Prediction of the flow‐induced crystallization in high‐density polyethylene by a continuum model

Abstract

In this work, the isothermal flow-induced crystallization (FIC) of highdensity polyethylene (HDPE) under a simple shear flow was investigated. Two experimental modes, including steady shear and preshear treatment, were performed on the polymer melt. Based on the nonequilibrium thermodynamic theory, the FIC process of HDPE was predicted through the modification of a continuum FIC model. The theoretical predictions of the evolution of both the viscosity in steady shear flow and the complex modulus under preshear treatment were essentially related to the crystallinity of HDPE, in agreement with the experimental findings. Both experimental and predicted results showed that the applied flow field could accelerate the crystallization kinetics of HDPE significantly. However, the effect of the intensity of shear flow on the crystallization of HDPE was finite, showing a saturation phenomenon, namely, the accelerated degree of crystallization tending to level off when the shear rate was large enough. In additional, it was found that the predicted crystallinity of HDPE was very low in induction period either in steady shear flow or by preshear treatment.

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

“…This significant increase in the onset temperature could be attributed to the fact that the crystallization process of PP was promoted by the flow field imposed in the rheological experiments, which made it possible for PP to crystallize at a higher temperature. The observed experimental results of flow-induced crystallization were consistent with that demonstrated in our previous work [ 8 , 51 , 52 , 53 ].…”

“…Therefore, the understanding of the crystallization process of polymers under the effect of flow makes it possible to control and predict the final morphologies and properties of the polymers [ 47 , 48 , 49 , 50 ]. Earlier, we investigated the effect of shear flow at various shear rates, shear time, and shear strains on the crystallization of polyolefin melts [ 8 , 51 , 52 , 53 ]. However, although the crystallization of PP/PEOc blends has been studied [ 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ], we know of no reports on the crystallization in LCB PP/PEOc blends under either quiescent or shear states.…”

Modeling of flow‐induced crystallization in blends of isotactic polypropylene and poly(ethylene‐co‐octene)

“…Following that theoretical work, we deduced a complete dimensionless expression of the continuum model to predict the whole crystallization kinetics of high‐density polyethylene (HDPE) in various shear flow fields. The predicted evolution of either the viscosity or the modulus of the HDPE melt was also in good agreement with experiments 10. Subsequently, Kannan and Rajagopal11 thought the approach of Doufas et al to be too sophisticated.…”

“…To get an insight into the FIC phenomenon, there has been much work reported concerning the prediction of the crystallization kinetics in a flow field based on different theories 9–17. For example, Doufas et al 9 developed a continuum model to simulate FIC of polymer melts in homogeneous flow fields under isothermal conditions.…”

Shear flow of molten polymer in melt blowing

“…So, there should be an annular distribution of contour line of shear rate in the fiber cross‐section, because there is the same shear rate with the same radius. Because shear flow was efficient to enhance the crystallization kinetics [23, 24], there might be an annual contour of microcrystallization gradient structure in the fiber cross‐section (see Fig. 5), similar with the sheath‐core structure in the literature [18].…”