Molecular weight and tacticity effect on morphological and mechanical properties of Ziegler–Natta catalyzed isotactic polypropylenes

Albert Van Reenen,Touhami Mokrani,Ismael Amer

doi:10.1590/0104-1428.2158

Albert Van Reenen, Touhami Mokrani + Show 1 more

Open Access

https://doi.org/10.1590/0104-1428.2158

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Journal: Polímeros	Publication Date: Dec 4, 2015
Citations: 37	License type: cc-by

Affiliation: Stellenbosch University, University of South Africa

Abstract

The morphological and mechanical properties of Ziegler–Natta catalyzed isotactic polypropylenes as influenced by the molecular weight and tacticity was investigated. Polypropylene samples were injection moulded into standard disks with a HAAKE MiniJet II injection moulder at 190 °C and 200 bar for morphological and mechanical tests. The morphological and mechanical properties of specimens were investigated by means of optical microscope (OM), scanning electron microscopy (SEM), microhardness (MH) and dynamic mechanical analysis (DMA). The samples exhibited a typical α-modification spherulite structure of isotactic polypropylenes crystallized from the melt. It was found that the most important factor affecting the structure and properties of these polymers is the isotacticity content. A clear molecular weight effect was also found for samples with low molecular weights. The microhardness and storage modulus values increased as crystallinity did. Accordingly, isotacticity degree is considered as the main parameter affecting the crystallinity of samples.

Highlights

Polypropylene is one of the most common polymers but the overall crystallization rate might increase because in use today
The aim of the current study is to explore narrowly weight[5-8], molecular weight distribution[9] and tacticity[10-13] the structure–property relationships of polypropylene
optical microscope (OM) and scanning electron microscopy (SEM) results showed that all isotactic polypropylene samples had well-defined α-spherulitic morphology

Summary

Introduction

Polypropylene is one of the most common polymers but the overall crystallization rate might increase because in use today. Its good mechanical properties and relatively an increasing number of intramolecular folded-chain nuclei low price result in the continuous growth of its production could result in a higher nucleation density[7]. Of crystallinity of isotactic polypropylene is commonly in The mechanical properties of the majority of polypropylene the range of 40 to 70%[1]. Isotactic polypropylene can The degree of crystallinity is considered to be the most crystallize in three different crystal forms as was described influential property affecting the physical and mechanical by Bruckner et al.[15], depending on the polymer structure and properties of a polypropylene sample[2-4]. An increase in the crystallization conditions: the α-form with a monoclinic, crystallinity is often related to an increase in properties such the γ-form with an orthorhombic and the β-form with a as the stiffness or storage modulus of a sample, while other hexagonal unit cell[15]

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