Preparation And Evaluation Of Polyolefin-Based Antimicrobial Multilayer Film Using Plasmas

In the current food packaging industry, polyolefin film is the most widely used packing material. Chitosan (CHI), with good antimicrobial capacity, excellent film forming properties and permselectivity, is a new potential packing material. Chitosan, mixed with preservatives, was coated in inlayer of polyolefin film to prepare antimicrobial multilayer film. The polyolefin film was treated with low-temperature plasma to improve the surface properties. The effect of surface modification to polyolefin membrane treated with different methods was evaluated. The antibacterial effects of the film and the release rule of antimicrobial substances were primarily evaluated. The research provided an experimental basis for the application of the antimicrobial film materials in food industry.1. The polyolefin film treated with low-temperature plasma, was studied by energy dispersive spectrometer and X-ray photoelectron spectroscopy to analyze the surface chemical elements. The energy dispersive spectrometer showed that after the dielectric barrier discharge plasma, weight percent of oxygen on polypropylene surface relatively reached maximum of11.62%. The X-ray photoelectron spectroscopy showed that the occurrence of oxygen-containing functional groups (i.e., C-O, C=O and O-C=O-) of the plasma-treated PE films increased from those of the untreated one. The treated film with was also studied by scanning electron microscopy and atomic force microscope to analyze the surface micro appearance. It showed that the surface of polyethylene treated with inductive coupled plasma, polypropylene and polyethylene terephthalate-polypropylene treated with dielectric barrier discharge plasma were rough. The vacuum plasma showed minimal impact on the film. Surface wettability was determined by water contact angle measurement. The water contact angle of polyethylene treaded with vacuum plasma and dielectric barrier discharge plasma change was the biggest about50°, followed by polyethylene terephthalate-polypropylene treated with vacuum plasma, changed form91.85°to38.96°, indicating that the vacuum plasma enhanced hydrophilicity of the films.2. Antibacterial effects of the multilayer films and compounded antimicrobials were tested. The target bacteria were the primary spoilage bacteria in food-St.aereus., E.coli, and B.subtilis. Chitosan, mixed with potassium sorbate, ε-poly-L-lysine and Calcium propionate showed good antibacterial effects against St.aereus., E.coli, and B.subtilis.However, contrasting with chitosan, there is a slight decline in the antibacterial effects against St.aereus and B.subtilis of chitosan-sodium benzoate compounded antimicrobials, but the antibacterial effects against E.coli increased significantly. The multilayer films exhibited appreciable antibacterial activity against E.coli and B.subtilis. The inhibition rates on E.coli, and B.subtilis reached almost100%, when concentration of preservatives reaches a maximum, while, the rates on St.aereus. was85%. Analysis of scanning electron microscopy shows that different layers had good compatibility. Tensile strength of multilayer films was no obvious change compared with that of polyolefin film.3. Considering how packing material should be used in practice, we researched the release rule of antimicrobial substances from the multilayer films in different temperatures, acidity levels and food simulation systems. Results highlight that antimicrobial substances release rate increased with the temperatures, acidity and initial concentration in the multilayer films of preservatives. Conversely, the release rate decrease significant with the increase of the ionic strength such as adding sodium chloride.