In Situ Visualization of Extensional Flow-Induced Crystallization in Polypropylene under High-Pressure CO2

被引:2
作者
Embabi, Mahmoud [1 ,2 ]
Shen, Xia Wei [1 ]
Tuccitto, Anthony V. [1 ,2 ]
Kweon, Mu Sung [3 ]
Pehlert, George [3 ]
Serles, Peter [4 ]
Filleter, Tobin [4 ]
Park, Chul B. [2 ]
Lee, Patrick C. [1 ]
机构
[1] Univ Toronto, Dept Mech & Ind Engn, Multifunct Compos Mfg Lab MCML, Toronto, ON M5S 3G8, Canada
[2] Univ Toronto, Dept Mech & Ind Engn, Microcellular Plast Mfg Lab, Toronto, ON M5S 3G8, Canada
[3] ExxonMobil Technol & Engn Co, Baytown, TX 77520 USA
[4] Univ Toronto, Dept Mech & Ind Engn, Nanomech & Mat Lab, Toronto, ON M5S 3G8, Canada
基金
加拿大自然科学与工程研究理事会;
关键词
polypropylene; quiescent crystallization; extensionalflow-induced crystallization; uniaxial extensional flow; supercritical CO2; crystal growth rate; cell growth; long-chain branching; SHEAR-INDUCED CRYSTALLIZATION; ISOTACTIC POLYPROPYLENE; RHEOLOGICAL PROPERTIES; CARBON-DIOXIDE; NONISOTHERMAL CRYSTALLIZATION; BRANCHED POLYPROPYLENE; GAMMA-PHASE; MORPHOLOGY; FOAM; MELT;
D O I
10.1021/acsapm.4c00165
中图分类号
T [工业技术];
学科分类号
08 ;
摘要
The crystallization behavior of semicrystalline polymers under foaming-relevant conditions is among the most critical factors dictating the morphology and properties of any foam product. While cell nucleation and growth are often discussed in the plastics foaming literature, extensional flow-induced crystallization experienced postdie exit during foam stabilization is overlooked. To address this gap, we aim to build a comprehensive understanding of the nonisothermal crystallization behavior under the effects of CO2 pressure, uniaxial extensional flow, and long-chain branching. Two grades of polypropylene (PP) were used: one linear and one long-chain branched. Under quiescent conditions, an increase in CO2 pressure led to a decrease in onset crystallization temperatures, a decrease in crystal growth rates, and an increase in nucleation densities in both resins. Additionally, X-ray diffraction analyses showed the promotion of gamma-crystals under higher CO2 pressures. Upon the introduction of uniaxial extensional flow, both resins nucleated elongated crystals (i.e., cylindrites) due to chain alignment and stretching. These cylindrites were observed via atomic force microscopy and shown to exhibit the classical shish-kebab structure. Interestingly, the long-chain-branched PP (LCB PP) nucleated more cylindrites with higher aspect ratios and exhibited a crystallization rate faster than that of its linear counterpart. Rheological characterization showed that this difference emerged from the longer relaxation behavior of the LCB PP chains. These findings may present value in modeling polymer processes while emphasizing the role of extensional flow-induced crystallization during cell growth and stabilization.
引用
收藏
页码:4089 / 4102
页数:14
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