Research On Thermal Stability And Crystallization Behavior Of Polypropylene/MWNTs Composites

As one of the five general plastics, polypropylene(PP) has broad applications in chemical 、machinery and automobile industries because it has advantages of low price、good formability、non-corrosive and good comprehensive performance. However, polypropylene(PP) is easy to cause fire because it is inflammable and it will release much heat when it burns. What’s more, the thermal stability is poor and the intensity of polypropylene(PP) is low. The further promotion of polypropylene(PP) in chemical equipment was limited by its disadvantages which also brings great inconvenience to life. Carbon nanotubes has excellent capabilities of good mechanical properties 、large elastic modulus and high specific surface area. In addition, carbon nanotubes have a similar structure with high polymer. Using carbon nanotubes to modify polymer has great prospect and important theoretical significance.In order to improve the thermal stability and fire resistance of polypropylene, in this work, three systems of multi-walled nanotubes were prepared via melt blending with three different specifications and different loadings of polypropylene. This work focus on researching the thermal stability and non-isothermal crystallization behavior of three multi-walled nanotubes(MWNTs) and discuss the influence on the thermal stability and fire retardancy of PP matrix through adding different sizes and contents of CNTs.The results of thermo gravimetric analysis show that: the thermal stability of composites was significantly improved after adding modicum MWNTs. With the increase of MWNTs content, the thermal decomposition temperature of PP composites first increased and then decreased; the thermal decomposition temperature of PP composites reach the largest when the content of MWNTs is 4wt%; the large of length to diameter ratio of MWNTs, the high of the thermal decomposition temperature of PP composites, With the increase of MWNTs content, the char residue of PP/MWNTs composites increased.Thermal decomposition temperature of PP and PP/MWNTs composites was investigated by equal conversion rate method. The results showed that the activation energy 、the thermal stability and the flame retardancy of PP/MWNTs composites were significantly improved after adding MWNTs. What’s more, the high of MWNTs content and the large of length to diameter ratio of MWNTS, the big activation energy of composites. The reaction mechanism changed from phase boundary controlled reaction(contracting volume) of PP to random nucleation with one nucleus on the individual particle.The results of differential scanning calorimety showed that adding MWNTs to PP base material can accelerate the crystallization as a role of heterogeneous nucleation, speeding up crystallization temperature of PP; enhancing the onset temperature、crystallization peak temperature and degree of crystallization of PP/MWNTs composites. With the increase of MWNTs content, the onset temperature and crystallization peak temperature decreased but the degree of crystallization first increased and then decreased.The non-isothermal crystallization kinetics of PP/MWNTs composites were investigated by Jeziorny method 、Ozawa method and Mo method. The result shows that Jeziorny method and Mo method can deal with the Non-isothermal crystallization process of PP/MWNTs composites, but there are big limitations when using Ozawa method to study the Non-isothermal crystallization process of polymer.