Qingliang He

This chapter provides an in-depth exploration of nitrogen-based flame retardants, a growing class of materials that has garnered significant attention in recent years due to their balanced performance and potential. Drawing from the latest research and industrial developments, the chapter delves into the underlying mechanisms of various highlighted classes of nitrogen-based flame retardants. Key compounds covered arise from diverse classes of materials, including melamine, ammonia, cyanurate, phosphazenes, oxyimides, triazoles, imidazoles, and radical generators, and their respective roles across a wide range of polymers that underscores the pivotal applications of these agents, highlighting their contributions to enhancing fire safety in various sectors. Furthermore, where applicable, this chapter aims to serve as a comprehensive guide on how each material is utilized in a myriad of potential formulations, offering readers a go-to source for understanding the state of the art in nitrogen-based flame retardants and employing them effectively.

A char forming agent (CFA) and silica-gel microencapsulated ammonium polyphosphate (Si-MCAPP) were selected to form novel intumescent flame retardant system to prepare flame retardant polypropylene (PP) composites, and then the influences of nanoporous nickel phosphates (NiP) on the thermal and flame retardant properties of flame retardant PP composites were studied by the real time FTIR (RTFTIR) spectra, limited oxygen index (LOI) test, and the scanning electron microscopy. RTFTIR shows the addition of NiP can improve the thermal stability of flame retardant PP composites. LOI test shows LOI value is increased with the increase of the content of NiP, and the optimized concentration of NiP is 1.0%. Furthermore, smoke toxicity of the novel flame retardant PP composites was studied by mice experiment. The upper limit of the no death smoke concentration of the composite is 12.37 mg/L.

Flame‐retardant polypropylene (PP)/carbon nanotubes (CNTs) nanocomposites influenced by surface functionalization and surfactant molecular weights are studied. 3‐Aminopropyl‐triethoxysilane (APTES) is utilized to modify the CNTs (f‐CNTs), and maleic‐anhydride‐grafted PP (MAPP) with two molecular weights ( of 800 and 8000 g mol⁻¹) is used to further improve the dispersion of f‐CNTs in the PP matrix. Thermal gravimetric analysis (TGA) and microscale combustion calorimetry (MCC) reveal that the molecular weight of MAPP directly affects the thermal stability and flammability of PP/f‐CNTs PNCs: both MAPP polymers ( of 800 and 8000 g mol⁻¹) increase the thermal stability of PP; however, the heat release rate of PP/f‐CNTs is reduced in the presence of MAPP ( of 800 g mol⁻¹) and increased in the presence of MAPP ( of 8000 g mol⁻¹). MAPP ( of 800 g mol⁻¹) also results in a lower viscosity of the PP/f‐CNTs PNCs compared with pure PP. image

Polypropylene grafted maleic anhydride (PP-MA, 2500 g mole⁻¹) has demonstrated its unique capability to synthesize 1-D ferromagnetic hard (292.7 Oe) γ-Fe₂O₃ nanochains made of ∼24 nm nanoparticles vs. PP-MA with 8000 g mole⁻¹ for the synthesis of 1-D ferromagnetic soft (70.5 Oe) γ-Fe₂O₃ nanochains (30 nm) made of flowerlike nanoparticles.

Contrary to the observed positive giant magnetoresistance (GMR) in as-received multi-walled carbon nanotubes (MWNTs), pure polyaniline (PANI) synthesized with Cr(VI) as oxidant and MWNTs/PANI nanocomposites with ammonium persulfate (APS) as oxidant, a room temperature negative GMR of around −2% was reported in MWNTs/PANI nanocomposites with Cr(VI) as oxidant. Different from a frequency switch of permittivity from negative to positive in MWNTs/PANI nanocomposites with APS as oxidant, unique negative permittivity was observed in MWNTs/PANI nanocomposites with Cr(VI) as oxidant within the measured frequency range from 20 to 2 × 10⁶ Hz. The obtained unique negative permittivity was explained by the plasma frequency from the Drude model, at which the permittivity changes from negative to positive and the material changes from a metamaterial to an ordinary dielectric medium. The observed positive and negative GMR behaviors in these disordered systems as verified by the temperature dependent resistivity exploration were well explained through a wave-function shrinkage model and orbital magnetoconductivity theory by calculating the changed localization length (a₀).

This critical review focuses on the property analysis of graphene and graphene nanocomposites (GNCs) and their demonstrated superior performances in energy storage and conversion, electrochemical- and bio-sensing, environmental remediation and flame retardant application and atomic thickness membrane separation. The performances of graphene and GNCs are strongly dependent on their chemical component, synthetic method, nanoscale morphology, and assembling structure of the hybrids. The current progress in supercapacitor energy storage density, solar cell power conversion efficiency, thermoelectric energy conversion efficiency, electrochemical sensing capability, biosensor sensitivity, heavy metal adsorption capacity and efficiency, photocatalytic degradation rate of organic dye, flame retardant polymer nanocomposites, graphene and porous graphene membranes is discussed with detailed examples through extensive analysis of the literature.

A novel function of polypropylene grafted with maleic anhydride (PP-g-MA) as synergistic additives to effectively reduce the combustion rates of polypropylene (PP) polymer nanocomposites (PNCs) reinforced with in situ synthesized cobalt (Co)–cobalt oxide core–shell nanoparticles (NPs) was reported. Two PP-g-MAs with molecular weights of ∼800 and 2500 g mol⁻¹ have been chosen to demonstrate this function. The combustion behaviors and thermal stability of the PP/Co PNCs were evaluated by micro-scale combustion calorimetry (MCC) and thermal gravimetric analysis (TGA). MCC result illustrated that the combustion behaviors of PP were altered by a reduction of ∼32% in the peak heat release rate (PHRR) with the incorporation of 20.0 wt% Co NPs; more importantly, further reduction in PHRR more than 50% was observed by adding only 5.0 wt% non-flame retardant PP-g-MA into PP/20.0 wt% Co system. This flame retardancy was elucidated through combining MCC with a fast TGA thermal degradation technique. The change of PP thermal degradation pathway by the synergistic and catalytic effects of PP-g-MA and Co NPs in the PP matrix was found to be responsible for the decreased combustion rates of PP. Strong interactions between PP and Co NPs formed by the PP-g-MA was further confirmed by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), which favor the decrease of interfacial tension. Differential scanning calorimetry (DSC) and melt rheometry also demonstrated the surfactant molecular weight dependent melting and crystalline properties, and the melt rheological behaviors of the PP matrix.