Urea-modified lignin was prepared according to the Mannich reaction and well characterized by Fourier transform infrared spectrometer, elemental ananlyses, and scanning electron microscopy (SEM). Ammonium polyphosphate (APP) and urea-modified lignin were added into poly(lactic acid) (PLA) as a novel intumescent flame-retardant (IFR) system to improve flame retardancy of PLA. The flammability of IFR-PLA composites was studied using limiting oxygen index, UL-94 vertical burning method and cone calorimeter test, and their thermal stability was evaluated by thermogravimetric analysis. The results showed that the urea-modified lignin combined with APP exhibited much better flame retardancy and thermal stability than that of the combination of virgin lignin and APP. The improvement may be attributed to the better char morphology with more phosphoric char evidenced by SEM and X-ray photoelectron spectroscopy.

Lignin–silica hybrids (LSHs) were prepared by sol–gel method and characterized by Fourier transform infrared (FT-IR) spectra, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). LSH and ammonium polyphosphate (APP) were added into poly(lactic acid) (PLA) as a novel intumescent flame-retardant (IFR) system to improve the flame retardancy of PLA. The flame-retardant effect of APP and LSH in PLA was studied using limiting oxygen index (LOI), vertical burning (UL-94) tests and cone calorimeter. The thermal stability of PLA/APP/LSH composites was evaluated by thermogravimetric analysis (TGA). Additionally, the morphology and components of char residues of the IFR-PLA composites were investigated by SEM and XPS. With the addition of APP/LSH to PLA system, the morphology of the char residue has obviously changed. Compared with PLA/APP and PLA/APP/lignin, a continuous and dense intumescent charring layer with more phosphor in PLA composites is formed, which exhibits better flame retardancy. All the results show that the combination of APP and LSH can improve the flame-retardant property and increase the thermal stability of PLA composites greatly.

The effect of different organic modified montmorillonites (DK1, DK2, and DK4) based on a novel intumescent flame retardant (IFR) poly(lactic acid) (PLA) system is reported. The IFR system was composed of microencapsulated ammonium polyphosphate and lignin. The morphological characterization of PLA/OMMT nanocomposites was conducted by X-ray diffractometry and transmission electron microscopy. The flame retardant and thermal properties of the composites were evaluated by limiting oxygen index (LOI), vertical burning test (UL-94), and cone calorimeter. From the results, it could be seen that the sample containing DK2 possessed the best flame retardance, such as lower peak heat release rate (pHRR) and higher LOI value. The thermal degradation and gas products of the samples were monitored by thermogravimetric analysis and thermogravimetric analysis infrared spectrometry. Scanning electron microscopy was used to explore the surface morphology of the char residues.

In order to improve the flame retardancy of polystyrene (PS), a phosphorus and nitrogen comonomer, named AC2NP2, was synthesized and then incorporated into various amounts of PS by seeded emulsion polymerization. The modified methacrylate (AC2NP2) was used as the core phase, the styrene as the shell phase, then flame‐retardant effect copolymers with core‐shell structure were prepared successfully. The particle size was ranged from 40 to 60 nm, and the structure and properties of the copolymers were characterized in detail. Notably, despite a few amounts of the AC2NP2 units in the copolymers, all the copolymers exhibited significantly enhanced thermal stability and reduced flammability as compared with pure PS. Furthermore, from differential scanning calorimetry test, it was observed that the glass transition temperature was tinily influenced with the incorporation of commoner. The incorporation of P‐N comonomer into PS backbone did not lead to negative effect on the glass transition behavior of PS.

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