Rheo-Raman | Combining Rheology and Raman Spectroscopy: Monitoring the Crystallization and Melting of LDPE and HDPE
By combining rheology and Raman spectroscopy, changes in rheological behavior can be directly correlated to molecular changes as presented for the in-situ monitoring of polyethylene crystallization and melting
Introduction
Material analysis is crucial for polymer manufacturing and processing applications as polymer properties are tailored per requirement.
Raman spectroscopy offers a rapid, non-destructive approach for polymer analysis by providing unique molecular insights and facilitating polymer identification, residual monomer detection, detailed characterization of tacticity, conformation, or crystal properties. When coupled with rheometry, the combination enables simultaneous monitoring of viscoelastic changes during melting and crystallization, correlating physical properties with underlying chemistry.
This combination is not only useful for quality control of polymer processing industries but also in R&D for polymer characterization during synthesis.
Polyethylenes
Polyethylenes are widely used semi-crystalline thermoplastics owing to their ease of processing, toughness, and chemical resistance . Their different forms are commonly distinguished by their densities, such as HDPE (high-density PE) and LDPE (low-density PE).
HDPE consists of mostly unbranched polymer chains leading to a dense packing and a high degree of crystallinity in the solid state. LDPE, on the other hand, exhibits large branches with non-uniform lengths. The crystallinity affects the response to deformation and impacts flow properties during polymer processing. The degree of crystallinity in a polymer is defined by the ratio of polymers in the crystalline phase present in the sample. Since the crystallinity of polyethylenes and their densities have a linear relationship, the density of the polymer is usually used.
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