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Polylactic acid ( PLA ) , the biodegradable polymer, has received increasing attending as alternate stuffs in packaging and biomedical applications. The general method for synthesis of PLA utilizing chemical-catalyzed polymerisation produces the accelerators residues which are toxicity. Therefore, the enzymatic polymerisation is a green alternate method to diminish this job. Several researches attempt to better the optimum status for synthesis of PLA by utilizing lipase as enzymatic-catalyzed.

For an illustration, Lassalle et Al. ( 2008 ) reported the synthesis of PLA

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by utilizing lipase as biocatalyst and focused on the process. The consequences found that immobilized CAL-B was the most effectual biocatalyst with 60 % LA transition

and 55 % recovered solid polymer in the reaction working at 60 & A ; deg ; C for

96 h. Furthermore, Hans et Al. ( 2009 ) researched to corroborate the mild reactions conditions for the ring-opening polymerisation of lactides by utilizing Novozyme 435 ( immobilized CAL-B ) 12 % wt. concentration in methylbenzene to synthesise the polymer at 70 & A ; deg ; C, D-lactide was catalyzed and 33 % of monomer was converted and could be isolated a polymer with 25 % output for a number-average molecular weight of 3,300 g mol-1. Finally, Garcia-Arrazola et Al. ( 2009 ) reported the synthesis of poly-L-lactide by used immobilized

CAL-B ( Novozyme 435 ) as biocatalyst for the ring-opening polymerisation of L-lactide at 65 & A ; deg ; C could be achieved utilizing supercritical C dioxide ( scCO2 ) . The L-lactide monomer could be converted as the PLA with a molecular weight 12,900 g mol-1 under the status at a biphasic scCO2/organic liquid system media and the optimum of temperature for the lipase activity. All of these present surveies are the fresh path to bring forth the polylactic acid and associate betterment of the new biomaterials.

Table OF CONTENTS

Page

Table OF CONTENT I

List OF TABLES two

List OF FIGURES iii

Introduction 1

Lipase 1

Polylactic acid: PLA 2

Synthesis of polylactic acid: PLA 4

3.1 The conventional procedure for synthesis of PLA 4

3.2 Procedure for synthesis of PLA by lipase-catalyzed polymerisation 5

Influence of several factors for the polymerisation 6

Influence of the sort of lipase 6

Influence of the enzyme concentration 8

Influence of the monomer concentration 10

Influence of the temperature 11

The betterment of procedure for lipase-catalyzed synthesis of PLA 12

Decision 14

LITERATURE CITED 15

List OF TABLES

Table Page

Comparison of natural stuff type and possibility of recycling and

biodegradation between PLA and PET polymer 3

Conversion ( % ) of LA, isolated enzyme after reaction,

recovered PLA, and molecular weight ( Mn ) ( Da ) as a map of

the sort of the different lipase 7

Consequences obtained for the ring opening polymerisation of L-LA

in scCO2 with 20 % ( w/v ) of L-LA and initial H2O content ( aw ) & A ; lt ; 0.16 13

List OF FIGURES

Figure Page

1 Chemical construction of Polylactic acid: PLA 2

2 Life rhythm of PLA 3

3 Polymerization paths to PLA 4

4 Polymerization reactions to synthesise PLA 6

5 Lactide transition as a map of reaction clip for

the ring opening polymerisation of DD-lactide at 70 oC with

a monomer to toluene ratio of 1:2 ( g: milliliter ) and utilize different

concentration of Novozyme 435 8

6 Molecular weight as a map of transition secret plans for

the ring opening polymerisation of DD-lactide at 70 oC with

a monomer to toluene ratio of 1:2 ( g: milliliter ) and utilize different

concentration of Novozyme 435 9

7 Lactide transition as a map of reaction clip for

the ring opening polymerisation of DD-lactide at different monomer

to toluene ratio ( monomer concentration ) at 70 oC with 15 wt.- % of

Novozyme 435 10

8 Lactide transition as a map of reaction clip for

the ring opening polymerisation of DD-lactide at different

temperatures with 15 wt.- % of Novozyme 435 and a monomer to

toluene ration 1:3 11

9 Number-average molecular weight as a map of temperature

for the ring opening polymerisation of DD-lactide at different

monomer transition with 15 wt.- % of Novozyme 435 and

a monomer to toluene ratio 1:3 12

SYNTHESIS OF POLYLACTIC ACID

BY LIPASE-CATALYZED POLYMERIZATION

Introduction

Lipase

Lipases or triacylglycerol acylhydrolases EC 3.1.1.3 are hydrolase which catalyze the hydrolysis of triglycerides to glycerol and free fatty acids under aqueous conditions. In add-on, lipases catalyze the tranesterification of other esters under micro-aqueous conditions. The ability of lipases has received increasing attending for used as catalyze in a broad array of biotechnology industry, such as nutrient engineering, detergent, chemical industry, decorative, organic synthesis, biomedical scientific disciplines and pharmaceutical applications ( Gupta et al. , 2004 ; Treichel et al. , 2010 ) .

Lipases are produced by assorted workss, animate beings and micro-organisms. Many micro-organisms which are known as manufacturers of extracellular lipases, including bacteriums, barm, and fungi. Particularly, bacterial lipases and fungous lipases are most widely used as a category of commercial enzymes in many applications. The of import commercial microbial lipases are Achromobacter sp. , Alcaligenes sp. , Arthrobactersp. , Bacillus sp. , Burkholderia sp. , Chromobacterium sp. , and Pseudomonas sp. from bacterium which are used successfully in the market with several merchandises names, such as Lumafast, Lipomax, Combizyme and Greasex ( Gupta et al. , 2004 ) . Furthermore, fungi produces the of import commercial lipases are Rhizopus sp. , Aspergillus sp. , Penicillium sp. , Geotrichum sp. , Mucor sp. , and Rhizomucor sp. ( Treichel et al. , 2010 ) which are used in the market with many merchandises names, such as Lecitase, Lipozyme, and Novozym 435 ( CAL-B ) .

Of these, the lipases from microbic have a stableness, selectivity, and wide substrate specificity for cultivation such as an applications by used substances form oil factory effluent, abattoir effluent, agroindustrial waste and maize steep spirits

( Gupta et al. , 2004 ; Treichel et al. , 2010 ) . Therefore, the recent microbic lipases have gained particular industrial attending for used as biocatalyst in quickly turning biotechnology.

Polylactic acid

Polylactic acid or the short name is PLA is a thermoplastic aliphatic polyester which a man-made polymer based on lactic acid ( LA ) and have a coiling construction was shown in Figure 1. PLA derived from the agitation of renewable resources such as maize amylum, tapioca merchandises and sugar canes.

Figure 1 Chemical construction of Polylactic acid: PLA.

PLA has received increasing attending as alternate stuffs in packaging and biomedical applications due to PLA is a biodegradable polymer, it easy degrades by simple hydrolysis of micro-organisms under the appropriate conditions ( Garlotta, 2001 ; Avinc and Khoddami, 2009 ) . PLA has a high-strength, high-modulus, brightness, barrier belongingss and good wet direction as a consequence of its interesting for used in packaging and composite stuffs for vesture applications ( Garlotta, 2001 ) . Furthermore, PLA has a biocompatible and bioabsorbable belongingss which can be used for broad scope applications in biomedical and pharmaceutical engineering, such as surgical suturas, tissue technology scaffolds, absorbable bone home bases, unreal tegument, 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 make

a biodegradability, PLA is to be a more environmentally-friendly polymer than poly ethylene terepthalate ( PET ) which is derived from a man-made petrochemical-based stuffs due to PLA is lower nursery gas emanation and important energy nest eggs, PLA avoids the jobs related to fictile waste accretion. The consequence of comparing between PLA and PET polymer was shown in Table 1.

Table 1 Comparison of natural stuff type and possibility of recycling and biodegradation between PLA and PET polymer.

Indexs

PLA

Pet

Initial natural stuff base

Renewable works stock

Petroleum merchandises

Non-renewable resources

Recycling of polymer wastes

Entire recycling possible

Entire recycling possible

Biodegradation of polymer wastes

Entire

Does non degrade

Beginning: Avinc and Khoddami ( 2009 )

PLA merchandises are easy composted or recycled under appropriate conditions at the terminal of the merchandise life. The Figure 2 show the life rhythm of PLA stuff degrades foremost by microbic hydrolysis, so the C dioxide and H2O which obtained from reaction became the basic necessities for a new growing and taking 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 rhythm of PLA.

Synthesis of polylactic acid: PLA

The synthesis of PLA starts with the extraction of sugars ( e.g. , glucose and dextroglucose ) from natural substances which used as a substrate in agitation of lactic acid by micro-organisms. Lactic acid ( LA ) is the get downing stuff for the PLA production procedure, through polymerisation. There are two major paths to synthesise PLA from LA monomer which are showed in Figure 3 ( Avinc and Khoddami, 2009 ) .

Figure 3 Polymerization paths to PLA.

From the Figure 3, polymerisation paths to PLA are distributed as two procedures, the first path is a polycondensation polymerisation and the 2nd path is a pealing gap polymerisation.

The conventional procedure for synthesis of PLA

The production procedure to synthesise PLA by polycondensation of LA is the conventional procedure for doing PLA. This procedure demand to transport out under high vacuity and high temperature, dissolver is used to pull out the H2O through the condensation reaction ( Avinc and Khoddami, 2009 ) .

However, PLA polymer merchandises obtained tends to hold low molecular weight. Therefore, the 2nd path is improved by pealing opening polymerisation of LA which is condensed of H2O and so converted into cyclic dimer of LA or lactide for used as a monomer in pealing opening polymerisation. PLA polymer merchandises obtained higher molecular weight than the first path and used milder conditions.

Polymerization of PLA need to utilize a accelerator for back uping the transition of LA to PLA. The accelerators are divided into two types, the first is the chemo-process which is the polymerisation by used a metal as a accelerator and the 2nd is the bio-process which is the polymerisation by used a LA-polymerizing enzyme as a accelerator.

The chemo-process made the residues of heavy metals based accelerators, such as oxides of Zinc ( Zn ) and Stannum or Tin ( Sn ) which are toxicity. Furthermore, the procedure need high pureness monomers, high temperature and high vacuity for functioning conditions reactions. On the other manus, the bio-process used an enzyme based accelerators such as lipases which are non-toxic. Besides, PLA polymer merchandises can be used for biomedical and pharmaceutical applications. Furthermore, polymerisation reaction can be run under mild and environmentally-friendly conditions ( Taguchi et al. , 2008 ; Lassalle and Ferreira, 2008 ; Hans et al. , 2009 ) .

Procedure for synthesis of PLA by lipase-catalyzed polymerisation

From the advantages of the bio-process or the enzymatic-catalyst polymerisation, there are several researches efforts to synthesise PLA by used enzyme as accelerator such as lipase-catalyzed in the ring opening polymerisation. The reaction of polymerisation can be set up follow with the Figure 4. In the reactor compounded with LA, lipase, dissolver and purging gas which is used for protection to happen of the regeneration of PLA. Furthermore, the entire reactions need to command the optimum temperature and reaction clip.

Figure 4 Polymerization reactions to synthesise PLA.

The measurings which used to stand for the belongingss of PLA polymer merchandises are considered in several parametric quantities. The of import of ratings are the transition of LA, the molecular weight of PLA polymer merchandises, the recovery of PLA and the recovery of lipases at the terminal of reactions.

Influence of several factors for the polymerisation

Production of a good PLA, must be use a good set up reaction of polymerisation. Otherwise, the influence of the several factors such as a sort of lipases, enzyme concentration, monomer concentration and temperature demands to be considered together.

Influence of the sort of lipase

Lassalle et Al. ( 2008 ) researched the influence of the sort of lipase for the synthesis of polylactic acid ( PLA ) by utilizing the three sort 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 beginning were used in the experiment. The reaction was carried out by operating of LA, lipase, and dissolver at 60 oC for 96 h. The public presentation of the three lipases was evaluated in a term of the transition of LA to PLA and expressed as per centum ( % ) transition.

Table 2 Conversion ( % ) of LA, isolated enzyme after reaction, recovered PLA, and molecular weight ( Mn ) ( Da ) as a map of the sort of the different lipase.

Enzyme

% Conversion

% recovered PLA

% recovered lipase

Manganese

( Da )

Imm.CAL-B

58

55

85

446

PCL

88

12

34

400

PPL

96

2

90

768

Beginning: Lassalle and Ferreira ( 2008 )

The consequence was presented in the Table 2, utilizing the immobilized CAL-B as accelerator obtained 58 % transition of LA, 55 % cured PLA, 85 % cured lipase, and 446 Da of Molecular weight. For utilizing PCL as accelerator obtained 88 % transition of LA, 12 % cured PLA, 34 % cured lipase, and 400 Da of Molecular weight. For utilizing PPL as accelerator obtained 96 % transition of LA, 2 % cured PLA, 90 % cured lipase, and 768 Da of Molecular weight.

From the consequence found that higher transition degrees were measured in the instance of soluble enzymes, but merely hints of solid polyesters were recovered in this instances. In contrast, sums of solid PLA were recovered utilizing immobilized CAL-B, and the transition was lower than soluble lipases. For the decision of the experiment, the immobilized CAL-B was the most effectual biocatalyst with 60 % transition of LA and 55 % recovered solid polymer in the reaction working at 60 oC for 96 H.

Influence of the enzyme concentration

There are several researches used the immobilized CAL-B lipase for esterification reaction due to its high catalytic activity but it does non propagate in polymerisation reaction. So, Hans et Al. ( 2009 ) researched to corroborate the synthesis of PLA by immobilized CAL-B ( Novozyme 435 ) accelerator in pealing opening polymerisation of lactide. The reaction was improved by adding N gas into the reactor for protected regeneration of PLA to LA and used methylbenzene as a dissolver for enzymatic polymerisation. The aim of this survey is find an optimum reaction status such as enzyme concentration, monomer concentration and optimum temperature.

Figure 5 Lactide transition as a map of reaction clip for the ring opening polymerisation of DD-lactide at 70 oC with a monomer to toluene ratio of 1:2 ( g: milliliter ) and utilize different concentration of Novozyme 435.

The first factor is influence of the enzyme concentration. The consequence was presented in Figure 5, the overall monomer transition additions when increasing sums of enzyme. The reaction catalyzed with 25 wt.- % of enzyme up to 100 % monomer transition after 2 yearss, while the reaction catalyzed with 10 wt.- % of enzyme up to merely 25 % monomer transition.

Figure 6 Molecular weight as a map of transition secret plans for the ring opening polymerisation of DD-lactide at 70 oC with a monomer to toluene ratio of 1:2 ( g: milliliter ) and utilize different concentration of Novozyme 435.

In contrast, the relation of molecular weight and transition are represented in Figure 6. The consequence 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 transition due to higher enzyme concentrations have more H2O which is introduced into the reaction and leads to a lessening of the molecular weight.

Sums of H2O within the reaction have an influence for the molecular weight PLA polymer merchandises ( Hans et al. , 2009 ) . The normal of reaction for synthesis PLA by lipase-catalyst distribute into 3 measure, the first measure is the monomer activation which is the combination of lipases and lactic acid ( LA ) , so the lipase-LA combine with H2O for extension of pre-polymer and let go of the constituent of lipase-OH in the induction measure, the last measure is the concatenation extension which increase the figure of monomer within polymer concatenation. In any instance, if there is a batch of H2O in the reaction, it will happen the conformation of the other constituent as free H2O and a linkage between lipase and H2O by slackly bound and tightly bound. The free H2O and lipase-water slackly bound can interrupt the polymer concatenation in the induction and affect to diminish a molecular weight of PLA polymer merchandises.

Influence of the monomer concentration

Han dynasties et Al. ( 2009 ) studied influence of the monomer concentration by expected that increasing monomer concentration, the polymerisation rate and the overall monomer transition will increase.

Figure 7 Lactide transition as a map of reaction clip for the ring opening polymerisation of DD-lactide at different monomer to toluene ratio ( monomer concentration ) at 70 oC with 15 wt.- % of Novozyme 435.

From the Figure 7 observed at the monomer to toluene ratio 1:2 and 1:3, the high transition addition and so diminish when the monomer concentration lessening. Exclusion a monomer to toluene ratio 1:1, the transition is besides lower which might ensue from a hapless solubility of the substrate and the precipitation of PLA.

For the decision of the experiment, the immobilized CAL-B was the most effectual biocatalyst with 33 % of monomer was converted and could be isolated a polymer with 25 % output for a number-average molecular weight of 3,300 g mol-1.

Influence of the temperature

Furthermore, Hans et Al. ( 2009 ) expected that the temperature affect to PLA polymer merchandises in pealing opening polymerisation as show in the Figure 8.

Figure 8 Lactide transition as a map of reaction clip for the ring opening polymerisation of DD-lactide at different temperatures with 15 wt.- % of Novozyme 435 and a monomer to toluene ration 1:3.

From the Figure 8 observed that increasing temperature, the monomer transition lessening. At 80 oC and 90 oC, a monomer transition does non transcend 25 % in 2 yearss while at 60 oC and 70 oC, a monomer transition reaches about 60 % and at 50 oC, a monomer transition range to 80 % .

In the instance of pealing opening polymerisation of lactide by lipase-catalyst at higher temperature might bring on an enhanced inactivation of the enzyme which led to low monomer transition.

Figure 9 Number-average molecular weight as a map of temperature for the ring opening polymerisation of DD-lactide at different monomer transition with 15 wt.- % of Novozyme 435 and a monomer to toluene ratio 1:3.

The relation of molecular weights and temperatures at different transitions are presented in the figure 9, at 60 % and 50 % transition obtained a highest molecular weights at 60 oC and drop off at higher temperatures. Explanation is an addition temperature release of free and slackly bound H2O which make denaturation of the enzyme. The other ground is a lessening in temperatures besides induces a lower solubility of the polylactide and affect hard to keep a homogenous solution.

The betterment of procedure for lipase-catalyzed synthesis of PLA

From the survey about the influence of several factors for pealing opening polymerisation by lipase-catalyst observed that the enzymatic synthesis of PLA by usage volatile organic compounds solvent do non promoting due to a hapless solubility of the substrates in polymerisation reactions. In add-on, the high temperature to make the runing point of LA at 92 oC-95 oC might do partial enzyme inactivation ( Garcia-Arrazola et al. , 2009 ) .

Garcia-Arrazola et Al. ( 2009 ) improved the polymerisation reaction to obtain PLA by used supercritical C dioxide ( scCO2 ) as a solvent replacing of the volatile organic compound ( VOCs ) . The advantage of scCO2 is non-expensive, non-flammable, non-toxic, low runing point, low viscousness, high diffusion coefficient, and friendly in man-made procedures.

Table 3 Consequences obtained for the ring opening polymerisation of L-LA in scCO2 with

20 % ( w/v ) of L-LA and initial H2O content ( aw ) & A ; lt ; 0.16.

Entry

Biocatalyst ( wt % )

Time ( yearss )

Polymer output ( % )

1

10

1

5.70

2

10

2

9.77

3

10

3

11.03

4

10

4

1.64

5

15

1

3.2

6

15

3

5.16

7

15

5

5.35

8

15

7

& A ; lt ; 1

Beginning: Garcia-Arrazola et Al. ( 2009 )

The consequence from this betterment of procedure by usage scCO2 as a dissolver was presented in the Table 3, the pealing opening polymerisation of LA at 10 wt % of enzyme obtained highest output of PLA as 9.77 % and 11.03 % in 2 yearss and 3 yearss severally. When addition sums of enzyme to 15 wt % , polymer output was lower than 10 wt % of enzyme with obtained highest output of PLA merely 5.16 % and 5.35 % in 3 yearss and 5 yearss severally.

The experiment pointed out that 10 wt % of the immobilized CAL-B in the ring gap polymerisation for synthesis of PLA by usage scCO2 at 300 saloon and 65 oC is the most appropriate status to obtain PLA with a molecular weight as 12,900 g mol-1.

Decision

Polylactic acid ( PLA ) is a biodegradable which derived from renewable resources. The synthesis of PLA from pealing opening polymerisation of lactic acid ( LA ) start at polycondensation of LA for obtain lactide formation, so lipase catalyse the reaction for obtain PLA. Using lipase-catalyst in pealing opening polymerisation is the environmentally-friendly reaction due to lipase-catalyst is non-toxic and can be run under a mild status. Furthermore, PLA polymer merchandise can be used in biomedical and pharmaceutical applications.

The appropriate of synthesis of PLA from LA by usage lipase as biocatalyst must see in several factors such as the sort of lipase, enzyme concentration, monomer concentration, reaction temperature and the sort of dissolver. Performance and belongingss of PLA need to see in the molecular weight at the first, due to the applications of PLA depends on the molecular weight which related with the belongingss of PLA merchandises applications.

LITERATURE CITED

Avinc, O. and A. Khoddami. 2009. Overview of poly ( lactic acid ) ( PLA ) fiber ; Part I: production, belongingss, public presentation, environmental impact, and end-use application of poly ( lactic acid ) fibres. Fibre Chemistry. 41 ( 6 ) : 391-401.

Garcia-Arrazola, R. , D.A. Lopez-Guerrero, M. Gimeno and E. Barzana. 2009.

Lipase-catalyzed synthesis of poly-L-lactide utilizing supercritical C dioxide.

J. Supercritical Fluids 51: 197-201.

Garlotta, D. 2001. A literature reappraisal of poly ( lactic acid ) . J. Polymers and the Environment. 9 ( 2 ) : 63-84.

Gupta, R. , N. Gupta and P. Rathi. 2004. Bacterial lipases: an overview of production, purification and biochemical belongingss. Appl. Microbiol. Biotechnol. 64: 763-781.

Han dynasties, M. , H. Keul and M. Moeller. 2009. Ring-opening polymerisation of D-lactide catalyzed by Novozyme 435. Macromolecular Biosci. 9: 239-247.

Lassalle, V.L. and M.L. Ferreira. 2008. Lipase-catalyzed synthesis of polylactic acid: an overview of the experimental facets. J. Chem. Technol. Biotechnol. 83: 1493-1502.

Taguchi, S. , M. Yamada, K. Matsumoto, K. Tajima, Y. Satoh, M. Munekata, K. Ohno,

K. Kohda, T. Shimamura, H. Kambe and S. Obata. 2008. A microbic mill for lactate-based polyesters utilizing a lactate-polymerizing enzyme. PNAS. 105 ( 45 ) : 17323-17327.

Treichel, H. , D. Oliveira, M.A. Mazutti, M.D. Luccio and J.V. Oliveira. 2010. A reappraisal on microbic lipases production. Food Bioprocess Technol. 3: 182-196.

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