Preparation And Properties Of Bacterial Cellulose Polysaccharide-based Composite Films

In order to reduce the environmental problems caused by non-biodegradable plastics,composite films were obtained by compounding different biodegradable polymers,which is expected to be used as a substitute for synthetic plastics for food packaging.The composite films were based on bacterial cellulose(BC),with chitosan(CS)and galactomannan(GG),which are extremely rich in nature,as functions components.The main findings of this thesis are as follows:(1)The bacterial cellulose/polyvinyl alcohol/chitosan composite films were prepared and characterized by the impregnation method.The original BC wet film was first used.BC/PVA/CS composite films were prepared by immersing BC in a mixed solution of CS and PVA with different concentration ratios.Fourier transform infrared spectroscopy(FTIR)and X-ray diffraction(XRD)indicated that BC,CS,and PVA had good compatibility forming intermolecular hydrogen bonding forces.Compared with BC,the excellent toughness of PVA could increase the elongation at break of the films.CS endowed the composite films antibacterial activities.When the concentrations of CS and PVA were 0.5% and 2.0% w/v,respectively,the composite films exhibited best inhibitory effect against Escherichia coli with the width of the inhibitory zone being 1.450±0.150 mm.(2)The forms of BC and chitosan participating in the films formation were improved.The bacterial cellulose/polyvinyl alcohol/chitosan composite films were prepared and characterized by the blending method.The research on the preparation of composite films using original BC wet film state has proved its feasibility,but the antibacterial properties of the products were not prominent.Therefore,BC was improved to being dispersed suspension liquid to prepare the composite films.Considering that direct mixing of BC suspension liquid and CS solution would cause flocculation of BC,PVA were first blended with BC to prepare a BC/PVA base film which was used as a control.At the same time,CS was made into chitosan nanoparticles(CSNPs).A series of characterizations of CSNPs revealed that CSNPs exhibited weaker crystalline properties and higher thermal stability than those of CS,and CSNPs possesses characteristics of easy agglomeration.(3)The bacterial cellulose/polyvinyl alcohol/chitosan composite films were prepared and characterized by the blending method.Two kinds of chitosan(CS and CSNPs)were incorporated into the above BC/PVA matrix to obtain BC/PVA/CS,BC/PVA/CSNPs composite films and the effects of different CS and CSNPs on the properties of films were compared.Scanning electron microscopy(SEM)and XRD showed that there was good compatibility between CS or CSNPs and BC/PVA matrix,but some nanoparticles agglomerated in the case of CSNPs films.CS and CSNPs respectively increased and decreased the tensile strength of the composite film,but the minimum value of all composite films was as high as 45.39±2.80 MPa.The hydrophilic groups of CS increased the moisture content of the composite films,and the compact nanostructure of CSNPs significantly reduced the penetration of water vapor in the films.Due to the higher surface charge density of CSNPs,the antibacterial properties of BC/PVA/CSNPs composite membranes are significantly greater than BC/PVA/CS at the same concentration.When the added concentration was 2.5% w/v,the width of the bacteriostatic zone of the BC/PVA/CSNPs and BC/PVA/CS composite membranes was 10.33±1.55 and 7.73±0.20 mm,respectively,which were much larger than those of composite films prepared with original BC wet film.BC/PVA/CS composite films had higher transparency,but the average transmittance at 200-280 nm was more than 30%,illustrating the poor ultraviolet(UV)barrier ability.While,BC/PVA/CSNPs composite films showed better UV blocking performance compared with BC/PVA/CS films.(4)The bacterial cellulose/galactomannan/chitosan composite films were prepared and characterized by the blending method.Considering the potential harm of PVA as a synthetic polymer,galactomannan from guar gum(GG)was incorporated to prepare composite films for the purpose of further improving UV barrier abilities as well.BC/GG was fabricated used as a control,and then BC/GG/CS and BC/GG/CSNPs composite films were obtained by embedding CS and CSNPs into BC/GG matrix.It was found that the interaction between CSNPs and the BC/GG matrix was not as strong as CS.As a consequence,CS improved the tensile strength and elongation at break of the composite film,while CSNPs caused a decrease in mechanical properties.Meanwhile,the capability of CSNPs was inferior to CS to decrease the moisture content,water solubility and water vapor permeability of the composite films.Compared with BC/GG film,the addition of low-concentration(0.5% w/v)CS and high-concentration(2.5% w/v)CSNPs enhanced the UV blocking performance of the films.However,the average transmission at 200-280 nm is less than 11% in the case of all composite films.At the corresponding concentration of CS or CSNPs,the BC/GG/chitosan composite film showed better UV(200-280 nm)barrier performance than BC/PVA/chitosan due to the presence of GG.