Ammonium polyphosphate modified with β-cyclodextrin crosslinking rigid polyurethane foam: Enhancing thermal stability and suppressing flame spread

Ammonium polyphosphate modified with beta-Cyclodextrin (beta-CD) as intumescent flame retardants was prepared and then incorporated in rigid polyurethane foam (RPUF) to improve thermal stability and flame retardancy. Scanning electron microscope (SEM), Transmission electron microscope (TEM), Fourier-transform infrared (FTIR) spectra and X-ray photoelectron spectroscopy (XPS) were used to characterize the modified APP (beta-APP). The results showed that the surface of beta-APP was covered of beta-CD and the dispersibility of beta-APP in substrate was improved apparently. In addition, the influence of beta-APP on the cell structure, crosslink density, thermal stability and flame retardancy of RPUF were investigated. The results showed that beta-APP was able to promote cellular distribution of RPUF into smaller and homogeneous. The results of dynamic thermomechanical analysis (DMA) and thermogravimetric analysis (TGA) indicated that the glass transition temperature (T-g) and crosslink density of beta-APP/RPUF increased obviously, and the thermal stability of beta-APP/RPUF was better than other FR-RPUFs. During combustion, flame spreading speed of 25 wt%beta-APP/RPUF reduced by 67.3% relative to pure RPUF and extinguish time decreased to 2.1s with the most complete inner char and the most dense outside char. In addtion, peak heat release rate (PHRR) of the sample decreased by 43.8% compared to pure RPUF. Therefore beta-APP exhibited a prominent charring property and flame-retardant effect in condensed phase for RPUF. (C) 2019 Elsevier Ltd. All rights reserved.