| Summary: | 碩士 === 國立海洋大學 === 食品科學系碩士在職專班 === 91 === Since applications and preparations of chitin and chitosan require comprehensions of the characteristics of the materials, determination of the degree of N-acetylation (DA) plays an important role. Many methods have been proposed to find out the degree of N-acetylation. However, these methods are either too complicated or not accurate. Developing a simple, fast, and systematic approach with reasonable accuracy is thus the purpose of this work.
After reacting chitin with alkali solution in various reaction conditions, chitosan with various degrees of N-acetylation can be made. In thermogravimetric analysis (TGA), it is found that the weight loss of water molecules on the first stage occurs before the temperature rises to 120℃ and the percentage of the weight loss decreases along with the rise of the degree of N-acetylation of chitosan. The second stage weight loss of chitosan with various degrees of N-acetylation takes place before the temperature rises to 550℃. The percentage of the weight loss increases along with the rise of the degree of N-acetylation of chitosan.
By using the differential scanning calorimeter (DSC) to determine the degrees of N-acetylation, it is found that an endothermic peak appears accompanying with the loss of water molecules before the temperature reaches to 150℃ while an exothermic peak emerges due to the decomposition of the N-acetyl group in the sample before the temperature rises to 330℃. As the degrees of N-acetylation of chitosan increases, the endothermic and exothermic heat per gram of sample decreases.
In linear least squares regression, TGA has a higher correlation coefficient than DSC. It shows that the degree of N-acetylation is more related to the weight loss than heat changes while heating chitinous products.
In quadratic regression, DSC has a higher correlation coefficient than TGA when the peak of water vaporization is used as the guidepost. The situation reverses when the peak of acetyl decomposition is used as the guidepost.
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