PLA-NatureWork.pdf

Polymer Degradation and Stability 80 (2003) 403–419

www.elsevier.com/locate/polydegstab

Applications of life cycle assessment to NatureWorks TM

polylactide (PLA) production

Erwin T.H. Vink a, * ,Karl R. Ra ´ bago b ,David A. Glassner b ,Patrick R. Gruber b

a CargillDowB.V.,Gooimeer6-10,1411DDNaarden,TheNetherlands

b CargillDowLLC,12700WhitewaterDrive,MS-130,Minnetonka,Minnesota55343,USA

Received 18 October 2002; received in revised form 6 November 2002; accepted 11 November 2002

Abstract

NatureWorks TM polylactide (PLA) 1 is a versatile polymer produced by Cargill Dow LLC. Cargill Dow is building a global

platform of sustainable polymers and chemicals entirely made from renewable resources. Cargill Dow’s business philosophy is

explained including the role of life cycle assessment (LCA),a tool used for measuring environmental sustainability and identifying

environmental performance-improvement objectives. The paper gives an overview of applications of LCA to PLA production and

provides insight into how they are utilized. The ﬁrst application reviews the contributions to the gross fossil energy requirement for

PLA (54 MJ/kg). In the second one PLA is compared with petrochemical-based polymers using fossil energy use,global warming

and water use as the three impact indicators. The last application gives more details about the potential reductions in energy use

and greenhouse gasses. Cargill Dow’s 5–8 year objective is to decrease the fossil energy use from 54 MJ/kg PLA down to about 7

MJ/kg PLA. The objective for greenhouse gasses is a reduction from +1.8 down to 1.7 kg CO 2 equivalents/kg PLA.

# 2003 Cargill Dow B.V. Published by Elsevier Science Ltd.

Keywords: Cargill Dow; Sustainability; Life cycle assessment (LCA); Eco-proﬁle; NatureWorks; Polylactide (PLA); Polylactic acid

1. Introduction

as the best candidate. In November 1997 Cargill Dow

LLC was founded as a 50/50 joint venture between

Cargill Inc and The Dow Chemical Company to pursue

the commercialization of PLA polymers under the trade

name NatureWorks TM .

A stand-alone company today,Cargill Dow is building

a global platform of sustainable and versatile polymers

and chemicals entirely made from renewable resources.

To achieve its objectives,Cargill Dow is using and fur-

ther reﬁning an optimal combination of agricultural

processes and biological and chemical technologies.

Cargill Dow’s philosophy is that its business system

should be sustainable from an economic,environmental

and social perspective,the so called ‘‘triple bottom line’’

of sustainability [1] . Cargill Dow uses life cycle assess-

ment (LCA) as a tool for measuring environmental

sustainability

In 1988 a project to develop polylactide (PLA) was

launched by Cargill Inc. The project goal was to estab-

lish new product and value opportunities for starch

processed by the company. Dr. Pat Gruber,now vice

president and chief technology oFcer for Cargill Dow,

was the initiator and project champion. Along with a

small group of scientists,Dr. Gruber developed key

processes for conversion of lactic acid into lactide,and

processes and technologies for puriﬁcation and poly-

merization/devolatilization of lactide. In 1994 the com-

pany built a 5000 metric tons per year PLA facility in

Savage,Minnesota to prove and further develop lactic

acid to PLA technology on a semi-works scale and to

catalyze the development of a commercial market for

PLA. In early 1995 Cargill realized it needed a partner

with a strong presence in the polymer market. Cargill

assembled a list of partner attributes and Dow emerged

and

identifying

environmental

perfor-

mance improvement objectives.

As of January 2002,Cargill Dow employed more than

250 people worldwide. Cargill Dow has its headquarters

in Minnetonka,Minnesota,USA with additional oFces

in Naarden,The Netherlands and Tokyo,Japan. Cargill

Dow has now expanded its capacity by building the

world’s only commercial production facility for PLA in

* Corresponding

author.

Tel.:

+31-114-315944;

fax:

+31-114-

315938.

E-mailaddress: erwin_vink@cargilldow.com (E.T.H. Vink).

NatureWorks TM : Trademark Cargill Dow LLC.

0141-3910/03/$ - see front matter # 2003 Cargill Dow B.V. Published by Elsevier Science Ltd.

doi:10.1016/S0141-3910(02)00372-5

404

E.T.H.Vinketal./PolymerDegradationandStability80(2003)403–419

toes can be used as a starch/sugar feedstock. Cargill

Dow is also working to develop new conversion tech-

nologies to facilitate the use of lignocellulosic biomass

feedstocks,such as corn stover (the residue left in the

ﬁeld),grasses,wheat and rice straws,and bagasse (the

residue of sugarcase production).

There are two major routes to produce polylactic acid

from the lactic acid monomer: direct condensation

polymerization of lactic acid and ring-opening poly-

merization through the lactide intermediate. The ﬁrst

route involves the removal of water by condensation

and the use of solvent under high vacuum and tem-

perature. With this route only low- to intermediate-

molecular-weight polymers can be produced,mainly

because of the presence of water and impurities. Other

disadvantages of this route are the relatively large reac-

tor required,and the need for evaporation,recovery of

the solvent and increased color and racemization. Mit-

sui Chemicals developed a new process based on direct

polycondensation of l -lactic acid to enable the produc-

tion of high molecular weight PLA without the use of

an organic solvent [3] .

Cargill Dow uses the second route: ring-opening poly-

merization through the lactide intermediate [4] . In the

ﬁrst step of the process water is removed under mild

conditions (and without the use of a solvent) to produce

a low moleculer weight prepolymer. This prepolymer is

then catalytically depolymerised to form a cyclic inter-

mediate dimer,referred to as lactide which is then pur-

iﬁed to polymer grade using distillation [5] . The puriﬁed

lactide is polymerized in a solvent free ring-opening

polymerization and processed into polylactide pellets

[6] . By controlling the purity of the lactide it is possible

to produce a wide range of molecular weights.

Because there are four unique groups attached to the

central carbon atom,lactic acid is a chiral molecule.

Chiral molecules exists as ‘mirror images’ or stereo-

isomers. The optically active lactic acid has an ‘‘ l ’’ and

‘‘ d ’’ stereoisomer. ‘‘ l ’’ and ‘‘ d ’’ are also referred to as R

and S. d =R=right handed and l =S=left handed.

Chemically synthesized lactic acid gives the racemic

mixture (50% d and 50% l ). Fermentation-derived lac-

tic acid typically consists of 99.5% of the l -isomer and

0.5% of the d -isomer. Production of the cyclic lactide

dimer results in three potential forms: the d , d -lactide

(called d -lactide), l , l -lactide (called l -Lactide) and l , d

or d , l lactide called meso lactide. Meso lactide has dif-

ferent properties from d and l lactide. The d and l lac-

tide are optically active,but the meso is not. Before

polymerization the lactide stream is split into a low d

lactide stream and a high d /meso lactide stream. Ring-

opening polymerization of the optically active types of

lactide can yield a ‘family’ of polymers characterized by

the molecular weight distribution and by the amount and

the sequence of d -lactide in the polymer backbone. Poly-

mers with high l -lactide levels can be used to produce

Nomenclature

B/WP Biomass/wind power

CWM Corn wet mill

GER Gross energy requirement

GFEU Gross fossil energy use

Lactic acid

LCA

Life cycle assessment

LCI

Life cycle inventory

LCIA

Life cycle impact assessment

Mega joules

PFD

Process ﬂow diagram

PLA

Polylactide

WWT

Waste water treatment

Blair,Nebraska,USA. At full production,the Blair

facility,which began operations in late 2001,can pro-

duce 140,000 metric tons of PLA per year [2] .

2. PLA production technology

Cargill Dow’s polylactide (PLA) is a versatile new

compostable polymer that is made from 100% renew-

able resources like corn,sugar beets or rice. Fig. 1 illus-

trates the various steps involved in the production of

PLA starting with corn growing and ending with the

production of PLA granules.

Today,the PLA life cycle starts with corn. All free

energy consumed by biological systems arises from solar

energy that is trapped by the process of photosynthesis.

The basic equation of photosynthesis is:

light

H 2 O þ CO 2 !

CH 2 O

Þ O 2

In this equation,(CH 2 O) represents carbohydrate,

primarily sucrose and starch. So,all the carbon,hydro-

gen and oxygen in the starch molecule as well as in the

ﬁnal polylactide molecule have their origin in water and

carbon dioxide. After harvesting,the corn is trans-

ported to a corn wet mill where the starch is separated

from the other components of the corn kernel (proteins,

fats,ﬁbers,ash and water) and converted via enzymatic

hydrolysis into dextrose. Cargill Dow ferments dextrose

into lactic acid at near neutral pH. Via acidulation and

a series of puriﬁcation steps the lactate salt fermentation

broth is then puriﬁed to yield lactic acid.

The ﬁrst generation of PLA will be produced from the

annually renewable resource corn,the cheapest,starch-

rich and most widely available raw material in the USA.

In other parts of the world,locally available crops such

as rice,sugar beets,sugarcane,wheat and sweet pota-

E.T.H.Vinketal./PolymerDegradationandStability80(2003)403–419

405

Fig. 1. PLA manufacturing overview.

crystalline polymers while the higher- d -lactide materials

are more amorphous.

4. Cargill Dow’s business philosophy and deﬁnition of

sustainability

In recognition of the opportunity and need for

sustainable,renewably-sourced plastics,Cargill Dow

has

3. NatureWorks TM PLA applications

adopted

ambitious

statement

business

Cargill Dow’s NatureWorks TM branded PLA is a

compostable polymer used in a wide range of packaging

(primarily for food),ﬁlm and ﬁber applications. Table 1

provides an overview of Cargill Dow’s current business

segments

philosophy:

‘‘CargillDowistheleaderinproducingplasticsfrom

renewableresources,and isdedicatedtomeeting the

world’s needs today without compromising the

earth’sabilitytomeettheneedsoftomorrow.’’

with

examples

commercially

available

applications [7,8] .

406

E.T.H.Vinketal./PolymerDegradationandStability80(2003)403–419

are needed [23] . The notion behind sustainability is that

with careful thought and innovative practice,economies

and societies can improve without degradation to nat-

ural environments. Ideally,sustainable development

means that activities that improve economic and social

welfare simultaneously improve environmental condi-

tions as well.

Cargill Dow deﬁnes sustainability based on a triple

bottom line approach in which economic sustainability,

environmental sustainability and social responsibility

are pursued and maximized simultaneously [10] .

Although implementation of this concept is challenging

in practice,explaining it is relatively simple. Economic

sustainability is about building and growing a viable

business that provides markets for agricultural pro-

ducts,new career opportunities for researchers and

staﬀ,and other economic beneﬁts to investors and

society. For a ‘‘start-up’’ company like Cargill Dow,

economic sustainability is measured against fairly tradi-

tional ﬁnancial and operations targets,including return

on investment and operating revenues netted against

expenses. From a societal perspective,economic sus-

tainability also involves the development of robust and

enduring markets for sustainable goods and services.

Social sustainability is reﬂected in social responsi-

bility,and involves concepts of equitable opportunity

for all participants in the value chain as well as strong

bias against business and operational practices that take

unfair advantage of particular segments of society.

From Cargill Dow’s perspective,social sustainability

implies that business success must not disadvantage,for

example,feedstock suppliers (farmers). More broadly,

the environmentally friendly production processes and

compostability and recyclability of PLA products helps

to ensure that production,use and ultimate disposal of

products do not impose disproportionate burdens on

any particular segment of society. For example,Cargill

Dow has eschewed the use of potential endocrine dis-

rupters in its products and refuses to allow PLA use in

tobacco products and packaging.

Environmental sustainability is about making pro-

ducts that serve useful market and societal functions

with less environmental impact than currently available

alternatives. Moreover,environmental sustainability

necessarily implies a commitment to continuous

improvement in environmental performance. The key

measurement tool for environmental sustainability is

life cycle assessment.

The ideal environmentally sustainable product pro-

vides equivalent function as products it replaces and is

available at competitive costs. It is made from renew-

able resources,can itself be constantly renewed without

degradation in quality or performance,and has a mini-

mum environmental impact. Such a product is made using

only substances known to be safe for both humans and the

environment. Ideally the life cycle of the sustainable

Table 1

Car gill Dow business segments

Business segment

Commercially available applications

Rigid thermoforms

— Clear,short shelf life trays & lids

— Opaque dairy containers

— Consumer displays & electronics packaging

— Disposable articles

— Cold drink cups

Biaxially-oriented

— Shrink wrap for consumer goods packaging

ﬁlms

— Twist wrap candy and ﬂower wrap

— Windows for envelopes,bags and cartons

Bottles

— Short shelf-life milk and oil packaging

Apparel

— Sport,active and underwear

— Fashion

Non-wovens

— Agricultural and geo textiles

— Hygiene products (diapers and feminine hygiene)

— Wipes

— Shoe liners

— Blends with natural ﬁbers–hemp,sisal and ﬂax

Household,industrial

and institutional

— Bedding,drapery,table cloths,

curtains,mattress ticking

fabrics

— Wall and cubicle fabrics,upholstery

Carpet

— Surfase yarns & ﬁbers

Fiberﬁll

— Pillows

— Comforters

— Mattresses

— Duvets

Foams

— Structural protective foams

Lactide

— Raw material for ethyl lactate production,

a high purity solvent

Stated another way,Cargill Dow seeks to be sustain-

able in its processes and activities,and to sell a product

that contributes to sustainability wherever it is used.

The concepts of sustainability and sustainable develop-

ment have become increasingly important in a world

where many fear vital natural resources and ecosystem

services are threatened or in decline. According to the

Living Planet Report 2002 of the World Wide Fund

current trends are moving humanity away from achiev-

ing the minimum requirements for sustainability,not

towards it [9] . According to the 2002 OECD report

‘Working Together Towards Sustainable Development’

there are still many pressing challenges and strength-

ened action to address them are needed now. These

challenges include the establishing of appropriate poli-

cies to combat the threat of climate change,to better

manage ﬁsheries and water resources,and to provide

greater protection of ecosystems and biodiversity. These

policies would result in a more marked decoupling of

environmental pressures from economic growth by

changing unsustainable consumption and production

practices. A better integration of the social,economic and

environmental dimensions of sustainable development

E.T.H.Vinketal./PolymerDegradationandStability80(2003)403–419

407

product is in balance with the surrounding ecosystem.

These attributes describe Cargill Dow’s environmental

goal for PLA.

Although LCA is an extremely valuable part of the

company’s strategy,Cargill Dow’s full range of environ-

mental sustainability eﬀorts extends beyond its commit-

ment to using LCA. The company has adopted product

development and design rules that seek to ensure that the

natural resource-base values of its products are not com-

promised. The company works with fabricators and pro-

cessors to ensure that additives,blends,treatments and

other compounds do not create a substantial risk to

human health or the environment,either in application,

use or disposal. Cargill Dow has adopted and employs

contractual provisions strengthening both up- and down-

stream inﬂuence and control of supply chain activities.

Other business practice activities include sustainability

reviews of business rules and the development of an

internal employee training program on sustainability.

And several key employees have explicit responsibility to

support the company’s mission of improving and inte-

grating every component of the triple bottom line of

environmental,economic and social sustainability.

Plastics and polymers have become an essential ele-

ment of modern life and can play a key role in global

progress toward sustainability. It is estimated that 150

million tons of polymers are produced from fossil fuels

today,and that production is increasing at a rate of

approximately 4–5% per year. This growth is fueled by

the many inherent advantages of plastics,including low

weight,high

maturity of the underlying manufacturing technologies.

Plastics extend storage life of perishables such as food

or medicine,and reduce environmental impacts asso-

ciated with transportation by reducing package or vehicle

weight. Polymer-based ﬁbers will play an increasingly

important role in providing clothing for the world’s

rapidly growing population.

The advantages of plastics and their use also lead to

some of the greatest concerns about fossil fuel-based

materials. Use of fossil fuels for polymers will increas-

ingly compete with use of fossil fuels for transportation

and industrial purposes,especially as exploration and

production costs of fossil fuels rise due to the ﬁnite nat-

ure of the underlying resource. The durability of many

plastics,under both aerobic and anaerobic conditions,

contributes to growing waste and waste disposal pro-

blems. Even improving recycling rates for many types of

plastics have not kept up with increases in overall plas-

tics consumption. And in some cases recycling yields

new problems associated with concentration of con-

taminants through the recycling process.

In all,and over the long run,Cargill Dow’s development

of PLA is based on ﬁnding a solution that both provides

society with the beneﬁts of plastics and polymers,and at

thesametimeeliminatesadverseenvironmentalimpacts

and supports sustainable development. As polymers are

increasingly derived from agricultural feedstocks,Cargill

Dow is working toward a future in which the agricultural

processes for producing feedstocks becomes increasingly

restorative—to agricultural ecosystems,agricultural com-

munities,and agricultural economies—as well.

strength,wide

application

range,and

Fig. 2. Phases of a life cycle assessment.

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