Rheo-chemistry in Reactive Processing of Polyolefin

Yu, Wei; Liu, J.; Zhou, Chixing

doi:10.3139/217.2431

Cited by 7 publications

(4 citation statements)

References 48 publications

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“…High mobility of degraded polymer chain (low molecular weight) will increase the possibility of chain contact, and thus increase the recombination rate, which actually decreases the apparent rate of chain scission. Such idea has been proved recently in the degradation of polymers under flow field. − The effect of temperature on the degradation of PPC was illustrated by the change of M w with time. This is shown in Figure for different processing temperatures between 130 and 180 °C.…”

Section: Resultsmentioning

confidence: 97%

“…The random scission rate constant k r increases slightly as rotational speed increases at low temperature (130 °C), but it is almost unchanged at high temperature. It has been shown that the degradation can be accelerated by applying flow field, whose effect depends both on the strength of flow field and molecular weight of polymer . Strong shear flow not only can promote the reaction kinetics of chain coupling but also even cause chain scission that cannot happen quiescently. − For PPC, the relaxation time is short at high temperature (see next section), and the flow field in the twin screw extrusion is not strong enough to accelerate the chain scission as compared with the fast quiescent chain scission.…”

Section: Resultsmentioning

confidence: 99%

“…It has been shown that the degradation can be accelerated by applying flow field, whose effect depends both on the strength of flow field and molecular weight of polymer . Strong shear flow not only can promote the reaction kinetics of chain coupling but also even cause chain scission that cannot happen quiescently. − For PPC, the relaxation time is short at high temperature (see next section), and the flow field in the twin screw extrusion is not strong enough to accelerate the chain scission as compared with the fast quiescent chain scission. As temperature decreases, the relaxation time of PPC increases and the quiescent chain scission slows down, so the chain scission under flow field becomes faster as the rotational speed increases.…”

Section: Resultsmentioning

confidence: 99%

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Study on the Thermal Degradation Kinetics of Biodegradable Poly(propylene carbonate) during Melt Processing by Population Balance Model and Rheology

Lin

Wang

et al. 2014

Ind. Eng. Chem. Res.

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The degradation behavior of poly(propylene carbonate) (PPC) was investigated during melt processing to infer the mechanism and kinetics of thermal degradation. First, the degradation experiments were carried out in a miniature conical twin-screw extruder at different temperatures, rotating speeds, and processing times. Gel permeation chromatography (GPC) was applied to analyze the molecular weight and molecular weight distributions (MWDs) of melt processed PPC samples. The degradation process at various processing conditions was described by the population balance equations (PBEs) with random chain scission and chain end scission. By comparing the prediction of PBE model with the experimental evolution of molecular weight, it is proposed that random chain scission and chain end scission occur simultaneously. At temperature higher than 160 °C, random chain scission dominates with the activation energy about 120 kJ/mol. Second, a method combining the PBE model and rheology was suggested to determine the kinetics of degradation directly from the torque of mixer during melt processing without further measurements on molecular weight. Such method was applied to melt mixing of PPC in a batch mixer, from which a higher kinetic parameter of thermal degradation and similar activation energy were successfully determined as compared to those obtained from extrusion experiments.

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Section: Resultsmentioning

confidence: 97%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Study on the Thermal Degradation Kinetics of Biodegradable Poly(propylene carbonate) during Melt Processing by Population Balance Model and Rheology

Lin

Wang

et al. 2014

Ind. Eng. Chem. Res.

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“…The implementation of mathematical models, namely macroscale modeling, mesoscale modeling, microscale modeling, single particle modeling, computational fluids dynamic modeling, microelements modeling, 2D finite element modeling, single pore modeling, and parti-level fragmentation modeling to determine the properties of the polyolefin, and the mass and heat transfer phenomena during the polymerization process. [8,11,12,22,[31][32][33][34] 7. Quality Control Different types of analysis such as nuclear magnetic resonance (NMR), temperature rising elution fractionation (TREF), gel permeation chromatography (GPC), rheological characterization (zero shear viscosity, zero shear viscosity, shear thinning behavior, dynamic modulus, loss angle, Van-Gurp-Palmen plot, Cole-Cole plot, activation energy, thermorheological complexity, strain-hardening effect, relaxation time, damping function, nonlinear dynamical oscillatory shear, and long-chain branching index), dynamic mechanical analysis, differential scanning calorimeter, neutron scattering, and molecular topology fractionation.…”

Section: Thermodynamic Propertiesmentioning

confidence: 99%

Advances in Mathematical Modeling of Gas-Phase Olefin Polymerization

et al. 2019

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Mathematical modeling of olefin polymerization processes has advanced significantly, driven by factors such as the need for higher-quality end products and more environmentally-friendly processes. The modeling studies have had a wide scope, from reactant and catalyst characterization and polymer synthesis to model validation with plant data. This article reviews mathematical models developed for olefin polymerization processes. Coordination and free-radical mechanisms occurring in different types of reactors, such as fluidized bed reactor (FBR), horizontal-stirred-bed reactor (HSBR), vertical-stirred-bed reactor (VSBR), and tubular reactor are reviewed. A guideline for the development of mathematical models of gas-phase olefin polymerization processes is presented.

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Rheological Measurements

2013

Encyclopedia of Polymer Science and Technology

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Rheology is the science to study the flow and deformation of matter. It becomes an important field in material science and engineering, food, biotechnology, and so on. The objects in rheological study are not the ideal solid and ideal fluid, which can be described by the Hookean elastic model and the Newtonian viscous model, respectively. Instead, the rheological study often focuses on materials that can exhibit viscous, elastic, and plastic behavior under different flow conditions. They are often termed as complex fluids or soft matter, which include polymers, gels, suspensions, emulsions, biofluids, foods, inks (1). In contrast to hydrodynamics, which often accounts for the complex flow behavior of simple fluids, simple geometry is utilized in rheological measurements to understand the rather complicated relationship between the mechanical input and output of complex fluids. The real flow fields encountered in many applications (such as polymer extrusion, injection molding, blow molding, fiber spinning, inkjet printing, coating) are rather complicated (2). It becomes a problem whether the rheological measurements that performed under simple flow fields are useful in understanding the complicated flow behaviors of complex fluids. Fortunately, it has been proved in many examples that the properties determined from simple rheological measurements are sufficient to quantify the material parameters in various constitutive equations, which have been used widely and successfully to simulate the flow behaviors in polymer processing (3-11). The most frequently used simple flow fields are simple shear flow and simple extensional flow.The simplest geometry that defines the simple shear is two infinite parallel plates separated by a distance h. The liquid is set between two plates with one plate moving parallel to the other (Fig. 1). In reality, when the length L and the width B are much larger than the gap h, the flow in the center regime resembles the flow between two infinite plates. It means that the edge effects are ignored in most experimental shear geometries. In rheological measurements, the flow between two plates should be laminar. Moreover, it is usually assumed that the velocity across the gap satisfies a linear profile. As shown in Fig. 1, if the bottom plate is fixed and the upper plate moves horizontally with the velocity V, the fluid velocity varies linearly from 0 at the bottom plate to V at the upper plate if the no-slip boundary condition is satisfied. The linear velocity profile generates a constant velocity gradient, which is known as the shear rate. Then, the flow field between two parallel plates is homogeneous in the shear rate. The homogeneous assumption is nontrivial in the rheological tests since the actual velocity

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Rheo-chemistry in Reactive Processing of Polyolefin

Cited by 7 publications

References 48 publications

Study on the Thermal Degradation Kinetics of Biodegradable Poly(propylene carbonate) during Melt Processing by Population Balance Model and Rheology

Study on the Thermal Degradation Kinetics of Biodegradable Poly(propylene carbonate) during Melt Processing by Population Balance Model and Rheology

Advances in Mathematical Modeling of Gas-Phase Olefin Polymerization

Rheological Measurements

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