Curing behavior and cured film performance of easy-to-clean UV-curable coatings based on hybrid urethane acrylate oligomers

A novel hybrid-nanocomposite of polyacrylamide-TiO₂ (PAM/TiO₂) with nano-anatase particles was synthesized in two steps. Firstly, the surface of nano-anatase particles was modified by 3-methacryloxy-propyl-trimethoxysilane (TMSM) as coupling agent by sol?Cgel method. Secondly, the surface modified nano-anatase particles were grafted onto the acrylamide monomer (AM) as an organic phase by free radical polymerization. The spectral (Fourier transform Infrared spectroscopy) and thermal (TGA) methods, verified the participation of coupling agent, polymer and titanium dioxide (anatase) into the hybrid structure. The results also showed that the degradation temperatures and residual content were obviously higher in nanocomposite than those of pure polyacrylamide (PAM). Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM) studies proved that the nano-anatase particles have been uniformly encapsulated inside the nanocomposite sample containing 5wt% TiO₂. However, the agglomeration of nano-particles in the nanocomposite with 20wt% of TiO₂ was detected by atomic force microscopy (AFM) and dynamic mechanical thermal analysis (DMTA) studies. Thermo-mechanical properties of acrylamide homopolymer (PAM) and their nanocomposites were investigated by DMTA. The shifts in storage modulus and tan?? peaks were attributed to morphological changes in the nanocomposites with increasing the amount of inorganic nano-particles and their distribution in polymer matrix. Flocculation behavior of PAM and PAM/TiO₂ in two different level of titanates (i.e. 5 and 20wt% TiO₂) for 0.25wt% nano-clay suspension was evaluated using batch method. The adsorption results showed that PAM/TiO₂ have ability for interaction with clay particles by means of adsorption through electrostatic interaction, Vander Waals forces and hydrogen bonding. However, it was found that the flocculation efficiency of the pure polymer (PAM) and the hybrid-nanocomposite (5wt% TiO₂) is much better than that of its high concentration (20wt% TiO₂) in the hybrid. This flocculation behavior can be attributed to uniform distribution of nano-particles and agglomeration possibility in the case of low and high concentration level of titanate in hybrid nanocomposite, respectively.