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Fossil-based polymers are the main ingredient of most consumer plastics, coatings and adhesives, but our over-reliance of synthetic polymers comes with an unacceptable cost to the environment. Cellulose is a widely available and renewable biopolymer, which can offer replacements for fossil-based polymers. Especially cellulosic nanomaterials have gained a lot of attention due to their outstanding material properties, such as low density and high mechanical strength. 

However, replacing synthetic polymers directly with nanocellulose is not possible due to their widely different material properties. Chemical modification of cellulose is therefore required to achieve similar material properties, such as flexibility and transparency that are commonly associated with synthetic polymers.

To facilitate the use of cellulose in replacing synthetic polymers, sustainable methods to modify cellulose nanomaterials are required.

‘A major hurdle in chemical modification of native cellulose comes from the strong network of hydrogen bonds within and between cellulose fibrils, which hinders the dissolution and dispersion of cellulose in common solvents and therefore largely prevents the introduction of desired functionalities,’ says Mauri Kostiainen, Professor at Aalto University, School of Chemical Engineering.

‘We addressed this problem by employing solid-state reactions, which minimizes or eliminates the use of solvents. Mechanochemistry, in particular, has become an increasingly important green method not only in organic and (metallo)organic synthesis but also in polymer science and materials chemistry’ explains Sandra Kaabel, Assistant professor at Aalto University, School of Chemical Engineering. 

Kaabel has recently established the Synthesis Technologies research group at the Department of Chemistry and Materials Science to look at how we can use the solid-state methods to make and modify insoluble materials, like cellulose and other polymers, which normally require harsh conditions and toxic solvents to bring into solution.

‘Our newly developed mechanochemical modification process enables us to graft different types of primary amines and esters regioselectively on the surface of native cellulose. Using mechanochemistry can reduce the amount of solvent more then 10-fold compared to conventional modifications, but also significantly reduce the reaction time’, explains Daniel Langerreiter, doctoral candidate at Aalto University.

‘An additional benefit of the mechanochemical modification was the possibility to functionalize multiple types of cellulose nanomaterials and using simple filter paper as a starting material’, Langerreiter added.

‘When we set-up and designed the project, we were lucky to have an ambitious and motivated summer student - Nashwa L. Attallah – working on the project, who is now working as a doctoral candidate at Aalto University’, said Kaabel.

The new developed modification method provides an efficient way to obtain amine and ester-functionalized cellulose. ‘It serves a wide variety of applications, for example for from development of environmentally friendly nanocomposites, cellulose based membrane technology and biomedical devices’, the authors conclude.

Read the original publication

The original publication “Mechanochemical Modification of Cellulose Nanocrystals by Tosylation and Nucleophilic Substitution” was published in Green Chemistry, 2024. You can read the publication .