Advancements in monomers and reinforcements of unsaturated polyester composites: Traditional, bio-based, and flame-retardant types

Unsaturated polyester Resins (UPR) are crucial in modern materials science due to their versatility, mechanical properties, and ease of processing. They find extensive applications in industries ranging from automotive to construction. This review comprehensively explores the diverse range of monomers and reinforcements used in UPR composites, emphasizing the significance of these monomers and reinforcements in tailoring the properties of UPR. For monomers used in UPR synthesis, the review emphasizing traditional, bio-based, halogen-containing flame-retardant, and phosphorus-based flame-retardant monomers. Bio-based monomers are gaining attention due to their potential to reduce dependency on petroleum resources and their lower environmental impact. The review discusses various bio-based and flame-retardant alternatives for diols, diacids and diluents, highlighting their role in advancing sustainable and fire safety polymer technology. The use of fiber and nano reinforcements for UPR composites are also summarized. The review focuses on the advantages and challenges of natural fibers compared to traditional glass and carbon fibers, and analyze different surface modification method for simultaneously improving interfacial compatibility and flame-retardant performance of UPR composites. In addition, nano flame-retardant reinforcements for UPR composites are highlighted in this review, due to the increasingly widespread use of nanomaterials in high-performance polymer composites. In summary, this review provides a detailed examination of monomer and reinforcements categories, reflecting their significance in advancing the high performance and sustainability in UPR composites. The discussion underscores the ongoing innovations and future directions in the field, aiming to address both functional and environmental challenges.