biopolymers as a sustainable alternative?

Biopolymers as a Sustainable Alternative?

Packaging Materials. As natural materials biopolymers are expected to solve the

disposal problems of current plastic packaging. But can they really do this with no

ifs and buts? What about competition with the food chain? Do they deliver the

ecological, service and disposal advantages expected of them to their full extent?

The following article attempts to answer these questions.

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Kunststoffe international 5/2011

HANS-JOSEF ENDRES ET AL.

In the current debate about sustain-ability and environmental awarenessin the food industry conventional

plastic packaging is time and again the fo-cus of attention. Its very good serviceproperties, such as good chemical resist-ance, optimized processing and high lev-el of design freedom are offset by dispos-al disadvantages, such as large volumes ofwaste, high persistence or the complexi-ties of single polymer recycling. On topof this they are predominantly based onlimited petrochemical raw materials and

therefore have a negative CO2 balancewhen incinerated.

For this reason the interest of the pack-aging industry in biopolymers has grownstrongly and there are already special le-gal provisions for them.For example sincethe beginning of this year the sale of plas-

tic carrier bags made from petrochemi-cal raw material has been banned in Italy.As a result of the revision of the Germanpackaging directive in May 2005 biopoly-mer packaging with certified composta-bility was freed from disposal fees, suchas the levy for the “Green Dot” (GrünerPunkt), until 2012 (Fig. 1).

With continuously growing quantitiesof biopolymers in the marketplace it is,however, increasingly necessary and sen-sible also to consider all other alternativedisposal options for biopolymer packag-ing alongside composting. Through in-telligent disposal in many cases addition-al (cascade) utilization can be achieved,meaning that alongside composting oth-er disposal routes are often feasible, forexample recycling, in similar ways to con-

Hanover University of Applied SciencesBio-Processing Section Department of EngineeringD-30453 Hanover / Germany TEL +49 511 9296-2212> www.fakultaet2.fh-hannover.de

Contacti

Translated from Kunststoffe 5/2011, pp. 34–40Article as PDF-File at www.kunststoffe-international.com; Document Number: PE110752

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W 2011 Carl Hanser Verlag, Munich, Germany www.kunststoffe-international.com/archive Not for use in internet or intranet sites. Not for electronic distribution

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SPEC I A L Pa ckag ing

© Carl Hanser Verlag, Munich Kunststoffe international 5/2011

ventional plastics, their use as substratesor co-substrates in biogas production, oras replacement fuels in energy produc-tion. In all these cases energy can be re-covered without setting additional CO2

free (Fig. 2).

Biopolymer Film and Packaging

In manufacturing and processingbiopolymers fundamentally the sametechnology can be used as for convention-al plastics. Since most biopolymer filmsare based on polylactide (PLA or polylac-tic acid) and starch blends (Fig. 3), thermo-plastic manufacturing techniques aredominant. An additional large group isformed by regenerated cellulose and var-ious polyvinyl alcohol (PVAL) films. Filmcasting techniques are overwhelminglyused for the manufacture of films fromthese [4].

In the last three to four years the pro-duction capacity for biopolymer packag-ing has increased after a fairly hesitantstart. The most important reasons citedfor this delay were the requirements forfood grade approval, important barrierproperties and the need for optimizationin industrial processability. For examplechanges in the composition and/ororganoleptic properties of the packaged

material due to migration of gases, aro-mas and moisture have to be excluded forbiopolymers as well [4].

Barrier Properties of Biopolymer Films

Barrier properties are one area wherebiopolymers with their polar structureshow a significant difference when com-pared to conventional polymers such aspolyethylene (PE), polypropylene (PP) orpolyethylene terephthalate (PET).

Amongst the biodegradable biopoly-mers only PLA, the biopolymer that hasbeen furthest developed as a packaging

material up until now, and polyhydroxy-alkanoates (PHAs) show a certain degreeof barrier functionality for water vapor(Fig. 4). Compared to PET, PE or PP how-ever, water vapor permeability is stillclearly higher.

The most promising possibility to im-prove the barrier properties of biopoly-mers is said to be coating. This is especial-ly true for PLA bottles and PLA filmswhere there are a number of approachesto coating. However, additional coatingalso means additional effort. On top ofthat these coatings are often not asdurable as the base material and are alsomore scratch and crease sensitive [4]. Asan alternative, work is being carried outon the manufacture of multi-layer films,that is the combination of biopolymersand (petrochemical) barrier materials.

Novel material developments, such asthe bio-PET that is partially manufac-tured from renewable raw materials(bioethanol) for Coca-Cola and DanoneWaters or the entirely bio-based Bio-PEfrom Braskem S.A., São Paulo, Brazil,make such coatings superfluous. In themeantime they offer a like for like replace-ment of conventional polymers and arealready partially replacing these. As socalled “drop in solutions” they have thesame chemical structure as their petro-chemical cousins and therefore representwith first biopolymers with high water va-por barrier properties. With these novelthird generation biopolymers the focus isno longer on biodegradability as a dispos-al option, but rather on the preferred useof bio-based raw materials as a feedstockfor the synthesis of durable polymericmaterials.

Sustainable Disposal ofBiopolymer Packaging

If a decision is taken to use packagingmade from renewable raw materials for

Materials

Sales, transport andouter packaging

Domestic wastewithout packaging

VerpackV

Other packaging in and outside of the

food sector

Compostablebiopolymers

Otherpackagingmaterial

Ecologicallyadvantageous

packaging

Ecologically disadvantageouspackaging incl. other

biopolymers

No take backobligation

Take back obligation, e.g. DSD levy

Compulsorydeposit

Compostablebiopolymers

+75 % renewableraw materials

AbfAblV

...Disposable drinkspackaging0.1–0.3 l

Beer,water,cola...

Milk,milk drinks

and fruit juice

...

Fig. 1. Waste groups as defined by the 5th edition of the German “Verpackungsverordnung”(Packaging Directive) [1]

© Kunststoffe

Biopolymerproduct

LandfillSalt waterLittering

Domesticcomposting

Thermalrecycling

Feedstockrecycling

Industrialcomposting

IncinerationBiogasplant

Breakdownin the ground

Digestion in thehuman body

Fig. 2. Disposaloptions for bio-polymers [2, 3]

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sustainability reasons, it is not sufficientin terms of an objective assessment of thesustainability of biopolymers only to con-sider the supply of the biogenic raw ma-terials and the energy required duringmanufacture (“cradle to gate”). It is alsonecessary – in the sense of “cradle tograve” – to assess the disposal properties.Through additional utilization duringdisposal an even higher degree of sustain-ability can be achieved (Fig. 5).

Composting: Up until now compost-ing was the center of attention forbiopolymer packaging. In general it canbe said for biopolymers that have beencertified as compostable that they can bebroken down effectively in industrialcomposting plants and digested to prod-ucts such as CO2, H2O or biomass/humus[5 to 7]. Fundamentally this means thatthe system of composting certifiedbiopolymers works from a technicalstandpoint. However, in respect of thecomposting logistics there is still a needfor some optimization. For example therequirement for separate collection andtransport represents a logistical, econom-ic and in particular ecological problem

since this is often associated with addi-tional overheads [2, 4].

In most cases the compostability cer-tificate also only confirms that an existingproduct (a specific material with a definedwall thickness) is biodegradable within acertain period of time under industrialconditions (e.g.defined quantities of oxy-gen and moisture, regular turning of thepile, temperature profile and the presenceof suitable micro-organisms). This can,

however, not be equated to a full decom-position in domestic compost [4].

At present the disposal logistics ofcompostable packaging including the re-lated legislation (e.g. the German com-posting directive) have not been accept-ably and coherently solved. For examplebiopolymer packaging in Germany de-spite appropriate marking of composta-bility certification and the dispensationunder the disposal regulations, i. e. thewaiver of disposal levies of for examplethe German DSD (Green Dot) is regard-ed as erroneous throw-in for the yellowand brown bins.

If composting, as in many cases, is sim-ply a part of the disposal process it is notone of the most sustainable disposal op-tions. Composting is sensible if the de-composition provides an additional func-tional advantage at the same time. Exam-ples of this are biodegradable flower potsor agricultural film that after use can besimply plowed in and do not have to becollected and disposed of, laundry bagsthat dissolve in the washing machine ormedical implants whose breakdown inthe body matches the healing process [4].

On top of this the quantity of CO2 pro-duced via the “cold burning” processes ofcomposting is exactly the same quantitythat would also be produced during di-rect incineration of the biopolymers orcombustion of the biogas produced fromthe biopolymers which have additionalenergetic utilization [1, 4].

Recycling: Alongside composting, in adifferentiated view of the disposal optionsattention must be given to classic recy-cling. However, there is hardly any expe-rience in the area of thermoplasticbiopolymers. It is likely that similar prob-lems will be found to those found whilerecycling conventional polymers. For ex-ample it is assumed that their generallylower thermal and chemical stability will

PHBs 2 %Biopolyester 1 %PVAL 10 %

Starch blends 26 %Others13 %

PLA blends41 %

Regenerated cellulose5 %Cellulose derivatives 2 %

Fig. 3. Overview ofthe biopolymer filmmaterials used by thecurrently known filmmanufacturers inEurope (approx. 60companies) [4]

© Kunststoffe

Hydrogen permeability (WVTR)

104

103

102

101

100

10-1

cm3/m2d bar

10-1

Oxy

gen

perm

eabi

lity

(OTR

)

100 101 102 g/m2d 103

23 °C, 85 % r.h.

LDPE

BOPPBOPS

PC PCL

PLAPLA, coated

PLA, specialbarrier coating

CH, specialbarrier coating

PHA

Cellulose derivative

CHCH,

coated

PVAL

BiopolyesterStarchblendPVC, soft

PVC, rigid

PLA blend

HDPE

PET

PA6

EVAL

Fig. 4. Comparison between the barrier properties of biopolymers with various conventional packag-ing plastics (0 to 5 % rel. humidity; BO = biaxially stretched/orientated, coated regenerated cellulose= metalized, coated PLA = SiOx-vapor deposition; CH = regenerated cellulose) [4]

© Kunststoffe

Raw material(iron, ethylene, cellulose, starch, ...)

Waste, Junk

Landfill

Failure

Usage

Material(steel, polymer,ceramic, ...)

Form(building, machine,component, packaging, product ...)

ateriallene, starch, ...)

Wast

Land

Fa

Usage

ine,ckaging,

A

E

V

G

K

W

Fig. 5. Various systemboundaries in eco-logical balancing(gray = “gate to gate”(processor), beige =“cradle to gate”, red =“cradle to waste”,black = “cradle tograve”) [4]

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lead to an even more pronounced down-cycling effect. In this respect experiencegained from pre-consumer (recycling ofproduction waste) and post-consumer re-cycling (recycling of mixed and soiledwaste) including sorting and possible sta-bilization from conventional plastics canand should be used.

In addition there is poor compatibili-ty between various biopolymer materialclasses as well as combinations with con-ventional plastics. Thus here as well withrespect to high quality secondary raw ma-terials there is a desire for the best possi-ble polymer type separation of wastestreams [2, 4].

At present, however, there is very littleinformation on how biopolymers affectthe overall waste stream. On the one handa possible contamination of secondaryraw materials through small quantities ofbiopolymers should be avoided, on theother hand separate treatment of individ-ual materials is only economic above acertain proportion of the waste stream,which is in practice around 10,000 t/a ofwaste. As the first trials performed on thepossible separation from the waste streamhave shown biopolymers can, fundamen-tally, be for example identified in thewaste stream from their characteristicNIR (near infrared) spectrum (Fig. 6).

Incineration: A significantly higheradditional utilization during disposal canalso be achieved with a direct (co-) incin-eration of biopolymers. An additionalseparation from the conventional plasticstream is not absolutely necessary for this.

The higher the proportion of bio-based material the more CO2 neutral isthe combustion energy that is made avail-able [1].

Figure 7 shows the bio-based carboncontent as a share of total carbon contentfor various specimen biopolymer mate-rials.With this information about the bio-based carbon and the associated share ofrenewable raw materials in the biopoly-mer it is possible to calculate the bio-based and therefore neutral CO2 pro-duced during incineration.

In a similar way to petrochemical plas-tics or generally for all energy sources thecalorific values are almost entirely de-pendent on the individual elementarycomposition (and the water content) ofthe material being burnt. The source ofthe carbon (petrochemical or bio-based)plays no part in respect of the resultingheating or combustion values. Only theratio of oxidizable to non-oxidizablecomponents is important here. In the caseof the materials investigated this is the ra-tio of carbon and hydrogen to oxygen andwater in particular. Therefore it is not sur-

Wave number

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

Abso

rban

ce u

nits

11,000 10,000 9,000 8,000 7,000 6,000 5,000 cm-1 4,000

Fig. 6. NIR spectra of various biopolymers [4]

© Kunststoffe

prising that the calorific value of bio-based PE is the same as that of conven-tional petrochemical based PE. As is alsothe case for conventional plastics like PAor PET hetero-atoms such as nitrogen oroxygen reduce the mass specific calorificvalue of biopolymers (Fig. 8).

In respect of combustion emissionsinitial investigations have shown that ina similar way to the calorific values for aparticular material the emissions are de-pendent only on the chemical composi-tion, including any additives, and thecombustion temperature. For biopoly-mers the toxic potential of emissions wasfound to be similar to that of wood com-bustion. Thus, as was expected, no mod-ifications of conventional incinerationequipment are required for the incinera-tion of biopolymers [8].

Biogas: A further disposal option forbiopolymers up until now hardly consid-ered by scientists or in practice is diges-tion to biogas. Since a biogas plant pro-duces biogas, with its principle compo-nent methane (CH4), in multiple stepsfrom organic substrates under anaerobicconditions in contrast to the CO2 pro-

100

80

60

40

20

0

%

PCLblend

Bio-

base

d ca

rbon

PHB PLA PLAblend

Copoly-ester

Starchblend

Starch/PP blend

Bio-PA Bio-PE Celluloseblend

48.6

96.3100

46.05

2.8

24.5

39.9

57.8

100

57.5

Fig. 7. Bio-derived carbon as a proportion of the total carbon content for various biopolymers

© Kunststoffe

Book TipEngineering BiopolymersMarkets, Manufacturing, Propertiesand ApplicationsBy Hans-Josef Endres, Andrea Siebert-Raths648 pagesCarl Hanser Verlag, Munich 2011 (to be published on 7 June 2011)ISBN 978-3-446-42403-6> www.hanser.de/978-3-446-41683-3

More on this Topici

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duced in aerobic composting, productionof biogas from biodegradable polymersseems to be fundamentally possible [4].

An additional follow-on option would bethe treatment of the biogas producedfrom biopolymers to bring it up to natu-

ral gas quality for feeding into the distri-bution network.

Alongside energy or fuel production anadditional advantage is the co-disposal ofpackaging and food content. Out of date,surplus production or spoilt food couldbe – without additional effort, for exam-ple through mechanical separation ofpackaging and content – fed directly in-to a biogas plant. In cooperation with theUniversity of Rostock, Germany, an ini-tial orientating analysis of the breakdownbehavior of biopolymers under anaero-bic conditions in a biogas plant has beenconducted (Fig. 9).

From the stoichiometric compositionthe theoretical yield of biogas was calcu-lated in advance assuming a completeconversion. As part of the initial investi-gations it was, however, found that mostbiopolymer esters, such as PLA or copoly-esters, can only be digested with great dif-ficulty. The highest yield of biogas camein contrast from starch based polymersand starch blends.

In follow-on investigations the rela-tionships between the biopolymers to bedigested (e.g. material type, molecularstructure and weight, crystallinity and ad-ditives) and the biogas plant process pa-

Calorific value

Polyethylene (PE)

Polypropylene (PP)

Polystyrene (PS)

Polyamide (PA)

Polycarbonate (PC)

Polyethylene terephthalate (PET)

Polyvinyl chloride (PVC)

Polytetrafluorethylene (PTFE)

Biopolyethylene

Polycaprolactone (PCL) blend

Biopolyester

Polyvinyl alcohol (PVAL)

Polyhydroxyalkanoates (PAHs)

PLA blend

Starch blend

Polylactide (PLA)

Cellulose derivatives/blends

PP + 30 wt.-% wood flour

Heating oil

Carbon

Wood

Paper

0 10 20 30 MJ/kg 50

18

45

43

40

31

31

22

4

44

32

26

24

24

21

21

19

18

32

43

30

19

19

Fig. 8. Calorificvalues of variousbiopolymers in com-parison to conven-tional polymers andpetrochemical ener-gy sources [4, 8]

© Kunststoffe

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rameters (e.g. residence time, tempera-ture and organic digester loading) in re-spect of conversion rates as well asmethane yield are to be analyzed. In ad-dition it will have to be establishedwhether and if so what effects possiblepre-treatments (e.g. thermal pre-treat-ment, size reduction and microwaves)have on the digestion and the resultinggas quantities and quality.

Conclusion

Biopolymer packaging is in particular ap-plication areas a good alternative to con-ventional plastics. However, use ofbiopolymer film should not take placewithout an additional ecological, serviceor disposal benefit.

In addition to the raw material side bio-based biopolymer materials offermany different advantages on the dispos-al side, the so called “end of life options”[2, 9].

Alongside composting, through intel-ligent disposal an additional cascade uti-lization in the form of a practically CO2

neutral generation of energy can beachieved. In this case biopolymers are asource of renewable energy that was pre-viously used mechanically, for example aspackaging. Thus the use of bioethanol asa polymer raw material with a subsequentmechanical recycling and final incinera-tion of the biopolymer with energy recov-ery represents a significantly higher uti-lization than the direct combustion of thebioethanol. The amount of CO2 generat-ed in each case is the same since from onecarbon atom a maximum of just one CO2

molecule can be produced regardless ofwhether the biopolymer is composted,directly combusted or takes the alterna-tive route as a fuel such as biogas or bio-fuel.�

REFERENCES

1 Endres, H.-J.; Kitzler, A.S.; Nelles, M.: ÖkologischeNachhaltigkeit von Verpackungen. DMZ 11/2008,pp. 24–27

2 Endres, H.-J.; Siebert, A.; Kitzler, A.-S.: Biopoly-mers – a discussion on end of life options. Bio-plastics Magazine 01/08, pp. 22–25

3 Endres, H.-J.; Kitzler, A.-S.: “End-of-life Options”

von Biopolymeren Duisburg: 3. BiokunststoffeTagung, Carl Hanser Verlag, Munich 2009

4 Endres, H.-J. Siebert-Raths, A.: TechnischeBiopolymere. Carl Hanser Verlag, Munich 2009

5 Klauß, M.; Bidlingmaier, W.: Biologisch abbaubareVerpackungen im Materialkreislauf. ModellprojektKassel. Bauhaus-Universität Weimar; ProfessurAbfallwirtschaft: s.n. Fachtagung der Bauhaus-Universität Weimar; Vortrag Recycling 2003(March 27, 2003). Available online in German at:http://www.uni-weimar.de/Bauing/aufber/Profes-sur/RC03/Vortrag Klauss RC03.pdf

6 Haldenwanger, H. H.; Göttner, G. H.: BiologischeZerstörung der makromolekularen Werkstoffe.Chemie, Physik und Technologie der Kunststoffe inEinzeldarstellungen, Vol. 15, Berlin 1970

7 Groot, L.; Paruschke, K. et al.: Biologisch ab-baubare Werkstoffe im Gartenbau. Kuratorium fürTechnik und Bauwesen in der Landwirtschaft e. V.,Darmstadt 2000

8 Endres, H.-J. et al.: Biopolymere als Energieträger.Carl Hanser Verlag, Munich 2010

9 Willocq, J. A.: New cradle-to-cradle approach forPLA. Bioplastics Magazine. 05/2009

THE AUTHORS

PROF. DR.-ING. HANS-JOSEF ENDRES, born in1966, has been Professor of Bioprocessing at theHanover University of Applied Sciences since 1999.

DIPL.-ING. (FH) ANN-SOPHIE KITZLER, born in1981, is a research associate at Hanover University ofApplied Sciences and Arts and is studying for her PhDat the University of Rostock in close cooperation withthe Hanover University of Applied Sciences.

PROF. DR. MONT. MICHAEL NELLES, born in 1966,is Professor of Agricultural and Environmental Sci-ences as well as Head of the Department of WasteManagement, Material Flow and Environmental Tech-nology at the University of Rostock.

DIPL.-ING. (FH) ANDREA SIEBERT-RATHS, born in1978, is a research associate at the Hanover Univer-sity of Applied Sciences and is studying for her PhDat the University of Rostock in close cooperation withthe Hanover University of Applied Sciences.

400

350

300

250

200

150

100

50

0Starch/

copolyesterblend

PLAcopolyester

blend

Celluloseblend

Celluloseester

Polyester(PBS)

PLA Starch blend PCL blend PVAL PP + starch

Biog

as [m

l(N

)/g

ots]

Calculated biogas yield Measured biogas yield of that measured methane

Fig. 9. Biogas yields for various biopolymers: Comparison between the calculated and measured values

© Kunststoffe



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biopolymers as a sustainable alternative?

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