Detailed explanation of different properties and structural features of PA . films
Since the amino groups on the molecular chain of PA can form strong intermolecular hydrogen bonds, PA has high Tf and thermal stability, high mechanical properties, high oxygen barrier, carbon dioxide barrier, aroma barrier, solvent resistance and other properties.
Of course, the highly polar amino group also leads to the water absorption performance of PA, the adsorbed water molecules will open the intermolecular hydrogen bonds of PA, reduce the hardness and improve the elasticity of PA, so that PA has better puncture resistance, viscosity and heat forming performance. These outstanding properties of PA, which are essential for packaging materials, are retained even after film formation.
PA exhibits high tensile strength, toughness and puncture resistance, therefore the composite film prepared with it as a substrate also has these excellent properties. The mechanical properties of PA are related to the amount of moisture absorbed, water as plasticizer can reduce the tensile strength and hardness of PA, and improve the toughness, impact performance and elasticity of the material. If it is single-mode PA, PA can absorb more water within minutes, even if PE blocks water outside PA, the mechanical ability of PE/PA/PE composite film will be affected by water.
See more: PE STRETCH FILM
PA films have a medium barrier to oxygen, 2 orders of magnitude higher than polyolefins and 1~2 orders of magnitude lower than high barrier EVOH membranes. The barrier properties of EVOH will drop to typical PA levels (such as MXD6) under higher humidity conditions. PA exhibits high barrier properties for low-level small molecule hydrocarbons, as well as for low-polar aromatics in foods (limonene, camphor oil, vanillin, menthol), only for highly polar molecules like water, ethanol, methanol… the barrier properties of PA will decrease.
Hot pressing performance:
If the PA film is used as the inner layer (heat sealing layer) of the composite film, it is usually required that the outer layer of the composite film has a higher heat resistance than the inner film before the new PA layer can be heat-sealed. If PA is used as the outer layer and PE is used as the inner layer, even if a higher heat sealing temperature is used, the sealing knife will generally not stick to the PA film and may experience sudden cooling.
Other properties of PA:
BOPA film has high rigidity, good printing performance, high tensile strength, high puncture resistance and low tensile fracture growth rate. The deformation of BOPA film under tension is elastic deformation, not viscous deformation, so it is more suitable as the substrate of vacuum aluminum plating film or vacuum silicon coating film. BOPA also has good printing performance due to small stretch deformation.
Compared with unstretched oriented PA (molded PA film, i.e. CPA), the oxygen barrier property of BOPA is 30% higher than that of CPA, but this difference is not much different from PET film plastic, for PET the barrier property of biaxially stretched polyester film (BOPET) is 3 times higher than that of non-stretch cast polyester film (CPET). OPET is 3 times higher than CPET.
Compared with BOPA, CPA has a lower modulus and easily produces ductility under tension, after which viscous deformation occurs, after which the molecular chain is stretched and oriented to cause stiffening stress. Compared with BOPET, although the elastic modulus of BOPA, its tensile strength and darts impact strength are also higher than BOPET, and its oxygen barrier property is higher than BOPET.