Anni Karppinen | July 5, 2016
Microfibrillated cellulose (MFC) is subject to high interest from both academia and the industry these days. A lot of exciting research is being conducted at various universities and research centers around the world. In this blog post I will review articles I found particularly interesting regarding the use of MFC in adhesives and coatings. Note that, for the sake of simplicity, I have used the term “MFC” throughout this text even if the researchers might have used a different name in their articles.
Can MFC improve wood adhesives?
Scientists at the Istanbul University in Turkey, and at Kangwong National University in South Korea (Ayrilmis and co-workers), have had a closer look at the use of MFC in urea-formaldehyde adhesives for wood based composites. The high surface area of MFC, along with the high stiffness and strength, makes the material a promising candidate for environmentally friendly reinforcement of wood adhesives and composites.
In this study they investigated the adhesive properties and bonding performance of urea-formaldehyde adhesives with different ratios between formaldehyde and urea and different amounts of MFC. It is desirable to have a low formaldehyde content in the adhesive, as free formaldehyde is toxic and carcinogenic to humans. However, the drawback with having a low formaldehyde content is that the adhesive becomes more brittle and has poorer bond performance and mechanical properties.
It was found that MFC enhanced the strength and ductility properties of the adhesives, especially for those with low formaldehyde content. The researchers conclude that MFC has potential as an environmentally friendly reinforcing additive for the improvement of bond formation in urea-formaldehyde adhesives.
How about using MFC in corrosion coatings?
At the Hiroshima University in Japan and the Telkom University in Indonesia, scientists (Yabuki and co-workers) have studied self-healing polymer coatings containing MFC, as release agents for corrosion inhibitors. This type of coatings is used for preventing corrosion of metal. An important property of the coating is to self-heal after suffering a mechanical damage.
The self-healing can be facilitated by adding a corrosion inhibitor to the coating system. It has been shown that coatings containing MFC and a corrosion inhibitor have a good self-healing performance. In this study oleic acid was used as a corrosion inhibitor, and an epoxy resin was used as a base polymer for the middle and top coat layers. Self-healing ability was achieved with 1% of MFC and oleic acid in the middle coating layer.
Moreover, it was found that the pH in the base polymer was important in order to have an efficient release of the oleic acid from the MFC surface when the coating was damaged. A pH of 11.4 gave the best performance. Very interesting results and perhaps something to consider if you are working with corrosive coatings.
...or to protect cherries?
My last example comes from cherry farming. Cherry rain cracking is something that can occur in the late stage of the cherry growth. What happens is that rainwater is easily absorbed through the cherry cuticles which increases the internal pressure in the fruit and eventually the skin bursts. Cherry rain cracking causes severe economic losses to the cherry industry.
Researchers at the Oregon State University and the University of Concepción in Chile (Jung and co-workers) have found a new solution to this problem by using a MFC based coating. The coating should have high wettability to ensure a good spreading and a high elasticity so that the fruit can continue to grow and yet be water resistant. The coating should, of course, not be harmful to the fruit or to humans.
The optimal coating formulation was found to contain MFC, potassium sorbate (antifungal agent), glycerol and a surfactant mixture (polyoxyethylene (20) sorbitan monooleate (Tween 20) and sorbitan monooleate (Span 80)). The coating significantly reduced cherry rain cracking in field trials and the coating did not have any negative effects on fruit growth or quality. Oregon State University has filed a patent application on this type of coatings and it will be interesting to see more results from this in the future.
