Performance Control And Research Of High Filled Thermally Conductive Nylon 6 Composites

Due to the light weight,low cost and convenient processing,thermally conductive polymer composites（TCPCs）have great potential to replace traditional metallic material.Nylon 6（PA6）is a commonly used engineering plastic,but its low intrinsic thermal conductivity has led to limited applications in thermal conductivity field.Flake graphite（FG）has excellent thermal conductivity,and its combination with PA6 can significantly improve the thermal conductivity of composites.However,FG is a flake filler and is easily oriented during the melt hot-pressing.This leads to the thermal conductivity of the composite has significant anisotropy.In this thesis,the third component filler to regulate the arrangement and stacking of FG in PA6 matrix to improve the thermal conductivity in the thickness direction of the composites.The main contents include the following:（1）Preparation and properties study of PA6/FG composites:When the FG filling amount was less than 50 wt%,FG cannot form a continuous thermal conductivity network in the PA6 matrix.As a result,the composites have low thermal conductivity（λ）.In contrast,when the filling amount reaches percolation threshold（50 wt%）or higher,λof the composites appears to be significantly enhanced.The in-plane thermal conductivity（λ_∥）is much higher than the through-plane thermal conductivity（i.e.,the thermal conductivity in the thickness direction,λ_⊥）after hot pressing.When the FG filling is 70 wt%,λ_∥andλ_⊥of the composites are 32.12 W m^-1K^-1 and 8.53 W m^-1 K^-1,respectively.（2）Effects of Al₂O₃ on the structure and properties of PA6/FG composites:During the melting process,FG was replaced by thermally conductive spherical alumina（Al₂O₃）to prepare PA6/FG/Al₂O₃ composites.The results show that when the FG filling amount is 70 wt%,introduction of 1 wt%20μm Al₂O₃ can improveλ_⊥of composite material from 8.53 W m^-1 K^-1 to 12.50 W m^-1 K^-1.This is mainly due to the“bridging”effect of spherical Al₂O₃ between FG sheets,reducing the interfacial thermal resistance,changing the orientation of flake graphite,and enhancing the connectivity of the thermal conductivity network in the thickness direction.（3）Effects of HGμS on the structure and properties of PA6/FG composites:Lightweight,thermally insulated hollow glass microspheres（HGμS）was used to prepare PA6/FG/HGμS composites.The results show that when the FG is at a high initial weight fraction（70 wt%）,adiabatic HGμS can change the orientation of parallel ordered FG.So that the FG thermal conductivity network has a better access in the thickness direction and enhance theλ_⊥of the composite from 8.53 to 10.78 W m^-1 K^-1.（4）Effects of PP on the structure and properties of PA6/FG composites:Polypropylene（PP）is incompatible with PA6 and was used to prepare PA6/PP/FG composites.The results show that FG will be selectively dispersed in the more polar PA6 phase,with an increase in effective concentration.When the mass ratio of PA6:PP is 9:1,the spherical island phase of PP also has the effect of changing the orientation of FG.λ_⊥of the composites is increased to 11.44 W m^-1 K^-1.There is a 34.1%improvement under the same FG filling amount（70wt%）.