Chem Project on Grafting of Starch

7/30/2019 Chem Project on Grafting of Starch

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GRAFTING OFSTARCH BY RADICAL

INITIATORS VINYLCHLORIDE

Under the supervision of Submitted byMr. RAMESH DOGRAPoonam Malik


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Bsc-III

ACKNOWLEDGEMENT

I Poonam Malik student of BSC-III year of S D College

Sector -32 C, Chandigarh gratefully acknowledge thevaluable contribution of the individual involved in thisproject grafting of starch. The acknowledgementsare due to all teachers of the department ofchemistry studies.

I sincerely thank Dr. Ramesh Dogra for guiding me inthis project. I also thank the members of Chemistry

department and my classmates who helped me a lotto prepare this project. I also took help from internetwebsite and magazine Extra Edge. I also thank thecollege library for providing internet website andbooks.

I also acknowledge the contribution of my parents fortheir valuable suggestions.

At last I would like to thank to all the person involvedto prepare this project

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SANDEEP KAUR

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1st Qtr 2nd Qtr 3rd Qtr 4th Qtr

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S.No. TOPICS PageNo.

1 INTRODUTION 3

2 STARCHOCCURANCE AND ISOLATION

4

3 COPOLYMERDIFFERENT TYPES OF

COPOLYMERSGRAFT COPOLYMERS

7

4 RADICAL POLYMERISATION 10

5 EXPERIMENTAL SETUPEXPERIMENTAL

CHARACTERISTICS OF GRAFTEDSTARCH

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6 OBSERVATIONS 15

7 RESULTS AND DISCUSSIONEFFECT OF TIMEEFFECT OF TEMPERATURE

EFFECT OF MONOMERCONCENTRATION

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8 EVIDENCES OF GRAFTING 19

9 REFERENCES 23


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INTRODUCTION

Naturally occurring organic polymers can be directedinto six categories:

1.Polysaccharides, a category that includes gums,chitins, pectin, alginic, acid, starch, cellulose andmany other.

2. Polypeptides or naturally occurring polyamides.This large group of macromolecules is foundboth in the vegetable and animal kingdom and isthe major constituents of such diverse materialsas silk, wool, horns, hoofs and feathers.

3. Polynucleotides or nucleic acids found in animalplant cells and in viruses.

4. Polyisoprenes, the constituent of hevea or

natural rubber balate and gutta percha.

5. Lignins or polymeric material of coniferyl alcoholand related substances found in wood tissues

.6.Miscellaneous: polymeric materials found in

nature such as some of the natural resins or forinstance polyesters found in membranes of

certain seeds and lichens.

In the present dissertation attempts have beenmade to modify natural polymers such as starch,cellulose and wool protein by graftcopolymerization. It is therefore, considered

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worthwhile to review the chemistry of thenatural polymer products.

STARCH

The word "starch" is derived from Middle Englishsterchen, meaning to stiffen. "amylum" is Latin forstarch, from the Greek , "amylon" whichmeans "not ground at a mill". The root amyl is usedin biochemistry for several compounds related tostarch.

Starch or amylum is carbohydrates consisting of alarge number of glucose units joined by glycosidicbonds. This polysaccharide is produced by all greenplants as an energy store. It is the most commoncarbohydrate in the human diet and is contained inlarge amounts in such staple foods as potatoes,wheat, maize (corn), rice, and cassava

Starch is processed to produce many of the sugars inprocessed foods. Dissolving starch in warm watergive which can be used as a thickening, stiffening or

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http://en.wikipedia.org/wiki/Etymologyhttp://en.wikipedia.org/wiki/Middle_Englishhttp://en.wikipedia.org/wiki/Latinhttp://en.wikipedia.org/wiki/Greek_languagehttp://en.wikipedia.org/wiki/Amylhttp://en.wikipedia.org/wiki/Polysaccharidehttp://en.wikipedia.org/wiki/Planthttp://en.wikipedia.org/wiki/Staple_foodhttp://en.wikipedia.org/wiki/Potatohttp://en.wikipedia.org/wiki/Wheathttp://en.wikipedia.org/wiki/File:Cornstarch_mixed_with_water.jpghttp://en.wikipedia.org/wiki/Middle_Englishhttp://en.wikipedia.org/wiki/Latinhttp://en.wikipedia.org/wiki/Greek_languagehttp://en.wikipedia.org/wiki/Amylhttp://en.wikipedia.org/wiki/Polysaccharidehttp://en.wikipedia.org/wiki/Planthttp://en.wikipedia.org/wiki/Staple_foodhttp://en.wikipedia.org/wiki/Potatohttp://en.wikipedia.org/wiki/Wheathttp://en.wikipedia.org/wiki/Etymology


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Structure of the amylopectin molecule

OCCURANCE AND ISOLATION

The starch industry extracts and refines starchesfrom seeds, roots and tubers, by wet grinding,washing, sieving and drying. Today, the maincommercial refined starches are cornstarch, tapioca,wheat and potato starch. To a lesser extent, sourcesinclude rice, sweet potato, sago and mung bean.Historically, Florida arrowroot was alsocommercialized. To this day, starch is extracted frommore than 50 types of plants.

Untreated starch requires heat to thicken orgelatinize. When a starch is pre-cooked, it can then

be used to thicken instantly in cold water. This isreferred to as a pregelatinized starch

.Although starch material has been found in somebacteria protozoa and algae, its main sources are in

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http://en.wikipedia.org/wiki/Amylopectinhttp://en.wikipedia.org/wiki/Cornstarchhttp://en.wikipedia.org/wiki/Tapiocahttp://en.wikipedia.org/wiki/Potato_starchhttp://en.wikipedia.org/wiki/Florida_arrowroothttp://en.wikipedia.org/wiki/Starch_gelatinizationhttp://en.wikipedia.org/wiki/File:Amylopektin_Sessel.svghttp://en.wikipedia.org/wiki/Amylopectinhttp://en.wikipedia.org/wiki/Cornstarchhttp://en.wikipedia.org/wiki/Tapiocahttp://en.wikipedia.org/wiki/Potato_starchhttp://en.wikipedia.org/wiki/Florida_arrowroothttp://en.wikipedia.org/wiki/Starch_gelatinization


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the higher plants, where the polysaccharide is laiddown in the form of granules, which are insoluble inthe cell medium. However, it is to be noted that thedistinction between starch as the food reserve

polysaccharide of plants and glycogen and thecorresponding reserve polysaccharide in animals isnot completely well defined, some animals canproduce starch like material and some plants canproduce glycogen like polymers.

Starch is found in all parts of plants, the leaves stem,shoot and storage organs such as tubers rhizomers

and seeds; the proportion varies from a few percentto 70 to 80% of the cereal grains. The starchgranules in most plant material can be easily isolatedbut the extraction and purification of starches fromcereal are difficult.

COPOLYMER

A heteropolymer or copolymer is a polymer derivedfrom two (or more) monomeric species, as opposedto a homopolymer where only one monomer is used.Copolymerization refers to methods used tochemically synthesize a copolymer.

Commercially relevant copolymers include ABSplastic, SBR, Nitrile rubber, styrene-acrylonitrile,styrene-isoprene-styrene (SIS) and ethylene-vinylacetate

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http://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Monomerhttp://en.wikipedia.org/wiki/Homopolymerhttp://en.wikipedia.org/wiki/ABS_plastichttp://en.wikipedia.org/wiki/ABS_plastichttp://en.wikipedia.org/wiki/Styrene/butadiene_co-polymerhttp://en.wikipedia.org/wiki/Nitrile_rubberhttp://en.wikipedia.org/wiki/Styrene-acrylonitrilehttp://en.wikipedia.org/wiki/Ethylene-vinyl_acetatehttp://en.wikipedia.org/wiki/Ethylene-vinyl_acetatehttp://en.wikipedia.org/wiki/Polymerhttp://en.wikipedia.org/wiki/Monomerhttp://en.wikipedia.org/wiki/Homopolymerhttp://en.wikipedia.org/wiki/ABS_plastichttp://en.wikipedia.org/wiki/ABS_plastichttp://en.wikipedia.org/wiki/Styrene/butadiene_co-polymerhttp://en.wikipedia.org/wiki/Nitrile_rubberhttp://en.wikipedia.org/wiki/Styrene-acrylonitrilehttp://en.wikipedia.org/wiki/Ethylene-vinyl_acetatehttp://en.wikipedia.org/wiki/Ethylene-vinyl_acetate


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Periodic copolymers with A and B unitsarranged in a repeating sequence (e.g. (A-B-A-B-B-A-A-A-A-B-B-B)n)

Statistical copolymers are copolymers inwhich the sequence of monomer residuesfollows a statistical rule. If the probability offinding a given type monomer residue at aparticular point in the chain is equal to the molefraction of that monomer residue in the chain,then the polymer may be referred to as a trulyrandom copolymer

Block copolymers comprise two or morehomopolymer subunits linked by covalent bonds(4). The union of the homopolymer subunits mayrequire an intermediate non-repeating subunit,

known as a junction block. Block copolymerswith two or three distinct blocks are calleddiblock copolymers and triblock copolymers,respectively.

Copolymers may also be described in terms of theexistence of or arrangement of branches in thepolymer structure. Linear copolymers consist of asingle main chain whereas branched copolymersconsist of a single main chain with one or morepolymeric side chains.

Other special types of branched copolymers includestar copolymers, brush copolymers, and comb

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copolymers. In gradient copolymers the monomercomposition changes gradually along the chain.

Graft copolymers

Graft copolymers are a special type of branchedcopolymer in which the side chains are structurallydistinct from the main chain. A special case wherethe main chain and side chains are composed ofdistinct homopolymers. However, the individualchains of a graft copolymer may be homopolymers or

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http://en.wikipedia.org/wiki/Gradient_copolymershttp://en.wikipedia.org/wiki/File:RAFT_Architecture.pnghttp://en.wikipedia.org/wiki/Gradient_copolymers


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copolymers. Different copolymer sequencing issufficient to define a structural difference, thus an A-B diblock copolymer with A-B alternating copolymerside chains is properly called a graft copolymer.

RADICAL POLYMERISATION

A free radical is an atom, molecule or complex whichcontains one or more unpaired e-. This definition isvery broad since it includes species such as nitricoxide NO, the chloride atom Cl, free methyl radicalCH3 and atoms of transition metal which contain an

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http://en.wikipedia.org/wiki/File:Lfg_polymer_milk_(cropped).jpg


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t-Butyl peroxide t-BuO-OBu.t 37 150t-Butylperbenzoate t-Buo-O-C-C6H5

34 125

Benzoyl peroxide

C6H5-C-O-O-C-C6H5

30 95

Acetyl peroxideCH3-C-O-O-C-CH3

30-32 85

Table 1lists some commercially available peroxidesthat are used as initiators. The table gives the

activation energy for the dissociation reaction andthe temperature at which the peroxide producesradicals with a 1 hour half life

The compound listed in the table is useful becausethey are stable enough to be synthesized at ordinarytemperature and can be stored for long periods

refrigerator. They can be used as initiator attemperature at which most bonds do not undergothermal hemolysis.

BPO is one of the peroxidic compounds that has beenextensively used in vinyl polymerization. The non-conceived mechanism for the unimolecular

decomposition of BPO has been demonstrated manytimes through the interception of benzoyloxy radicalby conventional scavengers including moist iodine(2)

Galvinoxyl(3) and vinyl monomers(4). The later studiesindicates that the activation energy for

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decarboxylation of this intermediate must be morethan 10 kal/m.

BPO is believed to decompose in the following

manner

When benzoyl peroxide is allowed to decompose inhot oxygen free benzene, the initially formedbenzoyloxys radicals rapidly decarboxylated(5).Furthermore both benzoyloxy radicals and phenylradicals can react by addition on by H abstraction.Conventional free radical initiators like BPO are

known to effect polymerization of vinyl monomers.

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EXPERIMENTAL SETUP

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EXPERIMENTAL

Materials and method

Unmodified dried soluble variety potato starch (BDH)has been used in all experiments(6). BPO was usedwithout further purification, a weighted amount of

BPO was dissolved in 1: 1 methanol-dioxane mixture.

Purification of Monomer

Monomers-vinyl acetate (VAc) (BDH) were purified bydistillation under reduced pressure in presence ofnitrogen atmosphere. Methyl acrylate (MA) (BDH)was shaken with 10% NaOH solution washed with

distilled water and dried over anhydrous sodiumsulphate and was then distilled under reducedpressure in presence of nitrogen. Purified monomerswere store in refrigerator at 00C.

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Graft copolymerization:

Pure dry starch (2.0 g) was dispersed in 100 ml ofcold deserted distilled water (600C) in a three neckedflask The temperature of starch dispersion wasbrought to the water bath temperature

Weighed amount of catalyst dissolved in appropriatesolvent (1:1 Methanol-dioxene) was added to thereaction flask. . Definite amount of monomer (VAc)was added dropwise from the separatory funnel intothe reaction mixture. The graft copolymerizaton wascarried out under constant stirring by a magneticstirrer.

After completion of reaction, the reaction mixture

was filtered and the residue was extracted for 24hours, with boiling water for the removal ofunreacted starch. The residue was then furtherextracted with appropriate solvent for 48 hours.Benzene was used as a solvent for Poly (VAc) and .After removal of homopolymer and unreacted starch,the residue was dried at 50C until constant weightwas obtained.

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MECHANISM FOR GRAFTING OFPOL(VAc) ONTO STARCH

I2 2I

-

I + M IM IMM

I + Starch Starch +IH

IMM+ Starch Starch + IMMH

Starch + M Starch-M Starch (M)nIMM + M IM-(Mn) H

Starch-(M)n + I Starch-(Mn)-I

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Characterization of grafted starch

The graft copolymers were characterized bydetermination of starch in graft copolymer byhydrolyzing weighed amount of graft starch. With 1

NHCl at 1100

C for two hours when all the starch wentinto solution as glucose. The liberated glucose wasestimated by titration with standard Fehling solutionby using methylene blue as indicator. From theamount of starch in graft copolymer, percentage ofgrafting and percent efficiency has been calculatedas follows:

% grafting = W2/W1 x 100

% grafting efficiency = W2/W3 x 100

Where W1, W2, W3 denotes respectively, the weight ofthe graft copolymer after water and benzeneextraction, the weight of the polymer grafted and theweight of the monomer used.

Percentage of grafting and efficiency weredetermined as functions of time, temperature,monomer con and catalyst concentration and theresults are in tables 2

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OBSERVATION

EFFECT OF TIME

EFFECT OF TEMPERATURE

Sl

No.

Conc.Vac

(mol/L)

Temperature(0

C)

Time(min

)

%

Grafting1. 1.0810-4 55 90 21.12. 1.0810-4 65 90 27.53. 1.0810-4 70 90 17.4

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SlNo.

Conc Vac(mol/L)

Temperature(0

C)Time(min)

%Grafting

1. 0.5 10-4 60 120 9.62. 0.510-4 60 60 10.6

3. 0.510

-4

60 90 29.0


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EFFECT OF MONOMER CONCENTRATION

SlNo.

Conc.Vac(mol/L)

Temperature(0

C)Time(min)

%Grafting

1. 1.0810-4 60 90 53.62. 0.710-4 60 90 1.33. 210-4 60 90 0.0

RESULT AND DISCUSSION

In a free radical polymerization percent conversion ofthe monomers is dependent upon the nature ofinitiator and monomer. Benzoyl peroxide is known toeffect polymerization by free radical mechanism. Infree radical polymerization after termination of thegrowing chain occurs through chain transfer. A

chain transfer reaction is defined as the phenomenonin which termination of growing chain occur withoutdestruction of the kinetic chain.

Abstraction of hydrogen atom or a labile atom bygrowing radical is a well-recognized and extensivelystudied reaction is free radical vinyl polymerization.During these processes, the propagating chain

terminates and a new radical is formed. Whenpolymerization of a vinyl monomer is carried out inthe presence of a backbone polymer (starch), thegrowing radical may abstract a hydrogen atom fromthe backbone polymer forming active sites uponstarch where grafting may occur by the addition of

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monomer. The following chain transfer mechanism issuggested for grafting of vinyl monomer into starchby free radical initiatorsI2 represents initiator molecules and M the

monomer.Since starch is easily dispersible in water, it is moreaccessible for attack by radical initiator. Cellulosebeing insoluble in water is less accessible and the no.of active sites generated on starch by hydrogenabstraction is expected to be larger.

Further according to the above mechanism %

grafting is dependent upon:1. Nature and concentration of the initiator.2. Nature and concentration of the vinyl monomer3. Type of the backbone upon which grafting

occurs.4. Nature of the reaction medium

Water has been used as medium in all the

experiments and hence the effect of solvent uponpercentage of grafting is ignored, since water has alow chain transfer constant. Starch has been used asa polymer backbone in all the experiments, so effectof the nature of polymer backbone is the same.

Therefore in the parent study, percentage of graftingis primarily determined by nature and concentrationof catalyst and by the concentration and reactivity of

vinyl monomer. Since starch is easily dispersible inwater (I) has a greater chance to react with starchand thus wastage of (I) by cage recombination isminimum when grafting is carried out in presence ofstarch. This explanation finds support in theobservation with increase in concentration of BPO,

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expected since chain transfer reactions usually havehigher energy of activation. Further increase intemperature leads to decrease in percent graftingdue to acceleration of some of the termination

process the exact nature of which remains to beelucidated.

Effect of monomer concentration

It can also be seen from the tables that withincrease in monomer concentration percent graftingincreases with Vac and reaches a maximum value.

Further increase in monomer concentration leads topreferential formation of homopolymer withmonomers. The growing polymeric radical at higherconcentration may terminate grafting by process 8and this should reduce % grafting. In fact it isobserved from tables that when the monomerconcentration exceeds 1.08 mole/L in case of Vac, %grafing decreases.

REFERENCES

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1.J.C.Bevington, Acrylonitrile in

macromolecules, Acad. Press London/New

York 1961

2.G.S Hammonol and L.M Sofffer , J.Am. Chem.

Soc, 85 ,3613(1963)

3.Shina, J. Waters and D.Hoffmans J. Am.

Chem. Soc, 85, 3613 (1963)

4.G. Ayrey Chem, Rev. 63, 645 (1963)

5.Y. Iwakura, T. Kurasaki and Y. Imai, J. Polym.

sci. , A, 3, (1965)

6.E-Marck

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Chem Project on Grafting of Starch