Can Nanotechnology Improve the Sustainability of Biobased Products? : The Case of Layered Silicate...

A P P L I C AT I O N S A N D I M P L E M E N TAT I O N

Can Nanotechnology Improvethe Sustainability of BiobasedProducts?The Case of Layered Silicate BiopolymerNanocomposites

Satish Joshi

Keywords:

biodegradablebioplasticcumulative energyenvironmentindustrial ecologylife cycle assessment (LCA)

Summary

Recent developments in nanotechnology, especially in the areaof nanoclay composites, are improving the technical perfor-mance of biobased polymers and moving them toward techni-cal and economic competitiveness with petroleum-based poly-mers and conventional composites. We assess whether thesedevelopments also improve the environmental sustainability ofbiopolymers, by using a life cycle approach. We estimate en-ergy use and emissions from the nanoclay production processand compare these with prior life cycle data for biopolymers aswell as other fibers, and we find that nanoclay production re-sults in lower energy use and greenhouse gas emissions thanproduction of many common biopolymers and glass fibers.Nanoclay composites hence can improve the life cycle en-vironmental performance of several common biopolymers.However, for some biopolymers the relative performance de-pends on the functional unit.

Address correspondence to:Satish JoshiDepartment of Agricultural, Food andResource Economics301C Agriculture HallMichigan State UniversityEast Lansing, MI [email protected]/faculty/joshi.htm

c© 2008 by Yale UniversityDOI: 10.1111/j.1530-9290.2008.00039.x

Volume 12, Number 3

474 Journal of Industrial Ecology www.blackwellpublishing.com/jie


Introduction

Biobased polymers hold promise for sustain-able development because (1) unlike petroleum-based polymers, these polymers are derived fromrenewable plant-based materials, and hence pro-duction can be sustained over the long run; (2)plant-derived polymers can contribute to green-house gas (GHG) emission reduction because ofcarbon capture during the plant growth; and (3)biodegradability of many of these polymers atthe end of life can alleviate problems associatedwith solid waste disposal and, at the same time,help close the material loop. Recognizing thispotential, the U.S. President’s Executive Order13134 calls for a tripling of the use of biobasedproducts in the U.S. economy by 2010 (FederalRegister 1999; USDOE and USDA 2000). Simi-larly, the 2020 vision statement of the Americanchemical industry sees a bright future for biobasedproducts (ACS 1996). A report by the Euro-pean Commission projects worldwide annual pro-duction of biopolymers at 1.3 million tonnesby 2010 without supportive government policiesand measures;1 nearly double that, at 2.5 milliontonnes, by 2010 with supportive policies and mea-sures; and between 2.2 and 4.2 million tonnes by2020 (Wolf et al. 2005). These represent annualgrowth rates of 40% to 50% during the period2000–2010 and 6% to 12% during 2010–2020.

At the same time, technical performance, eco-nomic feasibility, and environmental superior-ity of biobased polymers are subjects of debate.Critics point out relatively higher cost and in-ferior technical performance of biopolymers interms of lower strength, higher density, dimen-sional instability, thermal degradation, high gaspermeability, hydrophilic nature and associatedproblems when exposed to moisture, and fairlynarrow processing temperature windows. Further,extensive use of fossil fuels in current feedstockand biopolymer production processes can resultin higher life cycle GHG and other emissionscompared to petroleum-based polymers. Recentreviews by Patel and colleagues (2003), Dornburgand colleagues (2004), and Patel and Narayan(2005), however, conclude that biopolymers ingeneral have lower life cycle energy use and GHGemissions than comparable petroleum-basedpolymers.

Recent developments in nanotechnology, es-pecially in the area of nanoclay composites, areimproving the technical performance of biobasedpolymers and moving them toward technicaland economic competitiveness with petroleum-based polymers and conventional compositeswith fillers having micron dimensions. We re-view these developments. Nanoclay compositesincorporating less than 5 weight percentage of or-ganically modified layered silicate (OMLS) clayshave been shown to improve physical propertiessuch as strength, gas barrier, flammability, andthermal and environmental stability, when com-pared to pristine polymers, and the reinforcementefficiency of nanoclay composites can match thatof conventional composites with 40% to 50%loading with traditional fillers (Sinha Ray andBousmina 2005). Because of their relatively lowcost (Pandey et al. 2005), high potential feed-stock availability (Pandey et al. 2005; Xanthos2005), and ease in nanomaterial fabrication, claynanocomposites accounted for 24% by value ofglobal nanocomposite consumption of $252 mil-lion (10.4 gigagrams [Gg]) in 2005,2 comparedto a 15% share for carbon nanotube composites.Automotive parts, energy, and packaging werethe main nanocomposite applications. By 2011,global nanocomposite consumption is projectedto increase to $857 million (43 million kg), andthe market share for nanoclay composites is pro-jected to be 44% (McWilliams 2006).

Although nanoclay composites withpetroleum-based polymers have also beendeveloped, we focus on nanoclay compositeswith biodegradable, biobased polymers becauseof their attractiveness from a long-term sustain-ability perspective and potential large-volumeapplications in packaging and automotive com-ponents. We assess whether developments innanoclay composites also improve the environ-mental sustainability of biopolymers. We takea life cycle approach, modeling the nanoclayproduction process and estimating energy useand emissions, and compare these with priorlife cycle data for biopolymers, glass fibers, andnatural fibers. We find that, on a unit massbasis, production of nanoclay results in lower lifecycle environmental burdens than production ofcommon biobased polymers such as polylactidepolymers (PLA), polyhydroxyalkanoate (PHA)

Joshi, Can Nanotechnology Improve Sustainability of Biobased Products? 475


and polyhydroxybutyrate (PHB), and glass fibers.We qualitatively conclude that substitutingnanoclays for higher environmental burdenpristine polymers in nanoclay composites,combined with improved technical performance,will improve the environmental performanceof these biopolymers. For some biopolymers,however—for example, starch-based thermo-plastics (TPS)—product-specific life cycleassessments (LCAs) are necessary, because therelative environmental performance of thenanoclay composite depends on the functionalunit chosen.

Biodegradable BiobasedPolymers

Polymeric materials produced from renewablebiological sources that are biodegradable at theend of their useful life are ideal materials froma sustainability and industrial ecology perspec-tive, because they enable a closing of the materialloop. Common biodegradable, biobased polymers(called biopolymers for brevity) include thermo-plastics from starch (TPS); PLA; carbohydratepolymers synthesized by bacteria and fungi, suchas PHA and PHB, and epoxidized plant oils. Be-cause of large-scale availability of starch fromplants, easy biodegradability, and good process-ability, starch-based thermoplastics are consid-ered promising as a substitute for polystyrene (PS)in packaging applications such as foams, loose fillmaterials, and shape-molded parts. Starch poly-mers are vulnerable to degradation, however, andthe mechanical properties are, in general, infe-rior to PS. Commercial producers of starch-basedbiopolymers include National Starch and Chem-icals, in the United States (trade name: Eco-foam); Novamont, in Italy (Mater-Bi R©); Roden-burg, in the Netherlands (Solanyl R©); and BIOP,in Germany (BIO-Par R©).

PLA has good mechanical properties, pos-sesses thermal plasticity, and is readily fabricated.Hence, PLA and its copolymers are consideredpromising polymers for many end-use applica-tions as a substitute for low-density polyethylene(LDPE) and high-density polyethylene (HDPE;Sinha Ray and Bousmina 2005). Potential for us-ing PLA in food packaging applications is highdue to its transparency, good mechanical prop-

erties, and suitable moisture permeability. In thetransport sector, Toyota is currently developingapplications for PLA blends and fibers in auto-mobile interiors, including head liners, uphol-stery, and trimmings (Wolf et al. 2005). PLAcopolymers are currently being produced com-mercially by Natureworks PLA, whereas Hyacil,in the Netherlands, and Toyota’s Ecoplastics di-vision are planning commercial production.

PHA and PHB are naturally occurringpolyesters synthesized by a number of bacteria asintracellular energy reserves. Properties of PHB,such as melting point, crystallinity, and glasstransition temperature, are similar to those ofpolypropylene (PP), and PHB exhibits better re-sistance to solvents and ultraviolet light. PHBis stiffer, denser, and more brittle compared toPP, however. The long chain branching of PHAsallows a considerable range for tailoring the crys-tallinity, stiffness, toughness, and melting pointdepending on the application (Mohanty et al.2005). PHA and PHB are commercially pro-duced by Proctor and Gamble (Nodax R©) andMetabolix (Biopol R©) in the United States andBiomer, in Germany (Biomer R©). According toProctor and Gamble, Nodax PHA can be fullysubstituted for LDPE, HDPE, and PP in most ap-plications, whereas representatives from Biomerreported that P(3HB) from Biomer can be fullysubstituted for PP but partially substituted forHDPE (Wolf et al. 2005). Because PS, LDPE,HDPE, and PP together account for over 75% oftotal world thermoplastic consumption (Murphy2001) and TPS, PLA, PHA, and PHB can po-tentially replace these high-volume petroleum-based polymers and are currently produced com-mercially, we focus on these biopolymers.

Environmental Performanceof Biopolymers

Biopolymers are considered environmentallydesirable because of their use of renewable feed-stocks and biodegradability. Nevertheless, inview of high current use of fossil fuels in bothfeedstock production and biopolymer productionprocesses, the overall relative environmental su-periority in terms of cumulative energy use andlife cycle GHG emissions of biopolymers has beendisputed (Gerngross 1999; Gerngross and Slater

476 Journal of Industrial Ecology


2000). Still, subsequent LCA studies and com-parative reviews have concluded that, when ad-justed for feedstock energy and state-of-the-arttechnologies, biobased polymers generally resultin lower life cycle energy use and GHG emis-sions. Patel and colleagues (2003), Dornburg andcolleagues (2004), and Patel and Narayan (2005)provide comprehensive reviews of the studies an-alyzing the relative environmental performanceof biobased polymers and products. Table 1presents an updated summary (from Dornburget al. 2004) of various studies on the potentialsavings in cumulative energy use and reductionsin GHG emissions achieved when petroleum-based polymers are substituted with comparablebiopolymers. Patel and Narayan (2005), in theirreview, also indicate that the use of starch-basedfoam loose fills instead of PS loose fills and TPSfilms instead of LDPE films results in lower acidifi-cation, eutrophication, ozone depletion, and hu-man toxicity effects. They do not report suchcomparative results for other biopolymers, be-cause little information is available in publishedliterature about other environmental impacts.From table 1, we can conclude that substitutionof biopolymers for petroleum-based polymers willimprove environmental performance in terms ofenergy use and GHG emissions and in some casesother environmental impacts as well.

Nanotechnology andBiopolymer Composites

Large-scale use of biopolymers requires im-proving the technical performance of biopoly-mers with respect to petroleum-based polymers,without seriously compromising environmentalperformance. Very promising in this regard arethe recent developments in biopolymer layeredsilicate nanocomposites.

Various fibers and platelets have been used fora long time as reinforcements to improve the me-chanical properties of polymeric materials. Theuse of layered silicate clays as reinforcements isrelatively recent, beginning in the early 1990s.The commonly used clays for polymer compos-ites are montmorillonite (MMT), hectorite, andsaponite, which belong to the general family of2:1 phyllosilicates. Their crystal structure con-sists of layers composed of two silica tetrahedrals

fused to an edge-shared octahedral sheet of ei-ther aluminum or magnesium hydroxide. Indi-vidual layers are around 1 nanometer in thick-ness, and lateral platelet dimensions can varyfrom 30 nanometers to several microns, depend-ing on the particular silicate (Okamoto 2005),and hence are referred to as nanoclays. Thesenanometer-thick layers are capable of exfoliatinginto individual platelets when mixed with poly-mers. Exfoliated silicate nanoclays have high as-pect ratios (defined as the ratio of diameter tothickness for platelets) of 10 to 1,000, and hencea small weight percentage of nanoclays properlydispersed throughout the polymer creates a muchlarger surface area for the polymer–filler inter-actions than do conventional micron-sized re-inforcements. In their pristine form, nanoclaysare intrinsically hydrophilic in nature, leading tovery poor dispersion in organic polymers. Mod-ifying the surface chemistry of the nanoclays byion exchange reactions with cationic sulfactantssuch as quaternary alkylammonium or alkylphos-phonium has been shown not only to improvedispersion by rendering nanoclays organophilicbut also to improve adhesion with polymers byproviding functional groups that can react withthe polymers and, in some cases, by initiatingpolymerization of monomers (Messersmith andGiannelis 1995; Sinha Ray and Bousmina 2005).Organically modified montmorillonite (OMMT)clays with various specifications are commerciallyproduced by Southern Clay Products Inc. un-der the trade name Cloisite R© (Southern Clay2007).

Three general methods have been used inpreparation of layered silicate composites.

1. Intercalation of polymer from solution,where the OMLS is first swollen in a sol-vent such as chloroform or toluene andmixed with the polymer solution. Thepolymer chains intercalate and displacethe solvent within the interlayer of the sil-icate, forming a nanocomposite on solventremoval.

2. In situ intercalative polymerization, wherethe organically modified clay is swollenwithin the liquid monomer or a monomersolution, followed by polymerization.



Table 1 Life cycle nonrenewable energy savings and reductions in greenhouse gas (GHG) emissions perkilogram of biopolymer

Nonrenewable GHG reductionPolymer energy savings (kg CO2

types Product (MJ/kg) eq/kg) Notes Source

TPS versus LDPE Pellets 55.2 3.90 Cradle to grave,incinerationwithoutenergyrecovery

Dinkel et al.1996a

TPS versus LDPE Film 24.5 1.99 Cradle to grave,incinerationwithoutenergyrecovery

Dinkel et al.1996a

TPS versus EPS Loose fill 8.8 −0.28 Cradle to grave,incinerationwithoutenergyrecovery

Wurdinger et al.2002a

TPS versus EPS Loose fill 1.3 0.76 Cradle to grave,incinerationwithoutenergyrecovery

Estermann et al.2000a

PLA versus LDPE Pellets 23.6 1.2 Cradle to grave,incinerationwithoutenergyrecovery

Vink et al. 2003a

PHA versus HDPE Pellets −1.1 n/a Cradle to grave,incinerationwithoutenergyrecovery

Gerngross andSlater 2000a

PHA versus HDPE Pellets 13.8 n/a Cradle to grave,incinerationwithoutenergyrecovery

Heyde 1998a

PHB versus PS(best case)

Pellets 25.6 n/a Cradle tofactory gate

Heyde 1998

PHB versus PS(worst case)

Pellets −481.5 n/a Cradle tofactory gate

Heyde 1998

P(3HA) versus PP Pellets 27 1.64 Cradle tofactory gate

Akiyama et al.2003

P(3HB) versus PP Pellets 18 1.45 Cradle tofactory gate

Akiyama et al.2003

Note: The comparable petrochemical polymer data are from APME (Boustead 1999). TPS = thermoplastic starch;LDPE = low-density polyethylene; HDPE = high-density polyethylene; EPS = expanded polystyrene; PLA = polylacticacid; PHA = polyhydoxyalkonate; P(3HA) = poly(3-hydoxyalkonate); PHB = polyhydoxybutyrate; P(3HB) = poly(3-hydoxybutyrate); PS = polystyrene; PP = polypropylene.a These comparative data are as summarized in Dornburg et al. 2004 (table 1).



3. Melt-intercalation, where a mixture of thepolymer and OMLS is annealed above thesoftening point of the polymer staticallyor under shear (Sinha Ray and Bousmina2005).

Melt intercalation is emerging as a standardmethod because it is compatible with current in-dustrial processes, such as extrusion and injectionmolding. Further, due to the absence of organicsolvents and associated emissions, melt interca-lation is considered environmentally superior tothe other methods.

The strong interfacial interactions betweenthe polymer and organophilic layered silicates,availability of large surface area for such inter-action due to high aspect ratios, and good dis-persion achieved with organomodifiers result insignificant improvement in the technical perfor-mance of nanoclay composites. For example, me-chanical properties such as tensile strength andmodulus of nanoclay composites improve signifi-cantly with relatively low clay loading of less than5% by weight (Sinha Ray and Bousmina 2005).Reinforcement of polymers by nanoclays also in-creases heat distortion temperature, which is thetemperature at which a polymer sample deformsunder a specified load. The gas barrier proper-ties of nanocomposites are better than those ofpristine polymers, first, because nanoclays cre-ate a maze of tortuous paths that retard the flowof gas molecules through the polymer resin, andsecond, as Gusev and Lusti (2001) suggest, be-cause local molecular level transformation in thepolymer matrix in the presence of silicate gal-leries and organic modifiers also reduces per-meability. Thermal stability of polymeric ma-terials is usually studied by thermogravimetricanalysis, where weight loss due to formation ofvolatile products after degradation at high tem-perature is monitored. Dispersion of nanoclaysimproves the thermal stability of polymers, asthe silicate layers act as barriers to the flow ofthese volatile gaseous by-products and associatedheat.

Although the effect of nanoclays on the aboveperformance measures is positive, the directionof the effect on biodegradability of biopolymersis not unequivocal because the mode of attackby compost microorganisms varies depending on

nanocomposite and organomodifier characteris-tics and compost conditions. Quaternary alky-lammonium salts, the most commonly used or-ganic modifiers with nanoclays, are consideredbiodegradable under appropriate waste treatmentconditions (Orica 2007) and hence are not likelyto adversely affect biodegradability. Neverthe-less, some studies report that biodegradation isretarded because of higher barrier properties ofnanoclay composites (e.g., Maiti et al. 2003),whereas some studies find no differences in 60-day biodegradation between pristine biopolymersand their nanoclay composites (e.g., Sinha Ray,Yamada, Okamoto, Fujimoto, et al. 2003), andsome even show higher biodegradation rates fornanocomposites (e.g., Sinha Ray and Okamoto2003).

A number of experimental studies have doc-umented the significant improvements in theproperties of biopolymer–nanoclay compositescompared to pristine biopolymers (see Okamoto2005; Pandey et al. 2005; and Sinha Ray andBousmina 2005 for detailed technical reviews).These improvements include higher strength, in-creased storage moduli, lower heat distortion,lower gas permeability and flammability, and, of-ten, greater biodegradability. Nevertheless, theobserved degree of these improvements is acomplex function depending on the polymer,nanoclay, clay loading, organomodifier, compat-ibilizers, composite processing method, processoperating parameters, degree and nature of claydispersion, morphology, and testing conditions.Also, most studies report improvements over arange of these parameters, and these relationsare not generally linear. For example, mechanicalproperties such as tensile strength increase withthe increase in clay loading initially and begin todrop after a critical loading level. Similarly, thepercentage improvements in storage modulus de-pend on the temperature range tested. As a result,it is hard to summarize the results of various stud-ies in a comparatively consistent manner withoutspecifying all the technical details. In table 2, weselectively report results to indicate the rangeof performance improvements achieved. Nev-ertheless, the requirements of specific applica-tions determine which properties of the com-posites are relevant and the optimal processingparameters for obtaining these properties. For



Tabl

e2

Impr

ovem

ents

inpr

oper

ties

ofna

noco

mpo

sites

com

pare

dto

prist

ine

biob

ased

poly

mer

s(s

umm

ary

ofre

sults

from

sele

cted

stud

ies)

Mec

hani

calp

rope

rtie

sH

eatd

isto

rtio

n(%

chan

gefr

omte

mpe

ratu

re(H

DT

)T

herm

alSt

udy

Poly

mer

Nan

ocla

ypr

isti

nepo

lym

er)

chan

ge%

stab

ility

Perm

eabi

lity

Sinh

aR

ayan

dO

kam

oto

2003

PLA

C18

-MM

TFl

exur

alm

odul

us(+

17%

)H

DT

(+23

%)

Oxy

gen

gasp

erm

eabi

lity

(−14

%)

Flex

ural

stre

ngth

(+54

%)

Dis

tort

ion

atbr

eak

(+68

%)

Cha

nget

al.2

003

PLA

Clo

isit

e25

A-O

MM

TU

ltim

ate

stre

ngth

(+68

%)

Oxy

gen

gasp

erm

eabi

lity

(−56

%)

Ten

sile

mod

ulus

(+43

%)

Elon

gati

onat

brea

k(+

41%

)Si

nha

Ray

,Y

amad

a,O

kam

oto,

Oga

mi,

and

Ued

a20

03

PLA

OM

SFM

HD

T(+

51%

)

Cho

ieta

l.20

03PH

B-H

VO

MM

T(C

lois

ite

30)

You

ng’s

mod

ulus

(+15

%to

+65%

)3%

wei

ghtl

oss

tem

pera

ture

(+4%

)Pa

rket

al.2

002

TPS

OM

MT

(Clo

isit

e)T

ensi

lest

reng

th(+

28%

)W

ater

vapo

rper

mea

bilit

y(−

50%

)El

onga

tion

atbr

eak

(+21

%)

Not

e:PL

A=

poly

lact

ide

poly

mer

s;PH

B-H

V=

poly

hydr

oxyb

utyr

ate

co-h

ydro

xyva

lera

te;

TPS

=th

erm

opla

stic

star

ch;

MM

T=

mon

tmor

illon

ite;

OM

MT

=or

gani

cally

mod

ified

mon

tmor

illon

ite;

OM

SFM

=or

gani

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mod

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synt

heti

cflu

orin

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ica.



example, strength to weight ratios are likely to beimportant in automotive components, whereaspermeability is likely to be critical in packagingapplications.

From the results presented in table 2,it can be inferred that biopolymer–nanoclaycomposites under appropriate conditions haveimproved technical performance as comparedwith pristine biopolymers, making them morecompetitive with petroleum-based polymers andconventional composites.

Production Processfor Nanoclays

Given the qualitative judgment made in theprevious two sections that substitution of biopoly-mers for petroleum-based polymers can improveenvironmental performance and that use of nan-oclay fillers can improve the technical perfor-mance of biopolymers, the next logical ques-tion is, how do nanoclays compare with variousbiopolymers and other reinforcing materials, withrespect to environmental performance? We ana-lyze this question using a life cycle approach.

We model the organically modified nanoclayproduction process, which consists of the mainsteps shown in figure 1, namely clay mining,organomodifier production, and clay processingand modification. We estimate life cycle energy

Clay mining Clay purificationand modification

Ammonia production

Quaternary Ammonium Salt production

OMMT 1kg

Isobutylene production

Natural Gas 0.02 kg

Crude clay 1.483 kg

NH

Ammonium Salt0.35 kg

3

0.0795kg

Isobutylene 0.27 kg

Figure 1 Organically modified montmorillonite (OMMT) clay production process.

use and emissions from clay production and thencompare with available estimates of life cycle en-ergy use and emissions for biopolymers and otherreinforcing fibers. We use organically OMMTclay as a representative example of nanoclays. Be-cause quaternary alkylammonium salts are emerg-ing as the most commonly used organic modi-fier, we assume their use for organic modifica-tion. We use 1 kg of OMMT as the functionalunit.3 As melt-intercalation is commonly used inpreparation of glass fiber or natural fiber compos-ites, we assume that energy use and emissions innanocomposite preparation are similar to thosein melt-intercalation of other reinforcing fibersand limit our life cycle modeling to nanoclayproduction.

Information on the production processes,fuel, and other input requirements for produc-ing nanoclays is mostly proprietary and notgenerally available. We draw on estimates offuel and input requirements for production ofOMMT and their indirect inputs developedby Franklin Associates from various industrysources. We augment these with life cycle en-ergy use and emission estimates from Ecobi-lan’s DEAMTM LCA database, as detailed below(Ecobilan 2006). Figure 1 summarizes the mate-rial requirements at various intermediate produc-tion stages required for final production of 1 kgOMMT.



Clay Mining

MMT clay is commonly found in bentonitedeposits worldwide. Large deposits of bentonite,which contain greater than 50% of MMT, canbe found in the United States, western Europe,the Middle East, and China. During bentonitemining, the overburden is removed, the clay isremoved with shovels or draglines, and the clayis formed into disks and allowed to dry in the sun(Xanthos 2005). The estimated fuel inputs formining 1 megaton (Mt) of clay are 13.6 kilowatt-hours (kWh) electricity, 16.2 cubic meters of nat-ural gas, 6.17 kg of coal, and 0.025 liters of residualoil (Franklin Associates 2006).4

Clay Processing

Clay processing steps include separation, pu-rification, delamination, reaction with organicmodifiers, homogenization, dewatering, and sizereduction. The separation step uses slurries of wa-ter and clay to separate the clay from nonclaymaterials, such as quartz, gravel, and limestone.Counter ion techniques are used for delamina-tion. Organic modifier is then added. We as-sume that 35% by weight of quaternary alkylam-monium salt is used for nanoclay modification,though the actual weight fraction may vary. Forexample, the weight fractions of quaternary am-monium salts in various Closite R© OMMT claysfrom Southern Clay Products range between 30%and 43% (Southern Clay Products 2007). Clayslurries are dewatered with filter processes or ro-tary vacuum drum filters and then dried. The es-timated direct energy use in the processing of1 Mt of organically modified clay is 242 kWh ofelectricity, 111 m3 of natural gas, and 0.136 L ofdistillate fuel oil (Franklin Associates 2006).

Ammonium Salt Production

A number of processing routes are used forproduction of quaternary ammonium salts, de-pending on the desired halide and the organicgroup (tertiary amines). We assume that quater-nary alkylammonium salt is produced by the alky-lation of ammonia with isobutylene. Direct mate-rial inputs for producing 1 Mt of ammonium saltare estimated at 227 kg of ammonia and 773 kg

of isobutylene, and estimated direct energy inputsare 329 kWh of electricity and 30.9 m3 of naturalgas (Franklin Associates 2006).

Ammonia Production

Ammonia is assumed to be produced by streamreforming of natural gas. The estimated inputs forproduction of 1 Mt of ammonia include 133 kWhof electricity and 253 kg of natural gas (FranklinAssociates 2006).

Isobutylene Production

We assume the life cycle energy use andemissions from isobutylene production are thesame those from butenes production, and we useEcobilan-DEAMTM estimates for butenes (Eco-bilan 2006). The DEAM estimates are basedon data from 19 European crackers. We do nothave comparable data from U.S. refineries; how-ever, we believe that production technologiesof standard petrochemical intermediates, such asisobutylene, are similar across developed coun-tries. Some differences may, however, arise dueto regional differences in fuel mix. We believethat effects of these differences on the overallconclusions are likely to be minor.

Fuel Production and Combustion

We assume that natural gas, coal, and distil-late fuel oil used as fuels in the above processes arecombusted in industrial boilers and use the emis-sion factors from the DEAMTM database, whichare based on the U.S. Environmental ProtectionAgency’s AP42, 1998 emission factors. We usethe DEAM estimates for life cycle energy use andemission estimates for electricity, natural gas, bi-tuminous coal, and distillate fuel oil productionin the United States. Electricity use is assumed tobe from the U.S. average grid generation mix.

Transportation

The estimated direct and indirect transporta-tion involved in production of 1 Mt of OMMTare 323 Mt-km in diesel trucks, 1,077 Mt-kmin diesel railways, 28 Mt-km using barges, and5,299 Mt-km in ocean freighters.5 We use energy



and emission estimates for vehicle use as wellas fuel cycles for these transport modes for theUnited States from the DEAMTM database.

Environmental Burdens FromNanoclay Production

The results from the cradle-to-factory-gateLCA of OMMT and contributions from variousinputs are summarized in table 3. The first rowshows the quantity of various inputs required toproduce 1 kg of OMMT. For example, to produce1 kg of OMMT, we need to mine 1.483 kg ofcrude clay and produce 0.270 kg of isobutylene.The remaining rows show the estimated energyuse and emissions from each of these life cyclestages. These estimates include both direct pro-cess energy use and emissions and fuel cycle en-ergy use and emissions for the energy sources usedin each stage. The last column reports totals for1 kg OMMT.

The estimated cumulative energy use is40.1 MJ/kg OMMT, and the major contributorsto energy use are isobutylene production (43%)and clay processing and modification (35%).6 Ifwe aggregate energy use from ammonia produc-tion, isobutylene production, and ammonium saltproduction, it can be seen that the organic modi-fier, quaternary alkylammonium salt in this case,accounts for 56.4% of energy use, even thoughit amounts to 35% of the mass of OMMT. Simi-larly, organic modifier–related stages account for31% of global warming effects, 51% of sulfur diox-ide emissions, and 43.6% of nitrogen oxide emis-sions. The organic modifier’s share of energy useis higher than its share of GHG emissions mainlybecause the energy share includes feedstock en-ergy of isobutylene, which constitutes about 87%of its total primary energy. It is not surprisingthat most of the water emissions occur duringclay processing and modification.

These results suggest that a significant por-tion of environmental impacts from nanoclaysare likely to be from the organic modifier usedrather than the clay itself; hence, research thateither reduces the quantity of modifier used orexplores substitution with more environmentallyfriendly modifiers is worthwhile. For example, re-duction in quaternary ammonium salt mass frac-tion in OMMT from 35% to 30% will reduce

the total energy by 7.7%, to 37 MJ/kg OMMT,and total GHG emissions by 3.8%, to 1,465 gCO2-equivalent per kilogram (CO2-eq./kg).

Comparison With Biopolymersand Fibers

The question of interest is how the life cy-cle environmental performance of nanoclay–biopolymer composites compares with the lifecycle environmental performance of pristinebiopolymers in specific applications. One canmake qualitative judgments about the relativeperformance in many cases without detailedLCAs, simply by comparing the environmentalburdens per kilogram of nanoclay production es-timated above with environmental burdens perkilogram of different biopolymers, because nan-oclay displaces some fraction of the polymer (typ-ically less than 5% by weight) in the composite. Ifenvironmental burdens per kilogram of nanoclayare lower than the environmental burdens perkilogram of the polymer, such displacement willalways result in lower environmental burdens forthe nanocomposite. The improvement in envi-ronmental performance will further be enhancedby the likely lower weight of the functional unit,because of the improvements in technical perfor-mance; for example, improvements in gas barrierproperties of nanocomposite can reduce the re-quired film thickness in packaging applicationsand, hence, the mass of the functional unit. Sim-ilarly, improvements in mechanical strength canreduce the mass of the functional unit in automo-tive applications. In such cases, detailed LCAsare required mainly for quantifying the extent ofenvironmental improvements. In cases where en-vironmental burden per kilogram of nanoclay ishigher than environmental burden per kilogramof biopolymer, however, the addition of nanoclayworsens the environmental performance of thecomposite on a per kilogram basis, but the im-proved technical performance of the compositemay lower the mass of the functional unit andthe associated environmental burdens. The neteffect is hence uncertain, and detailed product-specific LCAs are required. Similarly, in caseswhere the weight of the functional unit increaseswith nanocomposites, detailed LCAs are neces-sary. We assume that the environmental burdens



Tabl

e3

Life

cycl

een

ergy

use

and

emiss

ions

per

kilo

gram

ofor

gani

cally

mod

ified

mon

tmor

illoni

te(O

MM

T)

clay

Inpu

ts/

Cla

yA

mm

onia

Qua

tern

ary-

amm

oniu

mC

lay

proc

essi

ngIs

o-bu

tyle

neT

rans

port

atio

nEm

issi

ons

min

ing

prod

ucti

onsa

ltpr

oduc

tion

and

mod

ifica

tion

prod

ucti

onM

t-km

Tot

al

Prod

ucti

onkg

perk

gO

MM

Tcl

ay1.

483

0.08

00.

350

1.00

00.

270

6.72

7

Tot

alen

ergy

MJ

2.17

00.

896

4.50

214

.091

17.2

041.

216

40.0

79A

irem

issi

ons

CO

2g

118.

8846

.61

258.

6576

4.01

135.

0084

.32

1,40

7.47

1M

etha

neg

0.51

00.

217

0.87

93.

118

0.00

00.

050

4.77

4N

2Og

0.00

10.

001

0.00

30.

008

0.00

00.

005

0.01

8G

WP

gC

O2

eq13

1.02

251

.757

279.

696

838.

219

135.

0086

.94

1,52

2.62

8C

Og

0.19

10.

170

0.70

51.

729

0.10

80.

197

3.10

0SO

xg

0.25

20.

100

1.09

02.

322

0.81

00.

920

5.49

5N

Ox

g0.

271

0.09

50.

543

1.57

31.

620

1.07

85.

180

PMg

0.02

90.

013

0.11

80.

700

0.21

60.

063

1.13

9W

ater

emis

sion

sB

OD

g0.

000

0.00

40.

000

0.02

70.

011

0.00

80.

049

CO

Dg

0.00

00.

000

0.00

10.

054

0.05

40.

066

0.17

5N

itra

teg

0.00

00.

018

0.00

00.

000

0.00

30.

000

0.02

2

Not

e:D

ata

incl

ude

both

dire

cten

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and

emis

sion

san

dlif

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cle

ener

gyan

dem

issi

ons

for

the

fuel

sus

edin

each

stag

e.M

t-km

=m

egat

on-k

ilom

eter

s;C

O2

=ca

rbon

diox

ide;

N2O

=ni

trou

sox

ide;

GW

P=

glob

alw

arm

ing

pote

ntia

l;C

O=

carb

onm

onox

ide;

SOx

=su

lfur

oxid

es;N

Ox

=ni

trog

enox

ides

;PM

=pa

rtic

ulat

em

atte

r;B

OD

=bi

olog

ical

oxyg

ende

man

d;C

OD

=ch

emic

alox

ygen

dem

and.



from the end-of-life stage are the same for bothpristine polymers and their nanocomposites. Be-cause nanoclays typically form less than 5% byweight of the composite, the assumption is un-likely to substantially affect our conclusions. Welimit our analysis only to making these quali-tative but useful conclusions and do not con-duct product-specific LCAs, mainly due to lackof product-specific data.

In order to make such qualitative judgments,we need to compare the life cycle burdens fromnanoclay production with the life cycle burdensof pristine biopolymers. Unfortunately, most ofthe available LCAs of biopolymers only reportenergy use and GHG emissions. The estimatedlife cycle nonrenewable energy use and GHGemissions for PLA are 57 MJ/kg and 3.84 kg CO2-eq./kg, respectively (Vink et al. 2003; Dornburget al. 2004). If we compare these with the energyuse and GHG emissions from OMMT produc-tion of 40.1 MJ/kg and 1.52 kg CO2-eq./kg, re-spectively, reported in the last column of table 3,it is evident that PLA–OMMT composites willhave energy and GHG performance superior topristine PLA both on a per kilogram basis and,potentially, on a per functional unit basis dueto better technical properties of PLA–OMMTcomposites.

The estimated nonrenewable energy use forPHA ranges between 66.1 MJ/kg (Heyde 1998)and 81 MJ/kg (Gerngross and Slater 2000).Hence, PHA–OMMT composites will havelower energy use per kilogram compared to pris-tine PHA. Similarly, Heyde (1998) estimates thatenergy use per kilogram of PHB ranges from66.1 MJ/kg in the best case to 573 MJ/kg inthe worst case, which again suggests that PHB–OMMT composites will result in lower overallenergy use. Akiyama and colleagues (2003), intheir best case scenario, estimate life cycle energyuse of 59 MJ/kg and GHG emissions of 0.46 kg/kgof P(3HB) produced by bacterial fermentation ofsoybean oil. This suggests that P(3HB)–OMMTnanocomposites will have lower energy use com-pared to pristine P(3HB) but that the relativeGHG performance may be worse or better de-pending on the choice of the functional unit.

The estimated life-cycle nonrenewable energyuse and GHG emissions for TPS are 25.4 MJ/kgand 1.14 kg CO2-eq./kg, respectively (Dinkel

et al. 1996; Dornburg et al. 2004). Compar-ing these with the energy use and GHG emis-sions from OMMT production, we can infer thatOMMT–TPS composites will have higher en-ergy use and GHG emissions per kilogram com-pared to virgin TPS. Overall relative environ-mental performance of pristine TPS compared toTPS–OMMT composite, however, depends onthe change in the mass of the functional unitachieved because of improvements in properties.Hence, the net effect will be application-specific,and product-specific LCAs will be necessary forenvironmental evaluation of TPS nanoclays.

Glass fiber is the most commonly used rein-forcing filler in composites. Natural fibers fromchina reed, hemp, kenaf, and jute are becom-ing popular as reinforcements in composites,however—especially in automotive componentsdue to their lower density, cost, and greenhouseimpacts. Hence, we also compare our estimates oflife cycle environmental impacts from nanoclayproduction with those from glass fiber produc-tion and china-reed fiber production in table 4.We choose china-reed fiber as representative ofnatural fibers used in composites. The glass fiberand china-reed fiber life cycle energy and emis-sions estimates are from Joshi and colleagues(2004) and are based on the original estimates byCorbiere-Nicollier and colleagues (2001).

As can be seen from table 4, the energy useand CO2 emissions for nanoclays are lower thanthose for glass fibers but significantly higher thanfor natural fibers. Water pollution associated withnanoclays is higher than that for glass fibers, how-ever. The only aspect in which natural fibers ap-pear to perform worse than nanoclays and glassfibers is in phosphate and nitrate emissions towater, which are mainly associated with farm-ing operations. Compared to glass fiber, nanoclayproduction results in higher carbon monoxideand nitrogen oxide emissions but lower sulfur ox-ide emissions.

Table 4 presents indicative comparisons, but amajor caveat is in order. Using a kilogram of filleras a functional unit is inappropriate in evaluat-ing relative performance of fillers in composites.The weight or volume percentage of reinforcingfiller used to achieve equivalent performance ofthe composite product can vary significantly de-pending on the properties of the polymer, filler,



Table 4 Life cycle environmental impacts fromproduction of glass fiber, china-reed fiber, andorganically modified montmorillonite (OMMT) clay

Environmental Glass China-reedimpact fibera fibera OMMT

Energy use (MJ/kg) 48.33 3.64 40.07Carbon dioxide

emissions (kg/kg)2.04 0.66 1.41

CO emissions(g/kg)

0.80 0.44 3.10

SOx emissions(g/kg)

8.79 1.23 5.50

NOx emissions(g/kg)

2.93 1.07 5.18

Particulate matter(g/kg)

1.04 0.24 1.14

BOD to water(mg/kg)

1.75 0.36 49.2

COD to water(mg/kg)

18.81 2.27 174.9

Nitrates to water(mg/kg)

14.00 24481 21.5

Phosphates towater (mg/kg)

43.06 233.6 0.01

∗Source: Corbiere-Nicollier et al. 2001; back-up tables ob-tained from the author.Note: CO = carbon monoxide; SOx = sulfur oxides;NOx = nitrogen oxides; BOD = biological oxygen de-mand; COD = chemical oxygen demand.

and compatibilizers used as well as the desiredfunctional property. For example, to achieveequivalent strength, the volume fraction of natu-ral fibers used is likely to be much higher than forglass fibers, mainly because of better mechanicaland adhesion properties of glass fibers. Because ofvery high aspect ratios and good dispersion, nan-oclays generally provide equivalent mechanicalperformance at much lower clay loading—lessthan 5% by weight compared to typical load-ings of 30% to 50% by volume of natural fibers.Higher loading with natural fibers may be de-sirable when the goal is weight reduction, be-cause of lower density of natural fibers comparedto most pristine polymers. Hence, comparativeLCAs of nanocomposites versus other fiber com-posites will need to be carried out on a case-by-case basis. The data presented in table 4 can helpin these assessments, once the appropriate rein-forcement weight fractions for equivalent func-

tional performance and application-specific func-tional units are determined.

Discussion and Conclusions

Several limitations of the above analyses haveto be considered before we can make generalconclusions. Most of these limitations arise fromchallenges in obtaining comprehensive, suffi-cient, high-quality data for carrying out rigorousLCAs, especially of new, emerging technologies.First, the above comparative analyses are basedon point estimates of production processes aswell as environmental burdens. We do not modelany of the obvious uncertainties due to process,model, and data variability. Second, our modelof the nanoclay production process is based oninternal, private industry estimates of input andfuel requirements for a specific process route andinputs. These data are not from public-domain,peer-reviewed literature and, as a result, sufferfrom lack of transparency and independent veri-fiability. Further, these estimates are not industryaverages and cannot claim to be representative ofgeneral practice, although some data, such as lifecycle data for energy inputs, ammonia, isobuty-lene, and so forth, are from a commercially avail-able database. Third, our comparative environ-mental analysis is mostly limited to energy useand GHG emissions, and other conventional pol-lutant emissions where data are available. We donot consider any of the special environmentalproblems associated with nanomaterials becauseof their extremely small size, high surface areas,and added surface functionalities, which are sus-pected to result in easy transport across biologicalmembranes, higher reactivity, and unintended ef-fects on nontarget materials/organisms. We feelthat these special problems are unlikely to besignificant in the case of nanoclay composites be-cause these clays are natural, benign materialsthat are found commonly and used extensivelyand that happen to exhibit nanoproperties underspecific processing conditions. Also, nanoclaysare mostly incorporated into materials used innondissipative applications.

Fourth, our analysis does not cover all the “cra-dle to grave” stages in the life cycle of nanocom-posites and is more of a “cradle to factory gate”analysis. Hence, it is not a complete, formal



LCA. We use the life cycle approach only asa framework to help decision making and toguide future research and data collection efforts.Including the use phase may further im-prove the relative environmental performance ofnanocomposites, especially in automotive com-ponent applications, because the reduced weightof nanocomposites can result in substantial re-ductions in energy use and emissions in the usephase. For example, Lloyd and Lave (2003) es-timate component weight reductions of 38% to67% when PP-nanocomposites are substituted forsteel in automobiles, which result in reductions ofuse-related CO2 emissions of 0.23 to 0.41 tonnesper vehicle annually. For other applications, suchas packaging, the lower weight per functional unitof nanocomposites will reduce product transport–related emissions and thereby improve the rel-ative environmental performance of nanocom-posites compared to pristine biopolymers. We as-sume that emissions from the end-of-life disposalpractices of biopolymers and their nanoclay com-posites are substantially similar. This assumptionappears reasonable because nanoclays constituteless than 5% and organomodifiers less than 2%by weight of the composites, and the incrementalemissions and energy recovery from these frac-tions are likely to be minor. Last, we limit thescope of analysis to biodegradable, biopolymer-nanocomposites and do not consider the poten-tial performance of petroleum-based polymer–nanoclay composites.

Subject to the above limitations, we canmake the following useful qualitative conclu-sions based on the results. Substitution of con-ventional petroleum polymers with biopolymerscan potentially lower fossil fuel consumptionand GHG emissions. Nanoclay composites canimprove the technical performance of biopoly-mers. A significant portion of the environmen-tal impacts from nanoclays is likely to be fromthe organic modifiers used, and, hence, futureLCAs should not disregard organomodifiers intheir modeling. Also, research aimed at reduc-ing the amount of organomodifer used or de-veloping more environmentally friendly alterna-tives appears worthwhile. Nanoclay compositeswill improve energy performance on both a perkilogram basis and a per functional unit basiscompared to pristine biopolymers PLA, PHA,

and PHB. OMMT–PHA composites also havelower GHG emissions than pure PHA. We candraw these conclusions without carrying out de-tailed product-specific LCAs, except in caseswhere the mass of the nanocomposite functionalunit is higher than comparable pristine polymercomponent. Detailed product-specific LCAs are,however, required for quantifying the improve-ments. The relative energy and GHG emissionperformance of TPS nanoclay composites is am-biguous and depends on improvements in theproperties with addition of nanoclay and corre-sponding changes in the functional unit. Hence,TPS–OMMT nanocomposites need to be eval-uated case by case, and detailed product LCAsare recommended. Overall, nanoclay technologycan potentially contribute toward improving theenvironmental performance of biopolymers andmoving them toward commercial success.

In comparing nanoclay–biopolymer compos-ites with conventional fiber–biopolymer compos-ites, our results indicate that on a per kilogrambasis, the environmental burdens from nanoclaysare worse than those from natural fibers on mostdimensions except phosphate and nitrate emis-sions, but nanoclays are better than glass fibersfrom an energy use and GHG emissions per-spective. Nevertheless, because such comparisonsbased on environmental burdens per kilogram ofreinforcement are inappropriate, we recommenddetailed product-specific LCAs. The data devel-oped in the study will be useful in such analyses.

Finally, the number of assumptions, approx-imations, and limitations alluded to throughoutthe study point out the need to generate com-prehensive, transparent, representative, and pub-licly available data for various process and mate-rial developments in nanotechnology that satisfythe data quality requirements outlined under ISOstandards for LCA. Investments in developingsuch LCA data sets are highly recommended.

Notes

1. One tonne (t) = 103 kilograms (kg, SI) ≈ 1.102short tons.

2. One gigagram (Gg) = 106 kilograms (kg, SI) = 103

metric tons.3. One kilogram (kg, SI) ≈ 2.204 pounds (lb).



4. One megaton (Mt) = one teragram (Tg, SI) = 106

tonnes (t) ≈ 1.102 × 106 short tons. Onekilowatt-hour (kWh) ≈ 3.6 × 106 joules (J,SI) ≈ 3.412 × 103 British Thermal Units(BTU). One cubic meter (m3, SI) = 103 liters(L) ≈ 264.2 gallons (gal). One liter (L) = 0.001cubic meters (m3, SI) ≈ 0.264 gallons (gal).

5. One kilometer (km, SI) ≈ 0.621 miles (mi).6. One megajoule (MJ) = 106 joules (J, SI) ≈ 239

kilocalories (kcal) ≈ 948 British Thermal Units(BTU).

Acknowledgments

The author would like to thank USEPA(STAR Grant #RD 830904) and the MichiganAgricultural Experiment Station for the finan-cial support and D. Ortega-Pacheco for researchassistance.

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About the Author

Satish Joshi is an associate professor in theDepartment of Agricultural, Food, & ResourceEconomics at Michigan State University, EastLansing, Michigan.


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