Morphological evolution of long-chain branched polypropylene under various processing conditions

Result code in IS VaVaI

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Result on the web

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DOI - Digital Object Identifier

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Result language

angličtina

Original language name

Morphological evolution of long-chain branched polypropylene under various processing conditions

Original language description

Polymorphism of polymers is a fascinating phenomenon that predicts the end-use properties of products. Therefore, to achieve the required characteristics, the thorough control of specific nucleation and processing parameters is necessary, e.g. flow induced crystallization is fundamental for injection moulding. One of the most commonly used polymorphic polymer is isotactic polypropylene (iPP) and its modifications, e.g. long-chain branched polypropylene (LCB-PP), owing to its flexibility in term of property function and processability. LCB-PP usually consists of monoclinic α-phase and orthorhombic γ-phase. However, using of processes where shear field is dominant, such as injection moulding, can promote the formation of trigonal β-crystalline structure, that modified mechanical properties of iPP toward better toughness at worse stiffness and heat resistance [1, 2]. In this work, the influence of important processing parameters of injection moulding on the morphology evolution and the β- and/or γ- crystals distribution in “skin–core” structure and Charpy impact strength was studied. Four sets of processing parameters were applied. In the P-set holding pressure varied within a range of 30–70 MPa by 10 MPa, in T-set mould temperature raised from 40 to 120 °C in 20 °C step, while in S-set1 and S-set2, injection speed increased from 20 to 140 mm/s in 30 mm/s step and mould temperature were 40 or 120 °C, respectively. Data derived from the wide-angle X-ray scattering demonstrated distinct ability of injection speed, mould temperature and holding pressure to affect the polymorphic composition of LCB-PP specimens (Figure 1). The joint effect of higher injection speed (140 mm/s) and mould temperature (120 °C) promoted the formation of trigonal β-phase in the skin layer. Under shear flow, an oriented centre can be easily initiated, which provides nucleation sites for β-crystal growth. Prolonged relaxation times of LCBs after deformation contribute to the incorporation of loosely coined linear chains on the surface by orientation of the induced nuclei and crystalize into β-crystals. On the contrary, a significant effect of growing holding pressure on the γ-phase is manifested predominantly in the core of specimens. The higher content of γ-phase is promoted by higher mould temperature and holding pressure. The polymorphic composition of the individual specimens is reflected in their impact strength. Co-existence of β-phase and γ-phase has a favourable impact on the enhancement of impact strength.

Czech name

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Czech description

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Type

O - Miscellaneous

CEP classification

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OECD FORD branch

10404 - Polymer science

Project

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Continuities

V - Vyzkumna aktivita podporovana z jinych verejnych zdroju

Publication year

2023

Confidentiality

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů