Abstract Polyurethane‐imide ( PUI ) foams containing both polyimide and polyurethane segments combined the advantage of fine mechanical properties as well as high thermal stability of the two polymers. To further improve the thermal stability and flame resistance of PUI foams, a series of PUI composite foams with different content of SiC (silicon carbide) as fillers were prepared. The cell structure, mechanical properties, flame resistance, and thermal properties of resulting PUI /SiC composite foams were characterized in detail. The experimental results showed that the cell size distribution became uneven, the apparent density was increased, and the compressive strength decreased with the increase in silicon carbide content. Meanwhile, the limiting oxygen index ( LOI ) showed an increase from 24.7% to 28.1% with increasing of SiC content from 0% to 9.6%. The thermogravimetric analysis showed that the addition of SiC could significantly enhance the thermal stability and flame retardancy of PUI foams.
Polyvinyl alcohol(PVA)/polypropylene grafted maleic anhydride(PP-g-MAH) blend films were prepared by melting process.The differential scanning calorimetry(DSC) was adopted to develop the crystallization and melting behavior of the blends.Results showed that with the increasing of PP-g-MAH content(less than 50 %),the crystallization and melting temperature of PVA phase increased,the crystallization rate rose,but crystallinity decreased.While with the increasing of PVA content(more than 30 %),the crystallization and melting temperature of PP-g-MAH phase decreased,crystallinity decreased,but the crystallization rate increased.The non-isothermal crystallization kinetics of PVA phase in the blend was studied according to Ozawa′s theory.Results showed that the primary crystallization of PVA phase was in a temperature range of 191~197 ℃,secondary crystallization was in a temperature range of 173~189 ℃.
Polyurethane-imide foams are prepared from polyphenyl polymethylene polyisocyanates, pyromellitic dianhydride and castor oil in presence of trolamine and dibutyltindilaurate catalysts. FTIR spectra proves the successful preparation of polyurethane-imide foams in prepolymer method. The investigation on catalytic mechanism shows that trolamine and dibutyltindilaurate are effective in promoting blowing and gelling reaction, respectively, so trolamine and dibutyltindilaurate are identified to be blowing catalyst and gelling catalyst, respectively. With the fixed amount of trolamine, the density and compressive strength of the resulting foams are enhanced with the increase of dibutyltindilaurate, but average cellular diameter and open cell contents are reduced. Similarly, with the fixed amount of dibutyltindilaurate, open cell contents of the resulting foams are enhanced with the increase of trolamine, while the density, compressive strength and average cellular diameter decreased. Thus PUIFs with variable properties can be prepared through changing the kind and ratio of mixed catalysts.
The foaming behavior of PVA influenced by different foaming agents(including the thermal release,thermal absorption,thermal equilibrium and reaction type) was studied,and the foaming samples were processed through the extruding method.The results of differential scanning calorimetry and thermogravimetric analyzer showed that all types of the foaming agents improved the degrees of crystallization and the crystallization temperature of PVA,while the thermal stability of PVA matrix reduced in different degrees.The results of electron microscopy scanner,density spectrometer and mechanical test showed that foamed PVA with the reaction type-foaming agent had more uniform cells and the lowest density,while its mechanical propertits was poor.
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