Study On Modification Of Polypropylene Via Grafting Reaction In The Melt

Most commodity iPP with high isotactic linear structure can be produced by Ziegler-Natta or metallocene catalysts. It leads to low melt strength in the flow dominated processes, such as thermoforming, extrusion coating, blow molding, and foaming etc. According to published reports, long branch chain (LCB) is one of the most effective methods to modify the rheological behavior of the PP, which can enhance the strain hardening and improve the melt strength. Additionally, the preparation of polarized PP is one of the hot topics on modifying PP.Firstly in this study, we used the functional polypropylene (PP-g-MAH) via the melting reaction between functional groups with ethylene diamine (EDA) or y-aminopropyl triethoxysilane (APTES) to prepare the long chain branched polypropylene (LCBPP) in the Brabender torque rheometer. We studied the difference among the products under the different ratio conditions mainly. The real-time torque curve of this reaction, its rheological behavior and the analysis of IR spectra, all of them showed that the structure of long chain branching was prepared, and the effect of APTES was better than that of EDA. However, for APTES, it was easy to produce cross-linking.Secondly, it was carried out by PP-g-MAH as raw material, EDA or APTES as the bridging agent to prepare LCBPP in a twin-screw extruder. Comparison to batch process, we focused on the effect of supercritical carbon dioxide (scCO2),the types and amount of bridging agent in the continuous procedure. And similar to the batch process, EDA as the bridging agent, the product did not produce gel; but APTES as bridging agents, reactive extrusion was extremely easy to produce gels. The storage modulus and loss modulus of products were more than that of raw materials, and it was found that the addition of scCO2 could reduce the process temperature to decrease the degradation of PP molecules significantly.Besides, the grafting reaction of maleic anhydride onto polypropylene macromolecular chain was carried out in a twin-screw extruder, using maleic anhydride as polar monomer, dicumyl peroxide (DCP) as initator, through melt extrusion to product maleic anhydride grafted polypropylene (PP-g-MAH), in order to achieve the functionalized PP. And than it investigated not only the influence of different processes and ingredients on the result, but also using scCO2 assisted reactive extrusion technology. The results showed that when the MAH content maintained the same levels, with the increase of DCP content, the grafting degree increased, but brought more serious degradation. When the speed of the screw increased, owing to the shorter mean residence time of the materials, the reactions of the degradation and grafting reduced. With scCO2 assisted, it is to promote the diffusion and mass transfer between macromolecules with small molecules, effectively to improve the degree of the grafting reaction.At last, we explored the processes that integrated both traditional preparation of PP-g-MAH by reactive extrusion and synthesis of LCBPP based on intermolecular functional reaction, in which we prepared the LCBPP in one-step in a twin-screw extruder by choosing a certain feeding strategy. The results demonstrated that when the maleic anhydride was a certain content, DCP content was in an optimal range. The products possessed the general characteristics of long chain-branched polymer and the rheological behavior has been obviously improved, such as higher value of stored module at low frequency, distinct decrease of loss angle, significant increase of complex viscosities and shear thinning less sensitive. Generally, compared to those untreated PP-g-MAH, we changed the mole ratio of MAH and NH2 to control the structure of the LCBPP:the number of the long chain branching increased, long-branching polymer's rheological characteristic became more pronounced, and the intersection of the curves of storage modulus and loss modulus shifted to the lower frequency. And we attempted to prepare long-branched polypropylene using scCO2 assisted by one-step method.