Biobased Packaging Materials

for the Food IndustrySTATUS AND PERSPECTIVES

Edited by Claus J Weber

A European Concerted Action

This report is a result of the combined effort of theproject partners of the Food Biopack Project fundedby the EU Directorate 12.

For more information, please contact:

Dr Claus J Weber

Department of Dairy and Food Science

The Royal Veterinary and Agricultural University

Rolighedsvej 30, 1958 Frederiksberg C, Denmark

Tel. +45 3528 3238

Fax +45 3528 3344

E-mail: clj@kvl.dk

Or visit http://www.mli.kvl.dk/foodchem/special/biopack/

November 2000 ISBN 87-90504-07-0

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For- og bagside 12/02/01 13:00 Side 1

Biobased Packaging Materials

for the Food IndustrySTATUS AND PERSPECTIVES

Edited by Claus J Weber

A European Concerted Action

Biopack 13.11.00 12/02/01 13:06 Side 1

be made when dealing with biobased food packaging. Compos-tability, legislative demands and the process of documentation inrelation to compostable packaging are described in Chapter 5.Chapter 6 deals with the environmental impacts of using bioba-sed materials. The market of biobased materials, and moreoverthe future of the same, are the objectives of Chapter 7, and fi-nally in Chapter 8, a joined conclusion of the potential of bioba-sed packaging for the food industry is outlined.

To produce a state-of-the-art report of biobased food packagingturned out to be quite a challenge, taken the rapid pace of de-velopments seen in this area into consideration. The presentedpublication does only report the information being part of thepublic domain and information on industrial R&D developmentsare not included. The state-of-the-art is very likely already tohave moved on when these lines are being read. However, thereport may also be read as a general introduction to the chal-lenge of using biobased materials for food packaging.

This report is a result of the EU concerted action project: Produc-tion and application of biobased packaging materials for thefood industry (Food Biopack), funded by DG12 under the con-tract PL98 4046.

Biobased food packaging materials are materials derived fromrenewable sources. These materials can be used for food appli-cations

5

Acknow-ledgements

A definition of biobased foodpackaging materials

PrefaceAt the turn of the last century most non-fuel industrial products;dyes, inks, paint, medicines, chemicals, clothing, synthetic fibresand plastics were made from biobased resources. By the 1970spetroleum-derived materials, had to a large extent, replacedthose materials derived from natural resources. Recent develop-ments are raising the prospects that naturally derived resourcesagain will be a major contributor to the production of industrialproducts. Currently, scientists and engineers successfully performdevelopments and technologies that will bring down costs andoptimize performance of biobased products. At the same timeenvironmental concerns are intensifying the interest in agricultu-ral and forestry resources as alternative feedstocks. A sustainedgrowth of this industry will depend on the development of newmarkets and costs and performance competitive biobased products. A potential new market for these materials is foodpackaging, a highly competitive area with great demands forperformance and cost.

The aim of this EU-concerted action project, Production andapplication of biobased packaging materials for the food indu-stry, is to evaluate the potential of biobased materials as foodpackaging. The mission of the report is to present the state ofthe art of biobased food packaging, and furthermore to outlinethe future scenarios and developments. In order to cover thewhole area, project partners represent the whole productionchain, from producers of biobased resins to converters, and foodpackaging users together with food scientists and polymer che-mists.

The report consists of eight chapters and an executive summary,which altogether aim at covering all aspects of biobased foodpackaging materials. Chapter 1 gives a general introduction tothe background of the project as well as to the interest in bioba-sed food packaging. The biobased polymers, materials andpackaging are presented in Chapter 2 together with an introduc-tion to their properties. Chapter 3 focuses on the potential foodapplications of biobased materials and furthermore outlines thespecific packaging demands of a range of food products. Theemphasis in Chapter 4 is on legislative demands for food contactpackaging materials and further, if any, specific considerations to4

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Table of ContentsExecutive summary 3Preface 41 Introduction 10

1.1 References 122 Properties of biobased packaging materials 13

2.1 Introduction 132.2 Food biobased materials a definition 132.3 Origin and description of biobased polymers 14

2.3.1 Category 1: Polymers directly extracted from biomass 152.3.2 Category 2: Polymers produced from classical chemical

synthesis from biobased monomers 222.3.3 Category 3: Polymers produced directly by natural or

genetically modified organisms 252.4 Material properties 27

2.4.1 Gas barrier properties 272.4.2 Water vapour transmittance 292.4.3 Thermal and mechanical properties 302.4.4 Compostability 32

2.5 Manufacturing of biobased food packaging 342.5.1 Possible products produced of biobased materials 342.5.2 Blown (barrier) films 362.5.3 Thermoformed containers 372.5.4 Foamed products 372.5.5 Coated paper 38

2.6 Additional developments 382.7 Conclusions and perspectives 392.8 References 40

3 Food biopackaging 453.1 Introduction 453.2 Food packaging definitions 45

3.2.1 Primary, secondary and tertiary packaging 453.2.2 Edible coatings and films 463.2.3 Active packaging 473.2.4 Modified atmosphere packaging 473.2.5 Combination materials 47

3.3 Food packaging requirements 473.3.1 Replacing conventional food packaging materials

with biobased materials a challenge 493.3.2 Biobased packaging food quality demands 50

3.4 State-of-the-art in biopackaging of foods 523.5 Potential food applications 53 7

AbbreviationsAl AluminiumAPET Amorphous Poly(ethylene terephthalate)BRED Biomass for Green House Gases emission RE-Duction,

a European projectCEN The European Committee of StandardizationECN Energy Research FoundationEPS Expandable PolystyreneEVA Ethyl Vinyl AcetateEVOH Ethyl Vinyl AlcoholFDA Food and Drug Administration (USA)GHG GreenHouse GassesGWP Global Warming PotentialHDPE High Density PolyethyleneLCA Life Cycle AnalysesLDPE Low Density PolyethyleneLFP Loose-Fill-PackagingLLDPE Linear Low Density PolyethyleneMAP Modified Atmosphere PackagingMDPE Medium Density PolyethyleneOPP Oriented PolypropylenePA PolyamidePC PolycarbonatePE PolyethylenePET PolyEthylene TerephthalatePETG Copolymer of PET and cyclohexane-dimethanolPHAs Poly(hydroxyalkanoates) PHB Poly Hydroxy ButyratePHB/V Poly Hydroxy Butyrate/Valerate PLA Polylactic acidPP PolypropylenePS PolystyrenePVC Poly Vinyl ChloridePVdC Poly Vinylidene ChlorideRCF Regenerated Cellulose filmRH Relative HumiditySCF Scientific Committee on FoodSiOx Silicium OxideTg Glass TemperatureTiO2 Titanium OxideTm Melting TemperatureUHT Ultra High TemperatureWOF Warmed-Over Flavour

6

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5.4.6 Natural materials 1125.5 Biodegradability under other environmental conditions 113

6 Environmental impact of biobased materials: Lifecycle analysis of agriculture 1146.1 A sustainable production of biobased products 1146.2 What is LCA? 1156.3 Environmental impact of agriculture 115

6.3.1 Crops for biofuels 1166.3.2 The ECN study 117

6.4 Environmental impact of biobased products 1176.4.1 The Buwal study on starch-based plastics 1186.4.2 The case of hemp-based materials: LCA does not allow

generic statements 1186.4.3 Compostos study on bags for the collection of organic

waste 1196.4.4 The Ecobilans study. The LCA of paper sacks 1196.4.5 The Ifeu-/BIFA-study. The LCA of loose-fill-packaging 119

6.5 Conclusions 1206.6 Acknowledgement 1226.7 References 122

7 The market of biobased packaging materials 1247.1 Introduction 1247.2 Market appeal 124

7.2.1 Market drivers 1247.2.2 Marketing advantages 1247.2.3 Functional advantage in the product chain 1257.2.4 Cost advantage in the waste disposal system 1257.2.5 Legislative demands 125

7.3 Consumers 1267.4 The market 126

7.4.1 Today 1267.4.2 Tomorrow 1287.4.3 Price 129

7.5 Conclusions 1297.6 References 130

8 Conclusion and perspective 1328.1 Performance of materials 1328.2 Food applications 1338.3 Safety and legislation on materials in contact with food 1338.4 The environment 1348.5 The market of biobased packaging materials 1348.6 Perspective 135 9

3.5.1 Fresh meat products 533.5.2 Ready meals 653.5.3 Dairy products 673.5.4 Beverages 683.5.5 Fruits and vegetables 693.5.6 Snacks 713.5.7 Frozen products 723.5.8 Dry products 73

3.6 Conclusions and perspectives 743.7 References 75

4 Safety and food contact legislation 854.1 Introduction 854.2 Biobased materials and legislation on food contact materials 86

4.2.1 Common EU legislation 864.2.2 Biobased materials 90

4.3 Petitioner procedures 934.3.1 Standardized test methods 944.3.2 Implications of EU legislation for food and packaging

industry 954.4 Assessment of potentially undesirable interactions 96

4.4.1 Migration of compounds from biobased packages to contained food products 97

4.4.2 Microbiological contamination of biobased food packages 984.4.3 Penetration of microorganisms through

biobased packaging materials 1004.4.4 Penetration of insects and rodents into biobased food

packages 1024.4.5 Collapse due to absorbed moisture from the environment

and the contained food product 1024.5 Conclusions and perspectives 1034.6 References 104

5 Environmental impact of biobased materials: Biodegradability and compostability 1075.1 Biodegradability 1075.2 The composting of biobased packaging 1075.3 The CEN activity 1085.4 The compostable packaging 109

5.4.1 Laboratory tests 1105.4.2 Characterization 1105.4.3 Laboratory test of biodegradability 1115.4.4 Disintegration under composting conditions and

verification of the effects on the process 1115.4.5 Compost quality: chemical and eco-toxicological analysis 1128

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layers of different plastics to achieve optimal barrier properties of the material. Furthermore, caution must be exercised whenre-using food contact materials, as there might be an unwantedbuild-up of contaminants from food components migrated intothe packaging materials after several re-uses. Organic recoveryby composting or biomethanisation offers an alternative wastedisposal route, in which both left-over foodstuffs and the foodpackaging are disposed of in the same process. The bottleneckin using organic recovery is the development of biobased com-postable packaging with the required properties for protectionof food during storage and furthermore, a waste infrastructurefor these compostable packages along with labelling to identifythe compostable packaging must also be developed. So far, thepotential compostability of these materials has been the centralpoint of interest for commercialization although composting inmany countries is not the common way of disposal. However, asthe performance of the biobased materials progressively is beingimproved, new and more advanced applications, such as foodpackaging, are now becoming within reach.

The materials used for food packaging today consist of a varietyof petroleum-derived plastic polymers, metals, glass, paper andboard, or combinations thereof. These materials and polymersare used in various combinations to prepare materials withunique properties which efficiently ensure safety and quality offood products from processing and manufacturing throughhandling and storage and, finally, to consumer use. Notably,these materials fulfil a very important task as absence of packa-ging or insufficient packaging would result in fast deteriorationof quality and safety giving way to massive commercial losses ofvaluable foodstuffs. Individual food products have specific optimum requirements for storage that the packaging materialsmust be able to provide. When contemplating the concept offood packaging, the entire dynamic interaction between food,packaging material and ambient atmosphere has to be conside-red. Hence, engineering of new biobased food packaging mate-rials is a tremendous challenge both to academia and industry.

The biobased materials are interesting from a sustainable pointof view. The question is whether they meet the standards of the materials used today or whether they even add value. Thisreport summarizes the state-of-the-art of biobased food packa- 11

1. IntroductionThe issue of sustainability has been high on the EU agenda for anumber of years, encouraging academia and industry to developsustainable alternatives thus aiming to preserve resources forfuture generations. At the same time, these sustainable alterna-tives address other key EU issues such as the use of surplusstocks in Europe and the production of higher added value agri-cultural products thereby promoting economic development inthe European agricultural sector. The successful promotion anduse of biological, renewable materials for the production ofpackaging materials will satisfy a number of the key EU objecti-ves. To date, packaging materials have been, to a large extent,based on non-renewable materials. The only widely used renew-able packaging materials are paper and board which are basedon cellulose, the most abundant renewable polymer world-wide.However, major efforts are under way to identify alternativenon-food uses of agricultural crops and the production of packa-ging materials, based on polymers from agricultural sources, could become a major use of such crops (Coombs and Hall,2000; Mangan, C 1998). Indeed, such alternative biobasedpackaging materials have attracted considerable research anddevelopment interest for a significant length of time (Coombsand Hall, 2000; Mangan, C 1998) and in recent years the mate-rials are reaching the market (see Chapter 7). The biological basisof the starting materials provides the material engineer with aunique opportunity to incorporate a very appealing functionalityinto the material, that of compostability. This property enablesthese new materials to degrade upon completion of useful life.Compostability has, so far, been the main focus for applicationsof biobased packaging materials which is the logical consequ-ence for the vast amount of packaging materials used and thewaste associated with it. Municipal plastic waste is difficult todeal with as it consists of a number of fractions of waste and several plastic types and it contains plastic types with a high degree of contamination from foodstuffs resulting in labour andenergy intensive recycling. To date, prevention or enhanced recovery of materials has been used to extend the lifetime of the available non-renewable materials. Recovery methodologyincludes recycling, reuse, energy recovery, composting and biomethanisation. Re-use and re-cycling of food packaging materials is problematic, as they often comprise mixtures of 10

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2. Properties of biobased packagingmaterials

2.1. IntroductionDesigning and manufacturing of packaging materials is a multi-step process and involves careful and numerous considerationsto successfully engineer the final package with all the requiredproperties. The properties to be considered in relation to food di-stribution are manifold and may include gas and water vapourpermeability, mechanical properties, sealing capability, thermo-forming properties, resistance (towards water, grease, acid, UVlight, etc.), machinability (on the packaging line), transparency,anti fogging capacity, printability, availability and, of course,costs. Moreover, a consideration of the cradle to grave cycleof the packaging material is also required, hence, the process ofdisposal of the package at the end of its useful life must also betaken into consideration.

The aim of this report is to evaluate the potential of biobasedpackaging materials for the food industry, and the most impor-tant properties in relation to food applications can be narroweddown to four intrinsic properties of the material: mechanical,thermal, gas barrier and water vapour properties, and the focusof this chapter will be on these four properties.

Compostability, which is a very appealing property when thepackaging meet its end of useful life, will also be described. Fora detailed discussion of biodegradability/compostability andwaste handling, please refer to Chapter 5 and issues of availabi-lity and costs are discussed in Chapter 7. Packaging of food andinteraction between foods and packaging materials will be dealtwith in Chapters 3 and 4, respectively.

The most common biobased polymers and potential biobasedpackaging materials are presented, followed by a discussion oftheir food packaging properties, and finally, procedures for pro-cessing biobased materials into food product packaging will bediscussed.

2.2. Food biobased materials a definitionAs previously described, we have chosen a definition of biobased 13

Robert van Tuil*1, Paul Fowler2,Mark Lawther3, and Claus J.Weber4

*To whom correspondenceshould be addressed

1ATO, Bornsesteeg 59, P.O.Box 17, NL-6700 AA Wagen-ingen, The Netherlands, E-mailr.f.vantuil@ato.wag-ur.nl, Tele-fax +31 317 475347, 2The BioComposites Centre,University of Wales, DeinolRoad, Bangor, Gwynedd LL572UW, United Kingdom, E-mailp.a.fowler@bangor.ac.uk, Te-lefax +44 1248 370594, 3 The Plant Fiber Laboratory,The Royal Veterinary and Agri-cultural University, Building 8-68, Agrovej 10, DK- 2630 Ta-astrup, Denmark, E-mailmla@kvl.dk, Telefax +45 35282216, 4 Department of Dairy andFood Science, The Royal Veter-inary and Agricultural Univer-sity, Rolighedsvej 30, DK-1958Frederiksberg, Denmark, E-mail clj@kvl.dk, Telefax +453528 3344

ging materials and provides scenarios for future use of biobasedpackaging materials in the food industry. The report is a result ofthe concerted action project Production and application of bio-based packaging materials for the food industry sponsored bythe EU Commission.

1.1. ReferencesMangan, C. (Ed.) (1998). The green chemical and polymerschain. European Commission, DG12, DG6, Luxenbourg. Officefor Official Publications of the European union, Belgium. (ISBN92-828-6116-3).

Coombs, J., and Hall, K. (2000). Non-Food Agro-Industral Rese-arch information. CD-rom version 1.2, issue 3, 2000 (ISSN 1368-6755, ISBN 1-872691-27-7), CPL Publishing Services, Newbury,UK.

12

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ral oil, biobased polymers have more diverse chemistry and archi-tecture of the side chains giving the material scientist uniquepossibilities to tailor the properties of the final package. Themost common biobased polymers, materials and packaging willbe presented in the following.

Figure 2.1 Schematic presentation of biobased polymers based on theirorigin and method of production.

2.3.1. Category 1: Polymers directly extracted from bio-massThe natural Category 1 polymers, most commonly available, areextracted from marine and agricultural animals and plants. Examples are polysaccharides such as cellulose, starch, and chitinand proteins such as casein, whey, collagen and soy. All thesepolymers are, by nature, hydrophilic and somewhat crystalline factors causing processing and performance problems, especiallyin relation to packaging of moist products. On the other hand,these polymers make materials with excellent gas barriers.

Polysaccharides To date, the principal polysaccharides of interest for material pro-duction have been cellulose, starch, gums, and chitosan. Likely,the more complex polysaccharides produced by fungi and bacte-ria (Category 3 biobased polymers) such as xanthan, curdlan, pul-lan and hyaluronic acid, will receive more interest in the future. 15

food packaging materials based on their origin and use, leadingto the following definition:

Biobased food packaging materials are materials derived fromrenewable sources. These materials can be used for food appli-cations.

In addition, packaging materials recognized as biodegradableaccording to the standards outlined by the EU StandardizationCommittee are also included in the project. This amendmentwas included not to exclude materials which currently, of practi-cal and economical reasons, are based on non-renewable re-sources, but at a later stage these materials may be producedbased on renewable resources.

2.3. Origin and description of biobased polymers Biobased polymers may be divided into three main categoriesbased on their origin and production:

Category 1 Polymers directly extracted/removed from biomass.Examples are polysaccharides such as starch and cellulose andproteins like casein and gluten.

Category 2 Polymers produced by classical chemical synthesisusing renewable biobased monomers. A good example is poly-lactic acid, a biopolyester polymerised from lactic acid monomers.The monomers themselves may be produced via fermentation ofcarbohydrate feedstock.

Category 3 Polymers produced by microorganisms or geneti-cally modified bacteria. To date, this group of biobased polymersconsists mainly of the polyhydroxyalkonoates, but developmentswith bacterial cellulose are in progress.

The three categories are presented in schematic form in Figure2.1.

Updated and detailed description of the polymers presented inFigure 2.1 may be found in numerous excellent review papersand books published recently (Petersen et al., 1999; Chandra andRustgi, 1998; Witt; et al., 1997; Guilbert et al., 1996; Krochtaand Mulder-Johnston, 1996) and it is not the purpose of thisreport to repeat the work done so well by the previous authors.In general, compared to conventional plastics derived from mine-14

Directly extracted from Biomass Classically synthesised Polymers produced from bio-derived monomers directly by organisms

Polysaccharides Proteins Lipids Polylactate PHA

Animals Plant

Casein Zein

Cross-linked tri-glyceride

Whey

Collagen/Gelantine

Soya

Gluten

Other Polyesters Bacterial cellulose

XanthanCurdlanPullan

Starch

Potato

Maize

Wheat

Rice

DerivativesCellulose

Cotton

Wood

Other

Derivatives

Gums

Guar

Locust bean

Alignates

Carrageenan

Pectins

Derivatives

Chitosan/Chitin

Biobased polymers

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during the last few years and are to day dominating the marketof biobased, compostable materials (see chapter 7).

Cellulose and derivatives Cellulose is the most abundantly occurring natural polymer onearth and is an almost linear polymer of anhydroglucose. Be-cause of its regular structure and array of hydroxyl groups, ittends to form strongly hydrogen bonded crystalline microfibrilsand fibres and is most familiar in the form of paper or cardboardin the packaging context. Waxed or polyethylene coated paper isused in some areas of primary food packaging, however thebulk of paper is used for secondary packaging. Cellulose is acheap raw material, but difficult to use because of its hydrophilicnature, insolubility and crystalline structure. To make cellulose orcellophane film, cellulose is dissolved in an aggressive, toxic mix-ture of sodium hydroxide and carbon disulphide (Xanthation)and then recast into sulphuric acid. The cellophane produced isvery hydrophilic and, therefore, moisture sensitive, but it hasgood mechanical properties. It is, however, not thermoplasticowing to the fact that the theoretical melt temperature is abovethe degradation temperature, and therefore cannot be heat-sea-led. Cellophane is often coated with nitrocellulose wax or PVdC(Poly Vinylidene Chloride) to improve barrier properties and insuch form it is used for packaging of baked goods, processedmeat, cheese and candies. However, there is considerable poten-tial for the development of an improved cellulose film product oran improved production method as the existing product is pro-blematic in both respects.

A number of cellulose derivatives are produced commercially,most commonly carboxy-methyl cellulose, methyl cellulose, ethylcellulose, hydroxyethyl cellulose, hydroxypropyl cellulose and cel-lulose acetate. Of these derivatives only cellulose acetate (CA) iswidely used in food packaging (baked goods and fresh produce).CA possesses relatively low gas and moisture barrier propertiesand has to be plasticized for film production. Many cellulose der-ivatives possess excellent film-forming properties, but they aresimply too expensive for bulk use. This is a direct consequence ofthe crystalline structure of cellulose making the initial steps ofderivatization difficult and costly. Research is required to developefficient processing technologies for the production of cellulosederivatives if this situation is to change. 17

Starch and derivatives Starch, the storage polysaccharide of cereals, legumes and tu-bers, is a renewable and widely available raw material suitablefor a variety of industrial uses. As a packaging material, starch alone does not form films with adequate mechanical properties(high percentage elongation, tensile and flexural strength) unlessit is first treated by either plastization, blending with other mate-rials, genetic or chemical modification or combinations of theabove approaches. Corn is the primary source of starch, altho-ugh considerable amounts of starch are produced from potato,wheat and rice starch in Europe, the Orient and the UnitedStates.

Starch is economically competitive with petroleum and has beenused in several methods for preparing compostable plastics.However, a challenge to the development of starch materials isthe brittle nature of blends with high concentrations of starch.

Overcoming the brittleness of starch while achieving full biode-gradability in blends can be accomplished by the addition of bio-degradable plasticizers. Common plasticizers for hydrophilic polymers, such as starch, are glycerol and other low-molecular-weight-polyhydroxy-compounds, polyethers and urea. Plasti-cizers lower the water activity thereby limiting microbial growth.

When starch is treated in an extruder by application of boththermal and mechanical energy, it is converted to a thermopla-stic material. In the production of thermoplastic starches, plasti-cizers are expected to reduce the intermolecular hydrogen bondseffectively and to provide stability to product properties. Becauseof the hydrophilicity of the starch the performance of materialsextruded with starch changes during and after processing as wa-ter contents changes. To overcome this challenge, many diffe-rent starch derivatives have been synthesized; recently, site-sele-ctive modifications have been reported. Blending with morehydrophobic polymers produce formulations that are suitable forinjection moulding and blowing films. Compatibility is an issuewhen these types of blends and laminates are used, and compa-tibilizers and other additives are used as processing aids.

Starch-based thermoplastic materials have been commercialized16

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rial engineer when tailoring the required properties of the packa-ging material.

For food packaging, edible coatings made of proteins are widelydescribed in the literature (see Chapter 3), but thermoplasticprocessable polymers may also be made out of proteins (deGraaf and Kolster, 1998). Due to their excellent gas barrier pro-perties, materials based on proteins are highly suitable for packa-ging purposes. However, like starch plastics mechanical and gasproperties are influenced by the relative humidity due to theirhydrophilic nature.

The major drawback of all protein-based plastics, apart from ke-ratin, is their sensitivity towards relative humidity. Blending or la-mination with other biobased materials may overcome this chal-lenge with lower sensitivity towards humidity (see Section 2.5).So far, research in this field has been limited. Another way tomodify protein properties is by chemical modification and, asseen in Figure 2.2, proteins contain a wide variety of chemicalmoieties which may help tailoring protein properties towardsspecific applications.

Figure 2.2 The numerous and diverse side chains of proteins of-fers the polymer scientist limitless opportunities to specificallytailor the properties of the final polymeric material by using che-mical modification. 19

Chitin/Chitosan Chitin is a naturally occurring macromolecule present in the exo-skelton of invertebrates and represents the second most abun-dant polysaccharide resource after cellulose (Kittur et al., 1998).Chitin is chemically composed of repeating units of 1,4-linked 2-deoxy-2-acetoamido--D-glucose, and chitosan refers to a familyof partially N-acetylated 2-deoxy-2-amino--glucan polymersderived from chitin. In general, chitosan has numerous uses:flocculant, clarifier, thickener, gas-selective membrane, plant di-sease resistance promoter, wound healing promoting agent andantimicrobial agent (Brine et al., 1991). Chitosan also readilyforms films and, in general, produces materials with very highgas barrier, and it has been widely used for the production of ed-ible coating (Krochta and Mulder-Johnston, 1997). Furthermore,chitosan may very likely be used as coatings for other biobasedpolymers lacking gas barrier properties. However, as with otherpolysaccharide-based polymers, care must be taken for moistconditions. The cationic properties of chitosan offer good op-portunities to take advantage of electron interactions with nu-merous compounds during processing and incorporating specificproperties into the material. The cationic property may furtherbe used for incorporation and/or slow release of active compo-nents, adding to the possibilities for the manufacturer to tailorthe properties (Hoagland and Parris, 1996). Another interestingproperty of chitosan and chitin in relation to food packaging aretheir antimicrobial properties (Dawson et al., 1998) and their abi-lity to absorb heavy metal ions (Chandra and Rustgi, 1998). Theformer could be valuable in relation to the microbial shelf-lifeand safety of the food product and the latter could be used todiminish oxidation processes in the food catalyzed by free me-tals. So far, the major interest for chitosan as a packaging mate-rial has been in edible coatings. However, Makino and Hirata(1997) have shown that a biodegradable laminate consisting ofchitosan-cellulose and polycaprolactone can be used in modifiedatmosphere packaging of fresh produce.

ProteinsProteins can be divided into proteins from plant origin (e.g. glu-ten, soy, pea and potato) and proteins from animal origin (e.g.casein, whey, collagen, keratin). A protein is considered to be arandom copolymer of amino acids and the side chains are highlysuitable for chemical modification which is helpful to the mate-18

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This behaviour in water is similar to that of gluten plastics.

Some patents from the beginning of the 1900 describe the useof soy protein as adhesives or plastics. Even the ancient Chineseused soy protein for non-food applications such as oil for lubrica-tion. The most successful applications of soy proteins were theuse in adhesives, inks and paper coatings.

KeratinKeratin is by far the cheapest protein. It can be extracted fromwaste streams such as hair, nails and feathers. Due to its struc-ture and a high content of cysteine groups, keratin is also themost difficult protein to process. After processing, a fully biode-gradable, water-insoluble-plastic is obtained. However, mechani-cal properties are still poor compared to the proteins mentionedabove.

The main drawback of all protein plastics, apart from keratin, istheir sensitivity to relative humidity. Either blending or laminationcan circumvent this problem. Research in this field has been limi-ted until now.

Collagen Collagen is a fibrous, structural protein in animal tissue, particu-larly skin, bones and tendons, with a common repeating unit:glycine, proline and hydroproline. Collagen is a flexible polymer.However, because of its complex helical and fibrous structurecollagen is very insoluble and difficult to process. Collagen is thebasic raw material for the production of gelatine, a commonfood additive with potential for film and foam production. Gela-tine is produced via either partial acid or alkaline hydrolysis ofcollagen. Such treatments disrupt the tight, helical structure ofcollagen and produce water-soluble fragments that may formstiff gels, films, or light foams. Gelatine is a very processable ma-terial, but it is extremely moisture sensitive. Therefore, for pro-longed use in packaging, research is needed for the chemicalmodification of gelatine to improve moisture sensitivity.

WheyWhey proteins are by-products from the cheese production andare particularly rich in -lactoglobulin. They have a relatively highnutritional value, are available in large amounts world-wide and 21

CaseinCasein is a milk-derived protein. It is easily processable due to itsrandom coil structure. Upon processing with suitable plasticizersat temperatures of 80-100C, materials can be made with me-chanical performance varying from stiff and brittle to flexible andtough performance. Casein melts are highly stretchable makingthem suitable for film blowing. In general, casein films have anopaque appearance. Casein materials do not dissolve directly inwater, but they show approx. 50% weight gain after 24 hoursof immersion. The main drawback of casein is its relatively highprice. Casein was used as a thermoset plastic for buttons in the1940s and 50s. It is still used today for bottle labelling becauseof its excellent adhesive properties.

GlutenGluten is the main storage protein in wheat and corn. Wheat isan important cereal crop because of its ability to form a visco-elastic dough. Mechanical treatment of gluten leads to disulfidebridge formation formed by the amino acid cysteine which is re-lative abundant in gluten. The disulphide bridges are responsiblefor the creation of a strong, visco-elastic and voluminous dough.Processing is, therefore, more difficult than in the case of caseinas the disulphide crosslinks of the gluten proteins have to be re-duced with a proper reducing agent. Processing temperaturesare, depending on the plasticizer contents, in the range of 70-100C. Mechanical properties may vary in the same range asthose for caseins. Gluten plastics exhibit high gloss (polypropy-lene like) and show good resistance to water under certain con-ditions. They do not dissolve in water, but they do absorb waterduring immersion. Due to its abundance and low price, researchon the use of gluten in edible films, adhesives, or for thermopla-stic applications is currently being carried out.

Soy proteinSoy proteins are commercially available as soy flour, soy concen-trate and soy isolate, all differing in protein content. Soy proteinconsists of two major protein fractions referred to as the 7S(conglycinin, 35%) and 11S (glycinin, 52%) fraction. Both 7Sand 11S contain cysteine residues leading to disulphide bridgeformation and processing is, therefore, similar to gluten with si-milar mechanical properties. The best results are obtained withsoy isolate (approx.90% protein) (Fossen and Mulder, 1998).20

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wheat or alternatively may consist of waste products from agri-culture or the food industry, such as molasses, whey, green juice,etc. (Garde et al., 2000; Sdergrd, 2000). Recent results pointout that a cost-effective production of PLA can be based on theuse of green juice, a waste product from the production of ani-mal feeds (Garde et al., 2000).

PLA is a polyester with a high potential for packaging applicati-ons. The properties of the PLA material are highly related to theratio between the two mesoforms (L or D) of the lactic acid mo-nomer. Using 100% L-PLA results in a material with a very highmelting point and high crystallinity. If a mixture of D- and L-PLAis used instead of just the L-isomer, an amorphous polymer is ob-tained with a Tg of 60C, which will be too low for some packa-ging purposes (Sinclair, 1996). A 90/10% D/L copolymer gives amaterial which can be polymerized in the melt, oriented aboveits Tg and is easy processable showing very high potential of me-eting the requirements of a food packaging. The temperature ofprocessing is between 60 and 125C depending on the ratio ofD- to L-lactic acid in the polymer (see Figure 2.5). Furthermore,PLA may be plasticized with its monomer or, alternatively, oligo-meric lactic acid and the presence of plasticizers lowers the Tg.As outlined above, PLA offers numerous opportunities to tailorthe properties of the finished material or package. PLA may beformed into blown films, injected molded objects and coatingsall together explaining why PLA is the first novel biobased mate-rial produced on a major scale (see Chapter 7).

Biobased monomersA wide variety of monomers, or chemical building blocks may beobtained from biobased feed stocks. These may be prepared using chemical and biotechnological routes, or a combination ofboth.

Since long, Castor oil has been recognized as an interestingstarting material for making polyurethanes. Due to their waterresistance some castor oil based polyurethane materials have found application in the electronics industry (Oertel, 1985) andcoating market (Kase et al., 1987). Some seed crops and flaxalso contain fatty acids and oils where the major components ofthe recovered oil are -linolenic acid, linoleic acid and oleic acid.This highly unsaturated material was of interest for application in 23

have been extensively investigated as edible coatings and films.This would seem to form the basis for a logical utilization stra-tegy for this protein in packaging. Whey proteins are readily pro-cessable and have some potential as exterior films, if, as with ge-latine, suitable modification strategies can be developed toreduce moisture sensitivity.

ZeinZein comprises a group of alcohol soluble proteins (prolamines)found in corn endosperm. Commercial zein is a by-product ofthe corn wet-milling industry. Today, zein is mostly used in for-mulations of speciality food and pharmaceutical coatings. How-ever, the potential supply of zein, estimated at 375,000 tons p.a.calls for expanded markets and drives research and developmentof novel value-added applications (Shukla, 1992). Film-formingproperties of zein have been recognized for decades and are thebasis for most commercial utilization of zein (Padua et al., 2000;Andres, 1984). Films may be formed by casting, drawing or ex-trusion techniques (Ha, 1999; Lai and Padua, 1997; Reiners etal., 1973). The films are brittle and needs plasticizers to makethem flexible. Zein-based films show a great potential for uses inedible coatings and biobased packaging (Padua et al., 2000).

2.3.2. Category 2: Polymers produced from classicalchemical synthesis from biobased monomersUsing classical chemical synthesis for the production of polymersgives a wide spectrum of possible bio-polyesters. To date, po-lylactic acid is the Category 2 polymer with the highest potentialfor a commercial major scale production of renewable packa-ging materials. However, a wide range of other biopolyesterscan be made. In theory, all the conventional packaging materialsderived from mineral oil today can in the future be producedfrom renewable monomers gained by e.g. fermentation. Today,this approach is not economically feasible due to the cost of theproduction of the monomers. However, it is an obstacle that thePLA producers seem to have overcome with success (see Chap-ter 7).

Polylactic acid (PLA)Lactic acid, the monomer of polylactic acid (PLA), may easily beproduced by fermentation of carbohydrate feedstock. The car-bohydrate feedstock may be agricultural products such as maize,22

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Terpene chemicals, isolated from pine trees for example, andtransformed to other materials have resulted in the availability ofa number of terpene based products such as terpineol, which areused as a fragrance ingredient (Gabelman, 1991). As well as this,other chemicals such as dipentene have been isolated and used toprepare resin materials. Due to the multifunctional nature of somebasic terpene chemicals a wide range of derivatives are possible.

Protein engineering is a field of growing interest for the produc-tion of synthetic analogues to natures polymers (OBrien et al.,1998). Other developments include the possible production ofbiodegradable polymers currently derived from petroleum sour-ces from biobased feedstock. An example of these developmentsis the work on Bionolle from renewable feedstock (ShowaDenko HighPolymer, Japan). At present, biobased monomersmay not be directly commercially attractive, however, biobasedmonomers derived by biotechnological pathways present pro-mising alternatives to petrochemical polymer routes.

2.3.3. Category 3: Polymers produced directly by natural or genetically modified organisms

Poly(hydroxyalkanoates) (PHAs)Poly(hydroxyalkanoates) (PHAs), of which poly(hydroxybutyrate)(PHB) is the most common, are accumulated by a large numberof bacteria as energy and carbon reserves. Due to their biodegrad-ability and biocompatibility these biopolyesters may easily find industrial applications. A general overview of the physical andmaterial properties of PHAs, along with accomplished applica-tions and new developments in this field, can be found in a recent review (Walle et al., (in press)).

The properties of PHAs are dependent on their monomer com-position, and it is, therefore, of great interest that recent rese-arch has revealed that, in addition to PHB, a large variety ofPHAs can be synthesized by microbial fermentation. The mono-mer composition of PHAs depends on the nature of the carbonsource and microorganisms used. PHB is a typical highly crystal-line thermoplastic whereas the medium chain length PHAs areelastomers with low melting points and a relatively lower degreeof crystallinity. A very interesting property of PHAs with respectto food packaging applications is their low water vapour perme-ability which is close to that of LDPE. 25

coatings and paints and in other potential applications utilizingan air drying process (Buisman, 1999). Other oils from marineand agricultural origin have been used in numerous applicationsincluding paints and other waterproof coatings (Carraher et al.,1981).

Oleochemicals, such as the unsaturated fatty acids oleic and rici-noleic acid, are derived from feedstocks such as coconut andcastor beans and have long been recognised as useful chemicalprecursors in preparing polymeric materials. For example, oleicacid may be chemically transformed to azelaic (di)acid which hasbeen used in polyamide synthesis. Other chemical transformati-ons of oleochemicals result in the preparation of multifunctionalalcohols, amines and esters. Some of these materials are prepa-red commercially by Cognis and Akzo Nobel amongst others,and are used for a variety of applications such as lubricants, surfactants and polycondensated monomers.

Carbohydrate sources such as woody material, molasses andmaize give rise to a rich array of chemical and biotechnologicaltransformations leading to a wide spectrum of potentially intere-sting chemicals. A well-established process which converts wo-ody biomass to chemicals is the production of furfural. Furfuralcan be transformed to furfuryl alcohol which can be reacted toform a furan resin. As well as furfuryl alcohol synthesis a widerange of useful furan chemicals may be prepared although someare still in the development phase (Schiweck, 1991). Another ex-ample of the utilisation of woody materials is the preparation oflevulinic acid from waste paper. Levulinic acid is a useful pre-cursor for the synthesis of various lactones, furans and other fu-nctional building blocks. Plans to build a commercial plant for le-vulinic acid productions are being explored (Fitzpatrick, 1998).

Fermentation of carbohydrate materials using selected microor-ganisms has led to efficient pathways to the formation of multi-functional acids such as succinic acid. Diols, such as 1,3-propa-nediol, have also been prepared directly via fermentation.Pathways to the highly interesting monomers adipic acid and1,4-butanediol, combine biotechnology and chemical transfor-mation. In the case of adipic acid, glucose is transformed usingmicrobes to muconic acid which is then chemically hydrogen-ated to adipic acid. 24

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Bacterial cellulose is processed under ambient conditions and thedegree of polymerization is 15000, 15 times longer than cellu-lose from woodpulp. Bacterial cellulose is highly crystalline. Inbacterial cellulose, 70% is in the form of cellulose I and the restis amorphous. This composition results in outstanding materialproperties: a modulus as high as 15-30 GPa was determinedacross the plane of the film.

Production costs of bacterial cellulose are high due to the low ef-ficiency of the bacterial process; approximately 10% of the glu-cose used in the process are incorporated in the cellulose. Thehigh price of bacterial cellulose of approximately 20 Euro/kghampers its applicability in low-added-value bulk products. Se-veral high-added-value specialty applications have been devel-oped. The material has been used as an artificial skin, as a food-grade non-digestible fiber, as an acoustic membrane, and as aseparation membrane (Van Damme et al., 1996).

2.4. Material properties

2.4.1. Gas barrier properties Many foods require specific atmospheric conditions to sustaintheir freshness and overall quality during storage. Hence, increa-sing amounts of our foods are being packed in protective atmos-phere with a specific mixture of gases ensuring optimum qualityand safety of the food product in question. To ensure a constantgas composition inside the package, the packaging material ne-eds to have certain gas barriers. In most packaging applicationsthe gas mixture inside the package consists of carbon dioxide,oxygen and nitrogen or combinations hereof. The objective ofthis section is to describe the gas barriers of biobased materialsusing mineral oil based polymer materials as benchmarks.

Literature provides a vast amount of information on the barrierproperties of biobased materials. However, comparisons betweendifferent biobased materials are complicated and sometimes notpossible due to the use of different types of equipment and dis-similar conditions for the measurements.

In Figure 2.3, different biobased materials are compared to con-ventional mineral-oil-based polymer materials. The figure is basedon information from literature and on measurements of commer-cially available materials performed by ATO (Wageningen, NL). 27

PHB resembles isotactic polypropylene (iPP) in relation to meltingtemperature (175-180C) and mechanical behaviour. PHBs Tg isaround 9C and the elongation to break of the ultimate PHB (3-8%), which is markedly lower than that of iPP (400%). An unfa-vourable ageing process is a major drawback for the commercialuse of the PHB homopolymer. It has been reported in the litera-ture that annealing can dramatically improve the mechanicalproperties of PHB by changing its lamellar morphology whilesubsequent ageing is prevented to a large extent. Incorporationof 3HV or 4HB co-monomers produces remarkable changes inthe mechanical properties: the stiffness and tensile strength de-crease while the toughness increases with increasing fraction ofthe respective co-monomer. Medium chain length PHAs, unlikePHB or its copolymers, behave as elastomers with crystals actingas physical crosslinks and, therefore, can be regarded as a classof its own with respect to mechanical properties. Elongation tobreak up to 250-350% has been reported and a Youngs modu-lus up to 17 MPa. These materials have a much lower meltingpoint and Tg than their PHB counterparts.

Applications that have been developed from PHB and relatedmaterials (e.g. Biopol) can be found in very different areas andcover packaging, hygienic, agricultural, and biomedical pro-ducts. Recent application developments based on medium chainlength PHAs range from high solid alkyd-like paints to pressuresensitive adhesives, biodegradable cheese coatings and biode-gradable rubbers. Technically, the prospects for PHAs are verypromising. When the price of these materials can be further re-duced, application of biopolyesters will also become economi-cally attractive.

Bacterial celluloseTo date, bacterial cellulose is rather unexploited, but it represents apolymeric material with major potential (Iguchi et al., 2000). Ba-cterial strains of Acetobacter xylinum and A. pasteurianus are ableto produce an almost pure form of cellulose (homo-beta-1,4-glu-can). Its chemical and physical structure is identical to the celluloseformed in plants (Brown, 1996). Plant cellulose, however, has toundergo a harsh chemical treatment to remove lignin, hemicellu-lose and pectins. This treatment severely impairs the material char-acteristics of plant cellulose: the degree of polymerisation decrea-ses almost ten-fold and the form of crystallization changes.26

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ternatives to presently available gas barrier materials like EVOHand PA6 and an equivalent biobased laminate would be an ou-ter-layer of plasticized chitosan, a protein or starch-derived filmcombined with PLA or PHA (see Section 2.5). Notably, the gasbarrier properties of PA6 and EVOH are sensitive towards mo-isture and the LDPE creates a very effective water vapour barrier ensuring that the moisture from the foodstuff does not in-terfere with the properties of PA6 or EVOH. In the same fashion,PLA and PHA will protect the moisture-sensitive-gas-barriermade of polysaccharide and protein. Some interesting develop-ments have made it possible to improve water vapour and gasproperties of biobased materials many-fold by using plasma de-position of glass-like SiOx coatings on biobased materials or theproduction of nano-composites out of a natural polymer andmodified clay (Fischer et al., 2000; Johannson, 2000).

In general, the oxygen permeability and the permeability of ot-her gases of a specific material are closely interrelated and, as arule of the thumb, mineral oil based polymers have a fixed ratiobetween the oxygen and carbon dioxide permeabilities. This relation is also observed for biobased materials. However, forsome biobased materials, e.g. PLA and starch, the permeabilityof carbon dioxide compared to oxygen is much higher than forconventional plastics (Petersen and Nielsen, 2000).

Gas barriers and humidityAs many of these biobased materials are hydrophilic, their gasbarrier properties are very much dependent on the humidityconditions for the measurements and the gas permeability of hy-drophilic biobased materials may increase manifold when humi-dity increases. Notably, this is a phenomenon also seen with con-ventional polymers. The gas permeability of high gas barriermaterials, such as nylon and ethylvinyl alcohol, is likewise affe-cted by increasing humidity. Gas barriers based on PLA and PHAis not expected to be dependent on humidity.

2.4.2. Water vapour transmittanceA major challenge for the material manufacturer is the by naturehydrophilic behaviour of many biobased polymers as a lot offood applications demand materials that are resistant to moistconditions. However, when comparing the water vapour trans-mittance of various biobased materials to materials based on mi- 29

Figure 2.3 Comparison of oxygen permeability of biobased ma-terials compared to conventional mineral-oil-based materials.Permeability of materials marked with * was measured by ATO,Wageningen, NL (23C, 50% RH), information on other materi-als is based on literature (Rindlav-Westling et al., 1998; Butler etal., 1996).

As seen in the Figure 2.3, biobased materials mimic quite wellthe oxygen permeabilities of a wide range of the conventionalmineral-oil-based materials and it is possible to choose from arange of barriers among the presented biobased materials. It isnoteworthy that developments are still being made.

The conventional approach to produce high-barrier films forpackaging of food in protective atmosphere is to use multi-layersof different films to obtain the required properties. A laminatethat is often used in food packaging consists of an layer of EVOHor PA6 combined with LDPE combining the gas barrier propertiesof PA6 or EVOH with the water vapour barrier, the mechanicalstrength and the excellent sealing properties of the LDPE. A si-milar multi-layer approach for biobased materials may likewisebe used to produce materials with the required properties. Asseen in Figure 2.3 starch-based materials could provide cheap al-

28

low medium high

1 2 3 4 5 6 7

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both polystyrene-like polymers (relatively stiff materials with in-termediate service temperatures), polyethylene-like polymers (re-latively flexible polymers with intermediate service temperatures)and PET-like materials (relatively stiff materials with higher servicetemperatures) can be found among the available biobased poly-mers.

The mechanical properties in terms of modulus and stiffness arenot very different compared to conventional polymers. In figure2.5 a comparison of the thermal properties of biobased poly-mers with existing polymers is made. The modulus of biobasedmaterials ranges from 2500-3000 MPa and lower for stiff poly-mers like thermoplastic starches to 50 MPa and lower for rub-bery materials like medium chain polyhydroxyalkanoates.Furthermore, the modulus of most biobased and petroleum-derived polymers can be tailored to meet the required mechani-cal properties by means of plasticizing, blending with other poly-mers or fillers, crosslinking or by the addition of fibres. A poly-mer like bacterial cellulose could for instance be used inmaterials which requires special mechanical properties. In theory,biobased materials can be made having similar strength to theones we use today (Iguchi et al., 2000).

31

neral oil (see Figure 2.4), it becomes clear that it is possible toproduce biobased materials with water vapour transmittance ra-tes comparable to the ones provided by some conventional pla-stics. However, if a high water vapour barrier material is requi-red, very few biobased materials apply. Notably, developmentsare currently focusing on this problem and future biobased ma-terials must also be able to mimic the water vapour barriers ofthe conventional materials known today.

Figure 2.4 Water vapour transmittance of biobased materialscompared to conventional packaging materials based on mineraloil. Water vapour transmittance of materials marked with * was measured by ATO (Wageningen, NL) at 23C, 50% RH.Transmittance of other materials are based on literature andmeasured at same conditions (Rindlav-Westling et al., 1998;Butler et al., 1996).

2.4.3. Thermal and mechanical propertiesNext to the barrier properties of the final packaging, the thermaland mechanical properties of the materials are both importantfor processing and also during the use of the products derivedfrom these materials. Most biobased polymer materials performin a similar fashion to conventional polymers. This indicates that30

low medium high

-5 -4 -3 -2 -1 0

-100 -80 -60 -40 -20 0 20 40 60 80 100 120 140-120

A.

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Figure 2.6. Indication of the time required for composting of va-rious biobased and synthetic polymeric materials. Measurementsof composting times were performed at ATO. The durations presented in this figure are based on an intermediate level of technology as observed in actively aerated and mechanically turned hall composting.

The durations presented in figure 2.6 are based on an intermedi-ate level of technology as observed in actively aerated and me-chanically turned hall composting. Furthermore, the compostingtime needed for complete disintegration is also affected by theparticle size of the material. For example, wood is rapidly com-posted in the form of sawdust and small chips. A wooden log,however, takes more than one year to be completely disintegra-ted. The durations presented in this figure are based on dimensi-ons regularly used for packaging applications.

The compostability of the materials are highly dependent on theother properties of the materials, e.g. the first step of the compo-sting is often a hydrolysis or wetting of the material. The rate ofthis step is very much related to the water vapour transmittanceand the water resistance of the material. Hence, the compostingrate of a material will be dependent on its other properties.

33

Figure 2.5 Comparison of the thermal properties of biobasedpolymers with conventional polymers. (All data is from companyinformation).

2.4.4. Compostability The issues of biodegradability and compostability are addressedin Chapter 5, but a comparison of the compostability of the ma-terials is also provided in this chapter. Figure 2.6 compares thecompostability of various biobased materials. Notably, the com-posting time depicted in the figure represents the approximateperiod of time required for an acceptable level of disintegrationof the material to occur. This means that the original materialshould not be recognizable anymore in the final compost (frac-tion < 10 mm) nor in the overflow (fraction > 10 mm). The composting time does not reflect the time required for the bio-degradation of the materials to be fully completed. The processcould subsequently be completed during the use of the com-post. The level of technology applied in the composting processhighly affects the composting time needed for complete disinte-gration. Hence, it takes much longer to obtain a mature com-post using low technology composting (e.g. passive windrowcomposting) than using high technology as in an intensively con-trolled tunnel composting process.

32

25 50 75 100 125 150 175 200 225 250 2750

B.

0 1 2 3 4 5 6

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regarded as the naturally occurring analogues of the syntheticpolyacetals; proteins (repeating peptide functionality) can becompared to the synthetic polyamides while polylactic acid ismerely an example of the diverse group of polyesters. Clearly,however, the gross physical and chemical properties of native bio-based materials and their synthetic counterparts are quite diffe-rent and this is a feature of additional chemical functionality in-herent in biobased materials. It should be expected that followingrequisite processing and product development of biobased ma-terials resulting properties should equal or better those of theconventional alternatives. However, such processing and productdevelopment is not always trivial and is unlikely to be cost effe-ctive in all cases.

It is not surprising, therefore, that the current applications of bi-obased materials seek not to emulate the properties of conventi-onal plastics, but to capitalize on inherent biodegradability andon other unique properties of these polymers. Biobased plasticapplications are currently targeted towards single-use, dispo-sable, short-life packaging materials, service ware items, dispo-sable non-wovens and coatings for paper and paperboard appli-cations. However, the possible products made from biobasedresources covers a broader range, and some of the potential pro-ducts and applications are summarized in Table 2.1. In general,the same shapes and types of food packaging can be made fromsynthetic and biobased resources. The question is whether thesame performance can be achieved by using the biobased mate-rials as with the synthetic ones.

35

2.5. Manufacturing of biobased food packaging Engineering of a biobased package or packaging material requi-res knowledge of the processing and material properties of thepolymers. If the properties of the native biopolymer are not iden-tical to the required one, or if the polymer by nature is notthermoplastic, a certain modification of the polymer must takeplace. For very specific requirements (very low gas permeabilityor high water resistance) it is unlikely that one polymer will beable to provide all required properties even after modifications.Hence, it is necessary to use multiple materials in a composite, alaminate or co-extruded material.

Figure 2.7. Designing and manufacturing of biobased packagesand packaging materials require a multistep approach.

In this section the main categories of food packaging will be di-scussed. For these categories the main material requirements willbe discussed and compared with the development of the materi-als from biobased polymers. Commercial and near commercialdevelopments in this area will be mentioned.

2.5.1. Possible products produced of biobased materialsThe fundamental repeating chemical units of the biobased ma-terials described so far are identical to those of a significant bodyof the conventional plastics. Thus, in the broadest sense, poly-saccharides possessing repeating acetal functionality can be 34

Biopolymers

Modifications

Thermoplastic

Product properties

Product

Modifications(physical/chemical)

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presently available gas barrier materials like EVOH and PA6 (see Figure 2.3).

The properties (mechanical strength, gas and water vapour pro-perties) of blown films can be improved by coating of a glass-likeultra thin layer of SiOx or by producing nano-composites. Addi-tion of nano-particles during processing of the film producescomposites with improved water and gas barrier properties (Fi-scher et al., 2000) and ongoing developments at TNO industry(NL) aims at producing hydrophobic starches based on thesecomposites. A similar approach is to use a glass-like ultra-thincoating of SiOx improving the barriers of the material immensely(Johansson, 2000 and 1997).

2.5.3. Thermoformed containersA next class of products is thermoformed containers for foodpackaging. In order to be able to thermoform a polymer it shouldbe possible to process this material from the melt (extrusion) intosheets and consequently thermoforming these sheets just abovethe Tg or Tm of the material. Thermoformed products can be found based on PLA and PHB/V. Again, it is possible to producethermoformed articles from laminates based on Paragon as wellas other thermoplastically processable biopolymers.

2.5.4. Foamed productsStarch-based foams for loose fill applications (Novamont, (I), National Starch (USA) a.o.) have been commercially introducedwith success some years ago and the market for these productsis still growing. Foamed products like trays and clamshells basedon starch for food packaging have not yet been introduced com-mercially. Products based on a molding technique from a slurryphase (Earthshell (USA), APACK (D)) are close to market introduc-tion. These products are produced form starch base slurries withinorganic and agrofiber based fillers. Other proposed techniquesinclude loose-fill molding (Novamont (I), Biotec (D)), foam extru-sion (Biotec (D)), and extrusion transfer molding (Standard Starch(USA)) and expandable bead moulding (Tuil et al., (In press)). Fo-amed products based totally on PLA are still in a developmentalphase.

In order to be able to use these starch-foamed products in foodcontact applications coatings should be applied on the starch- 37

Table 2.1 The major processing routes to potential biobasedproducts.

Processing route Product examples

(Co-)Extruded film Packaging film

Cast film Packaging film

Thermoformed sheets Trays, cups

Blown films Packaging film

Injection (blow-)moulding Salad pots, cutlery, drinking be-akers, cups, plates, drinks bott-les, trays

Fibres and non-wovens Agricultural products, diapers,feminine hygiene products, cer-tain medical plastics, clothing

Extrusion coating Laminated paper or films

2.5.2. Blown (barrier) filmsBlown films comprise one of the first product categories to bedeveloped based on mineral oil derived biodegradable poly-esters. They have successfully been applied as garbage bags andrelated applications. Film blowing grades of renewable polymershave been developed based on PLA. Blown films based on thesebiopolyesters exhibit excellent transparency and cellophane-likemechanical properties. The sealability depends on the degree ofcrystallinity and good printability can also be achieved. The pos-sibilities of film blowing PHB/V materials are at this time limiteddue to their slow crystallization and low melt strength.

In many food packaging applications, a water vapour barrier aswell as gas barriers are required. No single biobased polymer canfulfil both these demands. In this case, the use of co-extrusioncan lead to laminates which meet the objectives. Paragon(Avebe, NL) materials which are based on thermoplastic starchcan be film blown in a co-extrusion set-up with polymers likePLA and PHB/V as coating materials, resulting in a barrier coatingwhich, for example, proved to be successful in the packaging ofcheese (Tuil et al., 2000). The use of Paragon tie-layers providesthe adhesion between the coating and the base layer. In thisway, starch-based materials could provide cheap alternatives to36

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2.7. Conclusions and perspectivesDevelopments of polymeric materials based on biological resour-ces are being made with an ever-increasing rate making it almostimpossible to produce a paper on the state-of-the-art of thisarea. The information presented here may very likely be out-dated when these lines are being read and novel products, poly-mers and optimized performance of these are an expected sce-nario.

Biological derived polymers may be used for the production ofall types of packaging (trays, cups, bottles, films, etc.) using thesame equipment and technology used for conventional materi-als. However, these materials have to be well performing in or-der to be able to compete with the highly developed and sophi-sticated materials used today. Comparing the properties ofbiobased polymeric materials with the conventional synthetic petroleum-derived polymers shows a major potential of thesepolymers for the production of well-performing food packaging.However, when using proteins or polysaccharides in the materi-als their sensitivity towards relative humidity must be overcome.The biobased materials have an inherent potential of being com-postable which may help the commercialization of these materi-als. Similar to the synthetic materials used today it will be neces-sary to use several polymeric materials in multi-layers orcomposites tailoring the properties of the packaging to meet thedemands of specific foodstuffs. In general, the more diverse sidechains and functional groups of biobased polymers, comparedto conventional plastics derived from mineral oil, gives the resinand material manufacturer unique possibilities to tailor the pro-perties of the finished package. This advantage should be usedfurther to produce materials with even better properties thanthe ones we know today.

39

based foams. Adhesion between the foam and the coating is ofimportance. Paraffin and other oligomer based coatings are pro-posed next to PLA and PHB/V based coatings. Protein and me-dium chain length PHA based coatings (ATO, 2000) are close tomarket introduction.

2.5.5. Coated paperIt is expected that paper will stay an important biobased packa-ging material. Paper and board materials have excellent mecha-nical properties, however, the gas permeabilities are too high formany food applications. The hydrophilic nature of the paper-ba-sed materials is a major challenge of these materials whenpackaging moist foods. To date, the paper-based materials havebeen coated with a thin layer of synthetic plastic which has pro-vided the materials with the required gas property and water resistance. Alternatively, biobased materials might be used as coating materials thus paving the way for a 100% biobasedpackaging material. Paper-based materials coated with PE are readily repulpable as the hydrophobic PE is easily removed in thepulping process. Hence, paper-based materials coated with bio-based, hydrophobic polymeric materials are, likewise, going tobe repulpable.

2.6. Additional developmentsTo be able to produce a 100% biobased packaging developmentof biobased additives is needed. Additives used in the produc-tion of packaging are plasticizers, UV-stabilisers, adhesives, inksand paints, natural pigments and colorants. So far, few develop-ments have been made in this field and it is suggested to directresearch to this area.

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Fischer, S., Vlieger, de J, Kock, T., Gilberts, J., Fischer, H. and Ba-tenburg, L. (2000). Green composites the materials of the fu-ture - a combination of natural polymers and inorganic particles.Proceedings of the Food Biopack Conference, 27 29 August2000, Copenhagen, Denmark, p. 109.

Fitzpatrick, S.W. (1998). NEWS Chementator CO2 may stabil-ize radioactive wastes. A new look at an old levulinic acid route.Wastes yield high-octane fuel. A new US gasoline substitute?Chemical Engineering, 105(10): 25.

Fossen, M. and Mulder. W. (1998). Die Anwendung von Pflan-zenproteinen im Non-Food-Bereich, LVT, nr. 43, p. 108.

Gabelman, A. (Ed.) (1994). Bioprocess Production of Flavor,Fragrance and Color Ingredients, John Wiley & Sons, Inc.

Garde, A., Schmidt, A.S., Jonsson, G., Andersen, M., Thomsen,A.B., Ahring, B.K. and Kiel, P. (2000). Agricultural crops and resi-duals as a basis for polylactate production in Denmark. Proceed-ings of the Food Biopack Conference, Copenhagen, 27 29 Au-gust 2000, pp. 45 51.

Graaf, de L. A. and Kolster, P. (1998). Industrial proteins as greenalternative for petropolymers: potentials and limitations. Ma-croMolecular Symposia 127, p. 51.

Guilbert, S., Gontard, N and Gorris, G.M. (1996). Prolongationof the shelf-life of perishable food products using biodegradablefilms and coating. Lebensmittelwissenschaft und Technologie29: 10 17.

Ha, T.T. (1999). Extrusion processing of zein-based biodegrad-able plastics (pp. 166). Ph.D. Thesis, University of Illinois at Ur-bana-Champaign.

Haugaard, V. K. and Festersen, R. M. (2000). Biobased packa-ging materials for foods. Proceedings of the Food Biopack Con-ference, Copenhagen, 27 29 August 2000, pp. 119 120.

Hoagland, P.D. and Parris, N. (1996). Chitosan/pectin laminatedfilms. Journal of Agricultural and Food Chemistry, 44: 1915 1919. 41

2.8. ReferencesAndres, C. (1984). Natural Edible Coating has Excellent Moistureand Grease Barrier Properties. Food Processing, 45(13): 48-49.

ATO, Internal communication (2000).

Aydt, T.P., Weller, C.L., and Testin, R.F. (1991). Mechanical andbarrier properties of edible corn and wheat protein films. Trans-actions of the ASAE, 34: 207-211.

Brine, C.J, Sandford, P.A., and Zikakis, J.P. (Eds.) (1991). Advan-ces in chitin and chitosan. Elsevier Applied Sceince, London pp. 1 491.

Brown, R. M. (1996). The biosynthesis of cellulose. Pure and Ap-plied Chemistry, 33(10): 1345-1373.

Buisman, G. J. H. (1999). Focus: Biodegradable binders andcross-linking agents from renewable resources. Surface CoatingsInternational, 3: 127 130.

Butler, B.L., Vergano, P.J. Testin, R.F., Bunn, J.M. and Wiles, J.L.(1996). Mechanical and barrier properties of edible chitosanfilms as affected by composition and storage. Journal of FoodScience, 61(5): 953 956.

Carraher, E. (Ed.) (1981). Polymer Applications of Renewable Resource Materials, Sperling L. H., Plenum Press, New York andLondon.

Chandra, R. and Rustgi, R. (1998). Biodegradable polymers.Progress in Polymer Sciences 23: 1273 1335.

Dawson, P.L., Han, I.Y., Orr, R.V. and Acton, J.C. (1998). Chitosancoatings to inhibit bacterial growth on chicken drumsticks. Pro-ceedings of the 44th International Conference of Meat Scienceand Technology, Barcelona, Spain pp. 458 462.

Donnelly, M. J. (1995). Polyurethanes from renewable resources.III: Synthesis and characterisation of low molar mass polytetrahy-drofuran diols and their glucosides. Polymer International, 37: 1 20. 40

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Oertel, G. (1985). Polyurethane Handbook, PU Based on CastorOil Polyols in Telecommunications. Hanser Publisher, New York.

Padua, G.W., Rakoronirainy, A. and Wang, Q. (2000). Zein-basedbiodegradable packaging for frozen foods. Proceedings of theFood Biopack Conference, 27 29 August 2000, Copenhagen,Denmark, pp. 84 88.

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3. Food biopackaging

3.1. Introduction Food packages serve a number of important functions, includingcontainment and protection of food, maintaining the sensoryquality and safety of food, conferring convenience to food andcommunicating information about food to consumers (Robert-son, 1993). This chapter focuses on biobased packaging forfood and discusses critical packaging issues. The role that bioba-sed packaging materials can play in protecting the sensory qua-lity and safety of several groups of food products is discussed. Inaddition to sensory and safety aspects relating to food, it is re-cognized that other issues also require careful consideration inthe development and selection of biobased food packages.These aspects, which are discussed superficially in the chapter,include logistical, marketing, legislative, environmental and fi-nancial constraints to the production of the biobased materials.

3.2. Food packaging definitionsMost commonly used food packages clearly fall into primary, se-condary or tertiary packaging categories. For a variety of foodproducts, however, conventional packaging does not provideoptimal conditions for product storage (Petersen et al., 1999)and a number of approaches are used to design packages forspecific products. Such product-specific packaging includes ap-plying edible films and coatings, active packaging, modified at-mosphere packaging (MAP), and using combinations of packa-ging materials.

3.2.1. Primary, secondary and tertiary packagingPrimary packaging materials are those which are in direct con-tact with foods. Their functions are to contain, protect and facili-tate distribution and storage of foods while satisfying consumerneeds with respect to convenience and safety (Brown, 1992).The properties of the primary packaging materials should be tail-ored according to the requirements set by the packaged foods.Primary packaging is packaging where the material and foodmay be separated from each other. Thus, edible coatings do notfall into the primary packaging category. However, edible filmsmay perform similar functions to primary packaging.

45

Vibeke K. Haugaard1*, Anne-Marie Udsen2, Grith Morten-sen2, Lars Hegh3, Karina Pe-tersen4, and Frank Monahan5

*To whom correspondenceshould be addressed

1Department of Dairy andFood Science, The Royal Veterinary and AgriculturalUniversity, Rolighedsvej 30, DK 1958 Frederiksberg C,Denmark, Telefax: +45 35 28 33 44, E-mail: vkh@kvl.dk; 2Arla Foods amba, Innovation, Rrdrumvej 2, DK-8220 Brabrand, Telefax: +45 87 46 66 88; E-mail: anne.marie.udsen@arl-afoods.com or grith.morten-sen@arlafoods.com; 3Danisco Cultor, Edwin Rahrs Vej 38, DK-8220Brabrand, Denmark, Telefax: +45 89 43 51 29, E-mail: G8LAH@danisco.com; 4Department of Biotechnology,Technical University of Den-mark, Sltofts Plads, Building 221, DK-2800 Kgs.Lyngby, Denmark, Telefax: +45 45 88 49 22; E-mail: kp@ibt.dtu.dk; 5Food Science Department,University College Dublin, IE-Belfield, Dublin 4, Ireland, Telefax: +353 1 7061147, E-mail:frank.monahan@ucd.ie.

Sinclair, R.G. (1996). The case for polylactic acid as a commoditypackaging plastic. Polymeric Materials: Science and Engenne-ring, 72: 133 135.Sdergrd, A. (2000). Lactic acid based polymers for packagingmaterials for the food industry. Proceedings of the Food BiopackConference, Copenhagen, 27 29 August 2000, pp. 14 19.

Tuil R. van, Schennink, G., Beukelaer, H. de, Heemst, J. van andJaeger, R. (2000). Converting biobased polymers into food pack-agings. Proceedings of the Food Biopack Conference, Copenha-gen 27 29 August 2000, Copenhagen, Denmark, pp. 28 30.

Van Damme, Bruggeman G., De Baets S. & Vanhooren P.T.(1996). Useful polymers of microbial origin. Agro-food-industryHi-tech, sep/oct: 21-25.

Walle, van der G.A.M, Koning, de G.J.M., Weusthuis, R.A. andEggink, G. (in Press) Properties, modifications and applications ofbiopolyesters In: Advances in Biochemical Engineering/Biotech-nology Volume 71, Steinbchel, A. and Babel, W. (Eds.), SpringerVerlag.

Witt, U., Mller, R.-J. and Klein, J. (1997). Biologisch abbaubarePolymere. Status und Perspektiven. Publishers: Franz.Patat-Zen-trum Braunsweig, Germany ISBN 3-00-001529-9.

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mary synthetic packaging material used in a product or allowconversion from a multi-layer, multi-component packaging ma-terial to a single component material. Edible coatings may alsohelp maintain food quality by preventing moisture and aromauptake/loss, etc. after opening of the primary packaging.

3.2.3. Active packagingPackaging is termed active when it performs a role other thanproviding an inert barrier to external conditions. Active packa-ging solutions could involve the inclusion of an oxygen scaven-ger or an antimicrobial agent if microbial growth is the quality-limiting variable (Rooney, 1995).

3.2.4. Modified atmosphere packagingModified Atmosphere Packaging (MAP) is defined as the enclo-sure of food products in a high gas barrier film in which the ga-seous environment has been changed or modified to control re-spiration rates, reduce microbiological growth, or retardenzymatic spoilage with the intent of extending shelf-life (Smithet al., 1995). For example, red meats are packaged in atmosphe-res in which the oxygen and carbon dioxide contents are ele-vated, relative to air, to maintain product colour, yet inhibit mi-crobial growth.

3.2.5. Combination materialsCombining packaging materials in, for example, laminates or co-extrudates may improve barrier characteristics significantly. Oneexample is combining cardboard and plastics in gable top beve-rage packages. Cardboard provides stability and light protectionwhile the plastics contribute to an optimal packaging solution byproviding a water vapour barrier.

3.3. Food packaging requirements The packaging requirements of foods are complex. Unlike inertpackaged commodities, foods are often dynamic systems with li-mited shelf-life and very specific packaging needs. In addition,since foods are consumed to sustain life, the need to guaranteesafety is a critical dimension of their packaging requirements.While the issue of food quality and safety is first and foremost inthe mind of the food scientist, a range of other issues surroundingthe development of any food package must be considered beforea particular packaging system becomes a reality (see Table 3.1). 47

Secondary packaging is often used for physical protection of theproduct. It may be a box surrounding a food packaged in a flexi-ble plastic bag. It could also be a corrugated box containing anumber of primary packages in order to ease handling duringstorage and distribution, improve stackability, or protect the pri-mary packages from mechanical damage during storage and di-stribution. Secondary packaging may also provide crucial infor-mation on lot number, production dates, etc. aimed atdistributors and retailers. Furthermore, secondary packagingmay be used for marketing purposes, e.g. a box that may be un-folded into retail display cabinets in the supermarket.

Tertiary packaging incorporates the secondary packages in a fi-nal transportation package system. Again, the purpose is to faci-litate storage and handling and to protect the packaged productagainst mechanical damage, weather conditions, etc.. Examplesof tertiary packaging are boxes, pallets and stretch foils.

3.2.2. Edible coatings and films Edible coatings and films comprise a unique category of packa-ging materials differing from other biobased packaging materi-als and from conventional packaging by being edible. Films andcoatings differ in their mode of formation and application to fo-ods. Edible coatings are applied and formed directly on the foodproduct either by addition of a liquid film-forming solution ormolten compounds. They may be applied with a paintbrush, byspraying, dipping or fluidising (Cuq et al., 1995). Edible coatingsform an integral part of the food product, and hence should notimpact on the sensory characteristics of the food (Guilbert et al.,1997). Edible films, on the other hand, are freestanding structu-res, formed and later applied to foods. They are formed bycasting and drying film-forming solutions on a levelled surface,drying a film-forming solution on a drum drier, or using traditio-nal plastic processing techniques, such as extrusion. Edible filmsand coatings may provide barriers towards moisture, oxygen(O2), carbon dioxide (CO2), aromas, lipids, etc., carry food ingre-dients (e.g. antimicrobials, antioxidants, and flavour compo-nents), and/or improve the mechanical integrity or handling ofthe food product. Edible films and coatings may be used to se-parate different components in multi-component foods therebyimproving the quality of the product (Krochta and De Mulder-Jo-hnston, 1997). They may be used to reduce the amount of pri-46

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Environment Not endanger human Safe food contact in-safety teractions

Avoid physical harm

Use resources responsibly Have a positive LCA

Facilitate waste Should be recoverable.management Ought to be recycl-

able, burnable or com-postable

Legislation National laws Meet labelling, hygi-ene, migration condi-tions

Financial Cost effectiveness Acceptable price per food packagePrice of concomitant machinery

Biobased packaging materials must meet the criteria that applyto conventional packaging materials associated with foods.These relate to barrier properties (water, gases, light, aroma), optical properties (e.g. transparency), strength, welding and moulding properties, marking and printing properties, migra-tion/scalping requirements, chemical and temperature resistanceproperties, disposal requirements, antistatic properties as well asissues such as the user-friendly nature of the material and whet-her the material is price-competitive. Biobased packaging mate-rials must also comply with food and packaging legislation, andinteractions between the food and packaging material must notcompromise food quality or safety. In addition, intrinsic characte-ristics of biobased packaging materials, for example whether ornot they are biodegradable or edible, can place constraints ontheir use for foods.

3.3.1. Replacing conventional food packaging materialswith biobased materials a challengeOne of the challenges facing the food packaging industry in pro-ducing biobased packaging is to match the durability of thepackaging with product shelf-life. The biobased material mustremain stable maintaining mechanical and/or barrier propertiesand functioning properly during storage of the food. Ideally, thematerial should biodegrade efficiently on disposal. Thus, environ- 4948

Table 3.1. Food packaging requirements.

Area Overall Specific

Food Quality Maintain or enhance Maintain tastesensory properties Maintain smell

Maintain colourMaintain texture

Maintain the necessary Should not support microbiological standards the growth of unwan-

ted micro-organismsIf necessary, can be pasteurized or sterilized

Manufacturing Offer simple, economic Sheet, film, contai-processes for package ners, pouchesformation Adequate mechanical

properties

Give compatibility in Dimensional stabilityproduct filling Good runability on

filling linesCloseabilityCompatibility with existing machinery

Logistical Facilitate distribution Conform to industry requirements (e.g. size, palletisation)Carry the required co-des (bar code, productand sell-by)

Marketing Enhance point of sale Good graphicsappeal Aest