Welcome to Formulating Functional Films and Coatings III
19th August 2020 - Online
Morning Session
Afternoon Session
This should be sent to the conference secretariat
Chi Him Lo - Waterborne coatings for corrosion protection
Presentation - pdf
Chi Him Lo2, Bob Luigjes2, Simon R. Gibbon3, Stuart B. Lyon1, Lee A. Fielding1
1School of Materials, The University of Manchester, Manchester, M13 9PL, UK.
2AkzoNobel, Rijksstraatweg 31, 2171 AJ Sassenheim, The Netherlands.
3AkzoNobel, Stoneygate Lane, Felling, Gateshead, Tyne & Wear, NE10 0JY , UK
Surfactant additives are essential in waterborne direct-to-metal (DTM) formulations for attainment of coherent and defect-free films. However, residual surfactants are suspected of influencing film microstructure and can have adverse effects on the final coating properties (e.g. appearance, adhesion, viscoelasticity and/or barrier properties) [1,2]. In this work, atomic force microscopy infrared (AFM-IR) and scanning electron microscopy (SEM) are used to elucidate the additive-induced microstructural changes of polymer films and study the coating deterioration mechanisms after exposure to corrosive environments.
The results demonstrated AFM-IR can identify and map the sulfonate groups of anionic surfactants across the styrene-acrylic copolymer film. It has been found that varying the type or/and amount of sulfur-containing surfactant in the coating can cause significant differences in corrosion protection performance.
These findings can provide deeper insight into the relationships between binder-additive structures, film morphologies and the corrosion protection performance of formulated waterborne acrylic coatings.
Q&A
From Jordan Petkov : Do latex particles undergo coalescence the way emulsion droplets do? After all they have been polymerised prior ending up on the substrate? Isn't their deformability more important?
Answer: I would say that definitely, but also one thing we wanted to study in this project was how to adding a surfactant will affect the coating.
From Jordan Petkov : What is the hypothesis why the higher Tg results in larger three phase contact angle?
Answer: In this case is due to the increase in styrene content, we just change the monomer composition.
From Emma Michailidou : What is the effect of Tg on adhesion and corrosion protection you observe system specific or would you expect similar results with other types of polymers as well?
Answer: In this case I would say is more system specific, because we have to add extra coalescence to get the film formation so there are some effects coming from the coalescence agent and not just the binder.
From Dr Tolutope Siyanbola : What is the nature of your hardener in the water based coating system? How did you carryout its optimization in the system.
Answer: In terms of hardener do you meant the thickener or the binder?
From Koray Yıldırı: crosslinker maybe?
From Peter Collins : By hardener I think that the @chi means a 2 pack crosslinker, but I think that these are almost certainly 1 pack air drying coatings that don't have a hardener added.
Answer: Thanks Colin for the explaination…. Yes I didn't use hardener (or cross-linker) and the binder doesn't have cross-linking group
From Joe Keddie : Interesting work. After adding the coalescing aid, what is your VOC content?
Answer: we didn’t calculate because the VOC content in decorative paint it doesn’t count adding a high boiling point coalescence agent, but I would say is around 10% weight.
From Ayse Ersoy : Hi, What is the thickness of the coating? Transparent? Could it be applied to glass?
Answer: we did applied it to glass, but for this we applied it to polypropylene and to aluminium.
From Lee Farren : What film thicknesses have you done your corrosion testing at?
From Ayse Ersoy : what is the thickness please?
Answer: The dry film thickness of the coating is 50 microns.
From Jordan Petkov : Have you evaluated the wetability of the steel by the aqueous solutions of the surfactants?
From Jordan Petkov : Some surfactants subject of size, charge etc. can bring about depletion interaction that can destabilise the dispersion. Have you looked at this?
Answer : I didn't look at the wettability of the surfactant on steel, one of the problem we had with studying the surfactant solution on steel is that flash rusting can occur.
From Jordan Petkov : The wetability should be measured in the framework of seconds, this is relevant to what type of film you form in the first place. The hydrophobic surfactants clearly doesn't help wetability and it was manifested by bad corrosion.
Answer : Jordan, thanks for the interesting comment and I will have a look at the wettability later.....the hydrophobic surfactant is often used as wetting agent for waterborne coating but not specific for steel substrate.
Apoorva Ambarkar - Microstructure of packaging coatings
Presentation - pdf
Apoorva Ambarkar*‡§, Steve Edmondson‡, Keimpe van den Berg§
‡: School of Materials, The University of Manchester, Manchester, M13 9PL, England, UK
§ :AkzoNobel Coatings B.V, Sassenheim, 2171 AJ, The Netherlands
Organic coating systems play an important role in the protection of metallic surfaces from corrosion. It is often observed that coatings without an apparent defect, fail unexpectedly during use, allowing corrosion to occur in specific regions and not uniformly across the surface. Thus, fundamental understanding of organic coating microstructure may hold the key to understanding failure mechanisms in intact coatings. Despite prior efforts to characterize relevant coating microstructures, direct correlations to performance remain limited. To obtain further insight requires advanced characterization tools that allow simultaneous mapping of multiple properties across the surface, such as crosslinking, stiffness/hardness, water uptake etc. AFM-IR, a hybrid technique between AFM (Atomic Force Microscopy) and infrared spectroscopy, allows advanced characterization of organic coatings by mapping their infrared absorptions across the underlying microstructure.
In this study, two variants of BPANI (bisphenol A non-intended) food-can coating that are polyester based were chosen; Type A (chemical resistant type coating) and Type B (flexible type coating). Polyester based coating such type A & Type B are complex systems consisting of polyester as binder and several crosslinkers such as phenolics, Benzoguanamines, isocyanate etc., By studying their microstructure, it was discovered that Type B coating appears to be phase separated while Type A coating appears homogenous. Efforts were made to understand this distinction in the two variants, as it may be contributing in poor chemical resistance of Type B coating. AFM IR was used to map the chemical absorbance in the different phases of Type B coatings. The near industrial systems give a truer picture of microstructure but also introduce several complexities due to the complex chemistry involved between the binders & crosslinkers. Data processing was used to resolve height complexities and improve data interpretation. Simplified formulation made by varying the molar ratio of functional group between binder and crosslinkers further revealed crucial information on phase separation. AFM IR allowed identifying the phases in model systems and onset of phase separation. AFM IR technique has been useful in understanding chemical heterogeneity in complex systems.
References
[1] Knudsen and A, Forsgren, Corrosion Control Through Organic Coatings, 2006.
[2] S.B. Lyon, R. Bingham, D.J. Mills, Progress in Organic Coatings, 2017, 102, 2–7.
[3] T. Nguyen, J.B Hubbard, J.M Pommersheim, Journal of Coating Technology, 1996, 68(855), 45.
[4] Mills D.J, Mayne J.E.O., Corrosion Control by Organic Coatings, 1981, pp 12-17.
[5] S. Morsch, S. Lyon, S.D. Smith, S.R. Gibbon, Progress in Organic Coatings, 2015, 78, 293–299.
[6] A. Dazzi, F. Glotin, R. Carminati, J. Appl. Phys. 2010, 107
Q&A
From Dr Tolutope Siyanbola : What is the ratio of your polyol to that of your crosslinker (IPDI)?
Answer: in the full formulation the isocyanate is 4.5 time that of the polyester in terms of functional groups, by weight composition the polymer is 70% and the isocyanate is 16%.
From Dr Tolutope Siyanbola : Did you carryout any formulation with aromatic crosslinker?
Answer: No, we haven’t.
From Koray Yıldırım : Thank you very much Apoorva, great presentation, very enlighting. Do you think in some afm images at the beginning of your presentation, distrupted morphologies are caused by air release? Did you use any levelling agent?
Answer: there are no additives in the formulation. It may be what the question suggest, we are not using levelling agent but it doesn’t come out in the stiffness value. Maybe solvent evaporation.
Dye Containing Coatings for Corrosion Sensing Applications
Presentation - pdf
Craig Melton1, Dr. Simon Gill1 & Dr. Shiladitya Paul2
1 University of Leicester; 2 TWI
Coating systems are used to protect metallic structures against corrosion in aggressive environments. However, over their design life insufficient maintenance of these systems can result in concealing significant metal loss beneath the coating. The incorporation of pH sensitive dyes in to coating systems aims to highlight these areas of underlying corrosion for inspection engineers to observe.
This research presents the compatibility and functionality of two pH sensitive dyes (phenolphthalein and thymol blue) in combination with three coating formulations; liquid epoxy, powder epoxy, and powder polyester. These dyes and coatings were administered to three different substrates; glass slides, S355 steel and thermally sprayed zinc/aluminium (TSZA) (85%/15%) on S355 steel. The glass slides were then exposed to 0.1M NaOH solution to investigate dye chromophore activation. The steel and TSZA samples were exposed to synthetic seawater for 35 days to investigate dye chromophore activation as a result of iron or zinc/aluminium oxidation.
The results demonstrate that the liquid epoxy coating was not compatible with the dyes, however successful corrosion sensing behaviour, via dye chromophore activation, was demonstrated for the epoxy and polyester powder systems on all three substrates, with the thymol blue containing systems being the easiest to observe.
Q&A
From Stuart Lyon : I believe phenolphthalein goes colourless again at pH > 12.5
From Philip Gill : pH > 10 it turns colourless again
From Peter Collins : From my A level practical days (48yrs ago) I seem to recall that PP indicator can be tricky because atmospheric CO2 absorption leads to acidity which turns it back colourless, so you can easily overshoot the end point. I guess that the pink colouration might fade with time for the same reason.
Answer: These are fair comments. Phenolphthalein was our first choice because we thought we thought that pink is bright and would contrast. It is not really an engineering colour so it would be easy to detect. Phenolphthalein has more problems, like the ones I showed. It can function, but not as well as it would be needed for inspection engineers to use. In terms of real engineering is not the most feasible candidate. We looked at it because we thought that there were some practicalities.
From Bob Luigjes : What is the UV stability of these organic dye’s? Will the dye stay in its current form when exposed in outdoor weathering conditions?
Answer: I’m not sure. I have no thought about that, but that would be a useful bit of information to test about. We have some of these coating systems installed offshore in the coastline in Spain and taking regular photographs and we can look at this.
Raul Davalos Monteiro - Natural exposure and cyclic corrosion testing for the assessment of the performance of powder-coated steel
Presentation - pdf
Raul Davalos-Monteiro a,b, Gianfranco D’Ambrosio b, Xiaorong Zhou a, Simon Gibbon c and Michele Curionia
a Corrosion & Protection Centre, School of Materials, The University of Manchester, Manchester, UK
b AkzoNobel, Powder Coatings, Como, Italy
c AkzoNobel R&D, Felling, UK
This work studied the kinetics of corrosion propagation in natural exposure tests of powder coated steel samples and the relationship between natural exposure test results and accelerated cyclic corrosion testing performed according to the ISO-20340 standard. The results from a large number of test panels painted with 26 different powder coating systems suggest that, generally, corrosion propagation in natural exposure is defined by an initial growth in the corrosion area followed by a stage where the corroded area increases very slowly.
Consequently, the relative performance ranking of the coating systems fluctuates considerably as a function of the testing time. Correlations between natural exposure results and accelerated cyclic test results were not found, and for most types of coating classes, a good performance in one test is related with a poor performance in the other.
Q&A
From Philip Gill (Cranfield Uni) : @Raul. Are your observations of differences between natural vs accelerated testing due to the accelerated test conditions driving unrealistic chemical mechanisms, or does the ISO standard use inaccurate kinetic values for its predictions? (Normally both in my experience).
Answer: This is a good question. I think the ISO cyclic test that was selected for this project has components that are way more aggressive than the exposure site that we had for the natural exposure test. Of course it has an influence, of course has thermal stresses impacted from 60C and -20C in the same week, this is one of the limitations of accelerated corrosion test, that you cannot simulate them service performance or the environment, there is always a different response when you compare these two things. In literature some people have found good grade of correlation, so it was worth trying this. If you don’t scribe them they last a long time. I’m trying to combine these results with the microstructure and electrochemistry.
From Simon Gibbon : What stops corrosion just covering the whole metal sample over time?
Answer: The coating, I may have misunderstood. The coatings were never intact in the test and that is where corrosion starts.
From Simon Gibbon : I can see that the defect is where the corrosion starts and so limited corrosion to start with. This suggests that when you see a tractor outside and all the coatings is gone and corrosion is everywhere, it is a combination of corrosion and other local damage mechanisms to the coating meaning that corrosion starts in lots of different place which all join up. Rather than one defect and all the corrosion is caused by that single defect.
Answer : Yes I think the degradation of those type of protective powder coatings is also a combination of corrosion and local damages. I have tested the systems with intact conditions, and if present degradation was only at the edges (where the geometry of the edge influences the formation of weaker coating layers).
Stephanie Burg, University of Sheffield - Liquid-liquid phase separation morphologies in ultra-white beetle scales and a synthetic equivalent
Presentation - pdf
Stephanie L. Burg, Adam Washington, David M. Coles, Antonino Bianco, Daragh McLoughlin, Oleksandr O. Mykhaylyk, Julie Villanova, Andrew J. C. Dennison, Christopher J. Hill, Pete Vukusic, Scott Doak, Simon J. Martin, Mark Hutchings, Steven R. Parnell, Cvetelin Vasilev, Nigel Clarke, Anthony J. Ryan, Will Furnass, Mike Croucher, Robert Dalgliesh, Sylvain Prevost, Rajeev Dattani, Andrew Parker, Richard A. L. Jones, J. Patrick A. Fairclough, Andrew J. Parnell
Cyphochilus beetle scales are amongst the brightest structural whites in nature, being highly opacifying whilst extremely thin. However, the formation mechanism for the voided intra-scale structure is unknown. Here we report 3D x-ray nanotomography data for the voided chitin networks of intact white scales of Cyphochilus and Lepidiota stigma. Chitin-filling fractions are found to be 31 ± 2% for Cyphochilus and 34 ± 1% for Lepidiota stigma, indicating previous measurements overestimated their density. Optical simulations using finite-difference time domain for the chitin morphologies and simulated Cahn-Hilliard spinodal structures show excellent agreement. Reflectance curves spanning filling fraction of 5-95% for simulated spinodal structures, pinpoint optimal whiteness for 25% chitin filling. We make a simulacrum from a polymer undergoing a strong solvent quench, resulting in highly reflective (~94%) white films. In-situ X-ray scattering confirms the nanostructure is formed through spinodal decomposition phase separation. We conclude that the ultra-white beetle scale nanostructure is made via liquid–liquid phase separation.
Q&A
From Georgina Zimbitas : I was wondering wether you could suspend your films/scales in resin and allow to harden, FIB cut the resin and then examine (e.g. via SEM)? The resin might compress the material, but you could determine the degree of that and extrapolate.
Answer: So, anytime as soon as you cut the scale, that is it… that will giving fractions that were double what we measured with tomography. As far as I know, you have to measure them intact.
From Georgina Zimbitas : I meant keep the scales intact - resin on the outside and then cut.
Answer: I don’t think it would support the inner structure, that would give support to the outer structure. The fibres are not very connected, and just touching the top and bottom and you support the outside and cut it you will still get some distortion.
From Simon Gibbon : Where you saw the round fibres like structures (Cyphochilus), versus the non-fibrillar (L stigma) does this suggest a different mechanisms of formation (different evolutionary biology)? Or do you know the physical parameters which control the difference in the same spinodal decomposition?
Answer: This is a good question and if you run a spinodal simulation under flow, meaning that there is a direction of liquid flow in one direction you can actually elongate and create a stretch spinodal structure and if you remember from the way the beetles was, that could create this structure but that is another piece of work.
Stuart Lyon, The University of Manchester - Sustainable coatings by rational design (SusCoRD)
Presentation - pdf
Stuart Lyona, Tony Ryanb, Simon R Gibbonc
aCorrosion & Protection Centre, School of Materials, The University of Manchester, Manchester, UK
bDepartment of Chemistry, The University of Sheffield, Sheffield, UK
cAkzoNobel R&D, Felling, UK
The performance of protective organic coatings is controlled by their physicochemical properties. While many relationships between physicochemical properties and performance have been elucidated over the past decades. The prediction of performance and lifetime of protective coatings is still largely based on testing and formulation knowledge.
SusCoRD, sustainable coatings by rational design, is increasing predictability by combining machine learning, new research to learn new mechanisms of transport, state of the art characterisation equipment and multi-scale modelling approach. SusCoRD will develop new formulation rules to increase predictability of both the lifetime of coating performance and the coating development process.
Q&A
From Jordan Petkov : I understand that the underpinning mechanism for paint longevity is in the adhesion and the quality (penetration wise and mechanical) of the paint/film, but what about the development of biofilm that can result in aggressive environment from the outside? Is this something you look at?
Answer: No we are not looking at biofilms. That is important in some circumstances but not particularly important to what we are looking at. The main problem with corrosion protection is that damage occurs underneath the paint and you cannot see it. It is difficult to use clear laquers. We are not interested in what happens on top of the paint. We haven’t talked about UV and chemical stability, but those things are part of the program, but the main driver is corrosion protection. In the context of external environment, a methanol tanker, the methanol ingress will affect the coating that it makes it more likely to corrode in the future, we need to understand that. Microbial attack on the top of the coating may affect the surface, how the paint forms in the future and we need to capture that.
From Dr Tolutope Siyanbola : As much as I appreciate your view on focusing on protection of substrate I wouldn't like us to totally strike out aesthetics provided by coatings.
Answer: Appearance is critical, and corrosion damages appearance. You can say that old paints happily allow corrosion to occur and the customer was happy because they couldn’t see the corrosion, but that is not what we are interested.
From Dr Tolutope Siyanbola : How would you describe coating formulation failure caused by inadequate substrate preparation?
Answer: surface preparation is part of the story. We are trying to understand is what influlences surface preparation may have including surface treatment. Some surface treatment are blasting the surface. We are not interested in mechanical addition. The idea of making a surface more adherent doesn’t really hold true if you measure the pulloff strength of a paint on a polished surfaced and a properly abraded substrate, the pulloff strength is larger in the polished substrate. We are not interested at the moment in mechanical roughness but we are interested in chemical changes in the surface and the chemistry of the surface.
From Philip Gill : You report that the Tg of a polymer film varies with thickness. Have you observed a similar relationship with hardness? I ask because I’ve observed that the hardness of polymers in a solid filled composite changes around the fillers. We always assumed it was the filler influencing the polymer.
Answer: if you can give me a method to mesure hardness on a polymer film that is 50 nm thick on a hard surface , I can look into that, but the answer is no, we can’t do that. You can infer that a higher Tg would give a higher nominal hardness but how you measure that.
From Philip Gill : nano indentation? AFM?
Answer: for nano indentation you have a indentation depth of a few nm that is 10% of the coating thickness, it may be possible using an AFT trying to vibrate or oscillate the surface with and without the coatings, but I think none of these techniques have robust theory behind them.
From Stephenie Burg : The change in Tg vs thickness is my work, I have not looked at hardness yet. Those are possibilities for sure, if and when I manage to get back into the lab with any regularity I will think about it, thanks :)
From Koray Yıldırım : Do you plan to consider non metal coatings in suscord?
Answer: SusCoRD relates to corrosion protection, so the answer is no, but we believe that the techniques we will develop will be applicable for other surfaces. It has to be said that some of the techniques that we used that were previously developed at Sheffield were for emulsion paints, that have similar problems for reformulation. We take the experience that Sheffield had a long time ago in emulsion type paints and apply it to corrosion protection paints.