Preparation Of Hollow Silica Application To The Composite Foaming Agent

Research on new microcellular foams began in the 1980s.It has excellent properties such as impact strength,toughness,high fatigue life,higher thermal stability and lower thermal conductivity.The preparation of microcellular foams is mainly based on supercritical fluid foaming,which requires strict control of pressure and temperature parameters,and has high requirements on equipment and processes.However,the chemical foaming method has a large particle size due to the purification of the foaming agent itself,and agglomeration due to moisture or static electricity,which leads to excessive local foaming dose in the plastic matrix.It will ultimately affects the size and uniformity of the cell,that is to say,restricts application in the preparation of microcellular foams.Therefore,the chemical foaming agent is loaded in a uniform size hollow silica microsphere to prepare a composite foaming agent,and the composite foaming agent is used as a nucleation point of the bubble not only realizing the particle refining of the foaming agent,but also being expected to solve the problem of uneven cell pores of the foam prepared by the chemical foaming agent.In this paper,OBSH/SiO2 composite foaming agent was prepared by carrying out the solution impregnation method in inorganic hollow silica microspheres and microcellular foam was prepared in epoxy resin matrix.(1)Polystyrene microsphere(PS)template was prepared by a dispersion polymerization method.PS microspheres are prepared using styrene(St)as a monomer in a solvent of water and ethanol.The reaction time and the amount of polyvinylpyrrolidone(PVP),monomer and azobisisobutyronitrile(AIBN)can be adjusted to control the PS microspheres from 430 nm to 2600 nm.Among them,PS microspheres with a particle size of 1950 nm have the best dispersibility and uniformity.(2)The hollow silica microspheres is prepared using PS microspheres as a hard template.The catalyst is concentrated ammonia water.First,core shell particles are prepared by using tetraethyl orthosilicate(TEOS)as a silicon source,and then hollow silica microspheres are prepared by calcination.The amount of different TEOS,the surfactant cetyltrimethylammonium bromide(CTAB),ethanol and catalyst concentrated ammonia can adjust the micro-spherical shape of the hollow silica.The condition is adjusted while the shell thickness can be controlled between 55 nm and 130 nm.Among them,hollow silica microspheres with a shell thickness of 115 nm have good dispersibility,uniform microspheres.(3)The loaded foaming agent OBSH was carried out by a solution impregnation method using the obtained hollow silica microspheres as a carrier.The solidification NMR,thermal analysis,SEM and other characterizations prove that the foaming agent is combined with the core-shell structure.The control of the loading amount can be achieved by adjusting the concentration of the immersion liquid.The loading amount can be controlled between 8.61%and 38.60%.(4)Adjusting the amount of curing agent and composite foaming agent and mixing time,foaming temperature and other process conditions can control the cell size from 26 ?m to 52 ?m.Among them,when the average cell diameter is controlled at 26?n,the cell density can be controlled at 4.61 × 106 cells/cm 3.The obtained epoxy resin foam has a small cell size and uniformity.At the same time,the size of the cells increases as the size of the hollow silica microspheres increases.