Have you thought of spray drying a suspension created by sonicating the gelatinous layer. It might then not need grinding.

i think the best way is freeze-drying. freeze-drying can dry the cellulose into powder. then, you don't need to grind it. 

Anything that is gelatinous is not to be dried in oven directly. This is an universal thumb rule. Any way, I would suggest that you try to freeze the gelatinous mass (I am quite sure that it can not be pure cellulose) to -80C and then freeze dry it it should be OK. You may not get a powder per se, but then you may just pulverise it very lightly to get the desired powder.

 I also believe that the best way is spray dying. If you freeze dry the pellicle you have to grind it which has the result that you may damage the nano-fiber structure. After spray drying you gt what you want. 

It is not easy to use BC in spray dryer because of the fibril structure. You may not get nanostructure (couple microns) and fibril (spherical or doughnut shape particle with low aspect ratio) after spray drying. It seems FD is your best option. 

I have tried to mill BC by using liquid nitrogen but the result was flakes of BC. Freeze drying BC will not help to mill it as BC is in form of a paper-like sheet after freeze drying. The best option that has worked for me is using a machine called variable speed rotor mill pulverisette 14. I have analysed the resulting powder and the fibre network appears intact under scanning electron microscope. I hope this helps.

I freeze-dried a highly viscous plant cellulose and it  never came out in a powdered form. And yes Olajumoke, i had the same results as you had. I would suggest freezing the cellulose completely, then freeze-dry (will increases the brittle nature) then pulverize. It is likely to affect the nano structure of the cellulose depending on the  purpose of the study.

i have extracted cellulose from fiber now it is in semisolid state what is the best method to dry?

As I said earlier, freeze it hard and then dry it at a low temperature under vacuum. It will have an added advantage which is : you may get a crystalline mass which upon analysis will also tell you of the other impurities in it.

I think you can prepare bacterial cellulose powder by microwave drying under special wavelength (it is in any scale) and grind by ball meal (preferentially under nitrogen).

Aoa Khairul Azly Zahan ,

I have worked with BC and it is difficult to grind in wet form. I agree with method advised by Diana L. Reinecke , which is more suitable.

You may dry the BC in oven after complete washing from the culture medium remnant.

Try to remove water from BC at room temperature and then dry it at 60 degree Celcius, keep thorough follow up till complete drying.

Then cut it in pieces and use grinder (blades made of metal).

Pass the total mass through SS mesh of desired pore size and repeat the grinding process for the remaining BC.

thank you for your answers but the cellulose what i have extracted is from coconut shell powder, after delignification and removal of hemicellulose i get white semi solid paste which has to be dried? what would be the best method?

is there any other steps i have to undergo to purify it?

I have tried two methods:

1. freeze dying BC followed by dipping in liquid nitrogen for a few seconds and grinding in a ball mill.

2. freeze dying followed BC by keeping in the refrigerator overnight and grinding in a blender. The powder is sieved and bigger particles are put back in the blender for another round. (modified method of Munair Badshah )

Both of the methods gave BC in powder or particle form.

Smarak Bandyopadhyay , I would like to add some edition to the method 2. Dry BC sheet and cut in pieces and later on crush in grinder. This will help you in producing very fine BC powder particles.

Good day! I recommend to gently crush wet BC pellicle in ceramic mortar with liquid Nitrogen.