An Overview Of Lactic Acid Environmental Sciences Essay

Lactic acid has been produced on a industrial graduated table since the terminal of the 19th century chiefly to back up the demands of legion application were made from lactic acid such as in pharmaceutical, nutrient, leather and fabric industries ( Averous, 2008 ) . The demand for lactic acid tends to increase due to increasing application in readying of biodegradable polymers, medical suturas and green dissolvers ( Datta et al. , 1995 ; Litchfield, 1996 ) . Lactic acid ( I±-hydroxypropionic acid ) used as a substrate in the synthesis of poly lactic acid ( PLA ) , belongs to the hydroxyacids and it is characterised by greater sourness than acerb devoid of hydroxy groups since the presence of hydroxy well facilitates the dissociation of carbonyl groups ( Dutkiewicz et al.,2003 ) . Chemical such as acrylic acid, propene ethanediol, ethanal and 2-3 pentanedone were converted from lactic acid due to both hydroxyl and carboxyl groups that have high responsiveness ( Hurok et al. , 2004 ) .

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2.1.2 History of Lactic Acid

Historically, lactic acid was discovered in 1780 as constituent of rancid milk A by Swedish chemist, Carl Wilhelm Scheele ( Jim et al. , 2010 ) . The Gallic scientist Fremy produced lactic acid by agitation and this gave rise to industrial production in 1881. The lactic acid production was around 5,000 kilograms per twelvemonth and in 1982, it was about 24,000 to 28,000 metric metric tons per twelvemonth ( Naveena, 2004 ) . By 1990, the world-wide production volume of lactic acid had grown to about 40,000 metric metric tons per twelvemonth with two important manufacturers, CCA Biochem in The Netherlands, with subordinates in Brazil and Spain, and Sterling Chemicals in Texas City, TX, USA, as the primary makers ( Rojan et al. , 2007 ) .

Furthermore, Cargill joined forces with Dow Chemical and established a Cargill-Dow polylactic acid ( PLA ) polymer venture based on carbohydrate agitation engineering in late 1997 and brought out Dow from this joint venture and established NatureWorks LLC as a entirely owned subordinate in early 2005 ( Wee et al. , 2006 ) . NatureWorks LLC has late constructed a major lactic acid works in Blair, NE, USA, with a nameplate capacity of 300 million lbs per twelvemonth for the production of lactic acid and PLA, and it began runing in late 2002 ( Wee et al. , 2006 ; Datta and Henry 2006 ) . For merchandise commercialisation, they have partnered with many possible end-users and polymer processing equipment makers.

2.1.3 Properties of Lactic Acid

Lactic acid is a carboxylic acid incorporating three C organic acid: one terminus C atom is portion of an acid or carboxyl group ; the other terminal C atom is portion of a methyl or hydrocarbon group ; and a cardinal C atom holding an intoxicant C group ( Narayanan et al. , 2004 ) . Harmonizing to Narayanan ( 2004 ) , it is colorless to yellow liquid in which exists in two optically active isomeric lactic acid ( or it esters or amides ) may undergo are xanthation with C bisulphide, esterification with organic acids and dehydrogenation or oxygenation to organize pyruvic acid or its derived functions. Lactic acid is soluble in H2O and H2O mixable organic dissolvers but indissoluble in other organic dissolvers. It exhibits low volatility.

( B )

Figure 2.1: ( a ) L ( + ) Lactic acid and ( B ) D ( – ) Lactic acid ( Narayanan et al. , 2004 )

Table 2.1: physical belongingss of lactic acid ( Chemicalbook. Inc, 2008 and Narayanan et al. , 2004 ) .

Molecular weight

90.08 g/mol

Melting point

16.8 oC

Boiling point

82 oC at 5mmHg

122 oC at 14mmHg

Dissociation invariable, Kaat 25 oC

1.37 X 10-4

Heat of burning, a?†HC

1361 KJ/ mole

Specific Heat, Cpat 20 oC

190 J/mole/oC

2.2 Synthesis of PLA

The synthesis of PLA is a multistep procedure which starts from the production of lactic acid. There are two methods of synthesis which are the polycondensation of L ( + ) lactic acid and ring-polymerization ( ROP ) of the dimer signifier of lactic acid, lactide which carried out in majority or in solution ( Dutkiewicz et al. , 2003 ) .According to Jim ( 2010 ) , polymerisation of PLA has been conducted since 1932 and both of the procedure ( polycondensation or ROP ) rely on extremely purified polymer-grade lactic acid or lactide to bring forth PLA with a good quality, high molecular weight and high output. However, the production procedure, the output and the feature of PLA are influenced by the petroleum lactic acid with drosss whether it is chemical or optical pureness ( Garlotta, 2001 ; Mehta et al. , 2005 ; Henton et al. , 2005 ) .Thus, purification of lactic acid from agitation is decisive importance.

2.2.1 Polycondensation

Polycondensation or besides known as azeotropic condensation is a good studied polymerisation path conducted since 1994. The outstanding accomplishments in this field belong to Nipponese scientist ( Ajioka et al. , 1995 ) . Basically, the polycondensation of lactic acid used azeotropic distillment in a refluxing, aprotic dissolver consequences in PLA with low weight-average molecular weights about 300,000 ( Enomoto et al. , 1994 ; Kashima et al.,1995 ; Ohta et al.,1995 ) . It is hard to obtain high molecular weights in a solvent free system, but it has advantage that the polymer has a low cost.

Furthermore, the proper choice of accelerator in polycondensation is really of import. It is because it activates the desiccating reaction, deactivated the formation of lactide and increases the molecular weight ( Orozco et al. , 2007 ) . Orozco ( 2007 ) proposed that the accelerator activity is indispensable since it can alter the mutual opposition of the polycondensation system. Initially, lactic acid and its primary condensates have high mutual opposition since they are all consist both carboxyl and hydroxyl groups in a high ratio, while the concluding PLA contained of less polar ester group, taking to great lessening of mutual opposition, so it is really important to add the accelerator after desiccation of lactic acid and the formation of oligo ( lactic acid ) ( Moon et.al. , 2000 ) .

2.2.2 Ring-polymerization method

The ring-polymerization of the dimer signifier of lactic acid is a man-made tract that eliminates the usage of dissolvers. The procedure starts with a uninterrupted condensation reaction of lactic acid to bring forth low molecular weight PLA pre-polymer, which is so converted to a mixture of lactide stereoisomers utilizing Sn accelerators to heighten the rate and selectivity of intramolecular cyclization reaction ( Henton et al. , 2005 ) . The lactide is purified by vacuity distillment and ring-open polymerized in the thaw with a Sn accelerator. Upon completion of polymerisation, the unreacted lactide is removed by vacuity and recycled to the beginning of the procedure ( Averous, 2008 )

Figure 2.2: Synthesis methods for high-molecular-weight PLA ( Garlotta, 2001 )

2.3 Polylactic Acid ( PLA )

Nowadays, most plastics are derived from non renewable resources such from petroleum oil which is non environmental friendly. This has lead to the research on bring forthing biodegradable polylactic acid from renewable energy such as works ( Garlotta, 2001 ) . The other term of polylactic acid is known as polylactide, a biodegradable polymer with good belongingss such as mechanical strength, transparence, compostability, environmental safety and biocompatibility. PLA has assorted applications in industry which include the composite fabrication industry. The entire ingestion of biodegradable polymers such PLA are 14000 to 85000 m ton from 1996 to 2005 and it is projected that the ingestion will be double by 2010 ( Auras et al. , 2004 ) .

2.3.1 Properties of PLA

Polylactic acid ( PLA ) belongs to the household of aliphatic polyesther normally made from I±-hydroxy acids. It is one of few polymers in which the stereochemical construction can be easy modified by polymerising a controlled mixture ofland D-isomers ( Averous, 2008 ) . Lim ( 2008 ) claimed that polylactic acid can replaced polyolefin group in production of many stuffs due to its good physical belongingss if compared to polystyrene. This is because polylactic acid obtained high modulus and strength but low stamina. In add-on, polylactic acid able exhibit crystallinity behavior which depends on its monomer stereochemistry ; isotactic poly ( S-lactide ) is crystalline thermoplastic with passage temperature ( Tg ) about 60oC and runing temperature ( Tm ) 170oC to 180oC while ataxic polylactic acid has shown formless province behavior ( Lim et.al.,2008 ) .

Harmonizing to the figure 2.2, comparing of Tg and Tm value for polylactic acid with other thermoplastic stuffs were made and polylactic acid tend to hold comparatively high Tg and low Tm.

Figure 2.3: Comparison of glass passage and runing temperatures of PLA with other thermoplastics. ( Lim et al.,2008 )

PLA is a thermoplastic, high strength, high modulus polymer that have undergoes thermic debasement at temperature above 200 oC by hydrolysis, lactide reformation, oxidative chief concatenation scission and inter-or intramoleculat transesterification reactions ( Garlotta, 2001 ) . Its molecular weight is adjusted either through polycondensation polymerisation or pealing polymerisation method. High molecular weight of PLA is usually between 15,000 to 500,000 g/mol.

A

PLA

Pet

PS

Hip

PP

Tg ( C )

55

75

105

A

-10

Density ( g/cc )

1.24

1.33

1.05

A

0.9

Heat capacity ( BTU/lb- F )

0.39

0.44

0.54

A

0.3

Thermal Conductivity ( BTU/hr.lb.F )

0.075

0.105

0.121

A

0.068

Notched Izoc ( ft-lb/in )

0.24

2.6

0.5

2.3

2

Gardner Impact ( in-lb )

0.5

2.8

4.5

100

7

Tensile Strenght @ Break ( pounds per square inch )

7700

7900

6500

3300

4500

Tensile Modulus ( kpsi )

500

400

420

300

130

% Elongation

6

130

7

45

120

Table 2.2: Comparison of PLA belongingss to several crude oil based rosins ( Dorgan et al. , 2001 ) .

2.4 Kenaf fiber as natural stuff

Several natural stuffs have been evaluated as possible cheap substrates for lactic acid production. It is often derived from provender stocks such as maize, Beta vulgaris sugar, molasses, whey, and barley malt ( Narayanan et al. , 2004 and Maas et al. , 2008 ) . However these natural stuffs draw less economical for long term since it has viing nutrient value. Due to this issue, lignocellulosic biomass such deccan hemp fiber is chosen. Indeed, it is cheap and widely available renewable C beginning, natural, and organic with assorted possible applications.

2.4.1 Introduction

Kenaf ( Hibiscus cannabinus L ) is a warm season one-year fiber and non nutrient harvest.It is a member of household Malvaceae and found to be the 3rd largest fibre harvest of economic importance after cotton and jute ( Starr and Page 1990 ; Adegbite et al. , 2005 ) . Kenaf offers singular for both the production of industrial natural stuffs and as bio-fuel. Due to planetary environmental issues and unequal natural fiber resources, scientists worldwide have realise and begun to research the full potency of deccan hemp and its diverse utilizations ( Keshk et al. , 2006 ) . Kenaf in Malaysia was officially introduced in 2008 by former premier curate of Malaysia, Tun Abdullah Ahmad Badawi. During that clip, he announced and launched the East Coast Economic Regions ( ECER ) Kenaf Centre for aggregation, treating packaging and distribution in Bachok, Kelantan due to immense graduated table production and possible usage of deccan hemp for the industry. This fantastic harvest besides identified by National Tobacco Board, Malaysia to be an first-class addendum to tobacco but non to replace it ( Intropa, 2008 ) .

2.4.2 History

Historically, deccan hemp is believed to hold originated from Africa since it is grown as nutrient harvest in several African states. Harmonizing to Adegbite ( 2005 ) , it is most likely originated from Sudan and normally cultivated for both nutrient and fiber in West Africa. However, Kobayashi ( 1991 ) and Keshk ( 2006 ) claimed that it is believed to hold had its beginning in antediluvian Africa ( Western Sudan ) and have been cultivated in Egypt every bit early as 4000 BC. Furthermore, India has produced and used deccan hemp for the last 200 old ages, while Russia started bring forthing deccan hemp in 1902 and introduced the harvest to China in 1935 ( Dempsey, 1975 ; Weeber and Bledsoe 2002 ) . United States begun to demo their involvement on deccan hemp in 1941 ‘s after World War II when the import of jute was shut off ( Rymsa, 1999 ) . Get downing from that clip, research and production of deccan hemp has begun due to its possible to replace jute. The United States Department of Agriculture ( USDA ) had determined kenaf as a assuring “ new ” harvest. As a consequence of the New Crops, New Uses plan started in the 1950 ‘s and early 1960 ‘s by the President Dwight David Eisenhower.

Kenaf besides was determined to be the first-class cellulose fibers beginning for a big scope of paper merchandises such as newspaper and bond paper ( Weeber and Bledsoe, 2002 ) . Many research and development were done in 1990 ‘s which demonstrated deccan hemps suitableness for usage in edifice stuffs, adsorbents, fabrics, farm animal provender, and fibers in new and recycled plastics ( Bledsoe and Webber,2001 ; Webber and Bledsoe, 2002 ) .

2.4.3 Kenaf ‘s description and its application

Kenaf is largely unbranching and quickly reaches adulthood, in merely 4 to 5 months the workss can turn to 2 to 5 meters tall. Leafs are separately stalked and lobed to some grade. Flowers are xanthous or white with a ruddy Centre and can be up to 10cm in diameter. Fruits are heavy ; bring forthing seed capsules 1cm long incorporating many seeds. Seeds are brown and cuneus shaped, 5mm long with a 1000-grain weight of 25g ( Weeber and Bledsoe, 2002 ; Mache 2002 ) .

The traditional utilizations of kenaf focal point on its production for fiber used in doing rope, pokes, canvas and rugs ( Kaldor and Verwest, 1990 ) . The foliages may be comestible to both animate beings and worlds where they can be used as herbs in some dishes ( Mache, 2002 ) . Due to planetary environmental issues and inadequate of natural fibers resources, scientists explored the new diverse usage of deccan hemp. In such instance, kenaf fiber in both retted and natural signifiers is used in the industry cordage and newspaper. Leafs and little subdivisions have high digestibleness when land and can be used as beginning of fiber and protein for farm animal ( Wildeus et al. , 1995 ) . Other new applications of deccan hemp that had been discovered were in the mush and paper industry, for oil soaking up, as a potting medium, in the industry of broadcloth, in filtration, and as an additive in carnal provender ( Sellers and Reichert, 1999 ; Keshk et. al. , 2006 ) .

A new usage for deccan hemp was tested in July 1987, when paper made from kenaf fiber was used to publish 83,000 transcripts of the Bakersfield Californian newspaper ( Robinson, 1988 ) . Reports indicate that the paper has first-class ink-retention features and its high strength is good suited to new high-velocity imperativenesss. KP Products Inc. assumed name Vision Paper has been bring forthing and marketing paper merchandises made from 100 % deccan hemp fiber and from blends of deccan hemp fiber and recycled paper since 1992 ( Rymsza, 1998 ) . Rymsza ( 1999 ) claimed that about 80 % bast and 20 % nucleus of deccan hemp used in pulping as the whole chaff pulping of deccan hemp appears to offer the best economic sciences for the papermaker. Then this pulping procedure was continued with a single-stage H peroxide ( H2O2 ) bleach procedure. As a consequence, stronger, brighter, and cleaner pages documents were produced. ( Sanadi et al.,1995 ) .

Among the several applications of deccan hemp merchandises, at the present it is an involvement as biomass harvest for energy production, since output can make 22.75 t per hour angle of fresh stuff ( Danalatos and Archontoulis, 2005 ) . Furthermore, deccan hemp is besides utilized in composite industry. It becomes natural fibers composite stuff in which it is able to replace fiberglass and reinforce plastics as to fabricate medium denseness fibre board and particleboard. Due to that extend, Panasonic Malaysia has taken the chance to fabricate kenaf fibre boards and so export them to Japan. The initial purpose is to accomplish 1000 dozenss exported per month but this will anticipate to duplicate one time cargos to Japan get down ( Graupner et al. , 2009 ) .

2.4.4 Properties of deccan hemp

Kenaf ‘s belongingss fundamentally identified based on its constituent which includes chaffs, foliages, flowers, seeds, bast and nucleus. For illustration, Kenaf stalk outputs usually in the scope from 11 to 18 metric tons t per hour angle, oven dry weight while its foliages produced with saw-toothed borders on the chief chaff ( root ) and along the subdivisions. The place of these foliages alternate from side to side on the chaff and subdivisions. As the deccan hemp works matures and extra foliages are produced, the newer leaves start to distinguish into the leaf form feature ( Weeber and Bledsoe, 2002 ) .

Harmonizing to Mache ( 2002 ) , kenaf is best suited to the Torrid Zones or semitropicss where the average day-to-day temperature during the turning season is more than 20°C ; it is besides sensitive to photoperiod. The length of the turning season, the mean twenty-four hours and dark temperatures, and equal dirt wet are considered the cardinal elements impacting deccan hemp outputs. Furthermore, kenaf contain less lignin ; come close 9 % less than pine, approximately 10 % of hemicellulose and about 30 % cellulose.

Furthermore, deccan hemp ‘s production can be increased on widely changing dirt types. It can be besides adapted to a broad climatic scope even though the harvest is frost stamp. However, its production is hence limited to warm temperate zones through to the equator and this state of affairs is non bucked up North of southern Europe. Optimum temperatures for growing of deccan hemps are 15oC to 27°C. However, its average day-to-day temperatures which are above 20°C are favorable throughout the turning season ( Lapenta et al. , 1993 ; Mache, 2002 ) .

The advantages of deccan hemp as a beginning of mush and papermaking include: 1 ) it has a short turning rhythm of 120 to 130 yearss every bit compared to 13 to 16 old ages for trees ; 2 ) the possibility of turning two harvests per twelvemonth the under certain conditions ; 3 ) it has less lignin than soft or difficult forests ; 4 ) good growing or output with irrigation H2O in warm dry countries ; 5 ) its production costs that are half that of pulpwood and 6 ) the utilizations of deccan hemp in the newspaper industry will deter the depletion of woods and importing of wood mush from other states to Nigeria ( Adegbite et al. , 2005 ) .

2.5 Lignocellulose

Lignocellulose has great possible as a renewable feedstock or natural stuffs for production of high value biodegradable polymers and chemical via biological agitation. The illustrations of lignocellulosic stuffs are wood agricultural harvests, like jute or deccan hemp ; agricultural residues, such as bagasse or maize chaffs ; grasses ; and other works substances ( English et al. , 1994 ) . It represents the largest reservoir of organic C fixed by green works and signifiers structural model of the works cell palisade itself. The major constituent of lignocelluloses stuffs are polyoses ( cellulose and hemicelluloses ) and lignin.

Cellulose is the most abundant component and renewable biopolymers found in works as micro filaments ( 2 to 20 nanometers diameter and 100 to 40,000 nanometers long ) such as wood ( 30-40 % ) , paper, linen and cotton ( over 90 % ) ( Walford, 2008 and Nishiyama, 2009 ) . Harmonizing to Teter ( 2006 ) and Walford ( 2008 ) , it is homo polysaccharide composed wholly of I?-1,4-glucosidic linked glucose monomers and hydroglucopyronose polymer ( six-carbon sugars ) . The molecular weight of different cellulose can run from 200 to 2000 kDa where the figure of glucose residue can transcend 15, 000 per polymer molecule. Cellulose has such additive construction which enables the formation of extended H adhering due to the collection of overlapping, staggered glucose level sheets into non-water-soluble crystalline filaments which is extremely intractable ( Ding and Hemmel, 2006 ; Teter et Al. 2006 ; Walford, 2008 ) . Lone agents that can assail the glycosidic linkages between glucose residues or which can interrupt the H bonding can solubilise cellulose. This is because of the combination of construction and H bonding give the cellulose a high tensile strength other than makes it resistance against microbic onslaught and indissoluble in most dissolver ( Teter et al.,2006 and Walford 2008 ) .

Figure 2.4: Partial construction of cellulose ( Lee, 2003 )

Following, hemicelluloses which are works cell wall heteropolymeric sugars and sugar acids with a anchor of 1,4 linked I?- D pyranosyls in which O4 is in equatorial orientation ( Teter et al. , 2006 ) . Hemicelluloses are normally shorter than cellulose typically incorporating a figure of different sugars including both hexose ( glucose, mannose and galactose ) and pentoses ( xylose and arabinose ) since its major constituent is xyloglucan, a beta- ( 1a†’4 ) linked polymer of xylose with mono- , di- , or triglycosyl side ironss, via O6 composed of assortment substituent such as ethanoyl group, arabinosyl or glucuronosyl units ( Saha, 2003 ) . Other than that, Teter ( 2006 ) pointed out that it is normally consist of fewer than 200 1,4 linkage, low grade of polymerisation ( typically below 200 ) , extremely branched and easy hydrolyzed by acid or base. Furthermore, hemicellulose serves as the interface between cellulose and lignin in works cell walls and may organize covalent and non covalent linkages with other cell wall components such as pectin, glucans and proteins. It is classified harmonizing to the chief sugar in polymer anchor ; for illustration xylan and mannan ( Sun et al. , 2004 and Walford 2008 ) .

Furthermore, lignin is a complex three dimensional polymer formed by carbon-carbon or ether bonds between phenylpropane units ( Walford, 2008 ) . It is a extremely complex, formless and heterogeneous consisting syringyl, guaiacyl and p- hydroxyphenol constituent which is embedded in the hemicellose and cellulose. This polymers is extremely immune to enzymatic, chemical, and microbic hydrolysis because of its extended cross associating ( Teter et al. , 2006 and Walford 2008 ) .

2.6 Pre-treatment

Lignocellulosic stuffs such as deccan hemps fibre contain many different constituents which include polyoses, protein, lignin, lipoids and minerals. The major constituents are polyoses in the signifiers of cellulose ( 40 to 50 % ) and hemicellulose ( 25 to 30 % ) and, lignin ( 25 to 30 % ) ( Teter et al. , 2006 ) . However, cellulose tends to organize filaments which are embedded in supermolecules of hemicelluloses and lignin thereby make it of course resistant to breakdown to its structural sugars ( Zahedifa,1996 and Zhou, 1997 ) .

Cellulase enzyme is normally used to catalyse the lignocellulosic stuffs. However, the enzyme debasement rate of lignocelluloses stuffs which is low because of the immune crystalline construction of cellulose and the physical barrier formed by lignin that surrounds the cellulose ( Mc Millan,1994 ; Mtui et Al, 2009 ) . Mtui ( 2009 ) claimed that pre-treatment procedure such hydrolysis is an indispensable requirement to interrupt the lignin seal and thereby heightening the susceptibleness of lignocellulosic stuffs to enzyme action. Efficient pre-treatment reduces the lignin content, cellulose crystallinity and increase the surface country for enzymatic reactions ( Millett et al. , 1975 and Mtui 2000 ) .

The end of the pre-treatment procedure is to take lignin and hemicellulose, cut down the crystallinity of cellulose, and increase the porousness of the lignocellulosic stuffs. Pre-treatment must run into the undermentioned demands:

( 1 ) Better the formation of sugars or the ability to later organize sugars by hydrolysis

( 2 ) Avoid the debasement or loss of saccharide

( 3 ) Avoid the formation of by merchandises that are repressive to the subsequent hydrolysis and agitation procedures, and

( 4 ) Be cost-efficient

Harmonizing to Kumar ( 2009 ) , pre-treatment methods can be approximately divided into different classs: physical ( milling and crunching ) , physicochemical ( steam pre-treatment or car hydrolysis, hydrothermolysis, and wet oxidization ) , chemical ( base, dilute acid, concentrated acid, oxidising agents, and organic dissolvers ) , biological, electrical, or a combination of these. The undermentioned pre-treatment engineerings have promise for cost-efficient pre-treatment of lignocellulosic biomass for biological transition to chemical such lactic acid.

2.6.1 Physical pre-treatment

Physical pre-treatment can increase the accessible surface country and size of pores, and diminish the crystallinity and grades of polymerisation of cellulose. Different types of physical procedures such as milling ( illustration: ball milling, two-roll milling, cock milling, colloid milling, and vibro energy milling ) and irradiation ( illustration: by gamma beams, electron beam or microwaves ) can be used to better the enzymatic hydrolysis or biodegradability of lignocellulosic waste stuffs. However, this method is far excessively expensive which involved the higher ingestion of energy for size decrease of lignocellulosic stuffs ( Kumar et al. , 2009 )

2.6.2 Physicochemical pre-treatment

Common physicochemical pre-treatment is steam detonation. The chipped biomass ( decreased size of biomass normally 10 to 30 millimeters after come offing and 0.2 to 2 millimeters after milling or crunching ) is treated with high-pressure saturated steam and so the force per unit area is quickly reduced, which makes the stuffs to undergo an explosive decompression. Steam detonation ( car hydrolysis ) is initiated at a temperature of 160 to 260 A°C ( matching force per unit area 0.69 to 4.83 MPa ) for several seconds to a few proceedingss before the stuff is exposed to atmospheric force per unit area ( Sun and Cheng, 2002 ) . The factors that affect steam-explosion pre-treatment are abode clip, temperature, bit size, and wet content ( Duff and Murray, 1996 ; Wright, 1998 ) . Optimal hemicellulose solubilization and hydrolysis can be achieved by either high temperature and short abode clip ( 270 A°C, 1 min ) or lower temperature and longer abode clip ( 190 A°C, 10 min ) ( Duff and Murray 1996 ; Kumar et al. , 2009 ) . The advantages of steam-explosion pre-treatment include the low energy demand compared to mechanical comminution and no recycling or environmental costs.

2.6.3 Chemical pre-treatment

a ) Acid hydrolysis

Sulphuric acid ( H2SO4 ) is normally utilised as the chemical for lignocellulosic biomass hydrolysis such kenaf fiber. Based on the concentration of acid used, two types of hydrolysis, dilute and concentrated hydrolysis are used in laboratory research and pilot graduated table survey. Kumar ( 2009 ) stated that dilute acid hydrolysis is conducted with acerb concentrations of less than 2 % at temperature between 160 to 25oC ; for reaction clip less than one hr. However, Wyman ( 1999 ) came out with a new thought to carry on dilute acerb hydrolysis in 160oC for 20 min with 0.49 % concentration of sulfuric acid when covering with the maize stover output pre-treatment. It is found that the dilute-acid hydrolysis procedure uses high temperatures ( 160 to 230 A°C ) and force per unit areas ( 10 standard pressure ) ( Broder et al. , 1995 ; Patrick et al. , 1997 ) .

Taherzadeh and Karimi ( 2008 ) found that the dilute H2SO4 pre-treatment can accomplish high reaction rates and significantly better the cellulose hydrolysis. In add-on, dilute acid efficaciously removes and recovers most of the hemicellulose as dissolved sugars, and glucose outputs from cellulose addition with hemicellulose remotion to about 100 % for complete hemicellulose hydrolysis ( Chieffalo and Lightsey,1996 ) . Hemicellulose is removed when H2SO4 is added and this enhances digestibleness of cellulose in the residuary solids ( Mosier et al. , 2005 ) . High temperature in the dilute-acid intervention is favorable for cellulose hydrolysis ( McMillan, 1994 and Kumar et al.,2009 ) .

Concentrated acid hydrolysis is conducted with 35 to 60 % H2SO4 in temperature between 20 to 100 oC for reaction times of 10 proceedingss to 6 hours ( Zhou, 1997 ) . Due to big measures of acid used, a significant fraction of these acid used must be recovered to accomplish economic operation. Indeed, acerb hydrolysis engineerings lead to high operating costs and assorted environmental and corrosion jobs.

B ) Alkaline hydrolysis

Saponification of intermolecular ester bonds cross associating hemicellulose and other constituents is believed to be the mechanism of alkalic pre-treatment ( Sun and Cheng, 2002 ; Wang et al. , 2008 ) . Main consequence of alkalic pre-treatment is delignification- remotion of structural polymer lignin of lignocellulosic biomass, therefore heightening the responsiveness of the staying saccharides. Alkaline pre-treatments besides remove acetyl and different sorts of uronic acid permutations on hemicellulose, which lowers the extent of enzymatic hydrolysis of cellulose and hemicellulose ( Chang, 2000 ) . Surveies have been carried out utilizing Na hydrated oxide ( NaOH ) such as pre-treatment of natural jute cloth at 100 oC for 30 proceedingss ( Mahalanabis et al. , 2006 ) , coastal bermudagrass at 121 oC for 90 proceedingss ( Wang et al. , 2008 ) , dried land cattail at room temperature for 24 hours ( Zhang et al. , 2010 ) and maize corb at room temperature for 2 hours ( Ojumu et al. , 2003 ) . From the surveies, Na hydrated oxide is found efficaciously enhances lignocellulose digestibleness by increasing internal surface country, diminishing the grade of polymerisation and the crystallinity of cellulose, and dividing structural linkages between lignin and saccharides ( Fan et al. , 1987 ) . The digestibleness of NaOH-treated hardwood increased with the lessening of lignin content ( Millet et.al. , 1976, and Bjerre et al. , 1996 ) . Dilute Na hydrated oxide is normally used for alkali intervention ( Fan et al. , 1987 ) .

2.6.4 Biological pre-treatment

Biological intervention involves the usage of whole beings or enzymes in pre-treatment of lignocellulosic stuffs. Normally used micro-organisms are fungi and bacteriums. Fungal pre-treatment of agricultural residues is a new method for betterment of digestibleness ( Taniguchi et al. , 2005 ) . White- , brown- and soft-rot Fungis are used to degrade lignin and hemicellulose in waste stuffs whereby brown putrefactions chiefly attack cellulose, while white and soft putrefactions attack both cellulose and lignin. White-rot Fungis are the most effectual Basidiomycetess for biological pre-treatment of lignocellulosic stuffs ( Sun and Cheng,2002 ; Mtui 2009 ) . Phanerochaete chrysosporium, a species of white putrefaction Fungi produces both lignin peroxidases and manganese-dependent peroxidases for lignin debasement ( Waldner, 1988 and Boominathan, 1992 ) . Polyphenol oxidases, laccases, H2O2 bring forthing enzymes and quinosine-reducing enzymes besides degrade lignin ( Blanchette, 1991 ) . Biological intervention requires low energy and normal environmental conditions but the hydrolysis output is low and requires long intervention times.

2.6.5 Enzymatic hydrolysis

Enzymatic hydrolysis is normally done in order to heighten the chemical pre-treatment utilizing acid or alkaline. The enzymatic attack in which hydrolysing cellulose to glucose is assuring because enzymes can accomplish high outputs and do non catalyse glucose debasement reactions common to thin acerb procedure ( Schell et al. , 1992 ) . However, the cellulose must be accessible to enzymatic onslaught, which depends on the badness of the pre-treatment procedure. A greater grade of hemicelluloses and or lignin remotion during pre-treatment additions the handiness of cellulose, therefore the efficaciousness of enzymatic cellulose hydrolysis besides increases ( Taherzadeh and Karimi, 2008 ) . The reduction sugars are the merchandises of the enzymatic hydrolysis that is conducted at mild conditions ( pH 4.8 and temperature 45 to 50 A°C ) and due to that status it does non caused a corrosion job ( Duff and Murray, 1996 ) .

2.7 Optimization of procedure status

Since lignocellulosic stuffs such kenaf fiber is complex in construction. It needs to undergo the pre-treatment procedure in order to emancipate the sugar ( glucose ) before the agitation to lactic acid can be done. The optimisation is the important portion in the experiment. This is because the more liberated sugar that consequences from hydrolysis procedure, the more lactic acid can be produced. Several facets need to be considered in order to optimise the hydrolysis processes which are clip, temperature and the mass of natural stuff.

Temperature

To optimise on lignocellulosic stuffs, temperature is needed to take into consideration. From known pre-treatment temperature, the suited optimisation status can be determined. By and large, the temperature used to carry on the pre-treatment of lignocelluloses stuffs is about from the scope of 120 to 240 Os C. However, many surveies of pre-treatment is carried out in the temperature 180 to 210 Os C ( Torget et al. , 2000 ; Ahring et al. , 2003 ) . O’Connor ( 2009 ) argued that if the temperature is above 220 C, the side reactions ( irrespective pH ) of the pretreatment become so fast and overall procedure is hard to command. Examples of side reactions are lignin polymerisation and precipitation, debasement of sugar, complex formation between lignin and other constituent in the solution.

2.7.2 Time

O’Connor ( 2009 ) stated in his patent papers ( US20090176286 ) that the suited clip for pre-treatment of lignocelluloses stuff is between approximately 1 minute and about 24 hours, sooner between about 5 proceedingss and about 2 hours and more sooner between about 10 proceedingss and about 1 hr. By and large, the clip and temperature is inversely proportion. The addition the temperature of pre-treatment, the lessening or less clip needed.

Mass of natural stuff

Mass of the natural stuff besides needed to take into history for the optimisation of pre-treatment procedure ‘ intents. Harmonizing to Gao ( 2008 ) and Lu ( 2009 ) , the ratio of natural stuff to dissolver used is 3:10 ( w/w ) . However, some research worker claimed that they used 30g/L of natural stuffs for the pretreatment procedure ( ( Wee and Ryu, 2009 ) . Some of them used 250g/L of natural stuffs for the procedure ( Mahalanabis et al.,2006 ) . the natural stuff used is non specific into one status. It can be varied depends on the clip and temperature of the procedure.

2.8 Fermentation procedure

Lactic acid is of course happening organic acid that can be produced chemical synthesis and biological agitation. The ultimate aim of lactic acid production is to bring forth it in a procedure that is more effectual and economical ( Rojan et al. , 2007 ) . Between both procedures, biological transition has an of import function in waste use, and it is likely that assorted nutrients treating waste may incorporate utile substrates which can be used for lactic acid production. Other than that, biological agitation offer low cost of substrates, low production temperature, and low energy ingestion ( Pandey et al. , 2001 )

2.8.1 Chemical synthesis

Chemical synthesis of lactic acid is chiefly based on the lactonitrile by strong acids which provide merely racemic mixture of D- and L- lactic acid ( Rojan et al. , 2007 ) . Li and Cui ( 2010 ) explained, for chemical synthesis, ethanal and H nitrile are reacted in the presence of base under high force per unit area to bring forth lactonitirile. They besides claimed that purification of petroleum lactonitrile is done utilizing distillment. The purified lactonitrile is so hydrolyzed with sulfuric acid to bring forth lactic acid. A by-product of ammonium salt is besides produced ( Narayanan et al. , 2004 ; Wee et al. , 2006 ; Li and Cui, 2010 ) . Other possible chemical synthesis paths for lactic acid include base-catalyzed debasement of sugars, oxidization of propene ethanediol, reaction of ethanal, C monoxide and H2O at elevated temperatures and force per unit areas, hydrolysis of chloropionic acid and azotic acerb oxidization of propene among others ( Datta et al. , 1995 ) . There is no chemical synthesis path of lactic acid lead to feasibleness of economic system.

2.8.2 Biological agitation

Biological agitation or known as microbic agitation is a procedure which involved the catalyse of chemical reaction by micro-organism to interrupt simple sugars or aminic acids into lower molecular weight stuffs such as organic acids and impersonal dissolvers. Lactic acid was foremost produced commercially via agitation in the United States in 1881 ( Zhou, 1997 and Jim et al. , 2010 ) . Normally, three signifiers of lactic acid, L ( + ) , D ( – ) and inactive racemic D L mixtures are produced by different micro-organisms. Microorganisms contain enzyme ( s ) L ( + ) -lactate dehydrogenase ( EC 1.1.1.27 ) , D ( – ) -lactate dehydrogenase ( EC 1.1.1.28 ) or racemase produced different isomers of lactic acid transition from pyruvate ( Jim et al. , 2010 ) . In order to detect the new application of lactic acid for the biodegradable polymers which is polylactic Acid ( PLA ) industry, optically pure lactid acid ( L ( + ) ) is extremely preferable optical isomer ( Zhou, 1997 ) .

Figure 2.5: Overview of the two fabrication methods of lactic acid ; chemical synthesis ( a ) and microbic agitation ( B ) . ( Yong et al. , 2007 ) .

2.8.3 Microbial beginnings for lactic acid

Lactic acid can be produced by an tremendous assortment of bacteriums, barms, and fungi. On the footing of the nature of agitation, lactic acid micro-organism which is normally bacteriums is classified into ( 1 ) homofermentative and ( 2 ) heterofermentative. Homofermentative lactic acid bacteriums produce lactic acid as a exclusive terminal product- individual merchandise, whereas the hetero fermentative lactic acid bacteriums produce other merchandises such as ethyl alcohol, diacetyl, formate, acetoin or acetic acid and C dioxide along with lactic acid ( Rojan et al. , 2007 ; Zhou, 1997 ; Li and Cui, 2010 ; Jim et al. , 2010 ) . The desirable features of industrial micro-organisms are their ability to quickly and wholly ferment inexpensive natural stuffs, necessitating minimum sum of nitrogen-bearing substances, supplying high outputs of preferable stereo specific lactic acid under conditions of low pH and high temperature, production of low sums of cell mass and negligible sums of other by-products ( Narayanan et al.,2004 ) . The pick of an being chiefly depends on the saccharide to be fermented.

Most of microbic beginnings for lactic acid are anaerobiotic such as Lactobacillus, Leuconostoc, Pediococcus and Bifidobacterium, utilised pyruvate which is the end merchandise of Embden-Meyerhof tract. Narayanan ( 2004 ) said that Lactobacillus is found to be the most of import commercial species for lactic acid production by agitation. It is gram positive facultative anaerobic and microphilic bacteriums which has complex nutritionary demands, as they are those groups of micro-organisms that have lost their ability to synthesise their ain growing factors ( Beasley, 2004 ) . They can non turn entirely on C beginning and inorganic N salts. LactobacillusA is really heterogenous genus, embracing species with a big assortment of phenotypic, biochemical, and physiological belongingss ( Todar, 2009 ) .

Most species of Lactobacilli are homofermentative, but some are heterofermentative.A The genus has been divided into three major subgroups and over 70 species are recognized ( Hans et. al. , 2002 ) . Group I Lactobacilli are obligate gay fermentative and bring forth lactic acid as a major terminal merchandise ( & gt ; 85 % ) from glucose. They are represented byA L. delbrueckiiA andA L. acidophilus. They grow at 45oC but non at 15oC. Group II, besides homofermentative, turn at 15oC and demo variable growing at 45oC. Represented byA L. caseiA andA L. plantarum, they can bring forth more oxidised agitations ( e.g. ethanoate ) if O2A is present. Group III Lactobacilli are heterofermentative. They produce lactic acid from glucose, along with CO2A and ethyl alcohol ( Hammes and Whiley, 1993 ) .

Furthermore, the beginnings for production of lactic acid can besides be aerophilic micro-organisms such fungi – Rhizopus and Mucor ( Naveena, 2004 ) . When fungus such as Rhizopus is used, the aerophilic agitation requires important agitation and aeration with high energy cost and long agitation clip due to its slow growing and production rates ( Jim et al. , 2010 ) . Even though, Rhizopus promised a colourless and comparatively high pureness of lactic acid but still it has non been used commercially for lactic acid production ( Zhou, 1997 ) . However, approximately 90 % of the literature of lactic acid production is carried out utilizing anaerobiotic bacteriums since it offered a robust, fast turning, low pH, high output strain with low cost alimentary demand and low ingestion of energy for the agitation.