Polylactic acid (PLA), a biodegradable polymer, a derived from renewable agricultural resources, naturalsubstitute made from fermented plant starch (usually corn) is quickly becominga popular alternative to traditional Manmade fibres. PLAstaple fibers are 100% green and bio-degradable, having nothing to do withtraditional polyester. PLA could be easily de-composed by natural chemicalhydrolysis process. On later stage PLA is further easily degraded bymicroorganisms into CO2 and water.


Manufacturing process of PLA


First step is the process of separating starch from the bio-mass basically wet milling is the process adopted. The starch is processed into dextrose that is then converted to lactic acidusing a fermentation process using bacteria e.g. Homolactic Lactobacteriaceaefamily. Monomer lactide collected through condensation and then purifiedthrough vacuum distillation. Using a solvent free process like Ultrafiltration,Nanofiltration and Ion-exchange process we obtain PLA resin from the lactide.



Physical properties Nature Works PLA Biomer L9000
Melt flow rate (g/10min) 4.3 - 2.4 3 - 6
Density (g/cm3) 1.25 1.25
Haze 2.2
Yellowness index 20-60
Mechanical properties

Tensile strength at yield (Mpa) 53 70
Elongation at yield (%) 10-100 2.4
Flexular Modulus (Mpa) 350-450 3600
Thermal properties

HDT (C) 40-45, 135
VICAT Softening point ( *C ) --- 56
GTT ( *C) 55-56
Melting point 120-1704


PLA has excellent physical andmechanical properties, forced it to become a good challenger candidate for substitutionfor petrochemical thermoplastics. The high price for PLA was hurdle which madeits use to medical and specialty applications only, but recent breakthroughs inlactic acid fermentation technology have opened up possibilities for the production of PLA in bulk volumes also.


Process of PLA biodegradation


PLA heads to de-compose as it is from different origin thanthe regular plastic. The process of de-compose is very important process because of which PLA out served its usefulness.


PLA biodegrades slowly in this way - Initially polymer chainof 100,000 to 300,000 molecular weight, break down into its constituent parts(Carbon dioxide and water) within three months in a "controlled compostingenvironment". While compounding polymer if heat of 75C applied at steadyrate helps the microbes to decompose in controlled environment. But it will takefar longer in a compost bin and in a tightly packed landfill where no light and presence of oxygen are rare available to assist in the process. Indeed,analysts estimate that a bottle grade PLA may take approximate time from 100 to1,000 years to decompose in soil. Conventional PET polymer contains molecularweight of 170,000 to 350,000 hence it is highly tough to decompose.


 

Handling of PLA Fibres


The physical handling of PLA requires great caution particularly while storing, using, handling and disposal. PLA polymers are flammable and, once ignited, could burn rapidly under the right environmental condition. Dust control was important as same as in natural fibres. Workers should be protected from the possibility of contact with molten resin during processing of PLA chips. It is also likely that under amid hot condition minor polymer links and other decomposition may form fumes. But if PLA decompose into the marine environment or face continuous waterfowl or aquatic life, the PLA material may cause mechanical adverse effects very fast.


Cost of PLA


Future costs to the environment and human health of genetic modification are still largely unknown and could be very high. So, PLA staple fiber, which is 100% green and bio-degradable, having nothing to do with traditional polyester, but with the appearance, applications and functions nearly the same as normal PSF (Polyester Staple Fiber), denier from 1.5D to 6D under our current production, up to 15D can be made the same way. The current price (FOB base) of PLA is as below, provided by one of the major Taiwanese producer. 1.4Dx38mm for spinning -US$ 3.72/Kg, 1.5Dx38mm for spun-lace - US$ 3.30/Kg, 6D/15Dx 64mm for padding- US$ 3.33/Kg, 4Dx51mm LM for thermo bonding- US$ 3.5 8/Kg, which is very high compare to traditional polyester which is being sold at near by US$ 1.00/Kg.


The largest producer of PLA in the world is NatureWorks, a subsidiary of Cargill. PLA production technique was jointly developed by Cargill Dow. The PLA samples produced with this technology is being sold at €3.40/Kg to €2.20/Kg. Cargill Dow is also investigating on other ways to generate PLA including the use of renewable fuels from plants such as wheat, beets and other crops best suited to particular climates. After 2010, the use of renewable energy and alternative biomass feedstocks is expected to generate further improvements in price competitiveness. Hycail's predictions are more conservative (€2.00 per kg in 2007, €1.80 per kg in 2010, €1.50 - €1.60 per kg in 2030).


The fundamental polymer characteristics of PLA allows control of certain fiber properties and makes the fiber suitable for a wide variety of textile fiber applications, especially apparel and performance apparel applications. As far as concern of the PLA producers, they are not only looking at PLA's potential for substitution in conventional applications. We have to exploit the potentials of the PLA fibres as future costs to the environment and human health of genetic modification are still largely unknown and could be very high.


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