| Polypropylene (PP), as a commondity thermoplastic with many of desirable performance, is widely used in a number of fields such as electrical and electronics industry, car industry, and cable and wire, etc. The high performance and multiple functions of PP have been arose more attention. However, PP has only a limiting oxygen index (LOI) value of 18.1, and is flammable polymer material, which greatly limits its application fields. Flame-retardant polymer materials producing Halogen-free, no toxic or corrosive gases and smoke when they are exposed to fire have become a trend for environmentalism demand. Magnesium hydroxide [Mg(OH)2, MH] is the most widely used flame retardant due to its restraining smoke, loading, and low cost. In this paper, modification of PP filled with Mg(OH)2 thus was investigated. Deep investigation and analysis on the structure and properties, interface modification, synergistic flame retardancy, and toughened of PP/Mg(OH)2 composites were carried out. The main purpose of this work was to develop new halogen-free flame-retardant materials that can be used in the manufacture. Therefore, this work obtained the following new creative results and progress, and reaches the expect goals.1. The structure, morphology, thermal properties of super fine Mg(OH)2 powder were studied by FTIR, XRD, SEM and TGA. And the structure and properties and PP composites loading with MH were also studied. The results showed that more than 50% by weight of MH is required to obtain an adequate level of flame retardant property of PP matrix, and such high loading levels of MH seriously deteriorated mechanical properties of the composites.2. The interface behavior between filler and matrix of composites have greatly effect on mechanical properties of system. The effect of several surface modifiers, e.g. titanate, silane, silicon oil, and stearate salt on the properties of the PP/MH composites was studied. The results showed that surface treatment of MH could significantly improve tensile and impact strength of PP/MH composites due to its enhanced interfacial adhesion between MH and PP matrix. At the same time, the flame retardancy of composites was well improved. differential scanning calorimetry (DSC) results showed that MH had heterogeneous nucleation effect on PP. Surface treatment of MH weakened its heterogeneous nucleation effect. The scanning electron micrograph (SEM) photos showed that untreated MH particles in PP/MH composites is not well dispersed into the polymer matrix and that many debonded MH particles are clearly seen on the fracture surface. However, MH particles treated with surface treatments become more and more smaller, and MH particles distribution in PP matrix is narrower. Moreover, MH particles are better attached to the PP matrix. The data of thermal oxidative degradation kinetics of composites showed the activation energy of system was significantly improved due to the addition of fillers. The introduction of treatment agent further improved the thermal oxidative stability of the composite.3. In this paper, attempts have been made to develop high efficient MH-based HFFR for PP. This work is mainly devoted to investigate the synergistic effects of different particle size expandable graphite (EG) with MH in PP composites. The results showed that the particle size of EG had a great effect on the flammability of the PP/MH/EG composites. The EG2 with smaller particle size could apparently increase the LOI value and improved the UL-94 flammability properties rating of the PP composites. The data obtained from the TGA and FTIR curves indicated that the therm-oxidative stability of PP/MH/EG composites increased with decreasing particle size of EG And the smaller the particle size of EG, the higher the residues of the composite. This indicated that EG2 with smaller particles size had much better synergistic effect than EG1 with larger particles size with MH for the flame retardant improvement of PP/MH composites.4. Melt grafting and crosslinking of the multi-monomer system of maleic anhydride(MAH)/styrene (St) onto ethylene-octene copolymer (POE) was performed by a two-screw extruder. The primary aim was to provide a detailed investigation on melt grafting of MAH onto POE with St as a comonomer, as well as the influence of several factors on the grafting degree, melt flow index, dynamic rheological behaviors and thermal stability of MAH-St grafted POE. Manufacturing conditions for POE-g-(MAH-St) were proposed from which grafted and crosslinking POE with desired property was successfully prepared. St improves the grafting reactivity of MAH and reacts with MAH to form SMA before the two monomers graft onto POE. And high grafting degree could be obtained while the gel content was still low. Compared with pure POE, grafted POE shows different dynamic rheological behaviors and high thermal stability due to the incorporation of SMA.5. Ethylene-Octene copolymer (POE) is characterized by a narrow molecular weight distribution and homogeneous comonomer distribution and is used to increase the stiffness and toughness of the composites. Systematic investigations on the effect of POE and functionalized POE incorporation into PP/MH composites were carried out. Moreover, the fracture behavior and deformation mechanism of PP/POE/MH ternary composites were investigated. The results showed that the mechanical property of PP/POE/MH composites was greatly improved, especially, for toughness of composites. The fracture behavior of the PP/POE/MH ternary composites is strongly influenced by the POE content. In the case of brittle fracture, the debonding of filler particles dominated the deformation process strong shear yielding of the matrix ligaments between microvoids takes place after the brittle-ductile transition. SEM analysis of PP/POE/MH composites demonstrates that a mixture of separation and encapsulation microstructures exist in the matrix. Using reacting extrusion prepared POE-g-(MAH-St) as interface modifier, flame retardant PP composites with excellent mechanical properties, flame retardancy were successfully prepared.6. The variations of linear viscoelastic behavior of polymer composites filled with fillers can further confirm the structure and properties of composites. The dynamic rheological behaviors of PP composites filled with MH, PP/MH/EG composites, and PP/elastomer/MH ternary composites were investigated. The aim to this work is to found the relation between the structure and properties of PP matrix composites with fillers and elastomer.7. The flammability behavior, the pyrolysis, and flame retardation mechanism of the PP/MH,PP/MH/EG, PP/POE/MH composites with grafted POE were investigated and proposed by the cone calorimetry test (CCT), FTIR, and XPS analysis method. The results show that an effective char layer can form while burning for PP/MH/EG composites and grafted POE flame retardant PP/POE/MH composites, which can inhibit the gas and heat transfer more efficiently.
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