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Morphological modification as an enabler for impact copolymer PP
Morphological modification is a powerful tool for improving mechanical performance of impact copolymer PP (ICP). Zdenˇ
ek Burᡠn,
from Unipetrol RPA - Polymer Institute Brno, explains more
Passenger cars and light commercial vehicles produce around 14% of total CO2 emissions in the EU. The recently introduced EU Regulation (EU)2019/631 addresses that by setting demanding CO2 emission performance standards for new passenger cars and light commercial vehicles. One way car makers can meet these new targets is to reduce vehicle weight, but replacing steel parts with plastics requires high quality polymer materials with excellent mechanical properties. Impact copolymer PP (ICP) combines
the stiffness of PP and toughness of EPR (ethylene propylene rubber) and is a key polymer material used in many industrial sectors, including automotive. It can be employed alone or as the main component of a compound. The research team from Unipetrol RPA - Polymer Institute Brno has been working to improve the mechanical properties of ICP by modification of its morphology. This research was targeted on understanding how morphology can affect the ICP properties. Dispersion of the EPR particles in the PP
matrix — as well as their particle size — is a crucial parameter affecting toughness and other properties. The optimum particle size can be achieved by adjusting the viscosity ratio of the two basic components — the rubber and PP homopolymer. The size of the EPR particles can also be controlled by the ethylene- propylene copolymer composition. ICP stiffness can also be increased using suitable nucleating agents (NA). Inducing a greater number of nuclei leads to a decrease in spherulite size and an improvement in morphology of the
Figure 1: Influence of some nucleating agents on mechanical properties (compared to a non- nucleated reference)
homopolymer PP matrix. The increased crystallisation rate connected to the increased nuclei number has a strong influence on ICP stiffness. Some NAs affect not only stiffness, but also toughness (Figure 1). The results of this project have been
applied by Unipetrol in the development of a new high melt flow ICP material with high stiffness and toughness. Compared to former ICP materials, this new material shows enhanced toughness and stiffness especially in thin wall injection moulding applications (Figure 2).
Figure 2: Properties of newly formulated ICP material in a thin wall injection moulding application
www.unipetrol.cz/en
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