anionic/cationic membranes obtained by a radiation grafting method for use in waste water treatment

Polymer International 43 (1997) 321È332

Anionic/Cationic Membranes Obtained bya Radiation Grafting Method for Use in

Waste Water Treatment*

El-Sayed A. Hegazy,a¤ H. A. Abd El-Rehim,a Nevien A. Khalifa,bS. M. Atwac & H. A. Shawkyc

a National Center for Radiation Research and Technology, PO Box 29, Nasr City, Cairo, Egyptb Faculty of Science, Helwan University

c Desert Research Center, El-Matarya, Cairo, Egypt

(Received 30 September 1996 ; revised version received 20 November 1996 ; accepted 24 November 1996)

Abstract : Investigations were carried out on di†erent ionic membranes, whichwere prepared by radiation-induced graft copolymerization. Cationic (lowdensity polyethylene (LPDE)-g-poly(acrylic acid) (PAAc)) and cationic/anionic(LDPE-g-P(AAc/4-vinyl pyridine (4VP)) membranes) were used to elucidate thepossibility of their practical use. The metal uptake via their functional groupswas determined by using atomic absorption and X-ray Ñuorescence. The amountof metal uptake by the prepared membranes increased signiÐcantly as the pH ofthe metal feed solution increased (pH¹ 5É3) and the chelated metal ions wereeasily desorbed by treating the membrane with 0É1 M HCl for 2 h at room tem-perature. The maximum uptake for a given metal was higher for the cationic/anionic membranes than for the cationic ones. The selectivity of thecationic/anionic membranes towards di†erent metals was investigated using mix-tures of two or three metals in the same feed solution. The membranes showedhigh selectivity towards Fe(III) ions. Characterization of the graft copolymerscontaining metals was determined by thermogravimetric analysis (TGA) andX-ray di†raction (XRD). TGA results showed that the decomposition of the graftcopolymer in the presence of chelated metal ion occurred at temperatures above300¡C. The XRD of LDPE-g-P(AAc/4VP) treated with Fe(III) at various concen-trations showed that the crystallinity decreased to a certain limiting value. Thecomplexed copolymers could be recycled several times and showed high selec-tivity to the Fe(III) ion in the presence of the other metal ions investigated. Thismay make such grafted membranes acceptable for practical use in waste watertreatment.

Polym. Int. 43, 321È332 (1997)No. of Figures : 12 No. of Tables : 6 No. of References : 11

Key words : cationic membranes, cationic/anionic membranes, radiation graftcopolymerization, metal chelation.

* Presented at “The Cambridge Polymer Conference : Partnership in PolymersÏ, Cambridge, UK, 30 SeptemberÈ2 October 1996.¤ To whom all correspondence should be addressed.

3211997 SCI. Polymer International 0959-8103/97/$17.50 Printed in Great Britain(

322 E.-S. A. Hegazy et al.

INTRODUCTION

Environmental pollution due to developments in tech-nology is one of the most important problems of thiscentury. Heavy metals such as lead, cadmium andcopper in waste water are hazardous to the environment.Because of their toxicity, their pollution of our eco-system presents a possible human health risk. Treat-ment techniques that have been employed for treatingwaste, include ion-exchange, reverse osmosis, precipi-tation, Ðltration, coagulation and electrolyticrecovery.1h3 Potential treatments that are neitherenergy intensive nor expensive will be worth investigat-ing. The importance of chelating sorbents for chemicalapplications has been evident for a long period of time.Recently, there has been substantial growth of interestin and uses of chelating sorbents in the Ðeld of watertreatment and pollution control.4 Various forms of syn-thetic polymers containing complexing molecules whichare available at low cost have emerged as among themost important materials for the synthesis of new sorb-ents.5,6

In previous studies,7h9 copolymers of acrylic mono-mers grafted onto Ñuorinated polymers were obtained.The conversion of the graft copolymers into metal acryl-ate copolymer complexes was carried out by treatingwith di†erent metal salts. Electrical, mechanical andthermal properties of the complexes were measured.

In this work, radiation-induced graft copolymer-ization of a 4-vinyl pyridine/acrylic acid comonomersystem onto low density polyethylene Ðlms was studiedfor preparing ionic membranes, which can meet therequirements of toxic metal removal from waste water.Characterization and the possibility of their practicaluse in such applications were investigated.

EXPERIMENTAL

Materials

Low density polyethylene (LDPE) Ðlm of thickness80 km was produced by El Nasr Chemical Co., Egypt.

Acrylic acid (AAc), purity 99É99% (Merck, Germany)was used as received.

4-Vinyl pyridine (4VP), purity [ 96% (Merck,Germany) was used as received.

The other chemicals were reagent grade and wereused without further puriÐcation.

Graft copolymerization

The ionic graft copolymers were prepared by the directradiation grafting of AAc/4VP binary monomer systemsonto LDPE Ðlms using 60Co c-rays at a dose rate thatranged from 1É3 to 1É3 Gy s~1. Details of this techniqueare described in a previous study.7

Metal uptake measurement

The membrane was immersed in the metal feed solutionof initial concentration 2000 ppm. The remaining metalsalt in the feed solution was determined by atomicabsorption spectroscopy (Unicam Model Solaar 929)using lamps for Pb, Cu, Cd, Mn, Ni, Co, Zn and Fe. Inthese investigations, the experimental error wasabout ^5%.

X-ray fluorescence (XRF)

An HNU TEFA-PC XRF automated analyser (non-destructive elemental analyser) was used for the identiÐ-cation of chelated metals in the membranes.

Thermogravimetric analysis (TGA)

A Shimadzu TGA-30 was used for TGA in a nitrogenatmosphere at constant Ñow rate of 50 ml min~1 toprevent thermal oxidation of the polymer samples.

X-ray diffraction (XRD)

The XRD patterns of the polymer Ðlms were measuredwith a Shimadzu di†ractometer XD-D1 series, whichwas automatically operated.

RESULTS AND DISCUSSION

In this study, cationic/anionic membranes were pre-pared by the direct radiation-induced graft copolymer-ization of AAc/4VP binary monomers onto LDPEÐlms. Also, cationic membranes were prepared by indi-vidual radiation grafting of AAc onto LDPE Ðlms. Atrial was made to investigate the possible use of thegrafted membranes for removal of industrial heavy toxicmetals from waste water.

The metal uptake from waste water by the functionalgroups of the membranes was determined using atomicabsorption spectroscopy and XRF to identify theadsorbed metal ions. Selected metals which commonlyexist in waste water were investigated ; these were Pb,Cd, Zn, Mn, Fe, Co, Cu and Ni. Among the factorsa†ecting the treatment process are operation time,membrane selectivity and durability, pH of waste feedsolution, desorption and readsorption of metal ions,degree of grafting and amount/type of functionalgroups. The inÑuence of these parameters is presentedand discussed.

POLYMER INTERNATIONAL VOL. 43, NO. 4, 1997

Membranes obtained by radiation grafting 323

Effect of treatment time

The e†ect of treatment time on the rate and maximummetal uptake was investigated for di†erent metals andionic membranes. The metal uptake is expressed inmillimoles per gram (mmol g~1), i.e. millimoles of metaluptake by unit mass of the functional group of grafted

membrane. Two di†erent synthetic membranes wereinvestigated ; cationic (LDPE-g-PAAc) and cationic/anionic (LDPE-g-P(AAc/4VP)).

Figure 1 shows the metal uptake as a function oftreatment time for di†erent metals using a cationicmembrane LDPE-g-PAAc having 177% grafting. Themetal uptake increases with time to reach its maximum

Fig. 1. E†ect of treatment time on the metal uptake by LDPE-g-PAAc membrane with degree of grafting of 177%. (a) Mn;…, >,Fe ; Cu ; Cd. (b) Co ; Zn ; Ni ; Pb.L, |, …, >, L, |,



value (which is termed the maximum membranecapacity) after almost 2 h of treatment for all the metalsinvestigated. The initial rate of metal uptake is depen-dent on the type of metal, regardless of the value ofmaximum uptake. The e†ect of treatment time on themetal uptake for a LDPE-g-P(AAc/4VP) membrane isshown in Fig. 2. The behaviour observed is similar tothat found for the cationic membrane (Fig. 1).

In general, the cationic and anionic membranes showa good affinity for chelation and/or complexation withthe heavy or toxic metals investigated. The efficiency ofthe membranes is high and the maximum metal uptakeis reached quickly, within 2 h. The physical propertiesand molecular size of the metals investigated have agreat inÑuence not only on the maximum uptake butalso on its initial rate. This is reasonably explained by

Fig. 2. E†ect of treatment time on the metal uptake by LDPE-g-P(AAc/4VP) membrane with degree of grafting of 121%. (a) …,Mn; Fe ; Cu ; (b) Co ; Zn ; Ni ; Pb.>, L, |,Cd. …, >, L, |,



TABLE 1. Maximum metal uptake for different ionic hydrophilic membranes as measured by atomic absorp-

tion spectroscopy at 30ÄC. Initial concentration of metal feed solution, 2000 ppm; time of treatment, 2 h

Membrane type Degree of grafting (%) Maximum metal uptake (mmol gÉ1)

Pb Fe Cu Cd Co Ni Zn Mn

LDPE-g-PAAc 177 1·82 3·72 2·93 2·34 5·08 3·63 3·55 3·50

LDPE-g-P(AAc/4VP) 121 2·28 4·22 5·29 2·68 3·92 5·08 4·52 3·82

LDPE-g-P(AAc/4VP) 130 2·08 3·80 4·17 2·53 3·60 5·44 4·13 3·14

considering the di†usion coefficient of the metalthrough the porous ionic membrane, which is mainlydependent on its polarity, electronic structure and ionicradius, and also, importantly, on the nature of its inter-action with the functional groups of the membrane.

Table 1 shows a comparison of the variation of metaluptake, according to the type of functional groups inthe grafted membranes and also the degree of grafting.For the cationic membrane, it can be seen that themaximum metal uptake is in the sequence ;Co [ Fe[ Ni[ Zn[ Mn [ Cu [ Cd [ Pb. Thisagrees well with the reverse order of their atomic radii(except for Cu). In general, the lower the atomic radius,the higher the metal uptake. The introduction of 4VPgraft chains into the membranes changed the value ofthe maximum metal uptake and also the order, toNi[ Cu[ Zn[ Fe[ Co[ Mn [ Cd [ Pb. Thisorder of metal uptake for the cationic/anionic mem-branes also follows the reverse order of atomic radii ofthese metals, except for Co and Fe. The increase in the

TABLE 2. Selectivity ratio of LDPE-g-PAAc grafted

membrane towards two metal ions in a feed solu-

tion. Degree of grafting, 177%

Metal feed solution Metal uptake Selectivity ratio

mixture (mmol gÉ1) (M1/M2)

Fe(III) 3·15

½ 2·6

Co(II) 1·21

Fe(III) 3·35

½ 1·6

Ni(II) 2·12

Fe(III) 3·84

½ 192

Mn(II) 0·02

Ni(II) 3·12

½ 1·1

Co(II) 2·88

Zn(II) 2·56

½ 1·4

Cd(II) 1·89

Pb(II) 1·14

½ 1·1

Cd(II) 1·01

metal uptake by introducing 4VP to the acrylic acidmembrane is clearly shown in Table 1.

The exchange properties and/or complexationbetween the ionic membrane and the metals in the feedsolution seems to be changed by introducing anionicand cationic character together in the grafted mem-brane. It is suggested that the stability constant andcomplexation bond strength between the metals andfunctional groups are increased due to the incorpor-ation of pyridine rings ; these have a lone pair of elec-trons on the nitrogen atoms, which can easily formquaternary pyridinium metal salts or chelate. Theseresults are in good agreement with the IrvingÈWilliamsseries10 for the stability of various ligands, with nitro-gen and/or oxygen as coordinating atoms for divalentmetal ions, with the exception of Co(II) and Fe(III).IrvingÈWilliams series for a given ligand, the stabilityof complexes with dipositive metal ions follows theorder, Ba2`\ Sr2`\ Ca2`\ Mn2`\ Fe2`\ Co2`\Ni2`\ Cu2`[ Zn2`.

TABLE 3. Selectivity ratio of LDPE-g-P(AAc/4VP)

grafted membrane towards two metal ions in a feed

solution. Degree of grafting, 121%

Metal feed solution Metal uptake Selectivity ratio

mixture (mmol gÉ1) (M1/M2)

Fe(III) 3·88

½ 1·4

Co(II) 2·85

Fe(III) 4·27

½ 6·2

Ni(II) 0·69

Fe(III) 4·07

½ 13·6

Mn(II) 0·3

Ni(II) 3·02

½ 1·4

Co(II) 2·2

Zn(II) 1·89

½ 0·7

Cd(II) 2·85

Pb(II) 1·15

½ 1·1

Cd(II) 0·87



TABLE 4. Selectivity of different ionic membranes

towards three different metals in a feed solution

Mixture of metals Metal uptake (mmol gÉ1)

LDPE-g-PAAc LDPE-g-P(AAc/4VP)

(DG ¼177%) (DG¼121%)

Fe(III) 2·1 2·8

½

Cu(II) 0·3 1·2

½

Pb(II) 0·8 1·0

Cd(II) 1·1 1·7

½

Co(II) 1·8 1·1

½

Ni(II) 0·8 1·1

DG, degree of grafting.

Fig. 3. Selectivity of LDPE-g-PAAc membrane (177%grafting) towards (a) two and (b) three di†erent metal ions in a

mixture.

Selectivity of membrane towards different metals

The selectivity of di†erent ionic membranes, preparedby radiation grafting of AAc and 4VP onto LDPEÐlms, was investigated using mixtures of two or threemetals in the same feed solution. The selectivity ratioand metal uptake are listed in Tables 2 and 3 for PAAcand P(AAc/4VP) membranes, respectively. An equi-molar feed solution of two di†erent metals was pre-pared. The selectivity of the membranes towards bothmetals was determined by considering the uptake ofmetal by complexation and/or chelation with the mem-brane functional groups. From the data obtained, it isobvious that all the membranes have a great affinitytowards Fe(III), when it exists in a mixture with othermetals. In some mixtures, such as (Fe(III) ] Mn(II)), thetwo membranes investigated, show a great ability tochelate all the Fe(III) and a minor amount of Mn(II).

These results can be reasonably explained by con-sidering the valence of metals and their ionic radii. Thetrivalent Fe(III) forms a more stable and strong complexwith the functional groups of grafted membranes. Thereis competition between the di†erent metals and thefunctionalized membranes.

The chelating sorbent under investigation demon-strated some selectivity towards a mixture of three dif-ferent metal ions, namely Fe(III) ] Cu(II) ] Pb(II) andCd(II) ] Co(II) ] Ni(II), and the data are listed in Table4. Since Fe, Cu and Pb ions have di†erent valences andionic radii, it was expected that in the presence of Cuand Pb, Fe(III) ions would be selectively extracted by thegrafted membrane. Under competitive conditions, aselectivity factor is in fact observed for the preferentialextraction of Fe(III) over Cu(II) and Pb(II) ions by thesorbent membrane. In the case of other mixtures con-taining Cd, Co and Ni, the selectivity towards Cd(II) is



higher than that for the other two metal ions. The ionicradius is the e†ective factor in the case of Cd(II). Theselectivity of di†erent membranes towards di†erentmetal ions from the same feed solution is presented inFigs 3 and 4. The selectivity of each membrane towardsdi†erent metal ions is shown clearly.

In general, it can be concluded that the selectivity ofthe di†erent membranes investigated towards di†erentmetals in a mixture depends mainly on the ionic valenceand ionic radii of the metals. Also, the results show thatthe selectivity of the membranes obeys the IrvingÈWilliams series dealing with the stability of metalcomplex ligands.

Determination of membrane selectivity using XRF

For a comparison and conÐrmation of the resultsobtained by the atomic absorption technique, the metaluptake via di†erent functional groups of the membraneswas determined by XRF. The chelating sorbent

Fig. 4. Selectivity of LDPE-g-P(AAc/4VP) membrane (121%grafting) towards (a) two and (b) three di†erent metal ions in a

mixture.

LDPE-g-P(AAc/4VP) membrane demonstrated someselectivity towards two, three and four di†erent metalions from a solution of their mixture.

Table 5 shows that for a solution containing twometal ions, namely Fe(III) ] Cu(II), Fe(III) ] Pb(II) andCu(II) ] Pb(II), the selectivity order follows that ofvalence and ionic radii, the membrane possessing higherselectivity towards Fe(III) than for Cu(II) and Pb(II). Fora solution containing three metal ions, namely Fe(III) ]Cu(II) ] Mn(II), Fe(III) ] Cu(II) ] Pb(II) and Cd(II) ]Co(II) ] Ni(II), the metal selectivity order also followsthat of valence and ionic radii, except forCd ] Co ] Ni. The selectivity order is found to be :Fe(III) [ Cu(II) [ Mn(II) ; Fe(III) [ Cu(II) [ Pb(II) ; andCd(II) [ Ni(II)[ Co(II). For a mixture containing fourmetal ions, Fe(III) ] Cd(II) ] Pb(II) ] Cu(II) and Zn(II)] Ni(II) ] Co(II) ] Mn(II), the selectivity in the Ðrstmixture follows the valence and ionic radii rules with anexception of Cu(II), and the order is Fe(III) [ Cd(II) [Pb(II) [ Cu(II). The selectivity in the second mixture isin the order Zn(II) [ Ni(II) [ Mn(II) [ Co(II), whichfollows the IrvingÈWilliams series.

Effect of metal ion concentration

To explore the applicability of the sorbent membranes,it was necessary to obtain knowledge of their sorptioncapacity towards di†erent metal ions. Studies on the

TABLE 5. Selectivity of LDPE-g-P(AAc/4VP) mem-

branes towards different metals in a feed solution,

determined by XRF. Degree of grafting, 237%

Metals mixture Metal uptake (%)

Fe(III) 97

Cu(II) 3

Fe(III) 87

Pb(II) 13

Pb(II) 51

Cu(II) 49

Fe(III) 99

Cu(II) 1

Mn(II) 0

Fe(III) 94

Cu(II) 4

Pb(II) 2

Cd(II) 85

Ni(II) 9

Co(II) 6

Fe(III) 68

Cd(II) 14

Pb(II) 11

Cu(II) 7

Zn(II) 71

Ni(II) 18

Mn(II) 6

Co(II) 5



Fig. 5. E†ect of initial feed concentration of Cu2` on its uptake by LDPE-g-PAAc (177% grafting).

sorption capacity of the prepared membranes towardsdi†erent metal ions were carried out by equilibrating aÐxed amount of the sorbent with a series of metal ionsolutions of gradually increasing concentration. Amaximum amount of metal ion can be removed fromthe solution when the chelating sites of the sorbent aresaturated. From Figs 5 and 6, it can be seen thatincreasing the concentration of metal ions results in anincrease in the amount of metal ion uptake (ppm),Ðnally reaching a certain limiting value. This behaviouris observed for all the di†erent membranes havingvarious functionalized groups.

Effect of pH of feed solution

The availability of the chelating grafted polymer formetal ion complexation is dependent on pH. The sorp-tion characteristics of the sorbent towards Cu(II) metalions were investigated in an aqueous solution over a pHrange from 2 to 5É3. It was observed that the pH of thesolution could not increase above 5É3 owing to the for-

mation of the hydroxide.5 The sorption affinity of thesorbent is plotted as a function of pH in Fig. 7. Theamount of metal ion uptake by chelating polymerincreases signiÐcantly as the pH increases.

The results suggest that the chelating exchangers pos-sessed high affinity towards hydrogen ions in weak acidand/or weak base functional groups. As a result, theselective metal ion uptake under highly acidic condi-tions is sharply decreased for almost every chelatingexchanger due to formidable competition from H`.

Effect of degree of grafting on metal uptake

The degree of grafting, i.e. the number of functionalgroups existing in the membrane, plays an importantrole in determining the amount of metal uptake by themembrane. Figure 8 shows the relationship between theamount of Cu(II) uptake (expressed in ppm) and degreeof grafting for di†erent functionalized membranes(LDPE-g-PAAc and LDPE-g-P(AAc/4VP)). Theamount of metal ion uptake increases with increase in

Fig. 6. E†ect of feed metal concentration on metal uptake by LDPE-g-P(AAc/4VP) (degree of grafting 121%) for di†erent metals :Fe ; Zn ; Pb.L, >, …,



Fig. 7. E†ect of pH of Cu2` feed solution on its uptake byLDPE-g-P(AAc/2VP) (110% grafting).

the degree of grafting for all the membranes investi-gated. This clearly conÐrms that the metal chelation, orcomplexation, is mainly dependent on the amount offunctional reactive groups in the grafted membranes.

Fig. 8. E†ect of degree of grafting on the Cu2` uptake by dif-ferent functionalized membranes : LDPE-g-PAAc;L, |,

LDPE-g-P(AAc/4VP).

Desorption and readsorption of metal ions

Evidently, complexation of the di†erent kinds of mem-branes with metal ions is inhibited in strongly acidicconditions. Therefore, the recovery of metal ionsabsorbed is easy by treating with 0É1 M hydrochloricacid at room temperature for 2 h. The desorbed mem-brane is e†ective for the readsorption of metal ions.

TABLE 6. Effect of different metal ions on the thermal stability of different mem-

branes at various elevated temperatures. Degree of grafting, 237%

Membrane type Metal ions Weight loss (%)

300¡C 500¡C 600¡C

LDPE – 9·2 68 100

LDPE-g-P(AAc/4VP) Without 5·6 62·4 62·4

LDPE-g-P(AAc/4VP) Zn 5·6 44·8 54·4

LDPE-g-P(AAc/4VP) Cd 8 36·8 51·2

LDPE-g-P(AAc/4VP) Pb 5·6 17·6 36

LDPE-g-P(AAc/4VP) Zn ½Cd 8 43·2 56

LDPE-g-P(AAc/4VP) Zn ½Pb 4 32·8 46·4

LDPE-g-P(AAc/4VP) Cd ½Pb 4 21·6 36·8

LDPE-g-P(AAc/4VP) Zn ½Cd ½Pb 5·6 24·8 40



Fig. 9. Thermogravimetric curves for the blank LDPE, LDPE-g-P(AAc/4VP) and LDPE-g-P(AAc/4VP) treated with a singlemetal ion (degree of grafting, 237%).

From the economic point of view, the reuse of suchgrafted membranes, in which the removal of adsorbedmetal ions can be easily done in acidic medium, is agreat advantage.

Thermal stability of prepared membranes

Thermal resistance is a description of the chemical sta-bility of the polymer at high temperatures in vacuo, airor in an inert atmosphere. Thermal stability of the

membranes is an important factor for their durabilityduring practical use.

Table 6 shows the percentage weight loss at three ele-vated temperatures (300, 500 and 600¡C) during thedynamic TGA for LDPE-g-P(AAc/4VP) copolymer andalso for its metal acrylates of Pb, Cd, Zn, Zn] Cd,Zn] Pb, Cd] Pb and Zn ] Cd ] Pb. It is interestingto Ðnd that the decomposition of the grafted metalcopolymer complexes occurs at higher temperaturesthan that for the untreated grafted copolymer. The

Fig. 10. Thermogravimetric curves for the blank LDPE, LDPE-g-P(AAc/4VP) and LDPE-g-P(AAc/4VP) treated with two metalions (degree of grafting, 237%).



Fig. 11. Thermogravimetric curves for the blank LDPE, LDPE-g-P(AAc/4VP) and LDPE-g-P(AAc/4VP) treated with three metalions (degree of grafting, 237%).

results show that the thermal stability of the individualcopolymer and the copolymer treated with di†erentmetal ions (Pb, Cd and Zn) at 300¡C, is the same exceptfor the Cd-treated membrane. But at 500 and 600¡C, the

Fig. 12. Relationship between the intensity of XRD scans andFe3` content in LDPE-g-P(AAc/4VP) with degree of grafting

of 237%. (Fe3` content is measured by atomic absorption.)

stability for the membranes containing metal ions is inthe order ; Pb[ Cd [ Zn (Fig. 9). This result is sup-ported by the thermal stability of the individual graftedcopolymer and the copolymers treated with two metalions (Cd] Pb, Zn ] Pb and Zn] Cd), which is foundto be in the order : (Cd ] Pb) [ (Zn] Pb) [(Zn] Cd) (Fig. 10). Also, the thermal stability of amembrane treated with three metal ions(Cd] Zn] Pb) is higher than that for the grafteduntreated membrane (Fig. 11).

It can be suggested that the stabilization is governedby the strength of binding of the metal ion(s) with thecopolymer ; the stabilizing e†ect of metal ions resultsfrom the complexation strength between the ions andcarboxylic/pyridine groups. As has been noted fromvarious coordinations with polymers,11 the biggest sta-bilization e†ect is observed with metals having d5 andd10 electron conÐgurations. The thermal stability of thethree metalÈcopolymers under investigation can beexplained according to ligand Ðeld stabilizing energy(LFSE) and ionic radii, where the thermal stabilityincreases with increasing ionic radii.

X-ray diffraction (XRD)

The XRD patterns for LDPE, LDPE-g-P(AAc/4VP)and for the metal-treated LDPE-g-P(AAc/4VP) Ðlmswith di†erent concentrations of Fe(III) ions showed thatthe crystallinity content in LDPE decreases upon graft-ing. However, the grafted Ðlms treated with low Fe(III)concentrations possess a higher crystallinity than that forthe grafted untreated Ðlm. Thereafter, the crystallinitycontent decreases with increasing Fe(III) ion concentra-tion and reaches a constant value. This can be seen



from the change of intensity of the crystalline peak at2h, as shown in Fig. 12.

It can be assumed that the decrease in crystallinity ofLDPE, caused by the grafting, is due to the disorderingof its structure by the incorporation of P(AAc/4VP)graft chains. However, the introduction of a low Fe(III)concentration into the grafted Ðlm results in therearrangement of the amorphous phase due to metalÈpolymer complex formation. Increasing complex forma-tion, by increasing the concentration of Fe(III) ions,causes a decrease in the crystallinity due to disorderingof the crystalline domains in the polymer matrix until aminimum percentage crystallinity is reached, i.e. the Ðlmis almost amorphous.

CONCLUSIONS

The cationic/anionic membranes prepared possessedgood properties of great interest in separation of Fe(III)ions from a mixture containing other metal ions. Thesesynthetic grafted membranes can also be applied for thetreatment of contaminated water resources containing

heavy and toxic metals such as Pb, Cd, Fe and Cu.They possess high thermal stability and good hydro-philic properties. Such grafted membranes can be regen-erated easily for reuse by treating them with dilute HCl.

REFERENCES

1 Sengupta, A. K. & Cli†ord, D., J. Environ. Sci. T ech., 20 (1986)149.

2 Buckley, L. P., Vijayan, S., McConeghy, G. J., Maves, S. R. &Martin, J. F., Presented at 16th Annual EPA Research Symposium,Cincinnati, Ohio, 1990.

3 Stewart, S. C., Albert, F. & Peter, W., J. Environ. Sci. Health, A22(1987) 707.

4 Savostyanov, V. S., Pomogailo, A. D., Kritskaya, D. A. & Pono-marev, A. N., J. Polym. Sci.ÈPolym. Chem., 27 (1989) 935.

5 Onari, Y., J. Appl. Polym. Sci., 31 (1986) 1663.6 Chan, W. H., Lam-Leung, S. Y., Fong, W. S. & Kwan, F. W., J.

Appl. Polym. Sci., 46 (1992) 921.7 Hegazy, E. A., Dessouki, A. M., El-Sawy, N. M. & Abd El-

Gha†ar, M. A., J. Polym. Sci.ÈPolym. Chem., 31 (1993) 527.8 El-Sawy, N. M., Abd El-Gha†er, M. A., Hegazy, E. A. & Dessouki,

A. M., Eur. Polym. J., 28 (1992) 835.9 El-Sawy, N. M., Fagal, G. A. & El-Shobaky, G. A., J. Polym.

Sci.ÈPolym. Chem., 31 (1993) 3291.10 Irving, H. & Williams, R. J. P., Nature, 162 (1948) 746.11 Burrows, H. D., Ellis, H. A. & Vatah, S. I., Polymer, 22 (1981)

1740.


anionic/cationic membranes obtained by a radiation grafting method for use in waste water treatment

Documents