Linear low-density polyethylene LLDPE (1018M) is white powder/granular, tasteless and odorless, with a density of 0.918~0.935g/cm3. It is understood that LLDPE is a molecular structure formed by the copolymerization of ethylene and a small amount of α-olefin on the main chain of linear ethylene, with very short comonomer branches. Compared with LDPE, it has a higher softening temperature and melting temperature. , has the advantages of high strength, good toughness, high rigidity, good heat resistance, and good cold resistance. It also has good resistance to environmental stress cracking, impact strength, tear resistance, etc., and is resistant to acids, alkalis, organic solvents, etc. It is used in fields such as industry, agriculture, medicine, health and daily necessities.
Low-density polyethylene, also known as high-pressure polyethylene (LDPE), is the lightest variety among polyethylene resins. It is milky white, tasteless, odorless, non-toxic, and matte waxy particles. It has good softness, extensibility, electrical insulation, transparency, easy processing and certain breathability. It has good chemical stability and is resistant to alkali and general organic solvents. Suitable for food packaging of seasonings, pastries, sugar, preserves, biscuits, milk powder, tea, fish floss, etc. Pharmaceutical packaging such as tablets and powders, fiber product packaging such as shirts, clothing, knitted cotton products and chemical fiber products, etc.
The following characteristics of LLDPE are better than LDPE:
Melt processing performance:The melting performance is determined by the relative molecular weight , relative molecular mass distribution, long chain branches and other factors. Both LDPE and LLDPE have extremely good rheology or melt flowability. But LLDPE has less shear sensitivity because it has a narrow molecular weight distribution and short chain branches. During shearing processes (such as extrusion), LLDPE maintains a greater viscosity and is therefore more difficult to process than LDPE with the same melt index. LLDPE has a higher melt viscosity than LDPE, so the extrusion load increases during extrusion molding and the calorific value also increases. Due to the short melt stress relaxation time, the residual stress in the injection molded product is small, so the shrinkage rate is small and the warpage is also small. In melt extension, LLDPE generally has lower viscosities at various strain rates. In other words, it will not strain harden when stretched like LDPE. As the deformation rate of polyethylene increases, LDPE shows a surprising increase in viscosity, which is caused by molecular chain entanglement.
Thermal properties:The melting point of polyethylene is proportional to the completeness of crystallization and grain size. Therefore, the melting point of LLDPE is 10-15 degrees Celsius higher than that of LDPE. Even if the same LLDPE, the more carbons the copolymer monomer has, the higher its melting point. This law also applies to the Vicat softening point. The heat sealing performance of the film corresponds to the completely melted heat sealing temperature. The heat sealing temperature of LLDPE is 10-15 degrees Celsius higher than that of LDPE, and the melting point range of LLDPE is narrower than that of LDPE, so the heat sealing performance of the film is good. Regarding the cold resistance of LLDPE, judging from the relationship between catalytic temperature and melt flow rate, the embrittlement temperature of LLDPE is lower than that of LDPE and HDPE, which indicates that it can withstand lower temperatures.
Physical properties:Structurally, LLDPE is different from LDPE in the number and type of branches. High-pressure LDPE has long branches, while linear LDPE only has short branches. LLDPE forms a more crystalline structure because long chain branches are not present. The greater crystallinity of LLDPE produces a higher rigidity product. The tensile properties of LLDPE are higher than those of LDPE. The tensile number and tensile yield strength are large, especially the tensile breaking strength and elongation at break. Generally, the energy required for fracture can be calculated from the area of the stress-strain curve. Use this as an indicator of resin rigidity. It is understood that the physical and mechanical properties of LLDPE film are significantly better than LDPE, and its softness, toughness, cold resistance, and puncture resistance are all better than LDPE.
