Preparation And Properties Of Polyamide 6 Composites With High Thermal Conductivity

Thermal conductivity composites have been attracted significant interest in modern electronic devices,LED packaging and other fields.However,the thermal conductivity of polymer matrix is very low(<0.5 W·m^-1·K^-1),which limits its applications.Adding high thermal conductivity fillers to polymer is a feasible way.The obtained thermal conductivity composites have high thermal conductivity,low dielectric loss,light weight,easy processing,etc.Recently,melt blending is the most convenient and industrial applied method to prepare the filled thermal conductivity composites.Firstly,PA6/Al₂O₃ composites were prepared by the melt blending method.The effects of different particle size and content of Al₂O₃ on the properties of the composites were explored.The results show that the compatibility between PA6 and Al₂O₃ is well,and stearic acid（SA）has little effect on the thermal conductivity of the composites.The thermal conductivity of composites with large particle size Al₂O₃ is higher than the little one at the same content.Meanwhile,the thermal conductivity of the composites showed an upward trend as the increase of Al₂O₃ content.When the content of large particle size Al₂O₃ is 70 phr,the composites reached the highest thermal conductivity value of1.14 W·m^-1·K^-1,which was 2.8 times higher than that of pure PA6(0.3 W·m^-1·K^-1).Secondly,PA6/BN composites were prepared by selecting boron nitride（BN）sheet as the thermally conductive fillers,adding a small amount of SA,and the mass ratio of PA6 to BN was fixed at 50:50.The results show that the addition of a small amount of SA can significantly improve the thermal conductivity of the composites.On one hand,the addition of SA improves the dispersion of BN in the matrix.On the other hand,an appropriate amount of SA is mainly dispersed at the interface between PA6and BN,thus improving the interface adhesion of the two phases.When SA content is5 phr,BN has the best orientation in the matrix,which is conducive to the effective construction of thermal conductivity path.Moreover,the addition of SA promotes the crystallization of PA6,which is also conducive to the propagation of phonons in the composites.The PA6/BN composites corresponding to the SA content of 5 phr have the highest thermal conductivity of 3.59 W·m^-1·K^-1,which is 11 times and 1.6 times higher than that of pure PA6 and the composites without SA,respectively.Also,when the SA content is fixed at 5phr,the thermal conductivity of PA6/BN composites increases with the increase of BN content.When BN is increased to 50 phr,the thermal conductivity of the composite is increased sharply,indicating that at this content,a thermally conductive network is built inside the composite.At a loading of 60 phr BN,the thermal conductivity of the composite can reach 6.28 W·m^-1·K^-1.Finally,on the basis of maintaining the thermal conductivity of the composite,in order to reduce the BN content,a small amount of polypropylene（PP）was added to prepare PA6/PP/BN composite using two melt blending methods,that is,one-step method and master-batch method.The results show that the thermal conductivity of the composites prepared by the master-batch method is higher than that by the one-step method.At a loading of the same BN content,the thermal conductivity of the PA6/PP/BN composite with adding 10phr PP is 14.3%higher than that of the PA6/BN composite.It is due to the increase of the BN content in matrix PA6 caused by the addition of PP.