1. ECOFRIENDLY SYNTHETIC FIBRE FROM CORN
R.B.CHAVAN
Department of Textile Technology,
Indian Institute of Technology,
Hauz-Khas, New Delhi 110016
Abstract
The increase in population and human needs would put considerable strains on the
availability of fossil fuel such as oil, hydrocarbons, coal etc. In addition to cope up with the
depleting resources, there would be serious environment deterioration as most of the synthetic
fibre polymers currently used for textile and non-textile applications are non-biodegradable.
Attempts are therefore, being made to find renewable resources as raw material for textile
production to take care of depleting fossil fuel and synthesize biodegradable polymers for
environment protection. In the present paper, the development of new, totally biodegradable
hence ecofriendly synthetic fibre synthesized from renewable agriculture source corn as raw
material is discussed. It is envisaged that the new fibre based on polylactide (PLA), would
find diverse conventional textile, technical textile and non textile applications. Thus this new
fibre would prove to be revolutionary to meet the future requirements of renewable raw
materials as a substitute for depleting fossil fuel and environment protection due to its total
biodegradability.
Introduction
Textile clothing are essential for human presence because we have lost the ability as
species to survive the rigours of climate without some form of protection in the form of body
covering. The other reasons for clothing are adornment, the display of wealth or status,
physical or psychological comforts and modesty. New textile uses are also appearing on
continuous basis in the form of technical textiles such as textiles for architectural structures,
sporting and out door activities, geo- textiles for environment protection, space, defence,
automotive applications, composites, filter fabrics and various other industrial applications .
Current predictions are that population level will approximately double every 35 years
or so. While this may be taken as an indication of an increased need for textile goods, the
large number of people to feed will also require more land for growing foodstuffs. This will in
turn mean less space available for growing textile related crops especially cotton. While wool
and other animal hair fibres may enjoy the advantage of being able to grow on marginal land
and of providing ready source of food as well as fibres. In addition, people consume other
commodities besides food. Their needs will strain the worlds manufacturing resources
(especially oil) to the utmost. In consequence oil will become a scarce commodity and textile
fibres derived from it may be given lower priority than that accorded to more easily
recognized uses such as transportation, aerospace, Heavy chemical industries etc. In addition
to cope up with the depleting resources, there would be serious environment deterioration as
most of the synthetic fibres produced to day are non-biodegradable. Attempts are therefore
being made to find renewable sources as a raw material for textile production to take care of
depleting fossil fuel resources and synthesize biodegradable polymers for environment
protection.
2. Non-food crop as renewable source
Wide spread introduction of non-food crops as a major source of feedstock for
chemical industry has been recently recognized. In 1995 an article in Chemistry in Britain
reported that “biotechnology has the potential to make available a huge range of basic raw
materials, intermediate feedstock and even final end products for the chemical industry. In
1998, another Chemistry in Britain article stated that “there is now a growing sense of
urgency about the need to move away from our dependence on depleting fossil fuels and to
seek out new feedstock”. The article further added that “industry is now stepping up its efforts
to find renewable alternatives”.
The advantages of non-food crops as feedstock are:
• They are renewable resource, the use of which is sustainable in the long term. Unlike
fossil fuels, which are rapidly dwindling. At the current consumption levels crude oil
reserves are predicted to deplete within 50 years, gas reserves within 75 years, and coal
within about 200 years.
• The use of fossil fuels cause all kinds of pollution, whereas crops being generally less
polluting, lock up carbon dioxide from the atmosphere in the form of carbohydrates,
lipids and proteins, thereby mitigating the effects of global warming.
• Majority of products derived from plant feedstock would be completely biodegradable.
Need for biodegradable fibres and plastics
Solid waste disposal is a burning problem all over the world. The availability of
landfill space is decreasing, ocean dumping is illegal and the use of incineration as the way
to treat the majority of waste is no longer acceptable. For these reasons, organic waste
composting and the use of biodegradable fibres and plastics both have an obvious appeal
to the pollution control authorities and the public alike.
Theoretical basis for biodegradation of fibres
The biological degradation of fibres happens when depolymerization of polymer
that constitutes them takes place due to enzymes secreted from certain microorganisms.
These enzymes either hydrolyze or oxidize the polymer. They act on the extremities of the
polymer chain (end group attack) or any point on the chain (random attack). In order to
facilitate this reaction the enzymes must be able to tie themselves with the fibre and to
arrive to the centres that can be hydrolyzed or oxidized. Therefore, the main biodegradable
fibres are those of hydrophilic ones and formed from flexible chains with low level of
crystallization. Often they have the main chain with ties containing oxygen or nitrogen or
both. This description corresponds to greater part of natural fibres formed from natural
polymers. The non-biodegradable polymers have opposite characteristics. The polymers
without oxygen such as polyethylene, polypropylene resist completely the biological
degradation. The aromatic polyester (PET) although contains oxygen, perhaps resists
biodegradation due to chain rigidity and crystallization. The same applies to polyamides
although they contain nitrogen. Contrary to aromatic polyester, the aliphatic polyesters are
susceptible to biodegradation. In addition to biodegradability they are also thermoplastic
and like any other polyester can be converted into fibres and films,
Biodegradable Aliphatic polyesters
Biodegradable aliphatic polyesters (Fig. 1) can be formed on industrial scale by
polymerization of:
Glycollic acid (PGA), Lactic acid (PLA),
Hydroxybutyricacid (PHB), Caproloactone (PCL )
3. Fig. 1. Biodegradable aliphatic polyesters
In 1998, ten companies in Japan offered twelve different brands of biodegradable synthetic
fibres and plastics based on eight base materials such as
Polylactic acid, polycaprolactone, polybutylene succinate, polyethylene succinate,
modified starch alloys, cellulose acetate, polyhydroxy butyrate (PHB).
Among these, polymers based on polylactic acid (PLA), seems to be the most
promising.
Polylactic acid fibres
Polymerization of lactic acid was carried out by Carothers in 1932. However,
because of low melting point the polymer was not considered to be suitable and further
investigations were abandoned. Recently, polylactic acid has been suggested as
biodegradable binder for cellulosic non-wovens in preference to polyvinyl acetate or
copolymer of ethylene acrylic acid.
Kanebo (Japan) has introduced in 1994 the Lactron fibre and spun led non-woven.
Initially it was used for applications in agriculture (mulch film), and in 1998 other
applications were explored. Today in Japan PLA production is 500 – 1000 tons/annum. It
is used to develop PLA/rayon blends in order to reduce cost and improve biodegradability.
In 1997, Fiberweb (France), has developed non-woven and marketed under the
brand name Deposa. The Galactic laboratories (Belgium) have analyzed the future of the
polymers of PLA and forecasted that by 2008 the production would be around 390,000
tons/annum and the price would be around 2 Dollar/kg. Cargill Dow polymers (CDP) USA
has installed a new plant with 70,000 tons/annum capacity. Today Cargill Dow polymers is
the leader in the technology of polylactic acid (PLA). It is a 50:50 joint venture started in
1997. Currently their production capacity is 4000 tons/annum. In January 2001 they
announced to increase the production to 1,40,000 tons/annum to produce PLA under the
trade name Nature Works PLA a polymer completely derived from corn which is annual
renewable natural source at competitive price . It is anticipated that by 2002 many
competitors would enter into production of this new polymer.
4. Production route and chemistry of new synthetic fibre from corn
Production route
A new synthetic fibre marketed under the trade names Lactron (Kanebo, Japan) and
Nature Works PLA (Cargill Dow polymers, USA) is obtained from the renewable source
such as corn rather than petroleum for its feedstock. It is also possible to use other plant
materials such as rice, wheat, sugar beets and even agricultural waste. The steps involved in
the production of Lactron or Nature Works PLA fibre are as follows
Renewable resource
A renewable resource such as corn is milled, separating starch from the raw material.
Unrefined dextrose/sugar, in turn, is processed from starch. Future technology enhancements
may eliminate the milling step and allow for utilization of even more abundant agricultural
by-products such as rice, wheat, sugar beets and even agricultural waste.
Fermentation
The dextrose/sugar is turned into lactic acid using a fermentation process similar to
that used by beer and wine producers. This is the same lactic acid that is used as a food
additive and is found in muscle tissue in the human body
Intermediate production
Through a special condensation process, a cyclic intermediate dimer, referred to as
lactide, is formed.
Polymer production
This monomer lactide is purified through vacuum distillation. Ring opening
polymerization of the lactide is accomplished with a solvent free melt process.
Modification to customer needs
A wide range of products that vary in molecular weight and crystallinity can be
produced for wide range of applications.
Chemistry
Fig.2 Formation of lactide and its polymerization
5. Fig.3 Three forms of lactic acid and lactide
The chemistry involved in the polymerization of lactic acid through lactide is shown in fig. 2
and 3. Lactic acid is converted in the dimer lactide by elimination of water, which is then
polymerized by special ring opening polymerization to polylactide (PLA) (Fig. 2). The
family of polymers can be obtained depending on the stereo chemistry of lactic acid and its
dimer. The lactic acid could be present in three forms i.e. L-isomer, D-isomer and meso-
isomer (Fig.3). The polymerization of L-isomer produce crystalline polymers, while those that
contain more than 15% D-isomer produce amorphous polymers. Better control of stereo
chemistry of dimers explains the superiority of polyesters than those obtained by Carothers in
1932.
Properties
The key properties of new synthetic fibre derived from corn are as follows:
• Superior melt processability, can produce microfibres.
• Low moisture absorption, rapid wicking, excellent hand drape and resilience.
• Wrinkle resistance.
• Qualities from silk-like to cotton-like.
• Exceptional UV resistance.
• Low flammability, stain resistance.
• Can be washed,dry cleaned and commercially laundered.
The physical properties of PLA in comparison with other fibres are given in Table 1
Table 1 Comparison of fibre properties
Applications
Fibres
Desirable fibre properties
PLA is readily converted into variety of fibre forms, using conventional melt spinning
processes. Monocomponent and bicomponent, continuous (flat and textured) and staple fibres
of various types are easily produced. Fibres from PLA demonstrate excellent resiliency,
outstanding crimp retention and improved wicking compared with natural fibres. Microdenier
fibres are readily produced. Fabrics produced from PLA are being utilized for their silky feel,
drape, durability and moisture-management properties. Independent testing has confirmed
that PLA fibres have other key advantages over PET fibres, including:
• Low flammability and smoke generation.
• Excellent UV stability.
• High lustre.
6. • Lower density.
PLA is the first melt processable natural based fibre. When converted into fibre, PLA
provides a bridge between natural fibres such as wool, cotton and silk and conventional
synthetics. The result is a unique property spectrum for product creation. Existing fibre
spinning and downstream fabrication can process PLA. Specific processing advantages
include high extrusion or spin speeds, reduced temperatures and reduced energy
consumption.
Fibre Applications
PLA can be used in a wide range of woven, knitted and non-woven applications
including:
• Clothing (fashionwear, underwear, sportswear, uniform etc)
• Wool, silk and cotton blends.
• Wipes.
• Carpet tiles.
• Diapers.
• Feminine hygiene.
• Upholstery.
• Interior and outdoor furnishings.
• Filtration.
• Agricultural application (Geo-textiles for soil erosion control)
Packaging
Desirable properties
PLA is an alternative to traditional, disposable packaging. The desirable properties
are:
• Versatility and processability. PLA can be extruded, oriented, thermoformed and
coated with existing equipments at high speed.
• Outstanding clarity and gloss, equivalent to oriented PP and PET.
• Unique barrier properties.
• Low temperature heat seal.
• Crystallinity can be modified to suit product requirements.
• Tensile strength and modulus similar to PET.
• Excellent resistance to wide range of greases, fats and oils.
• Excellent printability.
• Biodegradability: PLA biodegrades completely in compost conditions.
• Natural origin: PLA comes entirely from annually renewable resources.
7. Applications
Above properties have led Cargill Dow polymers to focus initially on film,
thermoform applications.
Films
PLA has proven performance in a broad range of film end-uses including:
• High clarity/high stiffness films as an alternative to cellophane for uses such as
confectionery twist wrap, wrapping for flowers, toiletries and prestige gifts.
• Bags for compost and garden refuse as well as agricultural mulch films to replace
paper.
• Wide variety of multi-layer films for packaging uses such as flavoured cereals, coffee
packs and pet foods.
• Window films for envelopes, cartons and other packages.
• Lamination films including end-uses where cellulose acetate can be replaced.
• Low temperature heat seal layers and/or flavour and aroma barriers in co-extruded
structures where its combination of properties allows layer simplification or
replacement of nylons.
• Shrink sleeve films and high modulus label films.
• Non-fogging films for fresh produce packaging.
Rigid thermoformed containers
In addition to outstanding gloss and clarity, the relative ease of processing that
PLA exhibits in thermoforming enables it to be used for both conventional and form fill
seal applications. Its environmental attributes make it a preferred packaging alternative
where disposal requirements or consumer appeal are significant issues.
End use products
PLA can be successfully converted into various products such as for packaging of
dairy products, candy wrap, fast food cups, fresh food containers, paper ice cream holders,
flavoured cereal packaging, coffee packs, snack foods, milk and fresh yogurt, compost bags
etc. It is important to mention that these products are completely biodegradable in commercial
compost conditions.
Emerging applications
Cargill dow is also exploring and developing emerging applications such as:
Blow molding injection stretch blow molded bottles.
Emulsions water based emulsions for paper and board coatings and, paints, binders for non-
woven fabrics, binders for building products and adhesives.
Lactic acid derivatives To be used as chemical intermediates in products such as solvents,
hot melt adhesives, coatings, surfactants, acrylic esters and agricultural intermediates.
8. Environmental benefits and disposal options
Reduce fossil fuel use
Conventional hydrocarbon polymers utilize natural reserves of oil and natural gas as
their feedstock source. Fossil fuels take millions of years to regenerate. In contrast the
monomer for PLA is derived from annually renewable resource. Energy from the sun and
carbon dioxide from air are harnessed in agricultural crops. (Figure 4) One third of the energy
requirement of PLA is derived these renewable resources., resulting in PLA utilizing 20-40%
less fossil fuel than other polymers derived directly from hydrocarbons. As with conventional
synthetic polymers fossil fuel provides the energy to run the PLA production chain, e.g.
milling corn to produce starch, fermentation to produce lactic acid, heating to polymerize and
fuel for transportation.
Fig.4 Cycle of Lactron (PLA)
Carbon cycle
Carbon dioxide is believed to be a major contributor to global warming. Because carbon
dioxide is removed from the air when corn is grown, the use of PLA has the potential to result
in a reduced impact on global warming compared to most hydrocarbon based polymers (fig.4)
Biodegradability of PLA
It was observed that when the PLA fibre is subjected to ground burrying, marine water
and actived mud tests, there was decrease in tenacity and increase in weight loss. In the
ground test the fibre is practically decomposed within two years. The observation is similar
for the test of immersion in marine water. It is decomposed much quickly in activated mud.
The degradation is almost complete in 2-3 months time (Fig.5)
Fig.5 Biodegradability of Lactron (PLA)
The behaviour of PLA in comparison with other traditional fibres is:
• The conventional polyester (PET) retains the shape and properties under all
biodegradability tests.
• The cellulosic fibres (cotton and rayon) are decomposed more rapidly than PLA in actived
mud.
Waste disposal
At the end of their useful life, PLA products can be disposed of by all traditional waste
management methods. In addition PLA products can be composted in municipal composting
facilities.
9. Landfill
Although landfill tests have not been carried out with PLA polymers, its water induced
(hydrolysis) degradation mechanism is well understood. As long as moisture is present, PLA
polymers will degrade into lactic acid (monomer), even if microbes are not present. PLA
polymer degradation rate is dependent upon temperature and humidity. At typical landfill
temperatures, the expected degradation time frame would be between 2 and 10 years. Food
waste and paper may persist for longer periods of time in a landfill because they require
bacteria to degrade.
Incineration
PLA polymers incinerate cleanly and with reduced energy yield (8,400 BTU/lb)
compared to traditional polymers. PLA polymers burn much like paper, cellulose and
carbohydrates. It contains no aromatic groups or chlorine, burns with white flame, produces
few byproducts and 0.01% ash.
Municipal composting
Extensive testing demonstrates that PLA polymers are fully compostable in municipal
composting facilities. Composting is a method of waste disposal that allows organic materials
to be recycled into product that can be used as a valuable soil amendment. PLA is made from
an annually renewable resource and compost can be used to grow the crops to produce more
PLA.
PLA polymers compost by two step process. First chemical hydrolysis (reaction with water)
reduces the molecular weight of the polymer, then microorganisms degrade the fragments and
lactic acid into carbon dioxide and water. Heat and water stimulate degradation of PLA
polymers.
Post consumer recycling
In practice the following conditions need to be met in order to recycle any material:
1. The material is present in sufficient quantities in waste stream.
2. A disciplined collection system is put into place to collect.
3. The product is clearly marked and physically easy to separate.
4. There are outlets desiring to purchase the recycle feedstock stream.
This infrastructure does not currently exist for PLA. The impact of PLA on existing
recycle streams also depends on the above factors and needs to be studied case-by-case basis.
Because PLA polymers hydrolyze with water to generate lactic acid, it would be
straightforward
to completely degrade PLA into lactic acid and recover monomer.
Conclusion
The new ecofriendly synthetic fibre based on polylactide (PLA), synthesized from
corn as a renewable source would find wide acceptability in the area of conventional textiles,
technical textiles and non-textile applications. It would meet the requirements to cope up with
the depleting fossil fuel resources and environment protection. It is envisaged that in the near
future, many companies would enter into production of PLA fibres and resins.
References
1. Chem.Br., April 1995, p302
2. Chem.Br., February 1998, p49
3. Chem. Br., August 1995, p38
4. International Fibre J.,February 2001, p1
