How to improve the barrier properties of plastic packaging materials
2018/8/6 17:51:46
At present, the improvement of barrier properties is mainly targeted at plastic packaging materials. Commonly used improvement methods are:
Multi-layer composite
The film of different materials is compounded, and the barrier property of the obtained composite film is related to the number of layers to be composited, the barrier property of each layer of the material itself, and the thickness of the composite layer. At present, there are commonly used three-layer, five-layer and seven-layer composite films. Meanwhile, in order to obtain a high barrier composite film, the intermediate layer is usually made of a material having excellent barrier properties such as aluminum foil, EVOH, PVDC, PVA, PA, and the like. The composite processes used include dry compounding, multilayer coextrusion, and multilayer coextrusion casting.
Surface modification or plating
The surface modification mainly changes the polarity of the surface of the material by chemical reaction. The polarity of the polyolefin surface is enhanced by, for example, plasma polymerization to increase the gas barrier property. It is also possible to form an inorganic metal or an oxide or the like on the surface of a plastic film such as PET by a physical or chemical method to form a barrier layer of several tens to hundreds of nanometers. The method can increase the oxygen barrier and moisture barrier properties of the ordinary film by several tens to hundreds of times, and even obtain a transparent, high-strength composite film, thereby having great application potential.
Add filler
The addition of an inorganic filler to the polymer not only improves the mechanical strength of the material, but also effectively improves the barrier properties of the material. Especially since the 20th century, the rapid development of nanotechnology has led to the emergence of various new types of nano-fillers, opening up a new path for the preparation of high-barrier materials. The most widely studied and currently commercialized is a composite of nanoclay and polymer. Nanoclay is a layered and impermeable silicate. Due to its high aspect ratio, the addition of a small amount of nanoclay in the polymer can make the diffusion path of the gas molecules tortuous, thereby reducing the gas permeability of the material and improving the barrier property. Studies have shown that both non-polar PE, PP, and polar PA, PET can effectively reduce the transmission of O2 or CO2 by adding nano-montmorillonite or kaolin. Compared with ordinary PET, the PET with montmorillonite can increase the barrier property by 3~4 times, which can replace the traditional glass bottle for beer packaging. Other nano-fillers such as nano-silver, nano-titanium dioxide and other nano-metals and metal oxides, as well as nano-carbon materials, graphene, etc., have great application potential in the packaging field. In particular, due to environmental pollution and energy shortages, there is an urgent need to develop polymers that are both biodegradable and capable of meeting strength and barrier properties. However, many degradable polymers are faced with poor strength and sensitivity to water vapor. Composites obtained by combining them with nanoparticles will be expected to improve in these properties. For example, montmorillonite can be combined with polylactic acid (PLA) by solution intercalation, in-situ intercalation or melt intercalation to improve the mechanical properties, thermal stability and gas barrier properties of PLA. The addition of nano-silver and montmorillonite to the starch, due to the synergistic effect of nano-silver and montmorillonite, can reduce the diffusion coefficient of water molecules in the starch film by about 50%, and reduce the oxygen permeability coefficient by 85%. . Nanoparticles having antibacterial, antioxidative and the like functions can also be used for preparing active packaging to more effectively inhibit the growth of microorganisms on the surface of packaged foods and the oxidation of nutrients, thereby extending the shelf life. However, when used as food packaging, the migration and safety of nanomaterials is also one of the key issues to be considered. It is urgent to establish effective methods for detection and evaluation.