Hyperbranched Phosphorus-Containing Benzoxazine for Epoxy Modification: Flame Retardant and Toughening Agent

Abstract

To overcome the high flammability and brittleness of epoxy resin (EP) without sacrificing its glass transition temperature (T g ) and mechanical properties, a series of hyperbranched benzoxazines (HB1.0−HB2.5) were synthesized using 6-(bis(4-hydroxyphenyl)methyl)dibenzo[1,2]oxaphosphinine 6oxide (DOPO-2OH) as the "hard" segment and Jeffamine T403 as the "soft" segment. The property investigation revealed that HB2.0 with the optimized ratio of "hard/soft" segments was the appropriate additive for commercial EP. Furthermore, the comprehensive performance of the EP/HB2.0 system was significantly enhanced compared to the pristine EP, demonstrating a 115% increase in impact strength and 5.7 °C in T g . Impressively, when the loading of HB2.0 was only 10 phr (phosphorus content is 0.34 wt %), the modified EP passed the UL-94 V-0 rating and achieved a limited oxygen index (LOI) value of 30.8%, mainly resulting from the flame inhibition effect of the gaseous phase. This research provided an appealing technique for simultaneously improving the toughness and flame retardancy of EP.

Closed-Loop Recycling of Tough and Flame-Retardant Epoxy Resins

“…In addition, the av-EHC and av-CO 2 Y decreased from 22.7 MJ/m 2 and 1.5 kg/kg for EP to 21.3 MJ/m 2 and 1.1 kg/kg for FREP20, which indicated the gaseous phase flame-retardant effect of IA-EHBP. , As predicted, the residue char (RC) of FREPs steadily increased when increasing the concentration of IA-EHBP, and the RC of FREP20 (13.8 wt %) was much higher than that of EP (1.2 wt %). The addition of IA-EHBP facilitated the production of a physical barrier to prevent the underlying materials from transferring heat or mass, which was in accordance with the TGA results. , Moreover, the average mass loss rate (AMLR) of FREPs was significantly reduced when compared with those of EP, indicating that IA-EHBP effectively enhanced the charring of FREPs. Compared with previously reported works about flame-retardant materials, − IA-EHBP exhibited the superiority of simultaneous improvement in flame retardancy and toughness of FREPs.…”

“…The addition of IA-EHBP facilitated the production of a physical barrier to prevent the underlying materials from transferring heat or mass, which was in accordance with the TGA results. 61,62 Moreover, the average mass loss rate (AMLR) of FREPs was significantly reduced when compared with those of EP, indicating that IA-EHBP effectively enhanced the charring of FREPs. Compared with previously reported works about flame-retardant materials, 49−59 IA-EHBP exhibited the superi-ority of simultaneous improvement in flame retardancy and toughness of FREPs.…”

Water-Soluble Biobased Modifier Toward Epoxy/Cellulose Fabric Composite with Simultaneous Enhancement of Flame Retardancy and Interface Adhesion

“…Besides, the chemical compositions of the char residues were further identified by XPS, as shown in Figures c–f and S9b-c. As shown in Figures c and S9b, except for C, N, and O elements, two additional peaks at 133.8 and 191.2 eV attributed to P 2s and P 2p were detected in the char residue for F-SF/F-EP, which explained the important role of P element in the condensed phase. , Meanwhile, in the fine spectrum of F-SF/F-EP, the split peaks at 285.9 eV in C 1s (Figure d), 532.4 eV in O 1s (Figure e), and 133.6 eV in P 2p (Figure f) indicated the presence of P–O–C, and the signals at 288.8 eV in C 1s and 399.6 eV in N 1s (Figure S9c) were assigned to the formation of CN, contributing to the yield of a high-quality char layer . Compared with the results for SF/EP (Figure S10), which displayed a decreased relative content of unsaturated carbon and the absence of P–O–C signal, revealing the important role of PA, HGB, and DGEBDB in promoting the condensed phase.…”

Novel Multifunction Epoxy Thermoset Designed by Manipulating the Silicon-Oxidation Flexible-Rigid Network Topology: Toughening, Strengthening, and Acid/Alkali Resistance

“…Thermosetting epoxy resins (EPs) and their composites are widely used in various fields, such as aerospace, automotive, and construction, owing to their good strength, heat resistance, and dimensional stability. – Their superior performances are attributed to the presence of covalently cross-linked networks. – However, the structure of the cross-linked network is hard to control, leading to difficulties in regulating properties, such as strength, toughness, corrosion resistance, and thermal properties, and overcoming the inherent strength–toughness trade-off. , Generally, the highly rigid cross-linked structures make it difficult for thermosetting resins to dissipate internal stress caused by various applied loads, allowing the formation and evolution of cracks during use and finally resulting in the permanent failure of materials. , Considering the nonrecyclability of thermosetting materials, this problem shortens their service life and is not conducive to the safe use and sustainable development of EPs . Therefore, constructing and regulating cross-linked networks that couple hardness with softness to achieve controllable properties and overcome the trade-off effect between strength and toughness are the biggest difficulties faced in the development of EPs.…”