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Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength



Kh. M. Mostafa
 
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ABSTRACT

Methacrylamide (MAam) as a reactive monomer was directly grafted onto cotton yarns using a KMnO4 -HNO3 redox system by chemical initiation technique. The major factors affecting polymerization of MAam, such as KMnO4, nitric acid and MAam concentration as well as the reaction time (duration) and temperature of the polymerization were studied. This was done to establish the optimum conditions of grafting. It was found from the results that the graft yield is higher under the following conditions: using 0.07 N potassium permanganate as initiator, 80 meq L-1, nitric acid; 1 g, methacrylamide, reaction time, 60 min and polymerization temperature, 60 ° C, when using a material to liquor ratio of 1:50. On the other hand, the tensile strength of poly (MAam)-cotton yarn grafts copolymer having 18.55% graft yield exhibits a higher value than ungrafted cotton yarn. While, increasing the graft yields over 18.55% lead to a decrease in tensile strength of the grafted yarn.

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  How to cite this article:

Kh. M. Mostafa , 2005. Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength. Journal of Applied Sciences, 5: 341-346.

DOI: 10.3923/jas.2005.341.346

URL: https://scialert.net/abstract/?doi=jas.2005.341.346

INTRODUCTION

There has been considerable interest in recent years in the development of carbohydrate polymers with the capacity of creating effective functional groups for potential end use. A number of such materials have been prepared by grafting different vinyl monomers onto starch[1-7] and cellulose[8-14]. Of the chemical initiators used for the synthesis, the Mn (IV) ion in the presence of an activator has proved to be an efficient initiator[1,2]. The present study was undertaken with a view to develop improved conditions for vinyl graft co polymerization onto cotton yarns as well as studying the tensile strength of cotton yarn before and after grafting with respect to an increase in the initiator concentration in absence and presence of monomer. The up to date literature survey shows that it has been a very little work done on grafting on cotton yarns to examine such property[15,16].

MATERIALS AND METHODS

Cotton yarns (kindly supplied by Misr Company for Spinning and weaving, El-Mehala El-Kobra). Potassium permanganate, nitric acid, methacrylamide, sodium carbonate, ethanol and nonionic wetting agent were of pure grade chemicals.

Treatment of cotton yarn with Potassium Permanganate: Two grams of cotton yarn was immersed for 30 min at 50°C in 100 mL KMnO4 solution (0.01- 0.15 N) in a conical flask with a continuous shaking to ensure the homogeneity of MnO2 deposition all over the cotton yarn. After this treatment the yarn was thoroughly washed with distilled water several times to remove excess KMnO4 solution. It was then squeezed between two filter papers before being introduced into the polymerization solution.

Graft polymerization procedure: The graft polymerization reaction was carried out as follows: The potassium permanganate treated samples was introduced into a reaction flask containing different concentrations of nitric acid (10-150 meq L-1) and methacrylamide (0.5-3 g based on weight of substrate). A material to liquor ratio of 1:50 was used. The flask content was kept in a thermostatic water bath at different temperatures (30-80°C) for different durations (10-90 min). Nitrogen gas was purged into the reaction mixture to avoid the presence of oxygen and the flask content was shaken immediately and occasionally during the reaction. After the desired reaction time, the sample was removed and washed with cold water several times. The sample was then squeezed and dried in an electric oven at 105°C for 2 h and cooled over P2O5 in desiccators. It was found experimentally that, washing grafted cotton yarn with cold water 4-6 times is quite enough to remove the homopolymer (poly methacrylamide). Estimating the nitrogen% by a well-known Kjeldahal method of the grafted sample after each wash till constant nitrogen% evidences.

Determination of MNO2 quantity onto cotton yarn: The amount of MnO2 deposited onto cotton yarn was determined by adding 10 mL 0.1 N oxalic acid and 10 mL 2 N sulphuric acid to the cotton yarn treated with permanganate in a conical flask. The mixture was gently heated to about 60°C and then titrated against a KMnO4 solution of 0.01 N.

Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength

Where, V is the volume of KMnO4 equivalent to the MnO2 in the sample and W is the weight of the sample used.

Estimation of the graft yield: Graft yield of poly (MAam)-cotton yarn graft copolymer was estimated by measuring the nitrogen% by Kjeldahal method[17] and was determined as follows:

Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength

Testing
Tensile strength: It was measured according to ASTM procedure D-2256-66T.

N.B.: Tensile strength was measured three times for each sample and their standard deviation was calculated.

RESULTS AND DISCUSSION

Effect of potassium permanganate concentration on the amount of MnO2 Deposited Cotton yarn was treated with different concentrations (0.01-0.15 N) of KMnO4 solution as described in the Experimental section. The cotton samples treated with KMnO4 were monitored for MnO2 deposited over them.

Figure 1 shows the relation between the amount of MnO2 deposited onto the cotton yarn sample and the KMnO4 concentration. The data shows that the MnO2 deposit increases by increasing the KMnO4 concentration up to 0.07 N. Above this concentration no marked increase was observed and the amount of MnO2 deposited is almost the same over a range of KMnO4 concentration of 0.1-0.15 N.

Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
Fig. 1:
Effect of potassium permanganate concentrations on the amount of MnO2 deposited onto cotton yarns, Reaction conditions: Cotton yarn, 2 g; Treatment time, 30 min; treatment temperature, 50°C; nonionic wetting agent, 0.1%; material to liquor ratio, 1:50

Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
Fig. 2:
Graft yield of poly (MAam)-cotton yarn graft copolymer as a function of the amount of MnO2 deposited, Reaction conditions:Cotton yarn, 2 g; Methacrylamide, 1 g; HNO3, 80 meq L-1; Time, 60 min; Temperature, 60°C; material to liquor ratio, 1:50

It is logical to assume that MnO2 particles are deposited uniformly all over the cotton cellulose and are located at certain sites, most probably at the hydroxyl group of cotton cellulose. Once the accessible hydroxyl groups are occupied by MnO2 particles, extra deposition of MnO2 will be difficult and, if deposited, the particles will be easily removed during washing. This would explain why the amount of MnO2 deposited onto the cotton sample remains constant at higher concentrations of KMnO4, especially above 0.07 N.

Tentative mechanism of grafting: Cotton yarn was turned to a brownish, dark brownish or even black color when it was treated with KMnO4 solution, depending on the concentration of the KMnO4 solution used as described above. In the presence of an acid used HNO3 (HR), primary radical species formation occurs as a result of the action of an acid on the MnO2 deposited as follows:

Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
(1)

Once the free radical species Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength are formed, they produce cellulose macroradicals via direct abstraction of hydrogen atom from cellulose molecules. This reaction may be represented as follows:

Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
(2)

Where, Cell-OH represents the cotton cellulose molecule.

Cotton cellulose macro radicals may also be formed by direct attack of Mn4+ or Mn3+ ions on the cellulose molecule via abstraction of the hydrogen atom.

Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
(3)
Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
(4)

In the presence of a vinyl monomer the cellulose is added to the double bond of the vinyl monomer, resulting in a covalent bond between monomer and cellulose with creation of free radical on the monomer. i.e. a chain is initiated. Subsequent addition of monomer molecules to the initiated chain propagates the grafting reaction onto cellulose as follows:

Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
(5)

Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
(6)

Finally, termination of the growing grafted chain may occur via reaction with the initiator, coupling or combination and disproportionation as follows:

Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
(7)

Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
(8)

Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
(9)

Effect of MNO2 deposited on the graft yield: Figure 2 shows the graft yield of poly (MAam)-cotton graft copolymers versus the amount of MnO2 deposited onto cotton yarns. Obviously, the graft yields increases substantially as the MnO2 deposit increases until MnO2 concentration of 17.91 meq/100 g samples is reached and then remains constant. The enhancement in grafting by increasing the amount of MnO2 deposited up to 17.91 meq/100 g samples is duo to MnO2 and free radical species participate mainly in the creation of cellulose macro radicals, which are capable of initiating grafting. On the other hand, the fact that the graft yield remains constant after 17.91 meq/100 g sample is deposited onto the cotton yarns may be attributed to: (a) a faster termination rate between two chain radicals via bimolecular collision, (b) a lower diffusion rate of monomer from the aqueous phase to the cellulose phase duo to the excess amount of MnO2 deposited and © a higher oxygen production of inhibiting oxygen at a higher MnO2 concentration duo to the side reaction represented by the equation shown below:

Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
(10)

Effect of nitric acid concentration: Figure 3 shows the effect of the nitric acid concentration on the graft yield of poly (MAam)-cotton yarn graft copolymers. It is clear from the Fig. that increasing nitric acid concentration up to 80 meq L-1 is accompanied by enhancement in the graft yield. Above this concentration, grafting decreases.

Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
Fig. 3:
Effect of changing HNO3 concentration on the graft yield of poly (MAam)-cotton yarn graft copolymer, Reaction conditions: Cotton yarn, 2 g; MnO2, 17.91 meq/100 g sample; Methacrylamide, 1 g; Time, 60 min; Temperature, 60°C; material to liquor ratio, 1:50

Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
Fig. 4:
Effect of changing methacrylamide concentration on the graft yield of poly (MAam)-cotton yarn graft copolymer, Reaction conditions: Cotton yarn, 2 g; MnO2, 17.91 meq/100 g sample; HNO3, 80 meq L-1; Time, 60 min; Temperature, 60°C; material to liquor ratio, 1:50

The fall in the graft yield could be attributed to (a) the coagulation of colloidal homopolymer in the solution and in the fiber structure increases at lower pH. This retards the diffusion of both the monomer and the initiator into the fiber phase and (b) the side reaction as shown before in equation 10 increases at a higher acid concentration. Thus, besides consuming some MnO2 (required for the production of initiating species), it also leads to a constant production of inhibiting oxygen.

Effect of monomer concentration: Figure 4 shows the effect of MAam concentration on the graft yield of poly (MAam) -cotton yarn graft copolymers. The MAam concentration used ranged from (0.5-3 g). It was seen from the Fig. that, as the concentration of MAam increases, the graft yield also increases. This could have been associated with the higher availability of monomer molecules around the cellulose macroradicals.

Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
Fig. 5:
Effect of changing polymerization time and temperature on the graft yield of poly (MAam)-cotton yarn graft copolymer, Where, Series 1= 30°C, Series 2= 40°C, Series 3= 50°C, Series 4= 60°C, Series 5= 70°C, Series 6= 80°C, Reaction conditions: Cotton yarn, 2 g; MnO2, 17.91 meq/100 g sample; Methacrylamide, 1 g; HNO3, 80 meq L-1; material to liquor ratio, 1:50

The latter are relatively immobile and for grafting to occur, the monomer molecules need to be in close proximity to the substrate.

Effect of polymerization time and temperature: Figure 5 shows the graft yield of poly (MAam)-cotton yarns graft copolymer as a function of polymerization time at different temperatures. It is clear from the Fig. 5 that, the graft yields exhibiting an initial fast rate, which slows down with time, then levels off. This is observed regardless of the polymerization temperature used. The extent of grafting increases by raising the temperature from 30°-60°C. Increasing the temperature to 70°C and 80°C is accompanied by decreased grafting. The favorable effect of temperature (up to 60°C) on grafting could be ascribed to:

1. Higher diffusion from the aqueous phase to the cellulose phase;
2. Higher rate of initiation and propagation of the graft chain;
3. Greater swell ability of cotton fabric;
4. Better decomposition of the redox system, leading to more free radical species; and
5. Increased the mobility of the methacrylamide molecules.

On the other hand, the decrement in grafting observed at 70° and 80°C is perhaps duo to the faster termination rate and greater amount of homopolymer formation at higher temperatures.

Table 1:
Effect of changing KMnO4 concentration in absence of monomer on the tensile strength of cotton yarn
Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
Reaction conditions: Cotton yarn, 2 g; Treatment time, 30 min; treatment temperature, 50°C; nonionic wetting agent, 0.1%; material to liquor ratio, 1:50.
N.B.: Tensile strength was measured three times for each sample and their standard deviation was calculated

Table 2:
Effect of changing KMnO4 concentration in presence of monomer on the tensile strength of poly (MAam)-cotton yarn graft copolymers
Image for - Grafting of Methacrylamide onto Cotton Yarn Part I: Tensile Strength
Reaction conditions: Cotton yarn, 2 g; Methacrylamide, 1 g; HNO3, 80 meq L-1; Time, 60 min; Temperature, 60°C; material to liquor ratio, 1:50.
N.B.: Tensile strength was measured three times for each sample and their standard deviation was calculated

It may be further noted that leveling off grafting as the reaction proceed could be associated with depletion in monomer and initiator concentration as the reaction proceeds.

Tensile strength of cotton yarn before and after grafting: The tensile strength of cotton yarn before and after grafting was studied with respect:

1. Changing the KMnO4 concentration in absence of monomer.
2. Changing the KMnO4 concentrations in presence of monomer i.e. as the grafting proceeds.

N.B.: The tensile strength of cotton yarn before grafting was taken as a reference substrate just for comparison.

Effect of changing KMnO4 concentration in absence of monomer on the tensile strength of cotton yarn: Table 1 shows the effect of changing KMnO4 concentration on the tensile strength (g) of ungrafted cotton yarn. It is seen Table 1 that, increasing the initiator concentration from 0.01- 0.15 N without any monomer present in the reaction leads to a decrease in tensile strength of cotton yarns from 180 g in case of untreated cotton yarn to 157 g for that treated with 0.15 N KMnO4.

This can be attributed to both, the oxidation of cellulose and chain rapture, because of the initiator and the acidity of the reaction medium (15). On the other hand, the crystallinity of the fibers may be increases with increasing the initiator concentration, duo it is well known that grafting occurs on the amorphous region of cellulose as evidenced by Eichhorn[16].

Effect of changing KMnO4 concentration in presence of monomer on the tensile strength of poly (MAam)-cotton yarn graft copolymers: Table 2 shows the effect of changing KMnO4 concentration in presence of MAam on the tensile strength of poly (MAam)-cotton yarn graft copolymers. By increasing the graft yields to 18.35; the tensile strength increases then decreases by further increase in the graft yield. The increase in tensile strength by increasing the graft yield up to 18.35% may be duo to the strengthen of the yarn. While on the other hand a decrease in the tensile strength by increasing the graft yields may be duo to the combined effect of oxidation via initiator and grafting with the monomer.

On the other word, when the reaction is carried out in the presence of a monomer the oxidation or depolymerization is lower than in case of cotton alone, In this case the macro cellulose radicals generated by the initiator are used to carry out the graft copolymerization of the polymer and the degradation of the cellulose are reduced. Beside, the grafting of MAam onto the cellulose results in a reduction of the degree of crystalinity of the grafted fibers as shown before. While on the other hand, the effect of initiator concentration on the tensile strength of poly (MAam) –grafted cotton yarn is also noted. An increase in the amount of grafted MAam onto the cotton yarns results in a decrease of the crystalinity, because a large amount of a polymer is present on the grafted fibers (amorphous region). So, there is a noted decrease in the tensile strength as shown in tabular data presented in Table 2.

Nearly 38.6% graft yield on cotton yarn was obtained by applying the following reaction conditions: KMnO4, 0.07 N; HNO3, 80 meq/100 g sample; MAam, 1 g; Temperature, 60°C; Time, 60 min when using a material to liquor ratio of 1:50. On the other hand, the tensile strength of poly (MAam)-cotton yarn grafts copolymer having 18.55% graft yield exhibits a higher value than ungrafted cotton yarn. While, increasing the graft yields over 18.55% lead to a decrease in tensile strength of the grafted yarn.

ACKNOWLEDGMENT

I wish to express my deepest thank and appreciation to the spirit of Prof. Dr. M.I. Khalil Prof of Textile Chemistry, National Research Center for his valuable discussion, great support as well as all the facilities provided.

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