A Phosphorous-Based Bi-Functional Flame Retardant Based on Phosphaphenanthrene and Aluminum Hypophosphite for an Epoxy Thermoset

• Published in: International journal of molecular sciences 2022-10, Vol.23 (19), p.11256
• Main Authors: Xu, Bo, Liu, Yanting, Wei, Simiao, Zhao, Siheng, Qian, Lijun, Chen, Yajun, Shan, Hao, Zhang, Qinglei
• Format: Article
• Language: English
• Subjects: Aluminum; aluminum phosphinate; Chemical bonds; Composite materials; Decomposition; Efficiency; epoxy resin; flame retardant; Flame retardants; Free radicals; Gas chromatography; Gases; Hydrocarbons; Infrared spectroscopy; intramolecular P-P synergy; Investigations; Mass spectroscopy; Mechanical properties; phosphophenanthrene; Phosphorus; Phosphorus compounds; Photoelectron spectroscopy; Photoelectrons; Scanning electron microscopy; Thermogravimetry; Vapor phases; X ray photoelectron spectroscopy
• ISSN: 1422-0067; 1661-6596; 1422-0067
• DOI: 10.3390/ijms231911256

A phosphorous-based bi-functional compound HPDAl was used as a reactive-type flame retardant (FR) in an epoxy thermoset (EP) aiming to improve the flame retardant efficiency of phosphorus-based compounds. HPDAl, consisting of two different P-groups of aluminum phosphinate (AHP) and phosphophenanthrene (DOPO) with different phosphorous chemical environments and thus exerting different FR actions, exhibited an intramolecular P-P groups synergy and possessed superior flame-retardant efficiency compared with DOPO or AHP alone or the physical combination of DOPO/AHP in EP. Adding 2 wt.% HPDAl made EP composites acquire a LOI value of 32.3%, pass a UL94 V-0 rating with a blowing-out effect, and exhibit a decrease in the heat/smoke release. The flame retardant modes of action of HPDAl were confirmed by the experiments of the scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetry–Fourier transform infrared spectroscopy–gas chromatograph/mass spectrometer (TG-FTIR-GC/MS). The results indicate that the phosphorous-based FRs show different influences on the flame retardancy of composites, mainly depending on their chemical structures. HPDAl had a flame inhibition effect in the gas phase and a charring effect in the condensed phase, with a well-balanced distribution of P content in the gas/condensed phase. Furthermore, the addition of HPDAl hardly impaired the mechanical properties of the matrix due to the link by chemical bonds between them.