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Energy Procedia 17 ( 2012 )1850 – 1857

2012 International Conference on Future Electrical Power and Energy Systems

Synthesis and Characterization of Cinnamic Acid-Grafted

Poly(Vinylidene Fluoride) Microporous Membranes

Xuejun Zhang*, Huan Meng, Yujing Di

College of Science, ,North University of China, ,Taiyuan, China

E-mail:

zhangxuejun@

Abstract

Cinnamic acid (CA)-graft-poly (vinylidenefluoride) (PVDF) was synthesized via free radical polymerization using

benzoyl peroxide (BPO) as initiator in a N,N-dimethylforma- mide (DMF) solution. FTIR spectroscopy, DSC, and

TG analyses of the grafted polymers showed that the CA side chains were successfully grafted onto the PVDF

backbone. Contact angle measurements indicated that the modified PVDF showed better hydrophilicity than the

unmodified PVDF. Microporous membranes were prepared from the PVDF-g-P (CA) polymer with poly (vinyl

pyrrolidone) (PVP) as the pore former through the phase inversion technique. The morphology of the membranes was

studied by scanning electron microscope (SEM). The membrane cast from the DMF solution of PVDF-g-P (CA) had

a greater pore size distribution and higher porosities than those of the pristine PVDF. The membrane prepared using

the modified PVDF showed a higher flux than the unmodified PVDF membrane.

© 2012 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Hainan University.

© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of [name organizer]

Keywords:Poly (vinylidene fluoride); Cinnamic acid; Graft- ed polymer; Membrane; Hydrophilicity

uction

Poly (vinylidene fluoride) (PVDF) membranes are widely used in microfiltration (MF) and

ultrafiltration (UF) due to their excellent chemical resistance, well-controlled porosity, and good thermal

properties [1]. They are also used in other types of applications such as in the treatment of both industrial

and municipal wastewater [2-5] or biomedical application. Even with the good properties of PVDF,

however, fouling is economically one of its most problematic drawbacks, a consequence of its low

surface energy and hydrophobic character that have limited its use in materials for membrane separation

of oil and biological molecules [2]. During the filtration process, high hydrophobic property and low

fouling resistance of PVDF membranes lead to the protein adsorption, and thus membrane pores are

blocked. To improve the hydrophilicity of PVDF membranes, membrane surface modification usually has

to be performed.

Various techniques have been investigated with regard to making the membrane surface hydrophilic.

1876-6102 © 2012 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Hainan University.

doi: 10.1016/.2012.02.322

Xuejun Zhang et al. / Energy Procedia 17 ( 2012 ) 1850 – 1857

1851

In general, they can be classified into blend, coating, and grafting techniques. In the blend technique,

PVDF powder is mixed with a hydrophilic polymer or inorganic compound in a solution, to be made into

a membrane. Several pairs of blends have been investigated, such as PVDF/ZrO

2

[6, 7], PVDF/poly

(vinyl acetate) [8], PVDF/poly (ethylene glycol) (PEG) [9, 10], PVDF/poly (methyl methacrylate)

(PMMA) [11-16], PVDF/poly (acrylic acid) (PAA) [17], and PVDF/ poly (acrylonitrile) (PAN) [18].

Grafting has advantages over other methods in several points, including easy and controllable

introduction of graft chains with a high density and exact localization of graft chains to the surface with

the bulk properties unchanged. Furthermore, covalent attachment of graft chains onto a polymer surface

avoids their delamination, and assures the long-term chemical stability of introduced chains, in contrast to

physically coated polymer chains. But surface grafting is usually attended by changes in the membrane

pore size distribution, thus leading to reduced permeability. In addition, the surface grafting modification

technique imparts wettability to the membrane surface only, while the surface properties of the pore

channels remain largely unchanged. Based on these principles, it is necessary that PVDF powders are

modified in the first place and then made to be a membrane.

In this study, PVDF-g-P (CA) polymers were synthesiz- ed for the first time via free radical

polymerization. Cin- namic acid (CA) is similar to AA, including double bond and carboxyl group.

Carboxyl is a strong polar group that can exhibit hydrophilicity to a certain extent. CA includes double

bond, and the unsaturated bond can polymerize easily to form polymers with the PVDF free radical

induced by the initiator. The main objective of the present work was the preparation of hydrophile PVDF

membranes. The reactions involved are illustrated in Fig.1, in which the formed grafted polymers are

characterized by FTIR-ATR, and DSC/TG. The functional membranes were prepared using this grafting

copolymer and characterized by SEM. The hydrophilicity of the membranes prepared from the

CA-grafted PVDF using free radical polymerization was much better than that of the membranes

prepared from modified PVDF via other techniques.

Fig.1. Schematic representation of the process of free radical polymerization of CA onto the PVDF

mental

als

PVDF powders with a molecular weight of 500 000 obtained from Shanghai were used in this study.

DMF was obtained from the Beijing chemical plant and used as a solvent for the initiating agent treatment

and graft polymerization. BPO was obtained from the Sinopharm Chemical Reagent Beijing Company.

PVP was obtained from Tianjin Chemical Research Institute and used as a hollow agent.

ng of CA on PVDF Powders

Dope solution was prepared firstly by dissolving PVDF powders in DMF. The weight of the PVDF

powders was fixed at 2.0 g, and the volume of DMF was fixed at 40.0 ml. The concentration of the

monomer CA was varied from 2.0 to 20.0 % (CA/PVDF weight ratios).

The PVDF solution and the CA monomer were introduced into a four-necked flask equipped with a

muddler, dropping funnel, condenser and gas line. A continuous stream of N2 was bubbled through the

solution. The solution was placed in a water bath at 70 °C and saturated with purified argon at the same

time. After 30 min, BPO, as an initiator, was added to the reaction system. An argon flow was maintained