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Local heterogeneities can have significant effects on the performance of anti-corrosion coatings. Even small features can act as initiation points for damage and result in corrosion of the substrate material. Analysis methods with high spatial resolution and the ability to collect information relevant to crosslinking and degradation behavior of these coatings are therefore highly relevant. In this work, we demonstrate the utility of nanomechanical AFM measurements and nano-FTIR in investigating the nanoscale mechanical and chemical properties of two polyester coil coating clearcoats before and after weathering. On the nanoscale, weathering led to a stiffer and less deformable coating with less variation in the nanomechanical properties. Chemical degradation was quantified using changes in band ratios in the IR-spectra. Macro and nano-scale measurements showed similar trends with the latter measurements showing larger heterogeneity. Our results demonstrate the usefulness of the described analysis techniques and will pave the way for future studies of local properties in other coating systems and formulations. © 2024 The Authors, This work was supported by the Swedish Foundation for Strategic Research (SSF) grant FID18-0034.

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. Alt, Bandlackering är en process för att applicera stabila organiska beläggningar på metallytor för att skydda från korrosion och förbättra deras utseende. På grund av beläggningarnas omfattande användning så har utvärdering och analys av dem varit av intresse för både akademi och industri i flera årtionden. Detta långvariga intresse har ytterligare främjats av en ökade miljömedvetenhet och ett tryck att ersätta miljöfarliga och fossila råmaterial mot biobaserade och förnyelsebara alternativ. Målet med denna licentiatavhandling är att visa hur analysmetoder på makro-, mikro-, och nanonivå kan användas för att bättre förstå nedbrytning av bandlackerade beläggningar. Denna förståelse kan användas både för att utvärdera prestandan hos både nya redan befintliga system, men också för att kunna verifiera accelererade testmetoder vars mål är att minska tiden som krävs för utvärdering. Flera tekniker, med fokus på infraröd (IR) spektroskopi och atomkrafts-mikroskopi (AFM) använts för att analysera beläggningar före och efter att de blivit utsatta för olika typer av aggressiva miljöer. Spektroskopiska data utan spatial upplösning som attenuerad totalreflektions FTIR (ATR) och fotoakustisk spektroskopi (PAS) har kompletterats med spatialt upplösta fokalplans array (FPA) och s-SNOM mätningar. Kemisk information med spatial upplösning har använts för att utvärdera hur nedbrytningen nära ytan relaterade till nedbrytningen längre ner i beläggningen. Likheter och skillnader i nedbrytningen som skedde i en standardbeläggning och ett system med biobaserade additiv jämfördes efter både väderbestendighets-testning som skedde utomhus och i labb. Skillnader mellan dessa exponeringsmetoder diskuterades också. Nanomekanisk analys med hjälp av atomkraftsmikroskopi användes för att bestämma lokala förändringar av mekaniska egenskaper i förenklade klarlacker. Mätningarna visade att exponeringar i aggressiva miljöer leder till en lokal homogenisering av mekaniska egenskaper och ökad styvhet. Utöv, QC 2023-05-15

In light of the need to redesign industrially produced materials by utilizing renewable resources, nanoscopic forms of cellulose are regarded as a valuable asset. In this work, the potential of cellulose nanofibrils (CNFs) as an unconventional nanoadditive for a polyester-melamine coil coating formulation is explored. CNFs, hydrophilic nanomaterials with high aspect ratios, were successfully incorporated in the solvent-borne formulation. Coatings were prepared with extremely low loadings of the nanoadditive (0.5 and 0.7 wt%). At these concentrations, the volume fraction of the nanofibrils in the coatings was calculated to be close to their percolation threshold. Two different pathways of CNF surface modification were applied to allow for a good compatibilization in the resin matrix, and the formulations were cured in two different settings. The effective compatibilization of the nano -additive led to a significant variation of the viscoelastic properties in the coatings containing CNFs. The results from dynamic mechanical analysis (DMA) highlighted the effect of CNFs on the crosslinked network at the nanoscale, resulting in an increase in Tg. Additionally, an increase in the stress at break and Young's modulus was determined by tensile testing, while satisfactory elongation at break was preserved. Other relevant effects induced by the presence of CNFs on the properties of the coatings were highlighted, such as a significant matt effect, increased surface roughness and lower scratch resistance. A preliminary evaluation of the water barrier properties by electrochemical impedance spectroscopy (EIS) is also presented, suggesting that the incorporation of a hydrophilic nanoadditive did not lead to a deterioration of the coatings' performance., QC 20230607

Improved methods to assess the degradation of coil coatings to approximate lifetime have been an area of academic and industrial interest for decades. This work aims to elucidate the differences in the degradation behavior of two coil coating systems: one standard commercial formulation and one formulation with a significant addition of biorenewable reactive diluents. Depth-resolved degradation behavior of samples exposed to accelerated and natural field weathering is assessed. Focal plane array attenuated total reflection-Fourier transform infrared spectroscopy was used to acquire high-resolution chemical data from a sloping cross section. The results agreed with conventional photoacoustic spectroscopy. Degradation profiles for the two coatings were significantly different, with the biobased samples showing a more durable behavior. This study provides a method for detailed assessment of coating degradation, giving a good estimation of its durability. This is both a way to compare the performance of coating systems and to improve the understanding of the impact of exposure conditions, paving the way for the development of more sustainable coil coatings., QC 20230421

QC 20190918