Preparation Of Functional Magnesium Materials And Their Synergistic Effects On Intumescent Flame Retardant Polypropylene

In brine resource of our country, magnesium resource holds in store of rich, but its comprehensive utilization efficiency is low. To solve this problem, two kinds of functional magnesium materials, magnesia-silica mixed oxides and magnesium hydroxide sulfate hydrate whisker, were prepared by hydrothermal method with magnesium chloride and magnesium sulfate as raw materials in this thesis. The properties of the obtained samples, such as structure and morphologies were characterized through X-ray diffractometer, FT-IR spectrometers and scanning electron microscope. The synergistic effects of the two kinds of functional magnesium materials on intumescent flame retardant (IFR) system are investigated with polypropylene (PP) as the polymer matrix. The influence of two kinds of functional magnesium materials on the flame retardancy, smoke suppression, fire hazard, thermal stability and morphology of char residue was investigated by limited oxygen index (LOI), vertical burning test (UL-94), cone calorimeter test, thermogravimetric analysis (TGA), scanning electron microscope (SEM). The main results are as follows:(1) Several magnesia-silica mixed oxides were prepared by hydrothermal method with magnesium chloride, sodium metasilicate and sodium hydroxide as raw materials. Mg/Si molar ratios of magnesia-silica mixed oxides measured using EDTA complexometric titration and gravimetric method were 2.73:1,1.25:1,1:1.93,1:2.95. The properties of the obtained samples, such as structure, and morphologies, were characterized through X-ray diffractometer, FT-IR spectrometers and scanning electron microscope. The results show that MS3 and MS2 are spherical particles with amorphous structure, while MS and M3S are flake particles with crystalline structure.(2) Four magnesia-silica mixed oxides were introduced into intumescent flame retardant polypropylene system, and the influence of magnesia-silica mixed oxides on flame retardancy was studied by LOI and UL-94 tests. The results show that all of the magnesia-silica mixed oxides can significantly improve the flame retardancy of composites, and the synergistic effect of M3S was the most excellent.(3) Synergistic flame retardant effect and smoke suppression properties of M3S on intumescent flame retardant polypropylene composites were investigated with PP as polymer matrix. The beneficial effects of M3S on the flame retardancy, smoke suppression properties and thermal stability of intumescent polypropylene composites were intensively investigated by limiting oxygen index (LOI), vertical burning test (UL-94), the cone calorimeter (CCT), scanning electronic microscope (SEM) and TGA. Remarkably, the LOI results show that M3S can effectively increase the flame retardancy of intumescent PP composites. On the other hand, cone calorimeter test results reveal that the addition of M3S can apparently reduce heat release rate (HRR), total heat release (THR), total smoke reduction (TSR), fire growth index (FGI), etc. Here, M3S is considered to be a good synergist and an effective smoke suppression agent in intumescent flame retardant PP composites, which can greatly improve the quantity and quality of char residue realized by TGA and SEM results. In addition, adding of M3S can improve the tensile strength, but damage the impact resistance of the composites.(4) Magnesium hydroxide sulfate hydrate whisker (MHSH) was prepared directly by hydrothermal method with magnesium sulfate and sodium hydroxide as raw materials. Research on the influence of temperature and time on the crystal morphology and structure found that the optimal reaction conditions were 160 ℃ and 8 h. Mg2+/OH" molar ratio of reaction system was changed through changing concentration of magnesium sulfate and sodium hydroxide and its influence on the crystal morphology and structure was studied. When the value of Mg2+/OH- molar ratio is greater than 5.4, the production was dispersive whisker characterized as 5Mg(OH)2·MgSO4·3H2O. Influence of SO42-/Mg2+ molar ratio of reaction system on the crystal morphology and structure were studied. SO42-/Mg2+ molar ratio greater than 1.0 was beneficial to the growth of MHSH whisker. Influence of stirring of reaction system on the crystal morphology and structure were studied. The optimal whisker with a length greater than 20 μm and a diameter less than 0.5μm could be obtained with stirring speed as 200 r/min, Mg2+/OH- as 1.5, SO42-/Mg2+ as 1.0, hydrothermal temperature as 120℃ and hydrothermal time as 8h. The yield under the optimal reaction conditions can reach 90%.(5) The beneficial effects of magnesium hydroxide sulfate hydrate on thermal stability, flame resistance, smoke suppression and mechanical properties of polypropylene composites were evaluated by TGA, LOI, UL-94 test, cone calorimeter (CCT), SEM, tensile tests, flexural tests and Izod impact tests. TGA data indicate that T5wt%, Tmax and char residue of PP/IFR/MHSH is higher than those of neat PP and PP/IFR. Cone calorimeter results show a very significant decrease in HRR, THR, SPR, TSR, FGI and a significant improvement of TTI and FPI compared with samples without magnesium hydroxide sulfate hydrate. Remarkably reduction of smoke production rate and total smoke release of PP/IFR/MHSH10 composite indicates that MHSH significantly suppresses smoke production of the composite. Furthermore, digital photographs and SEM images of the char residues show that the char residue from PP/IFR/MHSH has a compact and tough char structure compared with that of the sample without magnesium hydroxide sulfate hydrate. The results of mechanical property tests show that MHSH could enhance the tensile strength and flexural strength of PP composite without decrease of the impact strength. All of the results indicated that adding MHSH with intumescent flame retardants is a promising strategy to simultaneously improve the flame retardancy, smoke suppression and mechanical properties of polymeric materials.(6) Synergistic effects of MS3, MS2 and MS with amorphous structure on the PP/APP/PER composites were investigated through LOI, UL-94 test, synergistic effectivity (SE), SEM and EDS. The results show that the SE values of three magnesia-silica mixed oxides was greater than 1.0, and SEMS3 was the greatest one. UL-94 ratings of PP composites increase from NR to V-0 with loading the magnesia--silica mixed oxides. P contents of char residues of PP composites increase with loading the magnesia--silica mixed oxides, which is due to the suppression effect of Si-O-P and Mg-O-P on the decomposition of P-O-P chains.(7) Synergistic effects of MS3 (amorphous structure), M3S (amorphous and crystal structure) and MHSH (crystal structure) on the PP/APP/PER composites were investigated through LOI, UL-94 test, TGA, SEM. It is found that all of them can improve the flame retardancy of the composites. Synergistic effectivity was used to evaluate the synergistic effect of three functional magnesium materials. The results show that the maximum values of MS3, M3S and MHSH appear at the 2%,1%,1% contents and the sequence of the maximum of the three magnesium materials is MHSH>M3S>MS3.(8) Several synergistic systems of APP/PER, APP/PER/MS3, APP/PER/M3S and APP/PER/MHSH were prepared by high speed mixer. They were characterized by thermogravimetric analysis and energy dispersive spectrometer. The results show that char residues of synergistic systems can increase significantly by loading MS3, M3S and MHSH into APP/PER system, from 53.97%、59.61%、45.23%. At 350 ℃, loading three functional magnesium materials can eliminate element N existed on the surface of char residues of APP/PER system.