PSI - Issue 40

S.N. Danilova et al. / Procedia Structural Integrity 40 (2022) 118–123 S.N. Danilova, A.A. Dyakonov, A.P. Vasilev, A.A. Okhlopkova / Structural Integrity Procedia 00 (2022) 000 – 000

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manufacturing of the products made of polymer-based composites, it is necessary to find efficient fillers based on natural raw materials and develop new technologies allowing to turn the natural compounds into a high-activity state. In this regard, mechanochemical methods of converting substance into a non-equilibrium metastable state have currently become widespread, particularly, in creation of PCM. These methods include mechanical activation, comprising a wide range of varied crushing equipment: planetary mills, disintegrators, attritors, etc. One of the common methods is the use of mechanical activation in a planetary mill attributable to low energy consumption and simplicity of this method. It is known that in case of mechanical activation, a solid particle is subjected to frictional and impact action of grinding media, which ensures structural homogeneity of the material and reduction of local stresses. Under the influence of mechanical forces, in the sublattices and lattices of solid bodies there occur defects, which intensify wettability of the surface layer with the binder matrix, thereby enhancing the adhesion. As a rule, in case of mechanical activation of the fibrous fillers, there occurs disintegration of particles into small fragments. As this takes place, the diameter of the fibers is not changing, and the length of the crushed fiber remains 10-20 times bigger than the diameter, but not less than the "effective length", i.e. the length is 10 times bigger than the diameter. In case of mechanical activation of UHMWPE, there occurs loosening of its particles and removal of the air from the free space of the spherical particles without change in the length of its macromolecules. The paper by Wannasri et al. (2009) is known showing the efficiency of mechanical activation of the original UHMWPE, in which the values of density, modulus of elasticity and Shore hardness number are increased after 20 minutes of mechanical activation. Due to a high elasticity of the UHMWPE macromolecules, the amount of specific energies during mechanical activation is not enough for breaking of carbon bonds (intramolecular), but can be sufficient for partial change of the supramolecular structure of the polymer (Selyutin et al. (2010)). Creation of active centers makes it possible to increase the speed of mutual diffusion between the PCM components, which enables better sintering. It is supposed that a mechanical co-activation of UHMWPE and BF will contribute to a homogeneous distribution of fiber particles in the polymer matrix with subsequent fixing of their position in the volume after hot pressing (Panin et al. (2010)). 2. MATERIALS AND METHODS As a target of research, GUR- 4130 UHMWPE was selected (Celanese, China) having a molecular mass 6.8·10 6 g/mole, density 0.93 g/cm 3 and crystallinity degree 61 %. BFs manufactured according to GOST ISO 1889-2013, with an average diameter of fibers 13-20 microns, linear density 68- 4800 tex and a true density ρ true =2.71 g/cm 3 were used as an enhancing agent for PCM. The joint mechanical activation of the PCM components was carried out in the planetary mill PULVERIZETTE-5 (FRITSCH, Germany) for 2 minutes and 20 minutes. Mixing of the composite components was carried out in a paddle mixer with a rotor speed of 1200 rpm. The specimens for the study were prepared using the hot- pressing technique at a temperature of 175°С and a pressure of 10 MPa with holding at the said temperature for 20 minutes with subsequent cooling to a room temperature. The mechanical properties of UHMWPE and PCM were studied using the Autograph AGS-J tensile testing machine (Shimadzu, Tokyo, Japan). The tensile strength and elongation at break were tested according to ASTM D3039/D3039M-14 at the moving gripper speed of 50 mm/min, the number of parallel tests for composite was six. The supramolecular structure of PCM was studied on the JSM-7800F scanning electron microscope (Jeol, Japan) with the X-MAX-20 attachment (Oxford Instruments plc., UK) in the secondary electron mode at an accelerating voltage of 1 – 1.5 kV. 3. RESULTS AND DISCUSSION Table 1 shows the results of examining the tensile strength, elongation at break and elastic modulus of UHMWPE and composites. It is evident from Table 1 that introduction of 2 wt.% BF into the polymer results in the increase of the tensile strength by 14 % and the elastic modulus by 7 % as compared with the original UHMWPE. When 0.5 wt.% of BF is introduced, a slight increase of the elongation at break occurs. In case of mechanical co-activation of the PCM components with the increase of the mechanical treatment time, the mechanical properties improve. It was found that the tensile strength in composites, which had been preliminarily mechanically activated for 20 minutes, has not