Improvement on physical properties of pullula n films by cross-linking
Date Issued
2014
Date
2014
Author(s)
Chen, Chieh-Ting
Abstract
Pullulan is an extracellular polysaccharide originated from Aureobasidium pullulans. The linear structure of pullulan consist of maltotrioses with α-1,6 glycosidic linkages. The purified pullulan films formed by casting or extruding methods possess several advantages including high transparency, low toxicity, good biodegradability, good mechanical properties, and low oxygen permeability, which are preferable features for packaging of food. However, the applications of pullulan films on packaging are limited due to its high solubility in water. In this study, glutaraldehyde was used as cross-linking reagent to improve the water resistance and physical properties of pullulan film. It reacts with the hydroxyl group on pullulan under mild reaction condition, forming acetal linkages between molecules of pullulan. The glycerol as plasticizer and high molecular weight fermented pullulan previously investigated in our lab, were also applied in this study to evaluate their functions and mechanisms in film forming. Effects of cross-linking reagent with different concentration on physical properties, including water absorptions, swelling behaviors, water vapor permeability and tensile strengths of films were determined, and the chemical structure of cross-linked pullulan film were also analyzed by Fourier transform infrared spectroscopy (FT-IR). When the ratio of crosslinking reagent to pullulan reaches 0.01 g/g, the water resistance was improved significantly. Better resistance to water and less swelling degree were observed when crosslinking reagent increased. The decreasing O-H stretching vibration (3300 cm-1) of films in FT-IR spectra indicate a higher degree of crosslinking was formed with increasing concentration of crosslinking reagent. The mechanical properties increased at 0.005-0.015 g/g of glutaraldehyde per gram of pullulan, and start to decrease when higher than 0.025 g/g of glutaraldehyde per gram of pullulan was used. However, the fragile property in films with high degree of cross-linking is unfavorable for industrial uses. In addition, the fermented pullulan possesses a high molecular weight of 2,570 kDa, which is much higher than commercial pullulan, and it exerts better performance in all properties we had tested. The addition of glycerol as plasticizer enhanced the extensibility of films as well as the hydrophilicty, resulting in higher water vapor permeability. It might be attributed from the disturbance of crosslinking. In summary, the crosslinking strategy effectively increase the weakness of pullulan films, yet needs futher studies such as optimization of the ratio of crosslinking reagent/glycerol for future application on food packaging.
Subjects
戊二醛
甘油
縮醛
機械性質
水氣穿透率
Type
thesis
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