Synthesis Polylactic Acid By Lipase Catalyzed Polymerization Biology Essay

Synthesis Polylactic Acid By Lipase Catalyzed polymerization Biology EssayPolylactic acid (PLA), the biodegradable polymer, has received increase attention as alternative materials in packaging and biomedical applications. The general method for price reduction of PLA using chemical-catalyzed polymerization produces the gass resi ascribables which atomic number 18 toxicity. Therefore, the enzymatic polymerization is a green alternative method to cliff this problem. Several researches attempt to improve the optimal condition for synthesis of PLA by using lipase as enzymatic-catalyzed.For an example, Lassalle et al. (2008) account the synthesis of PLAby using lipase as bio throttle valve and foc utilise on the procedure. The closures found that immobilized CAL-B was the most effective biocatalyst with 60% LA transmutationand 55% healed solid polymer in the answer working at 60 C for96 h. Furthermore, Hans et al. (2009) researched to confirm the mild reactions conditions for th e resile-opening polymerization of lactides by using Novozyme 435 (immobilized CAL-B) 12% wt. submerging in methylbenzene to synthesize the polymer at 70 C, D-lactide was catalyzed and 33% of monomer was converted and could be isolated a polymer with 25% yield for a number-average molecular charge of 3,300 g mol-1. Finally, Garcia-Arrazola et al. (2009) reported the synthesis of poly-L-lactide by used immobilizedCAL-B (Novozyme 435) as biocatalyst for the mob-opening polymerization of L-lactide at 65 C could be achieved using supercritical carbon dioxide (scCO2). The L-lactide monomer could be converted as the PLA with a molecular weightiness 12,900 g mol-1 chthonian(a) the condition at a biphasic scCO2/organic liquid system media and the optimum of temperature for the lipase activity. All of these present studies atomic number 18 the novel way of life to produce the polylactic acid and relate improvement of the new biomaterials.TABLE OF CONTENTS knaveTABLE OF CONTENT iLIST OF TABLES iiLIST OF FIGURES iiiINTRODUCTION 1Lipase 1Polylactic acid PLA 2Synthesis of polylactic acid PLA 43.1 The conventional bring for synthesis of PLA 43.2 address for synthesis of PLA by lipase-catalyzed polymerization 5 cast of some(prenominal) factors for the polymerization 6Influence of the kind of lipase 6Influence of the enzyme concent balancen 8Influence of the monomer concent proportionalityn 10Influence of the temperature 11The improvement of process for lipase-catalyzed synthesis of PLA 12CONCLUSION 14LITERATURE CITED 15LIST OF TABLES dining table PageComparison of raw material type and porta of recycle andbiodegradation between PLA and PET polymer 3Conversion (%) of LA, isolated enzyme after reaction,recovered PLA, and molecular weight (Mn) (Da) as a map ofthe kind of the different lipase 7Results obtained for the ring opening polymerization of L-LAin scCO2 with 20 % (w/v) of L-LA and initial water content (aw) 0.16 13LIST OF FIGURES check Page1 Chemical struc ture of Polylactic acid PLA 22 flavor cycle of PLA 33 Polymerization routes to PLA 44 Polymerization reactions to synthesize PLA 65 Lactide conversion as a function of reaction time forthe ring opening polymerization of DD-lactide at 70 oC witha monomer to methylbenzene ratio of 12 (gmL) and use different submersion of Novozyme 435 86 molecular weight as a function of conversion plots forthe ring opening polymerization of DD-lactide at 70 oC witha monomer to toluene ratio of 12 (gmL) and use differentconcentration of Novozyme 435 97 Lactide conversion as a function of reaction time forthe ring opening polymerization of DD-lactide at different monomerto toluene ratio (monomer concentration) at 70 oC with 15 wt.-% ofNovozyme 435 108 Lactide conversion as a function of reaction time forthe ring opening polymerization of DD-lactide at differenttemperatures with 15 wt.-% of Novozyme 435 and a monomer totoluene ration 13 119 Number-average molecular weight as a function of temperaturefo r the ring opening polymerization of DD-lactide at differentmonomer conversion with 15 wt.-% of Novozyme 435 anda monomer to toluene ratio 13 12SYNTHESIS OF POLYLACTIC ACIDBY LIPASE-CATALYZED POLYMERIZATIONINTRODUCTIONLipaseLipases or triacylglycerol acylhydrolases EC 3.1.1.3 are hydrolase which catalyze the hydrolysis of triglycerides to glycerol and supernumerary fatty acids under aqueous conditions. In addition, lipases catalyze the tranesterification of other esters under micro-aqueous conditions. The ability of lipases has received increasing attention for used as catalyze in a wide array of biotechnology industry, such(prenominal) as fodder technology, detergent, chemical industry, cosmetic, organic synthesis, biomedical sciences and pharmaceutical applications (Gupta et al., 2004 Treichel et al., 2010).Lipases are produced by various plants, animals and microorganisms. Many microorganisms which are known as producers of extracellular lipases, including bacteria, yeast, and fungi. Especially, bacterial lipases and fungal lipases are most widely used as a class of commercial enzymes in many applications. The important commercial microbial lipases are Achromobacter sp., Alcaligenes sp., Arthrobactersp., Bacillus sp., Burkholderia sp., Chromobacterium sp., and genus Pseudomonas sp. from bacteria which are used successfully in the market with several products names, such as Lumafast, Lipomax, Combizyme and Greasex (Gupta et al., 2004). Moreover, fungi produces the important commercial lipases are Rhizopus sp., Aspergillus sp., genus Penicillium sp., Geotrichum sp., Mucor sp., and Rhizomucor sp. (Treichel et al., 2010) which are used in the market with many products names, such as Lecitase, Lipozyme, and Novozym 435 (CAL-B).Of these, the lipases from microbial hand over a stability, selectivity, and broad substrate specificity for cultivation such as an applications by used substances form oil mill wastewater, slaughterhouse wastewater, agroindustrial was te and corn steep liquor(Gupta et al., 2004 Treichel et al., 2010). Therefore, the recent microbial lipases have gained special industrial attention for used as biocatalyst in rapidly growing biotechnology.Polylactic acidPolylactic acid or the short name is PLA is a thermop conkic aliphatic polyester which a synthetic polymer based on lactic acid (LA) and have a helical structure was shown in range of a function 1. PLA derived from the fermentation of renewable resources such as corn starch, tapioca products and sugarcanes. code 1 Chemical structure of Polylactic acid PLA.PLA has received increasing attention as alternative materials in packaging and biomedical applications due to PLA is a biodegradable polymer, it easily degrades by simple hydrolysis of microorganisms under the appropriate conditions (Garlotta, 2001 Avinc and Khoddami, 2009). PLA has a high-strength, high-modulus, brightness, barrier properties and good moisture management as a result of its interesting for used i n packaging and composite materials for clothing applications (Garlotta, 2001). Furthermore, PLA has a biocompatible and bioabsorbable properties which can be used for wide range applications in biomedical and pharmaceutical technology, such as surgical sutures, tissue engineering scaffolds, absorbable bone plates, artificial skin, and controlled drug-release systems (Lassalle and Ferreira, 2008 Avinc and Khoddami, 2009 Hans et al., 2009).Because of its compost based on a natural substance which shopa biodegradability, PLA is to be a more environmentally-fri discontinuely polymer than poly ethylene terepthalate (PET) which is derived from a synthetic petrochemical-based materials due to PLA is lower greenhouse gas emission and significant energy savings, PLA avoids the problems cogitate to plastic waste accumulation. The result of comparison between PLA and PET polymer was shown in Table 1.Table 1 Comparison of raw material type and possibility of recycling and biodegradation betw een PLA and PET polymer.IndexesPLAPETInitial raw material baseRenewable plant stockPetroleum productsNon-renewable resourcesRecycling of polymer wastesTotal recycling possibleTotal recycling possibleBiodegradation of polymer wastesTotalDoes not degradeSource Avinc and Khoddami (2009)PLA products are easily composted or recycled under appropriate conditions at the wind up of the product life. The Figure 2 show the life cycle of PLA material degrades first by microbial hydrolysis, then the carbon dioxide and water which obtained from reaction became the raw material necessities for a new growth and leading to produced lactic acid (LA) for re-used as a monomer in the production of a new PLA (Avinc and Khoddami, 2009).Figure 2 Life cycle of PLA.Synthesis of polylactic acid PLAThe synthesis of PLA starts with the extraction of sugars (e.g., glucose and dextrose) from natural substances which used as a substrate in fermentation of lactic acid by microorganisms. Lactic acid (LA) is the s tarting material for the PLA production process, through polymerization. There are two major routes to synthesize PLA from LA monomer which are showed in Figure 3 (Avinc and Khoddami, 2009).Figure 3 Polymerization routes to PLA.From the Figure 3, polymerization routes to PLA are distributed as two processes, the first route is a polycondensation polymerization and the second route is a ring opening polymerization.The conventional process for synthesis of PLAThe production process to synthesize PLA by polycondensation of LA is the conventional process for making PLA. This process get to carry out under high vacuum and high temperature, solvent is used to extract the water through the condensation reaction (Avinc and Khoddami, 2009).However, PLA polymer products obtained tends to have low molecular weight. Therefore, the second route is improved by ring opening polymerization of LA which is condensed of water and then converted into cyclic dimer of LA or lactide for used as a monomer in ring opening polymerization. PLA polymer products obtained higher molecular weight than the first route and used milder conditions.Polymerization of PLA need to use a catalyst for supporting the conversion of LA to PLA. The catalysts are divided into two types, the first is the chemo-process which is the polymerization by used a alloy as a catalyst and the second is the bio-process which is the polymerization by used a LA-polymerizing enzyme as a catalyst.The chemo-process made the residues of heavy metals based catalysts, such as oxides of Zinc (Zn) and Stannum or Tin (Sn) which are toxicity. Furthermore, the process need high purity monomers, high temperature and high vacuum for serving conditions reactions. On the other hand, the bio-process used an enzyme based catalysts such as lipases which are non-toxic. Also, PLA polymer products can be used for biomedical and pharmaceutical applications. Moreover, polymerization reaction can be run under mild and environmentally-friend ly conditions (Taguchi et al., 2008 Lassalle and Ferreira, 2008 Hans et al., 2009).Process for synthesis of PLA by lipase-catalyzed polymerizationFrom the advantages of the bio-process or the enzymatic-catalyst polymerization, there are several researches attempts to synthesize PLA by used enzyme as catalyst such as lipase-catalyzed in the ring opening polymerization. The reaction of polymerization can be set up follow with the Figure 4. In the reactor intensify with LA, lipase, solvent and purge gas which is used for protection to pass by of the regeneration of PLA. Furthermore, the total reactions need to control the optimal temperature and reaction time.Figure 4 Polymerization reactions to synthesize PLA.The measurements which used to represent the properties of PLA polymer products are considered in several parameters. The important of evaluations are the conversion of LA, the molecular weight of PLA polymer products, the recovery of PLA and the recovery of lipases at the end o f reactions.Influence of several factors for the polymerizationProduction of a good PLA, must be use a good set up reaction of polymerization. Otherwise, the ferment of the several factors such as a kind of lipases, enzyme concentration, monomer concentration and temperature needs to be considered together.Influence of the kind of lipaseLassalle et al. (2008) researched the influence of the kind of lipase for the synthesis of polylactic acid (PLA) by using the three kind of lipases as biocatalysts. Porcine pancreatic lipase (PPL) from mammalian, Candida antarctica lipase B (Immobilized CAL-B) from fungal, and Pseudomonas cepacia (PCL) from bacterial origin were used in the experiment. The reaction was carried out by operating of LA, lipase, and solvent at 60 oC for 96 h. The performance of the three lipases was evaluated in a term of the conversion of LA to PLA and expressed as destiny (%) conversion.Table 2 Conversion (%) of LA, isolated enzyme after reaction, recovered PLA, and molecular weight (Mn) (Da) as a function of the kind of the different lipase.Enzyme% Conversion% recovered PLA% recovered lipaseMn(Da)Imm.CAL-B585585446PCL881234400PPL96290768Source Lassalle and Ferreira (2008)The result was presented in the Table 2, using the immobilized CAL-B as catalyst obtained 58% conversion of LA, 55% recovered PLA, 85% recovered lipase, and 446 Da of Molecular weight. For using PCL as catalyst obtained 88% conversion of LA, 12% recovered PLA, 34% recovered lipase, and 400 Da of Molecular weight. For using PPL as catalyst obtained 96% conversion of LA, 2% recovered PLA, 90% recovered lipase, and 768 Da of Molecular weight.From the result found that higher conversion levels were measured in the case of soluble enzymes, but besides traces of solid polyesters were recovered in this cases. In contrast, amounts of solid PLA were recovered using immobilized CAL-B, and the conversion was lower than soluble lipases. For the ending of the experiment, the immobilized CAL-B was the most effective biocatalyst with 60% conversion of LA and 55% recovered solid polymer in the reaction working at 60 oC for 96 h.Influence of the enzyme concentrationThere are several researches used the immobilized CAL-B lipase for esterification reaction due to its high catalytic activity but it does not propagate in polymerization reaction. So, Hans et al. (2009) researched to confirm the synthesis of PLA by immobilized CAL-B (Novozyme 435) catalyst in ring opening polymerization of lactide. The reaction was improved by adding nitrogen gas into the reactor for protected regeneration of PLA to LA and used toluene as a solvent for enzymatic polymerization. The objective of this study is find an optimal reaction condition such as enzyme concentration, monomer concentration and optimal temperature.Figure 5 Lactide conversion as a function of reaction time for the ring opening polymerization of DD-lactide at 70 oC with a monomer to toluene ratio of 12 (gmL) and use differe nt concentration of Novozyme 435.The first factor is influence of the enzyme concentration. The result was presented in Figure 5, the overall monomer conversion increases when increasing amounts of enzyme. The reaction catalyzed with 25 wt.-% of enzyme up to 100% monomer conversion after 2 days, while the reaction catalyzed with 10 wt.-% of enzyme up to only 25% monomer conversion.Figure 6 Molecular weight as a function of conversion plots for the ring opening polymerization of DD-lactide at 70 oC with a monomer to toluene ratio of 12 (gmL) and use different concentration of Novozyme 435.In contrast, the relation of molecular weight and conversion are represented in Figure 6. The result found that 25 wt.-% of enzyme obtained the molecular weight of PLA lower than 15 wt.-% of enzyme and 10 wt.-% of enzyme at the same conversion due to higher enzyme concentrations have more water which is introduced into the reaction and leads to a decrease of the molecular weight.Amounts of water wit hin the reaction have an influence for the molecular weight PLA polymer products (Hans et al., 2009). The normal of reaction for synthesis PLA by lipase-catalyst distribute into 3 step, the first step is the monomer activation which is the combination of lipases and lactic acid (LA), then the lipase-LA combine with water for extension of pre-polymer and release the component of lipase-OH in the initiation step, the last step is the chain propagation which increase the number of monomer within polymer chain. In any case, if there is a lot of water in the reaction, it will occur the conformation of the other component as free water and a linkage between lipase and water by loosely bound and tightly bound. The free water and lipase-water loosely bound can break the polymer chain in the initiation and affect to decrease a molecular weight of PLA polymer products.Influence of the monomer concentrationHans et al. (2009) studied influence of the monomer concentration by judge that increas ing monomer concentration, the polymerization rate and the overall monomer conversion will increase.Figure 7 Lactide conversion as a function of reaction time for the ring opening polymerization of DD-lactide at different monomer to toluene ratio (monomer concentration) at 70 oC with 15 wt.-% of Novozyme 435.From the Figure 7 discover at the monomer to toluene ratio 12 and 13, the high conversion increase and then decrease when the monomer concentration decrease. exception a monomer to toluene ratio 11, the conversion is also lower which might result from a poor solubility of the substrate and the precipitation of PLA.For the conclusion of the experiment, the immobilized CAL-B was the most effective biocatalyst with 33% of monomer was converted and could be isolated a polymer with 25% yield for a number-average molecular weight of 3,300 g mol-1.Influence of the temperatureFurthermore, Hans et al. (2009) expected that the temperature affect to PLA polymer products in ring opening p olymerization as show in the Figure 8.Figure 8 Lactide conversion as a function of reaction time for the ring opening polymerization of DD-lactide at different temperatures with 15 wt.-% of Novozyme 435 and a monomer to toluene ration 13.From the Figure 8 observed that increasing temperature, the monomer conversion decrease. At 80 oC and 90 oC, a monomer conversion does not exceed 25 % in 2 days while at 60 oC and 70 oC, a monomer conversion reaches somewhat 60 % and at 50 oC, a monomer conversion reach to 80 %.In the case of ring opening polymerization of lactide by lipase-catalyst at higher temperature might induce an enhanced deactivation of the enzyme which led to low monomer conversion.Figure 9 Number-average molecular weight as a function of temperature for the ring opening polymerization of DD-lactide at different monomer conversion with 15 wt.-% of Novozyme 435 and a monomer to toluene ratio 13.The relational of molecular weights and temperatures at different conversions a re presented in the figure 9, at 60 % and 50 % conversion obtained a highest molecular weights at 60 oC and fuddle off at higher temperatures. Explanation is an increase temperature release of free and loosely bound water which make denaturation of the enzyme. The other reason is a decrease in temperatures also induces a lower solubility of the polylactide and affect difficult to maintain a homogeneous solution.The improvement of process for lipase-catalyzed synthesis of PLAFrom the study about the influence of several factors for ring opening polymerization by lipase-catalyst observed that the enzymatic synthesis of PLA by use volatile organic compounds solvent do not encouraging due to a poor solubility of the substrates in polymerization reactions. In addition, the high temperature to reach the melting point of LA at 92 oC-95 oC might cause partial enzyme deactivation (Garcia-Arrazola et al., 2009).Garcia-Arrazola et al. (2009) improved the polymerization reaction to obtain PLA by used supercritical carbon dioxide (scCO2) as a solvent replacement of the volatile organic compound (VOCs). The advantage of scCO2 is non-expensive, non-flammable, non-toxic, low melting point, low viscosity, high diffusion coefficient, and friendly in synthetic processes.Table 3 Results obtained for the ring opening polymerization of L-LA in scCO2 with20 % (w/v) of L-LA and initial water content (aw) 0.16.EntryBiocatalyst (wt%)Time (days)Polymer yield (%)11015.7021029.77310311.0341041.6451513.261535.1671555.358157