Fedrigoni’s role in the MADRAS project is to produce a transparent flexible substrate for the development of a geotracking battery-free flexible tag. Fedrigoni opted to produce the substrate based on cellulose materials and, more precisely, phosphorylated cellulose nanomaterials.
According to literature, cellulose phosphorylation is mainly carried out by reacting cellulose with urea and phosphoric acid. This process has several strong advantages: it is simple and easy to upscale, it brings flame retardancy to the material and the nanofibrils cellulose materials obtained are of great quality. Furthermore, high transparency materials can be obtained using phosphorylated cellulose nano fibres.
Figure 1: Proposed reaction mechanism of cellulose phosphorylation
The phosphorylation process proposed by Fedrigoni relies on 4 steps:
- Impregnation of a paper in the urea and phosphoric acid aqueous solution, then a light pressing is applied to remove the excess of solution in the paper.
- Drying of the paper by heating to remove the water inside the paper.
- The curing step. The reaction in Figure 1 is carried out by heating the dried paper above 150°C.
- Mechanical fibrillation of the phosphorylated cellulose raw materials.
This process was successfully adapted to a roll-to-roll pilot impregnation and drying process, as illustrated in Figure 2.
Figure 2: Phosphorylation impregnation pilot trials at Fedrigoni
The phosphorylated raw material was disintegrated into water and mechanically fibrillated. A strong gel was obtained. Scanning electron microscopy was done on a dried aerogel, allowing to observe the phosphorylated cellulose structure (figure 3).
Figure 3: SEM image of Aerogel of phosphorylated cellulose
Finally, a transparent and flexible cellulose substrate was produced by solvent casting, filtration degassing and plasticising.
Figure 4. CNF foils grade 1 and phosphorylated pulp (a) grade 1, (b) phosphorylated, (c) phosphorylated filtrated, (d) phosphorylated, filtrated, deaerated, plasticised with 20% sorbitol.
About the author
Dr. Gaël Depres, Senior Innovation & Grenoble R&D Center Manager at Fedrigoni Papers
- PhD in process engineering from Grenoble INP.
- Engineer in papermaking
- Expertise in European and National projects preparation and submission.
- Skills and experiences in projects management, paper, nanocellulose, printed electronics, antennas.
