Study On Preparation And Properties Of Toughened Thermally Conductive And Insulating Nylon 6 Composite Materials

With the quick development of the micro-electronic technology,the electronic components were gradually transformed from isolated to highly integrated.The unit power density continued to increase,and the accumulation of excess energy would lead to high operating temperature of the device,which greatly affected its accuracy,safety and service life.Nylon has been widely used in thermal insulation and other fields due to its excellent processing fluidity,low density and price.However,its poor thermal conductivity was far less than 0.50W/m·K,which could not meet the increasing demand for heat dissipation.Generally,the lack of thermal conductivity was compensated by increasing the contents of thermally conductive fillers or using expensive fillers with high thermal conductivity.However,the improvement of thermal conductivity would always be accompanied by serious decline in toughness,high cost,and poor processing performance.In this study,nylon 6(PA6)resin as the matrix,in view of the above problems that restricted the development and application of thermal insulation composites materials,the filler surface modification,toughening modification and supplementing a small amount of highly filled fillers have been tried,which aimed to prepare the PA6-based composite materials with high thermal conductivity,insulation performance,excellent processing fluidity and toughness.The specific research content were as follows:1.The surface of MH was modified by silane coupling agents KH550,KH560 and KH792,and the modified MH was used as thermal conductivity filler to prepare MH/PA6composites by extrusion and injection molding processes.The best modifier KH550 was selected by discussing the influence of different coupling agents on the key properties of composite materials such as insulation,thermal conductivity and mechanics.The effects of the contents of KH550-MH(MH-Si)on thermal conductivity,mechanical properties,insulation properties,crystallization properties,processing fluidity and thermal stability of composite materials were further studied by using flash thermal conductivity meter,high resistance meter,torque rheometer,DSC,TG and impact testing machine.The results showed that when the contents of MH-Si was 50wt%,the thermal conductivity and unnotched impact strength of the composite were 0.70 W/m·K and 24.0 k J/m²,respectively,which had excellent improvement basis.2.The EVA,chain extender,GF and POE-g-MAH were used as toughening agents to prepare toughened PA6-based composites.The effects of the types and contents of toughening agent on the thermal conductivity,insulation,toughness and processing fluidity of 50MH-Si/PA6-based composites were studied,and the toughening mechanism was investigated by SEM.The results suggested that GF effectively improved the strength and modulus of the composite materials and the thermal conductivity and toughness of the composite materials were enhanced significantly by the POE-g-MAH.In order to prepare PA6 composites with more excellent and balanced properties,the effect of the combination of GF and POE-g-MAH on50MH-Si/GF/POE-g-MAH/PA6 composites was further investigated.It turned out that when the contents of GF and POE-g-MAH were 7.5wt%and 10wt%,respectively,the thermal conductivity of the composite materials approached the maximum while meeting the toughness requirements,and the thermal conductivity and unnotched impact strength of the composites were 0.88W/m.K and 30.3 k J/m²,respectively.In addition,the influence of the contents of POE-g-MAH on the key properties of 60MH-Si/POE-g-MAH/PA6 composites were further discussed.The results demonstrated that when the filling amount of POE-g-MAH was 7.5wt%,the composite material obtained the maximum thermal conductivity of 0.96 W/m·K,and had a relatively high unnotched impact strength of 39.0 k J/m².3.Toughened thermally conductive and insulating PA6-based composite materials were prepared by POE-g-MAH,BN(BN-Si)and MH-Si.The BN was treated with 5 mol/L Na OH and KOH mixed alkali solution at high temperature to hydroxyl the surface of BN,and then the surface grafting of the coupling agent was carried out to achieve the deep modification of BN,thereby improving the compatibility with PA6 matrix resin.FTIR analysis showed that KH550was successfully grafted onto the surface of BN.Through the study of various properties of 50system(x BN)/10POE-g-MAH/PA6 composites prepared by the combination of BN and MH-Si before and after modification,it is observed and analyzed that the thermal conductivity and toughness of 50 system(XBN)/10POE-g-MAH/PA6 composites were improved more obviously by BN-Si than by BN.When the contents of BN-Si and MH-Si were 12wt%and38wt%,the thermal conductivity,unnotched impact strength and volume resistivity of the composite materials were up to 0.92 W/m·K,29.0 k J/m² and 6.3×10¹⁴?·cm,respectively.The thermal analysis results showed that the addition of BN helped to delay the thermal degradation process of the composite material.Furthermore,the effect of the combined use of BN-Si and MH-Si on various core properties of the 60 system(x BN-Si)/7.5POE-g-MAH/PA6 composites was further studied.The results showed that when the contents of BN-Si and MH-Si were 3wt%and 57wt%,the thermal conductivity and unnotched impact strength of the composite materials reached 1.03 W/m·K and 26.9 k J/m²,respectively,and also had execllent processing flow and insulation.