Preparation Of Phosphorus Layered Double Hydroxides And Their Flame Resistant Property In Polypropylene

Polypropylene（PP） is widely applied in the industries such as transportation, construction, wire cable due to low price and good processing properties. However, the application has greatly been limited in many fields because of its flammability. The development and application of the polypropylene materials is a hot topic, which is being discussed by researchers. Mg Al layered double hydroxides（LDH-C） have unique layered structure and adjustability of interlayer anions and layer cations, and it has become a hot point in flame retardant area due to high flame retardant efficiency, non-toxic and environmental protection. Unfortunately, the LDH-C is confronted with the defects of being incompatible with PP matrix and high adding, which weakens the mechanical properties of the PP. Improvement of the surface chemical performances for the LDH-C is one of the most effectual means to solve the problems of LDH-C flame retardants. In the dissertation,the LDH-C was modified using sodium tripolyphosphate（STPP） and rare earth coupling agent La OT as modifiers in order to prepare P₃O₁₀^5– intercalated double hydroxides（LDH-P） and La OT modified LDH-P（La-LDH-P）. PP and LDH-P composites（PP/LDH-P） including PP and La-LDH-P composites（PP/La-LDH-P） were prepared by melt-blending method. Furthermore, the flame retardant properties of PP/LDH-P and PP/La-LDH-P were studied. PP was melt-blended with the La-LDH-P using intumescent flame retardant ammonium polyphosphate（APP） as a synergist to investigate the synergistic effect between La-LDH-P and APP. The crystallization, thermal stability, mechanical properties and flame retardant performances of PP/LDH-P, PP/La-LDH-P and PP/La-LDH-P/APP composite systems were investigated. The main results are summarized as follows,1. The P₃O₁₀^5– intercalated double hydroxides（LDH-P） were prepared using carbonate intercalated Mg Al double hydroxides（LDH-C） as precursor by the reconstruction method. The processing parameters of the P₃O₁₀^5– intercalation was optimized by response surface method. By controlling the temperature of the intercalation, it was found that the amount of P₃O₁₀^5– anions, basicity and hydrophobicity of the LDH-P improved with increasing temperature, which were the maximum at 70 oC.2. The effects of the LDH-P and LDH-C on the mechanical properties, flame retardant performances and thermal stability of PP material as well as compatibility with PP matrix were investigated. The main reason was due to the enhancement of the hydrophobility for the LDH-P particles assigning to the surface and distribution.3. Thermodynamic property and kinetics of thermal decomposition of neat PP and PP/LDH-P composite were studied with TG-DTG techniques in the N₂ atmosphere. Compared with neat PP, the weightlessness temperature range of the PP/LDH-P was wider. The kinetic parameters of the thermal decomposition process were calculated through the K issinger and Flynn-Wall-Ozawa method. The thermal decomposition mechanism of the PP/LDHP was predicated by Málek method combining ?atava-?esták, Mac Callum- Tanner, Coats-Redfern and Achar methods. The results suggested that the process calculated could be attributed to the mechanism of Chemical reaction, F3, with the mechanism function being f（α） =1/2（1-α）3. The activation energy and pre-exponential factor of the PP/LDH-P composite were 231.1 k J?mol-1 and 1015.11 min-1, respectively. Compensation effect existed clearly in the thermal decomposition process in the kinetic analysis. And the kinetic equation might be expressed as follow,4. The studies of TG-DTG and thermal dynamics showed that the thermal stability was improved and residual mass at 600 oC was increased, which resulted in the lower thermal degradation rate when phosphorus incorporating to the PP/LDH-P composites, comparing to the PP/LDH-C composites. The phosphorus in the intercalated spaces of the LDH-P promoted the charring of the PP matrix in the pyrolysis process. The results indicated that the main role of LDH-P was condensed phase and its role on gas phase could not be neglected.5. The surface modification was carried out by rare earth coupling agent La OT, and the modification effects were characterized by activation index and contact angle. The conditions of the surface modification were optimized, and the La-LDH-P particles were prepared in the optimal conditions. The La-LDH-P was then characterized by XRD, FT-IR, TG-DTG and contact angle methods, and the analytic results suggested that the crystal structure of the LDH-P was not destroyed, and La O T attached onto the surface of the LDH-P, which made the surface of the La- LDH-P to be changed from hydrophilicity to hydrophobicity.6. PP/La-LDH-P composites were prepared by melt-blending method and characterized using XRD, TG-DTG and SEM technique as well as LOI, UL-94 and mechanical measurements, where the compatibility with PP matrix, thermal property, combustion and mechanical performances of the PP/La-LDH-P composites were investigated. The results showed that comparing to the LDH-P, the dispersion of the La-LDH-P particles in the PP matrix was improved by using the coupling agent La OT and the compatibility with PP matrix was greatly improved. At the same time, La-LDH-P had less impact on the mechanical performances of the PP/La-LDH-P composites, and the flame retardant properties could be mended.7. Incorporating intumescent flame retardant APP as synergistic agent with the La- LDH-P into PP matrix, the resultant composites（PP/La-LDH-P/APP） were investigated in terms of combustion and thermal decomposition. Based on the investigation, the synergistic mechanism was proposed. Results showed that the APP synergist could increase the oxygen index and the char residue of the PP/La-LDH-P/APP composite system. The char forming of the PP molecules could been promoted when the La-LDH-P and APP particles were added into the PP matrix, while the char foamed and expanded in the existence of APP and compact chars could be formed on the surface of the PP/ La-LDH-P/APP composite system, which was a critical factor for protecting PP matrix from burning.8. The thermal decomposition kinetics of the PP/La-LDH-P/APP composite system in air atmosphere was studied by TG-DTG technique. The kinetic parameters of the decomposition process were calculated through the K issinger and Flynn-Wall-Ozawa methods. The thermal decomposition mechanism of the PP/LDH-P was predicated by Málek method, and the accuracy of the decomposition mechanism was verified by the ?atava-?esták and Achar methods. The decomposition process calculated could be attributed to the mechanism of Two-dimension diffusion, spherical symmetry. The activation energy and pre-exponential factor of the PP/LDH-P composite were 219.1 k J?mol-1 and 1010.80 min-1, respectively. The changes of activation energy and pre-exponential factor with temperature had a same tendency, where there was a positive linear correlation between activation energy and pre-exponential factor and the correlation was good. Compensation effect existed clearly in the thermal decomposition process in the kinetic analysis. And the kinetic equation might be expressed as follow,...