Functionalization Of Mesoporous Silica And Study On Thermal Stability And Combustion Properties Of Epoxy Composites

Since mesoporous silica was found, it has attracted much interest for its widespread applications in molecular adsorption, catalysis, gas and biological sensors, due to its high surface area, tunable pore size and very narrow pore size distribution. One of the most promising applications of mesoporous silica was polymer/mesoporous silica composite, in which mesoporous silica endowed polymer composites more excellent performance. However, the application of epoxy/mesoporous silica composites maintained challenges yet:preparation of mesoporous hollow silica and the low flame retardant efficiency. This thesis proposed a new way to fabricate mesoporous hollow silica. On the based of different ideas, mesoporous silica assembled nanosheets, flame retardant modified mesoporous silica and mesoporous silica supported nanoparticle hybirds were prepared. Futhermore, we studied the thermal stability and flame resistance, and also proposed the plausible flame retardant mechanism.1. In view of high cost, low yield and complex preparation process, we developed a facile ultrasonic assisted method to prepare hollow mesoporous silica. The results showed that hollow mesoporous silica with different size can be successfully synthesized. Compared with the traditional method, the ultrasonic assisted method can precisely control the size of the hollow structure and realize mass preparation. The study found that:with the increase of ultrasonic processing power, the shell thickness of hollow mesoporous silica was reduced; the higher power was beneficial to form the hollow structure of the mesoporous silica. The volume ratio of ethanol/water was also an important factor affecting the formation of hollow mesoporous silica. On based of the results, we proposed a plausible mechanism.2. Hierarchical mesoporous silica@Co-Al layered double hydroxide (m-SiO2@Co-Al LDH) spheres were prepared through a layer by layer assembly process, in order to integrate their excellent physical and chemical functionalities. TEM results depicted that, due to the electrostatic potential difference between m-SiO2and Co-Al LDH, the synthetic m-SiO2@Co-Al LDH hybrids exhibited that m-SiO2spheres were packaged by the Co-Al LDH nanosheets. Subsequently, the m-SiO2@Co-Al LDH spheres were incorporated into an epoxy resin (EP) matrix to prepare specimens for investigation of reduced fire hazard behavior. Cone results indicated that m-SiO2@Co-Al LDH incorporated obviously improved fire retardant of EP. A plausible flame-retardant mechanism was speculated on the basis of the analyses of thermal conductivity, char residues and pyrolysis fragments. Labyrinth effect of m-SiO2and graphitized carbon char formation catalyzed by Co-Al LDH play key roles in the flame retardance enhancement.3. A self-assembly process was used to prepare hierarchical hollow mesoporous silica@Co-Al layered double hydroxide@graphene (HM-SiO2@CoAl-LDH@graphene), with the purpose of combining their outstanding performance. Hollow mesoporous silica was first synthesized as the core using a novel sonochemical method, followed by a controlled shell coating process and chemical reduction. As a result of the electrostatic potential difference among HM-SiO2, CoAl-LDH and graphene oxide, the HM-SiO2spheres were coated by CoAl-LDH and graphene. Subsequently, the HM-SiO2@CoAl-LDH@graphene spheres were incorporated into an epoxy resin matrix to prepare specimens for investigation of reduced fire hazard behavior. A possible flame-retardant mechanism was speculated on the basis of char residues and flammable gase.4. HM-SiO2@CS@PCL spheres were prepared through a self-assembly process, in order to integrate their excellent functionalities. The results depicted that, due to the electrostatic potential difference among HM-SiC>2, CS and PCL, the synthetic HM-SiO2@CS@PCL exhibited that CS and PCL molecules were penetrated into the mesochannels due to capillary force. Subsequently, the HM-SiO2@CS@PCL spheres were incorporated into an epoxy resin (EP) matrix to prepare specimens for investigation of reduced fire hazard behavior. Cone results indicated that HM-SiO2@CS@PCL incorporated obviously improved fire retardant of EP. A plausible flame-retardant mechanism was speculated on the basis of the analyses of char residues. Labyrinth effect of HM-SiO2and graphitized carbon char formation catalyzed by PCL play key roles in the flame retardance enhancement.5. HM-SiO2/NiCexOy was prepared by ion-adsorption and calcination methods and applied into epoxy matrix to study the fire-retardant properties. TEM and HRTEM results showed that we have successfully synthesized uniform size HM-SiO2/NiCexOy spheres, NiCexOy particles were uniformly distributed in the HM-SiO2surface and pores. Cone results indicated that HM-SiO2/NiCexOy incorporated obviously improved fire retardant of EP. SSTF studies showed that with addition of HM-SiO2/NiCexOy, CO concentration and smoke density of EP composites generated during combustion were reduced accordingly. A plausible flame-retardant mechanism was speculated on the basis of the analyses of char residues and pyrolysis fragments.