A fully bio-based coating made from alginate, chitosan and hydroxyapatite for protecting flexible polyurethane foam from fire

The present study reports the successful synthesis of the flame-retardant and smoke-suppressant flexible polyurethane foam (FPUF) through a fully bio-based coating. Hydroxyapatite (HAP) is added to the solutions containing sodium alginate (SA) and chitosan (CH), respectively, to create negative and positive polyelectrolytes for Layer-by-Layer (LbL) assembly. The influence of the solution concentrations and bilayers numbers deposited on the flame-retardant and mechanical properties of FPUF samples is investigated systematically. Benefitting from the presence of such a fully bio-based coating, the resultant FPUF affords excellent smoke-suppressant and flame-retardant features. In particular, the FPUF coated by 9 bilayers of HAP-SA/HAP-CH exhibits significantly declined peak heat release rate, total release rate and smoke production release by 77.7 %, 56.5 % and 53.8 %, respectively. The compression test verifies the coated FPUFs exhibit lower recovery properties compared with the uncoated one. These results demonstrate that a green and cost-effective strategy is provided for producing flame-retardant, anti-dripping and smoke-suppressant FPUFs.

Nitrogen and phosphorous doped graphene quantum dots: Excellent flame retardants and smoke suppressants for polyacrylonitrile nanocomposites

Nitrogen (N-GQD) as well as nitrogen and phosphorous co-doped (NP-GQD) graphene quantum dots were demonstrated as novel, low cost, green and highly effective flame retardants and smoke suppressants for polyacrylonitrile (PAN) nanocomposites. The N-GQD and NP-GQD samples were synthesized by hydrothermal method with citric acid as the main reactant. For the first time, the flame retardant and smoke suppressant properties of the NP-GQD were studied. The GQDs were introduced into PAN by solvent blending route. Subsequently, thermal stability, flame retardancy, fire behavior, fire hazard and structure of the residual char were investigated by thermogravimetric analysis (TGA), UL-94 vertical burning test, cone calorimetry, FE-SEM, and Raman spectroscopy. Results showed that both PAN/N-GQD and PAN/NP-GQD nanocomposites had higher flame retardancy and smoke suppressant behavior in addition to lower fire hazard properties than neat PAN. Furthermore, the residual chars for the nanocomposite samples were increased in comparison to the neat PAN. The improvements were even more significant in case of the PAN/NP-GQD due to the synergistic effect of nitrogen and phosphorous. The improvements were mainly ascribed to the ability of the N-GQD and NP-GQD to provide stronger and larger protective char barrier layers, which was even more pronounced in case of the NP-GQD.

A novel reutilization method for waste printed circuit boards as flame retardant and smoke suppressant for poly (vinyl chloride)

In this study, a novel reutilization method for waste printed circuit boards (PCBs) as flame retardant and smoke suppressant for poly (vinyl chloride) (PVC) was successfully testified. A supercritical water oxidation (SCWO) process was applied to treat waste PCBs before they could be used as flame retardants of PVC. The results indicated that SCWO conditions had a significant effect on the flame retarding and smoke suppressing properties of waste PCBs for PVC. Cu2O, CuO, and SnO2 were the main active ingredients in waste PCBs-derived flame retardants. A conversion of Cu elements (Cu(0)→Cu(+)→Cu(2+)) during SCWO process with the increase of reaction temperature was found to be the key influence factor for the flame retarding properties of SCWO-treated PCBs. The experiment results also showed that there was a synergistic effect of flame retardancy between Cu(+) and Cu(2+). After the optimized SCWO treatment, SCWO-treated PCBs significantly improved the flame retardancy and smoke suppression of PVC. Limiting oxygen index (LOI) and char yield (CY) increased with increasing SCWO-treated PCBs content in PVC, while smoke density rating (SDR) and maximum smoke density (MSD) decreased markedly. The mechanical properties of PVC samples were influenced in different degree by adding different content SCWO-treated PCBs.