Partially-filled Microcapsules With Viscoelastic Core Materials:Preparation And Damping Performance In Epoxy Resin

In people’s life,the problems of vibration-induced noise and fatigue damage are becoming more and more serious.Damping materials are widely used in real life because they can absorb vibrations and convert them into other forms of energy dissipation,thus reducing vibration-induced noise and its destructive effects,and have been widely studied.The damping performance of polymers can be improved to by changing the chain segment structure and cross-linking method,but the internal consumption of the materials cannot be improved indefinitely.The loss factor of viscoelastic polymers in the highly elastic and viscous flow states has a tendency to rise compared with the glass transition region,but they cannot be applied as solids in damping members because they have no strength.Microencapsulation of viscoelastic polymers can be used as damping fillers and overcome the limitations of performance enhancement of conventional damping polymers.At present,the connection between core-microencapsulation-substrate material is not clear,and the research focus stays on the enhancement of loss factor,lacking research on the broadening of the damping working temperature region of the materials.Therefore,the damping filler of microcapsule structure needs to be further developed.In this thesis,we have obtained three types of partially-filled microcapsules with different viscoelastic polymers encapsulated separately.Through the characterization of three types of microcapsules and the damping performance test of microcapsules/epoxy composites,the possible influence factors of the partially-filled microcapsules on the damping performance of epoxy resin are elucidated.We hope that these studies will provide experimental data and new ideas for the design and application of special structural damping fillers.The second chapter is the preparation of microcapsules containing polyacrylate core material and the study of their damping properties.The microcapsules with partially-filled structure were prepared using acrylate polymers as core material and their damping properties were investigated.The core materials with similar molecular weight were obtained by radical polymerization of butyl acrylate and methyl methacrylate with different feeding ratios.The_g of the core materials was ranged from-54℃to 34℃.Interfacial polymerization was used to coat the core materials in microcapsules（MP60 series）.The dynamic mechanical properties of the MP60s/EP composites were investigated.The results showed that MP60s loading could effectively adjust the tanδand the T_αof the epoxy E51.Especially,the composites with 15.4 wt.%concentration exhibit best damping properties.With the increase in T_gof the core material or the increase of the MP60s incorporation,the maximum values of the loss factors of the composites,tanδ_max,showed a tendency to increase and then decrease,and tanδ_max of MP60s/EP composite could reach 0.82.The main relaxation temperature T_αshowed a decreasing and then increasing trend,with the lowest T_αat77°C.Furthermore,the addition of MP60s could adjust the tanδof composites at the temperature region that composite is in the glassy state（tanδ_x）by controlling the_gof core material.The tanδ_x of composites could be increased to 0.28.In Chapter 3,the preparation of microcapsules containing cyano-polymer cores and their damping properties are investigated,with the aim of studying the effect of intermolecular forces of cores on the damping of partially filled structural microcapsules.The core materials with similar molecular weight were obtained by radical polymerization of butyl acrylate and acrylonitrile with different feeding ratios.The T_g of the core materials was ranged from-44℃to 13℃.Interfacial polymerization was used to coat the core materials in microcapsules（MPCN60 series）.The introduction of cyanole groups in the core polymers increased the roughness and strength of the microcapsule wall.The dynamic mechanical properties of the MPCN60s/EP composites were investigated.The results showed that MPCN60s loading could effectively adjust the tanδand the T_αof the epoxy E51.With the increase in T_g of the core material or the increase of the MP60s incorporation,the tanδ_max of MPCN60s/EP composite could reach 0.88.The T_αshowed a decreasing and then increasing trend,with the lowest T_αat 68°C.Furthermore,the addition of MPCN60s could adjust the tanδ_x by controlling the_g of core material.The tanδ_x of MPCN60-4/EP composites could be increased to 0.21.Chapter 4 describes the preparation of encapsulated organic-inorganic hybrid core microcapsules and the study of their damping properties.The core material was composed of 3-Aminopropyltriethoxysilane-modified silica（30 nm）and carboxyl-containing acrylate polymer.The incorporation of modified silica on the one hand that affected the flow performance of the core material,and on the other hand,it enhanced the roughness of the microcapsule shell.The dynamic mechanical properties of the MPBMA15/EP composites were investigated.With the increase of the modified silica content,the tanδ_max of the composites showed a tendency to increase and then decrease,and tanδ_max value of the composite could reach 0.74.There was little change in T_αof the composites.The increase of tanδ_x was significant,reaching a maximum value of0.35.It successfully broaden the high damping temperature zone of the composite to 90 ℃.