Green and Facile Synthesis of Bio-Based, Flame-Retardant, Latent Imidazole Curing Agent for Single-Component Epoxy Resin

Abstract

Developing bio-based flame retardants according to a green and simple strategy has drawn extensive attention recently. Hence, a biomass-derived, flame-retardant, latent curing agent (IMPA) was synthesized via the neutralization between imidazole and phytic acid in water at room temperature and was applied for single-component epoxy resin (EP). The results indicate that the shelf life of the resultant EP (EP/IMPA) increases from <1 day of the control single-component EP to 10 days at room temperature. Meanwhile, EP/IMPA features a fast curing rate at modest temperature (80–150 °C), and its gel time at 100 °C is only 14 min. Notably, EP/IMPA achieves superior flame retardancy with a limiting oxygen index of 34.7% and UL-94 V-0 rating. The peak heat release rate (PHRR), total heat release (THR), and total smoke production (TSP) of EP/IMPA are reduced by 43.0%, 31.9%, and 31.5% compared with the control sample. The enhanced fire safety is ascribed to the flame-retardant function of IMPA in both gaseous and condensed phases. Hence, this work provides a green and feasible method to create bio-based, flame-retardant, latent curing agents for one-component epoxy systems.

Preparation of a multifunctional flame retardant epoxy resin containing phosphorus and nitrogen and study of its properties

“…5 Therefore, the development of environmentally friendly and pollution-free flame retardant resin might prove a vital area for future research. 6,7 Researchers have investigated innovative halogen-free flame retardants to achieve environmentally friendly requirements, such as novel phosphorus-based flame retardants and nano-filled flame retardants. The tiny molecule phosphate ester accounts for the majority of phosphorus-based flame retardants, [8][9][10][11] ammonium polyphosphate (APP) class, [12][13][14] DOPO 11,15,16 class and inorganic phosphorus-based additive flame retardants.…”

“…Although traditional halogen flame retardants have high efficiency, they are prone to emitting poisonous fumes during burning, endangering the environment, wildlife, and human health 5 . Therefore, the development of environmentally friendly and pollution‐free flame retardant resin might prove a vital area for future research 6,7 …”

ADOPO‐anchored benzothiadiazole derivative toward efficiently P/N/S synergistic flame retarding of epoxy thermoset

“…Considering the diverse flame-retardant mechanisms for the different flameretardant elements (e.g., the phosphorus-containing flame retardants were beneficial to promote the formation of the carbon layer, the nitrogen-containing flame retardants could effectively play a crucial role in gas phase flame retardancy, the silicon-containing flame retardants were helpful to improving the stability of carbon layer), the attractive strategies including "grafted flame-retardants" and "multiple elements synergistic flame-retardants" were frequently introduced. 13,[17][18][19][20][21][22][23] In particular, the multiple elements synergistic flame-retardants could prepare the high-effective flame-retarded polymers under ultralow P content through combing the gas and condensed phase synergistic flame-retarding. Among the reported multiple elements synergistic flame-retardants, DOPO-based phosphoruscontaining flame retardants bridging with other elements stood out as the most promising candidates for fabricating the high flame-retarded polymers due to their multiple flame-retardant effects, high flame retardant efficiency, low environmental toxicity, and easy-to-design.…”

“…Consequently, the high‐effective flame‐retarded polymers under low phosphorus content are highly desirable. Considering the diverse flame‐retardant mechanisms for the different flame‐retardant elements (e.g., the phosphorus‐containing flame retardants were beneficial to promote the formation of the carbon layer, the nitrogen‐containing flame retardants could effectively play a crucial role in gas phase flame retardancy, the silicon‐containing flame retardants were helpful to improving the stability of carbon layer), the attractive strategies including “grafted flame‐retardants” and “multiple elements synergistic flame‐retardants” were frequently introduced 13,17–23 . In particular, the multiple elements synergistic flame‐retardants could prepare the high‐effective flame‐retarded polymers under ultralow P content through combing the gas and condensed phase synergistic flame‐retarding.…”

Design of New Functional Flame‐Retardant System for High‐Performance Epoxy Thermosets Enabled by Bifunctional Few‐Layer Black Phosphorus and Synergistic Strategy

“…Multiple types of flame retardants (i.e., phosphorus‐, nitrogen‐, silicon‐based flame retardants) have been adopted to achieve this goal. [ 7–14 ] Among these flame retardants, 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) has been widely utilized for lowering the flammability of epoxy thermosets attributed to its merits of high efficiency and low toxicity. [ 15–19 ] However, the high addition of DOPO (about 9 wt%) is usually needed to ensure the low flammability of epoxy thermosets, which will have a negative impact on other properties (i.e., mechanical and thermal properties) of the epoxy matrix.…”