Comparison of the Rheological Behavior of Iso- and Syndiotactic Polypropylenes

Year 2022, Volume: 12 Issue: 2, 1108 - 1121, 15.12.2022

Fatma Dinç

https://doi.org/10.31466/kfbd.1099271

Abstract

The rheological behavior of iso- and syndiotactic polypropylenes (iPP and sPP) for two different temperatures of 175 and 190˚C at atmospheric pressure is analyzed employing the Yahsi-Dinc-Tav (YDT) non-Newtonian viscosity model. The predicted viscosity with shear rates of 0.093 to 93.91 s-1 on PPs is compared with the corresponding estimations from the Cross-like model. The obtained results from the YDT model deviate from the reported experimental observations with 1.041 for iPP and 1.86 for sPP. From the zero shear viscosity correlation to temperature- and vacancy fraction- dependent thermo-occupancy function, Yh = Yh(h, T), viscosity parameters were ascertained and associated with polymer tacticity. From the zero shear viscosity relation, an increase in Yh = Yh(h, T) function and hole fraction loss results in increased viscosity. The dependence of the derivative of logarithm of viscosity (viscoholibility) on vacancy fraction, as a function of pressure and temperature, h=h(P,T), procured from Simha-Somcynsky hole theory displays an exponentially decreasing behavior.

Keywords

Simha–Somcynsky, Isotactic and syndiotactic polypropylenes, vacancy fraction, steric hidrance, viscoholibility, tacticity

İzo- ve Sindiyotaktik Polipropilenlerin Reolojik Davranışının Karşılaştırılması

Abstract

Newtonyen olmayan Yahşi-Dinç-Tav (YDT) viskozite modeli kullanılarak, izotaktik ve sindiyotaktik polipropilenlerin (iPP ve sPP) atmosfer basıncında 175 ve 190˚C'lik iki farklı sıcaklık için reolojik davranışı analiz edilmiştir. PP'ler üzerinde 0.093 ila 93.91 s-1 kayma gerinimleri ile tahmin edilen kayma viskozitesi, Cross-benzeri modelden karşılık gelen tahminlerle karşılaştırılır. YDT modelinden elde edilen sonuçlar, iPP için 1.041 ve sPP için 1.86 ile, bildirilen deneysel gözlemlerden sapmaktadır. Sıcaklık ve boşluk kesri ile ilişkili ısıl-doluluk fonksiyonu, Yh = Yh(h, T), ile sıfır kayma viskozite ilişkisinden, viskozite parametreleri belirlendi ve bu parametreler polimer taktisitesi ile ilişkilendirildi. Sıfır kayma viskozite ilişkisinden, Yh fonksiyonundaki bir artış ve boşluk fraksiyonu kaybı viskozitenin artmasıyla sonuçlanır. Viskozite logaritmasının (viskoholabilite) türevinin, Simha-Somcynsky boşluk teorisinden sağlanan sıcaklığın ve basıncın fonksiyonu olan boşluk kesrine, h=h(P,T) bağlılığı, üstel azalan bir davranış sergiler.

Keywords

İzotaktik and sindiyotaktik polipropilenler, boşluk kesri, sterik hidrans, viskoholibilite, Simha–Somcynsky, taktisite

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