To make CNF films more transparent, one can use processing techniques such as chemical- or electrochemical modification of the nanofibers, introduction of oxygen species into the films, post-processing treatments, or introduction of surfactants. Chemical modification techniques involve introducing a functional group to the nanofibers, which increases the film's transmittance. Electrochemical modification involves introducing acidic or basic functional groups which also increases the films transmittance. Post-processing treatments such as electron beam and ultraviolet irradiation can also be used to increase the films transmittance and introduce additional functionality. Finally, introduction of surfactants, such as detergents, can be used to fill in inter-fiber spaces and reduce light scattering, resultingin an increase in transmittance. Additionally, introduction of organic layers between the CNF can also provide a thin-film transmittance enhancement. In summary, there are several techniques available to make CNF films more transparent.

Can you share how you produced your CNF? And what diameter and length did you achieve?

Kurt Haunreiter

Hi Kurt, I am working on producing nanocellulose fibrils from Hemp fibers, mainly bast, and I have done acid hydrolysis and mechanical defibrillation with a grinder, but it turns out the nanofilms are still very translucent and opaque and not transparent.

I understand. So your carboxylic acid content must be quite low. If you want a more transparent film, then you will need to modify the surface of the nanofibers. This is a limitation of the acid hydrolysis process. It will not give you high surface charge. For that you will need TEMPO or ammonium persulfate treatment. See Dr. Sagayaraj's comments above regarding treatment. Also, depending upon how much lignin remains, that could add some color to your films. Often in the literature, the films shown are not 100% NFC but a mixture of PVA and nanofibers - for mechanical testing purposes. The result is that the films are quite clear and give the wrong impression. The films that I have produced through which you could read text behind them had carboxylic acid concentrations greater than 1.2 mmol carboxylic acid/g. What surface charge did you achieve with your nanofibers?

I am trying to produce films with hemp nanofibers and university of maine nanofibers.

The hemp fibers are milled, acid hydrolyzed, and bleached with peroxide in the lab.On the other hand, UMaine nanofibers were purchased, which are in freeze-dried conditions. Using just acid and peroxide for bleaching, I believe, wouldn't provide my nanopaper with carboxylic groups, is it?

Also, performing zeta potential it was found that the freeze-dried UMaine fibers had -3 Volts value, and hemp fibers had a lower value around -6 volts.

(my lab research associate carried out Zeta potential)

It is also possible that your nanofibers are simply too large. Reducing the size of your nanocellulose will also result in increased transparency.