Over the years, synthetic polymers made from oil or natural gas were developed with a wide range of functionalities, offering adaptable and durable solutions in many domains.
The drawbacks of these plastic are not only the fact they are made from oil, but recycling these polymers is also not an easy task.
In 2015, of all plastic waste ever been produced in the world, only 9% has been recycled, while 12% was incinerated and 79% is accumulated in the natural environment (Geyer R. and al, “Production, use and fate of all plastics ever made”. Science Advances 3, e1700782 (2017)). Concerning Electronics waste, it is even worse, with 50 million tons of waste generated in the world with a very low amount of electronics’ disposable material being recycled.
As smart objects and IoT wearables are booming today, it is very important to find alternatives to plastic for a more sustainable-friendly manufacturing of electronic products and implement more circular economy approaches. Thus, within MADRAS project, Arjowiggins developed Cellulose Nano Fibrils (CNFs) films aiming to propose an alternative to replace plastics substrates in electronic devices and boost the mass production of Organic and Large Area Electronics (OLAE), including the production of smart packaging, roll-up displays, flexible solar cells, single-use diagnostic devices and printed batteries along with other innovations.
Films made of cellulose, the most abundant natural polymer in earth
CNF films are made from cellulose, which is the most abundant natural polymer on earth and made from renewable resources, mostly wood. Furthermore, it has been proven that CNF films are recyclable in a same way as a paper. Actually, CNF are 1000 times smaller than cellulose fibres (see figure below).
Schematic representation of the wood structure, optical microscopy image of birch fibers and transmission electron microscopy image of birch CNF
Arjowiggins developed within MADRAS a high transparency CNF film, optimising it to up to a transparency of 90%, which is the level needed to replace most of the current Polyester films used at the moment. To reach this level of transparency, three new pre-treatments (before the mechanical treatment) on the cellulose were developed:
- Mercerisation followed by enzymatic treatment
A first development of nanocellulose was oriented around enzymatic hydrolysis, which resulted in cellulose being cut in various places. In order to increase the efficiency of the enzymes, and knowing that cellulose tends to be swollen in presence of sodium hydroxide, we investigated the combination of a swelling step followed by an enzymatic one.
- Carboxymethyl continuous adsorption
Another method to efficiently fragilize cellulosic fibres, is to increase their surface charge, which can be achieved by grafting (tempo oxidation, cellulose phosphorylation, carboxymethylation, etc…) or by adsorbing a polyelectrolyte (polymer acting as an electrolyte). In this case, we investigated a widely known and used cellulose derivative: carboxymethyl cellulose.
- Phosphorylation
As previously mentioned, another way to increase the fibrillation efficiency of cellulose fibres is to graft negatively charged group onto cellulose. In this case, a phosphate group is grafted.
In parallel, a planarization layer was tested, aiming to reduce the light scattering at the surface of the substrate. However, for achieving a high-quality CNF, to reach a transparency of a 90% was not needed at first glance.
Transparency of the CNF film depending of the pre-treatments and of the PVDC planarization
Nowadays, Arjowiggins believes that CNF films could replace plastics in many applications, even when transparency is mandatory.
About the author
Dr. Gael DEPRES, Central R&D Manager for the Arjowiggins group:
- 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.
Arjowiggins is a Medium sized company specialized in paper manufacturing, printed electronics and nanocellulose. Arjowiggins is an independent paper manufacturer with a rich history reaching back to the 17th century. Sustainability and respect for the environment remain more than ever at the heart of Arjowiggins’ activities, through a wide range of ongoing internal and external initiatives.
