Mechanical,Thermal And Tribological Properties Of Multi-scale Carbon Filled Discontinuous Polyetherimide Composites

Polyetherimide?PEI?is a type of high performance engineering plastic.It not only has high strength and modulus,excellent thermal resistance and corrosion resistance,but also has good dimensional stability and processing performance,which is an alternative material to traditional metal.In order to expand the applications of PEI in engineering fields such as military equipment,aerospace,automotive,machinery and electronics,it is necessary to further improve the performance of PEI.In this thesis,with short carbon fiber?SCF?and expanded graphite?EG?as filler,SCF/EG/PEI composites with fixed totally filler conent of 30 wt%were fabricated with extrusion mixing and injection molding techniques.In addition,SCF/EG/PEI composites incorporated with 0.4 wt%one-dimensional carbon nanotube?CNTs?and 0.4 wt%two-dimensional craphene?GR?were further prepared.The effects of micron carbon and nano carbon fillers on the mechanical properties,friction and wear properties and thermal properties of PEI composite were systematically investigated.It is revealed that the addition of EG has a negative effect on the tensile and flexural strength of PEI composites,while the addition of SCF has a positive effect.At the same time,the addition of SCF and EG both has a positively effect on the Young's modulus and flexural modulus of the composite.When the content of SCF is 30 wt%,the PEI composite exhibits the maximum tensile strength of 161.69 MPa and maximum flexural strength of 266.59 MPa.While when the SCF and EG content both is 15 wt%,the Young's modulus and flexural modulus reach the maximum of 10.12 GPa and 16.06GPa,respectively.Because the reinforcement efficiency of the SCF and EG at low conent is higher than that at large content,without further modulus increase is observed when the SCF content is higher than 15 wt%.In addition,the fracture toughness of PEI composites is reduced by the incorporatio of EG,but which is enchanced with the incorporatio of SCF and reaches the maximum with the SCF content of 30 wt%.Although the mechanical properties of the PEI composite is reduced by the incorporatio of EG,it improves the wear resistance of the PEI composites.The lowest friction coefficient and specific wear loss of the PEI composites is achieved with the incorporatio of 30 wt%EG and 30 wt%SCF,respectively.The PEI composite with a friction coefficient of 0.22 and a specific wear loss of 1.85×10^-6 mm³/Nm is achieved by simultaneously incorporatio of 15 wt%SCF and EG.The coefficient of thermal expansion?CTE?of PEI composites is largly reduced by the addition of SCF and EG,and the reduction efficiency of SCF is better than that of EG.The thermal conductivity of PEI composites is colosely related with the incorporatio of EG,and without obvious thermal conducitivity change is observed with the incorporatio SCF.The glass transition temperature and thermal degradation rate of the PEI composites both decrease with the incorporatio of micron carbon fillers.The glass transition temperature decreases with the increasing of SCF content,and the thermal degradation rate is independent with the relative content of SCF and EG.The mechanical properties of the SCF/EG/PEI composites are remain stable after the incorporatio of CNTs or GR.The addition of CNTs and GR has little effect on the friction coefficient of the SCF/EG/PEI composites,but which results a certain reduction on the specific wear loss of the composites.Compared with one dimensional CNT,the two-dimensional GR has a larger specific surface area and better interface effect,which benefits the formation of transfer film during wear.Thus,the wear resistance of the SCF/EG/PEI composite incorporated with GR is better than that incorporated with CNT.The addition of CNTs and GR has an insignificant effect on the CTE of the SCF/EG/PEI composite,which indicates that the CTE of the composites depends mainly on the content of SCF and EG.With the existance of SCF,the thermal conductivities of SCF/EG/PEI composite are slightly reduced by the addition of CNTs and GR.However,for the PEI composite with only 30 wt%EG,the thermal conductivity of the composites is signficantly reduced with the addition of CNTs and GR,and the reduction caused by GR is significant than that caused by CNTs.It was revealed that the incorporatio of nano carbon fillers result in the agglomeratio of EG,and the EG agglomeratio caused by GR is severe than that caused by CNTs.Moreover,the glass transition temperature of the SCF/EG/PEI composite is slightly increased with the addition of CNTs,but the addition of GR cuased slightly reduction of the glass transition temperature.The thermal degradation rate of the SCF/EG/PEI composites remains stable with the addition of CNTs and GR.