Abstract
Recently, lots of effort has been placed into stabilizing black phosphorus (BP) in the air to improve its compatibility with polymers. Herein, BP was chemically functionalized by aliphatic amine (DETA), aromatic amine (PPDA) and cyclamine (Pid) via a nucleophilic substitution reaction, aiming to develop an intensively reactive BP flame retardant for epoxy resin (EP). The -NH2 group on BP-DETA, BP-PPDA and BP-Pid reacted with the epoxide group at different temperatures. The lowest temperature was about 150 °C for BP-DETA. The impacts of three BP-NH2 were compared on the flame retardancy and thermal decomposition of EP. At 5 wt% loading, EP/BP-NH2 all passed UL 94 V 0 rating. The limiting oxygen index (LOI) of EP/BP-PPDA was as high as 32.3%. The heat release rate (HRR) of EP/BP-DETA greatly decreased by 46% and char residue increased by 73.8%, whereas HRR of EP/BP-Pid decreased by 11.5% and char residue increased by 50.8%, compared with EP. Average effective heat of combustion (av-EHC) of EP/BP-Pid was lower than that of EP/BP-DETA and EP/BP-PPDA. In view of the flame-retardant mechanism, BP nanosheets functionalized with aliphatic amine and aromatic amine played a dominant role in the condensed phase, while BP functionalized with cyclamine was more effective in the gas phase.
Highlights
Epoxy resin (EP), an important thermosetting polymeric material, is widely used in many fields, such as in coating, construction, transportation, electronic and electrical industries (EE) due to its excellent electrical insulation performance, high mechanical strength and good chemical resistance [1,2,3,4,5]
Three amine-containing compounds were chosen to functionalize black phosphorus (BP) via the nucleophilic substitution reaction, and its structure and composition was confirmed by FT-IR, XRD, Raman, XPS, and TEM
The results showed that the amino group of BP was modified by aliphatic amine and had the highest reactivity with the epoxy group, and the descending order of reactivity between amino and epoxy groups was EP-BP-DETA > EP-BP-PPDA > EP-BP-Pid
Summary
Epoxy resin (EP), an important thermosetting polymeric material, is widely used in many fields, such as in coating, construction, transportation, electronic and electrical industries (EE) due to its excellent electrical insulation performance, high mechanical strength and good chemical resistance [1,2,3,4,5]. BP is excellent in many ways, chemical degradation of phosphorous into phosphorus oxides in the presence of ambient oxygen and water results in the rapid loss of properties, due to the high reactivity of the lone pair of electrons in BP [19,20,21,22,23,24,25,26,27,28,29]. Chemical functionalization utilizes the lone pair of electrons present in the phosphorous atom to form direct chemical bonds and can protect BP from oxygen, to achieve long-term stability for BP at ambient conditions [22]. The results showed that, compared with aromatic amine and cyclamine, the amino group of BP modified by aliphatic amine had the highest reactivity with the epoxy group and the reaction temperature was about 150 ◦ C. The condensed-phase flame retardancy of aliphatic amine and aromatic amine modified BP in the epoxy matrix was dominant, while the cyclcamine modified BP mainly played the role of gas-phase flame retardancy
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