Holistic evaluation and testing of coil coatings
Time: Mon 2023-06-12 10.00
Location: D37, Lindstedtsvägen 5, Stockholm
Subject area: Chemistry
Doctoral student: Alexander Wärnheim , Yt- och korrosionsvetenskap, RISE Research Institutes of Sweden, Division of Materials and Production, Department of Corrosion,
Opponent: Professor Carita Kvarnström, University of Turku, Department of Chemistry, Turku University Centre for Materials and Surface
Supervisor: Professor C. Magnus Johnson, Yt- och korrosionsvetenskap; Professor Per M. Claesson, Yt- och korrosionsvetenskap; Doktor Dan Persson, RISE Research Institutes of Sweden, Division of Materials and Production, Department of Corrosion,
Coil coatings are durable organic coatings used to protect metal sheets from corrosion and improve their aesthetic properties. Because of their extensive use, coil coatings have long been of interest for industrial and academic researchers. This interest has recently been furthered by a societal push towards the replacement of fossil-based raw materials with alternatives that are biobased and renewable.
The aim of this licentiate thesis is to demonstrate how analyses on the macro-, micro-, and nanoscale can be used to better understand the degradation process of polyester-based coil coatings. The included manuscripts showcase methods for evaluating and comparing different coil coating formulations and for verifying accelerated weathering techniques.
Multiple techniques, focusing on infrared (IR) spectroscopy and atomic force microscopy (AFM), were used to analyze coating systems before and after different types of weathering. IR data acquired from techniques without spatial resolution, such as attenuated total reflection (ATR) and photoacoustic spectroscopy (PAS) have been expanded upon with spatially resolved focal plane array (FPA) and s-SNOM (scattering-type scanning near-field optical microscopy) measurements. Spatially resolved chemical data of coating cross sections were acquired and used to assess how the degradation at the surface and in the bulk was related. Additionally, differences between the degradation behavior of a standard fossil-based coating and a similar coating with biobased components as well as differences between the degradation caused by artificial and natural weathering was discussed.
Nanoscale mechanical measurements of simplified coating surfaces showed that weathering increased nanomechanical stiffness and led to homogenization of mechanical properties on the local level. In addition, measurements with nanoscale FTIR correlated with macroscale FTIR. Even relatively minor changes in band intensities could be tracked on a local scale. Although the simplified samples were chemically homogeneous, nanoscale FTIR shows great promise for the assessment of local degradation of full systems.