Microstructure And Properties Of PP/POE Blends

Properties of multiphase polymeric materials are related to their microstructure greatly,and the formation of their microstructure depends on processing condition.It is very important for the structural design and modification of polymeric materials.In this dissertation, isotactic polypropylene(PP)/ethylene-octene copolymer(POE) blends were prepared in melting state,their melting and crystallization behaviors,P-V-T properties,mechanical properties and viscoelasticity were systematically investigated,the morphological evolution of the dispersed phases and multi-layered microstructures of PP/POE blends during injection molding were discussed.The main conclusions are as following:1) At the low content of POE,the addition of POE decreases the apparent incubation period (⊿t_i) and the apparent total crystallization period(⊿t_c) of PP in blends due to the heterogeneous nucleation of POE.However,at high content of POE,the addition of POE decreases the mobility of PP segments due to their strong interrnolecular interaction and chain entanglements,resulting in retarding the crystallization of PP,decreasing in the amount ofβ-form PP crystals,and increasing in⊿t_i and⊿t_c of PP in blends.T_m,T_mp and T_m,onset of PP in PP/POE blends all shift towards lower temperature with addition of POE. The depressions in melting temperature of PP phase in the blends indicate that there might be a strong intermolecular interaction between PP and POE.PP spherulites in blends are defective and their crystallization behavior is influenced intensely by the incorporation of POE.Additionally,the non-isothermal crystallization of blends were analysed by Jeziorny, Ozawa,Urbanovici-segal,Mo and Ziabicki models,respectively.Urbanovici-segal and Mo models are more suitable to describe the non-isothermal crystallization of the blends.2) The rheological results measured by the capillary and torque rheometers are almost similar.PP,POE and PP/POE blend melts are pseudoplastic fluids.With increasing the POE content in blends,their non-Newtonian constant and apparent viscosity exhibit the behavior of the negative deviation blend(NDB),but their flow activation energy shows the behavior of the positive negative deviation blend(PNDB).3) During injection molding,PP/POE blends form the multi-layered structure,i.e.skin, transition,shear and core layers.In shear layer,POE phase has the largest deformation degree(D),thereby POE phases are elongated,broken and behave as flat ellipse ball.On the other hand,there exists no POE phase in the skin layer,but the content of POE phase in the core layer is highest.Based on experimental phenomena,a multi-layered structure model is proposed.Moreover,the shearing has an important effect on the formation ofβcrystals of PP phases in blends.There are someβcrystals of PP in skin and shear layers,but noβcrystal of PP appears in core layer. 4) The melting point(T_m) of PP phase in injection molding product at skin layer is closed to that of pure PP,and higher than those at other layers.T_peak and T_end of PP phase at core layer are a little higher than those at transitional and shear layers,but are lower than those of PP phase at core.Due to the rapid cooling rate at skin,the melting peak of PP phase at skin layer is wide and its crystallinity is low.However,the crystallinity of PP phase at core is highest.The dependence of crystallization temperature(T_c) of PP on pressure obeys the linear equation,T_c=T_c.0+kp.Additionally,with increasing POE content,the melting behaviors of PP phase in PP/POE blends at high pressure crystallization is different with those at low pressure crystallization.5) At the same processing temperature,the storage modulus(E') of PP/POE blends at core layer is higher than that at shear layer.With increasing the processing temperature,all E' values at core and shear layer increase at the same time.Moreover,the E' respondence to DMA frequency is different for PP/POE blends at core and shear layers.At the low processing temperature,the E' respondence of PP/POE blends at core is more obvious than that at shear layer.However,at the high processing temperature,the E' respondences of PP/POE blends at core and shear layers are almost the same.6) Tait Equation could be used to predict the P-V-T properties of PP/POE blends with partial compatibility and semi-crystallinity.The variation of specific volume(V_sp) value of PP during crystallization is bigger than that of POE.With increasing the POE content,the variation of V_sp value of PP/POE blend decreased during its crystallization.The expansivity coefficient(α) of PP in molten state is bigger than that in solid state,whilstαof POE at solid state is bigger than that at molten state.The variation ofαof PP/POE blend under different temperature and pressure depends on the composition of the blend.Additionally, Simha-Somcynsky model could be used to predict the P-V-T properties of blends in melting state. 7) With increasing the POE content,the storage moduli of PP/POE blends derease,but their loss moduli and tanδvalues increase.The glass transition temperature(T_g) of PP phase in blends tends to shift towards high temperature slightly with increasing the POE content, and T_g of POE shifts towards the low temperature obviously with increasing the PP content. T_g shifts of POE and PP phase in the blends indicate that there might be a strong intermolecular interaction between PP and POE.The Kerner's dispersed phase model and co-continuous phase model can reasonably predict the visco-elasticity and morphological structure of PP/POE blends with different composition.8) With increasing the POE content,the impact strength values of the PP/POE blends at ambient and -18℃increase,but their tensile strength and modulus derease.Their brittle-ductile transition(BDT) at ambient temperature appears when POE content is about 30%.The toughening mechanism of POE can be understood by crazing branch and percolation.