Sustainable polymers are emerging fast and have received much more attention in recent years compared to petro-sourced polymers. However, they inherently have low-quality properties, such as poor mechanical properties, and inadequate performance, such as high flammability. In general, two methods have been considered to tackle such drawbacks: (i) reinforcement of sustainable polymers with additives; and (ii) modification of chemical structure by architectural manipulation so as to modify polymers for advanced applications. Development and management of bio-based polyurethanes with flame-retardant properties have been at the core of attention in recent years. Bio-based polyurethanes are currently prepared from renewable, bio-based sources such as vegetable oils. They are used in a wide range of applications including coatings and foams. However, they are highly flammable, and their further development is dependent on their flame retardancy. The aim of the present review is to investigate recent advances in the development of flame-retardant bio-based polyurethanes. Chemical structures of bio-based flame-retardant polyurethanes have been studied and explained from the point of view of flame retardancy. Moreover, various strategies for improving the flame retardancy of bio-based polyurethanes as well as reactive and additive flame-retardant solutions are discussed.

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Lignin-containing micro/nano fibrillated cellulose (L-MNFCs) and phosphorylated L-MNFCs were produced from beechwood sawdust by combining steam explosion (SE) pretreatment, a bleaching step, a phosphorylation reaction using urea and etidronic acid, and an ultra-fine grinding. The contents of phosphorus and nitrogen on the cellulose surface were obtained by elemental analysis (P ≈ 2.7% and N ≈ 1.2% respectively). The chemical composition of the pulps was assessed by ionic chromatography (HPAEC PAD) and the morphology of phosphorylated (L-)NMFCs were analyzed by Morfi Neo. The successful grafting of phosphate groups was verified by FTIR, 13C CPMAS, 31P NMR. Thermal and fire behaviors were examined by TG/DTG analysis and pyrolysis combustion flow calorimetry (PCFC). It was found that SE pretreatment itself can significantly improve the thermal degradability and fire resistance of L-MNFCs. Phosphorylated (lignocellulosic) micro/nano fibrillated cellulose exhibiting a remarkable elevation in their thermal degradation and flame-retardancy have been produced.