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Colloids and Surfaces A: Physicochem. Eng. Aspects 366 (2010) 135–140

Contents lists available at ScienceDirect

Colloids and Surfaces A: Physicochemical andEngineering Aspects

journa l homepage: www.e lsev ier .com/ locate /co lsur fa

abrication and characterization of poly(vinyl alcohol)/alginate blend nanofibersy electrospinning method

d. Shahidul Islama,b, Mohammad Rezaul Karima,c,∗

Department of Applied Chemistry and Chemical Engineering, University of Dhaka, Dhaka 1000, BangladeshDepartment of Advanced Organic Materials Science & Engineering, Kyungpook National University, Daegu 702-701, South KoreaCenter of Excellence for Research in Engineering Materials, College of Engineering, King Saud University, Riyadh 11421, Saudi Arabia

r t i c l e i n f o

rticle history:eceived 7 April 2010eceived in revised form 24 May 2010ccepted 28 May 2010vailable online 8 June 2010

a b s t r a c t

Poly(vinyl alcohol) (PVA)/alginate (Alg) nanofibers are prepared using electrospinning method in aqueoussolutions with PVA (10 wt.%)/Alg (2 wt.%) blended system in a volume ratios of 100/0, 80/20, and 60/40.Because of biocompatibility and non-toxicity of PVA, it could be used in numerous fields. Alginate isan interesting natural biopolymer for many of its merits and good biological properties. The blended

eywords:lectrospinningoly(vinyl alcohol)lginatelend

nanofibers are characterized by scanning electron microscopy (SEM), thermal gravimetric analysis (TGA),differential scanning calorimetry (DSC), X-ray diffraction (XRD), Fourier transform infrared (FTIR), andmechanical measurement. XRD, FTIR and DSC data demonstrate that there are good interactions betweenPVA and Alg caused by possibly hydrogen bonds. The study shows that with a higher percentage of Alg inthe PVA/Alg blend nanofibers, superior onset temperature of the degradation and higher thermal stabilitycould be obtained above 350 ◦C. Moreover, the blend nanofibers exhibit improvement in mechanical

ure e

anofibers properties compared to p

. Introduction

The electrospinning technique has attracted great interestmong academic and industrial scientists due to its simple andffective approach to produce nanofibers, which have been found toe attractive for various applications in biomedical engineering, fil-ration, protective clothing, catalysis reactions, and sensors [1–5].oshi and Reneker [6] reported principle of the electrospinning

echnique adequately. In an electrospinning process, a polymerolution, held by its surface tension at the end of a capillary tube, isubjected to an electric field. Charge is induced on the liquid surfacey an electric field. Mutual charge repulsion causes a force directlypposite to the surface tension. As the intensity of the electric fields increased, the hemispherical surface of the solution at the tipf the capillary tube elongates to form a conical shape known ashe Taylor cone [7]. When the electric field reaches a critical valuet which the repulsive electric force overcomes the surface tensionorce, a charged jet of the solution is ejected from the tip of the Tay-

or cone. Because this jet is charged, its trajectory can be controlledy an electric field. As the jet travels in air, the solvent evaporates,

eaving behind a charged polymer fiber, which lies randomly on aollecting metal screen.

∗ Corresponding author at: Tel.: +966 14678929; fax: +966 14670199.E-mail address: mkarim@ksu.edu.sa (M.R. Karim).

927-7757/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.colsurfa.2010.05.038

lectrospun PVA with the addition of Alg.© 2010 Elsevier B.V. All rights reserved.

Polymer blending constitutes a very useful method for theimprovement or modification of the physicochemical properties ofpolymeric materials. Some polymer blends exhibit unusual proper-ties that are absolutely different from those of the homopolymers.An important property of a polymer blend is the miscibility of itscomponents because it affects the mechanical properties, the mor-phology, and the permeability and degradation. Polymer blendsare physical mixtures of structurally different polymers or copoly-mers that interact with secondary forces without covalent bonding[8], such as hydrogen bonding, dipole–dipole forces, and charge-transfer complexes for homopolymer mixtures [9–11].

Poly (vinyl alcohol) (PVA) is a semi-crystalline hydrophilicpolymer with good chemical and thermal stability. It is a highlybiocompatible and non-toxic polymer and it can be processedeasily and has high water permeability. PVA can form physicalgels in various types of solvents which lead to the use of PVAin a wide range of applications in medical, cosmetic, food, phar-maceutical and packaging industries [12–19]. Its flexibility andtoughness are good, so it is a typical synthetic polymer that isused to improve the physical properties through mixing with othermaterials that have poor physical properties. PVA with functionalgroups is useful in practical investigations of functional polymers

because of its easy preparation as a bulk material, films, and fibers[19–21].

Alginate employed in this work is an abundant polysaccha-ride, which can be supplied in plenty from marine algae. It is wellknown that alginate is a copolymer composed of �-d-mannuronate

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36 Md.S. Islam, M.R. Karim / Colloids and Surface

M) and �-l-glucuronate (G) resides in various M/G ratios; theseesides are arranged in a block-wise fashion, constructed not onlyf homopolymer blocks (MM or GG) but also alternating blocksMG) [22,23]. This carbohydrate polymer has been re-evaluatedecently as an attractive natural resource, possessing a potentialo be further developed for medical, pharmaceutical, and bio- andther industrial applications [24–27]. In contrast to the numeroustudies carried out on the physical properties and industrial appli-ations of alginate gels [28–33], there have been only a few studiesealing with alginate/synthetic polymer blends in the film form34,35]. However, to the best of our knowledge, no report about thelectrospinning of nanofibers from the blend solution of PVA/Alg isound in the literature.

In this study, a rigid natural polymer, Alg, is blended with a flex-ble synthetic polymer, PVA, to enhance the mobility of polymerhains during electrospinning process and to increase the onsetemperature of the degardation and the thermal stability of thatynthetic polymer at higher temperature (above 350 ◦C). Moreover,echanical properties of that blend nanofibers can be improved

ompared to pure electrospun PVA with the addition of Alg.

. Experimental

.1. Materials

PVA with number-average degree of polymerization of 1700fully hydrolyzed, degree of saponification = 99.9%) was obtainedrom DC Chemical Co., Seoul, Korea, and Alg material used had vis-osity of 700–900 cps purchased from Degussa Co., France. Doublyistilled water (DDW) was used as a solvent to prepare all solutions.

.2. Preparation of PVA/Alg blend solutions

Firstly, PVA and Alg were dissolved separately. Alg (2 wt.%) wasissolved in DDW at room temperature. Transparent solutions of

ig. 1. SEM images of electrospun PVA nanofibers prepared by using different PVA solutiond TCD = 15 cm).

ysicochem. Eng. Aspects 366 (2010) 135–140

PVA (8, 10, and 12 wt.%) were prepared by dissolving PVA in DDWat about 80 ◦C with continuous stirring for 3–4 h. Secondly, PVAsolutions were mixed with Alg solution to obtain the blends withthe volume ratios of PVA to Alg ranging 100/0, 80/20, and 60/40separately. Each blended solution was stirred for 2 h at room tem-perature.

2.3. Electrospinning of PVA/Alg blend nanofibers

During electrospinning, high-voltage power (model CPS-60K02VIT, Chungpa EMT Co., Ltd., Seoul, Korea) was applied tothe PVA/Alg solution in a syringe via an alligator clip attached tothe syringe needle. The applied voltage was adjusted at 15 kV. Thesolution was delivered to the blunt needle tip via a syringe pump tocontrol the solution flow rate. Fibers were collected on electricallygrounded aluminum foil placed at a 15 cm vertical distance to theneedle tip.

2.4. Characterization

The morphology and property characterization of the elec-trospun PVA/Alg blend nanofibers was conducted with scanningelectron microscope (model JSM-6380, JEOL) after gold coating, X-ray diffraction (X’Pert APD, Philips), and fourier transform infrared(IFS 120HR, Bruker). The fiber diameter was measured from thefield-emission SEM images, and five images were used for each fibersample. From each image, at least 20 different fibers and 100 dif-ferent segments were randomly selected, and their diameters weremeasured to generate an average fiber diameter with Photoshop

5.0 software. The thermal behavior of the PVA fibers was studiedwith DSC (model Q-10; TA Instruments, United States) and TGA(model Q-50; TA Instruments) techniques. The stress–strain mea-surements were determined with a Zwick (Germany) Z005 materialtesting machine.

n concentrations of (a) 8 wt.%, (b) 10 wt.%, and (c) 12 wt.% (Applied voltage = 15 kV,

s A: Physicochem. Eng. Aspects 366 (2010) 135–140 137

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Md.S. Islam, M.R. Karim / Colloids and Surface

. Results and discussion

.1. Morphology of PVA/Alg nanofibers

Morphology of electrospun nanofiber can be affected by thelectrospinning instrument parameters including electric voltage,ip to collector distance and solution parameters such as polymeroncentration, feed mass ratio and surface tension. Changing theolymer concentration could alter the fiber diameter and morphol-gy very effectively, as shown in Fig. 1. In a fixed applied voltage15 kV) and tip to collector distance (15 cm), it has been used 8,0, and 12 wt.% of PVA solution. It is found that 10 wt.% PVA solu-ion is ideal to obtain thinner and uniform PVA fibers [Fig. 1(b)] .t the 10 wt.% PVA concentration, uniform fibers with diametersf 500–50 nm are obtained for volume ratios of 100/0, 80/20 and0/40 of 10 wt.% PVA to 2 wt.% solutions [Fig. 2(a) and (c)]. However,ewer beads are found at the 60/40 of PVA/Alg blend ratio [Fig. 2(c)].verage diameter of electrospun PVA/Alg blend nanofibers with0 wt.% PVA solution are displayed in Fig. 3.

.2. Mechanical properties

In the course of studying PVA/Alg blends, we have found that Algorms optically clear homogeneous blends with PVA and that theoung modulus and the tensile stress of the blends are greater thanure PVA. The results of the stress–strain measurements of PVAnd PVA/Alg blend nanofibers are presented in Fig. 4. Upon mixingith PVA, both the tensile strength and elongation at break are

ncreased with increasing Alg contents. This appearance suggestshat the existence of specific intermolecular interaction betweenlg and PVA, such as those reported for the blend systems of silkbroin/NaAlg and poly(acrylamide)/NaAlg [36,37].

.3. Thermal properties

Generally, when PVA is pyrolyzed in the absence of oxygen,t undergoes dehydration and depolymerization at temperatures

ig. 2. SEM images of elctrospun PVA/Alg blend nanofibers with various volumer ratiosoltage = 15 kV, and TCD = 15 cm).

Fig. 3. Average diameter of electrospun PVA/Alg blend nanofibers with 10 wt.% ofPVA solution (alginate solution concentartion = 2 wt.%, Applied voltage = 15 kV, andTCD = 15 cm).

greater than 200 and 400 ◦C, respectively. The actual depolymeriza-tion temperature depends on the structure, molecular weight, andconformation of the polymer. Tsuchiya and Sumi reported that afterwater molecules are eliminated from PVA chain at 245 ◦C, it formsa conjugated polyene structure [38]. Meanwhile, three weight losspeaks are observed in the TGA curve for bulk PVA [Fig. 5(a)]. The firstpeak at 25–60 ◦C is due to moisture vaporization, the second peak at230–380 ◦C is due to the thermal degradation of PVA, and the thirdpeak at 430–480 ◦C is due to the byproduct formation of PVA dur-ing the TGA thermal degradation process. According to Holland andHay’s report [39], thermal degradation could lead to the production

of aldehyde and alkene end groups in the molten state, which couldlead to the formation of vinyl ester by the rearrangement. [Fig. 5(b) and (c)] shows similar thermogram trend for PVA/Alg blendnanofibers with 80/20 and 60/40 volume ratios of 10 wt.% PVA to

of 10 wt.%PVA to 2 wt.%Alg solutions of (a) 100/0, (b) 80/20, and (c) 60/40 (applied

138 Md.S. Islam, M.R. Karim / Colloids and Surfaces A: Physicochem. Eng. Aspects 366 (2010) 135–140

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ig. 4. Stress–strain curve of electrospun PVA/Alg blend nanofibers with variousolume ratios of 10 wt.% of PVA to 2 wt.% of Alg solutions of (a) 100/0, (b) 80/20, andc) 60/40 10 (applied voltage = 15 kV, and TCD = 15 cm).

wt.% Alg, respectively. Clearly, it can be concluded that highernset temperature of the degradation and thermal properties coulde obtained above 350 ◦C temperature with a higher volume ratiof Alg in the PVA/Alg blend electrospinning nanofibers.

Fig. 6 shows the DSC thermograms of electrospun pristine PVAnd PVA/Alg blend nanofibers with different volume ratios of0 wt.% PVA to 2 wt.% Alg. A relatively large and sharp endother-ic peak is observed at about 222.5 ◦C [Fig. 6(a)] and is assigned to

he melting temperature of pure PVA, which has a number-averageegree of polymerization of 1700, which agrees very well witheported data [40,41]. This peak is shifted to 216.50 and 212.50 ◦Cith the addition of 20 and 40 volume percentages of 2 wt.% Alg

olution [Fig. 6(b) and (c)], respectively. And these gradually shifthe melting temperature to lower values; which occur becausef the addition of Alg. This is because the majority of the chainsre noncrystalline state due to the rapid solidification process oftretched chains during electrospinning.

.4. XRD data

Fig. 7 illustrates the XRD patterns of electrospun pristine PVAnd PVA/Alg blend nanofibers of different volume ratios of 10 wt.%VA–2 wt.% Alg. The pristine PVA nanofibers shows a significantrystalline peak at about 19.3◦, which is due to the occurrencef strong intermolecular and intramolecular hydrogen bondingig. 7(a) [42]. As the quantity of Alg in the PVA/Alg blend nanofiberss increased, the intensity of the diffraction peak at about 19.3◦ ofristine PVA becomes lower and broader Fig. 7(b) and (c)]. Thisuggests that the crystallinity of PVA/Alg nanofibers with highermounts of Alg solution (80/20 and 60/40 volume ratios) is lowerhan that of the electrospun PVA nanofibers. The reduction of therystallinity of the electrospun PVA/Alg nanofibers can probablye attributed to the hydrogen-bonding interaction between Algnd PVA macromolecules. XRD indicates that PVA could possiblynteract with Alg through hydrogen bonding between hydroxylroups in PVA and the carboxyl or hydroxyl groups in Alg. There-ore, the strong molecular interactions and crystalline structure oflg are hindered by the addition of PVA. Subsequently, the electro-pinnability of Alg with PVA is greatly improved.

.5. FTIR data

Fig. 8 shows the FTIR spectra of electrospun PVA, Alg andVA/Alg blend nanofibers of different volume ratios of 10 wt.%

Fig. 5. TGA data of elctrospun PVA/Alg blend nanofibers with various volume ratiosof 10 wt.% of PVA to 2 wt.% of Alg solutions of (a) 100/0, (b) 80/20, and (c) 60/40(applied voltage = 15 kV, and TCD = 15 cm).

PVA to 2 wt.% Alg solutions. The frequencies and assignments forthe pristine PVA are indicated as follows: 2944 cm−1 for the CH2group stretching vibration, 1096 cm−1 for the C–O group, and3435 cm−1 for the stretching vibration peak of its side hydroxyl

groups [Fig. 8(a)]. On the other hand, for the Alg, the band appearsat 3430 cm−1 for the hydroxyl groups. It is worth mentioning thatthe bands appearing in the region of 3400 cm−1 belongs to the alltypes of hydrogen bonded OH groups. The bands appear at 1615

Md.S. Islam, M.R. Karim / Colloids and Surfaces A: Ph

Fig. 6. DSC data of electrospun PVA/Alg blend nanofibers with various volume ratiosof 10 wt.% of PVA to 2 wt.% of Alg solutions of (a) 100/0, (b) 80/20, and (c) 60/40(applied voltage = 15 kV, and TCD = 15 cm).

Fig. 7. XRD data of electrospun PVA/Alg blend nanofibers with various volume ratiosof 10 wt.% of PVA to 2 wt.% of Alg solutions of (a) 100/0, (b) 80/20, and (c) 60/40(applied voltage = 15 kV, and TCD = 15 cm).

Fig. 8. FTIR data of electrospun PVA/Alg blend nanofibers with volume ratios of10 wt.% of PVA to 2 wt.% of Alg solutions of (a) 100/0, (b) 80/20 and (c) bulk alginate(applied voltage = 15 kV, and TCD = 15 cm).

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ysicochem. Eng. Aspects 366 (2010) 135–140 139

and 1417 cm−1 belong to the asymmetric and symmetric –COO−

stretching vibrations, respectively [Fig. 8(c)]. With the addition ofAlg, the intensity of absorption peaks of PVA at 849, 1096, 1336,1440, and 2944 cm−1 decrease, and some peaks disappears becauseof the interaction between PVA and Alg [Fig. 8(b)]. For Alg, the char-acteristic bands appear at 1615, 1417, and 3430 cm−1 and thesethree bands are observed in the spectra of the blend [Fig. 8(b)].It is also observed that the bands of hydroxyl stretching becomemuch broader with adding Alg. This strongly supports the idea thathydrogen bonding could be formed between the hydroxyl groupsof PVA and that group of Alg. Therefore, the inclusion of PVA couldmoderate the interaction between Alg macromolecules and thusimprove the electrospinnability of Alg with PVA.

4. Conclusions

The results in this research show that a pure alginate system assuch could not directly be electrospun to yield continuous and uni-form nanofibers. Thus, to overcome the poor electrospinnability ofAlg solution, synthetic polymers such as PVA solution is blendedwith Alg solution to improve its spinnability. The intermolecularinteraction of PVA with Alg through hydrogen bonding improvessubstantially the spinnability of each blended solutions and con-sequently uniform and continuous nanofibers are electrospun. Itmight be concluded as well that the best synthesis conditions forthe ultrafine PVA/Alg blend nanofibers by the electrospinning tech-nique are 10 wt.% PVA with 2 wt.% Alg solution of volume ratio of80/20 of PVA to Alg at an applied voltage of 15 kV, and TCD of 15 cm.The higher the Alg percentage in the PVA/Alg blends nanofibers, thebetter the thermal stability is exhibited in the onset temperatureof the degradation and above 350 ◦C temperature. Furthermore,the blend nanofibers show advancement in mechanical propertiescompared to pure electrospun PVA with the addition of Alg.

Acknowledgments

The support of this research by the University of Dhaka,Bangladesh is gratefully appreciated. M.R. Karim gratefullyacknowledges supports from King Saud University and Ministry ofHigher Education, Kingdom of Saudi Arabia.

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