Research On The Rheological Behavior Of Polypropylene Filling And Blending Systems

Polypropylene has wide application value because of its excellent mechanical properties,good heat resistance and ease of processing and forming.However,its poor toughness,especially at low temperature,brittle and sensitive to notch,makes modified polypropylene become a research hotspot.Therefore,it is of great significance to study the rheology of polypropylene modified materials.The rheological behavior of polypropylene random coplymer(PPR),high melt strength polypropylene(HMSPP),and its carbon nanomaterial filling system and blending system were studied by using constant velocity capillary rheometer and rotary rheometer.Discussed from the following four aspects.Two types of polypropylene(PPR,HMSPP)with different molecular structures were selected to investigate the effects of different molecular structure,molecular weight and distribution,temperature and capillary length-diameter ratio on entrance pressure instability,extrusion distortion,shear viscosity,Extensional viscosity and dynamic rheological properties of the polymer.It was demonstrated that the HMSPP long branched chain structure was conducive to the stability of entrance pressure,and the polymer would not melt rupture at a high shear rate,while the capillary lengthdiameter ratio had weak effect on the entrance pressure instability.The long branched chain structure of HMSPP made the polymer melt showed the phenomenon of strain hardening in the tensile action,while the PPR of linear molecular structure showed the phenomenon of Extensional softening.Extensional viscosity of PPR(polypropylene random coplymer)and its composites with three kinds of carbon fillers with different dimensionalities,including multi-wall carbon nanotubes(MWCNTs),graphene(FLG)and carbon black(CB),was evaluated.It was demonstrated that the dimensionalities of the fillers played a significant role in the extensional viscosity for PPR composites.PPR / MWCNTs composites have increased the number of entanglement points due to the formation of their internal filler network,and show obvious strain hardening phenomenon.However,the extensional viscosity of PPR / FLG and PPR / CB composites only increased with the increase of filler components,and did not show strain hardening phenomenon.Mechanisms for the effects of these fillers on the the strain hardening phenomenon of composites were proposed according to the molecular structure and the movement of polymer chains.In order to further study the effect of multi-walled carbon nanotubes(MWCNTs)on the rheological properties of polymer filling system,three kinds of MWCNTs with different capillary length/diameter ratios were selected to prepare PPR/MWCNTs composites by melting and blending.It was demonstrated that only when the length-to-diameter ratio of MWCNTs reached a certain value did the composites exhibit strain hardening,and the hardening mechanism was discussed.At the same time,the different length-diameter ratio of MWCNTs also had an important effect on the dynamic rheological behavior of the composites.The rheological behavior of polypropylene blending system was studied.It was demonstrated that DSC test and cole-cole diagram showed that PPR had good compatibility with HMSPP.The n value of PPR/HMSPP blends decreased with the increase of PPR component content.The shear viscosity of PPR/HMSPP blends conformed to the ideal viscosity summation formula of Utracki.The extensional viscosity of PPR/HMSPP blends showed a complex variation pattern.When the HMSPP component content was greater than 50wt%,PPR/HMSPP blends exhibited "strain hardening" at a lower tensile rate.When a small amount of PPR was added to PPR/HMSPP blend,the strain hardening became more obvious.