Plastic composite membrane barrier performance influenced by what, the most comprehensive analysis

The influence factors of plastic composite membrane blocking in addition to molecular size and physical properties of the materials of gas, need plastic film itself composition, molecular structure and molecular aggregation state internal structure and the compatibility between plastic and permeability material, etc. 1. Molecular polarity when crystallinity certain polar molecules or strong polar molecules due to intermolecular combined closely and make the diffusion of gas in its internal difficulties. Molecular polarity is larger, the resin permeability rate is smaller, the better the performance of gas blocking. Commonly used plastic resin, PET and PVA as the strong polarity resin, PA, PVC resin for polarity, PS is the weak polarity resin, PE, PP for nonpolar resin. Their carbamate resistance increased with the increase of molecules, such as PET and PE to O2 transmittance differs very disparity. Water vapor is a polar molecule, according to the principle of similar miscibility, water vapor in polar molecules in the plastic into and diffusion velocity is greater than the nonpolar plastic molecules, its moisture permeability coefficient value is bigger also. High barrier property of PET molecular polarity is strong, and the moisture permeability coefficient value is greater than the non-polar molecule PE, so the PE is a kind of very good moisture-proof packaging materials. 2. Molecular crystal gas and water vapor through the spread of the energy needed to power a crystalline plastic film is higher than non-crystalline sex plastic film, diffusion coefficient is small, so the crystalline plastic film showed good resistance capability. In the rest of the conditions of the same situation, the higher the plastic membrane molecular crystallinity, showed the better blocking performance. 3. Molecular orientation plastic film for molding tensile and make plastic macromolecular under different degree of orientation, rules of distribution and closely packed, membrane barrier property. The higher the degree of orientation, the barrier property, the better. Especially after dealing with the two-way stretch film, not only the grain size can be greatly reduced, and the degree of crystallinity can be increased. Can be interpreted as tensile, on one hand the original crystalline grain breakage and smaller; Stretching increase the macromolecular orientation on the other hand, arrange more neat and orderly, so as to improve the arrangement of crystallinity and macromolecular density. 4. Molecular hydrophilic plastic film is hydrophilic can mainly with PVA, PA, etc. Due to its strong hydrophilic resin absorbent can make the resin swelling, increase the distance between the molecules is barrier property. Usually, the water vapor diffusion coefficient of hydrophilic plastic film is not a constant, it increases with the concentration of water vapor, lead to the change of the coefficient of permeability is; Rather than hydrophilic plastic film of moisture permeability was almost not affected by the influence of environmental humidity. 5. Environmental temperature temperature have an effect on the molecular structure of the plastic film, the temperature will reduce resin crystallinity, orientation degree, molecular spacing widening, density is reduced, which decreases the barrier performance of plastic film. General plastic film gas transmittance are according to the index law along with the change of temperature increase and decrease, by contrast, the resistance of PVDC became less affected by temperature, the influence of the temperature of the plastic material of aluminum foil hand smaller, therefore, generally choose this two kinds of film do high temperature cooking bags to be more appropriate. Compared with high barrier property of silicon dioxide film coating material of barrier property less affected by temperature. Practice, EVOH, PVDC copolymer, PAN copolymer, PA, such as PEN, PET material is often used as barrier property, including EVOH, PVDC, PAN copolymers and aromatic nylon MXD6 as the barrier property of material, including EVOH, PVDC, PAN copolymers and aromatic nylon MXD6 as the material of high barrier property, and PA, PET for secondary barrier property of materials. EVOH, PVDC, PEN, PEN, PAN is very good barrier property, but the processability is bad, or the price is higher, or performance is not comprehensive, is generally not used alone, is often used to blend, compound coating modification.