Excellent Fireproof Characteristics and High Thermal Stability of Rice Husk-Filled Polyurethane with Halogen-Free Flame Retardant

Abstract

The thermal stabilities, flame retardancies, and physico-mechanical properties of rice husk-reinforced polyurethane (PU–RH) foams with and without flame retardants (FRs) were evaluated. Their flammability performances were studied by UL94, LOI, and cone calorimetry tests. The obtained results combined with FTIR, TGA, SEM, and XPS characterizations were used to evaluate the fire behaviors of the PU–RH samples. The PU–RH samples with a quite low loading (7 wt%) of aluminum diethylphosphinate (OP) and 32 wt% loading of aluminum hydroxide (ATH) had high thermal stabilities, excellent flame retardancies, UL94 V-0 ratings, and LOIs of 22%–23%. PU–RH did not pass the UL94 HB standard test and completely burned to the holder clamp with a low LOI (19%). The cone calorimetry results indicated that the fireproof characteristics of the PU foam composites were considerably improved by the addition of the FRs. The proposed flame retardancy mechanism and cone calorimetry results are consistent. The comprehensive FTIR spectroscopy, TG, SEM, and XPS analyses revealed that the addition of ATH generated white solid particles, which dispersed and covered the residue surface. The pyrolysis products of OP would self-condense or react with other volatiles generated by the decomposition of PU–RH to form stable, continuous, and thick phosphorus/aluminum-rich residual chars inhibiting the transfer of heat and oxygen. The PU–RH samples with and without the FRs exhibited the normal isothermal sorption hysteresis effect at relative humidities higher than 20%. At lower values, during the desorption, this effect was not observed, probably because of the biodegradation of organic components in the RH. The findings of this study not only contribute to the improvement in combustibility of PU–RH composites and reduce the smoke or toxic fume generation, but also solve the problem of RHs, which are abundant waste resources of agriculture materials leading to the waste disposal management problems.

Novel Cast Polyurethanes Obtained by Using Reactive Phosphorus-Containing Polyol: Synthesis, Thermal Analysis and Combustion Behaviors

“…The T 1max , T 2max and T 3max temperatures corresponded to the degradation of phosphate groups, HS and SS, respectively. A similar course of the DTG curve in the air atmosphere, illustrating the degradation of phosphorus-containing PU, was presented by H. T. Q. Phan et al [51]. The best thermal stability in N 2 /O 2 atmosphere, among all the FPUs, was demonstrated for material, which had the highest amount of phosphorus polyol (FPU-9.5).…”

Recent Progress of Rice Husk Reinforced Polymer Composites: A Review

“…The silicate layers of clay produced a twisted path for the diffusion of volatiles, which in turn improved the thermal stability of the composite. The use of halogen-free flame retardants [ 77 ] increased the thermal stability by generating thermally stable substances such as aluminum oxide, silicon dioxide, and phosphorus-containing compounds. Increasing the fiber–matrix interaction increased the thermal stability of RH composites [ 78 ].…”

Effects of a Macromolecule Spirocyclic Inflatable Flame Retardant on the Thermal and Flame Retardant Properties of Epoxy Resin

“…In particular, quite small pores were formed in the exterior char layers of EP/SAPC-8 after burning, which may have been due to a strong airflow. It could be seen that, in accordance with the HRR, THR and TSR curves, honeycomb-shaped and a certain thickness of "foam" char layers were formed in the interior char layers, indicating that heat and smoke were gently released through these channels [46,47]. The honeycomb char structure acted as a good physical barrier to seal most of the smoke and flue gas that were generated by combustion, reducing the exchange rate of heat, combustibles and oxygen to the substrate [48,49].…”

“…TG-FTIR was performed to further analyze the gaseous pyrolysis products that were generated during thermal decomposition process. As shown in Figure 9, 3D TG-FTIR spectra were obtained gently released through these channels [46,47]. The honeycomb char structure acted as a good physical barrier to seal most of the smoke and flue gas that were generated by combustion, reducing the exchange rate of heat, combustibles and oxygen to the substrate [48,49].…”