Dear Christof Rein, please check the following documents. My Regards

https://doi.org/10.1155/2013/141034

https://www.researchgate.net/publication/274104324_Ketene_Acetylated_Wood_Cellulose_for_Industrial_Applications_in_Wood-base_and_Polymer_Industry

https://link.springer.com/article/10.1007/BF00705699

https://doi.org/10.1002/app.1989.070370414

Hi Christof,

the change of morphology might be related to swelling of the wood piece in the anhydride solution. You should consider what part of the wood you want to modify. Is maybe a acetylation at the surface of the wood sufficient or do you want to acetylate also the inside the sample? If the surface is enough, you can utlize lower amounts of anhdyride.

I can recommend you a quite old paper 10.1080/02773818608085236 reporting a very simple approach, in which you need smaller amounts of anhydride. You can probably control the extend of acetylation (throughout the sample) by varying the immersion time. Maybe this will help you. BTW we are working on related topics regarding cellulose, so feel free to contact me if you need furhter information.

All the best for your experiments.

KR,

Marco

Hi Marco,

actually this is just a side project, so I am not engaged into this topic otherwise. Indeed that deformation originates to the swelling and also the weight gain implies that also deep layers of the wood are acetylated. Nevertheless I just wanat the surface to be modified, therefore I also already tried to lower either the reaction time or I added more Xylene to the mixture, to decrease the amount of Ac2O. But sadly both methods just ended in a decrease of surface modification, not only in the bulk phase, but apparently also on the surface, as proven by contact angle measurement with water.

Therefore it was not possible to just modify the surface by either way so far. But the paper that you show seems very interesting, as it uses just a dip wetting of the wood instead of stirring in liquid phase. What simply confuses me is that any surface layer of Acetic Acid anyhdride should evaporate after some time at 120 °C in that oven reactor. But the graph shows an increase of weight (and therefore Acetylation) up to 4 hours. How is the Anhydride not already removed just by evaporation during all this time? I actually thought about dip coating, but as I saw that without heat there is no reaction, I did not go further into this route.

My regards,

Christof

Hi Christof,

I see so this method could be indeed very suitable.

Important is that you dry the wood piece before (to remove water) and then make sure that the amount of moisture uptake is minimal. You can transfer the wood after pre-drying into a desiccator and then just take it out directly prior to dippng in Ac2O.

Principally, the reaction should occur prior to evaporation and mediated by the heat and evaporation of the formed acetic acid (which has lower boilding point, acetic anhydride's boiling point is at 140°C). Of course, you will also evaporate a bit anhydride, so better to do this in the hood. Alternatively, you should be able to heat it as well in a closed round bottom flask (just add the dipped wood and heat at the given temperatre in a closed flask).

KR,

Marco