壳聚糖的制备及其性能研究

Polymer International Polym Int 55:1230–1235(2006)Preparation and properties of chitosan/poly(vinyl alcohol)blend foams for copper adsorptionXiao Wang,1Yong Sik Chung,2Won Seok Lyoo 3and Byung Gil Min 1∗1Schoolof Advanced Materials and System Engineering,Kumoh National Institute of Technology,Gumi,730-701,Korea2Departmentof Textile Engineering,Chonbuk National University,Jeonju,561-756,Korea3School of Textiles,Yeungnam University,Gyeongsan,712-749,KoreaAbstract:A new form of polymer blend,macroporous chitosan/poly(vinyl alcohol)(PVA)foams made by a starch expansion process,exhibits the functionalities of chitosan while avoiding its poor mechanical properties and chemical instabilities.The appropriate conditions for foaming are discussed using both insoluble and water-soluble chitosan.The chitosan/PVA foams demonstrated interconnected and open-cell structures with large pore size from tens to hundreds of micrometers and high porosities from 73.6to 84.3%.Glutaraldehyde was employed to improve the retention of chitosan and copper adsorption of the chitosan/PVA foams.While it increased the retention of chitosan and the adsorption capacities,glutaraldehyde decreased the pore size and porosity.The macroporous structure of the chitosan/PVA foams indicates extensive application prospects in terms of the considerable adsorption of heavy metal ions. 2006Society of Chemical IndustryKeywords:chitosan;poly(vinyl alcohol);heavy metal;foam;adsorptionINTRODUCTIONChitosan is prepared from chitin by partially deacety-lating its acetamido groups with a strong alkaline solution.1It is well known that chitosan is an important option for wastewater treatment,due to its adsorp-tion functionality by both amine and hydroxyl groups,biodegradability and biocompatibility.The removal of heavy metals in wastewater has been an important issue for many years due to their environmental harm and threats to life.The untreated effluents of industrial wastewater often contain larger amounts of heavy met-als than the maximum concentrations allowed in water or sludge,which are produced by many industries including the electroplating,metal-finishing,metal-lurgical,tannery,chemical manufacturing,mining and battery manufacturing industries.2–4Copper is a well-known contaminant that can not only be toxic to aquatic organisms but also accumulate in the liver.5Many researches have been carried out to find ways of removing pollutants such as metals,dyes and surfac-tants from wastewater using chitosan.5–11However,the forms of chitosan used have been focused on flake or powder,bead and film,which can hinder its application.The form is of much importance in wastewater treatment,which can affect a separation operation of the adsorbent material from water in practical applications and the adsorption properties.Flake and powder are not suitable for adsorbents because of possible dissolution and difficultcollection.12Another reason has also been discussed that raw chitosan can be characterized as a crystallized polymer and metal ions can only be adsorbed onto the amorphous region of the crystals.13Chitosan hydrogel beads have been made to improve the adsorption capacity of chitosan by reducing the crystallinity through the gel formation process,and also provide the potential for regeneration and reuse of the hydrogel beads after metal adsorption.14However,chitosan beads have defects like poor acidic resistance and mechanical strength.Thus,polymer blending or chemical modification was used to overcome these limitations.15Cellulose acetate/chitosan films and their application in extracting copper cations at solid/liquid interfaces have also been reported.16Compared with other forms,the foam that supports chitosan in macroporous matrices possesses desirable characteristics.Not only does it present high macroporosity and high surface area,but also it is easy to handle and separate in practical treatment.The macroporous structure improves adsorption through facilitating penetration and diffusion and decreasing contact time.Poly(vinyl alcohol)(PVA)is of great interest due to its nontoxic,water-soluble,biocompatible and biodegradable properties.17PVA foam from the starch expansion process has been commercialized and is widely used in cosmetic puffs and cleaning materials.PVA is employed here owing to,firstly,its∗Correspondence to:Byung Gil Min,School of Advanced Materials and System Engineering,Kumoh National Institute of Technology,Gumi,730-701,Korea E-mail:bgmin@kumoh.ac.krContract/grant sponsor:Ministry of Commerce,Industry,and Energy (MOCIE);contract/grant number:RTI04-01-04(Received 27November 2005;revised version received 6January 2006;accepted 21February 2006)Published online 19June 2006;DOI:10.1002/pi.20682006Society of Chemical Industry.Polym Int0959–8103/2006/$30.00Chitosan/poly(vinyl alcohol)blend foams for copper adsorptionability to provide a porous matrix and,secondly,its good mechanical and chemical properties.5Chitosan blended with PVA has been reported to have good mechanical and chemical properties.18The aim of the study reported here was to design a new form of chitosan/PVA blend by a starch expansion process to facilitate the effective chitosan adsorption of heavy metal ions.The application to heavy metal removal was tested using copper.Chitosan/PVA foams with and without glutaraldehyde and a chitosan powder/PVA foam were formulated to characterize the structures and test the copper adsorption.The effect of glutaraldehyde on the pore size,porosity,retention of chitosan and adsorption capacity is discussed. EXPERIMENTALMaterialsChitosans were purchased from Kumho Chemical Co. Ltd with a deacetylation percentage of approximately of41.5%for water-soluble chitosan and42.4%for insoluble chitosan(defined using an IR method). PVA with a degree of hydrolysis of87–89%and a degree of polymerization of1700and corn starch were obtained from Kolon company.Formalin (HCHO)and hydrochloric acid(HCl)were extra pure reagents from Daejung Chemicals&Metals Co.Ltd. Glutaraldehyde was obtained from Junsei Chemical Co.Ltd with a concentration of25%.Copper nitrate hemipentahydrate was purchased from Sigma-Aldrich. Ethylenediaminetetraacetic acid(EDTA)disodium salt of0.0097mol L−1,murexide and ammonium chloride–ammonium hydroxide buffer were obtained from Aldrich Chemical Co.Ltd.Preparation of chitosan/PVA blend foamsPVA/(water-soluble chitosan)blend solution was made by dissolving the two materials in water and heating at85◦C for1h.PVA/(insoluble chitosan) blend solution was prepared by dissolving the two materials in2wt%acetic acid under the same conditions.PVA/chitosan blend solutions were mixed with corn starch dispersed in water followed by the addition of HCHO and HCl.The mixtures were heated in an oven at90◦C for10h to form chitosan/PVA foams.The foams were washed in water and dried at60◦C.The preparation process of chitosan/PVA foams is shown schematically in Fig.1. The PVA/chitosan ratio used in this study wasfixed at 4.It was found that a considerable amount of chitosan could be released when making the foams. The amounts of HCHO and HCl had little effect on the weight change of the foams and,in other words, on the retention of chitosan.The retention of chitosan was calculated by the weight difference between the chitosan/PVA foam and the neat PVA foam divided by the original weight of chitosan.To reduce the release of chitosan,diluted glutaraldehyde was added into the solution after adding HCHO and HCl.Consequently, there was much improvement in the weight changeand Figure1.Schematic of chitosan/PVA foam preparation experiments. retention of chitosan.Weight ratios of PVA/starch=1, HCHO/PVA=0.9and starch/HCl=2were found appropriate for obtaining porous structures.The effect of glutaraldehyde was investigated by varying the glutaraldehyde/chitosan weight ratio from0to0.01. HCl plays two roles in the process.In the presence of HCl,acetal bridges form between the pendant hydroxyl groups of the PVA by HCHO.HCl is helpful in removing corn starch after foaming.These two factors should be taken into account when determining the amount of HCl.The pore size and porosity could be controlled by the concentration of PVA and the amount of corn starch.An(insoluble chitosan powder)/PVA foam was also attempted through mixing chitosan powder in PVA aqueous solution.In all,chitosan/PVA foams with and without glutaraldehyde and a chitosan powder/PVA foam were prepared.Equilibrium degree of swelling(EDS)of chitosan/PVA foamsThe swelling behavior of the(water-soluble chi-tosan)/PVA foams with and without glutaraldehyde was investigated from a gravimetric determination of the EDS.The EDS was calculated as19EDS=(W e−W d)/W dwhere W e is the weight of the swollen foams at equilibrium and W d is the initial weight of the dried foams.Morphology of foamsThe chitosan/PVA foams were analyzed using SEM (JEOL JSM-6500F).The fractured surfaces of the foams with and without glutaraldehyde were observed. Furthermore,the foams before and after adsorptionPolym Int55:1230–1235(2006)1231 DOI:10.1002/piX Wang et al.of copper ions were also investigated to examine the presence of copper in the foams.Sorption testsSorption experiments were performed by immersing the chitosan/PVA foams in copper solution.An approximately17.2mmol L−1copper solution was made from copper nitrate hemipentahydrate.Copper solutions(100mL)and the foams were put in conical beakers which were agitated by a shaker at30◦C for24h.The copper concentrations before and after adsorption were analyzed using the EDTA titration method.20Copper solution(5mL)was taken out and added to100mL distilled water followed by addition of5mL ammonium chloride–ammonium hydroxide buffer.After adding0.1g murexide as an indicator, which was diluted by NaCl powder in the ratio of 1:100,the solution was shaken for a while and then titrated using EDTA from a reddish yellow to a purple endpoint.Finally the adsorbed copper was calculated by the stoichiometric ratio for these amounts of foams. The process of the sorption experiments is repre-sented in Fig.2.RESULTS AND DISCUSSIONTable1indicates the swelling behavior of the(water-soluble chitosan)/PVA foams.These foams can swell more quickly and absorb much water,which improves their adsorption efficiency.With crosslinking by glutaraldehyde,the foam became denser but the swelling properties were not greatly decreased.SEM micrographs of chitosan/PVA foams are shown in Fig.3,where the pore sizes are of some hundreds of micrometers.The pore shapes aredifferent in the two types of chitosan foams.TheFigure2.Schematic of copper adsorption experiments.Table1.EDS of(water-soluble chitosan)/PVA foams Glutaraldehyde/chitosan(g(100g)−1)EDS(%) 0674 0.167587 0.333572 1465porosity of the(water-soluble chitosan)/PVA foam is about84.3%.The pores are interconnected and the porous foams have an open-cell structure.Figure4 shows that crosslinking by glutaraldehyde decreased the pore size to tens of micrometers.A decrease of porosity with crosslinking by glutaraldehyde was also found as noted in Table2.The pores were considered to be very helpful for mass transfer of copper ions.21Figure5shows an SEM image of an (insoluble chitosan)/PVA foam before and after copper adsorption.In comparison with Fig.5(a),a particle-like phenomenon was observed on the surface of the foam after adsorption,as shown in Fig.5(b),which was thought to be the adsorption of copper.As regards the(insoluble chitosan powder)/PVA foam,it can be observed in Fig.6(b)that there are some holes in the foam which have similar sizes to those in the insoluble chitosan powders in Fig.6(a).This means chitosan powder could be released when foaming or washing. The available adsorption of copper indicates that some chitosan still remained inside the foam.Figure7demonstrates the effect of crosslinking of chitosans by glutaraldehyde considering the probable retention of chitosans in foams.Withoutcrosslinking,(a)(b)Figure3.SEM images of chitosan/PVA foams:(a)(insoluble chitosan)/PVA foam;(b)(water-soluble chitosan)/PVA foam.1232Polym Int55:1230–1235(2006)DOI:10.1002/piChitosan/poly(vinyl alcohol)blend foams for copper adsorption(a)(b)Figure4.SEM images of(insoluble chitosan)/PVA foams:(a)without glutaraldehyde;(b)with glutaraldehyde.Table2.Porosity of(water-soluble chitosan)/PVA foams Glutaraldehyde/chitosan(g(100g)−1)Porosity(%) 084.3 0.16781.6 0.33374.9 0.173.6the weight of(insoluble chitosan)/PVA foam was less than the neat PVA foam.For water-soluble chitosan,there was also little retention of chitosan. It was estimated that much chitosan could remain in the residual solution when making foams without crosslinking by glutaraldehyde.The two curves in the Fig.7show a similar trend:the retention of chitosan increases with increasing glutaraldehyde.The(insoluble chitosan)/PVA foam without crosslinking did not show a good adsorption result due to loss of chitosan.Neat PVA foams showed very little adsorption,which could be ignored.Figure8 shows the effect of glutaraldehyde on copper adsorp-tion.The adsorption of copper was improvedby (a)(b)Figure5.SEM images of(insoluble chitosan)/PVA foams:(a)before copper adsorption;(b)after copper adsorption.adding more glutaraldehyde.Although the crosslink-ing can consume some amino groups in chitosan,this inverse effect is largely counteracted by the higher retention of chitosan.However,27.38mg g−1copper could be removed by the(insoluble chitosan)/PVA foam with1g/100g glutaraldehyde/chitosan.The adsorption capacity of insoluble chitosanflakes was 103.25mg g−1.The difference of adsorption capacities was caused by amino groups consumed by glutaralde-hyde and possible PVA crosslinking by glutaraldehyde. If more glutaraldehyde is used,the adsorption capac-ity can increase continually,but the porosity and pore size can decrease.The(water-soluble chitosan)/PVA foams were also tested for copper adsorption.How-ever,the adsorption effect was worse than that of the (insoluble chitosan)/PVA foam.This could be due to the low adsorption capacity of water-soluble chitosan itself.CONCLUSIONSThe chitosan/PVA foams were made using the starch expansion process by employing both insoluble andPolym Int55:1230–1235(2006)1233 DOI:10.1002/piX Wang et al.(a)(b)Figure 6.SEM images of chitosan powders and a (chitosan powder)/PVA foam:(a)insoluble chitosan powders;(b)(insoluble chitosan powder)/PVAfoam.Figure 7.Effect of glutaraldehyde on retention of chitosan in chitosan/PVA foams.water-soluble chitosan.The chitosan/PVA foams demonstrated interconnected and open-cell structures with large pore size and high porosities.Crosslinking by glutaraldehyde decreases the pore sizes as well astheFigure 8.Effect of glutaraldehyde on copper adsorption of chitosan/PVA foams.porosity.Without crosslinking by glutaraldehyde,the chitosan/PVA foams show much release of chitosan and thus little adsorption of copper.The (insoluble chitosan)/PVA foams show higher adsorption capac-ity than (water-soluble chitosan)/PVA foams.The desirable porous structure and swelling behavior of the chitosan/PVA foams indicate extensive application prospects.Since the glutaraldehyde can also affect the crosslinking of PVA,future researches should be focused on choosing a better crosslinking agent to improve the retention of chitosan,and avoid degrad-ing its adsorption functionalities,and seeking a precise way to evaluate the retention of chitosan in foams.ACKNOWLEDGEMENTThis work was supported by grant no.RTI04-01-04from the Regional Technology Innovation Program of the Ministry of Commerce,Industry,and Energy (MOCIE).REFERENCES1Drury JL and Mooney DJ,Biomaterials 24:4337(2003).2G´omez del R´ıo JA,Morando PJ and Cicerone DS,J EnvironManage 71:169(2004).3Chiron N,Guilet R and Deydier E,Water Res 37:3079(2003).4Benhammou A,Yaacoubi A,Nibou L and Tanouti B,J ColloidInterf Sci 282:320(2005).5Wan Ngah WS,Kamari A and Koay YJ,Int J Biol Macromol34:155(2004).6Wan Ngah WS and Liang KH,Ind Eng Chem Res 38:1411(1999).7Juang RS and Shao HJ,Water Res 36:2999(2002).8Evans JR,Davids WG,MacRae JD and Amirbahman A,WaterRes 36:3219(2002).9Dambies L,Guimon C,Yiacoumi S and Guibal E,Colloid SurfA 177:203(2001).10Zeng XF and Ruckenstein EJ,J Membr Sci 148:195(1998).11Chiou MS and Li HY,Chemosphere 50:1095(2003).12Varma AJ,Deshpande SV and Kennedy JF,Carbohydr Polym55:77(2003).13Li N and Bai R,Sep Purif Technol 42:237(2005).14Wan Ngah WS,Endud CS and Mayanar R,React Funct Polym50:181(2002).1234Polym Int 55:1230–1235(2006)DOI:10.1002/piChitosan/poly(vinyl alcohol)blend foams for copper adsorption15Jin L and Bai RB,Langmuir18:9765(2002).16Lima IS,Lazarin AM and Airoldi C,Int J Biol Macromol36:79 (2005).17Koyano T,Koshizaki N,Umehara H,Nagura M and Minoura N,Polymer41:4461(2000).18Jin L and Bai RB,Langmuir18:9765(2002).19Francis S and Varshney L,Radiat Phys Chem74:310(2005). 20Jeffery GH,Bassett J,Mendham J and Demney RC,Vogel’s Textbook of Quantitative Chemical Analysis,5th edition.Longman,Essex,pp.309–340(1989).21Jeon C,Park JY and Yoo YJ,Biochem Eng J11:159(2002).Polym Int55:1230–1235(2006)1235 DOI:10.1002/pi。