Synthesis and Characterization of Super Absorbent Polymers for Agricultural Purposes

Transcription

1 Interntionl Journl of Scientific nd Engineering Reserch Volume 6, Issue 3, Mrch Synthesis nd Chrcteriztion of Super Absorbent Polymers for Agriculturl Purposes Ens M. Ahmed*; Ftm S. Aggor; Smh S. Nd nd S. I. Hwsh Chemicl Engineering nd Pilot Plnt Deprtment, Engineering Reserch Division, Ntionl Reserch Center, Dokki, Ciro, Egypt Abstrct: Superbsorbent hydrogels (SAH) re very unique wter- bsorbing nd wter holding mterils. Superbsorbent polymers re environmentlly useful s wter retention gents, for purposes such s griculturl pplictions nd combting desertifiction. In this pper we investigte the preprtion of SAH to rech highest yield with mximum swelling. Also effect of different operting prmeters ws studied. Bench scle results were used for design pilot scle btch to produce 2 kg o SAH. The future objective of this study is the ppliction of the prepred SAH in griculture field. The product hs lredy been lunching in the cultivtion of sqush (Cucurbit pepo L.) nd the initil results were promising. Keywords: crosslinking; hydrophilic polymers, swelling, liquid crystls. Introduction Wter is n essentil nd key component of this plnet nd supports ll life tht exists on it. Of ll the globl wter, fresh wter is the most importnt to support life on this plnet. Aviling SAH would significntly contribute to the production of soil conditioner. Arid lnd reclmtion progrm in Egypt is centrl component in the Egyptin socil nd economic development strtegies in the lst decdes. The success of this progrm is mndtory to secure food supplies nd vil intensive job opportunities. Other trgets of reclmtion progrm re to estblish new gro-industril complexes to decrese popultion nd development pressures in the old Nile vlley. With the current degrdtion of significnt griculturl res in the vlley, to stisfy demnd for housing nd urbn services, it is necessry to develop new reclimed lnds. The min chllenges for most lnd reclmtion projects re the vilbility nd ccessibility of funding, wterp P[1]. Superbsorbent hydrogels hve been identified s three dimensionl crosslinked polymer networks cpble of bsorbing lrge quntities of wter, but remin insoluble due to chemicl or physicl crosslinks between individul polymeric chins [2]. Superbsorbent hydrogel (SAH) products constitute group of polymeric mterils, the hydrophilic structure of which renders them cpble of holding lrge mounts of wter in their three dimensionl networks. Extensive employment of these products in number of industril nd environmentl res of ppliction is considered to be of prime importnce. Superbsorbent hydrogel mterils re hydrophilic networks tht cn bsorb nd retin huge mounts of wter or queous solutions. A superbsorbent hydrogel ws prepred through polymeriztion of crylic cid/crylte under potssium persulphte initition nd N-N'- methylene biscrylmide s crosslinking gent. The polymers were synthesized by, free rdicl polymeriztion techniques. Superbsorbent polymers were first developed by USDA in 197s for pplictions in griculture to improve the wter holding cpcities of soils to promote seed germintion nd plnt growth nd now find extensive pplictions in disposble pds nd sheets, towels used in surgery, dult incontinence nd femle hygiene products [3]. Superbsorbent polymers cn be clssified into two types: bsed on chrge non-ionic nd ionic [4] nd bsed on its ffinity towrds wter hydrophobic nd hydrophilic [5, 6]. Ionic SAPs re further clssified into ctionic nd nionic [7]. In cse of ionic hydrogels mny structurl fctors like crosslinking density, properties of swelling medium like ph, ionic strength of counter ion nd its vlency influences the swelling properties [8]. Hydrogel which swell nd contrct in response to externl conditions like slt, ph nd temperture hve been studied [9-11]. In our recent reserch the preprtion nd chrcteristics of superbsorbent from Acrylic cid/ crylte, N,N -methylene-biscrylmide s crosslinker nd potssium persulphte s n inititor vi free rdicl polymeriztion technique were studied. Swelling studies of the cndidte polymer in tp wter nd different ph were lso done. In ddition, overll process steps for 2 kg of SAH (pilot scle) were clculted nd described. The purpose of this work is pplying the product in the griculture field. The product hs lredy been lunching in the cultivtion of sqush nd the initil results were promising. Mterils nd Methods Mterils Acrylic cid (AAc) in the monomeric form ws produced by PANREAC QUIMICA, Spin; N-N'-methylene biscrylmide (MBAAm) s crosslinking gent ws purchsed from Sigm Aldrich, CHEMIE, GmbH, Germny; potssium persulphte (KPS) s inititor ws supplied by Sisco Reserch Lb. Pvt. Ltd., Indi; potssium hydroxide (KOH) ws supplied by SDFCL, Indi. These regents were used s lbortory grde chemicls. Preprtion of Polycrylte Superbsorbent Polymer Preprtion of polycrylte superbsorbent polymer ws crried out ccording to modified procedure [12]. A mixed solution of crylic cid monomer nd potssium crylte ws prepred by mixing the monomer with N, N-methylene biscrylmide s crosslinker in

2 Interntionl Journl of Scientific nd Engineering Reserch Volume 6, Issue 3, Mrch presence of potssium hydroxide in distilled wter under mbient conditions. The mixture solution ws stirred t 35 rpm nd heted to 7 o C in wter bth for 15 min., followed by ddition of the inititor. The rection mixture ws kept under stirring for few minutes to complete polymeriztion rection. The prepred hydrogel ws then immersed in excess distilled wter to remove ny impurities then dried t 8 o C for bout 3 hours. Furthermore effects of vrition of MBAAm, KPS nd KOH doses were lso exmined. All of the experiments were duplicted to obtin verge results. A bench scle experiment ws crried out ccording to the optimum conditions by which the swelling rtio of the SAH ws in mximum rte nd economic. Mesurements nd Chrcteriztion Swelling Studies The swelling chrcteristics of the prepred hydrogel were mesured vi grvimetric nlysis [12]. The swelling rtio is the criterion of describing wter bsorption cpcity. Mesurement of the swelling rtio of the prepred hydrogel ws conducted by the so-clled te-bg method [13], nd using distilled wter s liquid to be bsorbed. The bgs used were mde of nonwoven polypropylene. The dried weighed smples confined in nonwoven polypropylene bgs were plced in different swelling medi with different ph vlues under mbient conditions nd tken from swelling medi t regulr intervls time. The surfce wter on the swollen hydrogel ws removed by soft pressing the bg smple between the folds of filter pper; the increse in weight ws determined. The equilibrium swelling of the gels ws determined s follows: gels were dried for 3 dys t room temperture nd were then dried under vcuum t 8 C. After weighing the dried smples ws determined, the smples were equilibrted in swelling medi for dy t room temperture nd then weighed gin. The swelling rtio (S) nd equilibrium swelling rtio (Seq) were clculted from the following equtions [14]: Aviling SAH would significntly contribute to the production of soil conditioner nd conductive gels. The mjor process opertions were: mixing; polymeriztion; wshing; drying nd pcking. The hydrogel structure is creted by the hydrophilic groups present in polymeric network upon the hydrtion in n queous environment. Wter bsorbing cpcity or swelling of the polymer cn be controlled by two methods - type nd degree of cross linking between polymeric chins nd morphology of the SAP. Xie et l. [15] discusses tht the wter bsorbing property of the SAPs cn be gretly ffected by type of cross-linking gent used. Also the cross linking gent vries the polymeric chin length longer polymer chins hve more network spce nd thus increses wter bsorbing cpcity [4]. Besides, the length of polymeric chin lso ffects its wter bsorption cpcity smller polymer chins hve more polymer ends which do not contribute to wter bsorption [16]. Superbsorbent hydrogel were prepred nd the yield percent ws found to be round 92.2 %. The effect of vrition of inititor (KPS), crosslinker (MBAAm) doses nd AAc/KOH rtio were investigted relted to the swelling behviour of the prepred SAH under investigtion. Figure 1 represents the effect of vrition of KPS on swellbility of SAH. It is shown tht swelling rtio incresed by incresing KPS dose from.2 g to.5 g to 48.8 g/g nd g/g, respectively. Further increse in KPS cuses decrese in swelling rtio up to 42 g/g. Thus, the optimum dose of KPS is.5 g Where, W, Wt, nd W eq re the weights of the smples in the dry stte, the swollen stte t certin time, nd the completely (equilibrium) swollen stte, respectively KPS dose (g) Scnning Electron Microscopy The morphology of the prepred dry hydrogel nd swelled hydrogel were chrcterized by scnning electronic microscopy technique (Electron prop micro nlyzer (JEOL, JXA 84 A) t Ntionl Reserch Centrl lbortory- Egypt. Results nd Discussion A superbsorbent hydrogel ws prepred through polymeriztion of crylic cid/crylte using potssium persulphte s inititor nd methylene biscrylmide s crosslinker. Superbsorbent Hydrogels hve been identified s polymeric cross-linked network structure. Figure 1: Effect of vrition of KPS dose on SAH swelling rtio Figure 2 illustrtes the effect of MBBAm dose s crosslinker on SAH swelling rtio. It is shown tht swelling rtio increses by incresing the crosslinker dose from.4g to.1g to 47.3 g/g to g/g, respectively. Further increse in MBAAm dose inhibits the swellbility of the SAH under investigtion. This is my be due to compliction of the net of crosslinkes.

3 Interntionl Journl of Scientific nd Engineering Reserch Volume 6, Issue 3, Mrch MBAAm dose (gr) ph Figure 2: Effect of vrition of MBAAm dose on SAH swelling rtio Figure 3 represents the effect of vrition of AAc/KOH rtio on SAH swelling rtio. It is shown tht swelling rtio increses from 54.2 g/g to 56.4 g/g by incresing the AAc/KOH rtio from.7 mole/mole to.9 mole/mole, then further increse leds to lck in swellbility AAc/KOH rtio (mole/mole) Figure 3: Effect of vrition of AAc/KOH rtio on SAH swelling rtio Figure 4: Swelling behviour of SAH t different ph vlues. Swelling behviour Swelling experiments were crried out t room temperture (25 ± 1 o C) to evlute the swelling cpcity in tp wter of the prepred SAH under investigtion. The increse in the weight of the swollen SAH ws directly relted to the time of swelling. Tht is, the increse in the weight of the swollen hydrogel incresed with incresing time of swelling (Figure 5). The swelling behvior observed ws ssocited with the bsorption mechnism, which, in turn, ws determined by the diffusion process Time (minutes) The swelling cpcity of the prepred SAH under investigtion in distilled wter, tp wter nd different ph vlues (3, 5, 8 nd 1) were crried out t room temperture (25 ± 1 o C). The results shown in figure 4 reveled tht, incresing lklinity of the swelling medi enhnced the swellbility of the prepred SAH till ph, 8. Further increse in lklinity of the swelling medi decreses the swellbility of SAP. Figure 5: Swelling behviour of SAH prepred t optimum conditions Swelling kinetics The controlling mechnism of the swelling processes ws visulized through kinetic models. The ltter were used to exmine the dt derived from the experimentl work. A simple kinetic nlysis is represented by second-order eqution, s given [17]: where ks is the swelling rte constnt nd Seq is the degree of swelling t the stte of equilibrium. After integrtion, when the initil

4 Interntionl Journl of Scientific nd Engineering Reserch Volume 6, Issue 3, Mrch conditions S = t t = nd S = S t t = t, were pplicble, eq. (3) becme s follows: where B = 1/Seq is the inverse of the mximum or equilibrium swelling nd A =1/kSSeq. 2 is the reciprocl of the rte of swelling t the initil stte [(ds/ dt)o] of the hydrogel. We exmined the kinetic models by plotting t/s versus t for the prepred SAH with optimum conditions. The swelling prmeters, including initil swelling rte (r), ks, nd mximum equilibrium swelling [(Seq)mx], were clculted from the equtions of the stright line given in Figure 6. The clculted vlues re listed in Tble I. which would prove the nomlous spects of diffusion even for molecule s smll s wter [12]. Tble 1: Some Swelling Prmeters of SAH Swelling prmeters SAH (optimum conditions) Experimentlequilibrium swelling (S eq ) mx (g/g) 66.7 K s r 1.57 n y =.6528x y =.152x R² = R² = Ln (t) Time (minutes) Figure 7: Swelling kinetic reltions of SAH Scnning Electron Microscopy Figure 6: Swelling rte reltions of SAH The surfce chrcteristics of dry nd swelled SAH were investigted by scnning electronic microscopy (SEM). Figure 8 shows the imges The mechnism of wter diffusion in swellble polymeric hydrogels of SEM for dry SAH prepred by different rtios of AAc/KOH. hs ttrcted much ttention becuse of its mny biomedicine, Figures 8 (,b, c nd d), represent the surfce morphology of dry SAH environmentl, phrmceuticl, nd griculture pplictions. The prepred with different rtios of AAc/KOH. The figures show diffusion of wter implied tht the hydrogel could be evluted with uniform nture with limited crcks on its surfce nd presence of KOH the following eqution [17]: prticles which increse by decresing AAc/KOH rtio. t/s Ln (S) b where K is the swelling constnt nd n is the swelling exponent clculted from the slopes of the lines of Ln S versus Ln t plots. For cylindricl shpes, n = nd corresponds to Fickin diffusion, wheres.5 < n < 1. indictes tht diffusion is non-fickin [18]. This eqution is pplied to the initil stges of swelling nd plots of Ln(S) versus Ln (t) yield stright lines. For the hydrogels, Ln(S) versus Ln (t) plots ws drwn using the kinetics of swelling nd some representtive results re shown in Figure 7. The swelling exponents n were clculted from the slopes of the lines nd re listed in Tble 1. The vlue of the diffusionl exponent is.652. Hence, the diffusion of wter into SAH hd non-fickin chrcter. The vlue of n higher thn.5 indicting diffusion of wter to the interior of ll the SAH, follows n nomlous mechnism. The nomlous behviour of the hydrogel is due to the regulrity of the chin nd strong interction vi the formtion of hydrogen bonding, leding to compct structure c Figure 8: SEM imges of dry SAH prepred with different rtios of AAc/KOH. d

5 Interntionl Journl of Scientific nd Engineering Reserch Volume 6, Issue 3, Mrch Figure 9 (,b, c nd d), represent surfce morphology of swelled SAH prepred with different rtios of AAc/KOH. The figures show smooth surfce nd crcks ppered due to swelling. The presence of KOH prticles on surfce of both dry nd swelled SAH smple increses by decresing AAc/KOH rtio. Figure 1 shows photogrph imge of dry SAH, it seems like hrd crystl prticles while Figure 1b represents the swelled SAH nd seems to be like wter crystls. AAc KOH MBAAm KPS wter Mixing 5 O C Polymeriztion 15 minutes 7 O C Distilled wter b Wshing wter Drying 8 O C c Grinding nd pcking Figure 11: The processing steps of SAH production. Conclusion Figure 9: SEM imges of swelled SAH prepred with different rtios A superbsorbent hydrogel ws prepred through polymeriztion of of AAc/KOH crylic cid/crylte under potssium persulphte initition nd methylene biscrylmide s crosslinker. The effect of vrition of inititor (KPS), crosslinker (MBAAm) doses nd AAc/KOH rtio were investigted relted to the swelling behviour of the prepred SAH under investigtion. The optimum conditions to prepre n efficient nd economic SAH re AAc, 6.2 %; KOH, 37.4 %; KPS, 2 %; MBAAm,.4 % nd AAc/KOH rtio,.9 mole/mole. Superbsorbent hydrogel were prepred using the optimum condition nd in bench scle nd the yield ws bout 92.2 %. Figure1: Photogrph imges of dry nd swelled SAH Block digrm of the preprtion of SAH A bench scle experiment ws crried out ccording to the optimum conditions by which the swelling rtio of the SAH ws in mximum rte nd economic. The dopted methodologicl milestones for preprtion of SAH comprises: A mixed solution of AAc monomer nd potssium crylte ws prepred by gitting the monomer with MBAAm s crosslinker in presence of KOH in distilled wter under mbient conditions. The mixture solution ws stirred nd heted to 7 oc, followed by ddition of the inititor (KPS). The rection mixture ws kept under stirring for few minutes to complete polymeriztion rection. The prepred SAH ws then wshed in excess wter to remove ny impurities then dried t 8oC for bout 3 hours. The overll processing steps for SAH re representing by the flow sheet illustrted in Figure 11. b References [1] Tlt H.A., Sorour M.H., Aboulnour A.G., Shln H. F, Ens M. Ahmed, Awd A.M. nd Ahmed M.A., Development of Multi-Component Fertilizing Hydrogel with Relevnt Techno- Economic Indictors. Americn-Eursin J. Agric. & Environ. Sci., 28, 3 (5): 764. [2] Kshyp, N., Kumr, N. nd Kumr, M. Hydrogels for Phrmceuticl nd Biomedicl Applictions, Criticl Review in Therpeutic Drug Crrier Systems, 25, 22 :17. [3] Liu, M. nd T. Guo., Preprtion nd Swelling Properties of Crosslinked Sodium Polycrylte. Journl of Applied Polymer Science 21, 82: [4] Buchholz, F.L. nd A.T. Grhm. Modern Superbsorbent Polymer Technology. In John Wiley & Sons Inc., [5] Att, A.M., R.A. El-Ghzwy, R.K. Frg, A.F. El-Kfrwy nd A.A. Abdel-Azim., Crosslinked cinnmoyloxyethyl methcrylte nd isooctyl crylte copolymers s oil sorbers. Polymer Interntionl 25, 54: 188.

6 Interntionl Journl of Scientific nd Engineering Reserch Volume 6, Issue 3, Mrch [6] Jng, J. nd B. Kim.,Studies of Crosslinked Styrene-Alkyl Acrylte Copolymers for Oil Absorbency Appliction. II. Effects of Polymeriztion Conditions on Oil Absorbency, Journl of Applied Polymer Science 2, 77: 914. [7] Kosms Deligkris, Tdele Shiferw Tdele, Wouter Olthuis, Albert vn den Berg. Hydrogel-bsed devices for biomedicl pplictions, Sensors nd Actutors B: Chemicl, 21, 147 (2, 3): 765. [8] Jihui Wu, Jinming Lin, Guoqing Li nd Congrong Wei, "Influence of the COOH nd COON groups nd crosslink density of poly(crylic-cid)/montmorillonite superbsorbent composite on wter bsorbency". Polymer Interntionl, 21,5 (9): 15. [9] G.R. Mhdvini, A. Pourjvdi, H. Hosseinzdeh, M.J. Zohurin, Slt- nd ph-resisting Collgen-bsed Highly Porous Hydrogel Euro. Polym. J., 24, 4: [1] Hennink, W.E.; Nostrum C.F. "Novel crosslinking methods to design hydrogels". Adv. Drug Delivery Rev., 22, 54:13. [11] Y. Qui, K, Prk, Environment-sensitive hydrogels for drug delivery, Adv. Drug Delivery Rev., 21, 53: 321. [12] Ens M. Ahmed, Ftm S. Aggor, Ahmed M. Awd, Ahmed T. El-Aref, An innovtive method for preprtion of nnometl hydroxide superbsorbent hydrogel, Crbohydrte Polymers 213, 91: 693. [13] Zho, Y., Kng, J., & Tn, T. Slt-, ph- nd temperture responsive semiinterpenetrting polymer network hydrogel bsed on poly(sprtic cid) nd poly(crylic cid). Polymer, 26, 47:772. [14] Ahmed, E. M., & Aggor, F. S. Swelling kinetic study nd chrcteriztion of cross linked hydrogels contining silver nnoprticles. Journl of Applied Polymer Science, 21, 117: [15] Xie, J., X. Liu, J. Ling nd Y. Luo. Swelling Properties of Superbsorbent Poly (crylic cid-co-crylmide ) with Different Crosslinkers. Journl of Applied Polymer Science 29, 112: [16] Liu, Z. S. nd G. L. Rempel. Preprtion of Superbsorbent Polymers by Crosslinking Acrylic Acid nd Acrylmide Copolymers. Journl of Applied Polymer Science 1997, 64: [17] Ens M. Ahmed, Ftm S. Aggor, Swelling Kinetic Study nd Chrcteriztion of Crosslinked Hydrogels Contining Silver Nnoprticles. Journl of AppliedPolymer Science, 21, 117: [18] Ftm S. Aggor ; Ens M. Ahmed, A.T. El-Aref nd M. A. Asem, Synthesis nd Chrcteriztion of Poly (Acrylmide - co - Acrylic cid) Hydrogel Contining Silver Nnoprticles for Antimicrobil Applictions. Journl of Americn Science, 21, 6 (12):