Synergistic Effects Of N-alkoxy Hindered Amine And Intumescent Flame Retardant On Flame-retarding Polypropylene And Its Mechanism

Polypropylene is widely used in internal and external decoration of cars, constructionmaterials, textile, furniture, electrical and electronic fields, and so on, due to its goodmechanical properties, light weight, easy processing, excellent resistance to chemicals andlow cost, etc. However, PP is a highly combustible material, which severely restricts itsapplication in many fields. Therefore, it is essential and urgent to endow it with good flameretardancy. Intumescent flame retardant (IFR) is one of the fastest growing halogen-free flameretardants. It provides a new idea and novel method for preparation of halogen-free flameretardant PP with high efficiency. However, there are some shortcomings with traditional IFR,such as low flame-retardant efficiency, poor thermal stability and single function, etc., whichnot only deteriorates the mechanical properties of PP but also makes its weather-resistancedecline. To solve these problems, in this dissertation, N-alkoxy hindered amine (NOR116)with free radical quenching capability was employed to combine with ammoniumpolyphosphate/pentaerythritol (APP/PER) to flame retard PP. The synergistic mechanismbetween NOR116and APP/PER was further investigated. Then, a silicon-containingmacromolecular triazine-based charring foaming agent (Si-CFA) was synthesized and mixedwith APP to form IFR (APP/Si-CFA). NOR116was used to combine with APP/Si-CFA toflame retard PP. Accordingly, flame retardant PP with highly efficient flame retardancy,outstanding ultraviloet aging resistance and good thermo-oxidative aging resistance wereprepared, and their flame retardant mechanism was intensively studied. The main researchcontents and results are listed as following:Firstly, the synergistic effects between N-alkoxy hindered amine (NOR116) andAPP/PER (the mass ratio of APP and PER was2:1, named IFR1) on flame retardancy andmechanical properties of PP were investigated. The thermostability, ultraviolet (UV) agingresistance, thermo-oxidative aging resistance and thermal degradation behavior of the flameretardant PP were also studied. And the flame retardant mechanism between NOR116andIFR1was further explored and revealed by thermogravimetry analysis (TGA), Fouriertransform infrared (FTIR), thermogravimetry-Fourier transform infrared (TG-FTIR), scanningelectron microscope-energy dispersive X-ray spectroscopy (SEM-EDX) and laser Raman spectroscopy (LRS). The results demonstrated that IFR1/NOR116was efficient in improvingthe flame retardancy, UV stability and thermo-oxidative aging performance of PP, but thevertical combustion performance should be further improved. When the amount of NOR116was0.5wt%(the total amount of flame retardant was25.0wt%), the LOI of PP/IFR1/NOR116composite was increased from31.0%to35.0%and the UL-94rating was V-2. Meanwhile,average heat release rate (av-HRR), average mass loss rate (av-MLR) and total smokeproduction (TSP) were reduced obviously compared to PP/IFR1, and the ignition time wasprolonged from23s to33s. Moreover, the initial decomposition temperature (Ti) of the flameretardant PP was increased by11℃. The apparent activation energy of thermal degradationfor PP/IFR1/NOR116was increased obviously compared to PP/IFR1. TGA, FT-IR, TG-FTIRand SEM-EDX results showed, during the combustion, NOR116not only quenched the activefree-radicals in the gas phase but also promoted the charring of IFR1and enhanced quality ofthe char layer, which effectively improved the flame retardancy of PP.Secondly, based on the molecular design, silicon-containing macromolecular triazine-based charring foaming agent (Si-CFA) with excellent thermostability and outstandingchar-forming ability was synthesized by using cyanuric chloride, ethanediamine andγ-aminopropyl triethoxysi-lane, etc., and it was combined with APP as a novel IFR system(APP/Si-CFA, the mass ratio was2:1, named IFR2). Then, NOR116was used to blend withIFR2to flame retard PP. It was found that NOR116had a positive synergistic effects with IFR2on enhancing the flame retardancy and smoke suppression of PP, and no dripping wasobserved. When the amount of NOR116was0.3wt%(the total amount of flame retardant was25.0wt%), the LOI of PP/IFR2/NOR116composite was increased from35.0%to42.5%andreached a UL-94V-0rating. The cone calorimetric test (CCT) results showed that the peakheat release rate (pHRR), peak of smoke produce rate (pSPR) and TSP were reduced by57.9%,51.7%and45.1%, respectively in comparision with those of PP/IFR2composite. Theignition time of PP/IFR2/NOR116was prolonged from25s to32s. Moreover, the addition ofNOR116could improve the thermostability and UV aging resistance of the flame retardant PP.TGA, FT-IR, TG-FTIR and SEM results showed that NOR116could promote the charringprocess of IFR2in lower temperature and enhance the thermostability and residual charamount in high temperature.