Emulsion grafting of glycidyl methacrylate onto polyethylene fiber

Abstract

Graft polymerization of glycidyl methacrylate (GMA) onto polyethylene fiber was carried out in emulsion solution obtained by dissolving GMA in water with sodium n-dodecyl sulfate (SDS) as a surfactant. GMA micelles diameter was 415 nm at 5% GMA with 4% SDS and increased up to 1840 nm at 10% GMA with 12% SDS. Degree of grafting (Dg) which was estimated by the weight gain after grafting increased with the increment of GMA concentration in the range 2 to 8% and slightly reduced at 10% GMA. The increment in SDS concentration from 4% to 16% at 5% GMA reduced Dg from 120% to 18%. In emulsion graft polymerization, Dg was affected by covered area by GMA/SDS micelles on the fiber.

Introduction

Chemical modifications of polymeric materials have been carried out by radiation induced graft polymerization (RIGP) and the resulting polymers were widely applied for the special purpose such as uranium recovery from seawater (Seko et al., 2003) and cadmium recovery from waste of fishing industry (Nakai et al., 2004). RIGP represents a useful way to improve the quality of a variety of natural materials and extend the range of their uses, and the technique can be done easily by using a conventional polymer-like polyethylene in various shapes such as membrane (Kawai et al., 2001; Chen et al., 2004) and fiber (Seko et al., 2005; Tamada et al., 2004). Furthermore, RIGP is practically interest owing to the process initiated without any chemicals such as initiator and sensitizer (Saito, 2002; Nasef and Hagazy, 2004). The process of making graft materials consisted of 3 steps. First, irradiation by an electron beam or gamma ray was conducted to produce radicals initiating the graft polymerization. Second step was grafting where the vinyl monomers were reacted with the radicals and the graft chains were propagated from the radicals in the trunk polymer. After grafting, the introduced graft chains were chemically modified to functional group having the selective affinity to the aiming metal ion.

It is well known that glycidyl methacrylate (GMA) is a useful precursor monomer for graft polymerization (Eckert et al., 2000; Saito et al., 2002; Hoshina et al., 2007). The epoxy group of GMA can be modified easily into functional groups which play roles of ion exchange and adsorption of toxic gases (Tsuneda et al., 1991; Hori et al., 1997). Generally, organic solvents such as alcohols and dimethyl sulfoxide were used for grafting reaction since GMA was dissolved well in organic solvents (Ren et al., 1993). Water has also been used as a solvent in a so-called “emulsion polymerization” in the presence of a surface-active agent. Polymerization in the solvent-based dispersion, that is, emulsion polymerization, is to graft polymerize a polymeric material through reaction with an emulsion comprising reactive monomers, a surfactant and water (Seko et al., 2007; Wada et al., 2008). A process for reaction of radiation-crosslinked polymers in an emulsion to form an electrochemical cell membrane has been proposed as a process for emulsion graft polymerization. Another process for polymerization in a monomer solution emulsified by a surfactant by an oxidation–reduction reaction using a redox catalyst has been also studied (Mosina, 1992).

However, emulsion graft polymerization has a problem that the dispersion turns heterogeneous, so the reaction fails to proceed fully. The problem is significant in the case of using reactive monomers with poor compatibility with water. An attempt to stabilize shapes of liquid droplets in the emulsion by continuously stirring the reaction system during the graft reaction has been disclosed (Kudrysvtsev et al., 2003), or emulsion graft polymerization of water-soluble polymers has been attempted (Kislenko, 1999). However, there have not yet been any successful cases of efficient polymerization of reactive monomers with general-purpose solid polymers without any crosslinking reaction pretreatment. Thus, there is a need for a process for emulsion graft polymerization in an aqueous emulsion directed to general-purpose polymers without any crosslinking reaction pretreatment, which can give desired specifically working functions to the polymers by efficient polymerization of reactive monomers having poor compatibility with water. There is also a need for a metal ion adsorbent prepared by the process for emulsion graft polymerization in the aqueous emulsion.

In the present work, the grafting onto polyethylene fiber was investigated in the emulsion solution of GMA. GMA was emulsified by sodium n-dodecyl sulfate (SDS) as a surfactant. In general emulsion polymerizations, the role of micelle size and its distribution, the morphology of particles and the surface characteristics have been considered crucially important. In novel emulsion graft polymerization, effect of surfactant concentration on degree of grafting was investigated and mechanism was considered.