Structure Regulation And Mechanical And Electrical Properties Of Poly (butylene Terephthalate) Based Nanocomposites

Poly(butylene terephthalate)(PBT),as one of the important engineering plastics,has excellent mechanical strength,heat resistance,wear resistance,and dimensional stability,which is widely used in the fields of automotive industry,electronics,and aerospace.However,the notch sensitivity of PBT leads to its low notched impact strength,which greatly limits the application range of PBT.Melt blending with elastomer is a common method to improve the toughness of PBT.However,due to the soft nature of the elastomer,the mechanical strength,mechanical modulus,and heat resistance of PBT material are greatly declined.Therefore,the toughening of PBT has been one of the important research topics of the high-performance PBT resin.On the other hand,due to the electrical insulation,the surface of PBT is prone to accumulate static charge when PBT is used in the field of electronic information,which adversely affects the operation of the equipment.Therefore,conductive PBT material has been another important research content for the development of high-performance PBT resin.This dissertation systematically explored the strength-toughness balance and conductive properties of PBT resin.By tailoring the microstructure of the PBT composites,the mechanical properties and electrical conductivity of PBT material were enhanced.In addition,the mechanism of the enhanced properties was explored,and the relationship between the structure and performance was established.The main results are as follows.Supertough PBT blends were prepared by melt blending with poly(ethylene-octene)(POE)elastomer and glycidyl methacrylate grafted POE(POE-g-GMA).The compatibility between PBT and elastomer was improved gradually with the increase of the POE-g-GMA content,while the notched impact strength of the blends increased at first and then decreased.The study of the toughening mechanism indicated that a suitable compatibility was significant for obtaining supertough PBT blends,because the good elastomers dispersion and suitable interfacial adhesion can be obtained simultaneously.The weak interface and the large particle size led to unstable crack propagation,while too strong interfacial adhesion prevented interface debonding and arrested matrix shear yielding.Microvoiding generated by both the debonding and internal cavitation of elastomers followed by matrix shear yielding was the main toughening mechanism in toughened PBT blends.Compared with PBT/POE-g-GMA binary blends,supertough PBT-based ternary blends with little rigidity loss were successfully obtained by constructing core-shell particles during melt blending.The core-shell particles consisted of polypropylene(PP)core and POE-gGMA shell,which were dispersed in PBT matrix.When PP with high melt flow index(HPP)was used,PBT/POE-g-GMA/H-PP(70/15/15)blends possessed the highest notched impact strength,which was 1.9-fold compared with PBT/POE-g-GMA(70/30)binary blends,while the tensile performance loss was little.The fibrillation of core-shell particles was able to activate intense matrix shear yielding,therefore,PBT/POE-g-GMA/PP ternary blends possessed much better resistance to crack propagation than PBT/POE-g-GMA binary blends.Compared with PBT/POE-g-GMA/L-PP blends with low melt flow index PP(L-PP),PBT/POE-g-GMA/H-PP blends possessed smaller and more uniform dispersed particle size.Therefore,the matrix plastic deformation in PBT/POE-g-GMA/H-PP blends was stronger,resulting in the higher impact strength.Carbon nanotubes(CNTs)were incorporated into the PBT blends with non-reactive elastomer POE and reactive elastomer POE-g-GMA.The CNTs showed uniform dispersion and formed the interconnecting networks at relatively high content.However,the location of the CNTs and the resulting morphology were different in these two nanocomposites as a result of the chemical interaction between the POE-g-GMA and functionalized CNTs.The CNTs enhanced the tensile strength and modulus of both nanocomposites,but decreased the toughness of the nanocomposites.The volume resistivity of both nanocomposites was extremely reduced with the addition of CNTs,and the volume resistivity of the PBT/POE/CNTs nanocomposites decreased more due to the more significant volume exclusion effect of POE.With the addition of the reactive elastomer POE-g-GMA and CNTs,electrical conductive PBT nanocomposites with balanced strength-toughness were obtained.Electrical conductive PBT/PP/CNTs nanocomposites with the double percolation structure were obtained by simple melt blending.The CNTs were selectively located in the PBT phase in the nanocomposites.Due to the high continuity of the PBT phase and the increased local concentration of the CNTs,the continuous conductive networks were built in the double percolation system.The percolation threshold was 2.0 phr.Thermal annealing further remarkably decreased the volume resistivity of the nanocomposites.During annealing,the relatively large CNTs agglomerates were redistributed to build more homogeneous CNTs networks,and the phase coalescence promoted the formation of the more perfect co-continuous structure.These phenomena helped to enhance the electrical conductivity of the nanocomposites.Flexural properties of the nanocomposites were also enhanced after annealing,which might be due to the more effective stress transfer between the polymer and CNTs induced by the reconstructed CNTs networks.Electrical conductive PBT/POE-g-GMA/PP/CNTs nanocomposites with the tricontinuous structure were prepared by the interfacial tension between the polymers and the interaction between the CNTs and POE-g-GMA.The continuous and thin POE-g-GMA layer was located at the interface of PBT/PP,and the CNTs were confined in the POE-g-GMA layer.Therefore,a continuous conductive pathway was built along the POE-g-GMA layer,leading to the excellent electrical conductivity with the percolation threshold of 1.0 phr.Thermal annealing retained the tri-continuous structure of the nanocomposites,and the CNTs were still selectively distributed in the continuous POE-g-GMA layer.The annealing induced complex effects on the microstructure evolution of the nanocomposites.After annealing,the distribution of the CNTs was more uniform,and the continuity of POE-gGMA phase was increased.However,the phase coarsening led to the increased thickness of the POE-g-GMA continuous layer.The combined effect of the above factors resulted in the reduced volume resistivity of the nanocomposite.