Preparation of Scratch and Abrasion Resistant Polymeric Nanocomposites by Monomer Grafting onto Nanoparticles, 3. Effect of Filler Particles and Grafting Agents

Abstract

After modification with different trialkoxysilanes, nano-sized silica and alumina particles were used as fillers in transparent UV/EB curable acrylates for polymer reinforcement, particularly to attain scratch and abrasion resistant coatings. The acid catalyzed condensation of the organosilanes forms a polysiloxane shell which covers the nanoparticle like a nanocapsule. CP MAS NMR spectroscopy and MALDI-TOF mass spectrometry proved to be useful for the characterization of the polysiloxane structures. Grafter oligomers with more than 20 monomeric units were observed. Nanoparticles modified by methacroyloxy(propyl)trimethoxysilane and vinyltri-methoxysilane can copolymerize with acrylates. Compared with the pure polymers, these crosslinked polyacrylate nanocomposites, containing up to 35 wt.-% silica, exhibit markedly improved surface mechanical properties. Promising scratch and abrasion resistance of radiation-cured nanocomposite materials were also obtained by propyltrimethoxysilane grafting which results in an organo-philation of pyrogenic silica. Both colloidal and pyrogenic nano-sized silica nanopowders were used as fillers in polyacrylate films. The concentration of colloidal SiO 2 in commercial acrylate formulations amounts up to 50 wt.-%, whereas pyrogenic silica, notwhithstanding their surface modification by silanes, results in a thickening effect which limits its content to about 35 wt.-%. Never-theless, a comparison showed a distinct improvement in the surface mechanical properties such as haze and diamond microscratch hardness for surface-modified pyrogenic silica.