18 TH INTERNATIONAL CONFERENCE ON COMPOSITE MATERIALS STRENGTH PREDICTION OF EPOXY NANOCOMPOSITE G. A. Forental*, S. B. Sapozhnikov Physics Dept., South Ural State University, Chelyabinsk, Russia * G. A. Forental (forental@newmail.ru) Keywords : epoxy resin, nanoparticles, strength, analytical model type mill (cooling of vessels with compound by cold 1 Introduction water) and is not changed during the process of Addition of micro- and nanoparticles to polymer mixing. material allows getting composite with improved Mixture time was chosen after series of experiments characteristics as strength, durability, thermal which was taken in two stages. The first stage is conductivity, moisture absorption and etc. careful observation of mixture (homogeneity without Nanometer-scale filler allows increasing the strength visible agglomerates). The second stage is devoted of polymer materials by 20 − 25% [1 − 4]. However, to control of compound viscosity. Viscosity was the strength of composite begins decreasing on measured with rotational viscometer Brookfield R/S reaching of certain volume fraction of particles. The plus during the process of mixing. Addition of fine model which can describe the non-monotone filler to resin leads to increasing the viscosity of dependence of strength of epoxy nanocomposite on compound. This process is asymptotical in time volume fraction of filler is suggested in present scale. The mixing time was stated when the viscosity work. of the mixture had become the maximum value. Effects of strength increase, increase of modulus of After mixing of epoxy resin with nanoparticles the elasticity and other properties are bound up with hardening agent was added to this compound agglomerates of nanoparticles and the shape of these 2 minutes before the end of mixing. Epoxy resin agglomerates. As shown in the work [4, 5], the creates the layer around every particle and has shape of particle agglomerates dictated the shape of sufficiently high viscosity which hinders from the a majority of crosslinked epoxy domains. sedimentation of particles. Then it is possible to There was introduced an interface layer around avoid the return agglomeration of nanoparticles particles, and assumed that thickness of this layer adding the hardening agent. does not depend on the size of particles in works The samples were cured in open forms under room [6, 7]. The presence of this layer explains breaking temperature during 12 hours. Then thin films were mixture laws of density of polymers in presence of cut out of prepared samples using microtome. The fillers. thickness of films was about 200 nm. The results of use of transmission electron microscopy are presented in the figure 1 а . It is easy 2 Electron microscopy of nanocomposite to see the nanoparticles of silicon oxide create the elongate structures of different sizes (from 40 till To analyze the structure of nanocomposite and the 150 nm) − the long chains of nanoparticles. We can distribution of particles into polymer the electron say here that creation of these long structures inside microscope (JEOL GEM-2100) of nanocomposite nanocomposite is the main goal of good mixing. was used. As is shown in work [8], the filling of polymer with The samples were made of epoxy resin, room nanoparticles increases the nanocomposite strength. hardening agent − polyethylene polyamine and filler At that the transmission electron microscopy results − nanoparticles of silicon oxide (average diameter show that the dispersed phases in the 9 nm) with volume fraction V = 1%. nanocomposites are much larger than the size of the Epoxy resin and nanoparticles were mixed using primary nanoparticles of silicon oxide. And the planetary-type mill AGO-2U under temperature agglomerates of nanoparticles have the elongate 25 С during 20 minutes, and then prepared mixture form. In the figure 1b the results are presented for was vacuumized. The temperature of mixing is polypropylene filled grafted nanoparticles of silicon determined the operating conditions of planetary-
oxide (nanoparticles were coated with polystyrene, fraction V e and the filler volume fraction V are average size of nanoparticles − 7 nm). connected with the constant k : . V k V (2) e 3 Determination of the properties of interface In this case the modulus of elasticity of layer nanocomposite can be calculated using empirical To determine the strength of nanocomposite here we law, eq. (3), which allows finding out the modulus use the idea of interface matrix layer around particle. of elasticity of composite with rigid macrofiller [9] The properties of interface layer are determined taking into account effective volume fraction, using two groups of experiments: measurement of eq. (2): density and modulus of elasticity of nanocomposite E with different volume fraction of filler. In order to 3,0 V , e e (3) determine the propertied of this specific layer the E m following admissions were introduced: the particles where E – the modulus of elasticity of filled of filler are equal and spherical, have known polymer; E m – matrix modulus of elasticity. diameter and volume fraction, and are situated at the In order to determine the density and thickness of cube corners. The interface layer has constant interface layer, and constant k the experiments were thickness around every particle. The properties of conducted using samples made of room hardening particles, interface layer and matrix are constants (it epoxy resin filled with nanoparticles of silicon oxide is obvious the interface layer does not have abrupt (average diameter 70 nm), volume fractions change to matrix as layer and matrix have the same V =0… 4 %, hardening agent − polyethylene nature. However, the considerations of simplicity polyamine. Mixing and curing technology were the force us to use this model of the piecewise function same one as discussed in the chapter 2. of polymer properties). The samples of epoxy nanocomposites with different The composite density is determined as the function volume fraction of filler had sizes 25 × 5 × 2 mm and of component properties, eq. (1): were tested by cyclical tension using dynamic , V V V 1 V V , (1) mechanical analyzer (DMA 242C, Netzsch). p l l m l Frequency of cycling was 1 Hz, load amplitude – where δ – interface layer thickness; V – nanoparticle 1 N, average load – 0.8 N. Temperature was varied volume fraction ; ρ p – density of nanoparticles ; ρ l – from 25 till 40 С . 3 Experimental and calculated values of relative 2 – interface layer density; 1 1 V V modulus of elasticity are shown in the figure 2 l d (points – experiments, line – calculation by eq. (3) layer volume fraction; d – nanoparticle diameter , ρ m for k= 2.89). – bulk matrix density. The nanocomposite density was measured using the Two parameters can change: density and thickness method of submergence into distilled water. of interface layer. If we use the assumption of low Experimental results and theoretical function of density of layer ( l 0), then the thickness of layer density of epoxy nanocomposite versus volume will be about 3 nm. If l =0,55 m the thickness is fraction of nanoparticles are shown in the figure 3 about 6 nm. So there is uncertainty which can be (points – experimental mean values, line – solved using additional information. It can be the calculation by using eq. (1) for k= 2.89). elastic modulus of nanocomposite. In this case the thickness of interface layer is The interface layer is formed by radial oriented δ=14.9 nm and density – ρ l =0.98 g/cm 3 . These molecules of polymer which were created during values of characteristics of layer will be used below thermally induced curing process near surface of to define the strength of nanocomposite. particle and it gives high modulus of elasticity of this layer. In this case it is possible to couple formally this layer with filler because the modulus of elasticity of such layer is much higher than the matrix modulus. The effective volume fraction of such couple is higher than volume fraction of only nanoparticles. For known diameter of particles and thickness of interface layer the effective volume
Recommend
More recommend
