Shape memory polyurethane-silica (SMPU-SiO2) hybrids were prepared in situ via sol-gel process with SMPU and tetraethoxysilane (TEOS) as precursor

solid acid p-toluenesulfonic acid (PTSA) as catalyst and the water in air as the source of hydrolysis reaction

then the hybrids prepared were applied to aramid fiber reinforced flexible composites to improve the interfacial compatibility between aramid fiber and SMPU matrix.Meanwhile

the interfacial bonding property between aramid fiber and resin matrix is inferior due to surface inert property of aramid fiber

thus

aramid fiber was modified by phosphoric acid solution to increase the surface activity.Fourier transform infrared (FTIR) spectrometer

X-ray photoelectron spectroscope (XPS)

universal tensile instrument

low-temperature thermal dilatometer and polarized light micrograph (PLM) were used to characterize the surface groups

single fiber strength of aramid fiber and the interfacial property of aramid fiber/SMPU matrix composites.The results show that the surface active groups and the single fiber strength are increased by the treatment of phosphoric acid.And the interfacial shear strength (IFSS) between aramid fiber functionalized with 10 wt% phosphoric acid and SMPU is enhanced.Meanwhile

the addition of SiO2 can effectively lower the coefficient of thermal expansion of SMPU around its glass transition temperature ( Tg ) and increase the IFSS between aramid fiber and matrix remarkably.