1.1 Reagents and instruments
Reagents: propylene oxide, sodium hydroxide, isopropyl alcohol, acetone, anhydrous ethanol
Alcohol, hydrochloric acid, Ammonium sulfate, calcium chloride, etc. are all of analytical grade, chitosan (CTS,
D. D=92.7%1 (Nantong Xingcheng Biochemical Company).
Instrument : pH DZ-2 pen type acidimeter, 721A spectrophotometer
meter, 170SX Fourier transform infrared spectrometer (American Nicolet Company 1.
1.2 hydroxypropyl shell Synthesis of polysaccharide (HPCTS)
Mix a certain amount of chitosan and isopropyl alcohol and stir for 30 minutes, add
50% NaOH aqueous solution, alkalize, stir for 60 minutes, and seal Overnight. times
day, add the catalyst and stir evenly, measure a certain amount of propylene oxide and add it to the stirring reactor, react at room temperature for 60 minutes, and then
React for a certain period of time at a certain temperature, then adjust the pH to neutral and disperse in ethanol/water solution, stir and filter continuously, and soak and wash repeatedly with acetone
p>
The dried product is obtained after washing and is ready for use.
1_3 Test
Molecular mass 21; degree of substitution [13, 141; infrared characterization: hydroxypropyl chitosan.
After purification, CTS and HPCTS were mixed with KBr and pressed into tablets, and measured with Fourier transform infrared spectrometer; solubility: dissolve 0.5 g HPCTS
In 20 mL distilled water, stir for a certain period of time and observe its dissolution in water; Hygroscopic and moisturizing properties 61
2 Results and discussion
2.1 Reaction 1.
1.2 Synthesis of Hydroxypropyl Chitosan (HPCTS)
Mix a certain amount of chitosan and isopropyl alcohol and stir for 30 min, add 50% NaOH aqueous solution, alkalize and stir for 60 minutes, seal overnight. After
times, add the catalyst and stir evenly, measure a certain amount of propylene oxide and add it
p>
React at room temperature for 60 minutes in a stirring reactor, then react at a certain temperature
for a certain period of time, then adjust the pH to neutral and disperse in ethanol
After continuous stirring and suction filtration in alcohol/water solution, repeatedly soak and wash with acetone
to obtain a dry product for later use
1_3 test
Molecular mass. 21; degree of substitution [13, 141; infrared characterization: hydroxypropyl chitosan
After purification, CTS and HPCTS were mixed with KBr and pressed into tablets, using Fu
Measurement by vertical leaf transform infrared spectrometer; solubility: Dissolve 0.5 g HPCTS
in 20 mL distilled water, stir for a certain period of time, and observe its dissolution in water
; Hygroscopic and moisturizing properties. .
61
2 Results and Discussion
2.1 Effect of reaction conditions on degree of substitution
2.1.1 Temperature
By Table 1 shows that as the reaction temperature increases, the degree of substitution Ds first increases and then decreases. The reason is that the higher the reaction temperature, the more complete the penetration between the reactants and the collision between propylene oxide and the active groups of the reactants, which speed up the reaction speed, and the side effects are Reactions will also occur, and propylene oxide has a low boiling point and is easily volatile. Too high a temperature is detrimental to the main reaction, resulting in a decrease in the degree of substitution. Therefore, the reaction temperature is preferably 60°C.
Table 1 Effect of reaction temperature on products
Note: Reaction for 8 h, chitosan 2 g, propylene oxide 20 mL, catalyst 1 mL.
2.1,2 The dosage of propylene oxide
It can be seen from Table 2 that as the dosage of propylene oxide increases, the degree of substitution of the product also increases
big. The reason is that increasing the amount of reactants can increase the diffusion rate of the reactants into
chitosan, and there is a sufficient amount of raw materials to react with the active groups of chitosan
, increasing the probability of collision between the reaction reagent and the active groups on the chitosan molecule
, thereby increasing the degree of substitution. Although the degree of substitution of the product can be increased by
increasing the dosage of propylene oxide, cost issues should also be taken into consideration during production, so the final requirements should be
Choose the appropriate dosage according to the purpose. In this experiment, the dosage of propylene oxide was chosen to be 20 mL.
Table 2 Effect of propylene oxide dosage on products
Note: Reaction at 60°C for 8 h, chitosan 2 g, catalyst 1 mL.
2.1.3 Time
As can be seen from Table 3, the longer the reaction time, the higher the substitution degree of the product and the better the dissolution
performance. The reaction between chitosan and propylene oxide is a solid-liquid heterogeneous
phase reaction. The initial stage of the reaction is the diffusion and penetration of propylene oxide and the stage when the alkali-shell polysaccharide is evenly mixed. , followed by the reaction of propylene oxide with the
reactive groups of chitosan, and the resulting product changes from swelling to dissolving.
The extension of time makes the reaction proceed. More fully, alkali chitosan will diffuse into each reactive group through the action of water to react with it. Finally, extending the reaction time can make the process of "diffusion-reaction-swelling-dissolution" repeated, making the reaction more complete, increasing the degree of substitution, and dissolving the product
Performance improvements. Therefore, water-soluble products can be obtained after 8 hours of reaction.
Table 3 Effect of reaction time on products
Note: Reaction temperature is 60°C, chitosan 2 g, propylene oxide 2O mL, catalyst 1 mL.
2.1.4 Other conditions
Using isopropyl alcohol as the solvent for alkalinization can ensure that the alkali aqueous solution is evenly dispersed
It is a good Dispersant. The heat released during the alkalization process is dispersed evenly and is easy to transfer, which reduces the hydrolysis reverse reaction of alkali chitosan and obtains more uniform alkali chitosan. In addition, the solubility of alkali in alcohol is lower than that in water, which allows more alkali to be absorbed by chitosan. Isopropyl alcohol can also increase reaction activity and improve the uniformity of the reaction.
The reaction between chitosan and propylene oxide is a heterogeneous reaction, but adding
a phase transfer catalyst can increase the contact opportunities between propylene oxide and chitosan,
Increasing the conversion rate of propylene oxide is beneficial to the progress of the reaction.
3 Conclusion
Using the reaction between propylene oxide and chitosan, chitosan derivatives with good dissolving
properties were prepared. The increase of reaction raw materials and the extension of the reaction time are beneficial to the improvement of the degree of substitution of the product, while the increase of the reaction temperature will first increase and then decrease the degree of substitution of the product. ． f between products and raw materials
vrIR
Infrared spectrum proves that the modified chitosan molecular chain (mainly on c_
OH has substituted 1 hydroxypropyl group. It is similar to the raw material CTS Ratio,
The modified product HPCTS has better solubility and hygroscopicity and moisture retention, and
water-soluble chitosan and its derivatives improve with the increase of substitution degree.
It has broad application prospects in textile, food, medicine, daily cosmetics and many other fields.