Preparation And Characterization Of Polymer/phosphonium Montmorillonites Nanocomposites

Polymer nanocomposties contanining montmorillonite (MMT) have been considered as a new generation of composite materials due to their expected mechanical, thermal and electrical properties attributed to the special structure of montmorillonite. Now, montmorillonite is commonly modified by alky quaternary ammonium with low thermal stability, the temperature of decomposition for this montmorillonite is always below 200℃. We have prepared phosphonium montmorillonites(P-MMT) using a simple one-step method followed by a cation exchange reaction, its temperature of decomposition reaches 275℃. Several typical Polymer/P-MMT nanocomposite were prepared by melting intercalation and characterized by different approaches. Then relationships among structure and flammability properties, thermal stability and mechanical properties of the nanocomposites were discussed in detail.Firstly, Phoshpoium montmorillonite (P-MMT) was used as a synergistic agent and prepared polypropylene/magnesium hydroxide/phoshpoium montmorillonite (PP/MH/P-MMT) nanocomposites. The synergistic effect of P-MMT with magnesium hydroxide (MH) as the halogen-free flame retardant for polypropylene (PP) was studied by thermogravimetric analysis (TGA) and cone calorimetry. Compared with that of Na-MMT, it indicated that addition of 3.0%wt P-MMT improve the thermal stability, increase the time of ignition (TTI), reduce the heat release rate (HRR) and mass loss rate (MLR), moreover the notched impact strength increased 12.5%. The morphology of char residual was studied by scanning electron microscopy (SEM), it was showed that the main advantage of P-MMT was related to enhancement of compactness of char layer formed.Secondly, the blend nanocomposites were prepared by melt mixing PLA with various amounts of wood flour and P-MMT. The influence of P-MMT and WF content on clay dispersion, physical and mechanical properties of PLA/WF/P-MMT composites were investigated. X-ray diffraction patterns (XRD) revealed that the nanocomposites formed were intercalated. The tensile mechanical tests showed an increase of tensile modulus of the composites upon increasing the WF content, together with a decrease of the elongation at break, impact strength and tensile strength. On the basis of the consideration of thermal and mechanical properties, it was found that 5.0 wt% of P-MMT content was optimal for preparation of PLA/WF nanocomposites. The temperature at 10.0% weight loss was 314℃, while the tensile strength and notched impact strength reached 40.66MPa and 2.30kJ/m2.Finally, poly(ethylene terephthalate) (PET)/P-MMT nanocomposites were prepared via melt extrusion. PET containing various incorporations of P-MMT was investigated. X-ray diffraction (XRD) results proved that P-MMT dispersion states could be ranging from exfoliation to agglomeration. Compared with neat PET, when addition of 0.5%wt P-MMT, the tensile strength of PET/P-MMT nanocomposites increased from 55.8MPa to 59.67MPa and the elongation at break increased from 6.6% to 9.4%; whereas addition of 5.0%wt P-MMT accelerated degradation process, the tensile strength decreased to 46.37MPa, the elongation at break also decreased to 5.36%, and the maximum-rate degradation temperature dropped from 433℃to 352℃.