One thing has puzzled me lately: How could I make my life easier when re-painting my house? Could I get away with only one coat of paint? Are there paints on the market that give sufficient coverage and protects my home in one layer? If so, are these coatings sprayable?As a DIY (do-it-yourself) customer, I think along these lines, and I assume that the producers of specialized coatings (spray for instance) are even more interested in these kinds of usability improvements. When re-painting the Golden Gate bridge in California, for instance, imagine the cost effectiveness of spray-coating it and avoiding the work and paint of one extra layer. Several additives have improved the performance of paints and coatings, but are there any new tools to achieve this? Well yes, in microfibrillated cellulose (MFC), I see this potential. Before you jump to the conclusion, “I have heard this before,” let me try to explain.
Thicker layers? How can I achieve that?
One way to reduce layers of coating and thus the costs is, of course, to increase your coating's thickness. It is not always true that thicker coatings protect better (and thicker coatings also comes at a cost), but in many cases it is. I have personally witnessed the potential achieved with MFC, and this is how it works:
- Coating with MFC is highly shear thinning. However, after application of the coating, the viscosity recovery is fast to prevent sagging. In spray coatings (and all other viscous liquids you want to spray) the anti-sag performance gives producers an opportunity to increase the coating thickness.
- Moreover, with MFC, the spraying ability of the coating is so good that the paint viscosity can be high. This way, you can increase the film thickness by increasing the particle load of the coating.
- The MFC network formation distributes forces in the coating's surface and enables it to dry at a controlled rate, (the water retention characteristics/water holding capacity) preventing cracking.
Why thicker one-layer coating can be more effective
Many producers of end products, such as automobiles, want to decrease the number of coating stages to make the production more efficient. To achieve that new types of coatings are required, which can make thick enough layer with one spraying. A coating formulation supplier and producer, Covestro, has introduced a new technology for coating plastic parts with one layer only. There are several benefits to the method according to Covestro: It can decrease energy consumption by 15% and CO2 emissions by 10% compared to the current best practices. I can hardly argue; If you can save for instance 20% of the work hours, 30% of the coating, and improve the end performance, it is a no-brainer. The data are convincing. In “Durable Bridge Coatings” Eric S. Kline describes very well the challenges and opportunities related to coating bridges. The data presents a saving, compared to the “Gold standard” three coat system, of 0,50 USD/sq ft. When talking about bridges of the size of the Golden Gate and similar, the cost performance is more than evident. By using less top coats, there are also excellent opportunities to contribute to less stress on the environment. The Society for Protective Coatings also presents the idea of a one-coating system as a way to reduce costs and painting time.
So where does MFC fit into all this? Its effect on rheology is evident in two areas:
- Shear thinning makes the coating easy to spray
- Quick viscosity recovery prevents sagging problems.
increased coating achievements and potential downsides
MFC looks like a fascinating material for coating thickness and strength purposes. So are there any downsides, and do they outweigh the potential winnings? Well, one downside to the commercially available MFCs is their limitations in product system compatibility. Since most of the MFCs are highly hydrophilic for the time being, the water-based or polar organic solvent systems are best fit. Also, MFC often comes as a rather dilute water suspension requiring room for the MFC suspensions or pastes with water in the formulation. Of course, the popularity of the water-based systems is growing, so there are many products in which MFC represents an opportunity. The lack of compatibility with hydrophobic systems, however, may pose a challenge for some.
Still, the ability to control an aqueous system with a non-soluble additive provides a superb opportunity to improve the stability, in-use performance, and after-use performance of the coatings. So next time I need to paint my house, I really hope the market can provide me with a superior spray coating, so that I can paint my house efficiently with little spill. And, hopefully, I will need one layer only! My guess is that MFC will contribute to that.