The Influence of Processing Parameters on the Phase Distribution of Polypropylene
Processing parameters of polymers can have a significant influence on their properties. In an injection molding process, numerous factors, such as mold temperature, injection speed, and holding pressure, change the polymorphic composition of long-chain branched polypropylene. X-ray diffraction is crucial to understanding the structure-property relationship as the phase content of polypropylene polymorphs influences the impact strength.
Introduction
The properties of materials depend on many different factors. A major factor in polymers is polymorphism, the realization of different crystal structures from the same material. It was previously shown that processing parameters can influence crystallization as well as the formation of polymorphs in polymers. (1) Therefore, for optimizing the physical properties of a material, it is crucial to understand the conditions that can be tuned during the processing. For injection molding examples of parameters influencing polymorphism include flow rate and temperature.
In this study, the influence of important processing conditions on the polymorphism of long-chain branched polypropylene (LCB-PP) is investigated. (2) While there are many different phases of LCB-PP, the β-phase is favored due to preferred mechanical properties such as enhanced toughness. However, under standard processing conditions, the formation of the β-phase is suppressed. Previously, it could be shown that injection molding results in desirable crystalline structures. (3) The objective of this study is to investigate how important processing parameters (injection speed, holding pressure, or mold temperature) influence the morphological evolution and the distribution of the β‑phase of LCB-PP. Understanding this structure-property-relationship is an important prerequisite for successful industrial utilization of the process.
X-ray diffraction (XRD) is an ideal characterization technique for studying the structure of polymers. (4) In this study, commercially available LCB-PP was used to prepare samples which were investigated with XRD using the Automated Multipurpose Powder X-Ray Diffractometer XRDynamic 500 from Anton Paar.
References:
- Somani, Rajesh H., et al. "Structure development during shear flow induced crystallization of i-PP: in situ wide-angle X-ray diffraction study." Macromolecules 34.17 (2001): 5902-5909.
- Gajzlerova, Lenka, et al. "The polymorphic composition of long-chain branched polypropylene processed by injection and compression molding." Express Polymer Letters (2023).
- Zhou, Shuai, et al. "Relationship between molecular structure, crystallization behavior, and mechanical properties of long chain branching polypropylene." Journal of Materials Science 51.12 (2016): 5598-5608.
Murthy, N. Sanjeeva. "X‐ray Diffraction from Polymers." Polymer Morphology: Principles, Characterization, and Processing (2016): 14-36.
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