Effect of silicon-containing nitrogen and phosphorus flame-retardant system on the mechanical properties and thermal and flame-retardant behaviors of corrugated cardboard

Abstract

In this paper, a new designed silicon-containing nitrogen and phosphorus flame-retardant system containing ammonium polyphosphate, modified molecular sieve and methylcellulose was used to prepare the flame-retardant corrugated cardboards (FRCCB). The samples before and after treatment were tested for combustion and thermal stability using vertical burning test (VBT), limiting oxygen index (LOI), cone calorimetric test (CCT) and thermogravimetry (TG). To further analyze the flame-retardant properties of the flame-retardant system, the microstructure, surface elements and functional groups of the materials were characterized by the scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). The mechanical properties of the samples were tested to analyze the effect of flame-retardant treatment on the strength. The VBT and LOI tests showed that the samples after the flame-retardant treatment were able to self-extinguish after ignition, achieving the flame-retardant B-1 grade. The CCT tests showed that the total heat release of treated samples was reduced by 49.90%, and the total smoke production was decreased by 27.64%. TG tests showed that the thermal decomposition temperature of FRCCB decreased but the residual carbon content increased largely. FTIR tests showed that the functional group changed at different temperatures. After flame-retardant treatment, a dense carbon layer was formed on the surface of the treated sample, including N, P, Si and Cu, measured by SEM and EDS. Combining with various characterization methods, the flame-retardant system can retard flame by releasing nonflammable gases, forming covers and catalyzing char formation.