Structure Control And Characterization Of Nylon 6 Conductive Composite

With the rapid development of electrical industry and communication technology,conductive polymer composite occupies a decisive position in the functional materials.This kind of conductive polymer composite has good processing performance,adjustable resistance,low cost and strong designability.It is widely used in energy,transportation,electronic and other fields.It is particularly important to study the new method to prepare conductive polymer composites with high performance and low cost and realize their application in the field of electromagnetic shielding.In this paper,nylon 6 was modified by added two kinds of conductive filler,carbon fiber and expanded graphite,The nylon 6 conductive composite with excellent performance was obtained through the control of the conductive network structure.The main findings are as follows:(1)PA6/EG composites were prepared by simple melt blending.With the addition of thermal expansion graphite,the conductive and thermally conductive networks formed between the conductive particles were improved,and the composites with excellent conductivity,thermal conductivity and electromagnetic shielding was obtained.When the addition of EG is 9.09 vol%,the conductivity of the composite reaches to 0.262S/m,and the thermal conductivity is also the best,which is 1.0202W/m?K,the electromagnetic shielding performance reaches to 23 d B.At the same time,the addition of EG can provide more heterogeneous nucleation sites for the composites,which improve the crystallization temperature and crystallinity of the composites,the crystallinity increased by 26.98% at most.Therefore,the dynamic storage modulus of PA6/EG composites is greatly improved,and the addition of filler has a limiting effect on the molecular chains of the polymer,so the Tg of the composites is also greatly improved.(2)The composites were prepared by adding CF to PA6 and EG melt blends,and the composites were prepared by changing the ratio of the two fillers.As a result,the reinforcing effect of CF on the composites was especially obvious.Compared with the PA6,the tensile and bending properties of the PA6/EG/CF composites were improved.When the addtion of CF is 20 wt%,the tensile strength,tensile modulus,bending strength,bending modulus of the PA6/EG/CF composites are achieve the best,which can reach 100.8MPa,4.67 GPa,95.7MPa and 6.42 GPa,increased by 41.69%,81.01%,86.55% and 293.87%.compared with pure PA6.The addition of EG is favors to the improvement of conductive,thermal and electromagnetic shielding properties of the composites.When the addtion of EG is 20 wt%,the conductivity of the composite is the highest,reach to 0.262S/m,which thermal conductivity up to 1.3379W/m?K,and the electromagnetic shielding performance can also reach to the application requirements of 20 d B.And the EG and CF particles have heterogeneous nucleation in the nylon 6 matrix,and the crystal nucleus growth rate is increased,crystallization is easier,thus increasing the crystallization temperature of the PA6/EG/CF.Moreover,the crystallinity of the PA6/EG/CF is enhanced firstly and then weakened with the increase of the EG:CF mass ratio.(3)The segregated structure PA6 composites with different filler of EG and CF were prepared by high speed mechanical blending and molding.The conductive percolation value was obviously reduced,which reached the desired result.The segregated structure PA6/EG system has a percolation value of 0.134 vol%,and the segregated structure PA6/CF system is 1.9 vol%.And with the increases of filler content,the completed conductive network is constructed in the PA6/EG(PA6/CF)composite,which makes the composite excellent in thermal conduction,electromagnetic shielding,dynamic mechanics and so on.It is observed that the shielding effectiveness of PA6/CF composites exhibits strong frequency dependence in the frequency range of 8.2~12.4 GHz.With the increase of frequency,the shielding effectiveness of PA6/CF composites is enhanced firstly and then weakened.And with the increase of CF content,the peak value of characteristic absorption is increasing.And the frequency of the characteristic peaks moves toward the high frequency as the CF content increases.(4)Series segregated structure PA6/EG/CF composite materials were prepared by adding a certain amount of CF in the preparation of PA6/EG composites,microstructure can be seen CF as a bridge of EG segregated conductive network,making the conductive network more perfect,formed a similar “shish calabash like” shaped structure.Compared of three lengths of CF prepared by the series segregated structure PA6/EG/CF composite conductive,electromagnetic shielding,dynamic mechanical and other aspects of performance found,the composites prepared by these three lengths of CF which percolation values respectively are 0.31 vol%?0.325 vol%?0.241vol%,the composite properties of this composite material prepared by 100 ?m carbon fiber were the best,followed by 5 mm carbon fiber preparation,and 700 ?m carbon fiber was relatively low.