Have you checked the lignin content of your delignified sample for example with the klason method. Your sample might have still some amount of lignin. If you find lignin remaining in the sample, please try the same procedure again until the lignin content is sufficiently small. It is generally difficult to tell how long deligninfication takes since the efficiency of delignification strongly depends on wood type you used (softwood is harder to be delignified than hardwood in general). Even if the lignin content is very small, you would find some colour in the cellulose (+hemicelluloses) sample. The colour is due to tiny amount of remaining lignin and some other chromophores in polysaccharides. To remove this colour, maybe you should bleach the sample as carried out in pulp industries, e.g under H2O2/H2O/pH 10/80 degree.

Another point I would like to mention is that you will have to additionally perform hemicellulose removal with Alkali if you want to obtain only cellulose.

I hope this will help you.

Thank you prof, I have checked the lignin content and holocellulose. I used softwood. Thank you very much for your great explanation. I will use hydrogen peroxide, but I am worry it will hydrolize the cellulose into HMF or glucose, because I am studying about catalytic activity.

I don’t think H2O2 hydrolyse cellulose since the acidity of H2O2 is considerably low (pKa is about 11-12), though it might cause some reactions, e.g. oxidation of the reducing end group to carboxylic acid. If your research propose is catalytic reaction toward cellulose, not obtaining “white” cellulose itself, you might not have to bleach the sample. The origin of the yellowish colour is the presence of some compounds, quinones and other aromatics, the amounts of which are usually ppm or even ppb order, if the sample is sufficiently delignified. Such tiny amount of compounds may not play any role in your catalytic reaction. I recommend you to prepare your sample fitting the objective of your research. I am not a professor, so please feel free to ask me any question.

Dear Noer,

There is no simple delignification process for wood pulps. In fact, if you would like to get as pure wood based cellulose as you can I suggest for you to purchase or just to ask from a pulping company to send you a small batch of dissolving pulp for your research project. But even the dissolving pulp will contain small fractions of lignin with amounts that are however somewhat irrelevant. Then by using a cold alkali extraction (which you probably already did with 10% NaOH [depending on temp. (20-40 deg centigrade]) you could get rid of the hemicelluloses that are still present in the pulp. There is a very good book called Handbook of Pulp (ed. H. Sixta) that you might refer to with your work. Especially its chapter No. 7 (in part 1.) titled "Bleaching" that covers chemical pulping process and a lots of bleaching chemistry. Bleaching in chemical pulping equals to lignin removal in contrast to mechanical pulping where bleaching just removes the color. So, to obtain pure cellulose from wood fibres you need a lots of work.

yes Mr Takashi, I have read several journal that using hydrogen peroxide to convert cellulose to HMF through like-fenton reaction, so basic the mechanism of this conversion is radical .OH. . I agree with you, I don't need to get white cellulose. I have been successful to reduce amount of lignin using NaOH. Sorry sir, I am still student so I have many questions and need to learn more in depth again. I like biomass and catalyst research topic. My undergraduate thesis focus on catalyst, I want to discuss with you about study of kinetic reaction. Thank you for your kindness.

Dear Carl Lange,

thank you for you reccommendation book , I know about bleaching using Chlorite or dichloride and hydrogen peroxide. I have using NaOH for delignification process at 50 degree celcius for 60 min. and the amount of klason lignin have successful reduce. I just want to use my cellulose as my substrat for catalytic reaction.

Thak you,

Fadlina

If you want to get pure cellulose from real biomass it will be beneficial to follow TAPPI method. This method can help you to separate lignin and hemicellulose from wood.

Best effective method is Chloride bleaching after NaOH treatment. 

Chemical analysis is difficult...you can use acid hydrolysis for removal lignin residue. for bleaching you can use peroxide hydrogen...for hard wood you should using higher percent of NaOH.