Effects Of Network Structure On Rheological Behaviors And Mechanical Properties Of Polymer Elastomeric Materials

Polymeric elastomer is a kind of material that can be deformed under external force and can restore to original state when external force is removed.Elastomeric materials play an important role in industrial technology,such as energy transfermation,industrial production,resource exploitation and biological engineering.The research is focused on the influence of the network structure of polymeric elastomer on the rheological and mechanical properties.By introducing network structure into polymer,the physical and chemical crosslinking degree in polymer will be increased.It is important to understand the relationship between network structure and the properties of materials.Then the relationship between the network structure and the rheological and mechanical performances in the practical application of elastomer materials is explored.High-shear processing is an effective method to increase the compatibility of polypropylene/rubber and increase the interfacial strength between the two phases.The phase structure of the blends will have significant influence on the mechanical properties of polymer blends.These researches provide the experimental basis and theoretical basis for the application of elastomeric materials.Specific content includes the following four aspects.1.A series of polyborosiloxanes(PBSs)was synthesized by mixing hydroxy-terminated polydimethylsiloxanes(PDMS)and boric acid(BA)in toluene at 120 ?.The molecular masses of selected PDMS precursors were in a wide range,covering from below up to far above the critical entanglement molecular mass of PDMS.The reaction kinetics was followed by using the Fourier transform infrared spectroscopy(FTIR).Unreacted BA was removed from raw PBSs after the reactions.The influence of molecular mass of PDMS precursors on the rheological property of PBSs was explored by dynamic oscillatory frequency sweeps.The results showed that the plateau elastic moduli of PBSs were highly dependent on the molecular mass of PDMS precursors.The plateau elastic moduli of PBSs decreased at first and then increased with increasing molecular mass of PDMS precursors.PBS1 and PBS2 prepared from unentangled PDMS precursors showed sufficient fits by using the two-mode Maxwell model,whereas PBS3 to PBS6 prepared from highly entangled PDMS precursors showed obvious deviations from the two-mode Maxwell model.It could be concluded that the changing trend of plateau elastic modulus of PBSs versus molecular mass of PDMS precursors was determined by the number density of supramolecular interactions(Si-O:B weak bonding and hydrogen-bonding of the end groups Si-O-B(OH)2)and the number density of topological entanglements.2.In this study three typical impact protective materials,D30,PORON XRD and DEFLEXION were chosen to explore the dependences of compression mechanical and rheological properties on the internal cellular structures.Scanning electron microscopy(SEM)was used to characterize the internal cellular structures of these three foaming materials,the rheological property was then characterized by using a rheometer,and mechanical properties in a compression mode were further examined by using an Instron universal tensile testing machine.The dependences of rheological parameters,such as dynamic moduli,normalized moduli and loss tangent on the angular frequency,and of the mechanical properties in compression,such as the degree of strain-hardening,hysteresis,elastic recovery on the strain rate for D30,PORON XRD and DEFLEXION can be well correlated to their internal cellular structural parameters,revealing,for an example,that PORON XRD and D30 exhibit simultaneously high strength and great energy loss to a high frequency impact,suitable for the use as soft,close-fitting materials;however,DEFLEXION dissipates much energy whether it suffers a large strain rate or not,suitable for the use as high-risk impact protective material.The rheometry and compression tests used in this study can provide the basic references for selecting and characterizing certain impact protective materials for practical applications.3.Neat iPP and iPP/SEBS 80/20 blend processed with different shear rates were prepared by using high-shear processing method to investigate the influence of shear rate on the microstructure and mechanical properties.It was found that the mechanical strength and toughness of the samples increased with increasing shear rate.The polarized optical microscopy observation showed that sample prepared with the higher shear rate was more easily orientated in shear field,indicating the presence of network structure.And it was found that high shear processing the toughness and strength of the blends could be enhanced.The rheological results showed that interfacial effect existed in the blend prepared with higher shear rate.The changes of microstructure of the samples were investigated by scanning electron microscope and atomic force microscope.It was found that the interfacial interaction of iPP/SEBS was stronger with higher shear rate.The effects of different shear rates on the microstructure and macroscopic properties of the blends were explored.4.Based on the results of previous chapter,the actual shear rate is further improved by increasing the amount of material used in the large screw extruder.Neat iPP and iPP/SEBS 80/20 blend were prepared by using high shear processing method with higher speeds.It was found that the research of the influence of rotational speed on mechanical properties was restricted by the speed range of the high-shear extruder in the previous chapter.The crystallization morphology,mechanical properties and rheological properties of the blends were characterized in detail.The results showed that the crystallization morphology of the blends depends highly on shear rate,the oriented crystalline morphology was observed for the sample prepared with the shear rate of 2586 s-1;the sample with the best mechanical performance was prepared in the middle shear rate,maximum shear rate led to poor performance;the viscosity and modulus firstly increased with the increasing shear rate and then decreased.Because in a certain range of speed,with the increase of shear rate,the size of SEBS phase will gradually become smaller,evenly dispersed in the iPP matrix,leading to the formation of network structure and enhancement of the interfacial interaction;when the speed continues to increase,polymer chain will become shorter under high-shear processing,leading to weak performance of iPP matrix,which makes the mechanical properties of blends decreased.Therefore,the improvement of properties of the sample with shear rate could only be applied in a certain range of speed.Only selected optimal shear rate of high shear processing would lead to high performance of the blends.