Becoming Familiar with Nanocellulose

These days, nanocellulose can be found in everyday products, like compostable plastic-like bags; however, the use of nanocellulose is still in its infancy in terms of research and use in art conservation.  (For example, these decomposable poop bags look like plastic bags, but can actually be tossed in your compost pile!)

Introduction

This post takes a look at how nanocellulose films might be used in art conservation.  To dip our toes in, experiments at the Cincinnati Art Museum were performed with a group of conservators who work in different specialties: textiles, objects, fine art, photographs and bound materials. We tried out various types of nanocellulose films and how they might be applied to a range of materials.

What is Nanocellulose?

Nanocellulose is made up of nanoscale cellulose particles that come from different sources, like:

• Wood: The most common source
• Non-Wood Plants: Cotton, ramie, sisal, bamboo, and agricultural by-products.  The decomposable poop bags mentioned above are made from corn starch nanoparticles!
• Tunicates: Marine invertebrates, the only animals known to produce cellulose microfibrils.
• Algae: Some species produce cellulose microfibrils within their cell walls.
• Bacteria: Certain bacteria, like Gluconacetobacter xylinus, can produce cellulose microfibrils under the right conditions.

Types of Nanocellulose:

In conservation, the field has been experimenting with two main types:

Where to Buy

Many labs and companies around the world make nanocellulose products like gels, nanopapers, and foams. Here are a few:

• Europe: Technical Center of Paper (CTP, France), EMPA (Switzerland), Weidmann Fiber Technology (Switzerland), Aalto University (Finland), VTT Technical Research Center of Finland, KTH (Sweden)
• North America: The University of Maine (USA), Forest Products Lab, Wisconsin (USA), American Process Inc., Atlanta (USA), Celluforce (Quebec), Kruger Inc. (Quebec)
• Asia: University of Tokyo, University of Kyoto, Asahi Kasei

What We Bought

In Cincinnati, we experimented with two products purchased from Weidmann Fiber Technology in Switzerland:

During practical applications, the MFC powder did not react the same way as the gel during the film creation. The powder precipitated out and did not cast a homogeneous film. 

While it may have been a mistake in our method of production, my guess is the powder isn’t as well fibrillated for casting and wonder if that’s why it stayed out of solution.

Next, I am eager to try the CNC form, which appears to be available at https://umaine.edu/pdc/nanocellulose/.

What makes nanocellulose films unique?

High Purity and Stability: They’re almost pure cellulose, super stable, and have a neutral pH. They’re less affected by temperature and humidity than regular paper.

Strong Yet Delicate: Mechanically, they’re stronger than traditional paper in some ways but less elastic and easier to tear.

Remarkable Transparency: The nanoscale dimensions of the fibers eliminate light scattering, resulting in highly transparent films, often called “nanopapers.” The transparency is influenced by the film’s structural density, particle size (MFC or CNC), the source material, and the manufacturing process. In practice, this transparency reminded me of the appearance of glassine tape.

How are nanocellulose films made?

There are various ways to make nanocellulose films, but conservators use one main method (as the others are found in larger scale manufacturing processes).

Casting Film by Evaporation: A low-cost and easily reproducible method where a nanocellulose solution is cast onto a substrate like a silicone mold or a polystyrene petri dish, allowing the solvent to evaporate. This technique produces homogeneous films.

Interestingly, it took an extraordinary amount of time for the solvents to evaporate at the Cincinnati Art Museum. Even after placing the trays in a fume hood to encourage drying, it took many days for the films to form during a low RH in December!

Glass and polyester dishes are not recommended for casting onto as the films will not release from these containers.

What are nanocomposite films?

Simply put, nanocellulose is combined with an adhesive.  During the film’s creation, the adhesive is added into the nanocellulose solution to enhance the film’s physical and optical properties. Common conservation adhesives added to films include Klucel G, wheat starch paste, methyl cellulose, and gelatin.

In our experiments, we used 5% Klucel G, 4% Methocel A4CP, and strained Zen Shofu wheat starch paste. Two batches were made of varying amounts of gel to see if there was a difference in thickness of the films (spoiler: I couldn’t tell a noticeable difference!). 

For another batch, Cecile also added in some QoR Golden watercolors that have an aquazol-based binder for a bit of a brown-toned tint that might be handy for filling losses in photograph conservation.

Applications of nanocellulose films in art conservation:

Nanocellulose film properties may be handy for use in art conservation for their:

• High transparency and stability. Used as a repair material, the films blend into substrates and supporting fragile artifacts.
• Compatibility with various adhesives
• Minimal discoloration after aging ensures long-term stability and visual integrity of treated artworks.
• Reversibility. They can be safely removed if needed.

Limitations to using nanocellulose films in conservation:

While promising, there are some downsides to consider:

• Lower tear strength compared to traditional paper.  The films are delicate and might not work for items that need to withstand a lot of use.
• Water Sensitivity: the films are highly reactive to moisture and require different application repair techniques than traditional paper repairs. For me, I wondered if the amount of time required for the learning curve of successful application was worth the result over traditional paper repairs.
• Long-term behavior of nanocomposite films and their interaction with art materials requires further research to ensure compatibility and prevent unintended consequences.

Testing the Films on Paper-Based Materials

Both pure nanocellulose films and nanocomposite films were tested on a non-collection items using a variety of techniques.

Pure films were applied with a range of adhesives while nanocomposite films were adhered either by remoistening/reactivating with solvents or adhered by applying additional adhesive to the film, in addition to what was mixed in during the casting.

While Cecile worked on a war bond poster, Obie worked on a garment, and Laura tested treatment on an ink jet print, I tried my luck on a map.

Together, we all tested a scrapbook owned by Kelly.

My Successful Applications

I had best luck with the nanocomposite films but only when they were reactivated with the adhesive they were made with. 

For example, the 20 ml 0.2% MFC gel created with 0.6 g 5% methocel film blended beautifully into the paper when reactivated with 5% methocel.  The methocel was brush applied thickly.  See the repair below along the left side in specular light.  It doesn’t even look like tape here!  The repairs blend nicely.  Between the two, I found the methocel nanocomposite film blended better than the wheat starch paste.

My second favorite options were the pure MFC films adhered with methocel and wheat starch paste.

My Application Failures

I could not for the life of me find a way to successfully apply the nanocomposite film with Klucel G to a paper substrate without it falling apart during the process. Cecile had better luck while for me, it stuck to everything!  I struggled both when it was reactivated with ethanol and when the film was brushed with the Klucel G solution.  Plus, it was super shiny and didn’t help the paper lie flat.

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I had even worse luck with the nanocomposite films when they were only reactivated with water.  I could easily apply them to the paper, however, these performed the worst out of all the repairs, with the methocel nanocomposite film failing to even hold the tear together!  See the two center repairs below in specular light.  The wheat starch paste held, but didn’t want to hold the tear well aligned.

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Compared to kozo tissue repairs (on the same paper): the nanocellulose repairs overall were shinier (more akin to glassine tape in appearance!), but they didn’t seem to cause any planar distortions like the kozo tissue naturally wants to do.  However, the kozo tissue blends visually into the paper better.  The kozo tissue repairs are the ones with the tails sticking off the edge of the paper.

Conclusion:

Nanocellulose films offer promising potential for art conservation but require a learning curve to handle and apply. Their unique properties, combined with ongoing research and development, could lead to innovative solutions for preserving cultural heritage, but research on long-term stability, compatibility with specific artwork materials, and ethical considerations will be crucial for wider adoption in the field.

Health and Safety:

Pure nanocellulose gels and films are generally considered safe to handle.

Resources

Most of the info here comes from resources shared by paper conservator, Cecile Mear who organized our informal experimentations. Photograph Conservator, Laura Moeller also provided additional resources she gathered from a workshop held at the Indiana Historical Society in June 2019.

1. bpga36-20.pdf  Detailed introduction to nanocellulose films use in conservation
2. Full article: A New Mending Material: Nanocellulose Film
3. Nanocellulose Films in Art Conservation: A New and Promising Mending Material for Translucent Paper Objects
4. bpga42-01.pdf  Photograph conservation
5. bpga41-01.pdf  Fan conservation treatment—application of nanocellulose in gel form
6. YouTube video: Practical techniques for creating nanocellulose film and the application of aqueous adhesives.
7. Canham, R. ” Nanocellulose Calculator.” Burr Oak Bookbinding. Article related to YouTube video.
8. Heritage Science. “Nano meets the sheet: Adhesive-free application of nanocellulosic suspensions in paper conservation.” Full Text.
9. Heritage Science. “New treatments for canvas consolidation and conservation.” Full Text.
10. Heritage Science. “Novel nanomaterials to stabilise the canvas support of paintings assessed from a conservator’s point of view.” Full Text.
11. Pinkney, J. “Nanocellulose for Conservation.” University of Birmingham.

Ashleigh Ferguson Schieszer – Special Collections Library Conservator