOUP, 2009). However, sorting efficiencies are problem-atic: efficiencies vary between plastics, but lower contaminationlevels scale with reduced yields from the sorting process so a com-promise must be achieved. Since waste streams are regarded ascontaminated if they contain even small amounts of other materialsthere is little opportunity at present for high-value polymers beingderived from mixed waste. The situation is improved if the wastestream consists only of plastic bottles, since the range of polymers islimited. Up to 8% of the waste stream may be HDPE and PET bottles(WRAP, 2009). Bottle recycling is well-established as an econom-ically viable process, with 39% recycling rates achieved in Europe(RECOUP, 2009).The alternative strategy is to focus on ways to optimize the valueof materials made from mixed polymers. Compatibilisers, solidphase dispersants (Scott, 2000), are added to improve the miscibil-ity of specific different polymers and to allow them to be extrudedtogether. It may not be possible to create this effect in more diversemixtures, so treatment more commonly involves downcycling bythe addition of a mechanically strengthening component. Plasticlumber is a popular product, particularly for polyolefins such as PE(e.g. Wastewatch, 2008).The environmental desirability of recycling mixed plastics is ahighly controversial topic. It can be assessed using a number ofmetrics for disparate environmental impacts, including potentialsfor global warming, eutrophication, acidification, human toxicity,ozone layer depletion and abiotic depletion (Shonfield, 2008). Thesituation is complicated: plastics from different sources will requiredifferent degrees of sorting and cleaning, and the balance of poly-mers influences the revenue which can be obtained. But one ofthe most important factors is the assumptions which are madein creating the scenarios for the analysis (WRAP, 2010). In thisstudy LCA data from eight publications are compared, assessingthe relative impacts of recycling, incineration with energy recovery,landfill and pyrolysis as end-of-life options for post-consumer plas-tics. Four key assumptions are identified which significantly affectthe environmental impact and relative ranking of the end-of-lifeoptions.The most important factor to the present study is the proportionof virgin material saved as a result of recycling. Recycling aims toreduce the amount of virgin material produced. Most LCAs assumethat the recycled polymer is of sufficiently high quality that it cansubstitute for virgin polymer in a 1:1 ratio, so 1 kg recycled polymerdirectly substitutes for 1 kg virgin polymer (WRAP, 2010). How-ever, this is almost certainly over-optimistic for most applications,although detailed information is difficult to obtain. For example,post-consumer closed-loop recycling of polymer (when recycledpolymer is used for the same applications as the virgin polymer)is in the UK confined to clear PET bottles and HDPE milk bottles(Hopewell et al., 2009), and even in these cases it is rare to find 100%substitution for virgin polymer. For other polymers, the expectationis that recycled polymer properties are inferior to virgin polymer asa result of contamination or thermal degradation, so applications ofrecycled polymers do not correlate with those for virgin polymers.For example, a more realistic scenario for low-grade post-consumerPET (Shonfield, 2008) assumes that substitution might be 20% vir-gin plastic, 40% wood and 40% concrete. Whilst the analysis for 1:1substitution of virgin polymer showed a substantial environmen-tal benefit for mechanical recycling (620 kg CO2e saved per tonneof polymer recycled), the more pessimistic scenario resulted in a
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net increase in CO2e emitted of 440 kg. On this metric, mechanicalrecycling would not be environmentally desirable.Another factor relates to the quality of the sorting processesinfluences yield rates for reclamation and recycling processes:higher loss rates are associated with reduction in environmentalbenefit of recycling. Even in the best closed-loop recycling pro-cesses there is some attrition of material, and with post-consumerwaste the loss may be as high as 50% (Shonfield, 2008). Materialis lost at every stage in the process: sorting is needed to separateplastics from other materials, and then to separate the plastics intodifferent types, and all these stages may involve losses of up to 10%.The material is then shredded, cleaned and extruded, and a furtherloss of 10% is typical.Another identified major factor relates to the origin of the energysaved. Energy comes mainly from nuclear fuel, natural gas or coal inproportions which vary from country to country, and each energysource carries its own environmental burden. A study must there-fore specify a country mix for its LCA.A final factor which has a profound influence on the numbers isthe assumptions for the timescale for degradation of polymers inlandfill sites. Most LCA studies assume 3% degradation of polymerover 100 years, but this is subject to debate, with some authoritiessuggesting that an infinite timescale is more realistic.2.3. Recycling of filmsThe most profitable post-consumer polymer recycling opera-tions focus on bottles (WRAP, 2007), where the small range ofpolymers helps with identification, and handling is comparativelyeasy. Recycling of film from the domestic waste stream is more dif-ficult. Correct identification of the polymer is problematic becausethe range of polymers is much greater, and some of the films aremulti-layer. Multi-layer films of any sort are rejected from recyclingwaste streams since they cannot be separated into single poly-mer types and so suffer the same problems as mixed polymerdiscussed in Section 2.2. Contamination levels are high from pack-aging contents (often food). Film recycling levels from this wastestream are, not surprisingly, very low, and energy recovery is thehighest reclamation outcome which can be hoped for.Recycling of films from industrial sources is potentially a morecommercially viable operation. The range of polymers is lower: 95%of film volume is LDPE, HDPE or PP, and quantities can be highenough to make collection by re-processors economically attrac-tive. These three polymers can be separated from the rest of thewaste stream using flotation or hydrocloning (Wastewatch, 2008),but cannot easily be separated from each other. The mixed poly-olefins do not have sufficient mechanical strength for film-blowingto be possible (RAPRA, 2013), so only lower-value applications areavailable for the recycled material. It is estimated that about 40%of recycled polymers originate as films from commercial sources,particularly wholesale and distribution (WRAP, 2007).Even when a waste stream consists of just one material, theremay be problems with recycling to high-value material. For exam-ple, LDPE or LLDPE stretch wrap or cling wrap film is commonlyused for primary packaging, for wrapping goods on pallets for trans-portation; typically 900 g of clear polymer film will be used perpallet (Scheirs, 1998). Clear polymer waste normally attract higherprices than coloured polymers, since the reclaimed polymer can beused for a larger range of higher-value applications. However, clingwrap film has been treated with tackifiers to help it to adhere toitself and the product, and these attract dirt, the removal of whichadds to recycling costs.In the USA, film recovery has increased by 31% since 2005(American Chemistry Council, 2011). 71% of the recovered filmcomes from commercial sources, and consists of HDPE, LDPE andLLDPE film. Interest in film recycling is increasing, because of thenear-zero cost of the waste material (particularly the ‘dirtier’ mixedgrades). 57% of the reclaimed material was exported, 20% was usedto manufacture plastic lumber, 16% to ‘other’ applications, and only7% was used to make film and sheet.3. Biodegradable polymers for food packagingPrimary food packaging is likely to be contaminated with foodwhen it has fulfilled its function and becomes waste. An obvioussolution to the waste problem is to use packaging material whichwill degrade in the same way as food waste, so can be disposedof together with food waste. The currently preferred option in UKfor organic waste is by composting (DEFRA, 2006). Composting isgenerally regarded as an environmentally responsible waste man-agement option (Song et al., 2009), involving biodegradation oforganic materials under aerobic conditions. Food packaging madefrom biodegradable polymer would at first sight seem to be attrac-tive.Biodegradable polymers may be derived from renewableor non-renewable (fossil) resources (Scott, 2000), and not allbiologically-derived polymers are biodegradable. The most promi-nent biodegradable plastic is poly-lactic acid, PLA, derived fromplant material, typically corn (maize). It is increasingly beingused for food applications, and is promoted as being compostable(e.g. Packaging Environmental, 2013). Production of PLA packag-ing material probably has a higher environmental footprint thanproduction of conventional oil-based polymers (Song et al., 2009).However, the lifecycle impact is reduced if composting is used atend-of-life (Pilz et al., 2010).There is much uncertainty about the likelihood of biodegrad-able plastics entering the appropriate waste disposal channels(Song et al., 2009). They currently comprise a small proportionof the total polymer waste stream: PLA has been estimated at 3%(WRAP, 2009). Conventional polymers do not degrade under com-posting conditions, so because of potential confusion all polymersare normally excluded from composting waste streams. Cateringoperations using nothing but biodegradable plastics may be able toguarantee a waste-stream which is entirely compostable, but thisis a small sector.Further problems arise from the diversity of composting opera-tions. Commercial systems operate at relatively high temperatures:standards for biodegradation (EN 13432, quoted by Song et al.,2009) specify degradation rates at 58◦C. Home composting degra-dation rates are given for temperatures of 20–30◦C, although in UKa temperature range of 20–25◦C is more usual (Song et al., 2009).Even if the environmental desirability of biodegradable plasticsis accepted, there are question-marks over the ability and suit-ability of PLA to take a major share of the packaging sector, for arange of reasons (Yates and Barlow, 2013). In the short and mediumterm, the industry does not currently have the capacity to increaseproduction to appropriate levels (Scott, 2000; Song et al., 2009).There is also the technical specification of the films to be taken intoconsideration, with the many functions which need to be fulfilled(Section 1.3). In common with other polymers, the expectation isthat multi-layer films are needed in order to compete with conven-tional packaging films. With currently available materials, this willresult in the biodegradability being compromised. This is an areaof active research and development (Robertson, 2013).4. ConclusionsThe environmental impact of meat and cheese packaging needsto take account of the full lifecycle of the packaging and theproducts. Packaging reduces food waste, but itself adds to envi-ronmental burdens by using material, requiring transport and
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requiring end-of-life disposal. Optimizing the packaging for allstages in its lifecycle is the ultimate goal of ‘sustainable packaging’,but solutions at present involve trade-offs.The limited lifecycle analysis conducted here indicates thatmoving towards packaging which is more recyclable should notbe the highest priority. The results show that minimization of thematerial used whilst retaining mechanical and barrier properties isthe best way to achieve a reduction in environmental impact.Biodegradable polymers may have a part to play in reducing theenvironmental impact of packaging, but the benefits are currentlythe subject of debate.FundingWe are grateful to Cryovac Sealed Air for the provision of fundingfor parts of this work.ReferencesACRR (Association of cities and regions for recycling). Waste plastics recycling:a good practices guide by and for local and regional authorities; 2002,www.pvc.org/upload/documents/ACRRReport.pdf. Retrieved 14.3.2013.American Chemistry Council. National Postconsumer Recycled plastic bag andfilm report, Feb 2011, prepared for the American Chemistry Council; 2011,http://www.americanchemistry.com/s plastics/sec content.asp?CID=1593&DID=11723. Retrieved 7.3.2013.Brent Strong A. Plastics: Materials and processing. 3rd ed. London: Prentice Hall;2005.British Polythene Industries http://www.foodproductiondaily.com/Packaging/BPI-counts-the-cost-of-raw-material-hikes-vows-recycling-ops-boost 2011.Retrieved 7.3.2013.CES Cambridge Engineering Selector. http://www.grantadesign.com/products/ces/2008DEFRA, 2006. Food industry sustainability strategy. www.defra.gov.uk. Retrieved18.3.2011.European Parliament and Council Directive 94/62/EC on Packaging and PackagingWaste, 1994 L0062 — EN — 05.04.2005 — 003.001 (1994) Retrieved 7.3.2013.Fiala N. Meeting the demand: an estimation of potential future greenhousegas emissions from meat production. Ecological Economics 2008;vol67(3):412–9.Garforth AA, Ali S, Hernandez-Martinez J, Akah A. Feedstock recycling of polymerwastes. Current Opinion in Solid State and Materials 2004;8(6):419–25.Hopewell J, Dvorak R, Kosior E. Plastics recycling: challenges and opportunities.Philosophical Transactions of the Royal Society B 2009;364:2115–26.Incpen. Factsheet ‘Why packaging’; 2010, 31/08/2010, http://www.incpen.org/displayarticle.asp?a=17&c=2. Retrieved 2.3.2013.Incpen. Public attitudes to packaging. Ipsos Mori 2008; 2008, sri environmentINCPEN summary report 271108(1).pdf. Retrieved 7.3.2013.Love food hate waste http://www.lovefoodhatewaste.com/. Retrieved 7.3.2013.Morgan DC. Recycling multi-layer barrier packaging waste. PhD thesis. U.K.: Univer-sity of Cambridge; 2010.Mortensen G. Putting packaging first. In: 5th IDF Symposium on Cheese Ripening,9–13 March; 2008, Bern.Packaging Environmental http://www.packagingenvironmental.co.uk. Accessed14.3.2013.Packaging Federation www.packagingfedn.co.uk. Retrieved 7.3.2013.Packaging Legislation, 2003. http://www.legislation.gov.uk/uksi/2003/1941/pdfs/uksi 20031941 en.pdfPilz H, Brandt B, Fehringer R. The impact of plastics on life cycle energy consump-tion and greenhouse gas emissions in Europe. Summary report, June; 2010,www.denkstatt.at. Retrieved 19.3.2011.Plastics Europe. Association of Plastics Manufacturers. An analysis of plasticsconsumption and recovery in Europe 2002–2003; 2004, 2002 20022003.pdf.