Comparative study about the thermal stability and UV resistance of some paint layers for electro-energetic equipment
In order to determine the durability of polymer coatings using investigation techniques based on X-rays diffraction and combined techniques for thermal analysis (TG-DTA-DTG), were determined the changes of structure and of their thermo-oxidative characteristics (6 different paint types having different characteristics) after exposure to UV radiation (60W/m2 in range of 300-400nm). The experimental results, indicate that UV radiation induce different changes (function of the commercial type of any paint) of the investigated topcoat paint films respectively, increase of the crystallinity (and, implicit, of the fragility) function of the exposure dose, which was between 0,0005 and 0,0150%/Wh/m2.
Ageing behavior of acrylic polyurethane varnish coating in artificial weathering environments
Acrylic polyurethane varnish coatings were exposed in two artificial weathering environments produced by a fluorescent UV/condensation weathering device and a xenon lamp exposure and weathering equipment for different time periods. The ageing behavior of the coating was evaluated by using film thickness gauge, glossmeter, spectrophotometer, scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR) and electrochemical impedance spectroscopy (EIS). The results showed that the Xenotest protocol had a significant effect on the thickness loss and gloss. However, the yellow index measurements and low frequency impedance showed that greater degradation was caused by the UV exposure protocol. These findings were supported by the results obtained from FTIR analysis. In the two artificial weathering environments, the low frequency impedance modulus of intact coatings decreased exponentially with increase of ageing time, and correlated with the changes of other properties of ageing coatings, which can be used to predict coatings lifetime.
Structure-property relations of 55 nm particle-toughened epoxy
Abstract 55-nm rubber particles significantly toughened two epoxy systems without loss of Young’s modulus, tensile strength and glass transition temperature. Transmission Electron Microscopy (TEM) showed that the nanoparticles are uniformly dispersed in matrix and have blurred interface with epoxy. 5 wt% rubber nanoparticles increased the critical strain energy release rate ( G 1c ) of Jeffamine D230 (J230)-cured epoxy from 175 J/m 2 to 1710 J/m 2 , while the 10 wt% increased G 1c of diaminodiphenyl sulfone (DDS)-cured epoxy from 73 J/m 2 to 696 J/m 2 . This is explained by comparing the surface–surface interparticle distance and total particle surface of nanocomposites with those of composites. The higher the matrix stiffness, the more nanoparticles needed for toughening. Although the 10 wt% J230-cured nanocomposite showed a 50% larger size of stress-whitened zone than the 5 wt% J230-cured nanocomposite, the 5 wt% nanocomposite showed a higher toughness. These nanoparticles were found to pose barriers to the vibration of crosslinked matrix molecules, leading to higher glass transition temperatures. While the matrix shear banding caused by nanoparticle expansion and growth is the major toughening mechanism for the J230-cured nanocomposites, the matrix plastic void growth and deformation are most probably the major mechanisms for the DDS-cured system. Under tensile loading, the nanoparticles in the DDS-cured epoxy created fibrils of 100–200 nm in diameter and 3–5 μm in length. TEM analysis in front of a subcritically propagated crack tip showed a number of voids of 30–500 nm in diameter in the vicinity of the crack, implying that rubber nanoparticles expanded, grew and deformed under loading. Unlike conventional epoxy/rubber composites in which all of the rubber particles in the crack front cavitated under loading, only a portion of the nanoparticles in this study expanded to create voids. Huang and Kinloch’s model developed from composites was found not fit well into these nanocomposites.