Preparation And Characterization Of Dielectric Nanocomposites Based On EVA/TPU Blend

With the rapid development of the electrical and electronic industry in decades,the demand of the materials with excellent comprehensive performance increase gradually.As a kind of important electrical material,dielectric materials with higher dielectric constant and lower dielectric loss are requied appling in the microelectronic devices.Although the traditional dielectric ceramic materials have good dielectric properties,however,their application is limited due to the unfriendly environmental and mechanical loss.In contrast,polymer-based composites with high dielectric properties because of their light weight,good processing performance and mechanical properties,low price,high energy density etc.play a critical role in a series of high-tech fields on which have been paid more attention recently.However,there are also many problems exsiting in the current research,especially the high dielectric loss arising from the high conductivity.Polymer blending is an effective way to develop new materials nowadays.When nanofillers are incorporated into the blend,composites with high strength and high conductivity can be achevied by controlling the selective localization of nanoparticles and the microstructure of the composite.Therefore,nanofillers were introduced into the polymer blends to prepare dielectric nanocomposites with higher dielectric constant and lower dielectric loss by controlling the selective distribution of nanoparticles and the morphologies of the composites in this paper.The mechanism of the effect of the composite morphologies,the dispersed phase domains size and the hybrid fillers on the dielectric prpperties of the ternary or quaternary nanocomposites were explored in this work.The results are as follows:?1?The CNTs were incorporated into the EVA/TPU blends by two-step melt blending method.Nanocomposites with different morphorlogies were obtained by changing the weight ratio of EVA and TPU and the loadings of CNTs.The dielectric properties characterization of the nanocomposites showed that the dielectric constant of nanocomposites with a morphology of sea-island structure increases and the dielectric loss of which is suppressed The microstructure characterization showed that CNTs was selectively distributed in the TPU dispersed phase and with the increase of TPU content,the morphology of the composites changed from the island structure to the co-continuous structure.The rheological properties showed that the CNT network in the nanocomposites with sea-island structure were denser.FTIR results showed that the hydrogen bond structure on the TPU molecular chain in the nanocomposites with sea-island structure is destroyed.The following explanations were responsible for the improved dielectric properties:1)conductive TPU dispersed phases which are distributed in the EVA matrix acted as the electrodes and the EVA layer between TPU domains acted as electric to form numerous micro-capacitors structures in the polymer matrix.The TPU dispersed phases were prevented from forming a conductive path by the EVA matrix at the same time.Thus,the dielectric constant increased largely and dielectric loss was suppressed.2)As for the ternary composites with sea-island morphology,the dense CNT network structure in the TPU phases destroyed the hydrogen bond structure on the TPU molecular chains,making the polarization of TPU chains more susceptible under the electric field.?2?The compatibilizers were incorporated into EVA/TPU/CNT system to change the interaction between EVA and TPU and then the size of TPU dispersed phase was tailored.It was found that the dielectric properties of the EVA/TPU/CNT nanocomposites were affected by the size of the microstructure of the dispersed phase,and there was a suitable domain size range?2?3.5?m or 8?10.5?m?causing that the dielectric constant of the composites was increased and the dielectric loss was kept low.This is related to the number of micro-capacitors formed by CNTs and TPU islands within the composites.Therefore,a series of polymer-based dielectric nanocomposites with different dielectric properties can be obtained by regulating the dispersed phase domain size of the composites.?3?BaTiO₃ and CNTs were incorporated into EVA/TPU blends to prepare quaternary dielectric nanocomposites.The dielectric constants of the quaternary nanocomposites with sea-island structure were increased and the dielectric loss was suppressed.The SEM results show that BaTiO₃ and most of CNTs are confined to the TPU dispersed phase,and parts of CNTs were selectively distributed at the interface.Rheological properties test showed that with the introduction of BaTiO₃ nanoparticles,the filler network structure in the nanocomposites become denser.This is due to the fact that the local content of BaTiO₃ nanoparticles in the sea-island structure nanocomposits is larger than that in co-continuous structure nanocomposites,which makes the barrier effect of BaTiO₃ in the naocomposites with sea-island structure on the CNT network structure larger than that in the naocomposites with co-continuous structure.