Functionalized ZrP nanosheet with free‐radical quenching capability and its synergism in intumescent flame‐retardant polypropylene

Abstract

The combination of catalyzing carbonization and free-radical quenching mechanism is proposed to be a promising strategy for the preparation of high-efficiency flameretardant polypropylene (PP). Herein, a novel functionalized zirconium phosphate (RQZrP) nanosheet with free-radical quenching capability was fabricated by decorating macromolecular N-alkoxy hindered amine (MNOR) onto the surface of ZrP. It was combined with an intumescent flame retardant (IFR) to flame-retard PP. The results showed that there was a good synergism between RQZrP and IFR, which effectively improved the fire safety of PP. When the content of RQZrP was 2 wt% and IFR was 23 wt%, the limiting oxygen index (LOI) of PP increased from 19.0% to 33.0%, and it achieved a UL-94 V-0 rating. Meanwhile, the peak heat release rate (PHRR), total heat release (THR), carbon monoxide production (COP), and carbon dioxide production (CO 2 P) were significantly decreased. It revealed that nitroxyl radicals generated by RQZrP could capture alkyl radicals and peroxy radicals that produced during the degradation and combustion of PP. Meanwhile, RQZrP acted as a solid acid that catalyzed PP chains rapidly cross-linking to form char on its surface, and it also played as a supporting skeleton to enhance the strength and compactness of the char layer, thus effectively preventing the transmission of heat, oxygen, and combustible gases.

N‐alkoxyamine‐containing macromolecular intumescent flame‐retardant‐decorated ZrP nanosheet and their synergism in flame‐retarding polypropylene

“…The absorption peaks at 592 and 521 cm −1 were assigned to Zr–O. The main characteristic peaks of RQMIFR exhibited the N–H stretching vibration peak at 3410 cm −1 , the –CH 2 – stretching vibration peak at 2930 cm −1 , and the triazine ring stretching and bending vibration peaks at 1580 and 801 cm −1 29 . For RQMIFR‐ZrP, it displayed the characteristic peaks of both ZrP and RQMIFR, which further proved the successful synthesis of RQMIFR‐ZrP.…”

“…In recent years, free‐radical scavengers such as fullerene (C 60 ) 24,25 and hindered amine 26–28 were proved to be good synergists in improving the flame retardancy of IFR. Our previous works 29–31 revealed that a very small amount of N ‐alkoxy hindered amines (NOR) efficiently improved the flame retardancy of PP by free‐radical quenching. During the combustion, nitroxyl radicals (NO•) were generated from NOR and effectively quenched peroxy radicals (ROO•) to inhibit the degradation of PP.…”

Recent advances in fire‐retardant carbon‐based polymeric nanocomposites through fighting free radicals

“…In addition to DOPO, other fire retardants with lower oxidation state P also possess a similar gaseous-phase free radical capture effect. For instance, Lai et al 106 reported a functionalized ZrP nanosheet (RQZrP) with a free-radical quenching capability, which shows improved flame retardancy for PP when combined with the IFR. Similarly, Xing et al 107 constructed an ionic liquid (IL) modified black phosphorus (BP) nanosheet (IL-BP) by self-assembly for flame retardancy of PU, and the final PU nanocomposite containing 2 wt% IL-BP achieved 38% and 20% reductions in PHRR and THR, respectively, as well as a 18 • C increase in the T onset compared with pure PU.…”

Synthesis of a novel N‐alkoxyamine containing macromolecular intumescent flame retardant and its synergism in flame‐retarding polypropylene

“…Excess hindered amine would promote the thermal decomposition of PP, and accelerated its molten droplets, thus limiting the further improvement of its flame-retardant efficiency. 25 Therefore, how to effectively regulate the N-alkoxy-hindered amine content in MIFR is a key factor to realize the high efficiency of intumescent flameretardant PP.…”

“…This was mainly because the nitroxyl radical (NO•) generated by RQMIFR quenched the active freeradicals produced by the pyrolysis of PP in gas phase and inhabited the β-degradation of PP. In condensed phase, NO• captured the PP macromolecular free radicals and cross-linked with RQMIFR skeleton under the catalysis of inorganic acids to form a dense char layer, which effectively prevented the degradation and combustion of PP 25. Cone calorimeter test (CCT) was also employed to investigate the large-scale combustion behaviors of flame-retardant PP.…”