Research Article Organic/Inorganic Superabsorbent ...

Research ArticleOrganicInorganic Superabsorbent HydrogelsBased on Xylan and Montmorillonite

Shuang Zhang1 Ying Guan1 Gen-Que Fu1 Bo-Yang Chen1

Feng Peng1 Chun-Li Yao1 and Run-Cang Sun12

1 Institute of Biomass Chemistry and Technology College of Materials Science and TechnologyBeijing Forestry University Beijing 100083 China

2 State Key Laboratory of Pulp and Paper Engineering South China University of Technology Guangzhou 510640 China

Correspondence should be addressed to Feng Peng fengpengbjfueducn and Chun-Li Yao chunliyao2006163com

Received 10 December 2013 Accepted 2 January 2014 Published 12 February 2014

Academic Editor Ming-Guo Ma

Copyright copy 2014 Shuang Zhang et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The unique organicinorganic superabsorbent hydrogels based on xylan and inorganic clay montmorillonite (MMT) wereprepared via grafting copolymerization of acrylic acid (AA) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) with NN-methylenebisacrylamide (MBA) as a cross-linking agent and potassium persulfate (KPS) as an initiator The effect of variables onthe swelling capacity of the hydrogels such as the weight ratios of MMTxylan MBAxylan and AMPSAA was systematicallyoptimized The results indicated that the superabsorbent hydrogels comprised a porous cross-linking structure of MMT and xylanwith side chains that carry carboxylate carboxamide and sulfate The hydrogels exhibit the high compressive modulus (E) about35ndash55KPa and the compression strength of the hydrogels increased with an increment of the MMT content The effect of variouscationic salt solutions (LiCl CaCl

2 and FeCl

3) on the swelling has the following order Li+ gt Ca2+ gt Fe3+ Furthermore the

influence of pH values on swelling behaviors showed that the superabsorbent composites retained around 1000 g gminus1 over a widepH range of 60ndash100Thexylan-based hydrogelswith the highmechanical and swelling properties are promising for the applicationsin the biomaterials area

1 Introduction

Superabsorbent hydrogels are slightly cross-linked hydro-philic polymers with a three-dimensional network structureThey can absorb water in the amount from 10 up tothousands of times based on their dry weight and retain largeamounts of aqueous fluids even under some pressure Due tothe special characteristics these materials have been widelyapplied in various fields such as agriculture [1 2] biomedicalarea [3 4] waste-water treatment [5 6] biosensors [7] andtissue engineering [8 9]

Polysaccharide-based hydrogels are currently attractingmuch interest for their unique properties that is biocompati-bility biodegradability renewability and nontoxicity Variouspolysaccharides such as chitosan [10] starch [11] cellulose[12] alginate [13] carrageenan [14] and gellan gum [15] havebeen investigated on hydrogel formulations Typically hemi-celluloses are the second most abundant polysaccharides

in biomass which are commonly defined as cell wall het-erogeneous polysaccharides Compared with other polysac-charides hemicelluloses have been somewhat neglected inresearch and are normally disposed as organic waste from theforest industry side streamsWhile recent research has shownthat hemicelluloses have significant potential as a materialresource for hydrogel preparation A series of hemicelluloses-based hydrogels were synthesized from galactoglucoman-nans via introducing functional monomers with unsatu-rated bonds to the backbone of hemicelluloses and chemi-cally cross-linking the modified hemicelluloses [16ndash20] Thehydrogels presenting good biodegradability nontoxicity andcontrollable swelling capacity were fully developed for drugdelivery systems In addition xylan-based hydrogels havealso shown potential applications as pH-sensitive controlleddrug delivery vehicles by blending aspen hemicellulosesand chitosan in acidic conditions [21] Furthermore xylan-rich hemicelluloses-based hydrogels were prepared and used

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2014 Article ID 675035 11 pageshttpdxdoiorg1011552014675035

2 Journal of Nanomaterials

as a novel porous bioabsorbent by graft copolymerizationof acrylic acid and hemicelluloses for absorption of heavymetal ions from aqueous solutions [22 23] Therefore theapplications of hemicelluloses in hydrogels field are graduallyexpanding

Arabinoxylans (AXs) are the main hemicelluloses ofGramineae which have been generally present in a varietyof tissue of the main cereals of commerce wheat rye barleyoat rice corn and sorghum as well as other plants pangolagrass bamboo shoot and ray grass [24] Gramineae is similarto hardwood xylan but the amount of L-arabinose is higherHydrogels have been prepared from AXs extracted fromwheat bran as controlled release matrices which were syn-thesized via the oxidative cross-linking using either chemical(ferulic chloride and ammonium persulphate) or enzymatic(laccaseO

2and peroxidaseH

2O2) free radical-generating

agents [25ndash27] The gels present interesting properties likeneutral taste and odor high water absorption capability(up to 100 g of water per gram of dry polymer) andabsence of pH electrolyte and temperature susceptibility[28] However the water absorption capacity andmechanicalstrength of the AXs hydrogels are much lower than thoseof petroleum-based hydrogels such as poly(acrylic acid)and poly(acrylamide) hydrogels Furthermore the absenceof multistimulus response properties severely restricts theirapplications Therefore more research attention should bepaid to develop new approaches for modifying and cross-linking AXs to improve the properties of the hydrogels suchas absorption capacity mechanical strength and stimuli-responsive physical properties (normally temperature- pH-salt- or osmosis-controlled changes)

Recently much attention has been focused on inorganicmaterials for preparation of superabsorbent composites suchas attapulgite [29] kaolin [30] and sodium silicate [31] Theintroduction of inorganic clay into polysaccharides not onlyreduces production costs but also improves the properties(eg swelling ability gel strength and mechanical andthermal stability) of hydrogels and accelerates the generationof new materials for special application [32] Among theclays montmorillonite (MMT) a layered aluminum silicatewith exchangeable cations and reactive ndashOH groups on thesurface has been widely used to improve the properties ofhydrogels due to its good absorption extensive swelling inwater and cation exchange capacity [33] Yet to the best ofour knowledge there has been no report on the preparationof superabsorbent hydrogels based on xylan and inorganicclays

Acrylic acid (AA) and 2-acrylamido-2-methylprop-anesulfonic acid (AMPS) are important monomers that arewidely used for the preparation of functional hydrogelsAMPS is hydrophilic monomer containing nonionic andanionic groups meanwhile AA is anionic monomer Theincorporation of ionic groups in the superabsorbent isknown to increase their swelling capacity while the nonionicgroups can improve their salt tolerance In this paper aunique organicinorganic hydrogel was prepared by graftingcopolymerization of AA and AMPS monomers along thechains of AXs in the presence of MMT The intermolecularinteraction and morphological change of the hydrogels

were characterized by FT-IR spectra and scanning electronmicroscope (SEM) Moreover the swelling properties andbehaviors under different pH and salt concentrations wereinvestigated

2 Experimental

21 Materials Xylan was isolated from bamboo (Phyl-lostachys pubescens) holocellulose obtained by using 3NaOH at 75∘C for 3 h with a solid to liquid ratio of 1 25(gsdotmLminus1) The holocellulose was obtained by delignifica-tion of the extractive-free bamboo (40ndash60 mesh) with 6sodium chlorite in acidic solution (pH 36ndash38 adjustedby 10 acetic acid) at 75∘C for 2 h The composition ofneutral sugars and uronic acids and the molecular weightsof the hemicellulosic samples were determined accordingto the literature [34] The sugar composition of the xylan(835 xylose 51 arabinose 42 glucose 04 galactoseand 68 glucuronic acid (relatively molar percent)) wastested by high performance anion exchange chromatography(HPAEC)Themolecular weights obtained by gel permeationchromatography (GPC) showed that the native xylan had aweight average molecular weight (Mw) of 13420 gsdotmolminus1 anda polydispersity of 41 corresponding to a degree of polymer-ization of 88 2-Acrylamido-2-methyl-1-propanesulfonic acid(AMPS) and montmorillonite (MMT) were purchased fromA Johnson Mattey Company NN-Methylenebisacrylamide(MBA) and potassium persulfate (KPS) were purchasedfrom Tianjin Jinke Refined Chemical Engineering ResearchInstitute China All of these chemicals were used without anyfurther purification AA (Beijing Yili Fine Chemical Co LtdChina) was purified by distillation under reduced pressureto remove the inhibitor hydroquinone before use All otherreagents used were analytical grade and all solutions were ofprepared with distilled water

22 Preparation of Hydrogels Xylan (10 g) was dissolved in350mL of distilled water in a three-neck reactor equippedwith a mechanical stirrer a reflux condenser and a nitrogenline at 85∘C until a homogeneous solution was obtainedThen appropriate amounts (000ndash012 g) of MMTwere addedto this solution with stirring to form a uniform stickysolution under nitrogen After cooling the reactant to 70∘C008 g of KPS were added stirred and kept for 10min togenerate radicals Subsequently the mixture of AA (143ndash286 g neutralization degree of 70 with sodium hydroxidesolution) AMPS (114ndash257 g) and MBA (005ndash025 g) wasadded to the flask All the reactions were carried out undernitrogen and the reaction mixture was continuously stirredfor 4 h At the end of the propagation reaction the gel productwas poured into excess ethanol (200mL) and remained for48 h to dewater Then the dewatered product was dried toconstant mass at 70∘C grounded and passed through 100-mesh sieve Finally the powdered products were stored awayfrom moisture heat and light The feed compositions of allsamples are listed in Table 1

Journal of Nanomaterials 3

Table 1 The reaction conditions for xylan-119892-poly(AA-AMPS)MMT hydrogels

Sample codes MMTxylan (g gminus1) AMPS (g) MBA (g) AA (g)1 mdash 100 010 2002 003 100 010 2003 005 100 010 2004 008 100 010 2005 011 100 010 2006 008 200 005 2007 008 200 010 2008 008 200 015 2009 008 200 020 20010 008 200 025 20011 008 114 010 22812 008 178 010 22213 008 200 010 20014 008 233 010 16715 008 257 010 143

23 Method of Characterization

231 FT-IR Spectroscopy FT-IR spectra of the MMT xylanxylan-g-poly(AA-AMPS) and xylan-g-poly(AA-AMPS)MMT hydrogels were recorded using a Thermo ScientificNicolet iN 10 FT-IR Microscopy (Thermo Nicolet Corpo-ration Madison WI) equipped with a liquid nitrogen cooledMCT detector Dried samples were grounded and palletizedusing BaF

2and their spectra were recorded from 4000 to

650 cmminus1 at a resolution of 4 cmminus1 and 128 scans per sample

232 Surface Morphology of the Hydrogels The equilibrium-swollen samples of the hydrogels in deionized water atroom temperature were quickly frozen and then freeze-driedfor morphological analysis Scanning electron microscopy(SEM) of the hydrogel samples was carried out with a HitachiS-3400N II (Hitachi Japan) instrument at 15 kV Prior totaking pictures the samples were sputter-coated with a thinlayer of gold Images were obtained at magnifications rangingfrom 200x to 5000x which was dependent on the feature tobe traced

233 SwellingMeasurements Thepreweighted dry hydrogelswere immersed into excessive distilled water to reach a stateof equilibrium swelling The swollen superabsorbent wasfiltered using 100-mesh sieve and drained for 20min until nofree water remained After weighing the swollen hydrogelsthe equilibrium water absorption was calculated by using thefollowing equation

119876eq =1198822minus1198821

1198821

(1)

where 119876eq is the equilibrium water absorption defined asgrams of water per gram of sample119882

1and119882

2are the mass

of sample before and after swelling respectively

234 Mechanical Measurement Dynamic mechanical anal-ysis (DMA TA Instruments Q800 Series) was used todetermine the compressive modulus of the swollen hydrogelsamples To reach swelling equilibrium hydrogels were incu-bated in distilled water for 24 h at room temperature beforetestThe disk-shaped samples were 1 cmtimes05 cm (diametertimesheight) in dimension and were tested in compression modeat 25∘C Rheological measurements were carried out at 25∘Con ARES-RFS III rheometer (TA Instruments USA) Themixture of xylan (10 g) KPS (008 g) AA (10 or 20 g) MBA(005ndash025 g) and MMT (000ndash012 g) was stirred to forma homogeneous solution This hybrid system was quicklytransferred into rheometer for testing

235 Swelling in Various Salt Solutions The swelling capacityof the hydrogels was measured in different concentrations(05 10 15 20 and 25molsdotLminus1) of LiCl CaCl

2 and FeCl

3

salt solutions according to the above method described forswelling measurement in distilled water

236 Swelling at Various pHs Individual solutions withacidic and basic pHs were prepared by the dilution of NaOH(pH 120) and HCl (pH 20) solutions to achieve pH ge 60and lt60 respectively The pH values were precisely checkedby a pHmeter (PB-10 Sartorius)Then the preweighted driedhydrogelswere used for the swellingmeasurements accordingto the above method described for swelling measurement indistilled water

237 Water Retention Measurement The water retention(WR) was determined by centrifuging the water-swollenhydrogels at 2000 rpmTheweight of the hydrogels was deter-mined every 30 s The WR of the hydrogels was calculatedaccording to

WR () =1198982

1198981

times 100 (2)


where 1198981is the weight of the fully swollen hydrogel and 119898

2

is the weight of the hydrogel centrifuged for different times at2000 rpm

3 Results and Discussion

31 Synthesis and Spectral Characterization The superab-sorbent hydrogel was prepared by the graft copolymer-ization of acrylic acid (AA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) onto xylan in the presenceof a cross-linking agent (MBA) powdery montmorillonite(MMT) and potassium persulfate (KPS) as an initiator Thepersulfate initiator was decomposed under heating to pro-duce sulfate anion radicals that abstract hydrogen atoms fromthe hydroxyl groups of the xylan backbones Therefore thisredox system resulted in active centers capable of radicallyinitiating the polymerization of AA and AMPS leading toa graft copolymer Since a cross-linking agent (MBA) waspresent in this system the copolymer comprised a cross-linked structure The MMT in the polymerization reactioncan also be considered as a cross-linking agent [35] Theproposed mechanism for the grafting and chemically cross-linking reactions is outlined in Figure 1

Infrared spectroscopy was carried out to confirm thechemical structure of the superabsorbent hydrogel FT-IRspectra of MMT xylan xylan-g-poly(AA-AMPS) andxylan-g-poly(AA-AMPS)MMT superabsorbent hydrogelare shown in Figure 2 In the spectrum (see Figure 2(c))of xylan the region between 3500 cmminus1 and 1800 cmminus1presents two major peaks at about 3411 cmminus1 (correspondingto the absorption of stretching of the hydroxyl groups) andat 2911 cmminus1 (corresponding to the CndashH stretching of theCH2groups) The absorption peak at 1600 cmminus1 is related

to the uronic acid carboxylate [36] The bands at the rangeof 1452 and 1048 cmminus1 are assigned to the CndashH and CndashObond stretching frequencies The low intensity of the peaksat 990 and 1166 cmminus1 suggests the presence of arabinosylunits which have been reported to be attached only atposition 3 of the xylopyranosyl constituents [37] A sharpband at 895 cmminus1 is due to 120573-glycosidic linkages between thesugar units On comparing the spectra of xylan and xylan-g-poly(AA-AMPS) (see Figure 2(d)) new characteristicabsorption bands at 1651 1558 and 1442 cmminus1 are assignedto the stretching vibration of C=O asymmetrical stretchingvibration of COOminus and symmetrical stretching vibrationof COOminus respectively [38] Moreover the characteristicabsorption peaks of AMPS units are shown at 1400 1040 and627 cmminus1 which are attributed to CndashN stretching vibrationof the amide SndashO stretching vibration of ndashSO

3H and CndashS

stretching vibration respectively [39] These bands indicatedthat AA and AMPS monomers were actually grafted ontothe backbone of xylan

In the spectrum (see Figure 2(a)) of MMT the character-istic vibration bands are shown at 3400 and 3630 cmminus1 whichcorrespond to ndashOH stretching band for absorbed interlayerwater and ndashOH stretching band for AlndashOH respectivelyThe absorption peaks at 1631 and 1423 cmminus1 are attributedto the deformation vibration of the hydroxyl groups The

characteristic peaks at 1150 and 1090 cmminus1 are due to SindashO stretching (out-of plane) for MMT and SindashO stretching(in plane) vibration for layered silicates respectively Thepeaks at 915 845 and 796 cmminus1 are assigned to AlndashAlndashOHAlndashMgndashOH and SindashOndashAl bending vibrations respectively[40ndash42] As can be seen compared to the spectrum ofMMT (Figure 2(b)) the intensities of absorption bands at3630 cmminus1 ascribed to ndashOH of MMT disappeared in thespectrum of xylan-g-poly(AA-AMPS)MMT (Figure 2(a))In addition the intensity of the absorption peaks due to SindashOstretching also decreased These results indicated that MMTparticipated in polymerization reaction through its active ndashOH groups and chemically cross-linked with polymer chainsTherefore it could be concluded that the superabsorbenthydrogel product comprised a cross-linking structure ofxylan and MMT with side chains carrying carboxylatecarboxamide and sulfate

32 Morphological Analysis The morphologies of thefreeze-dried xylan-g-poly(AA-AMPS) and xylan-g-poly(AA-AMPS)MMT composites are depicted in Figure 3respectively Obviously the surface morphology of thexylan-g-poly(AA-AMPS)MMT hydrogel is different fromthat of xylan-g-poly(AA-AMPS) It could be observedthat the cross-linked xylan-g-poly(AA-AMPS) (Figure 3(a))displayed a porous structure withmany large pores Howeverfor hydrogel containing MMT (Figure 3(b)) the pore sizebecame smaller and it showed a sheet-like structure withsignificant interconnection forming a three-dimensionalnetwork which was beneficial for the diffusion of aqueousfluid into the superabsorbent polymer and increasing thewater absorption rate [43 44] In addition the degree ofdispersion of clay micropowder in the polymer matrix ismore important for an organic-inorganic composite [45 46]As can be seen from Figures 3(c) and 3(d) themicrostructureof pure MMT clay was flaky (Figure 3(c)) while these clayswere randomly dispersed in the polymer matrix andalmost embedded within xylan-g-poly(AA-AMPS) in thecomposites (Figure 3(d)) and no flocculation of MMTparticles could be observed These SEM results confirmedthat the MMT was finely dispersed in the composite to forma homogeneous composition

33 Mechanical Properties of Hydrogels The mechanicalproperties of the xylan-based hydrogels with different ratiosof MMT to xylan have been determined Figure 4(a) presentsthe typical compressive modulus-strain curves of xylan-based hydrogels at room temperature Obviously all thesamples exhibited the high compressive modulus (E) about35ndash55KPa This indicated that the hydrogels had excellentmechanical properties As expected the compressive mod-ulus of the hydrogels increased with the increment of theMMT content in the hydrogels in the order Gel 5gt Gel 4gtGel 3gt Gel 2gt Gel 1 The results strongly demonstrated thatMMT contributed to the enhancement of the mechanicalproperties of the hydrogels On the other hand the strains ofhydrogels decrease from92 to 66 when theMMTcontentwas increased in the hydrogel


O

OO

OHRO

ORO OR n

O

OO

ROO

RO OR n

(hemicelluloses)

COOHO C

HC

HC CH

HN

HN

O O(MBA)

NaOHCH

C O

NH

C C S

O

O

OH

C O

NH

C C S

O

O

n m

HC

NH

NH

O

O

NH

NH

O

O

NH

NH

O

O

MMT

Hemicelluloses-g-poly(AA-AMPS) Hemicelluloses-g-poly(AA-AMPS)MMT hydrogel

MMT

Hemicelluloses-g-poly(AA-AMPS)

+

O∙

+

O ∙ + nH2C CH3 + mH2C

S2O8

SO∙minus

4HSO minus

4

SO minus

3

SO minus

3

SO minus

3

COOminus

COOminus

COOminus

COOminus

COOminus

COOminus

H3CH3C

CH3

CH3

H2

H2

H2

CONH2

CONH2

CONH2

CONH2

CONH2CONH2

CONH2

COOminus

COOminus

COOminus

COOminus

SO minus

3

SO minus

3

SO minus

3SO minus

3

SO minus

3

SO minus

3

SO minus

3

O ∙

∙

CH

minusO

Figure 1 Proposed reaction mechanism for synthesis of xylan-g-poly(AA-AMPS)MMT superabsorbent hydrogels

4000 3500 3000 2500 2000 1500 1000

Tran

smitt

ance

()

(a)

(b)

(c)

(d)1452

10489901166

16511558

1442 14001040

3630 34001631 1423 1150 1090915 845

627

796

3411

2911 1600 895

Wavenumbers (cmminus1)

Figure 2 FT-IR of (a) xylan-g-poly(AA-AMPS)MMT (b) MMT(c) xylan and (d) xylan-g-poly(AA-AMPS)

To monitor the gelation process a time sweep measure-ment for viscoelastic properties of each sample was carriedout at 25∘C [47] Figures 4(b) and 4(c) show the storagemodulus (G1015840) of hydrogels with different MMT concentra-tions and various MBA contents respectively Apparently asignificant increase of G1015840 values at about 300 s in Figure 4(b)indicated that the rapid gelation process and phase separationoccurred during the initial stage Moreover the maximumstorage modulus of the hydrogels increased with the increaseof the MMTxylan weight ratios from 000 to 011 It was

further proved that the MMT played an important role inimproving the strength of hydrogels Meanwhile Figure 4(c)shows the time dependence of the storage modulus of thehydrogels with different MBA contents Cross-linking agentinduced a stable network with the polymers by covalentbonds thus the increment of MBA content led to the regularincrease of the maximum storage modulus of the hydrogels

34 Effect of MMT Content on Swelling Capacity The influ-ence of MMTxylan weight ratio on water absorbency ofthe superabsorbent hydrogels is shown in Figure 5 It isobvious thatMMT content is an important factor influencingwater absorbency of the hydrogels Increasing MMTxylanweight ratios from 000 to 008 caused an increment in waterabsorbencyThemaximumwater absorbency (1423 g gminus1) wasobtained at weight ratio ofMMTxylan (008)This trend wasattributed to the fact that the active ndashOH groups of MMTcould react with the ndashOH ndashSO

3H and ndashCOOHgroups of the

polymeric chains as indicated by FT-IR spectra (Figure 2)Hence it can relieve the entanglement of graft polymericchains and weaken the hydrogen-bonding interaction amonghydrophilic groups which decreases the physical cross-linking degree and improves polymeric network As a resultthe water absorbency can be enhanced by introducing mod-erate amount of MMT However a further increase of MMTcaused a decrease in water absorbency This phenomenonmay be attributed to the fact that the MMT can act as anadditional cross-linking point in the polymeric network todecrease the elasticity of polymers Additionally the excessof MMT would also decrease the hydrophilicity as well as


(a) (b)

(c) (d)

Figure 3 SEM images of (a) xylan-g-poly(AA-AMPS) (b) xylan-g-poly(AA-AMPS)MMT at low magnification and (c) MMT (d) xylan-g-poly(AA-AMPS)MMT at high magnification

the osmotic pressure difference resulting in shrinkage of thecomposite [48]

35 Effect of MBA Content on Swelling Capacity The amountof cross-linking agent determines the cross-linking densityof the hydrogel network which is an important swelling-control element The effect of cross-linker (MBA) to xylanweight ratio on the swelling capacity of the superabsorbenthydrogelswas investigated As shown in Figure 6 the swellingratio rose from 585 to 864 g gminus1 when the MBAxylan weightratio increased from 005 to 02 while it decreased with afurther increase in the weight ratio The hydrophilic polymerchains would dissolve in an aqueous environment with just afew cross-linkers Therefore the network cannot be formedefficiently and the water molecules cannot be held whichresults in a decrease in the water absorbency Contrarily theexcess cross-linking concentration causes the higher cross-linking density and decreases the space of polymer three-dimensional network and consequently it would not bebeneficial to expand the structure and hold a large quantityof water

36 Effect of Monomer Ratio on the Swelling CapacityThe swelling capacity of hydrogels prepared with variousweight ratios of AMPSAA is shown in Figure 7 As canbe seen increasing the AMPS concentration at monomerfeed composition the swelling capacity increased Swellingand absorption properties are attributed to the presence of

hydrophilic groups such as ndashOHndash CONHndash ndashCONH2ndash and

ndashSO3H in the network ndashSO

3

minus groups associated to AMPSpresent better affinity than ndashCOOminus group of AA Moreoverthe nonionic groups such as CONHndash can improve their salttolerance

37 Equilibrium Swelling at Various pH Values The xylan-g-poly(AA-AMPS)MMT containing carboxylate carboxam-ide and sulfonate groups are the majority of anionic-typehydrogels Ionic superabsorbent hydrogels exhibit swellingchanges for a wide range of pHs Since the swelling capacity ofall ldquoionicrdquo hydrogels is strongly influenced by ionic strengthno buffer solutions are used Hence stock NaOH (pH 130)and HCl (pH 10) solutions were diluted with distilled waterto reach desired basic and acidic pH values respectivelyThese results are illustrated in Figure 8 The swelling ratiosof the superabsorbent hydrogels were finely preserved around1000 g gminus1 in a wide range of pH (60ndash100) However swellingcapacity was significantly decreased at pH lower than 60and higher than 100 which reached to 108 g gminus1 at pH 20and 148 g gminus1 at pH 120 respectively In acidic media thecarboxylate and sulfonate anions were protonated Moreoverthe hydrogen-bonding interactions among carboxylate andsulfonate groups were strengthened which generated theadditional physical cross-linking At higher pH (60ndash100)nearly all of the ndashCOOH and ndashSO

3H groups were converted

to ndashCOOminus and ndashSO3

minus Consequently the hydrogen-bondinginteraction was eliminated and the electrostatic repulsion


0 20 40 60 80 100

0

20

40

60

Com

pres

sive m

odul

us (k

Pa)

Strain ()

543

21

(a)

0 200 400 600 800 10000

500

1000

1500

2000

2500

3000

543

21

Time (s)

G998400

(Pa)

(b)

0 200 400 600 800 10000

500

1000

1500

2000

2500

3000

3500

1098

76

Time (s)

G998400

(Pa)

(c)

Figure 4 Compressive stress-strain curves for hydrogels with different MMT contents (a)The time dependence of storage modulus (G1015840) forhydrogels with different MMT contents (b) and different MBA contents (c)

among the anionic groups increased Therefore the polymernetwork tended to swell more At pHs greater than 10the excess Na+ cations from NaOH shielded the ndashCOOminusand ndashSO

3

minus groups which prevented effective anion-anionrepulsion

38 Swelling in Salt Solutions The characteristics of externalsolution such as salt concentration and charge valency greatlyinfluence the swelling behavior of the superabsorbent hydro-gels The swelling ratios of hydrogels in aqueous solutionof LiCl CaCl

2 and FeCl

3with various concentrations are

shown in Figure 9 Obviously the swelling ratio decreased

with increasing the concentration of external salt solutionsThis well-known undesired swelling loss is often attributedto a ldquocharge screening effectrdquo of the additional cations caus-ing a nonperfect anion-anion electrostatic repulsion [49]Therefore the osmotic pressure generating from the mobileion concentration difference between the gel and aqueousphases decreased and resulted in shrinkage of the networkIn addition as shown in Figure 9 the swelling ratio in multi-valent cationic saline (CaCl

2and FeCl

3) solution was almost

close to zero at the concentration above 01mol Lminus1 whileit reached 31 g gminus1 (01mol Lminus1) and 21 g gminus1 (025mol Lminus1) inmonovalent cationic solution (LiCl) which are probably dueto the complexation of the carboxylate and sulfonate groups


000 002 004 006 008 010 012900

1000

1100

1200

1300

1400

1500

In distilled waterIn 09 wt NaCl solution

MMThemicelluloses (gg)

Swel

ling

ratio

40

44

48

52

56

60

64

68

72

Swel

ling

ratio

Figure 5 Effect of MMT contents on water absorbency of thehydrogels

000 005 010 015 020 025 030500

550

600

650

700

750

800

850

900

MBAhemicelluloses (gg)

Swel

ling

ratio

25

30

35

40

45

50

Swel

ling

ratio


Figure 6 Effect of MBA contents on water absorbency of thehydrogels

with the multivalent cations inducing the formation of theadditional cross-link points at the surface of particles Hencethe network cross-link density was enhanced resulting in theshrinkage of the network As a result the water absorbencywas decreased considerably (LiCl gt CaCl

2gt FeCl

3)

39 Effect of MMT Content on Water Retention The waterretention ability is an important parameter for hydrogelsespecially used in dry and desert regionsThe water retentionabilities of the hydrogels with different MMTxylan weightratios are shown in Figure 10 From this figure the waterretention of the hydrogels was rapidly decreased within 30 swhile small changes in the water retention occurred withprolonging the time This behavior may be explained asfollows absorbed water in the network of hygrogels can existin three states bound half bond and free water Free wateris the easiest to remove compared with bound and half-bond

00 02 04 06 08 10 12 14 16 18 20400

500

600

700

800

900

1000

1100

AMPSAA (gg)

Swel

ling

ratio

20

25

30

35

40

45

50

Swel

ling

ratio


Figure 7 Effect of monomer ratios on water absorbency of thehydrogels

2 4 6 8 10 120

200

400

600

800

1000

Swel

ling

ratio

pH

Figure 8 Effect of external pH on the water absorbency of thehydrogels

water Additionally the water retention of the hydrogels withvarious MMTxylan weight ratios of 000 003 005 008and 011 was 65 69 74 60 and 53 respectively centrifugedat 2000 rpm for 360 seconds It can be concluded that thewater retention can be enhanced with the moderate amountof MMT This may be explained by the barrier effect ofpolymerMMT hydrogels [50] The nano-dispersed MMTin the composite acted as an additional crosslinking pointimpeded the diffusion of the water molecules and madethe diffuse path for water vapor longer However a furtherincrease of MMT caused a decrease in water retention whichwas probably due to that it was difficult to disperse MMT inthe homogeneous network solution at higher MMT contentresulted in decreasing the water retention ability


005 010 015 020 025

5

10

15

20

25

30

35

40

45

Swel

ling

ratio

Concentration of salt solution

LiClCaCl2FeCl3

Figure 9 Effect of different salt solution on the water absorbency ofthe hydrogels

50

60

70

80

90

100

Wat

er re

tent

ion

Time (s)

MMT0MMT1MMT2

MMT3MMT4

0 50 100 150 200 250 300 350 400minus50

Figure 10 Effect of MMT contents on water retention of thehydrogels

4 Conclusions

The superabsorbent hydrogels were prepared by the graftcopolymerization of AA and AMPS onto xylan in the pres-ence of a cross-linking agent (MBA) MMT and KPS as aninitiatorThe results of FT-IR showed that the superabsorbenthydrogel products comprised cross-linking structures ofxylan and MMT with side chains carrying carboxylate car-boxamide and sulfate SEM studies showed that a sheet-likestructure with significant interconnection formed a three-dimensional network where MMT was finely dispersed toform a homogeneous composition All the samples exhibitedthe high compressive modulus (119864) about 35ndash55KPa The

compressive modulus of the hydrogels increased with theincrement of the MMT content in the hydrogels in the orderGel 5gtGel 4gtGel 3gtGel 2gtGel 1Themaximumequilibriumswelling ratios of hydrogels in distilled water and 09 wtsodium chloride solutions were up to 1423 g gminus1 and 69 g gminus1respectivelyThe effect of various cationic salt solutions (LiClCaCl2 and FeCl

3) on the swelling has the following order

Li+ gtCa2+ gt Fe3+ As a result these inorganicorganic hydro-gels from xylan will have wide applications in the fields ofagriculture foods tissue engineering and drug delivery dueto their high swelling capacity and multistimulus responseproperties

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work was supported by Grants from 2013 NationalStudent Research Training Program (SRTP-201310022034)Excellent Youth Scholars of Ministry of Education of China(20110014120006) Ministries of Education (NCET-13-0670and 113014A) Postdoctoral Science Foundation of China(2012M510328) andMinistry of Science and Technology (973Project 2010CB732204)

References

[1] M R Guilherme A V Reis A T Paulino T A Moia L H CMattoso and E B Tambourgi ldquoPectin-based polymer hydrogelas a carrier for release of agricultural nutrients and removalof heavy metals from wastewaterrdquo Journal of Applied PolymerScience vol 117 no 6 pp 3146ndash3154 2010

[2] F Puoci F Iemma U G Spizzirri G Cirillo M Curcio andN Picci ldquoPolymer in agriculture a reviewrdquo American Journalof Agricultural and Biological Science vol 3 no 1 pp 299ndash3142008

[3] T Ooya H Mori M Terano and N Yui ldquoSynthesis of abiodegradable polymeric supramolecular assembly for drugdeliveryrdquo Macromolecular Rapid Communications vol 16 no4 pp 259ndash263 1995

[4] P S K Murthy Y Murali Mohan K Varaprasad B Sreedharand K Mohana Raju ldquoFirst successful design of semi-IPNhydrogel-silver nanocomposites a facile approach for antibac-terial applicationrdquo Journal of Colloid and Interface Science vol318 no 2 pp 217ndash224 2008

[5] W Kangwansupamonkon W Jitbunpot and S Kiatkamjorn-wong ldquoPhotocatalytic efficiency of TiO

2poly[acrylamide-co-

(acrylic acid)] composite for textile dye degradationrdquo PolymerDegradation and Stability vol 95 no 9 pp 1894ndash1902 2010

[6] H Kasgoz and A Durmus ldquoDye removal by a novel hydrogel-clay nanocomposite with enhanced swelling propertiesrdquo Poly-mers for Advanced Technologies vol 19 no 7 pp 838ndash845 2008

[7] L-M Zhang G-H Wang and Z Xing ldquoPolysaccharide-assisted incorporation of multiwalled carbon nanotubes intosol-gel silica matrix for electrochemical sensingrdquo Journal ofMaterials Chemistry vol 21 no 12 pp 4650ndash4656 2011


[8] F Brandl F Sommer and A Goepferich ldquoRational design ofhydrogels for tissue engineering impact of physical factors oncell behaviorrdquo Biomaterials vol 28 no 2 pp 134ndash146 2007

[9] K Y Lee and D J Mooney ldquoHydrogels for tissue engineeringrdquoChemical Reviews vol 101 no 7 pp 1869ndash1879 2001

[10] X Qu A Wirsen and A-C Albertsson ldquoNovel pH-sensitivechitosan hydrogels swelling behavior and states of waterrdquoPolymer vol 41 no 12 pp 4589ndash4598 2000

[11] S-Y Yang and C-Y Huang ldquoPlasma treatment for enhanc-ing mechanical and thermal properties of biodegradablePVAstarch blendsrdquo Journal of Applied Polymer Science vol 109no 4 pp 2452ndash2459 2008

[12] F Lenzi A Sannino A Borriello F Porro D Capitani and GMensitieri ldquoProbing the degree of crosslinking of a cellulosebased superabsorbing hydrogel through traditional and NMRtechniquesrdquo Polymer vol 44 no 5 pp 1577ndash1588 2003

[13] S Hua and A Wang ldquoSynthesis characterization and swellingbehaviors of sodium alginate-g-poly(acrylic acid)sodiumhumate superabsorbentrdquo Carbohydrate Polymers vol 75 no 1pp 79ndash84 2009

[14] A Pourjavadi and H Ghasemzadeh ldquoCarrageenan-g-poly(acrylamide)poly(vinylsulfonic acid sodium salt) asa novel semi-IPN hydrogel synthesis characterization andswelling behaviorrdquo Polymer Engineering and Science vol 47 no9 pp 1388ndash1395 2007

[15] Y Gong C Wang R C Lai K Su F Zhang and D-A Wang ldquoAn improved injectable polysaccharide hydrogelmodified gellan gum for long-term cartilage regeneration invitrordquo Journal of Materials Chemistry vol 19 no 14 pp 1968ndash1977 2009

[16] M S Lindblad A-C Albertsson E Ranucci M Laus andE Giani ldquoBiodegradable polymers from renewable sourcesrheological characterization of hemicellulose-based hydrogelsrdquoBiomacromolecules vol 6 no 2 pp 684ndash690 2005

[17] A-C Albertsson J Voepel U Edlund O Dahlman and MSoderqvist-Lindblad ldquoDesign of renewable hydrogel releasesystems from fiberboard mill wastewaterrdquo Biomacromoleculesvol 11 no 5 pp 1406ndash1411 2010

[18] A A Roos U Edlund J Sjoberg A-C Albertsson and HStalbrand ldquoProtein release from galactoglucomannan hydro-gels influence of substitutions and enzymatic hydrolysis by 120573-mannanaserdquo Biomacromolecules vol 9 no 8 pp 2104ndash21102008

[19] Y Lu L Zhang X Zhang and Y Zhou ldquoEffects of secondarystructure on miscibility and properties of semi-IPN frompolyurethane and benzyl konjac glucomannanrdquo Polymer vol44 no 21 pp 6689ndash6696 2003

[20] U Edlund and A-C Albertsson ldquoA microspheric systemhemicellulose-based hydrogelsrdquo Journal of Bioactive and Com-patible Polymers vol 23 no 2 pp 171ndash186 2008

[21] A M Karaaslan M A Tshabalala and G Buschle-DillerldquoWood hemicellulosechitosan-based semi interpenetratingnetwork hydrogels mechanical swelling and controlled drugrelease propertiesrdquo BioResources vol 5 no 2 pp 1036ndash10542010

[22] X-W Peng L-X Zhong J-L Ren and R-C Sun ldquoHighlyeffective adsorption of heavymetal ions from aqueous solutionsby macroporous xylan-rich hemicelluloses-based hydrogelrdquoJournal of Agricultural and Food Chemistry vol 60 no 15 pp3909ndash3916 2012

[23] X-W Peng J-L Ren L-X Zhong F Peng and R-C SunldquoXylan-rich hemicelluloses-graft-acrylic acid ionic hydrogels

with rapid responses to pH salt and organic solventsrdquo Journalof Agricultural and Food Chemistry vol 59 no 15 pp 8208ndash8215 2011

[24] T Ishii ldquoAcetylation at O-2 of arabinofuranose residues inferuloylated arabinoxylan from bamboo shoot cell-wallsrdquo Phy-tochemistry vol 30 no 7 pp 2317ndash2320 1991

[25] M C Figueroa-Espinoza and X Rouau ldquoOxidative cross-linking of pentosans by a fungal laccase and horseradishperoxidase mechanism of linkage between feruloylated arabi-noxylansrdquo Cereal Chemistry vol 75 no 2 pp 259ndash265 1998

[26] A Skendi C G Biliaderis M S Izydorczyk M Zervouand P Zoumpoulakis ldquoStructural variation and rheologicalproperties of water-extractable arabinoxylans from six Greekwheat cultivarsrdquo Food Chemistry vol 126 no 2 pp 526ndash5362011

[27] E Carvajal-Millan S Guilbert M-H Morel and V MicardldquoImpact of the structure of arabinoxylan gels on their rheolog-ical and protein transport propertiesrdquo Carbohydrate Polymersvol 60 no 4 pp 431ndash438 2005

[28] M S Izydorczyk and C G Biliaderis ldquoCereal arabinoxylansadvances in structure and physicochemical propertiesrdquo Carbo-hydrate Polymers vol 28 no 1 pp 33ndash48 1995

[29] J Zhang and A Wang ldquoStudy on superabsorbent compositesIX synthesis characterization and swelling behaviors of poly-acrylamideclay composites based on various claysrdquo Reactiveand Functional Polymers vol 67 no 8 pp 737ndash745 2007

[30] X Shi S Xu J Lin S Feng and J Wang ldquoSynthesis ofSiO2-polyacrylic acid hybrid hydrogel with high mechanical

properties and salt tolerance using sodium silicate precursorthrough sol-gel processrdquo Materials Letters vol 63 no 5 pp527ndash529 2009

[31] P K Sahoo and P K Rana ldquoSynthesis and biodegradabilityof starch-g-ethyl methacrylatesodium acrylatesodium silicatesuperabsorbing compositerdquo Journal of Materials Science vol 41no 19 pp 6470ndash6475 2006

[32] D Gao R B Heimann J Lerchner J Seidel and G WolfldquoDevelopment of a novel moisture sensor based on superab-sorbent poly(acrylamide)-montmorillonite composite hydro-gelsrdquo Journal of Materials Science vol 36 no 18 pp 4567ndash45712001

[33] Y Bao J Ma and N Li ldquoSynthesis and swelling behav-iors of sodium carboxymethyl cellulose-g-poly(AA-co-AM-co-AMPS)MMT superabsorbent hydrogelrdquo Carbohydrate Poly-mers vol 84 no 1 pp 76ndash82 2011

[34] F Peng J-L Ren F Xu J Bian P Peng and R-C SunldquoFractionation of alkali-solubilized hemicelluloses from delig-nified populus gansuensis structure and propertiesrdquo Journal ofAgricultural and Food Chemistry vol 58 no 9 pp 5743ndash57502010

[35] P Uthirakumar K S Nahm Y B Hahn and Y-S LeeldquoPreparation of polystyrenemontmorillonite nanocompositesusing a new radical initiator-montmorillonite hybrid via in situintercalative polymerizationrdquo European Polymer Journal vol40 no 11 pp 2437ndash2444 2004

[36] M Kacurakova N Wellner A Ebringerovaa Z Hromaad-kovaa R H Wilson and P S Belton ldquoCharacterisation ofxylan-type polysaccharides and associated cell wall componentsby FT-IR and FT-Raman spectroscopiesrdquo Food Hydrocolloidsvol 13 no 1 pp 35ndash41 1999

[37] A Ebringerova Z Hromadkova J Alfoldi and G BerthldquoStructural and solution properties of corn cob heteroxylansrdquoCarbohydrate Polymers vol 19 no 2 pp 99ndash105 1992


[38] W Wang Q Wang and A Wang ldquoPH-responsive carbox-ymethylcellulose-g-poly(sodium acrylate)polyvinylpyrrolid-one semi-IPNhydrogels with enhanced responsive and swellingpropertiesrdquo Macromolecular Research vol 19 no 1 pp 57ndash652011

[39] M Dalaran S Emik G Guclu T B Iyim and S OzgumusldquoRemoval of acidic dye from aqueous solutions usingpoly(DMAEMA-AMPS-HEMA) terpolymerMMT nanocom-posite hydrogelsrdquo Polymer Bulletin vol 63 no 2 pp 159ndash1712009

[40] S W Xu J P Zheng L Tong and K De Yao ldquoInteraction offunctional groups of gelatin and montmorillonite in nanocom-positerdquo Journal of Applied Polymer Science vol 101 no 3 pp1556ndash1561 2006

[41] H A Patel R S Somani H C Bajaj and R V Jasra ldquoSynthesisand characterization of organic bentonite using Gujarat andRajasthan claysrdquo Current Science vol 92 no 7 pp 1004ndash10092007

[42] M Baek J-H Choy and S-J Choi ldquoMontmorillonite inter-calated with glutathione for antioxidant delivery synthesischaracterization and bioavailability evaluationrdquo InternationalJournal of Pharmaceutics vol 425 no 1-2 pp 29ndash34 2012

[43] D R Nisbet K E Crompton S D Hamilton et al ldquoMor-phology and gelation of thermosensitive xyloglucan hydrogelsrdquoBiophysical Chemistry vol 121 no 1 pp 14ndash20 2006

[44] J Wang W Wang and A Wang ldquoSynthesis characterizationand swelling behaviors of hydroxyethyl cellulose-g-poly(acrylicacid)attapulgite superabsorbent compositerdquo Polymer Engineer-ing and Science vol 50 no 5 pp 1019ndash1027 2010

[45] F Santiago A E Mucientes M Osorio and C Rivera ldquoPrepa-ration of composites and nanocomposites based on bentoniteand poly(sodium acrylate) Effect of amount of bentonite on theswelling behaviourrdquo European Polymer Journal vol 43 no 1 pp1ndash9 2007

[46] T Gao W Wang and A Wang ldquoA pH-sensitive compositehydrogel based on sodium alginate and medical stone syn-thesis swelling and heavy metal ions adsorption propertiesrdquoMacromolecular Research vol 19 no 7 pp 739ndash748 2011

[47] C Chang S Chen and L Zhang ldquoNovel hydrogels preparedvia direct dissolution of chitin at low temperature structure andbiocompatibilityrdquo Journal of Materials Chemistry vol 21 no 11pp 3865ndash3871 2011

[48] L Wu and M Liu ldquoSlow-release potassium silicate fertilizerwith the function of superabsorbent and water retentionrdquoIndustrial and Engineering Chemistry Research vol 46 no 20pp 6494ndash6500 2007

[49] M Sadeghi and M Yarahmadi ldquoSynthesis and characterizationof superabsorbent hydrogel based on chitosan-g-poly (acrylicacid-coacrylonitrile)rdquo African Journal of Biotechnology vol 10no 57 pp 12265ndash12275 2011

[50] H Qiu and J Yu ldquoPolyacrylate(carboxymethylcellulose modi-fied montmorillonite) superabsorbent nanocomposite prepa-ration and water absorbencyrdquo Journal of Applied PolymerScience vol 107 no 1 pp 118ndash123 2008

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


as a novel porous bioabsorbent by graft copolymerizationof acrylic acid and hemicelluloses for absorption of heavymetal ions from aqueous solutions [22 23] Therefore theapplications of hemicelluloses in hydrogels field are graduallyexpanding

Arabinoxylans (AXs) are the main hemicelluloses ofGramineae which have been generally present in a varietyof tissue of the main cereals of commerce wheat rye barleyoat rice corn and sorghum as well as other plants pangolagrass bamboo shoot and ray grass [24] Gramineae is similarto hardwood xylan but the amount of L-arabinose is higherHydrogels have been prepared from AXs extracted fromwheat bran as controlled release matrices which were syn-thesized via the oxidative cross-linking using either chemical(ferulic chloride and ammonium persulphate) or enzymatic(laccaseO

2and peroxidaseH

2O2) free radical-generating

agents [25ndash27] The gels present interesting properties likeneutral taste and odor high water absorption capability(up to 100 g of water per gram of dry polymer) andabsence of pH electrolyte and temperature susceptibility[28] However the water absorption capacity andmechanicalstrength of the AXs hydrogels are much lower than thoseof petroleum-based hydrogels such as poly(acrylic acid)and poly(acrylamide) hydrogels Furthermore the absenceof multistimulus response properties severely restricts theirapplications Therefore more research attention should bepaid to develop new approaches for modifying and cross-linking AXs to improve the properties of the hydrogels suchas absorption capacity mechanical strength and stimuli-responsive physical properties (normally temperature- pH-salt- or osmosis-controlled changes)

Recently much attention has been focused on inorganicmaterials for preparation of superabsorbent composites suchas attapulgite [29] kaolin [30] and sodium silicate [31] Theintroduction of inorganic clay into polysaccharides not onlyreduces production costs but also improves the properties(eg swelling ability gel strength and mechanical andthermal stability) of hydrogels and accelerates the generationof new materials for special application [32] Among theclays montmorillonite (MMT) a layered aluminum silicatewith exchangeable cations and reactive ndashOH groups on thesurface has been widely used to improve the properties ofhydrogels due to its good absorption extensive swelling inwater and cation exchange capacity [33] Yet to the best ofour knowledge there has been no report on the preparationof superabsorbent hydrogels based on xylan and inorganicclays

Acrylic acid (AA) and 2-acrylamido-2-methylprop-anesulfonic acid (AMPS) are important monomers that arewidely used for the preparation of functional hydrogelsAMPS is hydrophilic monomer containing nonionic andanionic groups meanwhile AA is anionic monomer Theincorporation of ionic groups in the superabsorbent isknown to increase their swelling capacity while the nonionicgroups can improve their salt tolerance In this paper aunique organicinorganic hydrogel was prepared by graftingcopolymerization of AA and AMPS monomers along thechains of AXs in the presence of MMT The intermolecularinteraction and morphological change of the hydrogels

were characterized by FT-IR spectra and scanning electronmicroscope (SEM) Moreover the swelling properties andbehaviors under different pH and salt concentrations wereinvestigated

2 Experimental

21 Materials Xylan was isolated from bamboo (Phyl-lostachys pubescens) holocellulose obtained by using 3NaOH at 75∘C for 3 h with a solid to liquid ratio of 1 25(gsdotmLminus1) The holocellulose was obtained by delignifica-tion of the extractive-free bamboo (40ndash60 mesh) with 6sodium chlorite in acidic solution (pH 36ndash38 adjustedby 10 acetic acid) at 75∘C for 2 h The composition ofneutral sugars and uronic acids and the molecular weightsof the hemicellulosic samples were determined accordingto the literature [34] The sugar composition of the xylan(835 xylose 51 arabinose 42 glucose 04 galactoseand 68 glucuronic acid (relatively molar percent)) wastested by high performance anion exchange chromatography(HPAEC)Themolecular weights obtained by gel permeationchromatography (GPC) showed that the native xylan had aweight average molecular weight (Mw) of 13420 gsdotmolminus1 anda polydispersity of 41 corresponding to a degree of polymer-ization of 88 2-Acrylamido-2-methyl-1-propanesulfonic acid(AMPS) and montmorillonite (MMT) were purchased fromA Johnson Mattey Company NN-Methylenebisacrylamide(MBA) and potassium persulfate (KPS) were purchasedfrom Tianjin Jinke Refined Chemical Engineering ResearchInstitute China All of these chemicals were used without anyfurther purification AA (Beijing Yili Fine Chemical Co LtdChina) was purified by distillation under reduced pressureto remove the inhibitor hydroquinone before use All otherreagents used were analytical grade and all solutions were ofprepared with distilled water

22 Preparation of Hydrogels Xylan (10 g) was dissolved in350mL of distilled water in a three-neck reactor equippedwith a mechanical stirrer a reflux condenser and a nitrogenline at 85∘C until a homogeneous solution was obtainedThen appropriate amounts (000ndash012 g) of MMTwere addedto this solution with stirring to form a uniform stickysolution under nitrogen After cooling the reactant to 70∘C008 g of KPS were added stirred and kept for 10min togenerate radicals Subsequently the mixture of AA (143ndash286 g neutralization degree of 70 with sodium hydroxidesolution) AMPS (114ndash257 g) and MBA (005ndash025 g) wasadded to the flask All the reactions were carried out undernitrogen and the reaction mixture was continuously stirredfor 4 h At the end of the propagation reaction the gel productwas poured into excess ethanol (200mL) and remained for48 h to dewater Then the dewatered product was dried toconstant mass at 70∘C grounded and passed through 100-mesh sieve Finally the powdered products were stored awayfrom moisture heat and light The feed compositions of allsamples are listed in Table 1










119876eq =1198822minus1198821

1198821

(1)


1and119882

2are the mass




2 and FeCl

3




WR () =1198982

1198981

times 100 (2)



2






3H and CndashS







O

OO

OHRO

ORO OR n

O

OO

ROO

RO OR n

(hemicelluloses)

COOHO C

HC

HC CH

HN

HN

O O(MBA)

NaOHCH

C O

NH

C C S

O

O

OH

C O

NH

C C S

O

O

n m

HC

NH

NH

O

O

NH

NH

O

O

NH

NH

O

O

MMT


MMT


+

O∙

+


S2O8

SO∙minus

4HSO minus

4

SO minus

3

SO minus

3

SO minus

3

COOminus

COOminus

COOminus

COOminus

COOminus

COOminus

H3CH3C

CH3

CH3

H2

H2

H2

CONH2

CONH2

CONH2

CONH2

CONH2CONH2

CONH2

COOminus

COOminus

COOminus

COOminus

SO minus

3

SO minus

3

SO minus

3SO minus

3

SO minus

3

SO minus

3

SO minus

3

O ∙

∙

CH

minusO


4000 3500 3000 2500 2000 1500 1000

Tran

smitt

ance

()

(a)

(b)

(c)

(d)1452

10489901166

16511558

1442 14001040

3630 34001631 1423 1150 1090915 845

627

796

3411

2911 1600 895









(a) (b)

(c) (d)







3







0 20 40 60 80 100

0

20

40

60

Com

pres

sive m

odul

us (k

Pa)

Strain ()

543

21

(a)

0 200 400 600 800 10000

500

1000

1500

2000

2500

3000

543

21

Time (s)

G998400

(Pa)

(b)

0 200 400 600 800 10000

500

1000

1500

2000

2500

3000

3500

1098

76

Time (s)

G998400

(Pa)

(c)



3



2 and FeCl




2and FeCl




000 002 004 006 008 010 012900

1000

1100

1200

1300

1400

1500



Swel

ling

ratio

40

44

48

52

56

60

64

68

72

Swel

ling

ratio


000 005 010 015 020 025 030500

550

600

650

700

750

800

850

900


Swel

ling

ratio

25

30

35

40

45

50

Swel

ling

ratio




2gt FeCl

3)


00 02 04 06 08 10 12 14 16 18 20400

500

600

700

800

900

1000

1100

AMPSAA (gg)

Swel

ling

ratio

20

25

30

35

40

45

50

Swel

ling

ratio



2 4 6 8 10 120

200

400

600

800

1000

Swel

ling

ratio

pH




005 010 015 020 025

5

10

15

20

25

30

35

40

45

Swel

ling

ratio


LiClCaCl2FeCl3


50

60

70

80

90

100

Wat

er re

tent

ion

Time (s)

MMT0MMT1MMT2

MMT3MMT4

0 50 100 150 200 250 300 350 400minus50


4 Conclusions







Acknowledgments


References
































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials












119876eq =1198822minus1198821

1198821

(1)


1and119882

2are the mass




2 and FeCl

3




WR () =1198982

1198981

times 100 (2)



2






3H and CndashS







O

OO

OHRO

ORO OR n

O

OO

ROO

RO OR n

(hemicelluloses)

COOHO C

HC

HC CH

HN

HN

O O(MBA)

NaOHCH

C O

NH

C C S

O

O

OH

C O

NH

C C S

O

O

n m

HC

NH

NH

O

O

NH

NH

O

O

NH

NH

O

O

MMT


MMT


+

O∙

+


S2O8

SO∙minus

4HSO minus

4

SO minus

3

SO minus

3

SO minus

3

COOminus

COOminus

COOminus

COOminus

COOminus

COOminus

H3CH3C

CH3

CH3

H2

H2

H2

CONH2

CONH2

CONH2

CONH2

CONH2CONH2

CONH2

COOminus

COOminus

COOminus

COOminus

SO minus

3

SO minus

3

SO minus

3SO minus

3

SO minus

3

SO minus

3

SO minus

3

O ∙

∙

CH

minusO


4000 3500 3000 2500 2000 1500 1000

Tran

smitt

ance

()

(a)

(b)

(c)

(d)1452

10489901166

16511558

1442 14001040

3630 34001631 1423 1150 1090915 845

627

796

3411

2911 1600 895









(a) (b)

(c) (d)







3







0 20 40 60 80 100

0

20

40

60

Com

pres

sive m

odul

us (k

Pa)

Strain ()

543

21

(a)

0 200 400 600 800 10000

500

1000

1500

2000

2500

3000

543

21

Time (s)

G998400

(Pa)

(b)

0 200 400 600 800 10000

500

1000

1500

2000

2500

3000

3500

1098

76

Time (s)

G998400

(Pa)

(c)



3



2 and FeCl




2and FeCl




000 002 004 006 008 010 012900

1000

1100

1200

1300

1400

1500



Swel

ling

ratio

40

44

48

52

56

60

64

68

72

Swel

ling

ratio


000 005 010 015 020 025 030500

550

600

650

700

750

800

850

900


Swel

ling

ratio

25

30

35

40

45

50

Swel

ling

ratio




2gt FeCl

3)


00 02 04 06 08 10 12 14 16 18 20400

500

600

700

800

900

1000

1100

AMPSAA (gg)

Swel

ling

ratio

20

25

30

35

40

45

50

Swel

ling

ratio



2 4 6 8 10 120

200

400

600

800

1000

Swel

ling

ratio

pH




005 010 015 020 025

5

10

15

20

25

30

35

40

45

Swel

ling

ratio


LiClCaCl2FeCl3


50

60

70

80

90

100

Wat

er re

tent

ion

Time (s)

MMT0MMT1MMT2

MMT3MMT4

0 50 100 150 200 250 300 350 400minus50


4 Conclusions







Acknowledgments


References
































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





2






3H and CndashS







O

OO

OHRO

ORO OR n

O

OO

ROO

RO OR n

(hemicelluloses)

COOHO C

HC

HC CH

HN

HN

O O(MBA)

NaOHCH

C O

NH

C C S

O

O

OH

C O

NH

C C S

O

O

n m

HC

NH

NH

O

O

NH

NH

O

O

NH

NH

O

O

MMT


MMT


+

O∙

+


S2O8

SO∙minus

4HSO minus

4

SO minus

3

SO minus

3

SO minus

3

COOminus

COOminus

COOminus

COOminus

COOminus

COOminus

H3CH3C

CH3

CH3

H2

H2

H2

CONH2

CONH2

CONH2

CONH2

CONH2CONH2

CONH2

COOminus

COOminus

COOminus

COOminus

SO minus

3

SO minus

3

SO minus

3SO minus

3

SO minus

3

SO minus

3

SO minus

3

O ∙

∙

CH

minusO


4000 3500 3000 2500 2000 1500 1000

Tran

smitt

ance

()

(a)

(b)

(c)

(d)1452

10489901166

16511558

1442 14001040

3630 34001631 1423 1150 1090915 845

627

796

3411

2911 1600 895









(a) (b)

(c) (d)







3







0 20 40 60 80 100

0

20

40

60

Com

pres

sive m

odul

us (k

Pa)

Strain ()

543

21

(a)

0 200 400 600 800 10000

500

1000

1500

2000

2500

3000

543

21

Time (s)

G998400

(Pa)

(b)

0 200 400 600 800 10000

500

1000

1500

2000

2500

3000

3500

1098

76

Time (s)

G998400

(Pa)

(c)



3



2 and FeCl




2and FeCl




000 002 004 006 008 010 012900

1000

1100

1200

1300

1400

1500



Swel

ling

ratio

40

44

48

52

56

60

64

68

72

Swel

ling

ratio


000 005 010 015 020 025 030500

550

600

650

700

750

800

850

900


Swel

ling

ratio

25

30

35

40

45

50

Swel

ling

ratio




2gt FeCl

3)


00 02 04 06 08 10 12 14 16 18 20400

500

600

700

800

900

1000

1100

AMPSAA (gg)

Swel

ling

ratio

20

25

30

35

40

45

50

Swel

ling

ratio



2 4 6 8 10 120

200

400

600

800

1000

Swel

ling

ratio

pH




005 010 015 020 025

5

10

15

20

25

30

35

40

45

Swel

ling

ratio


LiClCaCl2FeCl3


50

60

70

80

90

100

Wat

er re

tent

ion

Time (s)

MMT0MMT1MMT2

MMT3MMT4

0 50 100 150 200 250 300 350 400minus50


4 Conclusions







Acknowledgments


References
































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




O

OO

OHRO

ORO OR n

O

OO

ROO

RO OR n

(hemicelluloses)

COOHO C

HC

HC CH

HN

HN

O O(MBA)

NaOHCH

C O

NH

C C S

O

O

OH

C O

NH

C C S

O

O

n m

HC

NH

NH

O

O

NH

NH

O

O

NH

NH

O

O

MMT


MMT


+

O∙

+


S2O8

SO∙minus

4HSO minus

4

SO minus

3

SO minus

3

SO minus

3

COOminus

COOminus

COOminus

COOminus

COOminus

COOminus

H3CH3C

CH3

CH3

H2

H2

H2

CONH2

CONH2

CONH2

CONH2

CONH2CONH2

CONH2

COOminus

COOminus

COOminus

COOminus

SO minus

3

SO minus

3

SO minus

3SO minus

3

SO minus

3

SO minus

3

SO minus

3

O ∙

∙

CH

minusO


4000 3500 3000 2500 2000 1500 1000

Tran

smitt

ance

()

(a)

(b)

(c)

(d)1452

10489901166

16511558

1442 14001040

3630 34001631 1423 1150 1090915 845

627

796

3411

2911 1600 895









(a) (b)

(c) (d)







3







0 20 40 60 80 100

0

20

40

60

Com

pres

sive m

odul

us (k

Pa)

Strain ()

543

21

(a)

0 200 400 600 800 10000

500

1000

1500

2000

2500

3000

543

21

Time (s)

G998400

(Pa)

(b)

0 200 400 600 800 10000

500

1000

1500

2000

2500

3000

3500

1098

76

Time (s)

G998400

(Pa)

(c)



3



2 and FeCl




2and FeCl




000 002 004 006 008 010 012900

1000

1100

1200

1300

1400

1500



Swel

ling

ratio

40

44

48

52

56

60

64

68

72

Swel

ling

ratio


000 005 010 015 020 025 030500

550

600

650

700

750

800

850

900


Swel

ling

ratio

25

30

35

40

45

50

Swel

ling

ratio




2gt FeCl

3)


00 02 04 06 08 10 12 14 16 18 20400

500

600

700

800

900

1000

1100

AMPSAA (gg)

Swel

ling

ratio

20

25

30

35

40

45

50

Swel

ling

ratio



2 4 6 8 10 120

200

400

600

800

1000

Swel

ling

ratio

pH




005 010 015 020 025

5

10

15

20

25

30

35

40

45

Swel

ling

ratio


LiClCaCl2FeCl3


50

60

70

80

90

100

Wat

er re

tent

ion

Time (s)

MMT0MMT1MMT2

MMT3MMT4

0 50 100 150 200 250 300 350 400minus50


4 Conclusions







Acknowledgments


References
































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




(a) (b)

(c) (d)







3







0 20 40 60 80 100

0

20

40

60

Com

pres

sive m

odul

us (k

Pa)

Strain ()

543

21

(a)

0 200 400 600 800 10000

500

1000

1500

2000

2500

3000

543

21

Time (s)

G998400

(Pa)

(b)

0 200 400 600 800 10000

500

1000

1500

2000

2500

3000

3500

1098

76

Time (s)

G998400

(Pa)

(c)



3



2 and FeCl




2and FeCl




000 002 004 006 008 010 012900

1000

1100

1200

1300

1400

1500



Swel

ling

ratio

40

44

48

52

56

60

64

68

72

Swel

ling

ratio


000 005 010 015 020 025 030500

550

600

650

700

750

800

850

900


Swel

ling

ratio

25

30

35

40

45

50

Swel

ling

ratio




2gt FeCl

3)


00 02 04 06 08 10 12 14 16 18 20400

500

600

700

800

900

1000

1100

AMPSAA (gg)

Swel

ling

ratio

20

25

30

35

40

45

50

Swel

ling

ratio



2 4 6 8 10 120

200

400

600

800

1000

Swel

ling

ratio

pH




005 010 015 020 025

5

10

15

20

25

30

35

40

45

Swel

ling

ratio


LiClCaCl2FeCl3


50

60

70

80

90

100

Wat

er re

tent

ion

Time (s)

MMT0MMT1MMT2

MMT3MMT4

0 50 100 150 200 250 300 350 400minus50


4 Conclusions







Acknowledgments


References
































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




0 20 40 60 80 100

0

20

40

60

Com

pres

sive m

odul

us (k

Pa)

Strain ()

543

21

(a)

0 200 400 600 800 10000

500

1000

1500

2000

2500

3000

543

21

Time (s)

G998400

(Pa)

(b)

0 200 400 600 800 10000

500

1000

1500

2000

2500

3000

3500

1098

76

Time (s)

G998400

(Pa)

(c)



3



2 and FeCl




2and FeCl




000 002 004 006 008 010 012900

1000

1100

1200

1300

1400

1500



Swel

ling

ratio

40

44

48

52

56

60

64

68

72

Swel

ling

ratio


000 005 010 015 020 025 030500

550

600

650

700

750

800

850

900


Swel

ling

ratio

25

30

35

40

45

50

Swel

ling

ratio




2gt FeCl

3)


00 02 04 06 08 10 12 14 16 18 20400

500

600

700

800

900

1000

1100

AMPSAA (gg)

Swel

ling

ratio

20

25

30

35

40

45

50

Swel

ling

ratio



2 4 6 8 10 120

200

400

600

800

1000

Swel

ling

ratio

pH




005 010 015 020 025

5

10

15

20

25

30

35

40

45

Swel

ling

ratio


LiClCaCl2FeCl3


50

60

70

80

90

100

Wat

er re

tent

ion

Time (s)

MMT0MMT1MMT2

MMT3MMT4

0 50 100 150 200 250 300 350 400minus50


4 Conclusions







Acknowledgments


References
































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




000 002 004 006 008 010 012900

1000

1100

1200

1300

1400

1500



Swel

ling

ratio

40

44

48

52

56

60

64

68

72

Swel

ling

ratio


000 005 010 015 020 025 030500

550

600

650

700

750

800

850

900


Swel

ling

ratio

25

30

35

40

45

50

Swel

ling

ratio




2gt FeCl

3)


00 02 04 06 08 10 12 14 16 18 20400

500

600

700

800

900

1000

1100

AMPSAA (gg)

Swel

ling

ratio

20

25

30

35

40

45

50

Swel

ling

ratio



2 4 6 8 10 120

200

400

600

800

1000

Swel

ling

ratio

pH




005 010 015 020 025

5

10

15

20

25

30

35

40

45

Swel

ling

ratio


LiClCaCl2FeCl3


50

60

70

80

90

100

Wat

er re

tent

ion

Time (s)

MMT0MMT1MMT2

MMT3MMT4

0 50 100 150 200 250 300 350 400minus50


4 Conclusions







Acknowledgments


References
































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




005 010 015 020 025

5

10

15

20

25

30

35

40

45

Swel

ling

ratio


LiClCaCl2FeCl3


50

60

70

80

90

100

Wat

er re

tent

ion

Time (s)

MMT0MMT1MMT2

MMT3MMT4

0 50 100 150 200 250 300 350 400minus50


4 Conclusions







Acknowledgments


References
































































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials

























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



Research Article Organic/Inorganic Superabsorbent ...

Documents

Transcript of Research Article Organic/Inorganic Superabsorbent ...