The Construction Approaches And Properties Of Polyether Ether Ketone Composites With High Thermal Conductivity

With the rapid development of 5G,Internet of Things,artificial intelligence and other new technologies,intelligent electronic devices are developing in two directions:first,the integration of chips and modules is increasing dramatically and the power consumption is rising;second,the density of components and parts is increasing with the products becoming lighter and thinner.As a result,the contradiction between power consumption and dissipate the heat becomes more prominent.New thermal conductivity materials have become a hot topic in the industrial development.High thermally conductive plastics has the advantages of corrosion resistance,high specific strength,high toughness,fatigue resistance,easy processing,light weight and low cost.The preparation of high thermally conductive materials has become a hot spot.Under certain conditions,conductive polymer materials also have high electrical conductivity and electromagnetic shielding properties to meet harsh external environment.As a kind of engineering plastics with high performance,Polyether ether ketone(PEEK)is a kind of semi crystalline polymer.Because of its special molecular structure,it has good heat resistance,excellent strength and stiffness,and high chemical stability.However,due to the poor solubility,high processing temperature and high melt viscosity of PEEK,the mechanical properties of the composites will deteriorate sharply if high fillers content is only used to obtain some properties.In this thesis,the aim is to prepare high thermal PEEK based composites with electrical conductivity,electromagnetic shielding and mechanical properties.The thermal and electrical conductivity and electromagnetic shielding of PEEK composites was improved by improving the interfacial compatibility,selecting effective fillers and using new technologies.The main research contents can be divided into the following parts:(1)Hydroxyphenolphthalein type polyether ketone grafted carboxyl carbon nanotubes(PEK-C-OH-g-MWCNTs-COOH)was prepared by esterification to improve the interfacial compatibility between CNTs and PEEK and reduce the interfacial thermal resistance.For comparison,carboxyl carbon nanotubes(MWCNTs-COOH)and PEK-C-OH-g-MWCNTs-COOH filled with PEEK were simply blended to prepare MWCNTs/PEEK composites,respectively.The thermal conductivity of PEK-C-OH-g-MWCNTs-COOH/PEEK is 0.71 W/(m·K),which is206%higher than that of PEEK,while the thermal conductivity of 26.1wt%MWCNTs-COOH/PEEK is 0.52 W/(m·K)under the same content of carbon nanotubes.The conductivity of PEK-C-OH-g-MWCNTs-COOH/PEEK composite is better than that of MWCNTs-COOH/PEEK.The conductivity of 30 wt%PEK-C-OH-g-MWCNTs-COOH/PEEK is 3.0 S/m,while that of 26.1 wt%MWCNTs-COOH/PEEK is 1.3 S/m under the same content of carbon nanotubes.The electromagnetic shielding effectiveness of PEK-C-OH-g-MWCNTs-COOH/PEEK composite is better than that of MWCNTs-COOH/PEEK.The electromagnetic shielding effectiveness of 30wt%PEK-C-OH-g-MWCNTs-COOH/PEEK is 22.9 dB(8.2GHz),while the electromagnetic shielding effectiveness of 26.1wt%MWCNTs-COOH/PEEK is 17.4 dB(8.2GHz)with the same content of carbon nanotubes.(2)In order to improve the electrical conductivity,electromagnetic shielding effectiveness and mechanical properties of the composites,we selected carbon fiber(CF)with excellent mechanical properties,and plated nickel metal on the surface of carbon fiber to the surface modification of carbon fiber,improving the surface activity of carbon fiber and the compatibility with PEEK.The conductivity of 40wt%Ni-CF/PEEK composite is 1.9×10~4 S/m,and its electromagnetic shielding effectiveness is 29dB(8.2GHz).The thermal conductivity of Ni-CF/PEEK composite is also improved.When the Ni-CF content reaches 40wt%,the thermal conductivity of Ni-CF/PEEK composite is 0.59 W/(m·K),which is 1.54 times higher than that of PEEK.The bending strength and tensile strength of 40wt%Ni-CF/PEEK composite is268.14 MPa and 150.56 MPa,respectively.(3)In order to further improve the thermal conductivity of PEEK composite,we selected three kinds of carbon nanotubes:Whisker-CNTs(Wh-CNTs),common MWCNTs(c-MWCNTs and s-MWCNTs),and added them into PEEK matrix by melt mixing method.It was found that Wh-CNTs was an ideal single filler to improve the thermal conductivity of PEEK composites.At 10wt%Wh-CNTs loading,the thermal conductivity of the PEEK composite is 0.741 W/(m·K),which is much higher than that of pure PEEK(0.232 W/(m·K).This is mainly due to the high crystallinity,less defects and easy dispersion of wh CNTs,which reduces the interfacial thermal resistance between Wh-CNTs and PEEK matrix.In addition,PEEK/Wh-CNTs composites were prepared by wet mixing method.Because the aspect ratio of carbon nanotubes is maintained during wet mixing process and the carbon nanotubes are more easily dispersed,the PEEK/Wh-CNTs composites have higher thermal conductivity(1.066 W/(m·K),out of plane and 1.50 W/(m·K),in plane)than PEEK/Wh-CNTs composites prepared by melt mixing and dry mixing.When the content of CNTs is 30wt%,the out of plane thermal conductivity of the wet mixed PEEK/Wh-CNTs composite can reach 2.09 W/(m·K),while the in plane thermal conductivity can reach 3.82 W/(m·K).Compared with PEEK,the thermal conductivity of the PEEK composites increased by 8 times and 15.5 times,respectively.The experimental results of in-plane thermal conductivity of PEEK/Wh-CNTs composites are in good agreement with the Nan model when the content of CNTs is less than 10wt%.When the content of CNTs exceeds 10wt%,the in plane thermal conductivity of the PEEK composites is more consistent with the Nan model.The PEEK/Wh-CNTs composite prepared by wet mixing method also has excellent electromagnetic shielding performance.When the filler is 10wt%,the electromagnetic shielding performance of the composite with thickness of 0.6mm is21.5 dB.(4)We prepared LIG by laser-induced PEEK sheet.In air,PEEK was decomposed,carbonized and graphitized to form three-dimensional porous graphene.This viewpoint was verified by Raman,SEM,TEM,XPS and XRD.The conductive and electromagnetic shielding properties of PEEK sheet induced by laser are good.At15%power,the highest value of material conductivity is 1.19 S/m,and the electromagnetic shielding effectiveness is 12.4 dB at 8.2 GHz.The laser-induced CF/PEEK sheet also shows excellent conductivity,thermal conductivity and electromagnetic shielding properties.When the carbon fiber content reaches 20wt%,the conductivity of LIG can reach 10.7 S/m,and the thermal conductivity can reach0.42 W/(m·K),which is 23.5%higher than before.At 8.2 GHz,the electromagnetic shielding effectiveness of CF/PEEK composites is 16.8 dB,which is 3.4 dB higher than before.