Effect of Shear Stress on Crystallization of Isotactic Polypropylene from a Structured Melt

Nanomechanical characterization of graphene platelets in polypropylene-based graphene nanocomposites using atomic force microscopy

“…Raman results confirmed that our sample have different degrees of crystallinity [3]. Isotactic polypropylene can be crystallized in three modifications, α-modification exhibit monoclinic lattice, β-modification exhibit hexagonal lattice and γ-modification exhibit orthorhombic lattice [8]. Fig.…”

Influences of pre‐ordered melt structures on the crystallization behavior and polymorphic composition of β‐nucleated isotactic polypropylene with different stereo‐defect distribution

“…systematically investigated the β‐crystallization of iPP/iPP fiber single composite and found that the partly melting of orientated fibers may provide locally ordered structures within certain orientation window, which play very important role in the β‐crystallization; Alfonso et al . studied the formation and relaxation of shear‐induced nucleation and found that shear flow and partially molten fiber have similar effect on the formation of β‐phase; Shen et al . explored the combined effect of ordered structures and shear flow on polymorphic nature of β‐cylindrites and found that only in the presence of ordered structures can iPP melt form β‐cylindrites under the influence of shear flow, showing that ordered structures under shearing is crucial to β‐crystallization of iPP.…”

“…The results above elucidated first evidence that for iPP nucleated with dual‐selective β‐NA, the presence of ordered structures in iPP melt plays a very important role. Moreover, considering the previous reports concerning the role of ordered structures under shearing or orientation in β‐crystallization of iPP as well as the studies focusing the β‐crystallization behavior of iPP induced by dual‐selective β‐NAs, our findings provided a very important speculation: under all the crystallization conditions mentioned above, the β‐nucleation mechanism might be similar, where ordered structures play a determining role. A possible mechanism depicting a two‐step β‐nucleation behavior of iPP had been proposed in the previous studies.…”

Influence of melt structure on the crystallization behavior and polymorphic composition of polypropylene random copolymer

“…To achieve better toughness, the enhancement of b-form content is an efficient way. However, the b-form can be obtained in large amount only under several specific conditions such as shearing [15][16][17][18][19], using specific b-nucleating agents (b-NA) [20][21][22][23] and directional crystallization in temperature gradient [24].…”

“…Zhang et al [18,19] investigated effects of ordered structures and shear flow on polymorphic nature of b-cylindrites of iPP and found that the survived ordered structures may remain in the melt which can act as shear-precursor during recooling, initiate the shear-induced crystallization and encourage the formation of b-cylindrites. Liu et al [15,44,45] introduced partly melting iPP fiber to homogeneous supercooled iPP melt, and systematically investigated the b-crystallization of iPP/iPP single fiber composite.…”