Indian Journal of Fibre & Textile Research Vol. 35, March 2010, pp. 9-14 Plasma induced graft polymerization of acrylic acid onto poly(ethylene terephthalate) monofilament Bhuvanesh Gupta a , Ankita Srivastava, Navdeep Grover & Shalini Saxena Department of Textile Technology, Indian Institute of Technology, New Delhi 110 016, India Received 9 February 2009; revised received and accepted 28 July 2009 The graft polymerization of acrylic acid has been carried out on poly(ethylene terephthalate) (PET) monofilament to introduce carboxylic acid groups. The filament is treated with oxygen plasma for the introduction of peroxides and subsequently grafted with acrylic acid. The influence of monomer concentration, plasma exposure time and reaction temperature on the degree of grafting has been investigated. The grafted filament is subsequently immobilized with chitosan. ATR-FTIR confirms the immobilization of chitosan. The contact angle decreases from 72° for virgin PET to 38° for 180s plasma exposured sample, 42° for the grafted and 36° for the chitosan immobilized sample which shows significant improvement in the wettability. The surface topography of filaments is characterized by atomic force microscopy. Keywords: Acrylic acid, Graft polymerization, Plasma, Poly(ethylene terephthalate) 1 Introduction Plasma treatment has been found to be an extremely attractive way to modify the surface chemistry and morphology of polymeric materials 1 . The plasma modification may be carried out in the presence of specific gases, such as oxygen, argon, nitrogen, and hydrogen. This results in the generation of active species which can activate and modify the material chemistry depending on the nature of the gaseous medium 2-5 . An interesting aspect of plasma treatment is that the changes are confined to a depth of a few nanometers at the surface because of the low level of penetration. This opens up possibilities for producing a wide spectrum of surface chemistry with desired compositions. The most attractive feature of the plasma processing is that by exerting proper control over the exposure conditions, a tailored surface with desired chemical functionality and morphology may be produced 4 . Radicals are formed on the surface of the polymeric materials by plasma surface treatments, and some of them can initiate graft polymerization of vinyl monomers. These reactions have been recognized for a long time and applied for the surface modification of polymers such as polyesters 5,6 . However, plasma graft polymerization has not been considered as often as plasma surface treatments and plasma polymerization. This is because of the fact that the total reaction process involved in the plasma graft polymerization is much more complicated. However, the advantage of plasma graft polymerization is the durability of the properties of the modified surface. The surface characteristics enhanced by the graft polymerization do not change easily, while the properties caused by plasma surface treatments often suffer from the recession with aging. Plasma modification of poly(ethylene terephthalate) (PET) has been studied by several workers and changes in the physical behavior and surface morphology have been reported 7-17 . It was found that under oxygen environment, the surface acquired oxygen containing polar functional groups such as -C=O, -OH and -OOH. During storage, the treated films underwent significant surface reorganization, where both the time and temperature contribute to the increase in the contact angle 2,4 . The nature of plasma also has significant impact on the surface behavior. It has been observed that the surface morphological changes are more severe with low pressure plasma as compared to the atmospheric plasma treatment and have been visualized in terms of the contact angle measurements and the atomic force microscopy 18 . Friedrich et al. 6 studied ageing and degradation of PET in an oxygen plasma and observed that the degradation reactions of PET in an oxygen plasma displayed many similarities to photo- and thermo-oxidative degradation reactions. Plasma discharges have been extensively used as a means to modify the surface characteristics and to improve the blood compatibility of polymeric ______________________ a To whom all the correspondence should be addressed. E-mail: bgupta@textile.iitd.ernet.in