Chuanbo Liu,Shutian Liu,Conglin Dong,Chengqing Yuan,Xiuqin Bai
Reducing the deformation of polymer matrix materials can decrease the fluctuation of coefficient of friction (COF), and friction-induced vibration and its amplitudes. HDPE composites with T-ZnOw as a fixed strengthening filler were modified with the addition of Si3N4particles at different concentrations. The COFs, wear rates, micro-morphologies, and friction-induced vibrations were obtained by conducting sliding tests against carbon steel balls in an aqueous environment at a low velocity and high load. The mechanism of the reduction in frictional fluctuation due to the addition of Si3N4particles was revealed through the frictional responses. The results demonstrated that 4 wt% addition of Si3N4in HDPE can enhance the strain–stress property and improve the lubrication by forming a lubricating film. Therefore, the surface deformation and the fluctuations of COFs and its vibrations were reduced. The aggregation phenomenon and reduced strain–stress response at a high concentration of Si3N4disrupted the positive fluctuating reduction, and resulted in a rough surface with severe tearing and cracking deformations. Additionally, it led to fluctuating wear behaviors with high COF and vibrations. The results obtained in this study can elucidate the effects of adding Si3N4particles to enhance lubrication in polymer composites. Additionally, the results provide a new research method for designing and manufacturing polymer-based composites with low friction-induced fluctuations.Keywords:HDPE composite;Si3N4;surface deformation;fluctuation reduction
In this research, a series of Eu 2 O 3 /B 4 C/HDPE composites containing micromorphology tunable Eu 2 O 3 submicron spheres as fillers are prepared for shielding neutron and gamma ray. The influence of microstructure of Eu 2 O 3 fillers on thermal stability, mechanical, and radiation shielding properties of composites are studied in detail. The growth process of Eu 2 O 3 precursor (Eu(OH)CO 3 ) follows the LaMer and Ostwald ripening mechanism. The FESEM reveal that the microstructure of synthesized Eu 2 O 3 is submicron sphere and the particle size decreases with addition of urea content in the reactant solution. HRTEM and SEAD images reveal that the overall crystal morphology of the Eu 2 O 3 fillers is polycrystalline. BET analyses reveal that the hysteresis loops of nitrogen adsorption-desorption isotherms changes from Type H1 to H3 after Eu 2 O 3 fillers are ball-milled, which is attributed to the suppression of nanoparticle agglomeration by ball milling. The FESEM images and EDS mapping of the fracture surfaces of the composites reveal that Eu 2 O 3 fillers are evenly distributed in the HDPE matrix. It is revealed that under the condition that the agglomeration of the nanoparticles is effectively suppressed, the higher BET-specific surface area and smaller size of Eu 2 O 3 fillers are conducive to the various properties of the composites. The superior composite containing Eu 2 O 3 (R = 1:30)/B 4 C/HDPE has a 99.1 % neutron shielding rate with 15 cm thickness under a 252 Cf neutron source and a 73.1 % gamma shielding rate with 15 cm thickness under a 137 Cs gamma source.
The combination of synergistic agent with intumescent flame retardant (IFR) systems provides a promising way to prepare high performance IFR composites. In this study, the effects of the synthetic zeolite 4 A in combination with the IFR system consisting of ammonium polyphosphate (APP) and tris (2-hydroxyethyl) isocynurate (THEIC) on thermal degradation , mechanical properties , flame retardancy and char formation of high-density polyethylene composites were investigated by limiting oxygen index (LOI) measurement, cone calorimetry , scanning electron microscopy and laser Raman spectroscopy . The LOI value of HD/FR/Z-0.5 composite with an optimum content of 0.5 wt. % zeolite 4 A and 25 wt. % of total flame retardant reaches 26.3 %. A low loading of zeolite 4 A can improve the bench-scale combustion performance as determined by cone calorimetry, and promote the formation of more compact char residue with a highly graphitic structure. However, a low loading of zeolite in combination with the IFR system consisting of APP and THEIC produces no significant changes in mechanical performance.
Ling-yan Li,Shuang-lin Li,Yan Shao,Rui Dou,Bo Yin,Ming-bo Yang
In this work, Polyvinylidene Fluoride (PVDF)/polystyrene (PS)/high density polyethylene (HDPE) ternary blends displayed a core-shell structure where HDPE was the core, PS was the shell, and this core-shell system dispersed in PVDF matrix. Here, multiwall carbon nanotubes (MWCNTs) and ferroferric oxide (Fe 3 O 4 ) was incorporated. F-F composites with MWCNTs was in PS shell and Fe 3 O 4 was in PVDF matrix and E-F composites with MWCNTs was in PS shell and Fe 3 O 4 was in HDPE core were fabricated by melt blending. It was indicated that the core-shell morphology between PS and HDPE was well retained with the incorporation of Fe 3 O 4 and MWCNTs. Both the electrical conductivity of F-F and E-F composites were similar without no obvious change with the incorporation of Fe 3 O 4 . Composites with greater than 20 dB shielding effectiveness were easy to obtain. The highest SE we observed was for the F-F composite with 1 vol% Fe 3 O 4 and 1 vol% MWCNTs was 25 dB at 9.5 GHz, and the SE was over 20 dB in the whole measured frequency(X-band). The E-F composites with SE greater than 20 dB in X-band was at 2 vol% Fe 3 O 4 and 1 vol% MWNCTs. Such effective and lightweight nanocomposites were obtained, resulting from the synergetic effect of MWCNTs and Fe 3 O 4 nanoparticles .
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