Studying the Influence of Mica Particle Size on the Properties of Epoxy Acrylate/Mica Composite Coatings through Reducing Mica Particle Size by the Ball-Milled Method

In this work, a series of epoxy acrylate (EA)/mica composite coatings were synthesized through introducing mica powders of different particle size into epoxy acrylate coatings and using an ultraviolet (UV) curing technique to investigate the influence of mica particle size on the coatings. Mica powders of different particle sizes were obtained by ball-milling for 4, 8, 12, 16, and 20 h with a planetary high-energy ball mill. The particle size and morphologies of ball-milled mica powders were characterized by laser particle size analyzer and scanning electron microscopy (SEM). The results indicated that planetary ball-milling reduced the particle size of mica powders effectively. Mica powders that were un-ball-milled and ball-milled were added into the epoxy acrylate matrix by a blending method to synthesize the organic-inorganic UV curable coatings. The optical photographs of the coatings showed greater stability of liquid mixtures with smaller particle size fillers. The chemical structures of EA/mica composite coatings were investigated by Fourier transform infrared spectroscopy (FTIR), and the conversion rate of C=C bonds was calculated. The results indicated that the C=C conversion of coatings with mica powders of smaller particle sizes was higher. Tests of mechanical properties and tests using electrochemical impedance spectroscopy (EIS) showed that pencil hardness, impact resistance, and coating resistance were improved due to the reduction of mica powders particle size.

KINETICS OF FORMATION AND PROPERTIES OF PHOTOCURED SIMULTANEOUS EPOXY-ACRYLATE IPNS WITH THE PREVAILING CONTENT OF AN EPOXY COMPONENT

The distinct features of UV induced polymerization of epoxy-acrylate blends leading to the formation of simultaneous interpenetrating polymer networks (IPNs) have been studied. Different ratios of components within a prevailing content of an epoxy one have been used for the synthesis. Such a content of epoxy monomer is required to create a barrier preventing oxygen diffusion into a curing sample. It allows retardation of the well-known oxygen-inhibition effect, which acrylate monomers are susceptible to. Hence, the conduction of their polymerization in open-air conditions is possible. The proceeding of the polymerization reactions of acrylate (TEGDM) via free radical mechanism and of epoxy (UP-650D) via cationic one have been monitored by FTIR-spectroscopy. Namely, the conversion degrees have been calculated for double bonds of TEGDM and for epoxy groups of UP-650D respectively. A mixture of triphenylsulfonium hexafluorophosphate salts, which is capable of generating both free radical and cationic reactive species, have been used as a single photoinitiator for the formulations being investigated. Almost complete conversion of acrylate double bonds was reached after 60 min of UV irradiation irrespective of epoxy content. On the contrary, conversion of epoxy groups of aliphatic epoxy, which is known to be rather unreactive towards cationic photopolymerization, when mixed may be either higher or lower compared to the neat epoxy network. Such results are attributed to dual influence of acrylate network on the formation of epoxy one. Firstly, cationic polymerization of epoxy component is sensitized by acrylate macroradicals in terms of free radical promoted cationic polymerization. On the other hand, the mobility of epoxy macrocations is restricted by the rapid build-up of acrylate network. At the weight ratio of UP-650D and TEGDM 70/30 the sensitizing effect of acrylate is revealed to be dominant, so the given composition may be considered as optimal. Regardless of low conversion of epoxy groups, the content of the estimated gel fraction is high, and the epoxy component is found not to be leached in the process of extraction in acetone. Furthermore, physicomechanical properties of obtained UV-cured IPNs have been investigated. The results of the measurements, namely, impact resistance by the Gardner test, crosshatch adhesion test to different substrates (including silicon), and accelerated weathering test in a climatic chamber, show that all the samples exhibit good operational properties essential for effective protecting coatings of outdoor exposure.