In order to achieve cellulose nanofibrils, CNF,  different processes have been proposed, and one these popular ways is chemical treatment, involving hydrolysis and pulping. for example if your cellulosic  source is wheat straw or something like that soda pulping process can solve your chemical process problem.

Overall, every thing depend on your final aim to isolate CNF. Good luck.

What is your goal? You said that they use hydrolsysis right? I think the hydrolysis in some cases will diminish the lenght of your fibril and you will not obtain cellulose nanofibrils (lenght > 1 um) , but a cellulose nanocrystals.

The condictions on the papers that you read are different because the raw material is probably different too. Even when is the same source could have a lot of differences.

In my oppinion, the review in the literature is just for you have a point of start. But you need to optimize your condictions for your raw material and test the better one(of course only if you have time and raw material enogh to utilize).

I think also have differences because have a lot of differences to obtain the final product. I already read some papers that obtained cellulose nanofibrils just by a special mill treatment.

You're right. I'm interested for obtaining both nanocrystals and nanofibrils, but for start let's go nanocrystals. For beginning I use MCC. Now...I use ultrasonic treatment, but want to know what is the best pretreatment metod (chemically) and parameters ? Acid or alkali, etc...

Will depends of your application. But in all cases you need to homogenize your material in solution in avoid possible aggregates (e.g use ultrassonic treatment, swealling overnight).

For example.

1) If your application depends of termal stability, use H2SO4 hydrolysis (55% w/w - 120 min, 8-10 mg(cellulose)/mL(media) - 55 C) is not the best shot (only if you desulfated your final nanocrystals), in that case you better use HCl hydrolysis (4 mol/L - 120 min, 8-10 mg (cellulose)/mL (Media) - 80 C) or a mix media containing HCl and H2SO4.

2) your final goal is to immobilize another molecules in the surface by covalent bound (like enzymes, antibodies, lectins, copolymerization) the best way I think is treat your MCC with ammonium persulfate (1 mol/L - 60 C - 120 min) that result in nanocrysltas with carboxyl decorated surface for futher modification as through EDC/NHS coupling peptide click.

The time is other paramether that you need to consider depends of your final application, due the more time will result in diminish of nanocrystals lenght and more homogenous size distribution profile.

For example:

1) Using H2SO4 for 120 min will result in nanocrystals in range of 200-400 nm in lenght and about -40 mV zeta potential (relates to OSO3- substitution), but using 480 min will resultin in nanocrysltas in range of 200-220 nm (lenght) and about -60 mV zeta potential.

2) Using a mix of HCl and H2SO4 for 12 hours of reaction will result in nanocrystals with sphere shape (20x20 nm).

So as you can see, depends of your final application the method. What your application?

Thank you for such a thorough explanation.

I used 64% w/w H2SO4, 120 min., 10g MCC / 200ml (64%) H2SO4, 45 C -as a pretreatment. After that, ultrasonic at max for 20 min...Problem that occured is small yield and certain level of cellulose degradation. I need to optimise this process, that's why I asked here this question. As I heard, lower % of H2SO4 increase yield, but also the dimension of nanocellulose. And increased time lowers the yield, but increases crystallinity....

I want to optimise yield. I'm required to obtain certain amount of nanocellulose for beginning, to use it in biocomposites to explore possible further research in this field. Thanks again for help.

Check this article DOI 10.1007/s10570-006-9061-4

Thank you again. This is very usefull.

I think, there are many different opinions about pre-treatment and sonication. 

If you start with MCC, then you can you sorter time to improve your NCC's yield. Many papers mentioned that, the yield of NCCs can up to 70% with H2SO4 64%,45oC, and 45min (using different cellulose sources). 

I did some research on that, in my research cellulose was treated at 50oC, 50 min, the yield of different cellulose sources may range of 25-30%. If you have long reaction time, the yield is decrease.

For sonication, there are several papers they pre-treated NCCs by NaOH, or neutralize by just centrifugation then sonication. 

Thank you for your answer.

Thank you dear Catherine ! Looking forward to see your results.