Synthetic resin barrier properties

日期:2019/5/17 8:24:41 / 阅读: / 来源:本站

Synthetic resin barrier properties
Commonly used synthetic resins have certain barrier properties. In general, high barrier resins are polyvinylidene oxide (PVDC), ethylene-vinyl alcohol copolymer (EVOH), aromatic nylon (MXD); medium barrier resins, polyamide (PA), polyester ( PET, PEN); polyethylene, polypropylene resin, has a good water vapor barrier.
1. Polyvinyl chloride (PVC)
Polyvinyl chloride has a certain gas barrier property, and water vapor barrier properties are poor. The hard PNC film has better oxygen barrier properties, while the soft PVC film has poor barrier properties. Soft PVC film does not have good barrier properties, but it is transparent, soft and self-adhesive. As a packaging film for meat in the supermarket, the meat can be kept red and the display effect is good. Therefore, the soft PVC film can be used as a food wrap for short shelf life.
2. Polyethylene
Polyethylene has poor gas barrier properties and good barrier to water and water vapor. Compared with LDPE, HDPE has higher crystallinity and a higher proportion of crystallization zone, and its gas and water vapor barrier properties are better than LDPE. LDPE is 5-6 times more breathable than HDPE.
Due to the excellent molding processability of polyethylene, the hot soldering initiation temperature is low, and the moisture resistance is good, and it is often used as a moisture-proof protective layer of a multilayer composite high barrier film. For example, polyethylene and EVOH are compounded, and their high barrier to moisture allows a moisture-sensitive resin such as EVOH to better exert its barrier effect on gases.
3. Polypropylene
The unstretched polypropylene film has poor barrier properties, but its gas barrier property is higher than that of LDPE and lower than HDPE. The stretch oriented polypropylene film (BOPP) has a significant improvement in moisture and air barrier properties. The coated polypropylene film also has good barrier properties. Therefore, BOPP film, vacuum aluminum plated PP film, PVDC coated PP film have good barrier properties.
The polypropylene film has good moldability. The film is highly transparent and has high mechanical properties. The stretched oriented BOPP film has poor heat sealability. When making a bag, a BOPP film having a heat seal layer or a blended heat seal resin is used. Among the multilayer high barrier films, a PP resin having a high barrier property to moisture is often used as an outer layer of a moisture sensitive resin such as EVOH.

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