Carbon Fiber Reinforced Polyamide 46 Composites with Low Water Absorption and Excellent Wear Resistance

Author:Ran Jin Cheng

Supervisor:zeng xing rong


Degree Year:2019





Polyamide(PA)is one of the five general engineering thermoplastics.It is widely used in electronic and electric,automotive,machinery,medical apparatus,as well as sports equipment,because of its excellent mechanical properties.In recent years,with the increasing performance requirement for engineering materials in the modern industrial field,the demand for engineering plastics with high temperature resistance has sharply expanded.Polyamide 46(PA46)is one of the few commercialized heat resistant nylons.It has a promising application prospect because of its high melting temperature,high crystallinity and good wear resistance.However,its water absorption is high due to the relatively high content of amide group in its structure.When being used in humid environment,its strength decreases greatly and the dimensional stability is worsen,which severely limits its further application.Accordingly,how to effectively reduce the water absorption,simultaneously improve the mechanical properties,wear resistance,heat resistance and flame retardancy of PA46composites has become the key issue needed to be addressed urgently.Poly(2,6-dimethyl-1,4-phenylene oxide)has low water absorption,good heat resistance and dimensional stability,which is usually utilized in the PA modification.In this work,PA46based composites with low water absorption and excellent wear resistance were prepared by melt blending via a twin screw extruder.Maleic anhydride grafted modified poly(2,6-dimethyl-1,4-phenylene oxide)(PPOG)was employed to reduce the water absorption of PA46,as well as organically modified nano-zirconium phosphate(FZrP)and polyurethane coated carbon fibers(PCF)were served as the reinforcing filler.The water absorption,mechanical properties,heat resistance,tribological properties and other performance of the composites were studied.The main contents and results are as follows:(1)The effects of PPOG on the water absorption,mechanical properties,flowability,heat deformation temperature(HDT),friction and wear properties of PA46 were investigated.It was found that PPOG could greatly reduce the water absorption of the PA46/PPOG composite.When the content of PPOG was 10 wt%,the water absorption of the composite decreased from 4.67%to 2.64%,and the composite retained the good mechanical strength,flowability and heat resistance.Scanning electron microscopy(SEM)results showed that PA46 and PPOG had a good compatibility.PPOG was uniformly dispersed in the PA46 matrix in small size.(2)Zirconium phosphate(ZrP)was first synthesized via hydrothermal method,and then decorated byγ-aminopropyltriethoxysilane(KH-550)to obtain an organically modified nano-zirconium phosphate(FZrP).Subsequently,PA46/PPOG/FZrP nanocomposites were prepared by melt blending.FZrP was characterized by water contact angle(WCA),SEM and X-ray diffraction(XRD)and other methods.The results showed that KH-550 significantly decreased the hydrophilicity of ZrP,and ZrP was exfoliated to thin nanosheets.FZrP remarkably improved the wear resistance and mechanical properties of the PA46/PPOG composite,and decreased its water absorption.With the incorporation of 2 wt%FZrP,the friction coefficient and wear volume of the PA46/PPOG composite were decreased from 0.53and 12.4 mm~3 to 0.23 and 0.7 mm~3,respectively.The tensile strength,flexural strength and impact strength increased from 81.9 MPa,127.3 MPa and 9.3 kJ/m~2 to 94.4 MPa,139.0 MPa and 12.7 kJ/m~2,respectively.The water absorption decreased from 2.64%to 2.43%.The SEM and energy dispersive X-ray spectrometry(SEM-EDX),X-ray photoelectron spectroscopy(XPS)and XRD results of the wear surface and debris suggested that,thanks to the strong interfacial interaction between FZrP nanosheets and the matrix,FZrP was difficult to be peeled off.During the wear process,FZrP retained and accumulated on the wear surface,thus forming a protective layer with good strength and lubricity on the surface.Therefore,the friction coefficient and wear volume decreased significantly.(3)The effects of polyurethane coated carbon fiber(PCF)on the water absorption,mechanical properties,thermal properties,friction and wear properties of the PA46/PPOG composites were studied.It was found that,the mechanical properties,heat resistance and wear resistance of the PA46/PPOG composites were greatly increased by PCF.The thermal conductivity was enhanced and the water absorption decreased in some extent.When the PCF content was 40 wt%,the tensile strength and flexural strength of the PA46/PPOG composite were increased from 81.9 MPa and 127.3 MPa to 282.5 MPa and 411.6 MPa,respectively.The wear volume was decreased from 12.4 mm~3 to 0.56 mm~3.When the PCF content was 20wt%,the composite had the highest impact strength,which increased from 9.3 kJ/m~2 to 15.1kJ/m~2.The SEM results showed that PCF had a good compatibility and interfacial interaction with the PA46/PPOG matrix,thus remarkably improved the mechanical properties.Laser Raman spectroscopy(LRS)result showed that during the wear process,some PCF was graphitized,and a lubricant layer was formed,which reduced the direct contact of the friction surface,thus decreased the friction coefficient.Therefore,the wear resistance of the composites was remarkably improved.Differential scanning calorimetry(DSC)and thermogravimetric analysis(TGA)results showed that PCF could improve the crystallinity and the heat resistance of the PA46/PPOG composites.When the amount of PCF was only 10wt%,the HDT of the composite as high as 281 ~oC,which was 110 ~oC higher than that of PA46/PPOG.(4)The PA46/PPOG/FZrP/PCF composites with low water absorption and excellent wear resistance were prepared by melt blending via a twin screw extruder,through incorporating FZrP and PCF into PA46/PPOG.It was found that adding both of FZrP and PCF significantly improved the water resistance,mechanical properties,wear resistance and fire retardancy of the PA46/PPOG composites.When the FZrP content was 2 wt%and the PCF content was 20 wt%,the tensile strength,flexural strength and impact strength of the composite were 240.0 MPa,334.2 MPa and 19.1 kJ/m~2,respectively.The water absorption was only 1.53%.The friction coefficient and wear volume were 0.23 and 6.4 mm~3,respectively.Compared with PA46/PPOG,the limiting oxygen index(LOI)was increased from 30.5%to 42.0%.Meanwhile,the time to ignition(TTI)of cone calorimetric test(CCT)was increased from 27 s to 40 s,and the peak heat release rate(PHRR)was decreased from807.6 kW/m~2 to 278.1 kW/m~2.The SEM results showed that FZrP could protect PCF from flaking and breaking,thus improved the wear resistance of the composites.The SEM,Fourier transform infrared spectroscopy(FTIR),LRS and XPS analysis of the char layer after burning showed that,during the combustion,carbon fiber acted as the framework,and FZrP efficiently catalyzed the carbonization of PA46/PPOG,which was beneficial to form a strong and compact protective char layer,thus effectively prevented the transmission of heat,oxygen and combustible gases.Therefore,the flame retardancy of the composites was greatly improved.