Preparation, Structure And Properties Of Gelatin-chitosan Based Biodegradable Films

Plastics have become the most popular packaging material due to their lightweight, durable, low cost and ease of molding, etc. However, plastic packaging materials are lack of recycling value after disposing and result in severe environment pollution. Therefore, biodegradable and edible new packaging prepared from natural biodegradable material is extremely important for sustainable development.Gelatin is obtained by partial hydrolysis of collagen, and the advantages of gelatin include abundant source, low-cost, good biodegradable property and biocompatibility. However, the film-forming properties, mechanical properties and water resistance of gelatin are poor. The advantages of chitosan include low-cost, good biocompatibility, biodegradable and antibacterial, etc. While the water vapor barrier of chitosan is poor. Gelatin blended with chitosan can improve the film-forming properties and mechanical properties of gelatin, and give good antibacterial property to composite films.In the present thesis, gelatin and chitosan were applied as matrix, the effects of chitosan content on the properties and structure of gelatin-chitosan composite films were systematically studied, the contents of chitosan in the composite films were optimized. X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FT-IR), scanning electron microscope(SEM), light transmittance and thermogravimetric analysis show interaction and good compatibility between gelatin and chitosan. The effects of chitosan content and relative humidity on absorption rate of gelatin-chitosan composite films were studied, and the results show that the moisture sorption ratio of composite films increases with the increase of chitosan content and relative humidity. The effect of chitosan content on tensile property of gelatin-chitosan composite films was studied. We found better property was obtained when chitosan content is 50%.In order to improve the physical and mechanical properties of gelatin-chitosan composite films, the films were prepared by using 50/50(mass ratio) of gelatin/chitosan, and physical modification of the films was carried out by using hydrophilic and hydrophobic modifiers to investigate the effects of modifiers on the structure and properties of gelatin-chitosan films. Glycerol, sorbitol, PEG 200, PEG 400, PEG 800 were used as hydrophilic modifiers, effects of polyol type and content on the structure and properties of gelatin-chitosan films were studied. The effects of polyol on the structure of gelatin-chitosan films were studied by using XRD and SEM. Mathematical model proposed by Peleg was used to study absorption dynamics of composite films at 43% and 75% relative humidity. Flory-Huggins, Oswin, BET(Brunauer-Emmett- Teller) and GAB(Guggenheim-Anderson-de Boer) model were used to fit the sorption isotherm data of gelatin-chitosan composite film modified with polyols. The results indicated that BET and GAB model could accurately fit all adsorption isotherms. Effects of polyol type and content on the properties of gelatin-chitosan films were analysed by testing light transmittance, water contact angle, moisture absorption, water vapor permeability, tensile properties, water solubility and natural degradation, etc. Considering various performance, PEG 200 with content of 20% and glycerol with 30% can be used as plasticizer.Sunflower seed oil was used as hydrophobic modifiers, and effects of sunflower seed oil content on the structure and properties of gelatin-chitosan composite films were studied. The results indicate poor compatibility between gelatin and chitosan, the addition of sunflower seed oil results the decrease in light transmittance, moisture sorption ratio, tensile strength, elongation at break, natural degradation, water vapor permeability and hydrophility.To reduce the water solubility and water vapor permeability, transglutaminase(TGase) was used to crosslink gelatin-chitosan solution containing 20% PEG 200, and effects of TGase content on the structure and properties of composite films were studied. The results indicate that TGase crosslinking results in the decrease of moisture sorption ratio at equilibrium, absorption isotherms and water vapor permeability, and the increase of water contact angle of gelatin-chitosan composite films. So TGase treatment can improve water barrier property of the films. Water solubility, swelling ratio and natural degradation decrease with the increase of TGase dosage, tensile strength and elongation at break of the films increase and then decrease. These phenomena were explained by effects of the cross-linking degree on structure and properties of the films. Composite film crosslinked with 0.6%TGase played a good preservation effect to fresh grapes.The innovations of this thesis are as follows. 1. Effects of plasticizer molecular structure on the aggregation structure of gelatin-chitosan composite films and effects of structure on properties were studied, and the plasticizing mechanism of gelatin-chitosan composite films using different plasticizers was expounded from viewpoint of molecular interactions between plasticizer and gelatin, plasticizer and chitosan. The effects of different plasticizers on the molecular interactions between gelatin and chitosan were discussed as well. 2. Various sorption isotherm models were used to fit the sorption isotherm data of the films plasticized with polyol. The results indicate that BET and GAB model could accurately fit all adsorption isotherms. BET and GAB model constants could explain the water vapor permeability of the films well. 3. Gelatin-chitosan solution containing 20% PEG 200 was crosslinked with TGase, the crosslinked composite film with water vapor permeable significantly decreased was prepared. The crosslinked composite films played a good preservation effect for grapes packing.