I used 7 g MCC in 100 ml of 65% sulfuric acid. Temperature and hydrolysis time were 40 C and 2 h respectively. After 10 min it's became yellow and at the end it was dark brown.
You describe oxidation basically, and to a great extent. I guess that other studies in which concentration, T and time are similar to those of yours have greater mass transfer limitations, so you may want to try with lower temperature.
But besides the color, does everything get dissolved? Have you gone further anyway? (separation and washing)
And just in case, when you prepare H2SO4 65% from H2SO4 96-98%, you wait till it cools down, right?
Hello Mohammad. Why don't you try to use a bleached pulp to make CNC? Using BHKP (Bleached hardwood kraft pulp) or BSKP (Bleached softwood kraft pulp). Using MCC to make CNC probably won't be economic feasibly.
Are you using a bleached pulp? If not the residual lignin is causing the color change. You are also sulfonating the cellulose which may give you a more yellow fiber.
Roberto Aguado
Hi, thanks for your explanations.
Yes, it's get dissolved and i'm going to freeze-dry the sample after centrifugation and dialysis.
About your second question i think it's better to explain step by step, at first i dissolved 7 g MCC in 35 ml DI water, then i added up 65 ml of H2SO4 dropwise to MCC solution (in ice bath). I then transferred the solution to the 40 C hot water bath under mechanical stirrer for 2 h.
Dose sample change color mean a failure in CNC synthesis?
Because i've read somewhere it's because the side reaction like dehydration or oxidation.
What mechanical treatment will you use? You may see a little color change after dialysis but the presence of lignin won't preclude nfc formation. If you can produce a clear thin film from the supernatant after mechanical treatment that is a positive sign. AFM would confirm your product.
Kurt Haunreiter I assume he means commercial microcrystalline cellulose from cotton, white powder, e.g., https://www.sigmaaldrich.com/specification-sheets/223/142/435236-BULK_______ALDRICH__.pdf
Lignin content in this case is negligible. But the low particle size may ask for milder conditions than fibers from a bleached woodpulp.
Mohammad Asgharzadeh As long as you are able to recover a solid, it is too soon to conclude that it was a failure. You may want to characterize it.
Roberto Aguado - I agree - the sulfuric acid may be too severe. It reminds me of the results you get when you perform Klason. Perhaps extending the dialysis an extra day and ensuring that you have water recycling may help. But I'm guessing that cellulose has been sulfonated and the color will persist regardless of what further treatment you do.
Mohammad Asgharzadeh here is a paper that may help - it appears to have similar observations to what you have noted. I agree with Dr. Aguado - don't give up just yet. The paper mentions TEM, but you can also use AFM.
Mohammad Asgharzadeh
Your reaction is too long for this acid concentration, then the yellow is formed due to chromatopto hores due to the glucose decomposition and dark due complete. You first prepared the acid media at this concentration, regulated the temperature, and then added cellulose?
I recommended using 57 wt%, 65 C, 500 rpm for 140 min with 10% of solid consistency. This will result in approximately 250 mMol/g of sulfate density and 65-70% of mass yield (from bleached cellulose sources).
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