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

Abstract

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flame retardants are undoubtedly damaging the environment. 3-6 Recently, halogen-containing flame retardants have been replaced by halogen-free counterparts, 7-9 which are characterized by their low fire toxicity.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...

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

“…There were some belonging to the amorphous carbon and the peak at 1600 cm −1 belonging to the crystalline carbon were named D peak and G peak, respectively. 5 Basically, the smaller the R (area ratio of the D and G peaks, R = I D /I G ) means the higher degree of graphitization, indicating better thermostability and barrier performance. 30 Besides, the R values of the inner and outer char layers of PP/RQMIFR/APP-3 were lower than those of PP/PECA/ APP.…”

“…[1][2][3] When being burned, IFR quickly forms intumescent char on the PP surface and prevents it from further burning. [4][5][6] However, its low flame-retardant efficiency and poor compatibility with PP remains as a grand challenge, which severely limits its practical applications. [7][8][9] Macromolecular intumescent flame retardant (MIFR) is a good candidate to address these problems.…”

High‐efficiencyammonium polyphosphate intumescent encapsulated polypropylene flame retardant

“…As a common flame retardant for high nitrogen and phosphorus elements, 11 ammonium polyphosphate (APP) is added with additives, 12–14 or used to form intumescent flame retardant to improve flame retardancy 15–26 . Microencapsulation is also wildly used to protect APP from degradation into small molecules in the processing of polymers at high temperature 27–35 . In previous work, sodium silicate (SS) was used to synthesize nanocomposite fire retardant 36–38 .…”

Cross-Linking Modification of Ammonium Polyphosphate via Ionic Exchange and Self-Assembly for Enhancing the Fire Safety Properties of Polypropylene

“…Polypropylene, one of the commercially available general-purpose plastics, has been applied in agriculture, industry automobile manufacturing and film packaging, owing to its low toxicity, excellent mechanical properties, electrical insulation, and chemical resistance [ 3 , 4 ]. However, its further application and development are restricted by its disadvantages, including the inherent flammability, severe dripping behavior, and the release of smoke and toxic gases during combustion [ 5 ].…”

“…Self-assembly technology has been applied to produce substances with specific structures by exploiting the interactions between structural units, such as hydrogen bonding and ionic interactions [ 4 , 18 , 19 , 20 ]. Recently, self-assembly technology has been adopted to prepare flame retardants due to its facile preparation method and environmentally friendly.…”