The Preparation Of Composite Foaming Agent Of Microcellular With High Performance By Using Silica Microspheres With Adjustable Porosity

In industrial applications,foam plastics with cell diameter less than100?m and cell density larger than 10⁶ cells/cm³ are called microcellular plastics.With the development of manufacture,the preparation technology of microcellular plastics with cell size less than 50?m is mature.Recently,the studies on the novel microcellular plastics with cell size less than 10?m and cell density larger than 10¹² cells/cm³ have attracted much attentions due to their high performance.Chemical foaming agents have been widely used industrially.However,its application in microcellular plastics is restricted by the disadvantages such as large particle size,easy agglomeration and difficult to dispersion in polymer matrics,etc.A novel composite foaming agent was prepared by loading the chemical foaming agent on the monodispersed porous SiO₂ microspheres,which is not only benefit for finely dispersion of the chemical foaming agent,but also favour to provide a large number of bubble nucleation sites by introducing inorganic particles.The porosity of SiO₂microspheres can be adjusted by Polymer Induced Colloidal Coagulation(PICA)process thus the loading of chemical foaming agent on the SiO₂microsphere can be regulated.On the bases of finely dispersion of the novel composites foaming agent in the epoxy resin,the viscosity of the polymer system is regulated with the curing degree and the temperature of foaming as well as other factors.These affects the stability of microcellular emitted from the decomposition of foaming agent in the final microcellular.The main progresses achieved in thesis are as follows.(1)Adjustment of porosities of monodisperse SiO₂ microsphere.Silica sol with different particle sizes were prepared by sol-gel method using tetraethylorthosilicate(TEOS).Urea-formaldehyde resin(UF)/SiO₂composites microspheres were obtained by PICA process using silica sol with different particle sizes ranged from 17nm to 234nm.Then the porous SiO₂microspheres were prepared by calcination.The diameter of silica sol particle mainly affects the pore diameter formed through silica particle stacking.UF resin with linear structure trends to form random 3-d cross-linked network aggregation.The degrees of polymerization and cross-linking of UF resin increased with the increase of the ratio of formaldehyde to urea.In the UF/SiO₂ microspheres,linear resin combined with small silica sol trends to entangle to form irregular aggregates and disordered piles led to much larger holes in porous SiO₂ microspheres after burning organic matter.However,when combined with larger silica sol particles,the resin with high crosslinking degree easy to form more regular and compact aggregation thus the silica sol particles are densely stacked in porous SiO₂ microspheres.The ratio of organic matter to silica sol affects the density of UF resin chain in composite microspheres,and ultimately the porosity of SiO₂ microspheres.Reaction temperature influences the size of composites microsphere by changing the interfacial tension.The calcination temperature had effects on the degrees of resin removal and the silica condensation lead to the variation of the porosity of SiO₂ microspheres.(2)Preparation of the novel monodisperse 4,4'-oxydibenzensulfony hydrozide(OBSH)/SiO₂ composites foaming agent.Porous SiO₂ microspheres were modified by 3-aminopropyltriethoxysilane(KH-550).The novel monodisperse OBSH/SiO₂ composites foaming agents were prepared by solution impregnation process.The loading of OBSH was ranged from ca.10.5 to 32.5wt%according to the porosity of SiO₂microsphere,respectively.(3)Preparation of the novel thermoset microcellular.The novel composites foaming agent was applied to the atmospheric foaming practice of epoxy resin.The addition of curing agent can lead to increase of the viscosity along with resin curing,which is beneficial to the stabilization of microcellular.Addition of inorganics may also increase the viscosity.However,the exothermic effect resulted from the curing reaction and decomposition of OBSH increase the temperature of the system,which accelerates the curing reaction in one hand,and to decrease the viscosity of the system on the other hand.The low viscosity of the system may lead to the merger and collapse of bubbles,which is not conducive to the preparation of microcellular.With the optimised conditions,ie.The mixing time of 2h,the curing agent dosage of0.4m L,the initial foaming temperature of 75?and the composites foaming agent dosage of 0.8g,a novel thermoset epoxy resin microcellular was produced.The maximum distribution cell size and cell density were ca.13.8?m and 3.7×10⁷ cells/cm³,respectively.About 21.5%of all cells were smaller than 10?m,and about 92.2%of all cells were less than 50?m in size.