Structure of skin layer in injection‐molded polypropylene

Fujiyama, Mitsuyoshi; Wakino, Tetsuo; Kawasaki, Youtoku

doi:10.1002/app.1988.070350104

Cited by 240 publications

(190 citation statements)

References 18 publications

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“…In processes such as fiber spinning, shish-kebabs are the dominant building block of the morphology and their alignment along the fiber axis leads to anisotropic mechanical properties. In injection molding, depending on the conditions, shish-kebabs can form close to the mold wall and thus affect the surface properties of the material (Fujiyama et al, 1988;Ogbonna et al, 1995).…”

Section: Shear-induced Crystallization Using a Slit Rheometermentioning

confidence: 99%

Polymer crystallization studies under processing-relevant conditions at the SAXS/WAXS DUBBLE beamline at the ESRF

et al. 2013

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Recent developments on the experimental infrastructure and the acquisition of new detectors on the Dutch-Belgian beamline BM26B at the ESRF offer novel and promising possibilities for synchrotron X-ray experiments in the field of polymer crystallization under processing-relevant conditions. In this contribution, some of the most recent experiments mimicking conditions similar to those relevant for the plastics processing industry are discussed. Simultaneous thermal analysis and wide-angle X-ray scattering (WAXS) experiments, at the millisecond time-frame level, on -nucleated isotactic polypropylene (i-PP) samples subjected to ballistic cooling up to 230 K s À1 , show that the efficiency of the nucleating agent can be suppressed when quenched cooling rates higher than 130 K s À1 are used. In situ WAXS experiments using small-scale industrial equipment during a real film blowing process reveal the dependence of the onset of crystallinity (the so-called freeze line) and the crystal orientation as a function of different take-up and blow-up ratios. In situ small-angle X-ray scattering (SAXS) experiments during high-flow fields reveal the formation of shish and kebab structures in i-PP as a function of the imposed stress. Quantitative analysis of i-PP flow-induced structures is presented. The beamline specifications required to obtain high quality and industrially relevant results are also briefly reported.

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Section: Shear-induced Crystallization Using a Slit Rheometermentioning

confidence: 99%

Polymer crystallization studies under processing-relevant conditions at the SAXS/WAXS DUBBLE beamline at the ESRF

et al. 2013

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“…The fibre axis (FA), formed by the axes c or c + a*, is roughly parallel to the direction FD. The origin of this 'bimodal' fibre structure is the epitaxic overgrowth of the a*-axis-oriented a-PP on c-axisoriented a-PP (cf Binsbergen & De Lange, 1968;Fujiyama, Wakino & Kawasaki, 1988). The only weak biaxial orientation is due to a-(010) planes lying parallel to the surface of the disc.…”

Section: Theory Of Texture Analysis Of Wide-angle Scattering Profilesmentioning

confidence: 99%

“…Therefore the elucidation of the morphology and texture in the cross section of the mouldings is of great practical importance (cf. Trotignon & Verdu, 1987;Fujiyama, Wakino & Kawasaki, 1988).…”

Section: Introductionmentioning

confidence: 99%

Small- and wide-angle X-ray scattering investigations of injection-moulded polypropylene

Zipper¹,

Jánosi²,

Wrentschur³

et al. 1991

J Appl Cryst

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The layered structure in 2 mm thick discs injection moulded from industrial polypropylene (PP) was studied by scanning the cross section of the mouldings by means of small-and wide-angle X-ray scattering (SAXS and WAXS), using a Kratky collimation system for position-resolved quantitative scattering measurements in both angular domains. The registration of so-called scattering profiles of the mouldings and a texture analysis of the WAXS profiles were established as novel approaches for studying the cross-section architecture. The results of the investigations comprise statements on the preferential orientation and the local distribution of a-and fl-PP in different layers of the cross sections, on crystallite sizes and on the behaviour of individual layers in tensile tests.

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“…The high yield stress of the skin layer is considered to be due to shish structures because fibrous crystals have high strength and a deeply penetrated texture [36]. Although shish structures are not detected by SAXS, they still exist and would enhance the yield stress.…”

Section: Mechanical Propertiesmentioning

confidence: 99%

Effects of gate design and cavity thickness on filling, morphology and mechanical properties of microinjection mouldings

Zhang

Choi

et al. 2015

Materials & Design

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Miniaturized parts weighing single or tens of milligrams represent a large category of microinjection moulded products. Both miniaturization and extreme processing under microinjection moulding subject material to high shear rates and high cooling rates, and cause the same material to have different morphologies and final properties when used in conventional injection moulding. It also makes mold design challenging. This study investigates the effects of micro gate design (opening and thickness) and cavity thickness (100-500μm) on filling, morphology and the mechanical properties of miniaturized dumbbell parts. It is found that a reduction of gate size has two conflicting effects, namely, increased shear heating increases flow length, and increased cooling rate reduces flow length. Filling increases significantly with an increase of cavity thickness. In addition, the thickness of the skin layer reduces from ~70% to ~10% when part thickness increases from 100μm to 500μm. This oriented skin layer determines molecular orientation and broadly influences Young's modulus, elongation and yield stress. Natural aging at room temperature induces an increase of modulus and yield stress, and a decrease of strain at break. The mechanical properties of microinjection moldings is significantly different from those of conventional injection moldings and measurement at microscale is required for miniaturized product design. 1 Effect of Gate Design and AbstractMiniaturized parts weighing single or tens of milligrams represent a large category of microinjection moulded products. Both miniaturization and extreme processing under microinjection moulding subject material to high shear rates and high cooling rates, and cause the same material to have different morphologies and final properties when used in conventional injection moulding. It also makes mold design challenging. This study investigates the effects of micro gate design (opening and thickness) and cavity thickness (100-500μm) on filling, morphology and the mechanical properties of miniaturized dumbbell parts. It is found that a reduction of gate size has two conflicting effects, namely, increased shear heating increases flow length, and increased cooling rate reduces flow length.Filling increases significantly with an increase of cavity thickness. In addition, the thickness of the skin layer reduces from ~70% to ~10% when part thickness increases from 100μm to 500μm. This oriented skin layer determines molecular orientation and broadly influences Young's modulus, elongation and yield stress. Natural aging at room temperature induces an increase of modulus and yield stress, and a decrease of strain at break. The mechanical properties of microinjection moldings is significantly different from those of conventional injection moldings and measurement at microscale is required for miniaturized product design.

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Structure of skin layer in injection‐molded polypropylene

Cited by 240 publications

References 18 publications

Polymer crystallization studies under processing-relevant conditions at the SAXS/WAXS DUBBLE beamline at the ESRF

Polymer crystallization studies under processing-relevant conditions at the SAXS/WAXS DUBBLE beamline at the ESRF

Small- and wide-angle X-ray scattering investigations of injection-moulded polypropylene

Effects of gate design and cavity thickness on filling, morphology and mechanical properties of microinjection mouldings

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