Study On Thermal Conductivity And Mechanical Properties Of Phenolic Synthetic Foam

Thermal insulation technology is currently the key technology to protect the aviation aerospace power grid as a spacecraft thermal protection system,Thermal insulation materials is the key structure to protect new aerospace vehicles.As a kind of thermal insulation material,the composite foam is widely used in the aerospace field.The phenolic composite foam has high thermal stability,excellent mechanical properties and thermal insulation performance.It is a typical representative of the synthesis foam.The modification of the hollow glass microsphere can obviously improve the interface performance between the glass microsphere and the resin matrix,and improve the performance of the composite foam.Filling the hollow glass microsphere in the phenolic resin can significantly reduce the density of the material,improve the specific strength and thermal insulation properties of the material,and introduce the high temperature resistant chopped carbon fiber to enhance the syntactic foam,further reducing the density of the composite foam,and the phenolic synthesis foam mechanical properties have improved significantly.The phenolic synthesis foam was prepared by modifying the surface of the hollow glass microspheres with different kinds of coupling agents.The phenolic resin were filled with modified microspheres.The surface properties of the hollow microspheres before and after modification were studied,The results show that the hollow microspheres after the coupling agent reduce the agglomeration between the hollow microspheres,increase the hydrophobicity of the surface,improve the compatibility with the matrix,the interface properties,and the composite materials performance.Among the different kinds of coupling agents,the titanate coupling agent is physically bonded to the phenolic matrix polymer chain,and the siloxane coupling agent has a chemical bond with the hydroxymethyl group in the resol phenol and the physical entanglement is still the main.In the phenolic composite,the titanate coupling agent is the most effective.The syntactic foam was prepared by filling the phenolic resin with different volume fraction of hollow glass microsphere.The thermal stability,mechanical properties and thermal insulation properties of the composites after heat treatment atdifferent temperatures were studied.The results show that with the content of hollow glass microspheres increasing,the thermal stability of the composite foam is increased.The compressive strength of the composite foam decreases with the increase of the microsphere,and the flexural strength increases with the increasing of the filling amount of the hollow glass microspheres.At 900 ° C,compared with 600 °C the mechanical properties of the syntactic foam increase due to the melting of the hollow glass microsphere and forming a reinforcing glass bridge to fill the cracks and pores in the matrix.The effective thermal conductivity of the composite foam decreases with the increase of the filling amount of the hollow glass microspheres.The low filling amount under the room temperature is close to the calculated value of the Russell model and the Hashin-Shtrikma upper model.The values are gradually close to the parallar model with the high filling amount under the room temperature.With the increase of temperature,the percentage of effective thermal conductivity of thermal radiation and meteorological heat conduction is increasing,and the thermal conductivity coefficient of solid phase is also increased greatly,so that the effective thermal conductivity is greatly increased.The fiber reinforced syntactic foam is filled with different mass fraction of carbon fiber,which has 50 vol% volume hollow glass microsphere.The results show that With the increase of the amount of chopped carbon fiber,the thermal stability of the composite foam increases under nitrogen condition,and the mechanical properties of the syntactic foam increased at first and then decreased,the mechanical properties reached the maximum at 3wt%.The effect of fiber content on the effective thermal conductivity of the syntactic foam is not obvious and the overall increase is slightly.