High Melt Strength Polypropylene Achieved By Melt Grafting

High melt strength polypropylene (HMSPP) has been studied since 1980s. Because of HMSPP's particular molecular structure,superior properties and huge application potentials,the study on HMSPP has been a field of growing interest during the past two decades of years.The purpose of this study was to obtain modified non-gel HMSPP and to investigate the technique of its production process via studying some influential factors.The hinges of this study included the formation of longer side chains in order to acquire higher bath strength and the control of degradation of iPP and cross-linking side reactions. Our work will provide an option for preparing the high melt strength polypropylene.In this work, melt grafting of iPP, by acrylates with various number of functional groups, in a double-screw extruder was studied. Peroxide was used as initiating agent. The resulting grafted material was characterized in terms of its IR spectrometry, tensile viscosity as well as its DSC diagram and the effects of various factors on the grafting process of GMA was investigated.A chosen amount of Polypropylene was weighed and well mixed with antioxidant and the rest additives. The monomer and initiator were weighed to precise amount and mixed together in acetone prior to being put into the extruder. Then the whole solution was equably added to the PP powder and thoroughly mixed. Allow some time for the complete evaporation of acetone before the mixture was put into a twin-screw extruder. Finally the grafted PP was obtained under certain reaction temperature and screw rotate speed.The main purpose of this study was to improve the bath strength of PP. The results showed that the number of functional groups of the graft monomer had effect on the modification result. Monomers with no less than two functional groups showed better modification results. As the bath strength is also closely related to fluidity of the melt, the amount of the initiating agent added would also influence the result. Forgrafts with same Melting Flow Rate, the modification result depended on the degree of extrude swell. It was showed that adding 0.04% initiating agent mostly promote the grafting process, Changing of the out-of-mold inflation ratio with Melt strength was also investigated. With the increasing MS, the inflation ratio gradually increased. The IR spectrometry indicated that the monomer had been linked to the PP backbone chain. Despite the molecular weight and its distribution remain almost constant prior to and after the grafting reaction, the tensile viscosity diagram showed the composite suffering from strain hardening, which might be attributed to the induction of long side chains to the original polymer. The modified polymer showed incline both in crystalline temperature and melting temperature.The affecting factors of the graft reaction were also investigated. It was found that process condition of 190℃, 100rpm was optimal for the graft reaction. The increase in dosage of monomer and initiating agent could both improve the graft ratio. The add of styrene as co-monomer could also benefit the graft process.In order to minimize the degradation of iPP, the dosage of initiating agent was reduced and styrene was added as co-monomer. The results showed that the add of styrene could effectively restrain degradation and increase the grafting ratio. It also helped to improve the mechanical property. Since the amount of gelatin in the graft rise with the increase of monomer and initiating agent concentration, it was reasonable to limit the dosage of both to minimize the gelation. The modified polymer showed decline in tensile strength but incline in benging and impact property.