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Chemically induced graft copolymerization of itaconic acid onto cellulose fibers
Polymer Testing 21 (2002) 337–343 www.elsevier.com/locate/polytest
Material Characterisation
Chemically induced graft copolymerization of itaconic acid onto cellulose fibers M.W. Sabaa a, S.M. Mokhtar b
b,*
a Chemistry Department, Faculty of Science, Cairo University, Cairo, Egypt Chemistry Department, Faculty of Women, Ain Shams University, Cairo, Egypt
Received 21 June 2001; accepted 19 August 2001
Abstract Itaconic acid was grafted onto cellulose fibers using potassium persulfate as initiator. The effect of initiator concentration, monomer concentration and the reaction temperature on the grafting percentage has been investigated. The IR spectroscopy, X-ray diffraction, as well as the surface morphology of the grafted fibers were also studied. Moreover, the dyeing characteristics of the grafted fibers dyed with two basic dyes together with the color fastness of these dyes towards UV radiation was also investigated. The thermal stability of the grafted fibers was also studied using a thermogravimetric technique. 2002 Elsevier Science Ltd. All rights reserved. Keywords: Grafting; Itaconic acid; Cellulose fabrics; Dyeability; Thermal stability
1. Introduction The formation of copolymers of cellulose and various synthetic polymers via graft copolymerization has been extensively studied [1–10]. The percentage of monomer which is grafted onto the polymer is an important factor in the economics of the grafting process. Grafting of vinyl and acrylic monomers onto cellulose using persulfate radicals is common and was studied by different authors [11–15]. Therefore, the reaction occurs between the KSO•4 radical and cellulose to form cellulose radicals directly.
Also, preparing graft copolymers of cellulose with different monomers has been done to produce cellulose materials with modified properties, especially for their abilities towards the dyeing process and light fastness [10,16,17]. The dicarboxylic acid monomers such as itaconic acid and others were used as crosslinking agents for cellulose [18,19]. Moreover, the grafting of dimethyl itaconate onto microcrystalline cellulose was also studied [14]. In the present investigation, the possibility of grafting itaconic acid (IA) onto cotton fabrics by using potassium persulfate was investigated. The investigation was extended not only for the investigation of the effect of monomer and initiator concentrations, and the effect of temperature on the percent graft, but also for the characterization of the grafted fabric including its surface properties, degree of crystallinity, thermal stability, dyeability with some basic dyes and color fastness towards UV light. 2. Materials and experimental techniques 2.1. Materials
* Corresponding author. E-mail address: [email protected] Mokhtar).
(S.M.
Cellulose fabrics were supplied from El-Nasr–El-Beda Co., El-Mahala, Egypt. Itaconic acid (I) (BDH) was pur-
0142-9418/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 2 - 9 4 1 8 ( 0 1 ) 0 0 0 9 4 - 0
338
M.W. Sabaa, S.M. Mokhtar / Polymer Testing 21 (2002) 337–343
ified by twice crystallizing from distilled water m.p. 166°C. Potassium persulfate (Hopkin & Williams Ltd.) was used as supplied. Two basic dyes, Methylene Blue (C.I. Basic Blue 9,52015) and Remacryl-Rot E-2BL basic dye supplied by Hoechest, Germany were used for the present investigation without further purification.
3. Experimenal techniques 3.1. Preparation of the fabrics The fabric was soaked in a detergent solution for 60 min, followed by extensive washing with tap water until free from any detergent. The clean fabric was then washed with distilled water, squeezed, and allowed to dry in an air oven at 60°C, and finally stored in a vacuum desiccator ready for use.
Fig. 1. Effect of monomer concentrations on the degree of grafting of cellulosic fabrics [KSO•4]=0.05 mol/l.
3.2. Graft copolymerization procedure The appropriate amount of fabric was placed in a round bottomed flask and stirred in a water solution containing an appropriate amount of the initiator. The appropriate amount of IA was added and the polymerization reaction was allowed to proceed in a preheated water bath at the desired temperatures for the required time. When the grafting time was over, the grafted fabric was washed thoroughly with distilled water, then extracted with hot water for 5 h in order to dissolve any homopolymer which may have adhered to the surface of the fabric. The grafted samples were then allowed to dry in an air oven at 60°C, until constant weight. The graft percentage was determined by the percent increase in weight as follows: (Wg−Wo)×100 %Graft⫽ Wo where Wo and Wg represent the weights of the initial and the grafted fabric, respectively. 3.3. Dyeing procedure [20] The fabric either grafted or ungrafted was immersed in a dye bath composed of 0.1% aqueous solution of the dye. The dye liquor ratio (1:100) was always kept con-
Fig. 2. Effect of initiator concentration on the degree of grafting of cellulosic fabrics with monomer concentrations=2.0 mol/l.
stant for all samples and the pH of the dye bath was adjusted by adding drops of 1% of acetic acid/sodium acetate buffer solution. The temperature of the dye bath was then gradually raised to 95°C over 30 min, and was kept at this temperature for an additional 50 min. The temperature of the dye bath was then allowed to cool to 60°C, the dyed fabric was squeezed, rinsed thoroughly
M.W. Sabaa, S.M. Mokhtar / Polymer Testing 21 (2002) 337–343
Fig. 3. Effect of temperature on the degree of grafting of cellulosic fabrics with IA monomer concentrations 2.0 mol/l and initiator concentration 0.05 mol/l.
339
Fig. 4. LogR of grafting of cellulose with IA vs 1/T.
with water and dried in air. The amount of the dye absorbed was measured by conventional colorimetric methods to measure the concentration of the dye remaining in the dye bath.
4. Instruments used in the characterization of grafted cellulosic fabrics 4.1. Infrared spectroscopy A Perkin Elmer 398 IR-transmission spectrophotometer ranging from 400 to 4000 cm⫺1 was used. 4.2. X-ray diffraction X-ray diffraction curves for the various investigated samples were measured using a Phillips apparatus (PW 1390 channel control and Pw goniometer supply) using nickel filtered Cu–Ka radiation. The measurements were performed on unoriented fabrics. 4.3. Themogravimetric analyses Thermogravimetry (TG) for the various investigated samples was performed using a Shimadzu TG-50H analyzer with a heating rate of 10°C min⫺1.
Fig. 5. Infrared spectra of ungrafted and grafted cellulosic fabrics with IA having different degrees of grafting: (a) ungrafted fabric; (b) Cell-g-IA, 5.8% grafting; (c) 12.76% grafting.
4.4. Ultraviolet fastness of the dyed samples The UV fastness of the various dyed samples was performed using a low pressure mercury lamp. 4.5. Color strength measurements Color strength expressed as K/S, was calculated from the reflectance values measured with Hunterlab colorimeter Model D 25-2 USA. The K/S values are calculated using the Kubelka–Munk equation [21]:
340
M.W. Sabaa, S.M. Mokhtar / Polymer Testing 21 (2002) 337–343
K/S⫽(1⫺R)2/2R where R is the observed reflectance, K is the absorption coefficient, and S is the scattering coefficient. 4.6. Scanning microscope The surface morphology of ungrafted and grafted fabrics was investigated using a JSM-T220 scanning microscope.
5. Results and discussion The mechanism of grafting vinyl monomers onto cellulose using potassium persulfate as oxidizing initiator is reported in the literature [22]. The effect of monomer concentration on the percent graft is represented in Fig. 1. The results clearly reveal the increase in the percent graft with increasing the IA concentration at constant initiator concentration. Fig. 2 on the other hand, illustrates the effect of initiator
concentration on the percent graft. The results reveal the increase in the amount of graft with the increase in the initiator concentrations up to 苲0.05 mol/l. A further increase in the concentration of the initiator leads to a decrease in the percent of graft. This is probably due to the increase in the amount of homopolymer as a result of increasing the initiator concentration above a certain limit, which will consequently oppose the diffusion of the monomers towards the surface of the fabric. The same results and explanation were reported previously in the literature [10], where the formation of homopolymer takes place at the expense of the grafting process. The effect of temperature for different time intervals on the percent graft is represented in Fig. 3. The results show that the percent graft increases with raising the temperature. The activation energy [22] (⌬E) which is a composite of Ep+1/2Ed⫺1/2Et (where Ep refers to the energy of propagation, Ed to initiator decomposition and Et refers to termination) was found to be equal to 32.25 kJ/mol, which is reasonable for a redox free radical polymerization (Fig. 4).
Fig. 6. X-ray diffraction of ungrafted and grafted cellulosic fabrics with IA, having different degrees of grafting: (a) ungrafted fabric; (b) Cell-g-IA, 8.1% grafting; (c) 26.34% grafting.
M.W. Sabaa, S.M. Mokhtar / Polymer Testing 21 (2002) 337–343
The IR spectra of ungrafted cellulose and cellulose fabric grafted to different extents with IA is illustrated in Fig. 5. The results give confirmation of the grafting process. This is illustrated by the appearance of a new band at 苲1731 cm⫺1, characteristic of the carboxylic group of IA. Moreover, the figure also indicates the increase in the peak intensities of the carbonyl group as a function of the percent graft. 5.1. X-ray diffraction of grafted fabrics The variation in the degree of crystallinity of the grafted cellulose fabric was studied by measuring the Xray diffraction of the grafted samples with different degrees of grafting together with the ungrafted ones (Fig. 6). The results clearly show a remarkable decrease in the degree of crystallinity with the increase in the percentage
341
of grafting (2q=23°, 15° and 16.5°). Moreover, the Xray diffraction shows a shift in the position at 2q=15° and 16°, with the disappearance of the peak at 2q=46.5°, which may reflect a change in the chemical structure and, consequently, a rearrangement in the morphology of the polymeric chain as a result of grafting. The lowering in the degree of crystallinity is attributed to an increase in the intermolecular distance between the cellulosic chains as a result of grafting, which consequently lowers the degree of H-bonding between the chains and thus increases the amorphous regions. 5.2. Surface morphology of the grafted fabrics The surface morphology of the grafted fabrics with IA and ungrafted fabrics has been investigated using a JSMT220 scanning microscope (Fig. 7). In order to elucidate
Fig. 7. Surface topology of (a) ungrafted and (b) grafted cellulosic fabrics with IA. (a) Order of magnitude 700; (b) order of magnitude 1000.
342
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Table 1 Thermal stability of cellulose fabrics and the grafted copolymer with IA in air, heating rate 10°C/min Samples
Ungrafted fabric Cell-g-IA 5.8%G Cell-g-IA 26.46%G a
IDT a (°C)
350 320 333.3
Wt loss (%) 350°C
400°C
450°C
500°C
4.0% 15.2% 19.6%
67.2% 55.20% 52.0%
82.4% 57.60% 69.0%
86.6% 60.20% 77.20%
IDT is the initial decomposition temperature.
the topological changes under the grafting reactions, the micrographs of the investigated samples are represented with two different instrument magnifications. The results show a pronounced swelling effect on the fiber and the diameter of individual fiber seems to become thicker with an increase in the degree of grafting, which indicates that the grafting mainly occurred within the fiber. Moreover, the results also reveal that there are no signs of cracks on the fibers due to grafting. 5.3. Thermogravimetry of the grafted cellulosic fabrics The effect of the degree of grafting on the thermal stability of cellulosic fabrics was studied using the thermogravimetric technique. Fig. 8 represent the TG curves for ungrafted fabric and for fabric grafted to various degrees. The results reveal a decrease in the thermal stability with an increase in the percent grafting. This may be attributed to the low thermal stability of poly itaconic acid [23] (as the increase in weight loss is most probably attributed to decarboxylation reaction of the grafted acid). The same results were reported when dimethyl itaconate was grafted onto microcrystalline cellulose [24]. Moreover, a little delay in the rate of ther-
Fig. 8. Thermalgravimetric (TG) analysis of ungrafted and grafted cellulosic fabrics with IA.
Table 2 The remaining and absorbed percent of dyes on the grafted and ungrafted samples Samples Methylene Blue Ungrafted Cell.-g-IA Cell.-g-IA Cell-g-IA Remacryl Rot Ungrafted Cell.-g-IA Cell.-g-IA
%G
Absorbed dyes(%)
Remaining dyes(%)
— 5.8 17.0 26.46
40.71 80.60 85.8 92.44
59.20 19.40 14.2 7.56
— 18.5 26.34
74.90 94.72 95.72
25.10 5.52 4.48
mal degradation of cellulose fabrics grafted with IA is observed at the later stages of degradation as seen from Table 1 and Fig. 8. 5.4. Dyeing and fastness properties of grafted fabrics The effect of grafting on the dyeability of cellulosic fabric was studied using both Methylene Blue and Remacryl Rot basic dyes. The amount of dye absorbed on the fabric was measured by two different techniques: The first one is performed by measuring the amount of remaining dye in the dye bath after the dyeing process was completed, and this is done by conventional colorimetric methods. The second is through measuring the amount of dye absorbed on the fabric (color strength) expressed as K/S. The results are summarized in Table 2. The results reveal a great improvement in the dyeability of fabrics grafted with IA as compared with the ungrafted fabrics for the two investigated dyes. Moreover, the results reveal that the amount of absorbed dye increases with an increase in the percent graft. The UV fastness of the various dyed fabrics either ungrafted or grafted to different extents has been determined using a low pressure Hg-lamp. The results show good fastness towards UV light for grafted samples as compared with the blank one (exposure time up to 10 h). Moreover, grafting by IA has improved some of the
M.W. Sabaa, S.M. Mokhtar / Polymer Testing 21 (2002) 337–343
physical properties of the cellulose fabrics such as appearance, softness and need for ironing.
References [1] A. Hebish, Koloriszt. Ert. 13 (1-2) (1971) 12. [2] J. Hermans, J. Pure Appl. Chem. 5 (1962) 147. [3] K. Hitoshi, K. Shin, J. Appl. Polym. Sci. 64 (16) (1997) 2259. [4] M. Ratzsch, L. Dunsch, G. Petzold, A. Petr, A. Heger, Acta Polym. 41 (12) (1990) 620. [5] J. Schurz, Papier 16 (1962) 525. [6] T. Liegui, Z. Yuqin, J. Kennedy, F. Guangzhou, Carbohydr. Polym. 19 (3) (1992) 191. [7] J.C. Arthur, J. Adv. Chem. Series 91 (1962) 547. [8] J.C. Arthur, J. Adv. Chem. Series 99 (1971) 321. [9] J.C. Arthur, J. Adv. Macromol. Chem. 2 (1970) 1. [10] S.M. Mokhtar, T.B. Mostapha, M.W. Sabaa. J. Polym. Plastics Technol. Eng., in press. [11] A.Y. Kulkarni, A.G. Chitale, B.K. Vaidya, P.C. Mehta, J. Appl. Polym. Sci. 7 (1963) 1581. [12] N.G. Gaylord, T. Tomono, J. Polym. Sci. B 13 (1975) 697.
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[13] K. Bardhan, S. Mukhopadhyay, S.R. Chatterjee, J. Polym. Sci. Chem. 15 (1977) 141. [14] E. Schwab, V.T. Stannett, J.J. Hermans, Tappi. 44 (1961) 251. [15] M.W. Sabaa, M.G. Mikhael, S.S. Elkholy, M.Z. Elsabee, Cell. Chem. Technol. 29 (1995) 671. [16] J. Dannhein, KH. Keil, T. Martini. Eur. Pat. Appl. EP 509, 397, 21 Oct 1992; DE Appl. 4, 11, 12, 227, 15 Apr 1991. 23 p. [17] H. Keil, T. Martini. Eur. Pat. Appl. EP 509, 277, 21 Oct 1992; DE Appl. 4, 112, 228, 15 Apr 1991. p. 16. [18] M.H. Choi, Text. Res. J. 62 (10) (1992) 614. [19] M.H. Choi, C.M. Welch, Text. Chem. Color 26 (6) (1994) 23. [20] M.W. Sabaa, H. Watamoto, M. Sakamoto, K. Furuhata, J. Appl. Polym. Sci. 31 (1986) 1131. [21] D.B. Judd, G. Wyszocki, Color in business, Science, 3rd ed., Wiley, New York, 1975. [22] A. Hebeish, J.T. Guthrie, Polymer properties and applications — 4. The chemistry and technology of cellulosic copolymers, Springer-Verlag, Berlin, 1981. [23] A. Isihara, E. Guth, Adv. Polym. Sci. 5 (1967) 233. [24] J. Reluert, P.M. Yazdani, J. Macromol. Sci. Chem. A 29 (1) (1992) 31.
Material Characterisation
Chemically induced graft copolymerization of itaconic acid onto cellulose fibers M.W. Sabaa a, S.M. Mokhtar b
b,*
a Chemistry Department, Faculty of Science, Cairo University, Cairo, Egypt Chemistry Department, Faculty of Women, Ain Shams University, Cairo, Egypt
Received 21 June 2001; accepted 19 August 2001
Abstract Itaconic acid was grafted onto cellulose fibers using potassium persulfate as initiator. The effect of initiator concentration, monomer concentration and the reaction temperature on the grafting percentage has been investigated. The IR spectroscopy, X-ray diffraction, as well as the surface morphology of the grafted fibers were also studied. Moreover, the dyeing characteristics of the grafted fibers dyed with two basic dyes together with the color fastness of these dyes towards UV radiation was also investigated. The thermal stability of the grafted fibers was also studied using a thermogravimetric technique. 2002 Elsevier Science Ltd. All rights reserved. Keywords: Grafting; Itaconic acid; Cellulose fabrics; Dyeability; Thermal stability
1. Introduction The formation of copolymers of cellulose and various synthetic polymers via graft copolymerization has been extensively studied [1–10]. The percentage of monomer which is grafted onto the polymer is an important factor in the economics of the grafting process. Grafting of vinyl and acrylic monomers onto cellulose using persulfate radicals is common and was studied by different authors [11–15]. Therefore, the reaction occurs between the KSO•4 radical and cellulose to form cellulose radicals directly.
Also, preparing graft copolymers of cellulose with different monomers has been done to produce cellulose materials with modified properties, especially for their abilities towards the dyeing process and light fastness [10,16,17]. The dicarboxylic acid monomers such as itaconic acid and others were used as crosslinking agents for cellulose [18,19]. Moreover, the grafting of dimethyl itaconate onto microcrystalline cellulose was also studied [14]. In the present investigation, the possibility of grafting itaconic acid (IA) onto cotton fabrics by using potassium persulfate was investigated. The investigation was extended not only for the investigation of the effect of monomer and initiator concentrations, and the effect of temperature on the percent graft, but also for the characterization of the grafted fabric including its surface properties, degree of crystallinity, thermal stability, dyeability with some basic dyes and color fastness towards UV light. 2. Materials and experimental techniques 2.1. Materials
* Corresponding author. E-mail address: [email protected] Mokhtar).
(S.M.
Cellulose fabrics were supplied from El-Nasr–El-Beda Co., El-Mahala, Egypt. Itaconic acid (I) (BDH) was pur-
0142-9418/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 1 4 2 - 9 4 1 8 ( 0 1 ) 0 0 0 9 4 - 0
338
M.W. Sabaa, S.M. Mokhtar / Polymer Testing 21 (2002) 337–343
ified by twice crystallizing from distilled water m.p. 166°C. Potassium persulfate (Hopkin & Williams Ltd.) was used as supplied. Two basic dyes, Methylene Blue (C.I. Basic Blue 9,52015) and Remacryl-Rot E-2BL basic dye supplied by Hoechest, Germany were used for the present investigation without further purification.
3. Experimenal techniques 3.1. Preparation of the fabrics The fabric was soaked in a detergent solution for 60 min, followed by extensive washing with tap water until free from any detergent. The clean fabric was then washed with distilled water, squeezed, and allowed to dry in an air oven at 60°C, and finally stored in a vacuum desiccator ready for use.
Fig. 1. Effect of monomer concentrations on the degree of grafting of cellulosic fabrics [KSO•4]=0.05 mol/l.
3.2. Graft copolymerization procedure The appropriate amount of fabric was placed in a round bottomed flask and stirred in a water solution containing an appropriate amount of the initiator. The appropriate amount of IA was added and the polymerization reaction was allowed to proceed in a preheated water bath at the desired temperatures for the required time. When the grafting time was over, the grafted fabric was washed thoroughly with distilled water, then extracted with hot water for 5 h in order to dissolve any homopolymer which may have adhered to the surface of the fabric. The grafted samples were then allowed to dry in an air oven at 60°C, until constant weight. The graft percentage was determined by the percent increase in weight as follows: (Wg−Wo)×100 %Graft⫽ Wo where Wo and Wg represent the weights of the initial and the grafted fabric, respectively. 3.3. Dyeing procedure [20] The fabric either grafted or ungrafted was immersed in a dye bath composed of 0.1% aqueous solution of the dye. The dye liquor ratio (1:100) was always kept con-
Fig. 2. Effect of initiator concentration on the degree of grafting of cellulosic fabrics with monomer concentrations=2.0 mol/l.
stant for all samples and the pH of the dye bath was adjusted by adding drops of 1% of acetic acid/sodium acetate buffer solution. The temperature of the dye bath was then gradually raised to 95°C over 30 min, and was kept at this temperature for an additional 50 min. The temperature of the dye bath was then allowed to cool to 60°C, the dyed fabric was squeezed, rinsed thoroughly
M.W. Sabaa, S.M. Mokhtar / Polymer Testing 21 (2002) 337–343
Fig. 3. Effect of temperature on the degree of grafting of cellulosic fabrics with IA monomer concentrations 2.0 mol/l and initiator concentration 0.05 mol/l.
339
Fig. 4. LogR of grafting of cellulose with IA vs 1/T.
with water and dried in air. The amount of the dye absorbed was measured by conventional colorimetric methods to measure the concentration of the dye remaining in the dye bath.
4. Instruments used in the characterization of grafted cellulosic fabrics 4.1. Infrared spectroscopy A Perkin Elmer 398 IR-transmission spectrophotometer ranging from 400 to 4000 cm⫺1 was used. 4.2. X-ray diffraction X-ray diffraction curves for the various investigated samples were measured using a Phillips apparatus (PW 1390 channel control and Pw goniometer supply) using nickel filtered Cu–Ka radiation. The measurements were performed on unoriented fabrics. 4.3. Themogravimetric analyses Thermogravimetry (TG) for the various investigated samples was performed using a Shimadzu TG-50H analyzer with a heating rate of 10°C min⫺1.
Fig. 5. Infrared spectra of ungrafted and grafted cellulosic fabrics with IA having different degrees of grafting: (a) ungrafted fabric; (b) Cell-g-IA, 5.8% grafting; (c) 12.76% grafting.
4.4. Ultraviolet fastness of the dyed samples The UV fastness of the various dyed samples was performed using a low pressure mercury lamp. 4.5. Color strength measurements Color strength expressed as K/S, was calculated from the reflectance values measured with Hunterlab colorimeter Model D 25-2 USA. The K/S values are calculated using the Kubelka–Munk equation [21]:
340
M.W. Sabaa, S.M. Mokhtar / Polymer Testing 21 (2002) 337–343
K/S⫽(1⫺R)2/2R where R is the observed reflectance, K is the absorption coefficient, and S is the scattering coefficient. 4.6. Scanning microscope The surface morphology of ungrafted and grafted fabrics was investigated using a JSM-T220 scanning microscope.
5. Results and discussion The mechanism of grafting vinyl monomers onto cellulose using potassium persulfate as oxidizing initiator is reported in the literature [22]. The effect of monomer concentration on the percent graft is represented in Fig. 1. The results clearly reveal the increase in the percent graft with increasing the IA concentration at constant initiator concentration. Fig. 2 on the other hand, illustrates the effect of initiator
concentration on the percent graft. The results reveal the increase in the amount of graft with the increase in the initiator concentrations up to 苲0.05 mol/l. A further increase in the concentration of the initiator leads to a decrease in the percent of graft. This is probably due to the increase in the amount of homopolymer as a result of increasing the initiator concentration above a certain limit, which will consequently oppose the diffusion of the monomers towards the surface of the fabric. The same results and explanation were reported previously in the literature [10], where the formation of homopolymer takes place at the expense of the grafting process. The effect of temperature for different time intervals on the percent graft is represented in Fig. 3. The results show that the percent graft increases with raising the temperature. The activation energy [22] (⌬E) which is a composite of Ep+1/2Ed⫺1/2Et (where Ep refers to the energy of propagation, Ed to initiator decomposition and Et refers to termination) was found to be equal to 32.25 kJ/mol, which is reasonable for a redox free radical polymerization (Fig. 4).
Fig. 6. X-ray diffraction of ungrafted and grafted cellulosic fabrics with IA, having different degrees of grafting: (a) ungrafted fabric; (b) Cell-g-IA, 8.1% grafting; (c) 26.34% grafting.
M.W. Sabaa, S.M. Mokhtar / Polymer Testing 21 (2002) 337–343
The IR spectra of ungrafted cellulose and cellulose fabric grafted to different extents with IA is illustrated in Fig. 5. The results give confirmation of the grafting process. This is illustrated by the appearance of a new band at 苲1731 cm⫺1, characteristic of the carboxylic group of IA. Moreover, the figure also indicates the increase in the peak intensities of the carbonyl group as a function of the percent graft. 5.1. X-ray diffraction of grafted fabrics The variation in the degree of crystallinity of the grafted cellulose fabric was studied by measuring the Xray diffraction of the grafted samples with different degrees of grafting together with the ungrafted ones (Fig. 6). The results clearly show a remarkable decrease in the degree of crystallinity with the increase in the percentage
341
of grafting (2q=23°, 15° and 16.5°). Moreover, the Xray diffraction shows a shift in the position at 2q=15° and 16°, with the disappearance of the peak at 2q=46.5°, which may reflect a change in the chemical structure and, consequently, a rearrangement in the morphology of the polymeric chain as a result of grafting. The lowering in the degree of crystallinity is attributed to an increase in the intermolecular distance between the cellulosic chains as a result of grafting, which consequently lowers the degree of H-bonding between the chains and thus increases the amorphous regions. 5.2. Surface morphology of the grafted fabrics The surface morphology of the grafted fabrics with IA and ungrafted fabrics has been investigated using a JSMT220 scanning microscope (Fig. 7). In order to elucidate
Fig. 7. Surface topology of (a) ungrafted and (b) grafted cellulosic fabrics with IA. (a) Order of magnitude 700; (b) order of magnitude 1000.
342
M.W. Sabaa, S.M. Mokhtar / Polymer Testing 21 (2002) 337–343
Table 1 Thermal stability of cellulose fabrics and the grafted copolymer with IA in air, heating rate 10°C/min Samples
Ungrafted fabric Cell-g-IA 5.8%G Cell-g-IA 26.46%G a
IDT a (°C)
350 320 333.3
Wt loss (%) 350°C
400°C
450°C
500°C
4.0% 15.2% 19.6%
67.2% 55.20% 52.0%
82.4% 57.60% 69.0%
86.6% 60.20% 77.20%
IDT is the initial decomposition temperature.
the topological changes under the grafting reactions, the micrographs of the investigated samples are represented with two different instrument magnifications. The results show a pronounced swelling effect on the fiber and the diameter of individual fiber seems to become thicker with an increase in the degree of grafting, which indicates that the grafting mainly occurred within the fiber. Moreover, the results also reveal that there are no signs of cracks on the fibers due to grafting. 5.3. Thermogravimetry of the grafted cellulosic fabrics The effect of the degree of grafting on the thermal stability of cellulosic fabrics was studied using the thermogravimetric technique. Fig. 8 represent the TG curves for ungrafted fabric and for fabric grafted to various degrees. The results reveal a decrease in the thermal stability with an increase in the percent grafting. This may be attributed to the low thermal stability of poly itaconic acid [23] (as the increase in weight loss is most probably attributed to decarboxylation reaction of the grafted acid). The same results were reported when dimethyl itaconate was grafted onto microcrystalline cellulose [24]. Moreover, a little delay in the rate of ther-
Fig. 8. Thermalgravimetric (TG) analysis of ungrafted and grafted cellulosic fabrics with IA.
Table 2 The remaining and absorbed percent of dyes on the grafted and ungrafted samples Samples Methylene Blue Ungrafted Cell.-g-IA Cell.-g-IA Cell-g-IA Remacryl Rot Ungrafted Cell.-g-IA Cell.-g-IA
%G
Absorbed dyes(%)
Remaining dyes(%)
— 5.8 17.0 26.46
40.71 80.60 85.8 92.44
59.20 19.40 14.2 7.56
— 18.5 26.34
74.90 94.72 95.72
25.10 5.52 4.48
mal degradation of cellulose fabrics grafted with IA is observed at the later stages of degradation as seen from Table 1 and Fig. 8. 5.4. Dyeing and fastness properties of grafted fabrics The effect of grafting on the dyeability of cellulosic fabric was studied using both Methylene Blue and Remacryl Rot basic dyes. The amount of dye absorbed on the fabric was measured by two different techniques: The first one is performed by measuring the amount of remaining dye in the dye bath after the dyeing process was completed, and this is done by conventional colorimetric methods. The second is through measuring the amount of dye absorbed on the fabric (color strength) expressed as K/S. The results are summarized in Table 2. The results reveal a great improvement in the dyeability of fabrics grafted with IA as compared with the ungrafted fabrics for the two investigated dyes. Moreover, the results reveal that the amount of absorbed dye increases with an increase in the percent graft. The UV fastness of the various dyed fabrics either ungrafted or grafted to different extents has been determined using a low pressure Hg-lamp. The results show good fastness towards UV light for grafted samples as compared with the blank one (exposure time up to 10 h). Moreover, grafting by IA has improved some of the
M.W. Sabaa, S.M. Mokhtar / Polymer Testing 21 (2002) 337–343
physical properties of the cellulose fabrics such as appearance, softness and need for ironing.
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