Acrylamide Grafting on Banana fibres

Final Year B.Tech Project byKetki Chavan

( B.Tech – F.T.P.T.)(2014)

Banana fibres

• Obtained from Pseudo-stem of fully grown banana plants, usually extracted after harvesting of fruits and uprooting of the grown plant.

• Chemical Composition:– Cellulose: 63 to 65%– Hemicellulose: 20 to 22%– Lignin: 12 to 16%

(chemical composition varies with the variety of the plant and geographical conditions where the plant was grown)

Characteristics of Banana fibres• Lignocellulosic fibre• Strong fibre, high tensile modulus, low

elongation at break• Average fineness 2400Nm• Light weight• Good spinnability• Strong moisture absorbing ability; absorbs as

well as releases moisture very fast.• Eco-friendly fibre.

Acrylamide Monomer• IUPAC name: Pro-2-enamide• Chemical formula: C3H5NO • Structure: CH2=CH-C=O NH2

• White odourless crystalline solid • Water, ether, ethanol and chloroform soluble• Carcinogenic if inhaled• Used for Polymer preparation or as Cross-linking

agent. Polyacrylamide is not carcinogenic.

Introduction to Grafting of cellulosic fibres

A graft copolymer consists of a polymeric backbone with covalently linked polymeric side chains. In principle, both the backbone and side chains could be homopolymers or copolymers.Grafting can be carried out in such a way that the properties of the side chains can be added to those of the substrate polymer without changing the latter.But with other types of grafting, the crystalline nature of the cellulose, for example, can be largely destroyed. This releases the natural absorbency of cellulose as well as adding that of the hydrophic side chains leading to very high water absorbency. This can be accomplished by a decrystallization procedure after grafting or, in the case of the hydrolyzed grafted products, by the process itself.

Methods for synthesis of Graft Copolymers

2 methods:1. Side chain polymer A could be linked directed

by a suitable chemical reaction to the backbone polymer B

2. Backbone polymer B could have active sites such as free radicals or ions formed upon it. These can then be used to polymerize a suitable monomer to produce the side chains of polymer A.

• The first method is difficult except in solution and perhaps the most successful has been by treating "living" polymers to a suitably reactive backbone. A good example is the polystyrene- polyvinyl pyridine system where both polymers have been used as backbones and side chains

• Advantages of this approach:– Simple Synthetic method– Fewer problems of homopolymer formation– Length and number of side chains could be controlled– Superior properties, including absorbency, because of the

higher degrees of substitution and shorter side chains• Disadvantages of this approach:– difficulty of inducing polymer reactions

Types of grafting

The second general method is much more successful and a large number of techniques have been developed. Essentially, these are free radical processes.Techniques:• Chain Transfer Method• Direct Oxidation• Initiators for Polysaccharide• Polysaccharide derivatives as Co-monomers• Direct Radiation

Chain Transfer Method

• In this method radicals are created on the polysaccharide backbone including cellulose and starch by use of the reactions:

R can be the growing chain of polymers formed by polymerization with a radical initiator in the presence of the polysaccharide, or by the primary radical from the initiator itself. The efficiency of this type of grafting reaction is also greatly improved by increasing the ratio of polysaccharide to monomers such as by using a simple swollen system or with the correct choice of swelling agents.

Direct Oxidation

• A number of oxidizing agents have been found to interact with polysaccharides to form macroradicals which, with monomer, form graft copolymers. The most successful and best studied of these is ceric ion. Briefly the reaction is as follows:

• In fact the reaction is much more complicated and the oxidation-reaction is often preceded by complexing of the ceric ion by the polysaccharides.

• Other oxidizing agents studied include pentavalent vanadium, manganese(III) and manganese(IV) ions.

Initiators for Polysaccharides• Initiators such as peroxides or diazonium salts can be

formed directly on the backbone molecules. Hydroperoxides and peroxides of unknown structure can be formed by ozonolysis or by treating with ultraviolet (UV) or high energy radiation in the presence of air.

• These initiators can then be used to bring about grafting by decomposing in the presence of monomer. The latter can be achieved by heat or by the addition of a reducing agent such as ferrous ammonium sulfate. The use of reducing agents largely eliminates the concurrent formation of homopolymer.

Polysaccharide Derivatives as Co-monomers

• A number of vinyl and allyl derivatives of polysaccharides may be synthesised quite readily. Direct free radical polymerization of a suitable monomer in the presence of these derivatives produces a mixture of grafting and cross-linking.

• With very low degrees of substitution and the proper choice of reactivity ratios and by the controlled addition of chain transfer agents essentially cross-link free grafted products can be prepared.

Direct Radiation• High energy radiation, both isotopic and with accelerated electrons

brings about grafting directly.• In the presence of air, radiation can be used to produce peroxides.• In the absence of air, 2 methods are available:

– Firstly, direct, mutual, irradiation of the polysaccharide in the presence of the monomer and a suitable swelling agent can be used. This normally produces a considerable amount of homopolymer which can be reduced to a very small proportion by various means, such as increasing the substrate to monomer level, addition of inhibitors, or using vapour phase addition of the monomer.

– The second method, often termed the pre-irradiation method, involves irradiating the polysaccharide and adding the monomer, plus any swelling agent needed, subsequently. This method is very valuable for monomers such as acrylic acid which polymerize rapidly with radiation.

Cellulose Grafting for Enhanced Water Absorbency

Cellulose is the key raw material for most commercial absorbent products. Because of the constant demand to increase the absorbency of these products, there has been a concomitant demand for improvement in absorbency of natural and regenerated cellulose fibres. The absorbency of cellulose fibres has been improved by modification of their chemical structure, the known techniques being: 1. By substituting new chemical groups at the site of the original

hydroxyl groups of the cellulose fibres; 2. By crosslinking cellulose chains into a network structure; 3. By introducing new groups and crosslinking them together; or 4. By grafting side chains onto the cellulose backbone.

• While many modified cellulose fibres have greater absorbency then unmodified cellulose fibres, they gain this absorbency at the cost of decreased softness and the loss of other desirable fibrous qualities.

• Therefore, even though many standard techniques of grafting hydrophilic monomers to cellulose fibres are possible, not all of them result in the most desirable superabsorbent fibres.

• The ideal superabsorbent fibre would be the one which would exhibit substantially enhanced absorbency, while essentially maintaining the flexibility of the initial fibre substrate.

• This challenge is being partially met by the introduction of a combination of ionic and non-ionic monomer grafting approach, focusing on meeting the requirements of disposable absorbent products.

Cellulose Grafting for Enhanced Water Absorbency

The grafting techniques for cellulose super-absorbency are broadly classified under 2 types:

• Saponifiable grafts to cellulose.

• Direct grafting of acrylic and methacrylic acids to cellulose.

• Saponifiable grafts to cellulose:In this approach monomers such as acrylonitrile, acrylamide, and various acrylate and methacrylate esters and their mixtures are grafted, followed by saponification to sodium polyacrylate or methacrylate. Non-saponifiable co-monomers are sometimes also used.

• Direct grafting of acrylic and methacrylic acids:A direct method is initiation by high energy radiation. Since these monomers homopolymerize rapidly with radiation, the pre-irradiation method is the most convenient. In principle, however, direct irradiation of cellulose in the presence of monomer could be used with the monomer in the vapour phase or in solution containing suitable inhibitors.

Materials & Methods

• Materials:– Banana fibres obtained from CIRCOT, Mumbai.– Acrylamide AR (monomer)– Ceric Ammonium Nitrate (initiator)– Sodium Hydroxide Pellets– Absolute AlcoholAll supplied by Ami Chemicals of S D Fine Chemicals, Mumbai.

Materials & Methods

• Methods:1. Pre-treatment of Banana Fibres2. Grafting3. Hydrolysis4. Precipitation

Procedure for Pre-treatment

Step 1: Treatment with 0.5% H2SO4 at 40°C for 30 mins. This is for degrading lignin. Treatment was followed by a hot and cold wash to remove acid.Step 2: Scouring of the fibres is done with 5% NaOH solution at boiling temperature in water-bath for 4 hours using 1:40 MLR. This is followed by hot and cold wash to remove alkali and also assist removal of floating impurities and pseudo stem residuals.

Procedure for Pre-treatment

Step 3: Bleaching of the scoured fibres os done using following recipe:• 4 vol H2O2 (50%(w/w))• 2 g/l Sodium Silicate• 2 g/l Non-ionic soapBleaching treatment is carried out at 85°C for 45 mins using 1:40 MLR. Care must be taken to avoid fibres to come to the surface so that air oxidation could be avoided.

Procedure for Grafting• Grafting is carried out in atmospheric conditions & not in inert

N2 atmosphere.• Variation in Parameters: (MLR used 1:50)

PARAMATER VALUES

Initiator Concentration (% wt/vol) 0.1, 0.2, 0.4

Monomer Concentration (% wt/vol) 1,2,3

Temperature of Grafting (°C) 30,70,100

Time for Grafting (hrs) 0.5,1,1.5,2,2.5,3

PLAN TO OPTIMIZE INITIATOR & MONOMER CONCENTRATION, TEMPERATURE OF GRAFTING AND TIME DURATION OF GRAFTING.

Treatments 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Initiator concentration(% wt/vol)

0.1 0.2 0.4 0.1 0.2 0.4 0.1 0.2 0.4 0.1 0.2 0.4 0.1 0.2 0.4

Monomer concentration(% wt/vol)

1 1 1 2 2 2 3 3 3 1 1 1 2 2 2

Temperature (°C) 30 30 30 30 30 30 30 30 30 70 70 70 70 70 70

Treatment 16 17 18 19 20 21 22 23 24 25 26 27

Initiator concentration(% wt/vol)

0.1 0.2 0.4 0.1 0.2 0.4 0.1 0.2 0.4 0.1 0.2 0.4

Monomer concentration(% wt/vol)

3 3 3 1 1 1 2 2 2 3 3 3

Temperature (°C) 70 70 70 100 100 100 100 100 100 100 100 100

In all experiments, time duration was kept constant at 2 hours.

The conditions which gave samples with good % weight add-on were analysed [refer results and discussions]Good values of % weight add-on were observed between temperatures 70 and 100°C when the monomer concentration was 2 and 3% wt/vol and initiator concentration was above 0.2% wt/vol.Optimising temperature and monomer concentration:

Treatment 28 29 30 31 32 33 34 35

Initiator Conc (%wt/vol)

0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

Monomer Conc (%wt/vol)

2 2 2 2 3 3 3 3

Temp (°C) 70 80 90 100 70 80 90 100

• Again the samples with max % weigth add-on were treated to be the optimum and so by maintaining these conditions the following plan was used for optimization of Time Duration for Grafting:

Thus a total of 41 samples were prepared and all of them were Hydrolyzed and Precipitated.

Treatment 36 37 38 39 40 41

Initiator Concentration(% wt/vol)

0.2 0.2 0.2 0.2 0.2 0.2

Monomer Concentration(% wt/vol)

3 3 3 3 3 3

Temperature(°C)

70 70 70 70 70 70

Time (hours)

0.5 1 1.5 2 2.5 3

• Procedure for Hydrolysis:Hydrolysis treatment of the grafted fibres is carried out using an 8% (wt/vol) NaOH solution at 70°C for 2 hours in atmospheric conditions.

• Procedure for Precipitation:Precipitation is done in Absolute Alcohol after completion of the Hydrolysis treatment.Use of safety goggles and gloves is a must during precipitation.

Testing procedure

1. Calculation of % Weight Add-on:• The fibres after bleaching and before grafting are dried

in an oven at 105°C for 30 mins and then weighed. This weight is abbreviated as Wb.

• The fibres obtained after Hydrolysis and Precipitation are also dried at 105°C for 30 mins and then weighed. This weight is abbreviated as Wg.

Now,% Weight Add-on = [ ( Wg - Wb ) / Wb ] x 100

Testing procedure

2. Calculation of Water Absorbency:1 gm of prepared grafted fibre was immersed in 100ml distilled water for 1hour to reach the swelling equilibrium at room temperature. The swollen fibres were filtered through a Nylon cloth and the remaining fibres were weighed.The water absorption Q (g/g) is given by; Q = [ Ws-Wd ] / Wd.

Where, Ws is the swollen weight of the sample. Wd is the dried weight of the sample.

Safety Precautions• Use of Hand gloves is a must always during the Pre-treatment

procedure for cleaning of banana fibres.• Use of Hand gloves as well as Safety Goggles and Face masks

during the Grafting Procedure to avoid contact of the hot fumes to be inhaled or contacted with eyes.

• Continue the procedure of hydrolysis with all the stated safety measures in point (ii) to avoid contact of the alkaline fumes to coming into contact with eyes or getting inhaled.

• Use of proper face masks, Safety Goggles and Hand Gloves is a must during the Precipitation process as Alcohol is involved in the process and a continuous exposure to the precipitating medium may cause severe headache and watering of eyes along with yellowing of hands.

RESULTS & DISCUSSIONS

Temp, Monomer & Initiator Conc. Optimization

Sample No. / Treatment No.

Weight Add-on(%)

Water Absorbency(gm/gm of grafted fibre)

1 18 9

2 19 10

3 20 12

4 19 9.3

5 21 12.5

6 23 13

7 25 13.5

8 27 15

9 30 16

Samples: Temp = 30°C; Monomer con = 1,2,3 (% wt/vol); Initiator con = 0.1,0.2,0.4(%wt/vol)

Temp, Monomer & Initiator Conc. Optimization

10 44 20

11 49.5 21

12 53 23.4

13 51 22

14 52 22.5

15 55 24.6

16 60 27

17 62 27.5

18 64 27.8

Samples: Temp = 70°C; Monomer con = 1,2,3(%wt/vol); Initiator con = 0.1,0.2,0.4(%wt/vol)

Temp, Monomer & Initiator Conc. Optimization

19 46 20.2

20 48 20.4

21 49 20.8

22 58 26.4

23 59 26.8

24 61 27.2

25 63 27.6

26 65 28

27 66 29.1

Samples: Temp = 100°C; Monomer con = 1,2,3(%wt/vol); Initiator con = 0.1,0.2,0.4(%wt/vol)

Temp & Monomer Conc. Optimization

28 52 22

29 51 22.5

30 53 23.6

31 52 22.1

32 62 27.4

33 63 27.5

34 64 27.8

35 65 28.1

Samples: Temp = 70, 80,90,100°C; Monomer con = 2,3(%wt/vol); Initator con = 0.2(%wt/vol)

Time Duration Optimization

36 44 19.5

37 49 21

38 52 22.1

39 58 26.4

40 63 27.6

41 68 29.5

Samples: Temp = 70°C; Monomer con = 3(%wt/vol); Initiator con = 0.2(%wt/vol);Time duration = 0.5,1,1.5,2,2.5,3 hours.

• Effect of Initiator Concentration:With constant monomer concentration and temperature it can be seen that % weight add-on and water absorbency increases with increase in Initiator concentration. As concentration goes above 0.2% wt/vol it can be seen that there is more amount of grafting which can be due to more number of active sites available for the monomer to polymerize.

• Effect of Monomer Concentration:With constant initiator concentration and temperature it can be seen that % weight add-on and water absorbency increases with increase in Monomer concentration upto a limit after which it decreases. As concentration goes above 2% wt/vol the availability of initiator gives good extent of grafting but as concentration increases further above 3% wt/vol, the formation of homopolymer becomes more prominent than actual grafting taking place. Thus the absorbency decreases.

• Effect of Temperature of Grafting:Increase in temperature of grafting from 30°C to 70°C gives a drastic increase in % weight add-on due to increase in extent of grafting. It can thus be noted that a temperature of minimum 70°C is required for grafting of Acrylamide onto Banana fibre cellulose. After further increase above 70°C towards 100°C, there is not much difference in the % weight add-on, only slight steady increase is seen. This indicated that a temperature of 70°C is sufficient for grafting rather than moving to higher temperatures. It was also seen in the cases where monomer concentration was 3% wt/vol that the fibre grafting taking place at temperature above 90°C was fast but the homopolymer formation was comparatively more than the grafted fibre formation. The reason here can be the higher temperature supporting the quick formation of homoplymer due to good availability of initiator and monomer rather than grafting onto the fibre cellulose. Thus higher temperature has selectivity to formation of homopolymer and thus it can be inferred that temperature between 70°C to 80°C is sufficient for selective grafting.

• Effect of Time duration of Grafting:With the conditions for maximum % weight add-on and good water absorbency obtained in terms of Initiator concentration, Monomer concentration and Temperature of Grafting, the time of grafting showed a positive effect on the % weight add-on and water absorbency value. Increase in time of grafting at optimized conditions of 0.2% wt/vol Initiator, 3% wt/vol Monomer and grafting at 70°C, showed a steady rise in % weight add-on as well as water absorbency. The increase in time duration of grafting helped completion of grafting onto fibre to give more weight add-on and thus increased water absorbency. But time taken more than 3 hours lead to hardening of the copolymer formed, thus creating a problem in Hydrolysis. Thus the time duration of Grafting was optimised to 3 hours.

Response Surface Diagrams for % Weight Add-on

• At Temp = 30°C

1

2

3

0

10

20

30

0.1

0.2

0.4

% Weight Add-on when Grafting at 30°C

Monomer ConcInitiator Conc

Response Surface Diagrams for % Weight Add-on

• At Temp = 70°C

12

3

0

10

20

30

40

50

60

70

0.1

0.2

0.4

% Weight Add-on when Grafting at 70°C

Monomer Conc

Initiator Conc

Response Surface Diagrams for % Weight Add-on

• At Temp = 100°C

12

3

0

10

20

30

40

50

60

70

0.1

0.2

0.3

% Weight Add-on when Grafting at 100°C

Initiator Conc

Monomer Conc

FT-IR Spectra• Raw Banana fibre

• The absorptions bands at 3600-3100 cm–1 can be assigned to stretching vibrations and other polymeric associations of hydroxyl groups. Symmetric stretching at 2913 cm–1 assigned to the CH2 groups present in polysaccharides. Angular deformations of C–H linkages of aromatic groups were observed at 858, 761, 668 and 576 cm–1. An overlapping of peaks was observed between 1654–1327 cm–1 and 1244–1026 cm–1 due to C–C, C=C, OH, CO, CHn, CH, and C–O–C vibrations. These are generally observed in cellulose, hemicellulose and lignin, suggesting an aromatic and ethereal character of the sample.

FT-IR Spectra• Bleached Banana fibre

• The differences in the FT-IR spectra of raw and Bleached Banana fibres are seen clearly. The change in the spectra occurs in between wavelengths 2913 cm-1 and 1654 cm-1. The removal of hemicellulose on other impurities after scouring and bleaching is indicated in between the stated wavelengths.

FT-IR Spectra• Acrylamide-g-Banana fibre:

The FT-IR spectrum shows characteristic broad bands at around 3400 and 1660 cm-1 which can be assigned to –NH2 and carboxamido groups, respectively. It also shows bands at 2880 and 2940 cm-1 which can be assigned to –CH2 and –CH3 groups of alkyl chains. Also, the bands at 2940 and 1060 cm-1 can be assigned to C–O-C ethereal group of the grafted copolymer.

ConclusionThis project was an attempt to utilize Banana fibre α-cellulose as a source of cellulose to prepare cellulose based SAPs. The procedure of the project was the optimization of the various parameters involved in the Graft Copolymerisation process of Acrylamide Monomer by Free radical Initiation technique using Ceric ammonium nitrate as the initiator. The parameters considered were Initiator Concentration, Monomer Concentration, Temperature of Grafting and Time Duration for Grafting.

The effects of each of the parameters were studied individually as well as relatively, on the water absorbency of the prepared grafted fibres. The results obtained showed that the optimum conditions involved in formation of the most absorbent copolymer were:• Initiator Concentration: Minimum 0.2% wt/vol• Monomer Concentration: Upto 3% wt/vol• Temperature of Grafting: 70°C• Time duration of Grafting: 3 hours