The flow-induced crystallization behavior in capillary extrusion of high density polyethylene melts
TL;DR: In this article, a simple method for estimation of crystalline degree in flow of polymer melts was proposed, on the basis of experimental observation, the crystallinity during capillary extrusion of the sample melts was estimated and the flow-induced crystallization mechanisms were analyzed.
About: This article is published in Polymer Testing.The article was published on 2001-01-01 and is currently open access. It has received 8 citations till now. The article focuses on the topics: Melt flow index & Crystallization.
Citations
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TL;DR: In this paper, the effect of high-density polyethylene (HDPE)/polypropylene (PP) blending on the crystallinity as a function of the HDPE melt index was studied.
Abstract: The effect of high-density polyethylene (HDPE)/polypropylene (PP) blending on the crystallinity as a function of the HDPE melt index was studied. The melting temperature and total amount of crystallinity in the HDPE/PP blends were lower than those of the pure polymers, regardless of the blend composition and melt index. The effects of the melt index, blending, and foaming conditions (foaming temperature and foaming time) on the void fractions of HDPEs of various melt indices and HDPE/PP blends were also investigated. The void fraction was strongly dependent on the foaming time, foaming temperature, and blend composition as well as the melt index of HDPE. The void fraction of the foamed 30:70 HDPE/PP blend was always higher than that of the foamed 50:50 HDPE/PP blend, regardless of the melt index. The microcellular structure could be greatly improved with a suitable ratio of HDPE to PP and with foaming above the melting temperature for long enough; however, using high-melt-index HDPE in the HDPE/PP blends had a deleterious effect on both the void fraction and cell morphology of the blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 364–371, 2004
86 citations
TL;DR: A broad overview of FFF processing of semicrystalline polymers can be found in this paper, where the impact of processing conditions and feedstock modifications, such as the incorporation of fillers or the formation of blends, on crystallinity as well as the microstructure of printed parts, the impact on the micro-structure on the mechanical performance, and general part quality.
56 citations
TL;DR: In this article, a blowing agent for polyoxymethylene (POM) foam based on azodicarbonamide (ADCA) is proposed, and the microstructure analysis based on the evaluation of folded chain crystal and extended chain crystal (ECC) by FTIR reveals that the compression pressure applied primarily initiates the ECC.
25 citations
TL;DR: In this paper, the advances of the polymer melt flow-induced crystallization behavior and its influence on mechanical properties of high density polyethylene (HDPE) in micron injection (MI) were studied.
Abstract: The advances of the polymer melt flow-induced crystallization behaviour and its influence on mechanical properties of high density polyethylene (HDPE) in micron injection (MI) were studied in the present paper. Analysis of mechanical performance, including yield stress and elongation at break, for samples adopted from different regions in a molded plaque showed that a higher injection speed, a higher mold temperature and a longer cooling time could effectively enhance the yield stress but negatively promoted the ductility. Then, the mechanisms of such variation of mechanical performance and the factors affecting it were investigated by means of differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and polarized light microscopy (PLM). The super high shear rate during cavity feeding in MI molding not only induced a typical three-layered structure but also developed a highly oriented fibrously morphological structure in the skin layer. However, such fully oriented morphology was much negative in the interlayer and even could not be observed in the core layer. The results from SEM and PLM observations indicated that the orientation morphology varied significantly through the plaque’s cross-section and thickness of the each layer changed with the process parameters and geometric position, and finally led to variation of the mechanical performance.
24 citations
TL;DR: In this article, the extrudate swell and flow instability behavior of kaolin-filled PP composite melts were investigated using a constant rate type of capillary rheometer at high extrusion rates and test temperatures varied from 165°C to 220°C.
Abstract: Kaolin-filled PP composites were compounded using a heated two-roll mill prior to extrusion process in order to improve the rheological properties of the samples. The extrudate swell and flow instability (melt fracture) behavior of kaolin-filled PP composite melts were investigated using a constant rate type of capillary rheometer at high extrusion rates and test temperatures varied from 165°C to 220°C. The extrudate swell studies demonstrate that the die swell ratio decreases with an increase in the processing temperature and filler loading at fixed shear stress. Nonetheless, the study on the effect of shear stress and shear rate showed that the die swell ratio (B) of the melts decreases linearly with increasing apparent shear stresses and shear rates for both systems, unfilled and filled PP only up to one point above the critical shear rate (1.8 × 10 s-1). The B values remained almost constant when the shear rate is greater than 1.8 × 10 s -1 at a constant temperature. Kaolin-filled PP composites exhibi...
14 citations
References
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TL;DR: In this paper, a new technique is described for measuring crystallization kinetics during isothermal flow at constant shear rate in a parallel plate rheometer, characterized by the time elapsed from the start of shearing until the rise in melt viscosity due to crystallization.
Abstract: Some principles of rheology are applied to the study of the shear-induced crystallization of molten polymers. A new technique is described for measuring crystallization kinetics during isothermal flow at constant shear rate in a parallel plate rheometer. The crystallization rate is characterized by the time elapsed from the start of shearing until the rise in melt viscosity due to crystallization. The measured-viscosity and induction time for crystallization are shown to be independent of sample geometry. Kinetic data are presented for crystallization of three linear polyethylenes at shear rates of 0.03 – 30 sec−1. It is shown that shear flow has a strong accelerating effect on crystallization when the deformation rate exceeds a critical value. Comparison of results for the different polyethylenes reveals that higher molecular weight materials crystallize faster at a given shear rate and temperature. Finally, shear-induced crystallization of propylene polymers is shown to be unaffected by the presence of either a carbon black additive or a heterogeneous nucleating agent. It is concluded that the hydrodynamic origin of the shear-induced crystallization is elastic chain extension due to entanglement couplings between molecules. Furthermore, it is suggested that transient orientation effects during the startup of shear flow may have a dominant influence on the observed phenomena.
212 citations
TL;DR: A review of the field of flow induced crystallization from solution can be found in this paper, where the authors discuss the major problems in the development of quantitative models for the growth mechanisms and the reasons for this are discussed.
Abstract: This paper presents a review of the field of flow induced crystallization from solution. Experimental facts concerning the nature of fibrous nucleation and the “shishkebob” morphology which results are reviewed. The discussion of growth models emphasizes the details of the nucleation control and flow control calculations which have been presented in the literature. A major problem in the development of quantitative models for the growth mechanisms has been the lack of a reproducible growth rate data base and the reasons for this are discussed. The review emphasizes those areas of the field both experimental and theoretical, where further studies are needed before a unified theory of flow induced crystal growth can emerge.
63 citations
Book•
01 Aug 1984
TL;DR: In this article, the authors present the secret to improve the quality of life by reading this interrelations between processing structure and properties of polymeric materials, which is a kind of book that you need now.
Abstract: Find the secret to improve the quality of life by reading this interrelations between processing structure and properties of polymeric materials. This is a kind of book that you need now. Besides, it can be your favorite book to read after having this book. Do you ask why? Well, this is a book that has different characteristic with others. You may not need to know who the author is, how well-known the work is. As wise word, never judge the words from who speaks, but make the words as your good value to your life.
44 citations
TL;DR: In this article, the effects of pressure and temperature on the melt density ( ρ m ) and the melt flow rate (MFR) of the low-density polyethylene (LDPE) and a glass bead-filled LDPE composite were investigated using a capillary plastometer.
29 citations
TL;DR: In this article, a large-amplitude oscillatory shear (γ = 4.5) at temperatures between 139 and 181°C was applied to after the grain structure with the objectives of removing the discontinuities at the grain boundaries and aligning the domains into a continuous ultrastructure.
Abstract: Linear viscoelastic properties are found to be a sensitive measure of flow-induced structural changes in a block copolymer. Styrene-butadiene-styrene block copolymer (SBS) with 26% polystyrene (PS) forms a macrostructure in the quiescent state with grains of the order of 1–10 μm. Within each grain, phase separation gives rise to a regular two-phase microstructure with cylindrical PS domains with radius of the order of 200 A. Large-amplitude oscillatory shear (γ = 4.5) at temperatures between 139 and 181°C was applied to after the grain structure with the objectives of removing the discontinuities at the grain boundaries and of aligning the domains into a continuous ultrastructure. The SBS behaved like a solid (tan δ 1) after shear modification. This change expressed itself in the removal of the long relaxation times from the linear viscoelastic spectrum; the intermediate and low relaxation times were not affected by the shear modification. The viscoelastic spectrum slowly recovered during annealing with recovery times of the order of the longest relaxation time of the quiescent structure. Birefringence studies showed that the SBS did not recover into its original grain structure but into a highly oriented domain structure. The discontinuities at the grain boundaries could not be removed completely.
27 citations