The sustainable flame retardancy of polymeric materials is a key focus for the direction of the next generation in the field of fire safety. Bio-derived flame retardants are gaining attention as environmentally friendly additives due to their low ecological impact and decreasing costs. These compounds can enhance char formation in polymeric materials by swelling upon heating, attributed to their functional groups. This review explores various biomolecules used as flame retardants, including phytic acid, chitosan, lignin, tannic acid, and bio-derived phosphorus and nitrogen compounds, emphasizing their flame-retardant properties and compatibility with different polymer matrices. The primary focus is on the structural characteristics, modifications, and flame-retardant behaviors of these bio-derived additives, particularly regarding their mechanisms of action within polymeric materials. Finally, the review explores the opportunities, current challenges, and future directions for the practical application of bio-derived flame retardants in polymer materials.

The amplified employment of rigid polyurethane foam (RPUF) has accentuated the importance of its flame-retardant properties in stimulating demand. Thus, a compelling research report is essential to scrutinize the recent progression in the field of the flame retardancy and smoke toxicity reduction of RPUF. This comprehensive analysis delves into the conventional and innovative trends in flame-retardant (FR) systems, comprising reactive-type FRs, additive-type FRs, inorganic nanoparticles, and protective coatings for flame resistance, and summarizes their impacts on the thermal stability, mechanical properties, and smoke toxicity suppression of the resultant foams. Nevertheless, there are still several challenges that require attention, such as the migration of additives, the insufficient interfacial compatibility between flame-retardant polyols or flame retardants and the RPUF matrix, and the complexity of achieving both flame retardancy and mechanical properties simultaneously. Moreover, future research should focus on utilizing functionalized precursors and developing biodegradable RPUF to promote sustainability and to expand the applications of polyurethane foam.

Rigid polyurethane foam (RPUF) is a widely utilized thermosetting polymer across various industrial applications, valued for its exceptional properties. However, the demand for sustainable alternatives to petroleum-based polymers has grown increasingly urgent due to rising environmental concerns. Despite its widespread use, RPUF faces challenges such as inadequate mechanical strength, limited thermal stability, and high flammability, all of which are crucial considerations in commercial and household applications. Globally, ongoing efforts are focused on developing innovative technologies that convert renewable sources into new monomers and polymers, some of which could serve as alternatives to traditional RPUFs. Several approaches have been explored to improve the thermal stability, mechanical strength, and flame retardancy of RPUFs, including the modification of bio-based polyols and the incorporation of performance-enhancing fillers. This review emphasizes recent advances in RPUFs derived from natural resources, focusing on their preparation, characterization, and properties, and strategies to enhance the mechanical strength and flame safety of bio-based RPUFs. Additionally, it explores the applications of RPUF materials across various fields, addressing the challenges and potential developments in packaging, household items, construction, and automotive applications.

Flexible polyurethane foam (FPUF) is extensively applied in multiple applications, including automotive, construction, furniture cushioning, and transportation seating, due to its outstanding mechanical properties, sound absorption, breathable characteristics, and versatility. However, FPUF is highly flammable and releases significant quantities of smoke and harmful gases when burned, which presents considerable safety hazards and has led to extensive research into flame retardant solutions. This review covers the development of both conventional and bio-based flame-retardant agents, including reactive-type and additive-type FRs, and surface coating methods, with a focus on their preparation, characterization methods, and underlying flame retardant mechanisms. Additionally, innovative flame retardant technologies, particularly surface coatings, are discussed in terms of their impact on thermal stability, mechanical performance, and smoke toxicity reduction in the resulting FPUFs. The review also highlights future research priorities and significant challenges, including environmental concerns, cost-effectiveness, and durability. Future research will need to focus on improving flame retardant efficiency while also considering the environmental impact and recyclability of materials, aiming for the green and sustainable development of FPUFs.

Graphene-like 2D nanomaterials, such as graphene, MXene, molybdenum disulfide, and boron nitride, present a promising avenue for eco-friendly flame retardants. Their inherent characteristics, including metal-like conductivity, high specific surface area, electron transport capacity, and solution processability, make them highly suitable for applications in both structural fire protection and fire alarm systems. This review offers an up-to-date exploration of advancements in flame retardant composites, utilizing pristine graphene-like nanosheets, versatile graphene-like nanosheets with multiple functions, and collaborative systems based on these nanomaterials. Moreover, graphene-like 2D nanomaterials exhibit considerable potential in the development of early fire alarm systems, enabling timely warnings. This review provides an overview of flame-retarding and fire-warning mechanisms, diverse multifunctional nanocomposites, and the evolving trends in the development of fire alarm systems anchored in graphene-like 2D nanomaterials and their derivatives. Ultimately, the existing challenges and prospective directions for the utilization of graphene-like 2D nanomaterials in flame retardant and fire-warning applications are put forward.