SBA-15 Preparation And Characterization Of Composite Materials Such As Poly (trimethylene Terephthalate) / Mesoporous Silica

In recent years, the mesoporous silica has drawn considerable attention from the field of polymer composites because of its characteristics with ordered pore structure, large specific surface area and high strength. Therefore, the polymer/mesoporous silica composites become a hot topic in the field of composite materials. As a relatively new type of linear aromatic polyester, poly(trimethylene terephthalate)(PTT) increasingly becomes a promising candidate in both the textile and engineering materials. Compounding PTT with mesoporous silica, on the one hand, may provide a promising way to prepare high-performance PTT, extending its applications; and on the other hand, to explore whether and how the ordered nano-pore structure of mesoporous silica affects the synthesis and hierarchical structures of PTT, developing new approach to control structure and properties of PTT.Thus, in this work, PTT was firstly synthesized by the transesterification method to explore appropriate synthesis process. Then, the poly (trimethylene terephthalate)/mesoporous silica (PTT/SBA-15) composites was prepared by in-suit polymerization based on the optimum synthesis conditions. The effect of mesoporous structure of SBA-15on the short-range structure (chain morphology), long-range structure (molecular weight) and supermolecular structure (crystallization) of PTT matrix was investigated in detail, aiming at figuring out the interaction between PTT chain and SBA-15particles. Finally, the PTT/SBA-15composites were further prepared by melt mixing the commercial PTT with the raw PTT/SBA-15materials prepared by in-situ polymerization for the mechanical property and viscoelastic behavior studies. The preliminary conclusions are as follows.(1) The polymerization reaction of PTT depends strongly on the reaction temperature and time as well as the amount of catalyst. The optimum synthesis conditions are as follows:the amount of catalyst-400ppm; the transesterification time-180min; polycondensation temperature-265℃; polycondensation time-40min; the amount of stabilizer-40ppm. The weight-average molecular weight of as-obtained PTT is about40,200g/mol, which reaches the level of commercial PTT products.(2) The SBA-15particles can be well dispersed in the PTT matrix of the composite system prepared by in-situ polymerization, and thier mesoporous structure remain well after in-situ polymerization. The hydroxyl groups from inside pore wall to outside surface of SBA-15particles can react with PTT chain and/or oligomers and as a result, PTT molecular weight decreases with increasing loadings of SBA-15particles relative to virginal PTT system. However, the viscosities of composite system increase to some extent because of the formation of grafted and/or crosslinked structures between SBA-15and PTT chain, as well as the flow-inhibiting effect by the presence of SBA-15particles.(3) The presence of SBA-15particles has heterogeneous nucleation effect on the crystallization of PTT, promoting the isothermal and non-isothermal crystallization rate as a result. The crystal surface folding free energy of the PTT chain decreases due to the nucleation of SBA-15particles, while the diffusion activation energy of PTT chain segment increases because of the flow-inhibiting effect of SBA-15particles. In addition, the decrease of molecular weight nearly had little effect on the crystallization rate of PTT;(4) PTT/SBA-15composites with high performance can be prepared by melt mixing the commercial PTT with the raw PTT/SBA-15materials prepared by in-situ polymerization. Compared with those of the neat PTT, the tensile strength and impact strength of as-obtained composite increase by about26%and10%even at the very low SBA-15loading level (0.5wt%). This is attributed to the compatibilization of low molecular weight PTT coated on the outside and inside pore walls of mesoporous SBA-15particles. In addition, the composites show better creep resistance ability than the neat PTT because of the restrain effect of mesoporous structure of SBA-15on the mobility of PTT chain, which is further confirmed by the higher glass transition temperature of the composites relative to the pure PTT.