Viscoelastic Properties of Borax-Loaded CMC-g-cl-poly(AAm) Hydrogel Composites (PDF)

Viscoelastic properties of borax loaded CMC-g-cl-poly(AAm) hydrogel composites and their boron nutrient release behavior Dhruba Jyoti Sarkar,1 Anupama Singh,1 Shalini Rudra Gaur,2 Aroon V Shenoy3 1 Division of Agricultural Chemicals, ICAR-Indian Agricultural Research Institute, New Delhi, India 2...

Viscoelastic properties of borax loaded CMC-g-cl-poly(AAm) hydrogel composites and their boron nutrient release behavior Dhruba Jyoti Sarkar,1 Anupama Singh,1 Shalini Rudra Gaur,2 Aroon V Shenoy3 1 Division of Agricultural Chemicals, ICAR-Indian Agricultural Research Institute, New Delhi, India 2 Division of Food Science and Post Harvest Technology, ICAR-Indian Agricultural Research Institute, New Delhi, India 3 SAICO- Technical Consultancy, Arlington Virginia Correspondence to: A. Singh (E-mail: [email protected]) ABSTRACT: Borax (Na2B4O7, 10.5% Boron) loaded CMC-g-cl-poly(AAm) hydrogel composites were prepared by in situ grafting of acrylamide on to sodium carboxymethyl cellulose in the presence of borax by free radical polymerization technique to develop slow boron (B) delivery device. The composition, morphology, and mechanical properties of synthesized composites were studied by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, texture analyser, and dynamic shear rheometer. Characterization revealed formation of borate ion (BO32 3 ) from borax during polymerization reaction leading to extensive crosslink- ing of cellulosic chains and generation of mechanically strong composite hydrogels. Dynamic release of BO32 3 from the synthesized composites hydrogels followed Fickian diffusion mechanism and composites with high mechanical strength resulted in slow release of B. VC 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43969. KEYWORDS: composites; gels; kinetics; rheology Received 24 November 2015; accepted 22 May 2016 DOI: 10.1002/app.43969 INTRODUCTION of borax are high at 2–5 kg/hectare and its use efficiency remains very low due to losses from light textured acidic soil In the present era of extensive agricultural practice, micronu- receiving high precipitation, red lateritic soil, calcareous soil, trients are critical inputs in realizing high agricultural produc- and soil with low organic matter.17 In polymer chemistry, borax tivity, but their low use efficiencies are current cause of was reported as a crosslinker for polysaccharide chains contain- concern. To address such issues, in our earlier work we reported ing hydroxyl groups and borax loaded composites were reported novel slow release zinc (Zn21) formulations using hydrogel with improve mechanical, thermal, chemical resistance, and bar- composites as carriers.1 Hydrogels and hydrogel composites are rier properties.19–21 For example, barrier properties of poly(vinyl now finding considerable attention in the field of agriculture alcohol)-graphene oxide composite film was improved by borax due to their unique water absorption and retention-release crosslinking.21 Borate orthoester covalent bonding between gra- properties.2–5 They have been reported effective in improving phene oxide nanosheets were reported to be one of the stiffest hydrophysical properties of soil and as carriers for controlled materials.22 Moreover loading of polymer with borax has been release of agrochemicals.6–10 More recently they are extensively found to improve the intercalation or exfoliation morphology reported as carrier for fertilizer formulations including macro of clay hybrid biocomposite as well as mechanical properties of and micronutrients.11–14 Although plant nutrients (N, P, K, and crosslinked polymer.23,24 Other than borax, introduction of micronutrients) fertilizer formulations based on hydrogels are nanoclay,25 double network structures,26 polyampholytes,27 tem- well reported, but their loading on viscoelastic properties of perature induced nonswellability,28 and so forth. have also been hydrogel carrier and release mechanism is hitherto unknown. reported recently to improve the mechanical strength of hydro- In the present work, we report synthesis of borax (10.5% B) gel by altering their viscoelastic and physical properties. The loaded CMC-g-cl-poly(AAm) hydrogel composites as slow B present work aims at revealing viscoelastic changes of CMC- delivery device and the effect of different synthesis parameters g-cl-poly(AAm) hydrogels when loaded with borax as a source on the viscoelastic properties and release behavior of B. Borax is of micronutrient (B) and their effect on B release pattern. This used in agriculture as a source of B, an important micronutrient type of information would be useful in developing agriculturally for crop health and its deficiency in soil is an important suitable hydrogel-based nutrient formulation for integrated problem and realized all over the world.15–18 Application rates water and nutrient management of industrial crops. C 2016 Wiley Periodicals, Inc. V WWW.MATERIALSVIEWS.COM 43969 (1 of 11) J. APPL. POLYM. SCI. 2016, DOI: 10.1002/APP.43969  10974628, 2016, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/app.43969 by Brock University, Wiley Online Library on [24/10/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License ARTICLE WILEYONLINELIBRARY.COM/APP EXPERIMENTAL between the cone and plate assembly. To determine gel points of Chemicals representative BSAPCs, temperature sweep tests were conducted Sodium carboxymethyl cellulose (NaCMC) (viscosity range with linear temperature change from 30 to 100 8C at a rate of 1100-1900cps), acrylamide (AM), N,N-methylene bisacrylamide 2 8C min21, at constant strain (0.1%) and frequency (50 rad s21). (MBA), ammonium peroxodisulphate (APS) were procured from For dynamic rheological tests, linear viscoelastic region (LVR) was Merck Specialties Pvt. Ltd., Mumbai, India and used as received established by conducting a strain test in the range of 0.1 to 100% without further purification. Borax (Na2BO4O7. 10H2O) was pur- at constant frequency of 10 rad s21. Following this, frequency chased from Thermo Fisher Scientific India Pvt. Ltd., Mumbai, sweep tests (frequency: 0.1 to 100 rad s21) in logarithmic progres- India. sion were performed in a controlled strain mode at constant strain of 0.1%, which lay well within the LVR for all the studied Preparation of Borax Loaded CMC-g-cl-Poly(AAm) hydrogels. Composites The borax loaded CMC-g-cl-poly(AAm) composites (BSAPCs) Swelling Investigation were synthesized by in situ grafting of AM on the NaCMC Accurately weighed powdered BSAPCs (0.1 g, particle size < 63 backbone in the presence of MBA, APS, and borax by free radi- lm) were taken in nylon bags and immersed in excess of dis- cal polymerization technique reported previously.1 The typical tilled water (100 mL) (pH 7.0, EC 0.001 Mhos cm21) and kept procedure used was as follows: Weighed quantities of AM and at constant temperature (30 8C) until equilibration was attained. MBA were dissolved in distilled water. A mixture of NaCMC The equilibrated swollen BSAPCs were allowed to drain for 10 and borax was added to the solution with continuous mechani- min to remove free water from nylon bags. Each bag was cal stirring till a homogenous mixture (feed mass) is formed. weighed to determine the weight of the swollen BSAPCs. The The polymerization was initiated by addition of APS. The feed water absorption capacity (QH2 O , g/g, dry weight basis) was cal- mass was kept at 80 8C till gel point was attained. The cross- culated using the equation: linked gel mass was oven dried at 70 8C till constant weight. QH2 O 5ðWe 2Wx Þ=Wx (3) The grafting yield (Gy) and grafting efficiency (Ge), to character- ize the composites synthesis process were calculated by the fol- Here, Wx is the weight of xerogel or BSAPCs in glassy state and lowing equations29: We is the weight of swollen BSAPCs at equilibration. Gy 5ðWBSAPCx 2WNaCMC Þ=WNaCMC (1) Determination of B Loading Efficiency Ge 5ðWBSAPC x2WNaCMC Þ=ðWBSAPC 2WNaCMC Þ (2) Di-acid digestion method31 was used to estimate the amount of B loaded in the matrices of BSAPCs. Briefly, accurately weighed Here, WNaCMC, WBSAPC, and WBSAPCx are the weight of NaCMC, developed composites (0.1 g, particle size 100–240 mesh) were BSAPC before and after extraction of homopolymer, respec- taken in conical flasks was treated with 10 mL of concentrated tively. AM homopolymer was removed by Soxhlet extraction nitric acid (HNO3) and kept under fume hood for overnight. with a 60:40 (V/V) mixture of ethylene glycol and acetic acid for After 12 h reaction mass was treated with di-acid mixture 2 h.30 (HNO3:HCLO3: 3:1, 12 mL) and further heated at 200  C for 4– Characterization 6 h till the disappearance of brown color. The content of the Prepared composites were characterized by wide angle X-ray dif- flask was filtered and volume made up to 100 ml. Estimation of fraction (XRD) using Philips PW1710 diffractometer equipped B in the sample was done by Azomethine-H method.32 Briefly, with Philips PW1728 X-ray generator. The scanning range and 1 mL of the sample filtrate was taken in 10–15 mL polypropyl- scanning rate were kept at 1–508 2u and 1.28 2u min21, respec- ene tube, on which 2 mL buffer solution (Ammonium acetate: tively. The functional group transformation were analyzed using EDTA: Acetic acid) and 2 mL Azomethine-H reagent (Azome- Bruker Fourier Transform Infrared Spectrophotometer (FT-IR) thine-H: L-ascorbic acid) was added. Azomethine-H forms a sta- (Model Alpha ATR & Bruker, KBR pelleting method) under dry ble colored complex with B at pH 5.1 in aqueous media and air at room temperature.Scanning electron microscopy (SEM) the color intensity was measured in UV-VIS to know the con- images were obtained using ZEISS EVO MA10, 20kV, and 10 pa centration of B. Loading efficiency of the B (BLC, %) was calcu- after 30 nm palladium coating. lated as follows: Tensile strength of representative BSAPCs was assessed using a BLC ð%Þ 5 ðB detected in BSAPCs=B introduced in BSAPCsÞ3100 R TA.XT2iV Texture Analyzer (Stable Micro Systems Ltd., God- (4) alming, Surrey, U.K.) programmed with the Texture Exponent Release of BO323 from BSAPCs software. The samples were cut into uniform strips 3 3 5.0 cm. As plant absorbs B in the form of H3BO3, the effect of reactants A probe labeled Tensile Grips (A/TG) was used to extend each namely borax, MBA, and AM content in the feed mass on sample until it breaks. release pattern of BO32 from BSAPCs matrix was assessed by 3 The rheological properties of equilibrated swollen BSAPCs were tea bag method as reported previously.1,16 Briefly a dry pow- measured using an dynamic shear rheometer (MCR-52, Anton dered BSAPC specimen (0.1 g, particle size 80 mesh) taken in Paar, Germany), fitted with cone and plate measuring system (50- nylon sachet (3cm 3 3 cm; 200 mesh) was immersed in dis- mm diameter) at 25 8C with a gap of 0.1 mm between the plates. tilled water (100 mL) and incubated at room temperature (30 6 An equilibration time of 5 min was provided for hydrogel com- 2 8C). On nth day 1 mL aliquot was analyzed by Azomethine-H 1,32 posite to attain measurement temperature after placing sample method for BO32 3 estimation. WWW.MATERIALSVIEWS.COM 43969 (2 of 11) J. APPL. POLYM. SCI. 2016, DOI: 10.1002/APP.43969  10974628, 2016, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/app.43969 by Brock University, Wiley Online Library on [24/10/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License ARTICLE WILEYONLINELIBRARY.COM/APP Figure 1. XRD of (a) BSAPC-E3 [CMC-g-cl-poly(AAm) loaded with 3.64% B]; (b) SAPC [CMC-g-cl-poly(AAm)]; (c) Boric acid (H3BO3); and (d) Borax (Na2BO4O7. 10H2O). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.] Korsmeyer–Peppas equation33 was used to describe the mecha- nism of BO32 3 release from BKSAPCs. Release data were ana- lyzed by the following equation: Figure 3. (a) Gel point analysis and (b) stress-strain curves of representa- tive BSAPCs. (BSAPC-E1, 11.6% borax; BSAPC-E2, 16.5% borax; BSAPC- E3 20.8% borax; BSAPC-E4, 28.3% borax). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.] Mt 5 at b (5) Mo Here, Mt is the BO32 3 form of B released at time t; Mo is the total B content of BSAPCs; a, kinetic constant, and b, the diffu- sion exponent that predicts the release mechanism. For hydro- gels, when b  0.5, the mechanism is Fickian diffusion.33 When b 5 1, Case II transport occurs, leading to zero-order release. When the value of b is between 0.5 and 1, anomalous transport is observed. RESULTS AND DISCUSSION Characterization of BSAPC Figure 1 shows XRD patterns of a representative BSAPC (BSAPC- E3), SAPC [CMC-g-cl-Poly(AAm)], borax, and boric acid. BSAPC- E3 showed diffraction peak at 2u, 358, corresponding to the peak of pure borax (2u, 34.98) indicating successful loading of borax in com- posite matrix. XRD spectrum of BSAPC also showed a small peak at 2u, 14.68 corresponding to boric acid (2u, 14.98) revealing formation of borate ion from borax (B4 O7 22 ! BO332 ) during present com- posite synthesis.34 This observation was substantiated by the presence of characteristic FT-IR bands of boric acid (asymmetric BAO Figure 2. FTIR spectra of (a) BSAPC-E3 [CMC-g-cl-poly(AAm) loaded stretching at 1310–1400 cm21 and in-plane BAOAH bending at with 3.64% B]; (b) SAPC [CMC-g-cl-poly(AAm)]; (c) Borax (Na2BO4O7. 1200 cm21) and borax (asymmetric BAO stretching band at 10H2O); and (d) Boric acid (H3BO3). 947 cm21 and in-plane BAOAH bending at 1150 cm21)35 in the WWW.MATERIALSVIEWS.COM 43969 (3 of 11) J. APPL. POLYM. SCI. 2016, DOI: 10.1002/APP.43969  10974628, 2016, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/app.43969 by Brock University, Wiley Online Library on [24/10/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License ARTICLE WILEYONLINELIBRARY.COM/APP Figure 4. Scanning electron micrographs and corresponding 3-D mesh diagrams of NaCMC (a,i); SAPC containing 0.0% B (b,ii); BSAPC-E1 containing 2.03% B (c,iii); BSAPC-E4 containing 4.95% B (d,iv). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.] WWW.MATERIALSVIEWS.COM 43969 (4 of 11) J. APPL. POLYM. SCI. 2016, DOI: 10.1002/APP.43969  10974628, 2016, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/app.43969 by Brock University, Wiley Online Library on [24/10/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License ARTICLE WILEYONLINELIBRARY.COM/APP Figure 5. Schematic diagram of composites synthesis (a) Sodium carboxymethyl cellulose (NaCMC); (b) Acrylamide (AM); (c) borate ion (BO32 3 ); (d) Ammonium peroxodisulphate (APS); (e) N,N-methylene bisacrylamide (MBA); and (f,g) borax loaded CMC-g-cl-poly(AAm) (BSAPC). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.] FT-IR spectrum of BSAPC-E3 (Figure 2). These bands were absent in dependent on the borax content. Incorporation of higher FT-IR spectrum of corresponding SAPC [Figure 2(b)]. Characteriza- amount of borax in BSAPCs resulted in a mechanically tougher tion through XRD and FT-IR established (i) successful loading of composites, indicated by higher E values (0.50 KPa, BSAPC-E4 borax in the composite matrix of BSAPCs and (ii) formation of versus 0.27 KPa, BSAPC-E1) and higher r values till borax con- 34 BO323 may be through partial in situ hydrolysis of borax. tent of 20.8% (1.61 KPa, BSAPC-E3 versus 1.25 KPa, BSAPC- E1), and lower e values (3.59 mm/mm, BSAPC-E4 versus The temperature sweep tests in rheometer showed significant 8.47 mm/mm, BSAPC-E1) as the borax content in the feed influence of borax loading on onset of gel point temperatures mass increased from 11.6 to 28.3%.36 of representative BSAPCs. At 70 8C, BSAPC-E1 remained in liq- uid form and on heating to 75.70 8C gelation was observed [Fig- Figure 4 shows SEM and corresponding 3D mesh diagram of ure 3(a)]. A steep increase in viscosity indicates that the feed NaCMC, SAPC, and BSAPCs (BSAPC-E1 and BSAPC-E4). SEM mass molecules of composites start to rearrange and by cross- images were subjected to digital image processing using image linking gel is formed. High content of borax in the feed mass of processing toolbox of MATLAB (R2011a) which can efficiently BSAPCs led to lowering of gel point temperature. Gelation tem- convert the SEM images to n by m 3D matrix from. The aver- perature of representative BSAPCs followed the order: BSAPC- age surface roughness (Ra) was calculated to differentiate surface E1, 75.70 8C > BSAPC-E2, 58.73 8C > BSAPC-E3, 57.65 8C > morphologies of samples.37 BSAPC-E4, 51.31 8C. This variation of gel point with more borax content in BSAPCs can be explained by higher availability 1X n Ra 5 jyi j (6) of BO32 n i51 3 for crosslinking of polysaccharide chain of composites. Figure 3(b) shows stress–strain curve of representative BSAPCs Here yi is the distance from the average height of a profile (the with different borax contents. Young’s modulus, E, Tensile mean line) for measurement i, and n is the number of measure- strength (ultimate stress), r, and Fracture strain (ultimate ments. Three-dimensioanl mesh diagram of indicates that due strain), E; of the representative hydrogel composites were highly to borax loading roughness of the composite surface (Ra) was WWW.MATERIALSVIEWS.COM 43969 (5 of 11) J. APPL. POLYM. SCI. 2016, DOI: 10.1002/APP.43969  10974628, 2016, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/app.43969 by Brock University, Wiley Online Library on [24/10/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License ARTICLE WILEYONLINELIBRARY.COM/APP Table I. Effect of Synthesis Parameters on Graft Yield and Graft Efficiency of BSAPCs Synthesis parameters BSAPCs AM: NaCMC MBA (ppm) Borax (%) Gea Gyb E1 2.5:1.0 748.5 11.6 0.88b 2.67E CD E2 2.5:1.0 748.5 16.5 0.82 2.73DE EF E3 2.5:1.0 748.5 20.8 0.75 2.83DE E4 2.5:1.0 748.5 28.3 0.73F 2.93CDE G D1 2.5:1.0 187.2 4.99 0.43 0.71G G D2 2.5:1.0 249.6 4.99 0.48 0.98G DE D3 2.5:1.0 499.2 4.99 0.78 2.08F D4 2.5:1.0 1246.9 4.99 0.73EF 2.05F a C1 3.0:1.0 748.5 4.99 0.98 3.14bCD bC C2 3.5:1.0 748.5 4.99 0.87 3.31bC CD C3 4.0:1.0 748.5 4.99 0.83 3.54b C4 5.0:1.0 748.5 4.99 0.81D 5.09a P-value D4, 0.089) (Table II). E3, and E4 at x of 1 radian s21 followed the order: E1 Similarly, B value of power equation (Table II) [eq. (8)] was WWW.MATERIALSVIEWS.COM 43969 (7 of 11) J. APPL. POLYM. SCI. 2016, DOI: 10.1002/APP.43969  10974628, 2016, 38, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/app.43969 by Brock University, Wiley Online Library on [24/10/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License ARTICLE WILEYONLINELIBRARY.COM/APP Table II. Effect of Synthesis Parameters on Viscoelastic properties, Crosslink Density, and Water Absorption Behavior of BSAPCs   K 0 n0 2n00 ðn00 2n0Þ x2 G0 5 m0 2ð12n0 Þxn 11x2 2 11 ð11n0 Þð11x2 Þ G0 5 AxB BKSAPCs K n0 n00 m0 R2 A B R2 CDa QH2 O b E1 482.00 0.080 0.090 0.952 0.996 471.35 0.065 0.980 0.191 51.33B E2 550.00 0.079 0.067 0.932 0.998 543.23 0.077 0.988 0.219 47.10C E3 691.00 0.074 0.067 0.945 0.998 673.76 0.064 0.988 0.275 47.21C E4 814.00 0.062 0.063 0.945 0.999 788.62 0.062 0.989 0.323 41.03D D1 1210.00 0.095 0.082 0.945 0.998 1019.60 0.092 0.976 0.419 52.86B D2 1230.00 0.095 0.096 0.858 0.996 1139.60 0.095 0.950 0.484 45.21C D3 1300.00 0.090 0.073 0.902 0.979 1199.30 0.082 0.966 0.488 40.65D D4 1410.00 0.089 0.096 0.956 0.993 1291.60 0.070 0.916 0.520 37.43DE C1 1570.00 0.043 0.051 0.930 0.990 1658.40 0.051 0.865 0.634 36.37E C2 1610.00 0.073 0.078 0.946 0.987 1520.10 0.062 0.912 0.642 37.37DE C3 1050.00 0.086 0.100 0.947 0.993 1062.90 0.078 0.946 0.419 48.06C C4 705.00 0.105 0.103 0.923 0.999 686.67 0.095 0.977 0.278 64.53A P-value C2 > C3 > C4. Mechanism of BO32 3 Release from BSAPCs Increase of borax and MBA content and decrease of AM: NaCMC ratio in the feed mass of BSAPCs resulted in slower rate of BO32 3 release from the matrix which in the present study is attributed to generation of more barrier properties induced by enhanced mechanical strength. The mechanism of BO32 3 release from BSAPCs has been predicted using diffusion expo- nent (b) value obtained from Korsmeyer–Peppas equation [eq. Figure 7. BO323 release behavior of BSAPCs with varied content of (a) (5)]. In the present study, the value b ranged from 0.13 to 0.34 borax, (b) MBA, and (c) AM. [Color figure can be viewed in the online (Table III) which indicates that the release mechanism followed issue, which is available at wileyonlinelibrary.com.] Fickian diffusion and was not a function of degree of swelling.33 Table III. Boron (B) Loading Efficiency, Release Kinetics Parameters, and Diffusion Coefficient of BO32 3 from BSAPCs Mt/Mo 5 atb BSAPCs Ba BLCb a b R Dic E1 2.03 91.09 6 1.72 0.15FG 0.26C 0.98 3.46 HI B E2 2.88 94.25 6 4.08 0.12 0.30 0.98 2.21 E3 3.64 89.69 6 3.69 0.11I 0.31B 0.97 1.86 E4 4.95 63.23 6 2.98 0.08J 0.34A 0.97 0.98 D1 0.87 90.92 6 1.09 0.23A 0.13H 0.97 8.13 CD FG D2 0.87 85.25 6 2.59 0.19 0.16 0.97 5.55 D3 0.87 72.80 6 3.72 0.17DE 0.18EF 0.98 4.44 D4 0.87 69.30 6 1.57 0.16EF 0.15G 0.96 3.93 C1 0.77 86.46 6 2.66 0.14GH 0.27C 0.99 3.01 E D C2 0.69 82.04 6 3.28 0.17 0.22 0.99 4.44 C3 0.63 74.60 6 4.51 0.21BC 0.19E 0.99 6.78 C4 0.54 73.60 6 3.60 0.23AB 0.16FG 0.98 8.13 P-value