The overall goal of this procedure is to produce a new class of cellulose based nanoparticles and biopolymers, including a unique nanocrystalline cellulose that bears both crystalline and amorphous parts, and is thus called hairy nanocrystalline cellulose. This method can help provide key building blocks to advance the sustainable nanotechnology field. The main advantage of this technique is that through simple chemical reactions, cellulose fibers are converted to highly functional nanoparticles and biopolymers.
The invention of hairy nanocrystalline cellulose has introduced a new opportunity to use cellulose, the most abundant biopolymer in the world, for advanced applications such as bionanocomposites, rheology modifiers, use in environmental remediation, hydrogels, and much more. Hairy nanocrystalline cellulose can be prepared as a-ly-nik neutral or ker-kyn-ickle nanoparticles, each of which has its own unique properties. To begin, tear up Q-90 softwood pulp sheets into approximately two centimeter square pieces.
Collect four grams and soak the pieces in water for at least 24 hours while stirring. Once soaked, use a mechanical disintegrator for about three minutes to make a near uniform dispersion of pulp in solution. Next, use a vacuum filter composed of a 20 micron nylon filter in a Buchner funnel to separate the disintegrated pulp from the liquid.
Then, weight the wet pulp and calculate the amount of adsorbed water. Next, prepare a fresh aqueous periodate oxidizing solution. The required ratio of sodium periodate to sodium chloride depends on the type of fibers being synthesized.
Now, add the wet pulp to the oxidizing solution. The total mass of water in the system should be 200 grams for SNCC, or 266 grams for ENCC. Then tightly cover the beaker with aluminum foil to prevent periodate deactivation.
Stir the mixture at 105 rpm at room temperature to make a favored aldehyde content, which can take several days. When the reaction is complete, add ethylene glycol to the mixture and continue the stirring for 10 minutes to quench the periodate. Then, collect the oxidized pulp by vacuum filtration as before, and redisperse the oxidized pulp in 500 milliliters of water with stirring for 30 minutes.
Then vacuum filter the pulp and repeat the redispersion and filtration process until the pulp has been washed five times. After five water washes, store the pulp at four degrees Celsius. Weigh the wet pulp and divide it by four, and remeasure the mass of stored water.
Then disperse one quarter in 100 total grams of water in a round bottom flask. Transfer the round bottom flask to an oil bath set to 80 degrees Celsius, and heat it for six hours with gentle stirring. Be aware that under certain heating conditions and residence time in water, the property of the dialdehyde cellulose can change.
Once the solution cools, centrifuge it at 18, 500 gs for 10 minutes. The precipitate is the first fraction of unfibrillated cellulose. Separate it from the supernatant.
Next, weigh the supernatant and separate the SNCC from the supernatant by adding 1.7 grams of propanol per gram of supernatant while stirring. This will produce a biphasic solution. Then collect the second fraction of SNCC by centrifugation at 3, 000 gs for 10 minutes.
Decant the supernatant and store the SNCC for further analysis. To each gram of supernatant, add precisely 3.5 grams of propanol. The white precipitate that forms is the third fraction, which is made up of DAMC.
After centrifugation, the DAMC makes a gel. To purify the SNCC or DAMC, redisperse either precipitate in 10 milliliters of water with vigorous stirring for one hour. Then place the dispersion in dialysis tubing and secure the top and bottom with clips.
Place the loaded dialysis bag in about four liters of distilled water and stir it for 24 hours to eject the salts. Change the water at least once throughout the dialysis process. Then collect the dialyzed solution and store it at four degrees Celsius.
In advance, prepare 0.5 molar sodium hydroxide and set it aside. Now measure the water content of the one quarter of wet oxidized pulp as with SNCC synthesis and calculate how much water is needed for a total of 50 grams. Into this volume of water, dissolve in 2.93 grams of sodium chloride and 1.41 grams of sodium chlorite.
Then add the oxidized pulp, followed by dropwise addition of 1.41 grams of hydrogen peroxide. Stir the suspension for 24 hours at room temperature at 105 rpm while maintaining the pH around five by adding drops of the prepared 0.5 molar sodium hydroxide. Expect the pH to drop rapidly after about 15 minutes.
Keep the pH at five for at least four hours before letting the reaction go overnight. In the morning, almost no solid should be observable in the solution. Do not overreact the particles or they may gradually lose their crystalline structure.
Next, divide the suspension evenly into two centrifuge tubes and centrifuge them at 27, 000 gs for 10 minutes. The supernatant contains the ENCC and DCC. Separate the microfibrous precipitate from the supernatant and weigh both.
To the supernatant, slowly add 0.16 grams of ethanol per gram of supernatant while stirring. The ENCC fraction will form as a white precipitate. Then use a 10 minute centrifugation at 3, 000 gs to separate the transparent gel-like ENCC.
Decant the supernatant. From the supernatant, collect the DCC fraction using a co-solvent precipitation. Then use the previously described dialysis procedure to purify both the ENCC and DCC fractions before further analysis.
After purifying the ENCC and SNCC particles, they were further analyzed. To measure the charge content of the purified ENCC, conductometric titration was performed. NCC and ENCC colloidal behavior was affected by the ionic strength and pH.
Next, their size was analyzed at different potassium chloride concentrations and pH. The circles represent NCC, and the squares ENCC. The stars represent dynamic light scattering size measurements.
Because SNCC is a neutral particle, its size was altered by adding propanol. Transmission electron microscopy images of ENCC and SNCC revealed their fundamentally similar structures. Bearing a high carboxyl group content, ENCC is able to separate a high amount of copper ions from aqueous systems.
FTIR spectra were used to reveal the chemical structure differences of the three fractions. Liquid phase C13 NMR was used to analyze the third fraction, or DCC. Solid state C13 NMR was used to compare a cellulose pulp, NCC, and SNCC.
Once mastered, this technique can be easily implemented in hours if it is performed properly. While attempting this procedure, it's important to remember to pay attention to the reaction times under solvent additions. Following this procedure, other functionizations can be performed, such as a shift based reaction to produce ker-hy-nick hairy nanocrystalline cellulose.
After its development, this technique has paved the way for researchers in the field of nanotechnology to explore green, sustainable nanomaterials for advanced applications. Don't forget that working with cellular reagents, such as periodate, hydrogen peroxide, and sodium hydroxide is extremely hazardous, and precautions such as wearing a lab coat, goggles, and gloves should be taken while performing this procedure.
