Full Length ArticlePreparation and characterization of surface grafting polymer of ZrO2 membrane and ZrO2 powder
Graphical abstract
Introduction
Ceramic materials have excellent chemical resistance and heat resistance compared to other materials [1], [2], [3]. Most ceramic materials are metal oxides, such as titanium dioxide (TiO2), zirconia (ZrO2) and alumina (Al2O3), which are commonly used to manufacture ceramic membranes. However, most of the surface of the material for preparing the porous ceramic membrane has a large amount of hydroxyl groups (OH), so that the porous ceramic membrane is naturally hydrophilic [4], [5], [6]. The lack of selectivity in ceramic materials has prevented the wider applications of ceramic membranes [7]. Therefore, an effective modification method for ceramic membranes from hydrophilic to hydrophobic is highly valuable in academic research and industrial practice.
Hydrophobic modification of ceramic membrane was prepared by functional polymer chain on the surface [8], [9], [10] while maintaining ceramic membrane basic geometry and excellent mechanical strength. However, surface modification methods (dipping or coating) negatively affects the physical and mechanical properties of the composite membranes due to the surface incompatibility the organic modifiers and the hydrophilic ceramic substrates, which hinder their practical application [11]. A new type of ceramic supported polymer (CSP) is expected to be especially useful in membrane separation applications because of its good chemical stability, suitable wettability, high permeability and selectivity, non-swelling and incompressible characteristic [12]. However, the nature of chemical bonds in inorganic materials and organic materials is different, and the interaction force between the interface layers is very weak. To achieve this aim, silane coupling agents are commonly used to introduce active sites on ceramic surfaces, and to stick together two materials that were primarily incompatible. The function of the silane coupling agent is to form a chemical bridge between the polymer and the inorganic membrane interface [13]. Silane molecules contain two different chemical functional groups. The hydrolysable functional groups can react with hydroxyl groups on the surface of inorganic materials (such as glass fibers, silicates, and metal oxides) to form stable covalent bonds, the organic functional groups can form covalent bonds with the functional groups of resins, So that the two materials with very different properties are “coupled” to form a bonding layer of the inorganic phase-silane coupling agent-organic phase, thereby obtaining a good bonding strength between the polymer and the inorganic material interface and to improve the performance of the composite material [14]. Several examples of graft-modified porous inorganic membranes for various applications are given in the literature. Faibish et al. [15] have reported that the fabrication of ceramic-supported polymer (CSP) for oil-in-water emulsion treatment, which grafted poly (vinyl pyrrolidone) (PVP) on vinyl silane modified zirconia membranes via a free-radical graft polymerization reaction. Ana et al. [16] grafted alumina membranes using PDMS by a two-step process. The cross-linking agent 3-aminopropyltriethoxysilane (APTES) was first coated on a ceramic membrane by gas or liquid phase method, and then the epoxy-terminated PDMS was grafted.
The main aim of the research was to grafted poly(vinyl acetate) (PVAc) on alumina supported zirconia (ASZ) membranes and ZrO2 powders via a free-radical graft polymerization reaction, using a vinyltrimethoxysilane (VTMS) as linking agent to the ASZ membranes leading to the creation of the stable polymer layer on the membranes. The free-radical graft polymerization of VAc on silylated ASZ membranes and ZrO2 powders was systematically studied. The influence of reaction conditions on the physical and chemical properties and grafting rate of ASZ membranes and ZrO2 powders were studied.
Section snippets
Materials
The commercial ASZ flat-sheet membranes with a diameter of 30 mm, a thickness of 2 mm and average pore size of 100 nm were purchased from HeFei Transcendent Technology Co., Ltd. ZrO2 powders were supplied from National Medicine Group Chemical Reagent Co. Ltd. ZrO2 powders and membranes surface were activated by using vinyltrimethoxysilane (VTMS) in xylene solvent. The polyvinyl acetate (PVAc) layer was prepared by graft polymerization using vinyl acetate monomer in ethyl acetate solvent
Morphology and structure analysis
The degree of modification of the membrane porous structure was measured by EDS and SEM images of unmodified, silylated and vinyl acetate grafted membranes, as shown in Fig. 2.
Although SEM cannot discern the fine surface structure, a series of pores with an average pore size of 100 nm can be easily seen on the unmodified ASZ membrane surface (Fig. 2a). From the cross-section of the ASZ membrane, it is found that the ASZ membrane is asymmetric and consists of three parts: the top separation
Conclusions
In this work, ASZ membranes and ZrO2 powders were modified by free-radical graft polymerization of VAc to prepare ceramic-supported polymer, focusing on the effects of initial monomer concentration, grafting time and grafting temperature on physicochemical characteristics of ZrO2 powders and ASZ membranes. The experimental results showed that the presence of monoclinic crystalline phase of ZrO2 fraction in the VTMS modified ZrO2 and silylation ZrO2 grafted polymerization with VAc was confirmed
Acknowledgments
The present paper supported by science and technology plan projects of Harbin (No. 2014DB4AP050) and the Central Guidance for Local Science and Technology Development Program (No. ZY17C10).
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