Experimental and Prediction Study of Displacement-Rate Effects on Flexural Behaviour in Nano and Micro TiO2 Particles-Epoxy Resin Composites

Abstract

Epoxy resin composites with different weight fractions of TiO 2 microparticles (1%, 5%, 10%, 15%, 20%) and of TiO 2 nanoparticles (0.5%, 1%, 2%, 3%) were prepared. The particle size of the nanoparticles was averaged around 21 nm while the particle size of the micro TiO 2 particles was averaged around 0.2 µm. The morphology of the manufactured particulate composites was studied by means of scanning electron microscopy (SEM). The mechanical properties of both nanocomposites (21 nm) and microcomposites (0.2 µm) were investigated and compared through flexural testing. Furthermore, the effect of displacement-rate on the viscoelastic behavior of composite materials was investigated. The flexural tests were carried out at different filler weight fractions and different displacement-rates (0.5, 5, 10, 50 mm/min). The influence of TiO 2 micro-and nanoparticles on the mechanical response of the manufactured composites was studied. For micro TiO 2 composites, a maximum increase in flexural modulus on the order of 23% was achieved, while, in the nanocomposites, plastification of the epoxy matrix due to the presence of TiO 2 nanoparticles was observed. Both behaviors were predicted by the Property Prediction Model (PPM), and a fair agreement between experimental results and theoretical predictions was observed.Polymers 2020, 12, 22 2 of 13 in improving the mechanical properties of the composite. The lower the filler diameter, the higher the filler surface/contact area is. Thus, in case of micron sized particles, the size of the low-density interfacial region of the pure polymer surrounding the inclusion is higher, so that the contribution of the filler is reduced, concluding that the mechanical properties of the composite will not be improved that much [6]. On the contrary, the nanoparticles can fill up the weak regions within the epoxy resin, and thus increasing the filler-matrix interaction force. The increase of the extent interfacial region can significantly improve the mechanical properties of the epoxy/nanocomposite. However, the nanoparticles have a difficulty to disperse into the matrix, so it is crucial to find the proper manufacturing technique to improve particle dispersion within the matrix material. A technique that is commonly applied is the ultrasonic homogenization; however, as every technique has its disadvantages. More precisely, this technique decreases the gelling time of the epoxy resin [7][8][9][10][11].The mechanical response of particulate reinforced composites also depends on the rate of deformation. It was found that particulates increase the strain rate sensitivity concerning tensile modulus, but this sensitivity decreases when measuring yield strength [12]. The effect of strain rate on the flexural properties of some polymer matrix composites has been studied and, as it was found, the flexural modulus and flexural strength both increase linearly with the logarithm of the strain rate [13]. Furthermore, the strain-rate sensitivity seems to be slightly more pronounced in shear than in tension and comp...

Hydrothermal Aging of an Epoxy Resin Filled with Carbon Nanofillers

“…Also, the agglomerates formed at high nanofiller contents can be considered as micro-inclusions (not nano-) which, however, were dispersed into the bulk matrix individually (L = 1). Analogous results were provided for the elastic modulus and strength of the epoxy filled with nano-and microparticles of TiO 2 in [15]. In addition to that, when adding nanofillers into a polymeric matrix, due to their nano-dimensions, they could "enter" into the polymers' free volume preventing the polymerization procedure.…”

“…Property prediction model has been developed [15] for the estimation of the composite property-value variation with filler concentration (C f ) in particulate composites as well as with any parameter affecting its behavior, such as water absorption concentration, time of immersion, etc. For the model application, only two experimental points are required.…”

“…Thus, by following the same procedure as described in [15], the two coefficients characterizing the degree of adhesion K and degree of dispersion L can be rewritten as:…”

“…The reason for it can be associated to different induced effects of moisture and temperature on the structure and properties of the matrix/filler interphase. Obviously, owing to high surface area of the nanoparticles at high filler contents and, subsequently, high contact area between filler and matrix, almost all matrix material can be transferred into "modified matrix", i.e., interfacial material [15]. Thus, for the filled epoxy at 0.3 wt.…”

“…The aim of this work was to establish the effect of environmental exposure on the durability of neat epoxy resin and filled with carbon nanofillers, CNT, CNF, and hybrid nanofiller (HN), which was evaluated by performing mechanical and thermomechanical characterization during and after water absorption and/or thermal heating. The environmental effects (moisture and temperature) on the modulus of elasticity in bending (hereinafter, elastic modulus) were evaluated by using the property prediction model (PPM), which was previously successfully applied for the prediction of elastic modulus and strength of epoxy resin filled with micro-and nanoparticles of TiO 2 as a function of filler concentration [15]. In the current paper and for the first time, PPM was developed and applied as a function of duration of environmental aging.…”