Characterization of i‐PP shear‐induced crystallization layers developed in a slit die

Farah, Marcelo; Bretas, Rosário Elida Suman

doi:10.1002/app.13576

Cited by 35 publications

(34 citation statements)

References 19 publications

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“…If no high pressure were applied, the increase in Q would increase the shear rate and therefore would decrease the time for the beginning of the flow induced crystallization as already confirmed in our labs [2]. However, during the injection molding packing stage, a high pressure is applied and crystallization occurs under the influence of this high pressure.…”

Section: Resultssupporting

confidence: 64%

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Optical monitoring of polypropylene crystallization during injection molding

Favaro

Marinelli

Farah

et al. 2007

Polymer Engineering & Sci

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The nonisothermal crystallization of polypropylene resins, i-PP, during injection molding, using an optical device inserted in the injection mold cavity was monitored. The device detected the change of optical properties which occurs in polymers during their crystallization process; thus the intensity of a laser beam after it passed through the crystallizing polymer was measured during an injection molding cycle. The collected light intensity after the end of the cycle was correlated with the morphologies and final crystallinity degree of the samples. The influence of nucleating agents and the change of the parameters of the injection molding process on the morphology and optical signals were also investigated. The morphologies were analyzed by polarized light optical microscopy, PLOM. The % of crystallinity of the samples was measured by wide angle X-rays diffraction, WAXS. It was concluded that the optical device was sensible to different polymer crystallization kinetics, morphology type, and changes in the injection molding parameters. It was also found that the mold temperature and packing pressure and time were the factors that affected most the kinetics of crystallization of these polymers in this particular disk geometry. The WAXS results showed that the lower the final light intensity the higher the % of crystallinity in the samples. POLYM. ENG. SCI.,

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Section: Resultssupporting

confidence: 64%

“…During processing, a polymer is subjected to high gradients of temperature, pressure, and deformation rates. Therefore, its morphology and crystallization kinetics under quiescent conditions will be different from that under processing conditions [1][2][3][4][5][6][7][8][9][10].…”

Section: Introductionmentioning

confidence: 99%

Optical monitoring of polypropylene crystallization during injection molding

Favaro

Marinelli

Farah

et al. 2007

Polymer Engineering & Sci

Self Cite

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show abstract

“…However, in the presence of flow, it is observed 12 that the i-PP chains orient, creating fibrillar nucleus. It has also be shown 1 that the quantity of β phase in i-PP samples processed in a slit die decrease with the decreasing of the shear rate imposed during the crystallization process;…”

Section: Introductionmentioning

confidence: 97%

“…Thus, the developed morphology reflects these flow patterns, and usually is composed of different and characteristic layers along the thickness of the sample [1][2][3][4][5][6][7][8][9] . In the case of semi crystalline thermoplastics with fast crystallization kinetics, this morphology is known as "skin-core" and is formed by three main zones [4][5][6][10][11][12][13][14][15][16] :…”

Section: Introductionmentioning

confidence: 99%

A X-ray study of β-phase and molecular orientation in nucleated and non-nucleated injection molded polypropylene resins

2009

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The development of α and β-phases and the molecular orientation of injection molded disks of two isotactic polypropylene (i-PP) resins were studied by wide angle X-ray diffraction (WAXD) and pole figures. A nucleated (NPP) and non-nucleated (HPP) polymers were analyzed. The main proposal of this article was the comprehensive study of the interrelations between the processing conditions, phase contents and PP α-phase molecular orientation of injection molded PP resins. In both resins, it was observed that the α-phase was present in all regions along the thickness while the β-phase was present mainly in the external layers, decreasing from the surface to the core; however this last phase was present in a very small amount in the NPP resin. For both polymers, the orientation of the macromolecules c-axis was higher along the flow direction (RD) than along the transverse direction (TD). The b-axis of the PP α-phase molecules was oriented to the thickness direction (ND). The orientation of the c-axis along RD and b-axis along ND of the NPP samples was considerably higher than of the HPP samples, due to the NPP faster crystallization kinetics. For both polymers, the most influential processing parameters on the molecular orientation were the mold temperature and flow rate. The results indicate that, as the mold temperature increased, the characteristic molecular orientation of PP α-phase, with c-axis along RD and b-axis along ND, decreased. With increase in the flow rate an increase of the c-axis molecular orientation of the samples along RD was observed.

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“…It is a well known fact that there are some crystal types of PP with different crystal systems, and surface roughness of BOPP films has been investigated in association with crystal types [2][3][4][5][6][7][8] . Many basic studies have been reported on the formation of α and β crystals [9][10][11][12][13][14] . Natta and Corradini reported in their report in 1960 that unit lattice of α crystal is the monoclinic system, and now it is known as being the most dominant crystal in PP 9) .…”

Section: Introductionmentioning

confidence: 99%

Crater formation mechanism on the surface of a biaxially oriented polypropylene film

Tamura¹,

Takino

Yamada

et al. 2012

J of Applied Polymer Sci

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Biaxially oriented polypropylene (BOPP) films are used in a variety of areas around the world. They are especially suited for food packaging and industrial usages due to their high productivity. Many studies on stretchability regarding crystal structure changes have been reported by various researchers, since the machine speed has been increasing and the demand to produce thinner films has been becoming more important.Furthermore, a number of studies on the surface structure of BOPP films with crater-like roughness have been reported since the 1980's. Although the crater-like surface roughness was formed under specific film process conditions, the formation mechanism and the controlling method of the crater-like film surface are yet to be clarified. In this report, the authors demonstrate a new hypothesis as to the crater-like film surface roughness formation mechanism by analyzing the morphology of the surface layer of polypropylene (PP) sheets and by investigating the relationship between the surface structure changes and the entire structure changes. As a result, it was found that it needs to have over critical crystallization time in order to form the crater on the surface of BOPP film, and the crater formation mechanism was closely related not only to the surface structure changes but also to the deforming phenomenon of spherulite in PP sheet during stretching. Furthermore, this report will show the controlling factors in the formation of the crater structure from the view point of production conditions.

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Characterization of i‐PP shear‐induced crystallization layers developed in a slit die

Cited by 35 publications

References 19 publications

Optical monitoring of polypropylene crystallization during injection molding

Optical monitoring of polypropylene crystallization during injection molding

A X-ray study of β-phase and molecular orientation in nucleated and non-nucleated injection molded polypropylene resins

Crater formation mechanism on the surface of a biaxially oriented polypropylene film

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