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Microwave induced graft copolymerization of binary monomers onto luffa cylindrica fiber: removal of congo red
Available online at www.sciencedirect.com
ScienceDirect Available online at www.sciencedirect.com Procedia Engineering00 (2017) 000–000
ScienceDirect
www.elsevier.com/locate/procedia
Procedia Engineering 200 (2017) 408–415
3rd International Conference on Natural Fibers: Advanced Materials for a Greener World, ICNF 2017, 21-23 June 2017, Braga, Portugal
Microwave induced graft copolymerization of binary monomers onto luffa cylindrica fiber: removal of congo red
a
Deepak Pathaniaa*, Arush Sharmaa, Vandana sethia
School of Chemistry, Shoolini University, Solan-173212, Himachal Pradesh, India
Abstract In this work, graft copolymerization of delignified Luffa cylindrica fiber with methyl acrylate (MA) and acrylic acid has been attempted in presence of microwave radiation. Different reaction conditions affecting the grafting percentage (Pg) were optimized to get the maximum graft yield. The grafted fibres were subsequently subjected for the evaluation of physico-chemical properties such as swelling behaviour, moisture absorbance and chemical resistance. Further, morphological and structural analysis of raw and delignified Luffa cylindrica-g-poly(MA/AA) were studied using Fourier transform infra red (FTIR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA).The tensile properties of grafted and ungrafted fibre samples were also reported. The adsorption potential of modified fiber was investigated using adsorption isotherms for hazardous congo red dye removal from aqueous system. The maximum adsorption capacity of dye onto grafted Luffa cylindrica fiber was found to be 19.24 mg/g with best fit for Langmuir isotherm. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 3rd International Conference on Natural Fibers: Advanced Materials for a Greener World. Keywords:Luffa cylindrical; binary monomers; grafting; microwave radiations; congo red; adsorption
* Corresponding author. E-mail address: [email protected]
1. Introduction Biodegradable polymeric materials have been considered as the most potential materials due to their easy availability and cost effectiveness. Cellulosic fibers have received increased attention from environmental scientists 1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 3rd International Conference on Natural Fibers: Advanced Materials for a Greener World.
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 3rd International Conference on Natural Fibers: Advanced Materials for a Greener World 10.1016/j.proeng.2017.07.057
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recently. These materials offer many advantages such as low specific gravity, suitable mechanical properties and recyclability. Moreover, they have lower weights and less cost than synthetic fibers [1]. Cellulose structure consists of monomeric unit of α, β-glucopyranose linked through1,4-glucosidic linkage. Cellulose is renewable, cheap, and low in density, exhibits better processing flexibility. Cellulose structure are linked through1,4-glucosidic linkage. Cellulose is renewable, cheap, and low in density, exhibits better processing flexibility. Cellulose is a highly functionalized, linear stiff chain homopolymer, characterized by hydrophilicity, chirality, biodegrability and broad chemical modifying capacity [2,3]. Due to the presence of hydrophilic hydroxyl groups on the surface of cellulosic fibers, their use is restricted under moist atmospheres and polar solvents [4-6]. Further these fibers are also more disposed to the attack acids, bases and salts. Therefore, these fibers need surface modifications in order to improve their properties before used in various applications. Grafting of vinyl monomers onto cellulosic fiber using initiators have been investigated by different researchers for producing desired alteration in physicochemical properties [710]. The grafting resulted in improved elasticity, water adsorption, ion exchange capability and heat resistance etc. Grafted cellulosic fibers have been currently used as adsorbents for the removal of hazardous metal ions and dyes from aqueous solutions due to good selectivity, stability, adjustable functionality, enhanced surface area and porosity. The polymer grafting fibers usually increased the density of adsorption sites and sorption selectivity for the target metal and dyes. Aquatic environmental contamination by synthetic dyes is a thrust area of research, due to their negative effects and bioaccumulation in flora and fauna [11-16]. Synthetic dyes released by pigment manufacturing, textile, paper, tanning, dyeing, painting, photographic, food and cosmetics industry affect photosynthesis and their adulteration also obstruct the light penetration into aquatic system. Additionally, dye molecules can also be decomposed into carcinogenic aromatic amines under aerobic conditions which causes serious health problems like allergy, dermatitis, skin irritation and cancer to animals and human beings [17,18].Therefore, this study deals with the investigation of effective, inexpensive, biodegradable and eco-friendly biosorbent prepared by graft copolymerization of methyl acrylate/ acrylic acid (MA/AA) onto luffa cylindrica fiber for the amputation of congo red dye from aquatic system. Moreover, instrumental techniques such as FTIR, SEM, XRD and TGA were used to characterize the raw and grafted fibre. 2. Experimental 2.1. Chemicals Vinyl monomer such as Methyl acrylate (MA), Acrylic acid (AA) were obtained from E-Merck chemicals, Sodium hydroxide, Ethanol, Congo red,acetone , nitric acid, dimethyl formamide and Benzene were received from CHD, India. All these chemicals were used as received. 2.2. Graft copolymerization of methyl acrylate/ acrylic acid (MA/AA) onto luffa cylindrica fiber Fiber (0.5 g) was activated by immersing in 100 mL of distilled water for 24 hours before grafting with binary monomer. Then a known amount of methyl acrylate/acrylic acid binary monomer was added in a definite ratio with constant stirring solution. Different reaction parameters have been optimized to get maximum grafting yield. The homopolymer formed during the graft copolymerization was removed with hot distilled water followed by methanol. The grafted sample thus obtained was dried at 500 C. The percentage grafting yield (%G) was determined as follow: % Grafting yield =
𝑊𝑊3 − 𝑊𝑊1 𝑊𝑊1
×100
(1)
where, W1 is the initial weight of the raw fiber and W3 is the final weight of the grafted fiber after extraction of homopolymer. The scheme of graft copolymerization of MA/AA ontoLuffa cylindrica fiber is shown as: Cellulose----OH
+ Poly--(MA/AA)
( L.cylindrica fiber ) ( binary monomer )
MW
Cellulose-----(MA/AA) n ( graft copolymer )
3. Results and discussion 3.1. Optimization of MA and AA concentration in MA/AA binary monomer: It has been clear from Table 1 and Fig.1a that graft yield was highest at low concentration of MA and decreased with increase in concentration. This was due to dominance of homopolymerization with increase in monomer
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concentration. The maximum grafting yield of 28% was observed at1.12 x10-3 mol/L concentration of MA in MA/AA binary monomer. The increase in grafting yield with the concentration of AA was observed initially and then decreases with further increase in the concentration. The decrease in grafting yield was due to the formation of the homopolymer (Table 2 and Fig. 1b). The maximum grafting yield (24.3 %) on Luffa cylindrica fiber was observed at 4.35 x10-3 mol/L concentration of AA in MA/AA binary monomer. Table 1.Optimization of MA concentration in MA/AA binary monomer. S. No.
MA/AA Conc. Ratio ( x 10-3mol/L)
% Grafting
1. 2. 3. 4. 5.
1.12 : 2.91 2.23 : 2.91 3.36 : 2.91 4.48 : 2.91 5.60 : 2.91
28.00 23.50 16.47 9.08 8.90
3.2. Effect of microwave exposure time The effect of microwave exposure time on the percentage grafting was shown in Fig. 1c. It is evident that higher the microwave irradiation time, more the number of free radical sites created on the Luffa cylindrica fiber which resulted in higher graft yield. But with further increase in reaction time, the decrease in percentage grafting was recorded due to homopolymer formation which hindered the grafting. Table 2.Optimization of AA concentration in MA/AA binary monomer. S. No.
MA/AA Conc. Ratio (x 10-3mol/L)
% Grafting
1. 2. 3. 4. 5.
2.23 : 1.45 2.23 :2.91 2.23 : 4.35 2.23 : 5.80 2.23 : 7.25
11.26 17.90 24.30 20.43 19.04
Fig.1(a-c) Variation of percentage grafting, (a) MA, (b) AA, (c) microwave exposure time, and X-ray diffraction pattern (d) raw fiber, (e) Lc-gpoly(MA/AA) fiber.
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3.3. Characterization of graft copolymer 3.3.1. X-ray diffraction (XRD) XRD pattern of raw fiber and Lc-g-poly(MA/AA) fiber were shown in Fig. 1(d-e). It is evident from the Fig. 1d that the raw fiber showed peaks at 22.350 and 15.480 with relative intensities of 779 and 442, respectively. Similarly, Lc-g-poly(MA/AA) fiber showed peaks at 22.600 and 15.060 with relative intensities of 888 and 518, respectively. The percentage crystallinity of raw fiber and Lc-g-poly(MA/AAm) was observed at 63.80 and 63.15. While, the crystallinity index was found at 0.43 and 0.35. It has been observed that the intensity of the Lc-gpoly(MA/AA) peaks decreased during grafting, so crystallinity of fiber decreased. The percentage crystallinity and crystallinity index was calculated by separating intensities due to amorphous and crystalline phase on diffraction pattern. It is clear that there was a slight decrease in percentage crystallinity of the fiber on graft copolymerization, which resulted in increase in randomness or disorder in the crystal lattice of cellulose fiber. It was due to incorporation of poly(MA/AA) chains on the active sites of backbone during grafting . 3.3.2. Fourier Transform Infra-red Spectroscopy (FTIR) The FTIR spectra of raw and binary grafted Luffa cylindrica fibers have been shown in Fig. 2(a-b). The absorption peak at 899 cm-1 was occured due to C-C stretching vibration of β-glycosidic linkage. The peaks at 2856 cm-1, 2925 cm-1 and 1456 cm-1 were recorded due to symmetric and asymmetric stretching of C-H bond of CH2 and CH2 scissoring vibrations. The broad peak at 3401 cm-1 was observed due to stretching vibration of –OH. The additional peaks for grafted sample at 1059 cm-1, 3429 cm-1and 1111 cm-1 have been obtained due to C-O-H deformation of raw fiber, O-H group of acrylic acid and C-O group. A sharp peak at 1736 cm-1 was observed due to C=O group of ester (methylacrylate). These spectral studies confirmed the grafting of MA/AA binary monomer onto Luffa cylindrica fiber.
Fig. 2 FTIR spectra (a) raw Luffa cylindrica fiber, (b) raw Lc-g-poly(MA/AA) fiber.
3.3.3. Thermogravimetric (TGA) and SEM analysis Thermo-gravimetric analysis of raw fiber and Lc-g-poly(MA/AA) was carried out as a function of weight loss verses temperature as shown in Fig. 3(a-b). The degradation may occur in various forms as deacetylation, dehydration, decarboxylation and chain scission. In TGA of raw fiber decomposition has been observed with maximum weight loss between 86.10C to 332.50C (59.5%) and 332.50C to 503.20C (30.8%). The first stage decomposition may be due to loss of moisture and second stage decomposition was due to cellulosic and lignin degradation [19-21]. The TGA of Lc-g-poly(MA/AA) also shows two stage decomposition. The first stage decomposition was occurred at between 49.80C to 277.60C (15.7%). The second stage decomposition was observed at 277.60C to 4240C (73.2%).It is inferred that grafted Luffa cylindrica infiber has improved thermal stability. Due to presence of poly-(MA/AA) the hydrophobic character of grafted sample was improved as compared to the raw fiber. Differential thermogravimetric curve indicated that in case of raw fiber the decomposition peak occurred at 319.80C, where as in case of Lc-g-poly(MA/AA) peak was obtained at 334.70C. Better thermal resistance of grafted copolymer were shown due to the incorporation of covalent bonding through inclusion of poly(MA/AA). SEM studies showed that the surface of binary grafted copolymer changed as compared to the raw cellulosic fiber. SEM micrographs of raw Luffa cylindrica and Lc-g-poly(MA/AA) graft copolymer were shown in Fig. 3(c-d). It has been observed that after grafting, the surface of cellulose fiber becomes rough due to the presence of binary
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monomers (MA/AA) on the active sites of fiber. 3.4. Physio-chemical behavior of Lc-g-poly(MA/AA) 3.4.1. Swelling behavior in different solvents The swelling studies of raw and grafted samples in different solvents were shown Fig. 4(a-b). It has been observed that the % swelling of the raw sample follow the order as water > DMF > benzene. It was due to more affinity of water for free -OH groups. After grafting the free active sites get blocked by binary monomer so the order became reversed as benzene > DMF > water. Percentage swelling =
𝑊𝑊𝑓𝑓 −𝑊𝑊𝑖𝑖 𝑊𝑊𝑖𝑖
×100
(2)
where, Wf is the weight after swelling of fiber and Wi is the weight of dry fiber. 3.4.2. Moisture absorbance studies (Mabs) The moisture absorbance studies on raw and grafted samples have been carried out. It has been observed that the raw fiber have high % Mabs (48%) due to presence of hydrophilic hydroxyl group. The % Mabs for grafted sample was found less (30%) due to blockage of active sites by graft copolymerization and decrease in hydrophilic character. The initial and final weight (g) of raw fibre was recorded to be 0.5 and 0.74, respectively. While,0.5 and 0.65 g of initial and final weight have been noted for grafted samples, respectively. Hence, grafted sample absorb less moisture than raw fibre. The % moisture absorbance was calculated according to Eq. 2. 3.4.3. Water uptake studies The water uptake capacity of raw and grafted sample was studied using the concept of capillary action. The water uptake capacity of Lc-g-poly(MA/AA) copolymer decreased, which may be due to addition of hydrophobic groups on fiber by graft copolymerization (Table 3). 3.4.4. Chemical resistance studies The chemical resistance of raw and Lc-g-poly(MA/AA) sample were determined in 1N HNO 3 and 1N NaOH. It has been observed that chemical resistance of grafted polymer was more than raw sample, which was due to deactivation of active sites on grafted polymer backbone by graft copolymerization. The % weight loss was found to be 89.2% and
Fig. 3(a-b)TGA of raw fiber andraw Lc-g-poly(MA/AA), (c-d)SEM images of raw Luffa cylindrica, andLc-g-poly(MA/AA), respectively.
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74% for raw fibre in1N HNO3and 1N NaOH, respectively. While, 73.3% and 35% weight loss recorded for Lc-gpoly(MA/AA) in 1N HNO3and 1N NaOH, respectively. Hence, Lc-g-poly(MA/AA) was found more chemically resistant than raw fibre. The % Weight loss was calculated according to following Eq: % weight loss =
𝑊𝑊2 − 𝑊𝑊1 𝑊𝑊1
(3)
×100
where, W1 is the initial weight of the sample and W2 is the final weight of sample after the treatment. Table 3. Water uptake studies of raw and Lc-g-poly(MA/AA) fiber. Samples
Length of fiber wick (cm)
Water uptake (cm)
Luffa cylindrica raw fiber Lc-g-poly(MA/AA) fiber
5.0 5.0
3.6 2.8
3.5. Dye adsorption from water system The graft copolymers have been used for removal of dyes from water system. The adsorption data obtained from experiments provides estimation of maximum adsorption capacity of the adsorbent and effectiveness of adsorbateadsorbent system. The adsorption capacity and other parameters were evaluated using Langmuir and Freundlich, isotherm models. The results of dye adsorption by Lc-g-poly(MA/AA) copolymer were shown in Table 4 and Fig. 4(c). It is evident from Fig. 4c that dye adsorption increased on grafted sample. It was due to the presence of high contents of ester and carboxylic functional groups, which have high affinity for dye. The adsorption capacity qe (mg g-1) of congo reddye was determined using following Eq: 𝑉𝑉
(4) qe = (C0 − Ce) 𝑀𝑀 where, C0 (mg L-1) and Ce (mg L-1) are the initial and equilibrium concentrations of congo red dye, V is the volume of solution (L) and M mass of adsorbent (g). 3.5.1. Isotherm models The Langmuir isotherm indicates monolayer adsorption onto a homogeneous surface without transmigration of adsorbed molecules and given as below [22]: 𝐶𝐶𝑒𝑒
𝑞𝑞𝑒𝑒
=
1
𝐾𝐾𝐿𝐿 𝑄𝑄𝑚𝑚
+
𝐶𝐶𝑒𝑒
𝑄𝑄𝑚𝑚
(5)
(5)
Table 4. Dye uptake studies of Lc-g-poly(MA/AA). S. No.
Amount of grafted sample (g)
Amount of dye added (mol/L)
Amount of dye added (mg/L)
Dye Adsorption (mg/L) (qe)
1.
0.05
1x 10-6
0.697
0.140
2.
0.05
5x 10-6
3.485
1.061
3.
0.05
1x 10
6.97
3.795
4. 5.
0.05 0.05
5x 10-5 1x 10-4
34.85 69.70
7.865 16.051
-5
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Fig. 4(a)Percentage swelling of raw sample in different solvents, (b) swelling of Lc-g-poly(MA/AA), (c)effect of dye concentration with adsorption maximum at 490 nm, (d) Langmuir isotherm, and (e) Freundlich isotherm for dye adsorption onto grafted sample.
Qm (monolayer adsorption capacity, mg/g) and KL (Langmuir adsorption constant (L/mg), related with the free energy of adsorption were calculated. It has been observed that the maximum adsorption capacity (Qm) was found to be 19.24 mg/g. A high value of coefficient of regression, R2 (0.998) inferred the applicability of Langmuir isotherm (Fig. 4d). The RL<1 (0.427) indicated spontaneous adsorption of dye from aqueous solution and computed from following Eq. RL=
1
(6)
1+𝐾𝐾𝐿𝐿 𝐶𝐶0
The Freundlich isotherm describe the heterogeneous surface with uneven distribution of energy level. This model is presented as below [23,24]: log 𝑞𝑞𝑒𝑒 = log 𝑘𝑘𝐹𝐹 +
1
𝑛𝑛
log 𝐶𝐶𝑒𝑒
(7)
Fig. 4(e) shows Freundlich isotherm from which value of KF and n have been calculated. The value of n>1 observed from Freundlich isotherm indicated favourable and heterogeneous adsorption of congo red dye. 4. Conclusions Herein, we report the graft copolymerization of Luffa cylindrica fiber with binary monomer units such as methyl acrylate (MA) and acrylic acid (AA).The anatomy, chemical compositions and stability of fibre have been examined by FTIR, TGA, and SEM instruments. The physico-chemical study inferred that Lc-g-poly(MA/AA) exhibits excellent chemical resistance over raw fibre. The grafted fibre has been investigated for the sequestration of noxious congo red dye from water system. Langmuir model display better regression coefficient (0.98) than Freundlich isotherm. It explain the monolayer adsorption of congo red dye onto Lc-g-poly(MA/AA).The maximum monolayer capacity of Lc-g-poly(MA/AA) was recorded to be 19.24 mg/g. Hence, our findings implied that Lc-g-
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poly(MA/AA)fibre has been successfully explored for the removal congo red dye from aquatic system. Acknowledgment The authors gratefully acknowledge the Shoolini University for providing all the necessary facilities to carry out this research. References [1] M. Constantin, I. Asmarandei, V. Harabagiu, L. Ghimici, P. Ascenzi, G. Fundueanu, Removal of anionic dyes from aqueous solutions by an ion-exchanger based on pullulan microspheres, Carbohydr. Polym.91 (2013) 74–84. [2] Z. Yang, S. Chen, W. Hu, N. Yin, W. Zhang, C. Xiang, Flexible luminescent CdSe/bacterial cellulose nanocomoposite membranes, Carbohydr.Polym.88 (2012) 173–178. [3]Z. Yang, S. Chen, W. Hu, N. Yin, W. Zhang, C. Xiang, Flexible luminescentCdSe/bacterial cellulose nanocomposite membrane, Carbohydr. Polym. 88 (2012)173–178. [4] T. Zeng, T. Pan, H.W.Gao, Heterodinuclear replacement complexationfor sensitive determination of iron ion in surface water with dibromocarbox-yarsenazo, J. Chin. Chem. Soc. 55 (2008)79–87. [5] V.K. Gupta, S. Agarwal, P. Singh, D. Pathania, Acrylic acid grafted cellulosic Luffa cylindrical fiber for the removal of dye and metal ions. Carbohydr. Polym. 98 (2013) 1214-21. [6] A. Mochalova, N. Zaborshchikova, A. Knyazev, L. Smirnova, V. Izvozchikova, V. Medvedeva, Y. Semchikov, Polym. Sci. A 48 (2006) 918– 923. [7] S.G. Kumbar, K.S. Soppimath, T.M. Aminabhavi, Synthesis and characterization of polyacrylamide‐grafted chitosan hydrogel microspheres for the controlled release of indomethacin, J. Appl. Poly. Sci. 87 (2003) 1525-36. [8] Z. Yang, Y. Yuan, Studies on the synthesis and properties of hydroxyl azacrown ether‐grafted chitosan, J. Appl. Polym. Sci. 82(2001) 18381843. [9] Z. Zhu, M. Li, E. Jin, Effect of an allyl pretreatment ofstarch on the grafting efficiency and properties of allylsta(rch-g-poly(acrylic acid), J. Appl. Polym. Sci. 112(2009) 2822–2829. [10] Y. Zheng, S. Hua, A. Wang, Adsorption behavior ofCu2+ from aqueous solutions onto starch-g-poly(acrylic acid)/sodium humate hydrogels, Desalin. 263 (2010) 170–175. [11] V.K. Gupta, D. Pathania, S. Agarwal, S. Sharma, Amputation of congo red dye from waste water using microwave induced grafted Luffa cylindrica cellulosic fiber, Carbohydr. Polym. 111((2014) 556-566. [12] H.Y. Zhu, Y.Q. Fu, R. Jiang, J.H. Jiang, L. Xiao, G.M. Zeng, S.L. Zhao, Y. Wang, Adsorption removal of congo red onto magnetic cellulose/Fe3O4/activated carbon composite: equilibrium, kinetic and thermodynamic studies, Chem. Eng. J. 173 (2011) 494–502. [13] A. Sharma, G. Sharma, A. Kumar, Z.M. Siddiqi, D. Pathania, Exclusion of organic dye using neoteric activated carbon prepared from Cornulacamonacantha stem: equilibrium and thermodynamics studies, Materials Sci. Forum. 875 (2016) 1-15. [14] H Yan, H Yang, A Li, R Cheng, pH-tunable surface charge of chitosan/graphene oxide composite adsorbent for efficient removal of multiple pollutants from water, Chem. Eng. J. 284 (2016)1397-405. [15] T Hao, X Rao, Z Li, C Niu, J Wang, X Su, Synthesis of magnetic separable iron oxide/carbon nanocomposites for efficient adsorptive removal of Congo red, J. Alloys Compd. 617 (2014) 76-80. [16] D. Pathania, A. Sharma, Z.M. Siddiqi, Removal of congo red dye from aqueous system using Phoenix dactylifera seeds, J. Mol. Liq. 219 (2016) 359-67. [17] H. Javadian, M.T. Angaji, M. Naushad, Synthesis and characterization of polyaniline/γ-alumina nanocomposite: A comparative study for the adsorption of three different anionic dyes, J. Indust. Eng. Chem. 20 (2014) 3890-900. [18] L. Zhou, J. Huang, B. He, F. Zhang, H. Li, Peach gum for efficient removal of methylene blue and methyl violet dyes from aqueous solution. Carbohydr. Polym. 101 (2014) 574-81. [19] D. Britto de, S.P. Campana-Filho, Kinetics of the thermal degradation of chitosan, Thermochim. acta. 465 (2007)73-82. [20] D. Pathania, D. Gupta, N.C. Kothiyal, G.E. Eldesoky, M. Naushad. Preparation of a novel chitosan-g-poly (acrylamide)/Zn nanocomposite hydrogel and its applications for controlled drug delivery of ofloxacin, Int. J. Boil. Macromolec. 84 (2016) 340-348. [21]F. López, A. Mercê, F. Alguacil, A. López-Delgado, A kinetic study on the thermal behaviour of chitosan, J. Therm. Anal. Calorim. 2007 91(2007) 633-639. [22] F. Nekouei, S. Nekouei, I. Tyagi, V.K. Gupta, Kinetic, thermodynamic and isotherm studies for acid blue 129 removal from liquids using copper oxide nanoparticle-modified activated carbon as a novel adsorbent, J. Mol. Liq. 201 (2015) 124-33. [23] Y. Li, H.Y. Bi, Y.S. Jin, Facile preparation of rhamnolipid-layered double hydroxide nanocomposite for simultaneous adsorption of p-cresol and copper ions from water,Chem. Eng. J. 308 (2017) 78-88. [24] Y. Guo, Z. Jia, Novel sandwich structure adsorptive membranes for removal of 4-nitrotoluene from water, J. Hazard. Mater. 317 (2016) 295-302.
ScienceDirect Available online at www.sciencedirect.com Procedia Engineering00 (2017) 000–000
ScienceDirect
www.elsevier.com/locate/procedia
Procedia Engineering 200 (2017) 408–415
3rd International Conference on Natural Fibers: Advanced Materials for a Greener World, ICNF 2017, 21-23 June 2017, Braga, Portugal
Microwave induced graft copolymerization of binary monomers onto luffa cylindrica fiber: removal of congo red
a
Deepak Pathaniaa*, Arush Sharmaa, Vandana sethia
School of Chemistry, Shoolini University, Solan-173212, Himachal Pradesh, India
Abstract In this work, graft copolymerization of delignified Luffa cylindrica fiber with methyl acrylate (MA) and acrylic acid has been attempted in presence of microwave radiation. Different reaction conditions affecting the grafting percentage (Pg) were optimized to get the maximum graft yield. The grafted fibres were subsequently subjected for the evaluation of physico-chemical properties such as swelling behaviour, moisture absorbance and chemical resistance. Further, morphological and structural analysis of raw and delignified Luffa cylindrica-g-poly(MA/AA) were studied using Fourier transform infra red (FTIR) spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA).The tensile properties of grafted and ungrafted fibre samples were also reported. The adsorption potential of modified fiber was investigated using adsorption isotherms for hazardous congo red dye removal from aqueous system. The maximum adsorption capacity of dye onto grafted Luffa cylindrica fiber was found to be 19.24 mg/g with best fit for Langmuir isotherm. © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 3rd International Conference on Natural Fibers: Advanced Materials for a Greener World. Keywords:Luffa cylindrical; binary monomers; grafting; microwave radiations; congo red; adsorption
* Corresponding author. E-mail address: [email protected]
1. Introduction Biodegradable polymeric materials have been considered as the most potential materials due to their easy availability and cost effectiveness. Cellulosic fibers have received increased attention from environmental scientists 1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 3rd International Conference on Natural Fibers: Advanced Materials for a Greener World.
1877-7058 © 2017 The Authors. Published by Elsevier Ltd. Peer-review under responsibility of the scientific committee of the 3rd International Conference on Natural Fibers: Advanced Materials for a Greener World 10.1016/j.proeng.2017.07.057
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recently. These materials offer many advantages such as low specific gravity, suitable mechanical properties and recyclability. Moreover, they have lower weights and less cost than synthetic fibers [1]. Cellulose structure consists of monomeric unit of α, β-glucopyranose linked through1,4-glucosidic linkage. Cellulose is renewable, cheap, and low in density, exhibits better processing flexibility. Cellulose structure are linked through1,4-glucosidic linkage. Cellulose is renewable, cheap, and low in density, exhibits better processing flexibility. Cellulose is a highly functionalized, linear stiff chain homopolymer, characterized by hydrophilicity, chirality, biodegrability and broad chemical modifying capacity [2,3]. Due to the presence of hydrophilic hydroxyl groups on the surface of cellulosic fibers, their use is restricted under moist atmospheres and polar solvents [4-6]. Further these fibers are also more disposed to the attack acids, bases and salts. Therefore, these fibers need surface modifications in order to improve their properties before used in various applications. Grafting of vinyl monomers onto cellulosic fiber using initiators have been investigated by different researchers for producing desired alteration in physicochemical properties [710]. The grafting resulted in improved elasticity, water adsorption, ion exchange capability and heat resistance etc. Grafted cellulosic fibers have been currently used as adsorbents for the removal of hazardous metal ions and dyes from aqueous solutions due to good selectivity, stability, adjustable functionality, enhanced surface area and porosity. The polymer grafting fibers usually increased the density of adsorption sites and sorption selectivity for the target metal and dyes. Aquatic environmental contamination by synthetic dyes is a thrust area of research, due to their negative effects and bioaccumulation in flora and fauna [11-16]. Synthetic dyes released by pigment manufacturing, textile, paper, tanning, dyeing, painting, photographic, food and cosmetics industry affect photosynthesis and their adulteration also obstruct the light penetration into aquatic system. Additionally, dye molecules can also be decomposed into carcinogenic aromatic amines under aerobic conditions which causes serious health problems like allergy, dermatitis, skin irritation and cancer to animals and human beings [17,18].Therefore, this study deals with the investigation of effective, inexpensive, biodegradable and eco-friendly biosorbent prepared by graft copolymerization of methyl acrylate/ acrylic acid (MA/AA) onto luffa cylindrica fiber for the amputation of congo red dye from aquatic system. Moreover, instrumental techniques such as FTIR, SEM, XRD and TGA were used to characterize the raw and grafted fibre. 2. Experimental 2.1. Chemicals Vinyl monomer such as Methyl acrylate (MA), Acrylic acid (AA) were obtained from E-Merck chemicals, Sodium hydroxide, Ethanol, Congo red,acetone , nitric acid, dimethyl formamide and Benzene were received from CHD, India. All these chemicals were used as received. 2.2. Graft copolymerization of methyl acrylate/ acrylic acid (MA/AA) onto luffa cylindrica fiber Fiber (0.5 g) was activated by immersing in 100 mL of distilled water for 24 hours before grafting with binary monomer. Then a known amount of methyl acrylate/acrylic acid binary monomer was added in a definite ratio with constant stirring solution. Different reaction parameters have been optimized to get maximum grafting yield. The homopolymer formed during the graft copolymerization was removed with hot distilled water followed by methanol. The grafted sample thus obtained was dried at 500 C. The percentage grafting yield (%G) was determined as follow: % Grafting yield =
𝑊𝑊3 − 𝑊𝑊1 𝑊𝑊1
×100
(1)
where, W1 is the initial weight of the raw fiber and W3 is the final weight of the grafted fiber after extraction of homopolymer. The scheme of graft copolymerization of MA/AA ontoLuffa cylindrica fiber is shown as: Cellulose----OH
+ Poly--(MA/AA)
( L.cylindrica fiber ) ( binary monomer )
MW
Cellulose-----(MA/AA) n ( graft copolymer )
3. Results and discussion 3.1. Optimization of MA and AA concentration in MA/AA binary monomer: It has been clear from Table 1 and Fig.1a that graft yield was highest at low concentration of MA and decreased with increase in concentration. This was due to dominance of homopolymerization with increase in monomer
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concentration. The maximum grafting yield of 28% was observed at1.12 x10-3 mol/L concentration of MA in MA/AA binary monomer. The increase in grafting yield with the concentration of AA was observed initially and then decreases with further increase in the concentration. The decrease in grafting yield was due to the formation of the homopolymer (Table 2 and Fig. 1b). The maximum grafting yield (24.3 %) on Luffa cylindrica fiber was observed at 4.35 x10-3 mol/L concentration of AA in MA/AA binary monomer. Table 1.Optimization of MA concentration in MA/AA binary monomer. S. No.
MA/AA Conc. Ratio ( x 10-3mol/L)
% Grafting
1. 2. 3. 4. 5.
1.12 : 2.91 2.23 : 2.91 3.36 : 2.91 4.48 : 2.91 5.60 : 2.91
28.00 23.50 16.47 9.08 8.90
3.2. Effect of microwave exposure time The effect of microwave exposure time on the percentage grafting was shown in Fig. 1c. It is evident that higher the microwave irradiation time, more the number of free radical sites created on the Luffa cylindrica fiber which resulted in higher graft yield. But with further increase in reaction time, the decrease in percentage grafting was recorded due to homopolymer formation which hindered the grafting. Table 2.Optimization of AA concentration in MA/AA binary monomer. S. No.
MA/AA Conc. Ratio (x 10-3mol/L)
% Grafting
1. 2. 3. 4. 5.
2.23 : 1.45 2.23 :2.91 2.23 : 4.35 2.23 : 5.80 2.23 : 7.25
11.26 17.90 24.30 20.43 19.04
Fig.1(a-c) Variation of percentage grafting, (a) MA, (b) AA, (c) microwave exposure time, and X-ray diffraction pattern (d) raw fiber, (e) Lc-gpoly(MA/AA) fiber.
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3.3. Characterization of graft copolymer 3.3.1. X-ray diffraction (XRD) XRD pattern of raw fiber and Lc-g-poly(MA/AA) fiber were shown in Fig. 1(d-e). It is evident from the Fig. 1d that the raw fiber showed peaks at 22.350 and 15.480 with relative intensities of 779 and 442, respectively. Similarly, Lc-g-poly(MA/AA) fiber showed peaks at 22.600 and 15.060 with relative intensities of 888 and 518, respectively. The percentage crystallinity of raw fiber and Lc-g-poly(MA/AAm) was observed at 63.80 and 63.15. While, the crystallinity index was found at 0.43 and 0.35. It has been observed that the intensity of the Lc-gpoly(MA/AA) peaks decreased during grafting, so crystallinity of fiber decreased. The percentage crystallinity and crystallinity index was calculated by separating intensities due to amorphous and crystalline phase on diffraction pattern. It is clear that there was a slight decrease in percentage crystallinity of the fiber on graft copolymerization, which resulted in increase in randomness or disorder in the crystal lattice of cellulose fiber. It was due to incorporation of poly(MA/AA) chains on the active sites of backbone during grafting . 3.3.2. Fourier Transform Infra-red Spectroscopy (FTIR) The FTIR spectra of raw and binary grafted Luffa cylindrica fibers have been shown in Fig. 2(a-b). The absorption peak at 899 cm-1 was occured due to C-C stretching vibration of β-glycosidic linkage. The peaks at 2856 cm-1, 2925 cm-1 and 1456 cm-1 were recorded due to symmetric and asymmetric stretching of C-H bond of CH2 and CH2 scissoring vibrations. The broad peak at 3401 cm-1 was observed due to stretching vibration of –OH. The additional peaks for grafted sample at 1059 cm-1, 3429 cm-1and 1111 cm-1 have been obtained due to C-O-H deformation of raw fiber, O-H group of acrylic acid and C-O group. A sharp peak at 1736 cm-1 was observed due to C=O group of ester (methylacrylate). These spectral studies confirmed the grafting of MA/AA binary monomer onto Luffa cylindrica fiber.
Fig. 2 FTIR spectra (a) raw Luffa cylindrica fiber, (b) raw Lc-g-poly(MA/AA) fiber.
3.3.3. Thermogravimetric (TGA) and SEM analysis Thermo-gravimetric analysis of raw fiber and Lc-g-poly(MA/AA) was carried out as a function of weight loss verses temperature as shown in Fig. 3(a-b). The degradation may occur in various forms as deacetylation, dehydration, decarboxylation and chain scission. In TGA of raw fiber decomposition has been observed with maximum weight loss between 86.10C to 332.50C (59.5%) and 332.50C to 503.20C (30.8%). The first stage decomposition may be due to loss of moisture and second stage decomposition was due to cellulosic and lignin degradation [19-21]. The TGA of Lc-g-poly(MA/AA) also shows two stage decomposition. The first stage decomposition was occurred at between 49.80C to 277.60C (15.7%). The second stage decomposition was observed at 277.60C to 4240C (73.2%).It is inferred that grafted Luffa cylindrica infiber has improved thermal stability. Due to presence of poly-(MA/AA) the hydrophobic character of grafted sample was improved as compared to the raw fiber. Differential thermogravimetric curve indicated that in case of raw fiber the decomposition peak occurred at 319.80C, where as in case of Lc-g-poly(MA/AA) peak was obtained at 334.70C. Better thermal resistance of grafted copolymer were shown due to the incorporation of covalent bonding through inclusion of poly(MA/AA). SEM studies showed that the surface of binary grafted copolymer changed as compared to the raw cellulosic fiber. SEM micrographs of raw Luffa cylindrica and Lc-g-poly(MA/AA) graft copolymer were shown in Fig. 3(c-d). It has been observed that after grafting, the surface of cellulose fiber becomes rough due to the presence of binary
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monomers (MA/AA) on the active sites of fiber. 3.4. Physio-chemical behavior of Lc-g-poly(MA/AA) 3.4.1. Swelling behavior in different solvents The swelling studies of raw and grafted samples in different solvents were shown Fig. 4(a-b). It has been observed that the % swelling of the raw sample follow the order as water > DMF > benzene. It was due to more affinity of water for free -OH groups. After grafting the free active sites get blocked by binary monomer so the order became reversed as benzene > DMF > water. Percentage swelling =
𝑊𝑊𝑓𝑓 −𝑊𝑊𝑖𝑖 𝑊𝑊𝑖𝑖
×100
(2)
where, Wf is the weight after swelling of fiber and Wi is the weight of dry fiber. 3.4.2. Moisture absorbance studies (Mabs) The moisture absorbance studies on raw and grafted samples have been carried out. It has been observed that the raw fiber have high % Mabs (48%) due to presence of hydrophilic hydroxyl group. The % Mabs for grafted sample was found less (30%) due to blockage of active sites by graft copolymerization and decrease in hydrophilic character. The initial and final weight (g) of raw fibre was recorded to be 0.5 and 0.74, respectively. While,0.5 and 0.65 g of initial and final weight have been noted for grafted samples, respectively. Hence, grafted sample absorb less moisture than raw fibre. The % moisture absorbance was calculated according to Eq. 2. 3.4.3. Water uptake studies The water uptake capacity of raw and grafted sample was studied using the concept of capillary action. The water uptake capacity of Lc-g-poly(MA/AA) copolymer decreased, which may be due to addition of hydrophobic groups on fiber by graft copolymerization (Table 3). 3.4.4. Chemical resistance studies The chemical resistance of raw and Lc-g-poly(MA/AA) sample were determined in 1N HNO 3 and 1N NaOH. It has been observed that chemical resistance of grafted polymer was more than raw sample, which was due to deactivation of active sites on grafted polymer backbone by graft copolymerization. The % weight loss was found to be 89.2% and
Fig. 3(a-b)TGA of raw fiber andraw Lc-g-poly(MA/AA), (c-d)SEM images of raw Luffa cylindrica, andLc-g-poly(MA/AA), respectively.
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74% for raw fibre in1N HNO3and 1N NaOH, respectively. While, 73.3% and 35% weight loss recorded for Lc-gpoly(MA/AA) in 1N HNO3and 1N NaOH, respectively. Hence, Lc-g-poly(MA/AA) was found more chemically resistant than raw fibre. The % Weight loss was calculated according to following Eq: % weight loss =
𝑊𝑊2 − 𝑊𝑊1 𝑊𝑊1
(3)
×100
where, W1 is the initial weight of the sample and W2 is the final weight of sample after the treatment. Table 3. Water uptake studies of raw and Lc-g-poly(MA/AA) fiber. Samples
Length of fiber wick (cm)
Water uptake (cm)
Luffa cylindrica raw fiber Lc-g-poly(MA/AA) fiber
5.0 5.0
3.6 2.8
3.5. Dye adsorption from water system The graft copolymers have been used for removal of dyes from water system. The adsorption data obtained from experiments provides estimation of maximum adsorption capacity of the adsorbent and effectiveness of adsorbateadsorbent system. The adsorption capacity and other parameters were evaluated using Langmuir and Freundlich, isotherm models. The results of dye adsorption by Lc-g-poly(MA/AA) copolymer were shown in Table 4 and Fig. 4(c). It is evident from Fig. 4c that dye adsorption increased on grafted sample. It was due to the presence of high contents of ester and carboxylic functional groups, which have high affinity for dye. The adsorption capacity qe (mg g-1) of congo reddye was determined using following Eq: 𝑉𝑉
(4) qe = (C0 − Ce) 𝑀𝑀 where, C0 (mg L-1) and Ce (mg L-1) are the initial and equilibrium concentrations of congo red dye, V is the volume of solution (L) and M mass of adsorbent (g). 3.5.1. Isotherm models The Langmuir isotherm indicates monolayer adsorption onto a homogeneous surface without transmigration of adsorbed molecules and given as below [22]: 𝐶𝐶𝑒𝑒
𝑞𝑞𝑒𝑒
=
1
𝐾𝐾𝐿𝐿 𝑄𝑄𝑚𝑚
+
𝐶𝐶𝑒𝑒
𝑄𝑄𝑚𝑚
(5)
(5)
Table 4. Dye uptake studies of Lc-g-poly(MA/AA). S. No.
Amount of grafted sample (g)
Amount of dye added (mol/L)
Amount of dye added (mg/L)
Dye Adsorption (mg/L) (qe)
1.
0.05
1x 10-6
0.697
0.140
2.
0.05
5x 10-6
3.485
1.061
3.
0.05
1x 10
6.97
3.795
4. 5.
0.05 0.05
5x 10-5 1x 10-4
34.85 69.70
7.865 16.051
-5
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Fig. 4(a)Percentage swelling of raw sample in different solvents, (b) swelling of Lc-g-poly(MA/AA), (c)effect of dye concentration with adsorption maximum at 490 nm, (d) Langmuir isotherm, and (e) Freundlich isotherm for dye adsorption onto grafted sample.
Qm (monolayer adsorption capacity, mg/g) and KL (Langmuir adsorption constant (L/mg), related with the free energy of adsorption were calculated. It has been observed that the maximum adsorption capacity (Qm) was found to be 19.24 mg/g. A high value of coefficient of regression, R2 (0.998) inferred the applicability of Langmuir isotherm (Fig. 4d). The RL<1 (0.427) indicated spontaneous adsorption of dye from aqueous solution and computed from following Eq. RL=
1
(6)
1+𝐾𝐾𝐿𝐿 𝐶𝐶0
The Freundlich isotherm describe the heterogeneous surface with uneven distribution of energy level. This model is presented as below [23,24]: log 𝑞𝑞𝑒𝑒 = log 𝑘𝑘𝐹𝐹 +
1
𝑛𝑛
log 𝐶𝐶𝑒𝑒
(7)
Fig. 4(e) shows Freundlich isotherm from which value of KF and n have been calculated. The value of n>1 observed from Freundlich isotherm indicated favourable and heterogeneous adsorption of congo red dye. 4. Conclusions Herein, we report the graft copolymerization of Luffa cylindrica fiber with binary monomer units such as methyl acrylate (MA) and acrylic acid (AA).The anatomy, chemical compositions and stability of fibre have been examined by FTIR, TGA, and SEM instruments. The physico-chemical study inferred that Lc-g-poly(MA/AA) exhibits excellent chemical resistance over raw fibre. The grafted fibre has been investigated for the sequestration of noxious congo red dye from water system. Langmuir model display better regression coefficient (0.98) than Freundlich isotherm. It explain the monolayer adsorption of congo red dye onto Lc-g-poly(MA/AA).The maximum monolayer capacity of Lc-g-poly(MA/AA) was recorded to be 19.24 mg/g. Hence, our findings implied that Lc-g-
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poly(MA/AA)fibre has been successfully explored for the removal congo red dye from aquatic system. Acknowledgment The authors gratefully acknowledge the Shoolini University for providing all the necessary facilities to carry out this research. References [1] M. Constantin, I. Asmarandei, V. Harabagiu, L. Ghimici, P. Ascenzi, G. Fundueanu, Removal of anionic dyes from aqueous solutions by an ion-exchanger based on pullulan microspheres, Carbohydr. Polym.91 (2013) 74–84. [2] Z. Yang, S. Chen, W. Hu, N. Yin, W. Zhang, C. Xiang, Flexible luminescent CdSe/bacterial cellulose nanocomoposite membranes, Carbohydr.Polym.88 (2012) 173–178. [3]Z. Yang, S. Chen, W. Hu, N. Yin, W. Zhang, C. Xiang, Flexible luminescentCdSe/bacterial cellulose nanocomposite membrane, Carbohydr. Polym. 88 (2012)173–178. [4] T. Zeng, T. Pan, H.W.Gao, Heterodinuclear replacement complexationfor sensitive determination of iron ion in surface water with dibromocarbox-yarsenazo, J. Chin. Chem. Soc. 55 (2008)79–87. [5] V.K. Gupta, S. Agarwal, P. Singh, D. Pathania, Acrylic acid grafted cellulosic Luffa cylindrical fiber for the removal of dye and metal ions. Carbohydr. Polym. 98 (2013) 1214-21. [6] A. Mochalova, N. Zaborshchikova, A. Knyazev, L. Smirnova, V. Izvozchikova, V. Medvedeva, Y. Semchikov, Polym. Sci. A 48 (2006) 918– 923. [7] S.G. Kumbar, K.S. Soppimath, T.M. Aminabhavi, Synthesis and characterization of polyacrylamide‐grafted chitosan hydrogel microspheres for the controlled release of indomethacin, J. Appl. Poly. Sci. 87 (2003) 1525-36. [8] Z. Yang, Y. Yuan, Studies on the synthesis and properties of hydroxyl azacrown ether‐grafted chitosan, J. Appl. Polym. Sci. 82(2001) 18381843. [9] Z. Zhu, M. Li, E. Jin, Effect of an allyl pretreatment ofstarch on the grafting efficiency and properties of allylsta(rch-g-poly(acrylic acid), J. Appl. Polym. Sci. 112(2009) 2822–2829. [10] Y. Zheng, S. Hua, A. Wang, Adsorption behavior ofCu2+ from aqueous solutions onto starch-g-poly(acrylic acid)/sodium humate hydrogels, Desalin. 263 (2010) 170–175. [11] V.K. Gupta, D. Pathania, S. Agarwal, S. Sharma, Amputation of congo red dye from waste water using microwave induced grafted Luffa cylindrica cellulosic fiber, Carbohydr. Polym. 111((2014) 556-566. [12] H.Y. Zhu, Y.Q. Fu, R. Jiang, J.H. Jiang, L. Xiao, G.M. Zeng, S.L. Zhao, Y. Wang, Adsorption removal of congo red onto magnetic cellulose/Fe3O4/activated carbon composite: equilibrium, kinetic and thermodynamic studies, Chem. Eng. J. 173 (2011) 494–502. [13] A. Sharma, G. Sharma, A. Kumar, Z.M. Siddiqi, D. Pathania, Exclusion of organic dye using neoteric activated carbon prepared from Cornulacamonacantha stem: equilibrium and thermodynamics studies, Materials Sci. Forum. 875 (2016) 1-15. [14] H Yan, H Yang, A Li, R Cheng, pH-tunable surface charge of chitosan/graphene oxide composite adsorbent for efficient removal of multiple pollutants from water, Chem. Eng. J. 284 (2016)1397-405. [15] T Hao, X Rao, Z Li, C Niu, J Wang, X Su, Synthesis of magnetic separable iron oxide/carbon nanocomposites for efficient adsorptive removal of Congo red, J. Alloys Compd. 617 (2014) 76-80. [16] D. Pathania, A. Sharma, Z.M. Siddiqi, Removal of congo red dye from aqueous system using Phoenix dactylifera seeds, J. Mol. Liq. 219 (2016) 359-67. [17] H. Javadian, M.T. Angaji, M. Naushad, Synthesis and characterization of polyaniline/γ-alumina nanocomposite: A comparative study for the adsorption of three different anionic dyes, J. Indust. Eng. Chem. 20 (2014) 3890-900. [18] L. Zhou, J. Huang, B. He, F. Zhang, H. Li, Peach gum for efficient removal of methylene blue and methyl violet dyes from aqueous solution. Carbohydr. Polym. 101 (2014) 574-81. [19] D. Britto de, S.P. Campana-Filho, Kinetics of the thermal degradation of chitosan, Thermochim. acta. 465 (2007)73-82. [20] D. Pathania, D. Gupta, N.C. Kothiyal, G.E. Eldesoky, M. Naushad. Preparation of a novel chitosan-g-poly (acrylamide)/Zn nanocomposite hydrogel and its applications for controlled drug delivery of ofloxacin, Int. J. Boil. Macromolec. 84 (2016) 340-348. [21]F. López, A. Mercê, F. Alguacil, A. López-Delgado, A kinetic study on the thermal behaviour of chitosan, J. Therm. Anal. Calorim. 2007 91(2007) 633-639. [22] F. Nekouei, S. Nekouei, I. Tyagi, V.K. Gupta, Kinetic, thermodynamic and isotherm studies for acid blue 129 removal from liquids using copper oxide nanoparticle-modified activated carbon as a novel adsorbent, J. Mol. Liq. 201 (2015) 124-33. [23] Y. Li, H.Y. Bi, Y.S. Jin, Facile preparation of rhamnolipid-layered double hydroxide nanocomposite for simultaneous adsorption of p-cresol and copper ions from water,Chem. Eng. J. 308 (2017) 78-88. [24] Y. Guo, Z. Jia, Novel sandwich structure adsorptive membranes for removal of 4-nitrotoluene from water, J. Hazard. Mater. 317 (2016) 295-302.