Radiation induced graft polymerization of glycidyl methacrylate onto sepiolite

Highlights

• Radiation induced polymerization was used to graft GMA onto sepiolite.

• Effect of absorbed dose and monomer concentration on grafting yield were studied.

• Maximum grafting of 665% was obtained at 15 kGy and 7.5% monomer concentration.

• Grafting of sepiolite was confirmed by FT-IR spectroscopy.

• GMA grafted nanohybrid polymer was converted into metal ion adsorbent.

Abstract

Radiation induced graft polymerization (RIGP) was used to develop glycidyl methacrylate (GMA) grafted nanohybrid polymer. The absorbed dose and monomer concentration significantly affect the degree of grafting on vinyl modified sepiolite (VMS). Maximum grafting of 665% was achieved at optimized absorbed dose and monomer concentration. Post-polymerization modification of the nanohybrid with maximum grafting was carried out with sodium sulfite. Structural studies by ATR-FTIR and XRD analysis of the synthesized nanohybrids confirmed modification at different stages. The morphological changes studied by field emission scanning electron microscopy (FESEM) showed the conversion of sepiolite fiber into globular structure. Thermal gravimetric analysis (TGA) revealed an increase in thermal stability of the GMA grafted nanohybrid with the increase in grafting yield. The sulfonated form of the nanohybrid showed highest adsorption for Cu(II) at 4 pH value which indicates its potential as metal ion adsorbent for the recovery of metals from wastewater.

Introduction

In recent years, hybrid materials, comprising of inorganic and organic components, have received much attention due to their excellent properties, including thermal resistance, mechanical stability, and catalytic, magnetic and electric properties. Generally, inorganic constituent in the form of clay, glass, carbon material etc. provide a stable base structure, whereas organic constituent (polymer) impart functionalities that can be used as such or converted into other chemical form. The combined effect of these components showed remarkable properties and have found applications in adsorption, drug delivery, catalysis, sensing etc. (García et al., 2011; Raza et al., 2020b).

The grafting of monomers/polymer on solid substrates forms polymeric assemblies, either through covalent attachment or by physical adsorption (Hassan et al., 2019; Idota et al., 2010). In many cases, inorganic substrates are used in polymer grafted nanohybrids (Raza et al., 2020). Polymer grafted nanohybrid, have played a major role as functional materials in surface coatings with excellent durability, long-term chemical and mechanical stability. Functional characteristics of these materials have resolved the compatibility issues and are preferred to be used as nanofiller in polymer matrix for various applications (Hou et al., 2014; Shafiq et al., 2012).

Radiation grafting of monomers on a substrate is well established technique and have many commercialized products (Güven, 2017, Chmielewski et al., 2005). In radiation grafting, ionizing radiation such as: gamma rays or electron beam are used to initiate the graft polymerization reaction. Radiation induced graft polymerization (RIGP) is an attractive technique to design and develop polymer nanohybrid (Flores-Rojas et al., 2020; Khan et al., 2017; Nasir et al., 2020; Taimur et al., 2017). The final products obtained by this technique are free from initiator and other chemical residues. Moreover, the polymerization reaction occurs at room temperatures. The versatility, uniform kinetics and eco-friendly nature of radiation applications in other fields encourages researchers to use this technique to develop new materials for environmental, industrial and biomedical applications. Degree of grafting on a substrate is greatly affected by the parameters such as; absorbed dose and monomer concentration (Seko et al., 2010). Therefore, it is very important to optimize these parameters to achieve maximum degree of grafting.

Glycidyl methacrylate (GMA) is a remarkable chemical (Jazani et al., 2017) and has been used in resins coating, adhesives, textile finishing and ion exchange resins (Madrid et al., 2013). It contains reactive vinyl group that can undergo chain polymerization and pendant epoxy group. The epoxy group of GMA has the ability of ring-opening reactions which makes it capable for post polymerization modification. In post-polymerization modification, the functional groups of monomers which are inert towards polymerization are converted by subsequent reaction into other desirable functional groups. Elkady et al. have synthesized nano-sulfonated poly (glycidyl methacrylate) cations exchanger for cadmium ions removal (Elkady et al., 2011). Seko et al. synthesized amine-type adsorbents used ionizing radiation for graft polymerization of glycidyl methacrylate (Seko et al., 2007). GMA has also been successfully grafted onto PE/PP nonwoven fabric by radiation and converted to amidoximate form (Korpayev et al., 2018). Radiation-induced GMA/DMMA graft copolymerization onto porous PE hollow-fiber membrane has also been studied (Xv et al., 2019). Kavakli et al. worked on preparation and characterization of Fe (III)-loaded iminodiacetic acid modified GMA grafted nonwoven fabric adsorbent for anion adsorption (Kavakli et al., 2014). Choi and Nho developed phosphonated type cation exchange adsorbents by radiation grafting of GMA onto polyolefin (Choi and Nho, 1999).

Naturally occurring clays are low-cost materials having high surface area, good chemical and thermal stability. Clays like sepiolite have shown flexible surface chemistry with high aspect ratio, adsorption capacity and thermal conductivity. It has been used in many industrial applications including as additives in polymer composites to improve the thermo-mechanical properties of polymer matrix (Masood et al., 2018). It has also been used as a base to graft different moieties using its hydroxyl functionality. These features make it a valuable material for the development of new materials by introducing polymerizable groups on its surface. Variety of monomers has been grafted on its surface using in-situ graft polymerization. Taimur et al. prepared nanohybrids by radiation grafting of acrylonitrile and styrene on sepiolite (Taimur et al., 2017a, 2018).

RIGP has been used to graft GMA on different bases but its grafting onto sepiolite has not been reported in the literature. In this work, novel sepiolite grafted GMA nanohybrid was synthesized using gamma radiation. The effect of absorbed dose and monomer concentration are optimized. Moreover, post-polymerization modification of the developed nanohybrid was carried out to study its potential for metal adsorption. The developed polymer nanohybrid is characterized by ATR-FTIR, TGA, XRD and SEM techniques.