Introduction to plastic related raw materials
DATE：2022/12/16 8:52:20 / READ： / SOURCE：This station
Polyethylene (PE) is polymerized from ethylene monomer. Polyethylene plastic is made by granulating polyethylene resin as the base material with a small amount of antioxidant, smoothing agent and other plastic additives.
Polyethylene is a kind of density/(8 series of varieties with multiple structures and characteristics, which can be produced by multiple processes. There are hundreds of varieties. At present, many varieties are used, including low-density poly (Z-alkene) (LDPE), high-density polyethylene (HDPE), linear low-density polyethylene (LL refractive index DPE) and some varieties with special properties, such as ultra-high molecular weight polyethylene (UHM WPE), low molecular weight polyethylene (LMWPE) HMWHDPE, VLDPE, VPE, CPE and various ethylene copolymers.
Low density polyethylene (LDPE) is polymerized with ethylene as monomer and organic peroxide as initiator under 100~300MP high pressure, so it is also called high pressure polyethylene. The density is within the range of 0.91~0.925g/cm3. In addition, the density is 0.926~0.940g/cm ³ Is called medium density polyethylene; Very low density polyethylene (VLDPE) is called when the density is below 0.910g/cm3.
Low density polyethylene (LDPE) is an opalescent waxy translucent solid particle, non-toxic and tasteless, with a density in the range of 0.910~0.925g/cm3. Among polyethylene resins, it is the lightest variety except ultra-low density polyethylene resin. Compared with HDPE, its crystallinity (55%~65%) and softening point (90~100 ℃) are lower; Good softness, extensibility, transparency, cold resistance and processability; Good chemical stability, resistant to acid, alkali and salt aqueous solutions; Good electrical insulation and air permeability; Low water absorption; A flammable gas that emits a paraffin odor. Disadvantages: The mechanical strength is lower than that of high-density polyethylene, and the moisture permeability, heat resistance, oxidation resistance and sun aging performance are poor. Under the action of sunlight or high temperature, it is easy to age, decompose and discolor, and the performance is reduced. Therefore, antioxidant and ultraviolet absorber should be added to improve the shortcomings of low-density polyethylene when it is applied. In addition, the adhesiveness and printability of low-density polyethylene products are very poor. In order to improve the application in this field, the surface can only be applied after corona treatment or chemical corrosion. The performance parameters of polyethylene with different densities are shown in Table 2-1.
Table 2-2. See Table 2-3 for comparison of new and old brands.
Table 2-3 Comparison table of new and old national standards for low-density polyethylene resin.
Low density polyethylene resin can be used to form plastic products by extrusion, injection, blow molding and tape casting.
Extruder can be used to extrude films, pipes, sheets, various profiled materials, wire insulation protective layers and other products. In addition, hollow containers such as extrusion blow molding bottles and barrels can be formed by extrusion blow molding method.
The injection molding machine can be used for injection molding of daily necessities, stationery, toys and some industrial accessories.
In addition, extrusion coating and composite film are used to compound with paper, board and other plastic films to form packaging paper with moisture-proof function for packaging various articles.
The rigidity, abrasion resistance and air permeability of medium density polyethylene are between those of low-density polyethylene and high-density polyethylene. Generally, it is only suitable for extruded pipes, lining films of cooking bags and packaging films.
Author：admin