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Biodegradable synthetic fibre from corn


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  • 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 theavailability of fossil fuel such as oil, hydrocarbons, coal etc. In addition to cope up with thedepleting resources, there would be serious environment deterioration as most of the syntheticfibre 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 textileproduction to take care of depleting fossil fuel and synthesize biodegradable polymers forenvironment protection. In the present paper, the development of new, totally biodegradablehence ecofriendly synthetic fibre synthesized from renewable agriculture source corn as rawmaterial is discussed. It is envisaged that the new fibre based on polylactide (PLA), wouldfind diverse conventional textile, technical textile and non textile applications. Thus this newfibre would prove to be revolutionary to meet the future requirements of renewable rawmaterials as a substitute for depleting fossil fuel and environment protection due to its totalbiodegradability.Introduction Textile clothing are essential for human presence because we have lost the ability asspecies to survive the rigours of climate without some form of protection in the form of bodycovering. 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 oncontinuous 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 yearsor so. While this may be taken as an indication of an increased need for textile goods, thelarge number of people to feed will also require more land for growing foodstuffs. This will inturn mean less space available for growing textile related crops especially cotton. While wooland other animal hair fibres may enjoy the advantage of being able to grow on marginal landand of providing ready source of food as well as fibres. In addition, people consume othercommodities besides food. Their needs will strain the worlds manufacturing resources(especially oil) to the utmost. In consequence oil will become a scarce commodity and textilefibres derived from it may be given lower priority than that accorded to more easilyrecognized uses such as transportation, aerospace, Heavy chemical industries etc. In additionto cope up with the depleting resources, there would be serious environment deterioration asmost of the synthetic fibres produced to day are non-biodegradable. Attempts are thereforebeing made to find renewable sources as a raw material for textile production to take care ofdepleting fossil fuel resources and synthesize biodegradable polymers for environmentprotection.
  • 2. Non-food crop as renewable source Wide spread introduction of non-food crops as a major source of feedstock forchemical industry has been recently recognized. In 1995 an article in Chemistry in Britainreported that “biotechnology has the potential to make available a huge range of basic rawmaterials, intermediate feedstock and even final end products for the chemical industry. In1998, another Chemistry in Britain article stated that “there is now a growing sense ofurgency about the need to move away from our dependence on depleting fossil fuels and toseek out new feedstock”. The article further added that “industry is now stepping up its effortsto 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 bypolymerization of: Glycollic acid (PGA), Lactic acid (PLA), Hydroxybutyricacid (PHB), Caproloactone (PCL )
  • 3. Fig. 1. Biodegradable aliphatic polyestersIn 1998, ten companies in Japan offered twelve different brands of biodegradable syntheticfibres and plastics based on eight base materials such asPolylactic 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 mostpromising.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 furtherinvestigations were abandoned. Recently, polylactic acid has been suggested asbiodegradable binder for cellulosic non-wovens in preference to polyvinyl acetate orcopolymer 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 otherapplications were explored. Today in Japan PLA production is 500 – 1000 tons/annum. Itis 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 thebrand name Deposa. The Galactic laboratories (Belgium) have analyzed the future of thepolymers of PLA and forecasted that by 2008 the production would be around 390,000tons/annum and the price would be around 2 Dollar/kg. Cargill Dow polymers (CDP) USAhas installed a new plant with 70,000 tons/annum capacity. Today Cargill Dow polymers isthe leader in the technology of polylactic acid (PLA). It is a 50:50 joint venture started in1997. Currently their production capacity is 4000 tons/annum. In January 2001 theyannounced to increase the production to 1,40,000 tons/annum to produce PLA under thetrade name Nature Works PLA a polymer completely derived from corn which is annualrenewable natural source at competitive price . It is anticipated that by 2002 manycompetitors 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) andNature Works PLA (Cargill Dow polymers, USA) is obtained from the renewable sourcesuch as corn rather than petroleum for its feedstock. It is also possible to use other plantmaterials such as rice, wheat, sugar beets and even agricultural waste. The steps involved inthe production of Lactron or Nature Works PLA fibre are as followsRenewable 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 enhancementsmay eliminate the milling step and allow for utilization of even more abundant agriculturalby-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 tothat used by beer and wine producers. This is the same lactic acid that is used as a foodadditive and is found in muscle tissue in the human bodyIntermediate production Through a special condensation process, a cyclic intermediate dimer, referred to aslactide, is formed.Polymer production This monomer lactide is purified through vacuum distillation. Ring openingpolymerization 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 beproduced for wide range of applications.ChemistryFig.2 Formation of lactide and its polymerization
  • 5. Fig.3 Three forms of lactic acid and lactideThe chemistry involved in the polymerization of lactic acid through lactide is shown in fig. 2and 3. Lactic acid is converted in the dimer lactide by elimination of water, which is thenpolymerized by special ring opening polymerization to polylactide (PLA) (Fig. 2). Thefamily of polymers can be obtained depending on the stereo chemistry of lactic acid and itsdimer. 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 thatcontain more than 15% D-isomer produce amorphous polymers. Better control of stereochemistry of dimers explains the superiority of polyesters than those obtained by Carothers in1932.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 ApplicationsFibresDesirable fibre properties PLA is readily converted into variety of fibre forms, using conventional melt spinningprocesses. Monocomponent and bicomponent, continuous (flat and textured) and staple fibresof various types are easily produced. Fibres from PLA demonstrate excellent resiliency,outstanding crimp retention and improved wicking compared with natural fibres. Microdenierfibres are readily produced. Fabrics produced from PLA are being utilized for their silky feel,drape, durability and moisture-management properties. Independent testing has confirmedthat 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 ofdairy 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 bagsetc. It is important to mention that these products are completely biodegradable in commercialcompost conditions.Emerging applicationsCargill 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 astheir feedstock source. Fossil fuels take millions of years to regenerate. In contrast themonomer for PLA is derived from annually renewable resource. Energy from the sun andcarbon dioxide from air are harnessed in agricultural crops. (Figure 4) One third of the energyrequirement 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 conventionalsynthetic 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 andfuel for transportation. Fig.4 Cycle of Lactron (PLA)Carbon cycleCarbon dioxide is believed to be a major contributor to global warming. Because carbondioxide is removed from the air when corn is grown, the use of PLA has the potential to resultin 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 waterand actived mud tests, there was decrease in tenacity and increase in weight loss. In theground test the fibre is practically decomposed within two years. The observation is similarfor 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 wastemanagement methods. In addition PLA products can be composted in municipal compostingfacilities.
  • 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, PLApolymers will degrade into lactic acid (monomer), even if microbes are not present. PLApolymer degradation rate is dependent upon temperature and humidity. At typical landfilltemperatures, the expected degradation time frame would be between 2 and 10 years. Foodwaste and paper may persist for longer periods of time in a landfill because they requirebacteria 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 andcarbohydrates. It contains no aromatic groups or chlorine, burns with white flame, producesfew byproducts and 0.01% ash.Municipal composting Extensive testing demonstrates that PLA polymers are fully compostable in municipalcomposting facilities. Composting is a method of waste disposal that allows organic materialsto be recycled into product that can be used as a valuable soil amendment. PLA is made froman annually renewable resource and compost can be used to grow the crops to produce morePLA.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 andlactic acid into carbon dioxide and water. Heat and water stimulate degradation of PLApolymers.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 existingrecycle 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 bestraightforwardto completely degrade PLA into lactic acid and recover monomer.Conclusion The new ecofriendly synthetic fibre based on polylactide (PLA), synthesized fromcorn 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 withthe depleting fossil fuel resources and environment protection. It is envisaged that in the nearfuture, many companies would enter into production of PLA fibres and resins. References1. Chem.Br., April 1995, p3022. Chem.Br., February 1998, p493. Chem. Br., August 1995, p384. International Fibre J.,February 2001, p1
  • 10. 5. – Nature Works PLAFig 2
  • 11. Fig 4Table 1
  • 12. Fig 3Fig 5