Radiation grafting of styrene onto polypropylene fibres by a 10 MeV electron beam

https://doi.org/10.1016/j.radphyschem.2006.05.009Get rights and content

Abstract

The radiation-induced graft copolymerization is an effective method for modification of the chemical and physical properties of polypropylene. Graft copolymerization of styrene onto polypropylene fibers has been studied by simultaneous irradiation method, using a 10 MeV electron beam. Samples were irradiated in an environment of nitrogen gas. The effects of radiation dose and styrene concentration in methanol, on the grafting yield were investigated. The effects of polyfunctional monomer, i.e., trimethylopropane trimethacrylate (TMPTMA) and acid (sulfuric acid) on the grafting yield were also examined. The grafted samples were then sulfonated and allowed to react with solution of a basic dye. The samples were characterized by mechanical properties and thermal stability. The mechanical properties of the radiated samples were reduced and the grafted samples had lower mechanical properties.

Introduction

Radiation-induced graft copolymerization has been used to modify the properties of polymeric materials. This method is applicable for many polymer/monomer combinations and unlike chemically initiated grafting, there is no contamination from initiators. Graft copolymerization takes place as a result of the formation of active sites on the polymer backbone. The active sites may be free radicals or ionic chemical groups, which initiate polymerization reaction. The formation of active sites on the polymer backbone can be carried out by several methods such as plasma treatment (Wavhal and Fisher, 2002) , ultraviolet (UV) light radiation (Choi et al., 2003), decomposition of chemical initiator (Xu and Wang, 2002) and high-energy radiation (Mazzei and Tadey, 2003).

There are essentially two basic methods for radiation grafting:

  • 1.

    Simultaneous method. Also sometimes called as mutual method. The polymer substrate is immersed in the monomer, which may be a liquid, vapour or diluted with solvent and may contain additives, and then exposed to ionizing radiation.

  • 2.

    Pre-irradiation method ( post-irradiation grafting). In this method, the polymer substrate is first exposed to ionizing radiation in vacuum or under an inert atmosphere to generate radicals before being exposed to a monomer (Nasef and Hegazi, 2004).

Radiation technique is a strong method for modifying the polymer structure by graft copolymerizing various monomers on different polymeric substrates like polycarbonate (Aliev et al., 2000), ethylene vinyl acetate (Ringrose and Kronfli, 1999), cellulose triacetate (Mazzei et al., 2002), fluoropolymers (Dargaville et al., 2003), PE (Hegazy et al., 1999) and PP (Bucio et al., 1998) useing as substrates.

Many monomers had been grafted onto polypropylene such as styrene (Mazzei and Tadey, 2003), acrylic acid (Chen et al., 2004), acryl amid (Chen et al., 1999), methyl methacrylate (Lopergolo et al., 2000), 2-vinyl pyridine (Kaur et al., 1999), and 2,3-epoxypropyl methacrylate (Nho et al., 2002).

Mazzei et al.(2002) studied radiation grafting of styrene, acrylic acid and methyl methacrylate monomers onto PP foils irradiated with a 25 MeV proton beam. They showed the grafting yield of acrylic acid, methyl methacrylate and styrene as a function of proton fluency and dose. With increase in the radiation dose, up to almost 200 kGy , the graft yield increased with a high rate and after that the rate of increase slowed down then reached a plateau (Mazzei and Tadey, 2003).

Gamma rays was employed to graft copolymerize acrylamide onto PP film by preirradiation grafting. Hydrophobicity or hydrophilicity is greatly influenced by type of solvent used for grafting media. It was shown that the water contact angle of PP film grafted in the presence of water was much lower than in the presence of acetone. The blood compatibility of the grafted PP films was evaluated by the determination of platelet adsorption and thrombus. The blood compatibility of grafted PP films was better than that of original PP films (Chen et al., 1999). Preirradiated (gamma rays) isotactic polypropylene (IPP) powder has been modified by grafting with 2-vinyl pyridine and styrene in an aqueous medium. Maximum grafting percent of 2-vinyl pyridine (180%) and styrene (117%) was obtained under optimum conditions (Kaur et al., 1999).

Lopergolo et al. have grafted methyl methacrylate onto polypropylene fibres. They reported that the direct method showed much higher efficiency over the preirradiation one (Lopergolo et al., 2000). Nho et al.(1999) reported graft polymerization of styrene onto preirradiated PP fabric using gamma rays. The samples irradiated in nitrogen gas gave a much higher grafting yield than those in air. The addition of sulfuric acid and polyfunctional monomer in the grafting solution enhanced the grafting yield significantly (Nho et al., 1999).

In this work, the effect of electron beam radiation on graft copolymerization of styrene onto polypropylene fibers by a simultaneous method is investigated. The effect of the radiation dose and styrene concentration on grafting yield was studied in the styrene–methanol system. The effect of the additives such as acid and polyfunctional monomer on the grafting yield was also investigated. The grafted samples sulfonated and then allowed to react with solution of a basic dye. The samples were characterized by their mechanical properties (tensile strength) and thermal stability in each section of the process.

Section snippets

Materials

Commercial polypropylene BCF yarn of 1600 dTex (Iran Risse Co. Ltd.) was used as a substrate for the grafting reaction. Styrene (Merck), methanol (Merck), trimethylopropane trimethacrylate (TMPTMA) (Aldrich) and sulfuric acid (Merck) were used. Styrene monomer were freed from inhibitor using aluminum oxide (basic) column. Other chemicals were reagent grade and were used without further treatment.

Equipments

The electron beam (EB) irradiation was carried out under a rodotron TT200 electron accelerator with

Results and discussion

The grafting and sulfonation were verified by Fourier transform infrared spectroscopy (FTIR). Fig. 2(a)–(c) show FTIR spectra of non-irradiated PP, grafted PP and sulfonated samples, respectively.

The peaks above 3000 cm−1 in the spectrum of grafted PP sample (Fig. 2b) are characteristic for C–H groups of double bond. Also the peaks at 1425, 1583 and 1600 cm−1 represent t he presence of Cdouble bondC bond in benzene rings of the grafted pp-styrene fibers. The broad band about 3500 cm−1 in FTIR spectrum of the

Conclusion

Electron beam radiation decreases the mechanical properties of polypropylene fibers. Maximum grafting yield is achieved at concentration of 80% (styrene in methanol). Acid and polyfunctional monomers caused an increase in grafting yield. The inclusion of sulfuric acid and TMPTMA had a synergic effect. Sulfonation had a very destructive effect on the mechanical properties of the fibers. Polypropylene fibers basic dye absorption (K/S) was increased by increasing of sulfonation and grafting yield

Acknowledgements

One of the authors (A.V.) wishes to acknowledge the kind cooperation of Yazd Radiation Processing Center (YRPC).

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