Comparison of structure development in injection molding of isotactic and syndiotactic polypropylenes

Choi, Dongman; White, James L.

doi:10.1002/pen.11059

Cited by 31 publications

(28 citation statements)

References 26 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…A microestrutura desenvolvida em peças injetadas de termoplásticos semicristalinos durante a moldagem por injeção é relatada amplamente na literatura [4][5][6][7][8]13,14,17,[19][20][21][22] . Essa estrutura, no caso de polímeros de cristalização rápida, é caracterizada por um conjunto de arranjos macromoleculares e por um gradiente de morfologia que, em uma descrição simples, é composto de duas camadas externas altamente orientadas, chamadas peles, por uma zona de transição apresentando esferulitos deformados e por um núcleo esferulítico central.…”

Section: Introductionunclassified

Avaliação da orientação molecular de moldados de polipropileno utilizando figuras de pólo obtidas por difração de raios X

2007

View full text Add to dashboard Cite

Resumo: Neste trabalho, avaliou-se a influência do perfil de velocidades de injeção utilizado durante a etapa de preenchimento na orientação molecular da fase cristalina, de amostras de polipropileno moldadas por injeção. As medidas de orientação molecular foram realizadas nas posições central e lateral da superfície de corpos-de-prova de tração injetados, utilizando figuras de pólo obtidas por difração de raios x de altos ângulos. Os resultados demonstraram que as variações na orientação molecular dos cristalitos de polipropileno estão relacionadas aos diferentes perfis de velocidades de injeção utilizados durante o processamento, sendo que um aumento na velocidade leva a um aumento do grau de orientação. Observou-se que a estrutura cristalina das moléculas do polipropileno apresenta orientação bimodal e que o grau de orientação médio é maior na posição lateral do que na posição central.Palavras-chave: Orientação molecular, figuras de pólo, difração de raios x, polipropileno, moldagem por injeção. Evaluation of the Molecular Orientation of Injection Molded Polypropylene Using X-Ray Pole FiguresAbstract: In this work, the influence of the injection velocity profile on the crystalline phase molecular orientation of injection molded polypropylene samples has been evaluated. The molecular orientation has been evaluated both in the central and lateral positions on the surface of the injected tension specimens, using x-ray pole figures. The results demonstrated that the variations in molecular orientation of polypropylene crystallites were correlated to the different velocity profiles employed during the processing, showing that an increase in the velocity increases the orientation degree. It has been observed that the crystalline structure of the polypropylene molecules shows bimodal orientation and that the orientation degree at the lateral position is higher than that at the central position. Keywords: Molecular orientation, pole figures, x-ray diffraction, polypropylene, injection molding. IntroduçãoO processo de moldagem por injeção é uma das mais proeminentes técnicas de processamento de polímeros, devido à sua versatilidade e alta produtividade, permitindo que grandes volumes de peças, com formas complexas e excelente tolerância dimensional sejam produzidos com baixos custos [1][2][3] . Durante o processo de moldagem por injeção, o polí-mero sofre diversas transformações devido a variações no ambiente termomecânico ao qual ele encontra-se restrito. Esse ambiente, marcado por taxas de aquecimento e resfriamento e campos de tensões diversos, faz com que a peça moldada apresente uma microestrutura heterogênea intrínseca, caracterizada por uma variação gradual de sua morfologia, cristalinidade, orientação molecular e, conseqüentemente, de suas propriedades finais. As variações no ambiente termomecânico estão associadas às condições de processamento, à geometria do molde e às propriedades do polímero [4,5] . Os parâmetros de processamento que exercem maior influência sobre a microestrutura das peças injetadas são: ...

show abstract

Section: Introductionunclassified

Avaliação da orientação molecular de moldados de polipropileno utilizando figuras de pólo obtidas por difração de raios X

2007

View full text Add to dashboard Cite

show abstract

“…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

View full text Add to dashboard Cite

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.

show abstract

“…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

View full text Add to dashboard Cite

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.,

show abstract

Comparison of structure development in injection molding of isotactic and syndiotactic polypropylenes

Cited by 31 publications

References 26 publications

Avaliação da orientação molecular de moldados de polipropileno utilizando figuras de pólo obtidas por difração de raios X

Avaliação da orientação molecular de moldados de polipropileno utilizando figuras de pólo obtidas por difração de raios X

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

Optical monitoring of polypropylene crystallization during injection molding

Contact Info

Product

Resources

About