Comparison of properties of HDPE, LDPE and LLDPE resin materials

Production raw materials, molecular structure, density, crystallinity, softening point, corrosion resistance, temperature range, mechanical properties, tensile strength, elongation at break, environmental stress cracking resistance and industrial The production principle, process and additives are used to analyze the engineering application scope of the three materials and the characteristics and applicable engineering scope of their respective applications. Polyethylene (Polyethylene) is one of the five major synthetic resins, and it is the variety with the largest production capacity and the largest import volume among synthetic resins in my country. At present, my country is the world's largest importer of polyethylene and the second largest consumer. Polyethylene is polymerized from ethylene monomer. Polyethylene plastic is a plastic product made of polyethylene resin as the base material and adding a small amount of antioxidants, slip agents and other additives. Polyethylene is mainly divided into three categories: linear low density polyethylene (LLDPE), low density polyethylene (LDPE) and high density polyethylene (HDPE). 1 High-density polyethylene, the English name is“High Density Polyethylene”,Referred to as“HDPE”. HDPE is non-toxic, tasteless and odorless, and its density is 0.940-0.976g/cm3. It is the product of polymerization under low pressure under the catalysis of Ziegler catalyst, so high density polyethylene also becomes low pressure polyethylene. HDPE is a kind of thermoplastic resin with high crystallinity and non-polarity formed by the copolymerization of ethylene. The appearance of the original HDPE is milky white, and it is translucent to a certain extent in the thin section. It has excellent resistance to most household and industrial chemicals, it can resist the corrosion and dissolution of strong oxidants (concentrated nitric acid), acid-base salts and organic solvents (carbon tetrachloride). The polymer is non-hygroscopic and has good water vapor resistance and can be used for moisture and seepage resistance. The disadvantage is that its aging resistance and environmental stress cracking are not as good as LDPE, especially thermal oxidation will reduce its performance, so HDPE adds antioxidants and UV absorbers when it is made into plastic coils to improve its performance. shortcomings. 2 Low density polyethylene, the English name is“Low density polyethylene”,Referred to as“LDPE”. LDPE is non-toxic, tasteless and odorless, with a density of 0.910-0.940g/cm3. It is polymerized under the high pressure of 100-300MPa with oxygen or organic peroxide as a catalyst, and it is also a high-pressure polyethylene. Low-density polyethylene is the lightest variety of polyethylene resins. Compared with HDPE, its crystallinity (55%-65%) and softening point (90-100℃) are lower; it has good flexibility, extensibility, transparency, cold resistance and processability; its chemical Good stability, acid, alkali and salt aqueous solution; good electrical insulation and air permeability; low water absorption; easy to burn. It is soft in nature and has good extensibility, electrical insulation, chemical stability, processing performance and low temperature resistance (can withstand -70 ° C). The disadvantage is that its mechanical strength, moisture barrier, gas barrier and solvent resistance are poor. The molecular structure is not regular enough, the crystallinity (55%-65%) is low, and the crystalline melting point (108-126°C) is also low. Its mechanical strength is lower than that of high-density polyethylene, and its impermeability coefficient, heat resistance and sunlight aging resistance are poor. Antioxidants and UV absorbers are added to remedy its deficiencies. 3 Linear low density polyethylene, English name“Linear Low density polyethylene”,Referred to as“LLDPE”. LLDPE is non-toxic, tasteless and odorless, and its density is between 0.915 and 0.935g/cm3. -1, etc.) A copolymer formed by high pressure or low pressure polymerization under the action of a catalyst. The molecular structure of conventional LLDPE is characterized by its linear main chain, with only a few or no long branches, but contains some short branches. The absence of long chain branches makes the polymer more crystalline. Compared with LDPE, LLDPE has the advantages of high strength, good toughness, strong rigidity, heat resistance and cold resistance. In summary, the above three materials play their respective important tasks in different types of anti-seepage projects. HDPE, LDPE and LLDPE all have good insulation, moisture-proof and anti-seepage properties, and their non-toxic, tasteless and odorless properties make them extremely suitable for applications in agriculture, aquaculture, artificial lakes, reservoirs, and rivers. It has been widely promoted and widely used by the Fisheries Bureau of the Ministry of Agriculture of China, the Shanghai Fisheries Research Institute, and the Fishery Machinery and Instrument Research Institute. In the medium environment of strong acid, strong base, strong oxidant and organic solvent, the material properties of HDPE and LLDPE can be well used and utilized, especially the properties of HDPE in resistance to strong acid, alkali, strong oxidation and organic solvent. The aspect is much higher than the other two materials, so HDPE anti-seepage and anti-corrosion coil has been fully utilized in the chemical and environmental protection industries. And low density polyethylene also has good acid, alkali, salt solution characteristics, and has good extensibility, electrical insulation, chemical stability, processing performance and low temperature resistance. Therefore, it is widely used in agriculture, aquaculture, packaging, especially low-temperature packaging and cable materials.