Multi‐element heterocyclic compound derived from DOPO and thiadiazole toward flame‐retardant epoxy resin with satisfactory mechanical properties

Abstract

In order to comply with the environmentally friendly flame retardant requirements of epoxy resin and strive to maintain the comprehensive performance of the epoxy resin matrix, a P/N/S-containing heterocyclic halogen-free reactive flame retardant (VAP) was constructed. Vanillin (VA), 2-amino-5-mercapto-1,3,4-thiadiazole, and 9,10-dihydro-9-oxa-10-phosphaphenanthrene10oxide (DOPO) were chosen as raw materials to prepare VAP through a simple one-pot reaction. The addition of VAP slightly decreased the curing activity of the system while the transparency of the samples was maintained well. Moreover, the maximum degradation rate of VAP modified samples dropped by 47.26% and the amount of char residue at 800 C increased. When 10 wt% VAP (0.66 wt% P) was added, EP-10 passed UL-94 V-0 rating and the limited oxygen index value reached 30.3%. In contrast to pure EP, the peak heat release rate, total heat release, and total smoke production of EP-10 were reduced by 36.87%, 25.61%, and 29.07%, representing good smoke and heat suppression effect.Besides, the glass transition temperature (T g ) of the samples remained above 165 C, showing a slight drop. Due to the existence of heteroatoms and the introduction of heterocyclic structure, the enhancement of intermolecular force in the system counteracted the deterioration of mechanical properties caused by the reduction of crosslinking density, maintaining the excellent mechanical properties of epoxy resin.

Facile Preparation of a Novel Vanillin-Containing DOPO Derivate as a Flame Retardant for Epoxy Resins

“…It has previously been demonstrated that the N/S-containing thiazole has great potential for the construction of efficient FRs [28][29][30]. A novel bio-based FR (marked as AVD) has synthesized from the reaction of DOPO, vanillin, and 2-aminobenzothiazole.…”

The synthesis of biphenyl ether/vanillin‐based flame retardants for enhancing both the flame retardant properties and mechanical performance of epoxy resin

“…As displayed in Figure 4a,b, the elastic modulus and tensile strength of the cured EP/DVD samples were taller than those of pure cured EP, especially EP/DVD‐1, which reached the maximum tensile strength. Comparing the contents of the previous research and comparing the effects of flame retardants on the properties of EP under different added contents, it could be found that the tensile strength of the DVD studied in this paper increased significantly when the high addition amount was 7.2 wt%, and the mechanical properties were outstanding 31,32,34,37,38 . Furthermore, the supplement of DVD obviously improved the bending modulus and strength.…”

“…Mechanical properties of epoxy resin (EP)‐diaminodiphenylmethane (DDM) and EP/DVD‐DDM composites: (a) elastic modulus and tensile strength, (b) flexural modulus and strength, and (c) impact strength, and (d) comparison of the tensile strength improvement of this product with other intumescent flame retardant EPs at high dosage 31,32,34,37,38 . [Color figure can be viewed at wileyonlinelibrary.com]…”

“…Comparing the contents of the previous research and comparing the effects of flame retardants on the properties of EP under different added contents, it could be found that the tensile strength of the DVD studied in this paper increased significantly when the high addition amount was 7.2 wt%, and the mechanical properties were outstanding. 31,32,34,37,38 Furthermore, the supplement of DVD obviously improved the bending modulus and strength. The enhancement in tensile and bending properties could due to the introduction of massive rigid benzene rings into the EP matrix due to the incorporation of DVD.…”

“…However, compared to pure EP, the mechanical properties of flame retardant epoxy resin (FREP) using PAPDOPO as a flame retardant have hardly changed. Zou et al 32 synthesized a P/N/sulfur containing compound (VAP) using VA as raw material, which exhibited good flame retardancy when used for EP modification. When VAP was 10 wt% (0.66 wt% P), EP‐10 was rated UL‐94 V‐0.…”