Shear‐induced β‐form crystallization in isotactic polypropylene

Dragaun, H.; Hubeny, H.; Muschik, H.

doi:10.1002/pol.1977.180151008

Cited by 119 publications

(75 citation statements)

References 12 publications

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“…These results agree with the results of Turner-Jones et al, 35 Moos and Tilger41 and Dragaun et al 54,56 and differ from the results of Ullmann and W e n d~r f f ,~~ where the K value was independent of the melting temperature in a range of 190-260OC. In a low melting temperature range, the nuclei or associations of molecular chains persist in the melt, and the formation of the p-crystals results from these association^.^^ It seems likely that since the associations of the molecular chains which play an assistant role in the formation or growth of nuclei by the nucleator decrease with increasing melting temperature, the formation of the p-crystals is suppressed as the melting temperature increases.…”

Section: Influences Of B-nucleator Content and Casting Conditions Onsupporting

confidence: 79%

Study on rough‐surface biaxially oriented polypropylene film. I. Formation of β‐form crystals in sheet cast with T‐die extruder

Fujiyama

Kawamura

Wakino

et al. 1988

J of Applied Polymer Sci

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SynopsisSheets were cast by extruding polypropylenes (PP) which contained y-quinacridone, a /?-crystal nucleator, at levels of 0-10 ppmusing a 30 mm + extruder with a T-die at extrusion temperatures of 200-260°C and chill roll temperatures of 30-90°C. The influences of raw resin characteristics such as y-quinacridone content and MFI of the base PP and casting conditions such as extrusion temperature and chill roll temperature on the amount of 8-crystals formed in the sheet were studied. The amount of the 8-crystals formed was larger as the y-quinacridone content was higher and the extrusion temperature was lower and almost independent of the chill roll temperature. As for the influence of MFI of the base PP, the amount of the 8-crystals formed was maximum at MFI = 8 dg/min.

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Section: Influences Of B-nucleator Content and Casting Conditions Onsupporting

confidence: 79%

Study on rough‐surface biaxially oriented polypropylene film. I. Formation of β‐form crystals in sheet cast with T‐die extruder

Fujiyama

Kawamura

Wakino

et al. 1988

J of Applied Polymer Sci

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“…Effect of T e on the crystal structure and morphology of the iPP supercooled melt C for 1 h. The skincore structure 55,56 is shown in Figure 5, from which two distinct regions were observed: the rownucleated cylindritic region and the spherulite region. In the row-nucleated cylindritic region, the b-iPP cylindrite crystals, about 100 lm in radius, were found near the wall, and the density of the biPP cylindrite nuclei decreased rapidly with increasing T e .…”

Section: Resultsmentioning

confidence: 99%

Crystal morphology and structure of the β‐form of isotactic polypropylene under supercooled extrusion

Zhang

Shen

2011

J of Applied Polymer Sci

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A supercooled melt of isotactic polypropylene (iPP) was extruded through a capillary die. Polarized light microscopy (PLM), wide-angle X-ray diffraction (WAXD), and differential scanning calorimetry (DSC) were used to investigate the effects of the relatively weak wall shear stress (r w ), extrusion temperature (T e ), and crystallization temperature (T c ) on the structure and morphology of b-form isotactic polypropylene (b-iPP). b-cylindrites crystals could be observed by PLM in the extruded specimen even at a lower r w 's (0.020 MPa), and the b-iPP content increased with decreasing T e . Under a given T e of 150 C, the increase in r w positively influenced the b-iPP content. The DSC and WAXD results indicate that the total crystallinity and b-iPP content increased when T c was set from 105 to 125 C; the other experimental parameters were kept on the same level. Although T c was above 125 C, the b-iPP content obviously decreased, and the total crystallinity continued to increase. On the basis of the influences of r w , T e , and T c on the b-iPP crystal morphology and structure, a modified model is proposed to explain the growing of shearinduced b-iPP nucleation.

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“…However, !-phase is occasionally observed during crystallization from melt. It can be obtained mainly by introducing specific nucleating agents in the melt using processing equipment such as extruders [13][14][15] incorporating an appropriate filler in micron and nanometer scale in the melt using internal mixers and extruders [16,17], inducing temperature gradients [18] and by shear forces in controlled flow fields [19][20][21]. A toughness improvement is associated to !-PP, being attributed to the development of a more perfect crystalline structure, with higher continuity of the amorphous phase and more connecting bridges between individual crystallites than a material containing solely "-crystallites [22]; and to the occurrence of a !-" transformation during loading which is accompanied with volume contraction in respect to the related crystallographic densities [23].…”

Section: Introductionmentioning

confidence: 99%

Mechanical performance of double gated injected metallic looking polypropylene parts

Costantino¹,

Pettarín²,

Pontes³

et al. 2015

Express Polym. Lett.

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Abstract. The metallic effect obtained by incorporation of metal particles in polymers by injection molding has the advantage of eliminating post-processing techniques reducing production cost and time. Nevertheless, undesired defects in the final appearance of parts are common. In this work PP/aluminum pigments were obtained by direct injection molding and the influence of metallic particles on the aesthetic, morphological and mechanical properties of the parts was assessed. Aesthetic aspects could be improved by manipulating processing conditions: high melt temperatures diminished differential shrinkage and made weld lines less noticeable. Also at high melt temperatures Al particles increased thermal conductivity of PP generating a thicker skin, which combined with an inherent gradient temperature and typical shear stresses developed during injection molding, induced the formation of !-PP phase. Mechanical performance of parts showed to be dependent on PP morphology. Distinct deformation behaviors were seen according to the presence of PP polymorph, !-PP counteracting the detrimental effect of not bonded Al flakes, and making PP-Al moldings to have similar toughness as PP moldings with the added value of metallic looking.

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Shear‐induced β‐form crystallization in isotactic polypropylene

Cited by 119 publications

References 12 publications

Study on rough‐surface biaxially oriented polypropylene film. I. Formation of β‐form crystals in sheet cast with T‐die extruder

Study on rough‐surface biaxially oriented polypropylene film. I. Formation of β‐form crystals in sheet cast with T‐die extruder

Crystal morphology and structure of the β‐form of isotactic polypropylene under supercooled extrusion

Mechanical performance of double gated injected metallic looking polypropylene parts

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