Adsorption And Diffusion Behavior Of Solvent Molecules In Biaxially Oriented Polypropylene Films

The residue solvent problem in food flexible packaging is a hot issue in the food industry and the packaging industry in recent years,which is related to food safety and consumer health.Residue solvent in food flexible packaging are mainly derived from the inks used by packaging companies to print plastic flexible packaging,as well as the polyurethane adhesives used in plastic composites.Therefore,the study of the adsorption and diffusion behavior of solvent molecules in food flexible packaging films has theoretical guiding significance for the production of flexible packaging materials.Biaxially oriented polypropylene film(BOPP)is one of the most commonly used materials for food flexible packaging and is often used as a composite film printing layer.In this paper,two kinds of BOPP films(unmodified BOPP film and nano-SiO2 modified BOPP film)prepared by laboratory research are evaluated,and a self-made permeation chamber + GC test equipment is built.The test method of solvent molecular diffusion coefficient,permeability coefficient and solubility was established to investigate the adsorption and diffusion behavior of single solvent or two-component mixed solvent on BOPP film.The effect of film microstructure(crystallinity)on the adsorption-diffusion behavior of small molecule solvents was studied,and the feasibility of nano-modified silica to modify the solvent residue in the film was verified.This provides theoretical guidance for the production of flexible packaging materials that are more food safe.The experimental results show that for ethyl acetate,butyl acetate,ethanol,isopropanol,acetone,butanone solvent molecules,their permeation parameters(diffusion coefficient,permeability coefficient and solubility)in modified BOPP film are smaller than unmodified BOPP film.For solvent molecules with the same functional group,the permeation parameters increase as the number of carbon atoms increases.The permeation parameters of solvent molecules of different polarities decrease as the polarity of the molecule increases.The reasons for the permeability parameter of the solvent molecule in the modified BOPP film are smaller than that of the unmodified BOPP film are as follows: A layer of high crystallinity dense layer exists in the modified BOPP film,which makes it difficult for solvent molecules to penetrate.The crystallinity of the nano-silica modified BOPP film is 3.7% higher than that of the unmodified film.The nano-silica particles promote the formation of a large number of small-sized crystal grains in the polypropylene matrix.These crystal grains form the network fiber bundle structure,which makes the solvent molecule diffusion path tortuous,and further improves the barrier property of the film to solvent molecules.In the two-component mixed solvent in which ethyl acetate is the main component,when ethyl acetate is mixed with a highly polar solvent such as ethanol or methyl ethyl ketone,the permeation parameter of ethyl acetate is decreased;When ethyl acetate was mixed with a less polar butyl acetate,the permeation parameter of ethyl acetate increased.