Chitosan is a product of n-deacetylated chitosan. Chitin, chitosan and cellulose have similar chemical structure. Cellulose is hydroxyl group at C2 position, chitin and chitosan are replaced by an acetyl group and an amino group respectively at C2 position. Chitin and chitosan have many unique properties such as biodegradability, cell affinity and biological effect, especially chitosan containing free amino group, which is the only basic polysaccharide in natural polysaccharides. Chitin,Chitosan,Chitosan Oligosaccharide,Carboxymethyl chitosan Allied Extracts Solutions , https://www.alliedbiosolutions.com
The amino groups in the chitosan molecular structure are more reactive than the acetylamino groups in the chitin molecule, which makes the polysaccharide have excellent biological functions and can carry out chemical modification reaction. Therefore, chitosan is considered as a functional biomaterial with greater application potential than cellulose.
Chitosan is the product of natural polysaccharide chitin removing part of the acetyl group, with biodegradability, biocompatibility, non-toxicity, antibacterial, anti-cancer, lipid-lowering, immune enhancement and other physiological functions. Widely used in food additives, textile, agriculture, environmental protection, beauty care, cosmetics, antibacterial agent, medical fiber, medical dressings, artificial tissue materials, drug slow release materials, gene transduction carrier, biomedical fields, medical absorbable materials, tissue engineering carrier materials, medical and drug development, and many other fields and other daily-use chemical industry.
Study on disintegration temperature of freeze-dried products
For the eutectic of freeze-dried products, we are already familiar with it, it is the real cure point of the product. That is, the product must be cooled below the eutectic point before vacuuming, otherwise the product will foam when evacuated, and the product will not exceed this temperature during sublimation heating, otherwise the product will melt. Therefore, the eutectic point is a temperature value that needs to be controlled during the pre-freezing phase and the sublimation phase.
A concept of disintegration temperature is now introduced, which is another temperature different from the eutectic. A normal sublimation product, when the sublimation is carried out to a certain extent, the upper layer of the dry layer and the lower layer of the frozen layer will appear. The interface between the two layers is the sublimation surface, and the sublimation surface is declining as the sublimation progresses. of.
The dried product should be loose and porous and kept in this stable state so that the water vapor which is sublimated from the lower frozen product can pass smoothly, so that all products are well dried.
However, some products that have been dried will lose their rigidity and become sticky when the temperature rises to a certain value. A collapse-like phenomenon occurs, which causes the dried product to lose its loose and porous state, and closes the water vapor of the lower frozen product. The escape path hinders the continuation of sublimation.
As a result, the sublimation rate is slowed down, and the sublimation heat absorbed from the frozen product is also reduced, and the heat supplied by the ply layer will be excessive, which causes the temperature of the frozen product to rise, and when the temperature rises to a temperature above the eutectic point, the product Melting or foaming will occur, causing lyophilization to fail.
The temperature at which disintegration occurs is called the disintegration temperature of the product. For such products to obtain good drying, only the temperature of the dried product in the sublimation is below the disintegration point until the frozen product is fully sublimated, so that the product temperature continues to rise. At this time, due to the absence of frozen ice in the product, even if the dried product disintegrates, it will not affect the drying of the product, because the product has been transferred from the sublimation stage to the desorption drying stage.
The dry product which does not disintegrate and the dry product which disintegrates are not visually different from the naked eye, and the structural change can only be seen under the microscope. When the freeze-drying process of the product is observed under a microscope, if the disintegration is observed, the temperature at this time is the disintegration temperature of the product.
Some products have a disintegration temperature higher than the eutectic temperature, so it is only necessary to control the product temperature below the eutectic point during sublimation; however, some products have a disintegration temperature lower than the eutectic temperature, so it is possible to control sublimation according to the general method. Disintegration occurs, and such products are only sublimed at a lower temperature, so the freeze-drying time must be extended.
The eutectic point of the product can be known by electrical resistance, differential thermal analysis and direct observation by cryogenic microscopy, but the disintegration temperature of the product can only be known by direct observation under a freeze-drying microscope.
The disintegration temperature of the product depends on the variety of the product itself and the type of protective agent; the disintegration temperature of the mixed substance depends on the disintegration temperature of each component. Therefore, when selecting the lyoprotectant of the product, the material with higher disintegration temperature should be selected so that the sublimation drying can be carried out at a very low temperature to save the energy consumption and time of lyophilization and increase the productivity.
The product disintegration temperature test was performed using a freeze-drying microscope to measure the temperature of the ascorbic acid disintegration point, and the collapse temperature was verified using the Bokang Pilot 2-4 pilot test model. The verification results show that the temperature of the disintegration point is closely related to the performance of the freeze dryer. The pre-freezing speed and heat transfer coefficient of the freeze-drying machine determine the structure and rigidity of the product ice shelf, which determines the temperature of the product's disintegration point. At different pre-freezing speeds, the temperature at the disintegration point of the product is quite different.
Protective agents such as glycine, mannitol, dextran, xylitol, povidone and protein mixtures can increase the disintegration temperature of the product.
Attachment: Disintegration temperature of common substances °C.
Disintegration temperature of common substances °C
Substance name
concentration%
Temperature °C
Substance name
concentration%
Temperature °C
Dextran (dextran)
-9
lactose
-32
sucrose
-32
maltose
-32
Polysucrose
-19.5
Methylcellulose
-9
fructose
10
-48
MSG
-50
Drosophila
-44
Ovalbumin
-10
glucose
-40
Polyethylene glycol
-13
D-glucose
-41.5
Povidone (PVP)
-twenty three
gelatin
-8
Sugar alcohol
-45
Inositol
-27
Persimmon alcohol
-26
Sculler
5 to 50
-25
Sodium chloride
-11
glucose
10
-40
GABA
10
-20
lactose
10
-19
NaCl
10
-twenty two
Manitou
10
-4
KCl
10
-11
Sorbitol
10
-42
Acetic acid
10
-27
Orange
10
-44
Tannic acid
10
About <50
Polyglucose low m.wt.
10
-3
Thiamine nitrate
10
-5
PEG600
10
-10
Pyridoxine
10
-4
Gu Lixin
10
-3
ascorbic acid
5
-37
Alanine
10
-3
ascorbic acid
10
-37
β-A
10
-13
Naaskot
10
-33
Arginine
10
-35
Nicotinamide
10
-4
EACA
10
-15
Pantopronium
10
-19
AMCHA
5
-4
Amine acetate
10
-25
Barbital
10
-4