Shear-induced pre-crystallization structures of long chain branched polypropylene under steady shear flow near the melting temperature

Tailoring microstructure and mechanical properties of injection molded isotactic–polypropylene via high temperature preshear

“…For the intrinsic nature of soft matter, the long and flexible chains constituting polymer could be easily oriented by shear in molten state. Recently, study on shear induced long‐lived precursors in the polymer melt at temperatures near or even above the melting point has been of recent interest . For example, with a specially synthesized linear high density polyethylene exhibiting a bimodal molecular weight distribution, Balzano et al demonstrated that a large number of metastable needle‐like precursors could be generated at high temperature (142°C) even above its equilibrium melting temperature ( °C).…”

“…For example, with a specially synthesized linear high density polyethylene exhibiting a bimodal molecular weight distribution, Balzano et al demonstrated that a large number of metastable needle‐like precursors could be generated at high temperature (142°C) even above its equilibrium melting temperature ( °C). According to the study by Kitade et al string‐like structures induced in linear PP melt at a low shear rate of 2 s −1 at 170°C (well above its nominal melting temperature ( ) which was no higher than 165°C), could be directly observed by polarized optical microscopy (POM). Somani and Hsiao quantitatively measured the limiting temperature at which no oriented structure survived in iPP melt by using in situ rheo X‐ray scattering and Couette flow geometry.…”

Good extrusion foaming performance of long‐chain branched PET induced by its enhanced crystallization property

“…The LCB structure will result in longer relaxation time and the entangled long chains aid the formation of pointlike precursors, which resulted in the creation of new nucleation sites. [19,25,26] Nofar et al [27,28] demonstrated that LCB poly(lactic acid) (PLA) had faster cold and melt crystallization rates than those of linear PLA. Besides, shear-induced crystallization nucleation for linear PLA and LCB PLA was implemented, and the saturate crystallization nucleation density for LCB PLA was twice as much as that for linear PLA under the same shear condition.…”

Shear-induced β -form polypropylene in long chain branching isotactic polypropylene

“…Reports show that LCBPP exhibits longer relaxation time than linear iPP , which inspires us to speculate that LCBPP may form β ‐crystal under shear conditions more easily than linear iPP. Nevertheless, to our best knowledge, only sparse studies on the shear‐induced crystallization behavior of LCBPP have been reported in the literatures . Agarwal et al demonstrated that oriented crystalline fraction was higher in LCBPP than that in linear iPP, and the crystallization kinetics of LCBPP was enhanced by more than one order of magnitude under shear when compared to linear iPP.…”

“…Vega et al compared the shear‐induced crystallization behaviors of linear iPP and LCBPP by using rheometry, in which lower values of the induction time for the onset of crystallization process were found at the low and moderate preshear conditions, and the effect was much more pronounced for LCBPP than for linear iPP . Recently, Kitade et al studied the shear‐induced crystallization of LCBPP at 170°C, close to the melting temperature, and at a low shear rate of 2 s −1 , which proved that shish‐like structures predominately formed and the further growth to kebabs was suppressed in LCBPP . These results are of great meaning, but the synergistic effects of the branching structure and shear conditions on the crystallization behavior of LCBPP is still elusive up to date.…”