Review on intrinsically recyclable flame retardant thermosets enabled through covalent bonds

Abstract

Developing thermosets with inherent recyclability and flame retardancy is a great importance from the views of fire safety, resource conservation and environmental protection. Owing to their superior mechanical properties, versatility, outstanding adhesion‐ability, durability, thermal, and solvent stability comparable to conventional thermosets while demonstrating end‐of‐life reuse, recyclable thermosetting materials have gained much interest as an attractive class of sustainable thermosets. The chemical structure of thermosets includes dynamic covalent networks that provide durability and reprocessability. However, these recyclable thermosets possess significant flammability, limiting their application in automobiles, railways, aircraft, buildings, and electronic items. Thus, it is urgent to include them with flame retardants. The goal of this review paper is to give a broad understanding of the study by highlighting and discussing recent advances as well as future prospects for inherently recyclable flame retardant thermosets (RFRs). Moreover, synthesis methods have been highlighted to improve the design of internally recyclable fire retardant thermosets. A distinct emphasis will be given on the inherent RFRs in terms of flame retardancy, recycling property, physical properties, and thermal stability. Finally, we will explore the importance and threats that intrinsically recyclable flame retardant thermosets face in the future.

A Quercetin-Derived Polybasic Acid Hardener for Reprocessable and Degradable Epoxy Resins Based on Transesterification

“…Conventional epoxy thermosets have excellent mechanical performance, dimensional stability, adhesion to diverse substrates, and chemical resistance. However, they cannot be repeatedly processed as thermoplastics by remelting because of their extremely stable cross-linked structure. − As a result, the epoxy wastes generated in the manufacturing process or at the end of service life are generally disposed of by landfill and incineration, which would bring about serious environmental problems. , Therefore, endowing epoxy thermosets with inherent recyclability is of great importance in view of environmental and economic factors. The incorporation of dynamic covalent bonds has been reported to be an effective approach to develop recyclable thermosets.…”

“…In addition to the recycling issue, conventional epoxy thermosets are usually produced from nonrenewable fossil resources . Developing epoxy thermosets from biomass resources has attracted extensive consideration from academic scholars, industrialists, and government communities. − Recently, numerous epoxy thermosets prepared from renewable vegetable oils, , cardanol, isosorbide, , rosin, gallic acid, ferulic acid, and lignin and its derivatives − have also been reported in the literature. Apart from these, biobased polyphenolic compounds are another class of promising starting materials because of their abundant reactive sites, rigid skeleton, biodegradability, and inherent abundance at lower cost. − Li and coworkers reported biobased epoxy thermosets cross-linked by polyphenolic tannic acid.…”

Investigation of recycling effects on the mechanical properties of short carbon and glass fiber reinforced polyetherimide composites

“…Polymer composites reinforced by carbon and glass fibers have been widely utilized in many engineering fields including aerospace aircrafts, wind turbine blades, and automotive industries due to their high strength and stiffness, outstanding wear resistance, long service life, and excellent corrosion/fire resistance, and so forth 1–3 . Nonetheless, the broad applications of fiber reinforced polymer (FRP) composites have accompanied the significant quantities of waste, which leads to a huge energy consumption and a series of environmental problems 4,5 .…”

“…Polymer composites reinforced by carbon and glass fibers have been widely utilized in many engineering fields including aerospace aircrafts, wind turbine blades, and automotive industries due to their high strength and stiffness, outstanding wear resistance, long service life, and excellent corrosion/fire resistance, and so forth. [1][2][3] Nonetheless, the broad applications of fiber reinforced polymer (FRP) composites have accompanied the significant quantities of waste, which leads to a huge energy consumption and a series of environmental problems. 4,5 As reported, over 6000 civil aviation aircrafts will be decommissioned by 2030 6 and it was also predicted that about 43 million tons of turbine blade wastes would be generated worldwide by 2050, 7 where there would be huge amounts of FRP composite wastes in the world that require to be treated properly.…”

Developing Easy Processable, Recyclable, and Self-Healable Biobased Epoxy Resin through Dynamic Covalent Imine Bonds

“…Traditional epoxy thermosetting polymers have excellent mechanical strength and dimensional stability, good adhesive forces to diverse substrates, and extraordinary chemical and thermal resistivity, − but they cannot be reprocessed like thermoplastics. − Furthermore, it is familiar that the existing degradation and reutilization of traditional thermosetting polymers are extremely exclusive and require considerable energy due to the stable three-dimensional (3D) cross-linked structures. − As a result, more waste will be generated in production and in the end-of-life products and dumped as landfill or incinerated, which significantly creates environmental problems . Hence, it is crucial to create renewable new thermosets such as thermoplastics to satisfy the urgent needs for the sustainable improvement of society.…”