| Blending is a simple,effective and cheap way to obtain new polymer materials.However,most polymers are thermodynamically immiscible.Under the effect of load,cracks tend to initiate and expand at the interface of two phase,resulting in material failure.Therefore,improving the interfacial strength is the key to the preparation of blends with excellent fracture toughness.Generally,the method of improving the interfacial strength of the two phase is to introduce a certain amount of compatibilizer,but the complex synthesis of compatibilizer,the long development cycle and the high cost greatly limit its application in industry.It is well known that brittle-ductile transition is a common phenomenon in elastomer toughening polymers,and the brittle-ductile transition behavior of the blends is mainly related to the properties of the matrix,the properties of the elastomer,the interfacial strength of the two phase and the distance between the particles of the elastomer.In recent years,the researchers have introduced inorganic nanoparticles into immiscible blends,which can not only show the effect of compatiblization,but also induce the change micromorphology of the blends,and then affect the brittle-ductile transition behavior of the blends.Among the numerous inorganic nanoparticles,one dimensional carbon nanotubes(CNTs)is considered as an ideal reinforced and toughening filler of polymer materials for its excellent mechanical properties.A large number of studies have shown that the introduction of CNTs into some blends can greatly improve the impact strength of the material,and its toughening mechanism is mainly be attributed to that CNTs can induce the change of the microstructure of the blend,the formation of network structure of CNTs in the system and the role of CNTs bridged two phase interface.Although the introduction of CNTs can realize the toughening of immiscible blends,the study on inducing the brittle-ductile transition behavior of immiscible blends is still inadequate.In order to deeply explore the CNTs inducing the brittle-ductile transition behavior of immiscible blends,this work focuses on introducing CNTs to the binary PP/EPDM blends.This thesis mainly investigates the design mechanism of the microstructure and morphology of immiscible blends induced by CNTs,and reveals the influence of CNTs on the brittle-ductile transition behavior of the immiscible blends.On the basis of this,the crystallization properties of matrix is further regulated,and the influence of CNTs on toughening efficiency and brittle-ductile transition behavior of blends under different crystal size is studied.Finally,CNTs is introduced into immiscible Epoxy/CTBN blend,and the toughening mechanism of CNTs in thermosetting system is discussed.The main research results are as follows:(1)CNTs was introduced into PP/EPDM blends with different component ratios by melt extrusion,and the ternary nanocomposites were successfully prepared.The microstructure,the dispersion states of CNTs and crystallization behavior were characterized by scanning electron microscopy,transmission electron microscopy and differential scanning calorimetry.The results indicates that the selective distribution of CNTs in the elastomer phase makes the phase of the elastomer slightly increase,but the blends still exhibit a typical island structure,and the introduction of CNTs does not cause the change of the crystallization behavior of the matrix.The impact test results shows that the introduction of CNTs can not only improve the impact strength of the material,but also induce the change of brittle-ductile transition behavior of the blends.For the binary PP/EPDM blend system,the impact strength of the material increases with the increasing of EPDM content,and when the content of EPDM reaches 35 wt%,the blends shows obvious brittle-ductile transition behavior.For the ternary PP/EPDM/CNT nanocomposites,the introduction of CNTs can improve the impact strength of binary PP/EPDM blends.Moreover,the brittle-ductile transition point of the blends shifts to the low elastomer content direction.The introduction of 1 wt%and 2 wt%CNTs result in the change of brittle ductile transition of the blends to 30 wt%and 25 wt%respectively.The toughening mechanism mainly depends on the CNTs stress transfer effect,thus promoting the superposition effect of the stress field around the elastomer,and then induces the plastic deformation of the matrix to increase the impact toughness of the blends.(2)CNTs and nucleating agents were simultaneously introduced into binary PP/EPDM(85/15 wt/wt)blends by melt extrusion,and the nanocomposites with low elastomer content and high impact strength were successfully prepared.The micromorphology of the blends,the distribution of CNTs and the crystal size of the matrix were characterized by scanning electron microscopy,differential scanning calorimetry and polarizing microscope.The results shows that CNTs selective locate in the elastomer phase and at the interface of two phase,but the introduction of CNTs has little influence on the microstructure of the blends.The introduction of the nucleating agent shows a significant nucleation effect on the crystallization behavior of the matrix,and the crystal size of the matrix decreases with the increase of the nucleating agent content.The impact test results shows that 0.2 wt%nucleating agent and 1 wt%CNTs make the impact strength of the binary PP/EPDM blend system increase from 13.5 kJ/m~2 to 51.2 kJ/m~2,inducing the brittle-ductile transition behavior successfully.Further research shows that the toughening efficiency of CNTs has a strong dependence on the crystal size of the matrix.Only the crystal size of the matrix is very small,can CNTs exhibits a good toughening efficiency.When the crystal size of the matrix is small,the path of crack propagation can be increased on the one hand,and the diffusion speed of the stress field can be increased on the other hand,and the stress field around the elastomer is more likely to exhibit superposition effect,thus improving the impact toughness of the blends.(3)CNTs was introduced into binary immiscible Epoxy/CTBN blends by solution blending,and the ternary nanocomposites were successfully prepared.Scanning electron microscope and dynamic mechanical analysis were used to characterize the microstructure and the interaction between two phases of materials.The results show that in the case of low CTBN content,the blend system shows typical island-sea structure,but with the increase of CTBN content,the microstructure of the blend system transforms from island-sea structure to homogeneous structure.For Epoxy/CTBN(100/10 wt/wt)system,the introduction of CNTs has little effect on the microstructure of blend.The impact test results show that the impact strength of the blend increases firstly and then decreases with the increase of CTBN content for the binary Epoxy/CTBN blend.When the content of CTBN is 15 wt%,the blend exhibits the best impact performance.Introducing CNTs into binary Epoxy/CTBN(100/10wt/wt)blends,the impact strength of the composites also shows a trend of first rise and then decrease.When the content of CNTs is 0.2 wt%,the blend shows the best impact performance,and the impact strength is improved from 28.5 kJ/m~2 to 37.1 kJ/m~2.Further studies show that CNTs is mainly distributed in the Epoxy matrix.Due to the weak interaction of the interface between CNTs and the matrix,when the material is loaded under force,the debonding of CNTs causes a large number of micro-cracks,thus absorbing a large amount of impact energy.The CTBN particles can terminate and inhibit the propagation of the cracks,and further prevent cracks connect each other which result in material failure. |
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