Preparation And Properties Of Graphene/polypropylene Composites Assisted By Supercritical CO₂

Due to its excellent strength,thermal conductivity and electrical conductivity,graphene has become a research hotspot.However,due to the van der Waals force between graphene sheets,it is difficult to separate them,which has certain influence on the preparation process and limits its good application.Previous studies were only limited to the preparation method of graphene or directly purchasing graphene with many sheets to fill the polymer.The preparation of graphene/polypropylene composites was innovated with the help of supercritical fluid.The effects of graphene addition,supercritical CO2 system and processing temperature on the properties of composites were studied.The mechanical properties,thermal stability and crystallization properties of the composites were tested and analyzed,and reference for the industrial production of graphene/polypropylene composites were afforded.The subject content and conclusion are divided into several points.(1)To research the influences of supercritical CO2 system for stripping graphite,explored the best infiltration process conditions,the results show that by setting the different condition such as temperature,pressure and infiltration time,under the saturation temperature of 85?,graphite,stripped of best quality,layer separation is more obvious,multilayer distributed state.With the increase of the wetting pressure and the extension of the wetting time,the spacing between sheets was the most obvious,and the degree of graphite stripping was also enhanced,and the content of graphene was also increased.(2)Explores the extruder different processing temperature effect on the properties of graphene/polypropylene composites,the results show that after adding 3wt%flake graphene,the crystallization of the composite material of curve moves to the right,obviously higher crystallization temperature,the peak,the crystallization is also becoming more narrow and steep,the melting enthalpy change of the composite increased from pure PP system 51.81 J/g to 93.48 J/g,crystallization system more fully.With the increase of composite materials processing temperature,crystallization temperature rise after lower first,crystallinity increase with the decrease of the first,the sample of the thermal decomposition ability gradually improve,thermal stability,the thermal decomposition rate of maximum corresponding temperature increasing,tensile strength and bending strength of composite slow first increases and then decreases,the highest temperature of 200? when processing,the maximum tensile strength and bending strength were 37.29 MPa and 45.7 MPa.The elongation at break of composite material increases gradually,and the isotropy of composite material changes little with the increase of processing temperature,indicating that the change of processing temperature has little influence on the isotropy of polypropylene.In order to make the composite material's comprehensive performance prominent,the extrusion processing temperature of composite material was selected as the experimental group of 200?,205?,210? and 210?,so as to provide better experimental processing temperature for subsequent experiments.(3)Using the same process flow and the best processing temperature,to explore the system of supercritical CO2 on the influence of the preparation of graphene/polypropylene composite material performance,the results show that adding graphene,the thermal stability of PP,and treated by supercritical CO2 composites have better thermal stability,PP thermal weight loss rate of maximum temperature from 459.6? to 466.7?.The tensile strength and bending strength of graphene composites were improved by the filling of graphene.Compared with the non-wetted composites,the tensile strength and bending strength of the composites impregnated by supercritical carbon dioxide increased from 33.04MPa to 35.82MPa,32.50MPa to 40.75MPa,respectively.The tensile strength increased by 8.4%,and the bending strength increased by 25.4%.The addition of graphene reduced the impact strength of the composite material from 22.56kJ/m2 to 8.04kJ/m2.Compared with the unsaturated composite material,the impact strength of the composite material after supercritical CO2 infiltration and stripping treatment was reduced to 7.20kJ/m2.That was down 64.4 percent and 10.4 percent,respectively.