Components Of Micro-structure Of Polypropylene Binary And Ternary Blends Crystallization Behavior And Morphology

Polypropylene (PP) in-situ alloy is a type of high-impact propylene that owns excellent mechanical properties and has a wide range of applications. It consists of a series of components with different microstructures, which makes it difficult to study the structure-property relationship of PP alloy.In this paper, we first extracted the following copolymer fractions from a common ethylene-propylene copolymer: soluble EPR fractions (sol-EPR) and insoluble EPR fraction (insol-EPR) in n-octane at room temperature, ethylene-propylene copolymers extracted with n-octane at 90℃ (EP90) and 120℃ (EP120), respectively. Then one or more copolymer fractions were used to blend with PP in appropriate proportions. The crystallization behavior and morphology of these blends were studied by differential scanning calorimetry, wide angle X-ray diffraction, polarized optical microscope and scanning electron microscope.In all the PP blends we found that phase separation occurs, the copolymer factions added can nucleate crystallization of PP and the relative content of beta-crystal changes with the proportion of the copolymer fractions.The crystallization behavior and morphology of binary blend mainly depend on the compatibility of PP and copolymer fractions. The sol-EPR fractions are highly incompatible with PP and the crystallization behavior of PP does not change with the proportion of sol-EPR much. In contrast, the long propylene segment in the insol-EPR fraction may be incorporated into the crystalline PP region and thus the crystallization behavior of PP changes with the proportion of insol-EPR. The size of the insol-EPR phase is smaller than that of the sol-EPR at the same proportion. PP/EP90 and PP/EP120 behave similarly, but EP90 copolymer fraction has a greater influence on crystallization behavior of PP than EP120.It may be because EP90 is more compatible than EP120. The crystallization kinetic data indicate that the folding surface free energy of PP crystals in PP/EP90 becomes smaller with addition of copolymer fractions, on the contrary, the folding surface free energy of PP crystal in PP/EP120 becomes larger than that of neat PP.In PP/EP90/EPR ternary blends, as a compatilizer, EP90 can be miscible withEPR to form domains containing both EP90 and EPR or can form domains containingonly EP90. In the ternary blends, the domain sizes are smaller that those in the binaryblends.And the folding surface free energy of ternary blends decreases with EPR increasing.