Shear-induced crystallization in phase-separated blend of isotactic polypropylene and poly (ethylene-co-octene)

et al. 2008

Polymer

105

100

a b s t r a c tDue to both theoretical and practical importance, the formation mechanism of shear-induced shishkebab and the precise microstructure and molecular composition in shish-kebab have been extensively investigated for many years. However, a systematic review on the manipulation of shish-kebab superstructure in the injection-molded specimens, taken account of combining theoretical understanding, preparation processing, structural/morphological control and macroscopic properties, has rarely seen in the open publication by far. In this article, we will discuss mainly the topic of formation of fine polyolefin shish-kebab superstructure facilitated by ''melt manipulation'' strategy in injection-molding process. The main body of this review is governed by a logical sequence of (fundamental research)-(injection molding of melt manipulation)-(manipulation of shish-kebab)-(macroscopic mechanical properties). The fundamental understandings of the early stage of shish-kebab crystallization, transition process from random entangled chains network to stable shish-kebab cylindrulite, and the role of long polymer chains on shish-kebab formation, are very helpful for in-depth comprehension of shear-induced shishkebab in realistic processing. Various highly oriented morphologies with fine shish-kebab superstructure in injection-molded bars of polyolefin melts, including single component polyolefin melt, biphase melts of blend and heterogeneous melts of polyolefin/inorganic filler composites, could be achieved via ''melt manipulation'' strategy, as demonstrated by the work mainly from our group.

Section: Shish-kebab Generated From the Biphase Melt Of Polyolefin Blendsupporting

confidence: 57%

Shish–kebab of polyolefin by “melt manipulation” strategy in injection-molding: A convenience pathway from fundament to application

Wang

Chen

et al. 2008

Polymer

105

100

“…In our previous38 and other researchers'39, 40 works, the higher T m of iPP has been detected, which is due to the melting of shear induced shish structure of iPP. Meng et al41 and Somani et al42 have proposed the formation mechanism of such a structure. However, when iPP becomes the minor phase (for example, DPL70), only one peak, located at 163°C, is observed.…”

Section: Resultsmentioning

confidence: 99%

Epitaxial crystallization and oriented structure of linear low‐density polyethylene/isotactic polypropylene blends obtained via dynamic packing injection molding

Wang

Polymers for Advanced Techs

et al. 2011

In this work, as a part of a long-term project aimed at controlling of crystal structure and phase morphology for a injection molded product, we investigated the oriented structure and possible epitaxial growth of polyolefin blend (low-density polyethylene (LLDPE)/isotatic polypropylene (iPP)), achieved by dynamic packing injection molding, which introduced strong oscillatory shear on the gradually-cooled melt during the packing process. The crystalline and oriented structures of the prepared blends with different compositions were estimated in detail through 2D X-ray diffraction, calorimetry, and optical microscopy. As iPP was the dominant phase (its content was more than 50 wt%), our results indicated that it could be highly oriented in the blends. In such case, it was interesting to find that LLDPE epitaxially crystallized on the oriented iPP through a crystallographic matching between (100) LLDPE and (010) iPP , resulting in an inclination of LLDPE chains, about 50-to the iPP chain axis. On the other hand, as iPP was the minor phase, iPP was less oriented and no epitaxial growth between iPP and LLDPE was observed; even LLDPE remained oriented. The composition-dependent epitaxial growth of LLDPE on oriented iPP could be understood as due to:(1) the effect of crystallization sequence, it was found that iPP always crystallized before LLDPE for all compositions;(2) the dependence of oriented iPP structure on the blend composition; (3) the ''mutual nucleation'' between LLDPE and iPP due to their partial miscibility.

“…Several researchers have analyzed in detail the crystallization behaviour of iPP/PEOc blends [40,41,42,43,44]. In our previous study, we demonstrated that the presence of the highly viscous elastomer, PEOc, tended to promote the nucleation of the supercooled iPP melting at the interface of two-phases due to their long relaxation behaviour in shear flow field [45,46].…”

Section: Introductionmentioning

confidence: 93%

Isothermal and Non-Isothermal Crystallization Studies of Long Chain Branched Polypropylene Containing Poly(ethylene-co-octene) under Quiescent and Shear Conditions

2017

Polymers

Isothermal and non-isothermal crystallization behaviours of the blends of long chain branched polypropylene (LCB PP) and poly(ethylene-co-octene) (PEOc) with different weight ratios were studied under quiescent and shear flow using polarized optical microscopy (POM), differential scanning calorimetry (DSC), and rheological measurements. Experimental results showed that the crystallization of the LCB PP/PEOc blends were significantly accelerated due to the existence of the long chain branches (LCBs), the blends being able to rapidly crystallize even at 146 • C. The addition of PEOc that acts as a nucleating agent, could also increase the crystallization rate of LCB PP. However, the crystallization rate of LCB PP was reduced when the PEOc concentration was more than 60 wt %, showing a retarded crystallization growth mechanism. The morphology of the binary blend was changed from a sea-island structure to a co-continuous phase structure when the PEOc concentration was increased from 40 to 60 wt %. In comparison with linear isotactic iPP/PEOc, the interfacial tension between LCB PP and PEOc was increased. In addition, flow-induced crystallization of LCB PP/PEOc blends was observed. Possible crystallization mechanisms for both LCB PP/PEOc and iPP/PEOc blends were proposed.