Synthesis of Zinc Oxide Doped Magnesium Hydrate and Its Effect on the Flame Retardant and Mechanical Properties of Polypropylene

In this work, an effective flame retardant consisting of nanoscale zinc oxide doped on the surface of hexagonal lamellar magnesium hydrate (ZO@MH) has been successfully synthesized via a hydrothermal process. Approximately 3-methacryloxypropyltrimethoxysilane (KH-570) is chosen as a modifier of ZO@MH for the purpose of enhancing the interfacial interaction between ZO@MH and the polypropylene (PP) matrix and reducing the agglomeration of ZO@MH. Afterwards, ZO@MH and KH-570 modified ZO@MH (KZO@MH) filled PP (PP/ZO@MH and PP/KZO@MH) composites are respectively prepared via the melt blending method. The flame retardant and smoke suppression properties of PP/ZO@MH and PP/KZO@MH composites are estimated by a cone calorimetry test (CCT). The peak value of the heat release rate of the PP/40KZO@MH composite is 327.0 kW/m2, which is 6.1% and 31.2% lower than that of the PP/40ZO@MH and PP/40MH composites, respectively. The lowest peak values of CO and CO2 production, 0.008 and 0.62 g/s, also appeared in the PP/40KZO@MH composite, which are 11.1% and 10.1% lower than those of the PP/40ZO@MH composite. Analysis of char residues indicates that nanoscale ZO and modification of KH-570 improve the amount and quality of char residues, which should be the main reason for the good flame retardant and smoke suppression properties of KZO@MH. Impact strength and nominal strain at break results show that the PP matrix is toughened by ZO@MH rather than KZO@MH. Tensile properties and the quantitative interfacial interaction calculated by the Turcsányi equation both prove the reinforcement of KZO@MH on the PP matrix.

Intumescent flame retardancy and smoke suppression of Eucommia ulmoides gum/natural rubber blends based on synergistic g-C3N4@Fe3O4 nanocomposites

A flame retardant synergist (g-C3N4@Fe3O4) was designed through an in situ co-precipitation method by using graphitized carbon nitride (g-C3N4) and Fe3O4, and its structure was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). A series of different contents of g-C3N4@Fe3O4 and intumescent flame retardant (IFR) were simultaneously added into eucommia ulmoides gum/natural rubber (EUG/NR) blends to improve the flame retardancy and reduce the smoke release. The flame retardancy, smoke suppression performance, thermal degradation behaviors and thermal stability of EUG/NR blends were evaluated by the limiting oxygen index (LOI), UL-94, cone calorimetry test (CCT) and thermogravimetric analysis (TGA). The results showed that using g-C3N4@Fe3O4 as a flame retardant synergist, the LOI value of the 9 phr g-C3N4@Fe3O4 synergist (EUG/NR 5) blend was 29.5%, which was much higher than the 20.0% of the original composite. Moreover, the 6 phr g-C3N4@Fe3O4 synergist (EUG/NR 4) and EUG/NR 5 passed the UL-94 V-0 rating, while the pristine EUG/NR blends showed no rating. Moreover, the total heat release rate (THR), peak of heat release rate (PHRR) and total smoke production (TSP) of the EUG/NR blends in the CCT test were much lower than those of the pristine EUG/NR blends. In particular, PHRR, THR and TSP of EUG/NR 5 decreased by 37.1%, 16.2% and 18.0%, respectively. This indicated that the introduction of g-C3N4@Fe3O4 decreased the release of combustible gases. TGA results also showed that the addition of g-C3N4@Fe3O4 accelerated the thermal degradation of the EUG/NR blends and changed the thermal degradation mechanism of the EUG/NR blends, indicating the synergistic effect of g-C3N4@Fe3O4. Finally, a possible degradation mechanism of EUG/NR blend composites was proposed.

Anti-flammability, mechanical and thermal properties of bio-based rigid polyurethane foams with the addition of flame retardants

Adding efficient and environmentally friendly flame retardants to polyurethane foams is the preferable way to improve their flame resistance ability. In this work, bio-based rigid polyurethane foams (RPUFs) were prepared with the addition of dicyclohexyl aluminium hypophosphate (DAH) or aluminium diethyl phosphinate (ADP) as the flame retardant. The mechanical properties, thermal degradation and flammability behavior of the obtained RPUFs were evaluated by means of compressive strength tests, thermogravimetry analysis, vertical burning test and scanning electron microscopes. The characterization results indicate that, with the same content of flame retardant, the compressive strength at the deformation of 10% for each RPUF prepared with the addition of DAH is higher than that of the foams with ADP addition, which fully meets the specifications for building insulation materials. Moreover, the average flame height of each RPUF with the addition of flame retardants is less than 250 mm, whereas the average burning time of RPUF with 15 wt% addition of DAH is only 4.4 s, far less than that (12.5 s) of the foam with the same addition amount of ADP. The RPUFs with DAH addition have the potential advantages for thermal insulation applications in various fields.

Recent studies on the decomposition and strategies of smoke and toxicity suppression for polyurethane based materials

This review provides insight into recent studies related to thermal degradation, smoke and toxicity production and their reduction strategies for polyurethane-based materials.