Poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate)/clay composites

https://doi.org/10.1016/j.matchemphys.2011.03.018Get rights and content

Abstract

In this study, macroporous composites of poly(glycidyl methacrylate-co-ethylene glycol dimethacrylate) i.e. poly(GMA-co-EGDMA) and clay were prepared by radical suspension copolymerization. The composites with either raw (S0) or acid-modified clay (SA) were characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric (TG) and textural analysis. The morphological, textural and thermal properties of the composite with raw clay (CP-S0) differed slightly from those of the copolymer (CP), with exception of the thermal stability expressed in the shifting of the initial degradation temperature from 125 °C for CP to 210 °C for CP-S0. On the other hand, composite with modified clay (CP-SA) was a material with significantly changed morphology, porous structure parameters and a qualitatively different thermal behavior in comparison to CP and CP-S0. CP-SA had mass residue, after heating at 600 °C, three times higher than the amount of SA introduced into the reaction system. This indicates a different manner of incorporation of SA, compared to S0, into the composite. Both the obtained composites retained their macroporosity and might be used in all applications that involve macroporous copolymers and, due to the altered thermal properties, their application may be extended.

Highlights

► We synthesized macroporous composites of poly(GMA-co-EGDMA) and either raw or acid modified clay. ► Morphological, textural and thermal properties of the composite with acid modified clay were significantly changed with retained macroporosity. ► Composite with raw clay has enhanced thermal stability.

Introduction

Crosslinked macroporous poly(GMA-co-EGDMA) can be synthesized in the shape of resin beads by suspension polymerization in the presence of low-molecular weight inert component. The amount of crosslinking agent (EGDMA), the amount and composition of the inert component and the stirring speed have a significant influence on the properties of the resins (size, porosity, etc.). Varying those parameters results in copolymers with the same chemical composition, but with different porosities and particle sizes [1], [2].

Poly(GMA-co-EGDMA), due to their macroporous structure, are very useful as sorbents and column packing in different types of chromatography [3], as enzyme supports [4], in biotechnological and biomedical applications [5], for heavy and precious metal sorption [6], the sorption of organic compounds [7], etc.

Literature data show that the process of pore diffusion and the surface area in the pores determine the sorption rate and capacity, respectively. The pores reduce the mass transfer resistance and facilitate the intrapore diffusion of a sorbate due to the large internal surface area with a low diffusion resistance [8]. As an example, a comparison of sorptive properties of non-porous and macroporous PGME copolymers was reported, and the latter proved to be far more efficient as sorbents [9].

In general, polymer clay composites fall into three categories [10]: (i) microcomposites: the clay tactoids exist with no penetration of the polymer into the clay lamellae; (ii) exfoliated composites: the individual clay layers are dispersed as single platelets into a continuous polymer matrix; (iii) intercalated composites: in an intercalated composite the insertion of polymer into the clay structure occurs so as to swell the spacing between platelets in a regular fashion, regardless of the clay to polymer ratio [11].

Composites of poly(GMA) and clays have been reported. Çelik and Önal investigated nanocomposites of poly(GMA) and Na-montmorillonite [12] using X-ray diffraction, FTIR, SEM and TGA. They showed that those composites have significantly improved thermal properties compared to polymer. Another group of authors employed dynamical mechanical analysis that demonstrated that introduction of a small amount of clay/PGMA nanofiller in epoxy resins can significantly improve its mechanical properties [13]. However, there is a lack of literature regarding macroporous composites based on GMA and clay.

In this study, a macroporous poly(GMA-co-EGDMA) copolymer and its composites with bentonite were synthesized by radical suspension copolymerization. The goal of these investigations was to obtain a composite material with enhanced thermal properties and retained macroporosity. In this manner, the application area of the synthesized copolymer could be extended. Copolymers with increased thermal stability could be used at higher working temperatures that are beneficial in endothermic processes. In addition, the application areas of macroporous composites could be similar to those of macroporous copolymers.

This type of composite with a porous structure has not been reported.

Section snippets

Materials

Bentonite clay was obtained from the coal and bentonite mine Bogovina (Serbia). It was crushed, ground and sieved through a 74-μm sieve. The obtained fraction of clay was entitled raw clay (starting sample) S0. The Na and K contents were analyzed by flame emission spectrometry (PFP7, Jenway). All other elements were determined by Spectro Spectroflame M – inductively coupled plasma (ICP) optical emission spectrometer. The chemical composition (wt.%) of S0 dried at 110 °C, was: SiO2—57.51; Al2O3

Results and discussion

Chemical compositions of the organic constituents determined by microanalysis are given in Table 1.

The elemental analysis data for the sample is in fair agreement with the theoretical value (59.85 wt.% of C and 7.06 wt.% of H) for the copolymer with a GMA: EGDMA ratio of 60:40. The difference is within the limits for suspension copolymerizations [4].

Acknowledgements

This work was supported by the Ministry of Science and Technological Development of the Republic of Serbia (Projects III 45001 and III 43009).

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