Acrylamide Grafting on Banana Fibres for Increased Water Absorbency and Retention

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... Pl

Acrylamide Grafting on Banana

fibres

Final Year B.Tech Project by

Ketki Chavan ( B.Tech – F.T.P.T.)

(2014)

(chemical composition varies with the variety of the plant and

geographical conditions where the plant was grown)

Characteristics of Banana fibres

• Strong moisture absorbing ability; absorbs as well

as releases moisture very fast.

• Eco-friendly fibre.

• 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

• 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 reaction is often preceded by complexing of the ceric ion by the polysaccharides.

oxidation-• 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 Alcohol

All supplied by Ami Chemicals of S D Fine Chemicals, Mumbai.

Materials & Methods

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 soap

Bleaching 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.

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

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:

• 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

• 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)

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

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

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

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

Initator con = 0.2(%wt/vol)

Time Duration Optimization

• 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.