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Structure and Performance of Poly(vinylalcohol)/Poly(γ-benzyl L-glutamate)Blend MembranesGuoquan Zhu a , Qiaochun Gao a , Fagang Wang a & Hua Zhang aa School of Materials Science and Engineering, Shandong Universityof Technology , Zibo, P. R. ChinaPublished online: 26 Jul 2011.

To cite this article: Guoquan Zhu , Qiaochun Gao , Fagang Wang & Hua Zhang (2011) Structureand Performance of Poly(vinyl alcohol)/Poly(γ-benzyl L-glutamate) Blend Membranes,International Journal of Polymeric Materials and Polymeric Biomaterials, 60:9, 720-728, DOI:10.1080/00914037.2010.551357

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Structure and Performanceof Poly(vinyl alcohol)/Poly(c-benzyl L-glutamate)Blend Membranes

Guoquan Zhu, Qiaochun Gao, Fagang Wang, and

Hua Zhang

School of Materials Science and Engineering, Shandong University of Technology,Zibo, P. R. China

Poly(vinyl alcohol) (PVA)=poly(c-benzyl L-glutamate) (PBLG) blend membranes withdifferent PBLG wt contents were prepared by pervaporation. Structure and surfacemorphologies of PVA=PBLG blend membranes were investigated by Fourier transforminfrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Thermal,mechanical, and chemical properties of PVA=PBLG blend membrane were studied bydifferential scanning calorimeter (DSC), tensile strength tests, and other physicalmethods. It was revealed that the introduction of PBLG homopolymer into PVA couldexert an outstanding effect on the properties of PVA membrane.

Keywords membrane, performance, PVA=PBLG blend, structure

INTRODUCTION

Poly(vinyl alcohol) (PVA) is a polymer of great interest due to its desirable

characteristics, specifically for various biomedical and pharmaceutical

applications [1–3]. Polymer blending has been a most useful method for the

improvement or modification of the physicochemical properties of polymer

materials [4–12]. An important property of the polymer blend is the miscibility

Received 11 August 2010; accepted 11 November 2010.This work is supported by the Natural Science Foundation of Shandong Province (No.ZR2009FL019). Support from Shandong University of Technology is also appreciated.Address correspondence to Guoquan Zhu, School of Materials Science and Engineering,Shandong University of Technology, Zibo 255049, P. R. China. E-mail: guoquanzhu888@163.com

International Journal of Polymeric Materials, 60:720–728, 2011

Copyright # Taylor & Francis Group, LLC

ISSN: 0091-4037 print=1563-535X online

DOI: 10.1080/00914037.2010.551357

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of its ingredients, because it affects the mechanical properties, the

morphology, its permeability and degradation [4,13]. There have been many

investigations into the miscibility of multi-component polymer systems.

Among them, the polymer blends between biopolymers and synthetic polymers

are of particular significance as they could be used as biomedical and biode-

gradable materials [14–16].

Based on its easy preparation, nontoxicity, noncarcinogenicity, biodegrad-

ability and bioadhesive characteristics, excellent chemical resistance and

physical properties, poly(vinyl alcohol) (PVA), a water-soluble polyhydroxy

polymer, has received a lot of interest for its potential applications

[1,4,17,18]. PVA, as an excellent biomaterial, could be used as natural tissues,

contact lenses, the lining for artificial organs, and drug delivery, etc [19–22].

Although PVA possesses good mechanical properties in the dry state, its high

hydrophilicity also limits its potential applications [23]. Compared with poly-

mer homopolymers, some of the polymer blends usually exhibit unexpected

properties [4].

As noted, polypeptides with better biocompatibility and biodegradability

also could be used for biomaterials [24–29]. Compared with the soft and hydro-

philic PVA materials [4], polypeptide material such as PBLG holds rigid and

hydrophobic characteristics [24,25]. The introduction of a PBLG homopolymer

into a PVA membrane is expected to improve the physicochemical properties of

the PVA membrane. The formation of intermolecular hydrogen bonds between

PVA molecules and PBLG molecules promotes the miscibility of PVA segments

and PBLG segments [15,30]. However, to the best of our knowledge, no experi-

mental work has been reported on the studies of the structure and perform-

ance of a PVA=PBLG blend membrane. In the present work, a series of

PVA=PBLG blend membranes with different PBLG wt contents were prepared

by pervaporation. Structure and surface morphologies of PVA=PBLG blend

membranes were investigated by FT-IR and SEM. Thermal, mechanical,

and chemical properties of PVA=PBLG blend membranes were studied by

DSC, tensile strength tests, and other physical methods. It was revealed that

the introduction of a PBLG homopolymer into PVA could exert an outstanding

effect on the properties of PVA membrane.

EXPERIMENTAL

MaterialsPoly(vinyl alcohol) (Mw¼ 79000, degree of hydrolysis 99mol%) was pur-

chased from Sigma, Inc. (USA), and used without further purification. Hexane,

tetrahydrofuran (THF), and 1,4-dioxane were of analytical grade and dried

with sodium to remove water before use. Dimethyl sulfoxide (DMSO) and other

solvents were of analytical grade and used without further purification.

Structure and Performance of PVA=PBLG Blend Membranes 721

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Synthesis of Polypeptide HomopolymerPBLG homopolymer was prepared by a standard N-carboxyl-c-benzyl-L-

glutamate anhydride (NCA) method [31,32]. The molecular weight of the

PBLG homopolymer was estimated from the [g] value measured in dichloroa-

cetic acid (DCA), according to the document [33]. The molecular weight of the

PBLG homopolymer used in the study is 75000. Figure 1 presents the pro-

posed structure of the PVA=PBLG blend showing the interactions between

PVA and PBLG.

FT-IR MeasurementsFT-IR spectra of PVA, PBLG, and PVA=PBLG blend samples were

measured on a Nicolet 5700 FT-IR spectrometer in the range of 4000–400 cm�1.

SEM PhotomicrographsSEM testing specimens were prepared by casting membranes from

30-35wt% PVA=PBLG blend solution in DMSO onto clean glass plates and

drying them under vacuum at 50�C. Gold was sprayed on the samples in vac-

uum. The investigation was carried out using a scanning electron microscope

(Sirin 200, FEI, Holland). Acceleration voltage was 10kV.

DSC MeasurementsDSC measurements were made on a DSC Q100 differential scanning

calorimeter; the temperature was calibrated with indium in a nitrogen atmos-

phere. About 8mg sample was weighed very accurately. The temperature

was controlled within the range between 90�C and 230�C; the heating rate

was 10�C=min.

Figure 1: Proposed structure of PVA=PBLG blend showing the interactions between PVAand PBLG.

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Tensile Strength TestsTensile strength tests were carried out with an Instron 4468 machine. The

sample membranes were 100mm� 15mm� 0.06mm, and the crosshead

speed was set to 150mm=min. For each data point, six samples were tested

and the average value was taken.

Water-Resistant Pressure MeasurementsThe water-resistant pressure (mm) measurements of PVA=PBLG blend

membranes were carried out according to a conventional method. The sam-

ple membranes were round with a diameter of 32mm and a thickness of

0.1mm. The sample membranes were used to seal the mouth of a long, round

tube with graduation in millimeters (tube diameter: 8mm). After the tube

mouth sealed with membrane was upset, deionized water was added into

the long, round tube drop by drop. As soon as the deionized water permeated

the membrane, the height of the water column was written down [34]. For

each data point, five samples were tested and the average value was taken.

RESULTS AND DISCUSSION

FT-IR AnalysisCurves a, b, and c in Figure 2 present the FT-IR spectra of PBLG, PVA,

and PVA=PBLG blend, respectively. The FT-IR spectrum of the pure PVA

presents the main characteristic bands: 3200-3600 cm�1 corresponding to

Figure 2: FT-IR spectra of (a) PBLG, (b) PVA, and (c) PVA=PBLG blend.

Structure and Performance of PVA=PBLG Blend Membranes 723

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stretching of the O-H group, 2930 cm�1 corresponding to stretching of the C-H

group, and 1092 cm�1 corresponding to stretching of the C-O group [35,36].

The FTIR spectrum of the pure PBLG shows the main characteristic bands:

3286 cm�1 corresponding to the N-H stretching vibration, 1654 cm�1 corre-

sponding to the a-helix amide I, 1544 cm�1 corresponding to the a-helix amide

II, 1730 cm�1 corresponding to C¼O stretching [37]. By comparing spectrum c

with spectra a and b, it is seen that spectrum c covers the main characteristic

bands of both spectrum a and spectrum b, and no new characteristic peaks

appear, indicating that no chemical reaction occurs during the blending

process of PVA and PBLG.

Morphological StudiesThe surface morphologies of the PVA=PBLG blend membrane were

evaluated by a scanning electron microscopy technique. Figure 3 shows the

Figure 3: SEM photographs of surface morphologies of PVA=PBLG blend membranewith various PBLG contents. PBLG content (wt%): (a) 0, (b) 1, (c) 3, and (d) 5 (magnification5000�).

724 G. Zhu et al.

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photographs of surface morphologies of the PVA=PBLG blend membrane with

various PBLG contents (wt%): (a) 0, (b) 1, (c) 3, and (d) 5 (magnification

5000�). As seen from Figure 3, the introduction of PBLG into PVA exerts a

marked effect on the surface morphologies of the PVA membrane. With the

increase of PBLG contents, the surface morphologies of the PVA=PBLG blend

membrane tend to change from a plane with flower pattern to compacter and

larger aggregates to looser and smaller aggregates. As is known, PBLG mole-

cules and PVA molecules could form some intermolecular hydrogen bonds and

the introduction of PBLG into PVA could destroy the intermolecular or intra-

molecular hydrogen bonds of PVA molecules, suggesting that the change of the

surface morphologies of PVA membrane could be attributed to the introduction

of PBLG segments.

DSC AnalysisFigure 4 presents the DSC curves of the PVA=PBLG blend membrane

with various PBLG contents (wt%): (a) 0, (b) 1, (c) 3, and (d) 5. By comparing

curves a, b, c, and d, it is found that the melting point of PVA segments in

PVA=PBLG blend membranes increases with the increase of PBLG content

in the blend membrane. As is known, PVA molecules and PBLG molecules

could form some intermolecular hydrogen bonds promoting the miscibility

between PVA segments and PBLG segments, indicating that the increase

of the melting point of PVA segments in PVA=PBLG blend membranes could

be attributed to the introduction of PBLG segments with higher melting

points.

Figure 4: DSC curves of PVA=PBLG blend membrane with various PBLG contents. PBLGcontents (wt%): (a) 0, (b) 1, (c) 3, and (d) 5.

Structure and Performance of PVA=PBLG Blend Membranes 725

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Tensile Strength TestsFigure 5 shows the relationship between the tensile strength of the PVA=

PBLG blend membrane and PBLG content in the blend. As seen from Figure 5,

the tensile strength of the PVA=PBLG blend membrane increases with the

increase of PBLG content. As mentioned earlier, PVA molecules and PBLG

molecules could form some intermolecular hydrogen bonds, and the formation

of the hydrogen bonds promotes the miscibility of PVA segments and PBLG

segments, and relatively upgrades the interaction of soft PVA segments and

rigid PBLG segments, suggesting that the increase of the tensile strength of

the PVA membrane also could be attributed to the introduction of rigid PBLG

segments. For such a blend system, the higher the PBLG content, the higher

the tensile strength of the PVA=PBLG blend membrane.

Figure 5: Tensile strength of PVA=PBLG blend membrane vs. the content (wt%) of PBLGin the blend.

Figure 6: Water-resistant pressure (mm) of PVA=PBLG blend membrane vs. the content(wt%) of PBLG in the blend.

726 G. Zhu et al.

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Water-Resistant Pressure (mm) MeasurementsFigure 6 indicates the relationship between the water-resistant pressure

(mm) of the PVA=PBLG blend membrane and PBLG content in the blend.

As shown in Figure 6, the water-resistant pressure of the PVA=PBLG blend

membrane increases with the increase of PBLG content in the blend. As noted,

PVA is a soft and hydrophilic material and PBLG is a rigid and hydrophobic

material [4,24,25], suggesting that the increase of the water-resistant press-

ure of the blend membrane is related to the introduction of hydrophobic PBLG

segments. For the blend system, the higher the PBLG content, the higher the

hydrophobicility of the blend membrane.

CONCLUSIONS

A series of PVA=PBLG blend membranes with different PBLG wt contents

have been prepared by pervaporation. FT-IR, SEM, DSC, and tensile strength

test techniques were used to investigate the structure and performance of the

PVA=PBLG blend membrane. FT-IR spectra proved that no chemical reaction

occurred during the blending process of PVA and PBLG. SEM photographs

demonstrated that the introduction of PBLG exerts a marked effect on the

surface morphologies of the PVA membrane. DSC measurements verified that

the melting point of PVA segments in the PVA=PBLG blend membrane

increases with the increase of PBLG content in the blend. The tensile strength

tests showed that the tensile strength of the blend membrane increases with

the increase of PBLG content in the blend. The water-resistant pressure tests

confirmed that the increase of PBLG content promotes the hydrophobicility of

the blend membrane.

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