Synthesis of an integrated intumescent flame retardant and its flame retardancy properties for polypropylene

In order to improve its water resistance and compatibility with polymer matrix, ammonium polyphosphate (APP) is modified with melamine-trimesic acid (MEL-TA) aggregates by supramolecular self-assembly technology. Chemical structure and morphology of APP@MEL-TA are investigated by Fourier transform infrared spectroscopy and scanning electron microscopy (SEM), respectively. Intumescent flame retardant system of APP@MEL-TA and charring-foaming agent is introduced into polypropylene (PP) matrix. The flammability and combustion behavior of PP composites are investigated by limiting oxygen index (LOI), UL-94 vertical burning, and cone calorimetry tests. In terms of LOI values and cone combustion results, APP@MEL-TA performs better than pristine APP. Char residue of PP composites is investigated by SEM and Raman spectra. Flame retardant mechanisms are proposed based on thermal decomposition, combustion results, and analysis on char residue. K E Y W O R D S ammonium polyphosphate, flame retardant, polypropylene, supramolecular self-assembly, thermal stability 1 | INTRODUCTION Polypropylene (PP) is widely applied in a variety of applications, such as transportation, cables, housing, and electric industry. However, PP burns very rapidly with the release of a great deal of heat, which limits its applications in many fields. Thus, the improvement in flame retardant properties of PP has become an important research. Zhang et al 1 reviewed the research progress of halogen-containing flame-retarded PP. The obvious disadvantages of traditional halogen-based flame retardants are high fire toxicity and releasing of smoke during the combustion. 2 In addition, environment amity is the theme of whole society, and some halogen-containing flame retardants are undoubtedly damaging the environment. 3-6 Recently, halogen-containing flame retardants have been replaced by halogen-free counterparts, 7-9 which are characterized by their low fire toxicity. Intumescent flame retardants (IFRs) are the most popular halogen-free retardants because of their advantages of low smoke and toxicity during combustion. 10,11 Wang et al 12 prepared a novel IFR by the reaction of melamine (MEL) with methyl hydrogen siloxane, and this flame retardant system can effectively improve flame retardancy of PP.Acid catalyst, blowing source, and charring agent are three main ingredients for IFR system. 13,14 According to its elemental composition, ammonium polyphosphate (APP) acts as acid catalyst and blowing source because of its high phosphorus and nitrogen contents, both of which are primary flame retardant elements. 15,16 However, as an important component of IFR, APP has obvious disadvantages of weak water resistance and poor compatibility with polymer matrix. 3,17,18 Hence, it is of great significance to modify the surface of APP and improve flame retardant properties of resulting composites. In view of these deficiencies, many researches on surface modification of APP have been carried out. The surface characteristics of APP are modified by other flame retard...

Section: Resultsmentioning

confidence: 89%

Supramolecular self‐assembly modification of ammonium polyphosphate and its flame retardant application in polypropylene

Yuan

Dong

et al. 2020

“…When heated to about 450°C, the CC absorption at 1648 cm −1 was observed. The peak at 3083 cm −1 (stretching vibration of HCC) and 890 cm −1 (deformation vibration of HCC) also proved the formation of unsaturated bond . The gaseous degradation products of PP/IFR and PP/IFR/SiO 2 ‐NH 2 were generated similarly, so the synergistic flame‐retardant effect of SiO 2 ‐NH 2 and IFR was not exerted in the gas phase.…”

Section: Resultsmentioning

confidence: 96%

Synergistic effect of cocondensed nanosilica in intumescent flame‐retardant polypropylene

Ding

Liu

Gao

et al. 2019

Amino‐functionalized nanosilica (SiO2‐NH2) was prepared through cocondensation method using aminopropyltriethoxysilane as comonomer to hydrolyze and cocondense with tetraethylorthosilicate. The synergistic effect of combination of ammonium polyphosphate and pentaerythritol with SiO2‐NH2 on the thermal and flame‐retardant properties of intumescent flame‐retardant (IFR) polypropylene (PP) has been investigated by thermogravimetric analysis (TGA), scanning electron microscopy, Raman spectra, X‐ray diffraction (XRD), limiting oxygen index (LOI), and UL 94 tests. When 1.0 wt.% SiO2‐NH2 was added, the LOI value of the PP/IFR composite with 25 wt.% of IFR increased from 26.6% to 31.7%, while the UL 94 rating raised from not classified to V‐0. The TGA data demonstrated that the SiO2‐NH2 nanoparticles increased the charred residue of the PP/IFR composites. The morphological structures and the orderliness of the charred residue proved that SiO2‐NH2 promoted the formation of compact intumescent charred layer, which effectively protected the underlying polymer from burning. The XRD patterns of the charred residue indicated that nanosilica reacted with APP to form SiP2O7 crystal structure during combustion, which was beneficial to the formation of compact charred layers. In comparison with the inorganic SiO2‐cal nanoparticles, the amino‐functionalized nanosilica revealed much more efficient synergistic flame‐retardant effect due to the difference of surface properties.

“…[2][3][4] In recent years, with the improvement of environmental awareness and the deepening of the global green strategy, development of environmentally friendly flame retardants, which are low smoke, low toxicity, and halogen-free, is the focus of current research. [5][6][7] Among these flame retardants, intumescent flame-retardant (IFR) is low halogen, low smoking and low pollution and is suitable for flame retardant of PP. Generally, IFR system includes three basic parts: an acid source, a carbon source, and a gas source.…”

Section: Introductionmentioning

confidence: 99%

Effects of a semi‐bio‐based triazine derivative on intumescent flame‐retardant polypropylene

Wang

2019

A semi‐bio‐based synergist (N, N′, N″‐1, 3, 5‐triazine‐2, 4, 6‐triyltris‐glycine [TTG]) was prepared by using glycine and cyanuric chloride. The structure of TTG was characterized by 1H NMR and Fourier transform infrared spectroscopy. The TTG was applied in polypropylene (PP)/intumescent flame‐retardant compounds to improve its flame retardancy. The flame‐retardant properties of PP compounds were evaluated by limiting oxygen index and vertical burning tests (UL‐94). The results showed that 17 wt% intumescent flame‐retardant and 1 wt% TTG makes PP achieve the UL‐94 V‐0 rating without drippings, and the limiting oxygen index value is increased to 29.5 vol%. The thermal degradation behavior and char morphology of PP compounds were investigated by thermogravimetric analysis and scanning electron microscopy. The results indicated that TTG accelerates the formation of char layer, regulates the porous structure of char layer, and enhances its barrier property. Therefore, the temperatures of PP compound after two ignitions during the UL‐94 test are decreased significantly as shown in infrared thermal imaging. In addition, the combustion characteristics of PP compounds were investigated by cone calorimeter. The peak of heat release rate (PHRR) of PP compound is 67% reduced, and the tPHRR is delayed from 223 to 430 seconds, indicates that the combustion risk of PP compound is reduced.