Preparation, Property Characterization And Fresh-keeping Applications Of Polymer-based Composite Membranes

Carbon nanotubes and zeolites are both porous inorganic materials with unique structure and excellent performance. Recently, they have been received ever-increasing interests as they have been widely used to modify polymer matrix for fabricating composite membranes of various interests. In this thesis, these two inorganic materials were attempted to fabricate polymer-based composite membranes for goods packaging purpose. Thus the properties of resultant membranes and the fillers themselves were examined and polyethylene-based composite membranes were employed to pack cherries for fresh-keeping practice purpose.First of all, the purification and modification of carbon nanotubes and zeolites were studied. Mixed acids of sulfuric and nitric acid at a ratio of 3:1 in volume were used to modify multi-walled carbon nanotubes (MCNT) in order to enhance the compatibility with the polymer and improve its dispersion in the matrix. The result shows that, after processed at 80oC in a water bath for 4 hours along with simultaneous reflux condensation, the IR absorption peaks of multi-walled carbon nanotube become stronger and wider. It can be inferred that there are many groups such as -COOH and -OH over the surface of carbon nanotubes after modifications. At 90oC constant temperature, zeolites were dried to remove moisture and gas prior to any property characterizations and subsequent uses.Five different MCNT-incorporated composite membranes were made by incorporating different loadings of MCNT into polyethersulfone. Our results show the tensile strength declines as the MCNT content increases. The MCNT content is found to have little effect on the weight loss features of the membranes. In the meantime, MCNT and polyethersulfone independently follow their own thermal decomposition behaviors. However, these MCNT-filled composite membranes are not good in quality as carbon nanotube particles can not evenly dispersed in the matrix.A series of zeolite-incorporated membranes were fabricated by incorporating different amounts of beta zeolite into polyethylene. The tear, friction, stretching, resistance and optical properties of the resultant membranes were examined and the X-ray diffraction, TGA, FTIR analyses were carried out. Experimental results show that, the microstructure and properties of zeolite and organic polymer matrix can be independently reserved. The presence of zeolites has influenced all the physical properties of resultant composite membranes. Over all the composite membranes, the M3 membrane containing 7.5 wt% of zeolite has appreciated integrated property.Polyethylene-based composite membranes were then used to pack the freshly-harvested cherries for fresh-keeping considerations. The fresh-keeping properties were evaluated by observing the changes in the appearance of cherries and weight loss, refractive index, respiratory strength and hardness. It is found that the addition of H-βzeolites could restrain the respiration rate of cherry, to some extent, and then extend the shelf life. Among the composite membranes, the M3 at zeolite content of 7.5 wt% is the best and the shelf life of cherry can be prolonged up to 13 days.