Research On Thermally Conductive PP/BN Composites:Preparation,Properties And Thermal Conductivity Modelling

Thermally conductive polymer composites have been widely used in electrical and electronics area,heat exchangers and aerospace industries due to advantages such as low weight,high thermal conductivity(TC),easy processing,good chemical and corrosion resistance.The incorporation of thermally conductive filler can improve the TC of composites.Hexagonal boron nitride(h-BN)has good chemical stability,electrical insulation property and excellent thermal property.The present work aimed at creating polypropylene(PP)composites with high TC using h-BN,maleic anhydride grafted polypropylene(PP-g-ma)and polydopamine.First,h-BN and PP-g-ma were simultaneously blended with PP to fabricate thermally conductive composites using a twin-screw extruder.The microstructure of the composites was analyzed with XRD and SEM.The mechanical properties and thermal properties of the composites were investigated.The results show that the elongation at break and tensile strength are enhanced and the TC is improved significantly because of strong interaction between h-BN and PP chained by PP-g-ma.When the content of h-BN is 25wt%,the TC of the composites containing PP-g-ma is 0.512W/(m·K),1.08 times to the value of PP/h-BN composites and as high as 2.26 times to that of PP.Then,in order to improve the compatibility between h-BN and PP,a polydopamine layer was coated onto h-BN surfaces and the π-π interactions between polydopamine and h-BN allowed the non-covalent functionalization of h-BN(f-BN),as confirmed by the SEM,TGA,FTIR and contact angle analysis.The catechol and amine groups in polydopamine could form chemical bonding with PP-g-ma,resulting in much improved interfacial adhesion between the filler and matrix.The PP/PP-g-ma/f-BN composites demonstrate the best filler dispersion and the least void formation and phonon scattering with the highest TC.While for PP/f-BN composites,there shows the most voids and some filler aggregation,causing the strongest interruption of the thermal paths.With the addition of 2.5wt% PP-g-ma,the PP/PP-g-ma/f-BN composites achieve much larger TC improvement of 0.576W/(m·K),with an enhancement of 2.59 times to PP at 25wt% filler loading.Finally,a unit cell was abstracted for analytic modeling based on the morphological observation of prepared composites to analyze the factors affecting TC quantitatively.Thermal resistance method was used to derive the TC of the composites containing flake-shaped fillers with anisotropic TC.The calculated TC was compared with the experimental result and those calculated by classical models.The results show that the TC of the newly developed model fits well with the experimental result.Besides,the TC of composites can be significantly enhanced when the h-BN fillers are aligned according to the model.These modelling results can provide guidance for improving the TC of composites.