Polylactic acid: Difference between revisions
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Polylactic acid | ==Overview== | ||
Polylactic acid is a thermoplastic suitable for light weight applications and plastic extrusion by 3D printers (reprap wiki). Polylactic acid is actually a polyester and is bio-degradable. Lactic acid can be formed by fermentation of sugars by microorganisms or synthetically from petroleum. Lactic acid is polymerized via sequemtial condensation reactions with a catalyst and in 130-160 C. Polylactic acid is currently in first generation large scale production using corn starch as a feedstock. | |||
==Biological materials and hardware== | |||
Initial feedstocks will be converted to input lactic acid by microorganismal fermentation; a feedstock with a high fermentable sugar content should be chosen and an appropriate bacterial strain selected. A fermentation chamber will need to be developed and prototyped. Further research is needed into methods of purifying lactic acid. Lactic acid will be polymerized in a reaction chamber to which must also be developed and prototyped. Quality control is needed for high purity lactic acid necessary for polymerization. | |||
==Feedstock starting materials== | |||
A variety of feedstocks can be used as a source of sugar for fermenting microorganisms including high starch plants, high sugar plants, or dairy. Feedstocks should be chosen based upon a high yield of sugars suitable for Polylactic Acid Bacteria to metabolize. | A variety of feedstocks can be used as a source of sugar for fermenting microorganisms including high starch plants, high sugar plants, or dairy. Feedstocks should be chosen based upon a high yield of sugars suitable for Polylactic Acid Bacteria to metabolize. | ||
==Fermentation== | |||
Organisms are chosen with the metabolic capabilities to utilize sugars in the feedstock. Homofermentative species that produce lactic acid as a sole product should be used for maximum yield and to reduce complicating substrates. | Organisms are chosen with the metabolic capabilities to utilize sugars in the feedstock. Homofermentative species that produce lactic acid as a sole product should be used for maximum yield and to reduce complicating substrates. | ||
From “There are two main hexose fermentation pathways that are used to classify LAB genera. Under conditions of excess glucose and limited oxygen, homolactic LAB catabolize one mole of glucose in the Embden-Meyerhof-Parnas (EMP) pathway to yield two moles of pyruvate. Intracellular redox balance is maintained through the oxidation of NADH, concomitant with pyruvate reduction to lactic acid. This process yields two moles ATP per mole of glucose consumed. Representative homolactic LAB genera include Lactococcus, Enterococcus, Streptococcus,Pediococcus, and group I lactobacilli.” Fermentation is inhibited by endproducts and advances in fermentation technique includes methods to remove lactic acid as it forms allowing continuous operation of bioreactors and higher conversion rates. A schematic of fermentor that could operate in batch-fed or continuous mode is below | From “There are two main hexose fermentation pathways that are used to classify LAB genera. Under conditions of excess glucose and limited oxygen, homolactic LAB catabolize one mole of glucose in the Embden-Meyerhof-Parnas (EMP) pathway to yield two moles of pyruvate. Intracellular redox balance is maintained through the oxidation of NADH, concomitant with pyruvate reduction to lactic acid. This process yields two moles ATP per mole of glucose consumed. Representative homolactic LAB genera include Lactococcus, Enterococcus, Streptococcus,Pediococcus, and group I lactobacilli.” Fermentation is inhibited by endproducts and advances in fermentation technique includes methods to remove lactic acid as it forms allowing continuous operation of bioreactors and higher conversion rates. A schematic of fermentor that could operate in batch-fed or continuous mode is below | ||
==Bacterial strain selection and care== | |||
Strains could either be isolated from a fermented product or ordered from a supplier. A relatively simple procedure for isolating and identifying LAB from an enriched media can be found here. Alternatively a strain may also be found by contacting relevant research laboratories. IN industry Lactobacillus delbrueckii, L. amylophilus, L. bulgaricus and L. leichmanii. Mutant fungal strains of Aspergillus niger are also reportedly used. A wide variety of carbohydrate sources, e.g. molasses, corn syrup, whey, dextrose and cane or beet sugar, can be used.” | Strains could either be isolated from a fermented product or ordered from a supplier. A relatively simple procedure for isolating and identifying LAB from an enriched media can be found here. Alternatively a strain may also be found by contacting relevant research laboratories. IN industry Lactobacillus delbrueckii, L. amylophilus, L. bulgaricus and L. leichmanii. Mutant fungal strains of Aspergillus niger are also reportedly used. A wide variety of carbohydrate sources, e.g. molasses, corn syrup, whey, dextrose and cane or beet sugar, can be used.” | ||
The pH of the media will be lowered by the production of lactic acid and maintaining pH in the range of 5-6 is essential to culture health and maximum yield. Older more developed techniques were to add calcium stearate or other salts, which neutralized the pH and precipitated the salt form of lactic acid, however an equal amount of waste is produced alongside the purified lactic acid. Constant removal of waste products and maintenance of optimal growing conditions is the study of cutting edge polylactic acid producers. | The pH of the media will be lowered by the production of lactic acid and maintaining pH in the range of 5-6 is essential to culture health and maximum yield. Older more developed techniques were to add calcium stearate or other salts, which neutralized the pH and precipitated the salt form of lactic acid, however an equal amount of waste is produced alongside the purified lactic acid. Constant removal of waste products and maintenance of optimal growing conditions is the study of cutting edge polylactic acid producers. | ||
Purification | ==Purification of lactic acid== | ||
Isomers are molecules of the same chemical formula that exhibit chirality or a difference in positioning on a carbon attached to four different chemical groups. The chemical formula of lactic acid is CH3CHOHCOOH Isomer composition is important to crystallization with heterogenous mixtures forming amorphous configurations. Purification is aided by single isomer production in the fermentation route. Advances in purification have involved semipermeable membrane sieves and more recently electrophoresis technology. “This process uses a desalting ED unit to remove the multivalent cations and concentrate the lactate salt, followed by a ‘watersplitting’ ED unit with bipolar membranes to produce concentrated lactic acid and alkali for recycle.” Alternatively other salts could be used that produce a waste that is easier to handle and recover. | Isomers are molecules of the same chemical formula that exhibit chirality or a difference in positioning on a carbon attached to four different chemical groups. The chemical formula of lactic acid is CH3CHOHCOOH Isomer composition is important to crystallization with heterogenous mixtures forming amorphous configurations. Purification is aided by single isomer production in the fermentation route. Advances in purification have involved semipermeable membrane sieves and more recently electrophoresis technology. “This process uses a desalting ED unit to remove the multivalent cations and concentrate the lactate salt, followed by a ‘watersplitting’ ED unit with bipolar membranes to produce concentrated lactic acid and alkali for recycle.” Alternatively other salts could be used that produce a waste that is easier to handle and recover. | ||
Polymerization | ==Polymerization== | ||
The preferred route of creating polylactic acid uses the dilactide. Direct polymerization involves a condensation reaction that is near equilibrium and a method to remove water. Catalysts used include tin and zinc. A small scale experiment uses a microspatula of Tin(II) chloride to catalyze 5 ml of lactic acid under high heat conditions. Cobalt chloride paper can be used to test for water vapor indicating the reaction is proceeding. | The preferred route of creating polylactic acid uses the dilactide. Direct polymerization involves a condensation reaction that is near equilibrium and a method to remove water. Catalysts used include tin and zinc. A small scale experiment uses a microspatula of Tin(II) chloride to catalyze 5 ml of lactic acid under high heat conditions. Cobalt chloride paper can be used to test for water vapor indicating the reaction is proceeding. | ||
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==Quality control== | |||
Revision as of 19:17, 11 February 2012
Overview
Polylactic acid is a thermoplastic suitable for light weight applications and plastic extrusion by 3D printers (reprap wiki). Polylactic acid is actually a polyester and is bio-degradable. Lactic acid can be formed by fermentation of sugars by microorganisms or synthetically from petroleum. Lactic acid is polymerized via sequemtial condensation reactions with a catalyst and in 130-160 C. Polylactic acid is currently in first generation large scale production using corn starch as a feedstock.
Biological materials and hardware
Initial feedstocks will be converted to input lactic acid by microorganismal fermentation; a feedstock with a high fermentable sugar content should be chosen and an appropriate bacterial strain selected. A fermentation chamber will need to be developed and prototyped. Further research is needed into methods of purifying lactic acid. Lactic acid will be polymerized in a reaction chamber to which must also be developed and prototyped. Quality control is needed for high purity lactic acid necessary for polymerization.
Feedstock starting materials
A variety of feedstocks can be used as a source of sugar for fermenting microorganisms including high starch plants, high sugar plants, or dairy. Feedstocks should be chosen based upon a high yield of sugars suitable for Polylactic Acid Bacteria to metabolize.
Fermentation
Organisms are chosen with the metabolic capabilities to utilize sugars in the feedstock. Homofermentative species that produce lactic acid as a sole product should be used for maximum yield and to reduce complicating substrates.
From “There are two main hexose fermentation pathways that are used to classify LAB genera. Under conditions of excess glucose and limited oxygen, homolactic LAB catabolize one mole of glucose in the Embden-Meyerhof-Parnas (EMP) pathway to yield two moles of pyruvate. Intracellular redox balance is maintained through the oxidation of NADH, concomitant with pyruvate reduction to lactic acid. This process yields two moles ATP per mole of glucose consumed. Representative homolactic LAB genera include Lactococcus, Enterococcus, Streptococcus,Pediococcus, and group I lactobacilli.” Fermentation is inhibited by endproducts and advances in fermentation technique includes methods to remove lactic acid as it forms allowing continuous operation of bioreactors and higher conversion rates. A schematic of fermentor that could operate in batch-fed or continuous mode is below
Bacterial strain selection and care
Strains could either be isolated from a fermented product or ordered from a supplier. A relatively simple procedure for isolating and identifying LAB from an enriched media can be found here. Alternatively a strain may also be found by contacting relevant research laboratories. IN industry Lactobacillus delbrueckii, L. amylophilus, L. bulgaricus and L. leichmanii. Mutant fungal strains of Aspergillus niger are also reportedly used. A wide variety of carbohydrate sources, e.g. molasses, corn syrup, whey, dextrose and cane or beet sugar, can be used.”
The pH of the media will be lowered by the production of lactic acid and maintaining pH in the range of 5-6 is essential to culture health and maximum yield. Older more developed techniques were to add calcium stearate or other salts, which neutralized the pH and precipitated the salt form of lactic acid, however an equal amount of waste is produced alongside the purified lactic acid. Constant removal of waste products and maintenance of optimal growing conditions is the study of cutting edge polylactic acid producers.
Purification of lactic acid
Isomers are molecules of the same chemical formula that exhibit chirality or a difference in positioning on a carbon attached to four different chemical groups. The chemical formula of lactic acid is CH3CHOHCOOH Isomer composition is important to crystallization with heterogenous mixtures forming amorphous configurations. Purification is aided by single isomer production in the fermentation route. Advances in purification have involved semipermeable membrane sieves and more recently electrophoresis technology. “This process uses a desalting ED unit to remove the multivalent cations and concentrate the lactate salt, followed by a ‘watersplitting’ ED unit with bipolar membranes to produce concentrated lactic acid and alkali for recycle.” Alternatively other salts could be used that produce a waste that is easier to handle and recover.
Polymerization
The preferred route of creating polylactic acid uses the dilactide. Direct polymerization involves a condensation reaction that is near equilibrium and a method to remove water. Catalysts used include tin and zinc. A small scale experiment uses a microspatula of Tin(II) chloride to catalyze 5 ml of lactic acid under high heat conditions. Cobalt chloride paper can be used to test for water vapor indicating the reaction is proceeding.
Alternatively, the reaction will proceed under a vacuum and temperatures 150-300 C using distillation equipment to remove formed water. This configuration can be used with or without a catalyst and is an active area of research.