Introduction to Low-Density Polyethylene (LDPE):
Basic Information: Low-density polyethylene (LDPE), also known as high-pressure polyethylene, is polymerized from ethylene through a free radical polymerization mechanism under high temperature and high pressure conditions. It is milky white, odorless, stinkless, non-toxic, and appears as waxy particles without a glossy surface.
Performance Characteristics
Physical Properties: It is light in weight, with a density ranging from 0.910 to 0.925 g/mL and a crystallinity of 45% to 65%. The film is slightly milky and transparent, soft. Its strength is smaller than that of high-density polyethylene, while its impact resistance is greater than that of high-density polyethylene.
Thermal Properties: It is resistant to cold, low temperatures, and relatively high temperatures. A relatively thick film can withstand the sterilization process of being soaked in 90°C hot water. The melting point is 110-115°C, and the processing temperature is 150-210°C. In an inert gas environment, it remains stable even at a temperature of up to 300°C. However, when the melt comes into contact with oxygen, it is prone to degradation.
Chemical Properties: It has good moisture resistance and stable chemical properties, and is insoluble in common solvents. It has relatively large air permeability and poor oil resistance. The products can be slowly swollen, and they will age after long-term exposure to ultraviolet light and heat.
Processing Properties: It has good flexibility, extensibility, electrical insulation, heat-sealing properties, and easy processability, making it suitable for various thermoplastic molding processes.
Production Methods
Tubular Method: The reactor is a long and slender high-pressure alloy steel tube. The materials flow in a plug-like manner inside the tube, with no backmixing phenomenon. The reaction temperature varies along the length of the reaction tube, and the resulting polyethylene has a relatively wide molecular weight distribution. The reaction pressure is approximately 200-350 MPa, the temperature is 250-330°C, the fluid velocity is 10-15 m/s, the single-pass conversion rate is 20%-34%, and the maximum single-line production capacity can reach 100000 tons per year.
Kettle Method: The materials can be fully mixed, the reaction temperature is uniform, and it can also be operated in different zones to obtain polyethylene with a relatively narrow molecular weight distribution. The reaction pressure is usually lower than that in the tubular method, ranging from 110-250 MPa, the temperature is 130-280°C, the single-pass conversion rate is 20%-25%, and the maximum single-line production capacity can reach 180000 tons per year.
Application Fields
Packaging Field: It is suitable for packaging seasonings, pastries, sugar, preserved fruits, and other food items. It is also used for packaging tablets, powders, and other pharmaceutical products. Additionally, it can be used for packaging fiber products such as shirts and clothes, as well as for packaging daily chemical products like laundry powder and detergents. It is usually used as the inner layer of composite packaging bags, that is, the heat-sealing base material of multi-layer composite films.
Agricultural Field: It can be used to manufacture agricultural films, such as greenhouse films and agricultural films, which can play roles such as heat preservation, moisture retention, and pest prevention, and contribute to the growth and protection of crops.
Medical Field: It is used to manufacture medical devices, such as syringes, infusion tubes, blood bags, etc. Due to its good flexibility and chemical stability, it can meet the usage requirements of medical products.
Other Fields: It can also be used for injection-molded products, such as plastic toys, stationery, and daily necessities; as well as for blow-molded hollow products, such as plastic bottles and plastic barrels. In addition, it has applications in fields such as electronics and electrical engineering, mechanical equipment, and automotive manufacturing.
| Product name: |
Low Density Polyethylene |
| Appearance: |
white powder |
| CAS No.: |
9002-88-4 |
| EINECS No.: |
618-339-3 |
| Molecular formula: |
(C2H4)n |
| Monomer molecular weight: |
28.05 |
| Density: |
0.962g/mLat 25°C |
| Melting point: |
92°C |
| Boiling point: |
48-110 °C(Press: 9 Torr) |
| Flash point: |
270°C |
| water-solublility: |
Soluble in acetone and benzene. Insoluble in water. |
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