LASER-INDUCED SURFACE GRAFTING OF 2-HYDROXYETHYL METHACRYLATE AND N-VINYL-2-PYRROLIDONE ONTO ETHYLENE-PROPYLENE RUBBER AS BIOCOMPATIBLE MATERIAL

Attempts have been made to provide hydrophilic sites onto the surface of ethylene-propylene rubber (EPR) by grafting 2-hydroxyethyl methacrylate (HEMA) and N-vinylpyrrolidone (NVP) onto the surface of this elastomer using CO2-pulsed laser as excitation source. The effect of benzophenone (BZP) and azoisobutyronitrile (AIBN) as photosensitizer upon the graft level has been evaluated. CO2-pulsed laser grafting of HEMA and NVP was found to be dependent upon the wavelength, repetition rate, and fluence of laser. Hydrophilicity of EPR increased upon grafting HEMA and NVP with CO2-pulsed laser. Surface characterization has been carried out using attenuated total reflectance infrared spectroscopy (ATR-IR), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA). IR-laser grafting of these monomers is not possible unless the system is irradiated by pulses with the wavelength corresponding to the either maximum absorption of monomer or sensitizer accessible to the laser equipment gain. As the absorption of EPR at these wavelengths is quite low, it is believed that depending upon the wavelength, either photosensitizer and/or monomer molecules are excited through an infrared multiphoton excitation (IRMPE) process above the dissociation energy leading to the decomposition of the excited molecules. Addition of a multifunctional acrylate (MFA) such as 1,1,1-trimethylolpropane-trimethacrylate (TMPTA) to the grafting system enhanced the graft yield. Poly(HEMA) grafted onto the surface of EPR by CO2 pulsed laser tends to form a fractal type of morphology. The shape and size of fractals depends upon both laser parameters and HEMA concentration. EDXA analysis showed the presence of ungrafted (hydrophobic areas) as well as hydrophilic sites (fractals) on the surface of modified samples. Finally, the bulk mechanical properties of EPR after being laser-grafted with HEMA or NVP did not change, as shown by DMTA.