Crystallization and morphology of reactor-made blends of isotactic polypropylene and ethylene-propylene rubber

Abstract

ABSTRACT:The crystallization and morphology of reactor-made blends of isotactic polypropylene ( PP ) with a large content of ethylene -propylene rubber ( EPR ) (i.e., ú 50%) were investigated. In the blends, PP was found to form spherulites during the crystallization process, with the growth rate constant under isothermal conditions. For crystallization temperatures in the range of 118 -152ЊC, the birefringence of the spherulites varied from negative to positive by decreasing crystallization temperature, while homopolypropylene ( homo-PP ) , the same as used in the blends as a matrix, showed negative spherulites in the whole temperature range investigated ( 118 -152ЊC ) . Both the spherulite growth rate and the overall crystallization rate were slower for the blends than for homo-PP. The density of the crystallization nuclei was lower in the blends than in the homo-PP. It was concluded that a large amount of EPR content in the reactor-made blends of PP retards and hinders the crystallization of the matrix.

Development of Crystalline Morphology, Structure, and Impact Property of Isotactic Polypropylene and Poly(cis-Butadiene) Rubber Blends During Mixing

“…Therefore, isotactic polypropylene (PP), being sensitive and brittle at low temperatures or high impact rates (due to a highly regular inner structure), has been sufficient for a wide range of engineering uses. However, most of the research on toughening PP by blending is focused on changing added components [1] , adjusting the blend ratio [2] and selecting different mixing methods [3] . Little attention is paid to researching the development of crystalline morphology and the structure of blends during mixing.…”

Crystallization kinetics of thermoplastic elastomeric blends based on ground tyre rubber

“…As the rubber content increases a reduction on the nucleation rate and crystallization temperature is observed, which can be explained by an increasing restraining effect by EPR and EPDM on the mobility of the PP molecular chains , …”

Synthesis and Structural Elucidation of 2′-Deoxy-4′-thio-L-threo-pentofuranosylpyrimidine and -purine Nucleosides

“…The kinetics parameters of isothermal crystallization were determined by the following modified Avrami equation:1, 2, 4, 5, 14–21 where X ti is the relative crystallinity at crystallization time t i , K is a crystallization kinetic constant, and n is the Avrami exponent.…”

“…In a spherical three‐dimensional crystallization process controlled by a heterogeneous nucleation where the Avrami exponent n is 3, the rate constant is expressed as2, 4, 5, 12, 15, 19 where N and G are the number of effective nuclei per unit volume and the spherulite growth rate, respectively. It is usually assumed that nonintegral values of n are caused by such factors as mixed nucleation modes, secondary crystallization, or intermediate dimensionality of crystal growth.…”

“…Thus, the absolute crystallinity as a function of time was determined according to the following structure:4, 10 where Δ H ( t ) is the enthalpy of crystallization at time t , and Δ Hf is the enthalpy of melting of a fully crystallized polymer (here, 209 J/g for PP). The relative crystallinity is expressed as1,7,15 where Xc ∞ is the crystallinity at equilibrium, and dH / dt is the heat‐evolution rate.…”