Study On The Structure And Properties Of PP/EVA/nano-CaCO₃ Compsites

The polypropylene/elastomer/inorganic nano particles ternary composites seystem is the important modified system to balance the toughness and strength of PP.In this dissertation the relationship between the structure and the property of the ternary composites prepared by using different ways of blending ethylene vinyl acetate copolymer(EVA),nanometer calcium carbonate(nano-CaCO3)and PP(polypropylene)is studied.In this dissertation both blending methods F and B were used to produce PP/EVA/nano-CaCO3 ternary composites of F series mainly with the dispersed structure and B series with mainly the encapsulation structure,respectively,by blending nano-CaCO3,PP and EVA.The observation by using SEM reveals that in the F series there is the dispersed structure that EVA phase and nano-CaCO3 phase are independently dispersed in the PP matrix.Whereas in the B series composites there is the encapsulation structure that the nano-CaCO3 acts as a core encapsulated by EVA shell.The observation of an optical polarizing microscopy shows that with an increase in EVA and nano-CaCO3,there is a decrease in the spherulite size of PP for F series and B series PP/EVA/nano-CaCO3 ternary composites gradually,which was promoted by the nucleation introduced by nano-CaCO3.And the interphase between spherulites of PP within the ternary composites F and B series are getting unclear.The spherulite size and the interphase between spherulites of PP for F series is much more smaller and unclear,respectively,than that for B series,respectively,which due to that there are more EVA and nano-CaCO3 in F series than that in B series.DSC and XRD spectrum indicates that for F series and B series PP/EVA/nano-CaCO3 ternary composites the melting peak area and the crystallinity of PP decrease with the increasing content of EVA and nano-CaCO3.And the crystallinity of PP in F series is higher than that of in B series.The results of the tensile and impact testing as well as the thermal performance for PP/EVA/nano-CaCO3 ternary composites show that the yield strain,the elongation at break and the impact toughness of the ternary composites gradually increase,but the yield strength,Young's modulus and the Vicat softening temperature gradually reduce.The maximum value of the yield strength and Young's modulus for composite B1 is 29.7 MPa and 1.33GPa,respectively.While the maximum value of the yield strain and the elongation of the composite F3 is 24.7%and 677.2%,respectively.And the vicat softening temperature is 146.6 and 119.1°C for the composite B1 and F3,respectively.However,the value of the impact toughness for the composite F3 and B1 is 13.2 and 4.3 KJ/m2,respectively.The extent of yielding and toughness of PP/EVA/nano-CaCO3 ternary composites both F series and B series are improved with the increasing content of EVA and nano-CaCO3,which is consistent with the test results of the gradually increasing impact toughness of the ternary composites.In the composites of B series,the EVA-nano-CaCO3 increase the interaction between EVA and nano-CaCO3,which restricte the cavitaton and elongation of EVA under the impact force.And In the composites of F series,a lot of EVA demonstrates effective cavitation and intensive yielding,thus the composites of B series have the lower impact toughness compared with composites of F series.In the further study,the effect of different nano-CaCO3 content to the performance of PP/EVA/nano-CaCO3 ternary composites of B series and F series are investigated.The results show that the yield strength and the vicat softening temperature of the composites gradually increase and the toughness of the composites gradually decrease by increasing nano-CaCO3 content as 3?4?5 and 6 at a fixed mass ratio of PP:EVA= 120:25.The impact toughness of F series composites that exhibit the characteristics of the yield deformation of the EVA microfiber is higher than that of B series,which demonstrate the characteristics of the cavitaton of encapsulation bulk and EVA phase.What's more,nano-CaCO3 plays the role of heterogeneous nucleation.With the increasing nano-CaCO3,the effect of heterogeneous nucleation is growing,led to the smaller spherulite size of PP,the fuzzier spherulite morphology of PP and the higher crystallinity of PP in the PP/EVA/nano-CaCO3 ternary composites.