Investigation On Flame Retardant Synergistic Effect, Catalytic Carbonization And Novel Intumescent Flame Retardant System Based On Polypropylene

Polypropylene (PP) has broad applications in electronics, architectural materials, cars and so on, due to its easy processing, chemical resistance and other excellent properties. However, PP is flammable, so it is necessary to improve the flame retardancy of PP in order to expand its application. In this dissertation, a lot of literatures have been reviewed on the basis of intumescent flame retardant PP and flame retardant PP nanocomposites. Some porous metal phosphates were prepared by hydrothermal synthesis, and were used in the intumescent flame retardant PP. We also prepared flame retardant PP/layer double hydroxide (LDH) nanocomposites, some semi-biodegradable flame retardant PP composites, and new high efficiency intumescent flame retardant PP materials with good water resistant property. Main research works are as follows:1. A novel synergist-nanoporous nickel phosphates VSB-1 was prepared by hydrothermal synthesis. Then we investigated the synergistic effect of the VSB-1 with intumescent flame retardants (IFR, APP/PER=2:1) in PP matrix. From the results of LOI, UL94 and Cone test, it can be found that flame retardant PP material with the suitable content of VSB-1 has a better flame retardant properties and a higher fire safety. Compared with ZB,4A zeolite and OMT which are very effective synergists with intumescent flame retardants, VSB-1 shows the best synergistic effect at the same loading. In addition, real-time infrared studies thermo-oxidative degradation mechanism of the intumescent system, and the addition of VSB-1 is found to increase the thermal stability. Scanning electron microscopy (SEM) is used to characterize the morphology of char layer after the oxygen index test, and the result shows that the VSB-1 containing char layer is more compact. Mechanical testing shows that keeping the flame retardant properties unchange, the addtion of VSB-1 can significantly improve the mechanical properties of flame retardant PP. Through the research we want to provide a more promising way for design new efficient intumescent material that can further reduce the addition of flame retardants.2. We continue further study of previous work by the isomorphous substitution of transition metal ions (Fe, Zn) into the nickel phosphates VSB-1 framework. Then, the two kinds of transition metal ion-incorporated nickel phosphates (TMIVSB-1) materials were synthesized using a hydrothermal method. Meanwhile, a low cost synergist-ferric pyrophosphate (FePP) was used in intumescent flame retardant PP. The synergistic effects of TMIVSB-1 or FePP with intumescent flame retardants (IFR, APP/PER=2:1) in PP matrix were investigated. According to their flammability tests (LOI, UL94 test), TMIVSB-1 or FePP can obviously improve the flame retardant properties of PP composites. The results of XPS show that the addition of FePP can greatly improve the high temperature performance of flame retardant PP.TG-IR results also demonstrate that the flame retardant mechanism of PP/IFR/FePP system is in the condensed phase rather than in the gas phase.3. Sodium dodecyl sulfate modified zinc-aluminum layered double hydroxide ZnAl(SDS)-LDH was prepared via one-step method, and its structure was characterized. Intumescent flame retardant PP/ZnAl(SDS)-LDH nanocomposites were prepared by melt blending. The effects of organic modified LDH on the flame retardant properties, thermal stability and crystal properties of the intumescent flame retardant PP composites have been studied by limiting oxygen index (LOI), thermal gravimetric analysis (TGA) and differential scanning analyzer (DSC). The influence of preparation method on flame retardant performance of materials has been studied as well.4. Combining synchrotron radiation vacuum ultraviolet single-photon ionization and reflection time of flight mass spectrometry technology to characterize vacuum pyrolysis products of PP in order to study the mechanism of PP pyrolysis; PP/organically modified montmorillonite (OMT)/Ni2O3 composite were prepared by melted blending, and then investigated the influence of different factors such as atmosphere, temperature, composition on the carbonization of PP composites. In this work a detailed mechanism for the formation and the growth of MWCNTs is proposed based on the experimental analysis. Furthermore, the flame retardancy of PP composites was also investigated. From this work, we hope to help theoretical research and engineering applications of novel flame retardant polymer composites.5. Starch containing polypropylene (SCP) semi-biocomposites were prepared by melted blend method. Microencapsulated ammonium polyphosphate (MCAPP) was added to the SCP not only to improve its flame retardant properties but also to restrain the reaction between ammonium polyphosphate (APP) and starch during processing. The flame retardant properties of the flame retardant SCP composites have been investigated by limited oxygen index (LOI), UL94 test and cone calorimeter test. The results show that flame retardant properites of SCP improve substantially compared with that of pure PP. MCAPP and starch can form an intumescent system to protect the matrix from further burning, so the flame retardant properties of SCP semi-biocomposites improve.6. A novel flame retardant PP materials were prepared by the addtion of the intumescent flame retardants (IFR) consisting of a novel char forming agent (CFA) and MCAPP. With the loading 30wt% IFR(CFA/MCAPP=1/2), PP composites present the most effective flame retardancy ability with the value of LOI to 36.5. Even with 25wt% IFR (CFA/MCAPP=1/2), PP composites can still pass V-0 rating. The results of cone calorimeter show that heat release rate peak (pHRR), total heat release (THR), and the mass loss rate (MLR) of PP/30wt% IFR(CFA/MCAPP=1/2) decrease substantially when compared with those of pure PP, the pHRR decreasing from 1140 to 100 kW/m2, the THR decreaing from 96 to 16.8 MJ/m2and the MLR decreasing from 100% to 40%. SEM demonstrates the quality of char layers of PP/MCAPP/CFA systems are superior to those of PP/MCAPP and PP/CFA systems. From water resistant test, it shows that the sample of PP/30wt% IFR(CFA/MCAPP=1/2) also has excellent water resistant property, after 168h the sample can still obtain a UL94 V-0 rating.