Vinylidene chloride copolymer

(2) Vinylidene chloride copolymer
1. Introduction to vinylidene chloride copolymer
Vinylidene chloride (VDC) is a high barrier resin with a slightly higher transmittance coefficient of O2 than EVOH, and a lower transmittance coefficient of both CO2 and H2O than EVOH. Pure vinylidene chloride has very poor processability and is difficult to process alone. For this reason, vinylidene chloride is commonly used to copolymerize with other monomers to obtain vinylidene chloride copolymer, commonly known as polyvinylidene chloride, abbreviated as PVDC in English. Copolymers have slightly reduced barrier properties but improved processability. There are a variety of comonomers available for vinylidene chloride, but vinyl chloride (VC) monomer is the most commonly used. The copolymer of vinylidene chloride and vinyl chloride is also known as "sailon", and the content of vinyl chloride is 10%~15%.
The price of PVDC is much lower than EVOH, and it is more commonly used in China.
2. Structural performance
In PVDC, the higher the VDC content, the higher the barrier property, and vice versa.
(1) General properties The appearance of PVDC is white powder, which is a semi-crystalline polymer. The relative density is 1.7, the water absorption rate is less than 0.1%, the thermal shrinkage rate is 25%~50%, the flame retardant is good, it is a self-extinguishing resin, the transparency is good, and it is easy to print.
(3) Mechanical properties The mechanical strength is high, the tensile strength is 80~120MPa, which is higher than EVOH, and the elongation at break is less than 84% longitudinally and 100% laterally; PVDC has good abrasion resistance.
(4) Environmental resistance: Good environmental resistance, resistant to oil, grease and various solvents, weak acid, but not alkali. It has poor UV resistance and is prone to brittleness.
(5) Barrier performance PVDC has excellent barrier properties, with a transmittance coefficient of 0.5~4 (cm3) for O2, 1.2 (cm3) for CO2, and 0.2~6 (g) for water.
PVDC barrier properties are less sensitive to humidity than EVOH. However, it is very sensitive to temperature, and its transmittance coefficient increases by a factor of 100 when the temperature rises from 20°C to 60°C.
3. Molding processing
(1) Processing characteristics PVDC is a heat-sensitive polymer, and heat stabilizers and plasticizers must be added during processing. The heat stabilizer is the same as PVC, but is added in larger amounts.
PVDC is easy to release hydrogen chloride (HCl) gas during processing, and it is easy to corrode the screw, which needs to be protected by chrome plating.
PVDC is easy to decompose, and processing waste should not be reused.
(2) Processing method PVDC can be processed by injection molding, extrusion, compounding, coating and blow molding, and the coating method is the main method.
PVDC can also be used as an intermediate layer for co-extrusion compounding, but because it is easy to decompose, it has more restrictions on composite materials, and can only be co-extruded with materials with lower processing temperatures. The more suitable materials are PVC, EVA, CPE, etc.
4. Scope of application
PVDC barrier materials have a wider range of applications than EVOH, and can be used not only for fresh-keeping packaging materials, but also for carbonated beverages, moisture-proof and flavor-preserving packaging.
(1) Moisture-proof packaging All kinds of dry food, dried vegetables, milk powder, tea, spices, etc.
(2) Fresh packaging shelves for cooked food.
(3) Carbonated beverage packaging: soft drinks, beer, etc.
(4) Marine supplies: fishing nets, ropes, etc.
(5) Coatings.