The ability of nanocellulose and microfibrillated cellulose to provide strength in different products has been discussed and studied for a long time. MFC fibers are strong and lightweight and has large surface area which makes it an excellent candidate for strengthening aid. Some are referring to the composites containing MFC as being “the next world-changing supermaterial” (Gizmodo, 2014), while others believe that they can be part of car production (Financial Post 2017). So how is this actually working?
Light-weight fibers with large surface area: key to its strength
MFC is basically highly fibrillated cellulose fibers which are entangled into a dense, three-dimensional network, as is shown in the figure below. These physical entanglements are crucial for the strength of the MFC films. In addition, the fibers have very high surface area with many hydroxyl (OH) groups. These OH groups are able to form inter-fibrillar hydrogen bonding and contribute to the strength of the film. Thus, one can say that both physical and chemical forces are working to increase the strength attained from MFC. These functionalities can be utilized in a various of products, from coatings and adhesives, to composites and concrete. To give you a concrete example of this, I am using the example of films made from MFC.
MFC network in microscopy at magnification (Exilva MFC from Borregaard).
Strong, flexible MFC films by a roll-to-roll process
Pure MFC films are strong but also rather brittle. The flexibility can be improved by adding softening aids into the film. VTT (Technical Research Centre in Finland) has developed a continuous process for producing MFC film. They can manufacture the film at semi-pilot scale and the technology is based on casting the film on a plastic substrate (patented technology WO2013060934 A2). They have also found out that adding sorbitol into the film makes it more flexible without sacrificing the other properties too much.
MFC films (Exilva by Borregaard) with sorbitol as a softener produced by VTT.
The picture above shows the MFC film with 30% sorbitol produced by VTT from Borregaard’s Exilva MFC. Sorbitol improves the strain at break compared to pure MFC whereas the tensile strength is reduced slightly. This kind of change is expected when a softener is added to a material. The tensile strength and modulus of the MFC/sorbitol film are higher than typical plastics, high density polyethylene (HDPE) or polypropylene (PP). The results show that MFC has potential to be used as a strength agent in composites or as reinforcing layer in multi-layer structure.
MFC can be a good alternative for strength improvements going forward
All in all, microfibrillated cellulose is showing some very interesting reinforcement and strength functionalities that can be useful for several purposes. This may in the future give a high number of composite product opportunities. Certain challenges require more research, like poor compatibility of hydrophilic MFC with non-polar matrices. In the meantime, polar systems can find great help in these performance additives as illustrated with anti-cracking effects in coatings , or as shown by the University of Maine in paper products. Who knows, perhaps microfibrillated cellulose can be the material enabling us to take new steps towards improved materials, with a much more sustainable environmental footprint in the future.
Stay curious, and be the one who tests and finds out!