Construction of CS@APP@UiO-66 through self-assembly technology as flame retardant and smoke suppressant for epoxy resins

Abstract

To achieve fire-resistant epoxy resin (EP), a UiO-66-based novel flame retardant coating (CS@APP@UiO-66) was prepared by modifying UiO-66 with chitosan (CS) and ammonium polyphosphate (APP) through a layer-by-layer (LbL) self-assembly method, which was then introduced into an EP system to improve its fire safety. The results of scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy show that the unsaturated Zr atoms in the UiO-66 framework provide many active sites conducive to modification, so that the UiO-66 particles, which originally had a regular octahedral structure, are more dispersed by LbL modification without causing doping or distortion issues. The thermogravimetric analysis results indicate that the char residue of EP/2% UiO-66 is increased by 2.52% compared with that of pure EP, indicating that the thermal properties of the EP composite are improved after modification. In addition, the cone test results indicate that EP/2%UiO-66-5L has good flame retardancy and smoke suppression properties, and the peak heat release rate, total smoke production and rate of CO generation values are 25.2%, 5.7% and 38.5% lower than those of the unmodified EP. Moreover, it can be concluded from the Raman test that the graphitization degree of the modified EP composite is strengthened. The above results indicated that after the incorporation of CS@APP@UiO-66 into the EP composites, more char layers formed as physical barriers to prevent the transfer of mass and heat, thus reducing the speed of flame propagation. Therefore, the flame resistance and smoke suppression of the EP composites improved. These favorable characteristics, including high flame retardant efficiency and good smoke suppression, make LbL-functionalized UiO-66 promising for flame retardant polymer applications.