Thermal-Oxidation Degradation And Its Mechanism Of Hybrid Modified Polypropylene

Polypropylene (PP), one of general plastics, is liable to degradation forits tertiary hydrogen and which will make its useless. PP/SiO₂, PP/TiO₂,PP/OMMT nano composite materials were prepared by twin screw extruderto study the nanoparticles effect on PP thermal oxidation degradation andmechanical properties. The distribution of nanoparticles was observed byTransmission Electron Microscope(TEM) and X-ray DiffractionAnalysis(XRD). The results showed that nano SiO₂ and TiO₂ weredispersed in nanoscale. And OMMT was dispersed in intercalation andexfoliate states.The results of Polarized Light Microscope(PLM) and DSC showed thatthe three nanoparticles as heterogeneous nucleations changed thecrystallization degree and crystallization rate of PP. The crystalline state ofPP/SiO₂ wasβcrystal and PP/OMMT wasαcrystal.The rearch of PP mechanical properties indicated that PP nano compositematerials had better tensile and impact strength than pure PP. PP/SiO₂ had the biggest tensile strength and PP/OMMT had the biggest impact strength.And the thermal analysis showed that PP composite materials had higherheat deflection temperature (HDT).PP materials were aged by thermal oxidation oven. The results illustratedthat nanoparticles improved the PP thermal oxidation degradation. The PPmodified by nanoparticles had less cracks on surface, higher conservationrate of mechanical strength and less change of carbonyl groupconcentration. Among the three kinds of nanoparticles, the SiO₂ had thebest effect on PP thermal oxidation degradation. The results of oxidativeinductive time(OIT) showed that the OIT of PP nano composite materialswas much longer than pure PP, and OIT of PP/OMMT was the longest.The results of thermal gravimetric analysis(TG) indicated that PP modifiedby nanoparticles had higher initiate decomposed temperature in thecondition of oxygen or nitrogen than pure PP. And PP composite materialshad much higher temperature in oxygen atmospherere than in nitrogenatmospherere. Among them, PP/OMMT had the highest initiatedecomposed temperature in both conditions.The parameters of non-isothermal degradation kinetics of PP materialswere obtained by Doyle method. The results proved that the PP, PP/SiO₂,PP/TiO₂ and PP/OMMT were observed first grade reaction and PP/OMMThad the highest activation energy. The research will afford new technique and theory for preparingweathering PP material.