Recently, polypropylene has skyrocketed, driving polyethylene to climb. The short-term L1901 is expected to challenge the previous high of 9,870 yuan / ton, which makes plastic people bloody. As a plastic person, everyone basically knows the term 'polyethylene', then Specific to HDPE, LDPE, LLDPE, how to distinguish, how to identify, how to apply it? The following small series will take you to explore.
Polyethylene is one of the five major synthetic resins. At present, China is the world's largest importer of polyethylene and the second largest consumer. Polyethylene is mainly divided into high density polyethylene (HDPE) and low density polyethylene (LDPE). , linear low density polyethylene (LLDPE) three major categories.
1, low density polyethylene (LDPE)
LDPE is odorless, odorless, non-toxic, and has a density of about 0.910~0.940g/cm3. It is polymerized by oxygen or organic peroxide under high pressure of 100~300MPa. It is also called high pressure polyethylene. It is insoluble in water. , slightly soluble in hydrocarbons, toluene, etc., resistant to most acid and alkali corrosion, less water absorption, can maintain softness at low temperatures, high electrical insulation. LDPE is generally referred to as PE pipe in the irrigation industry, such as The PE pipe for irrigation has the advantages of quick installation, no scaling, convenient maintenance, etc. It is widely used in irrigation systems.
advantage:
LDPE is the lightest grade in polyethylene resin. Compared with HDPE, its crystallinity (55%~65%) and softening point (90~100°C) are lower; it has good softness, extensibility and transparency. Properties, cold resistance and processability; good chemical stability, acid resistance, alkali and salt aqueous solution; good electrical insulation and gas permeability; low water absorption; easy to burn. softer, with good extensibility , electrical insulation, chemical stability, processability and low temperature resistance (resistant to -70 ° C).
Disadvantages:
The disadvantages are poor mechanical strength, moisture barrier, gas barrier and solvent resistance. The molecular structure is not regular, the crystallinity (55%-65%) is low, and the crystalline melting point (108-126 °C) is also low. The mechanical strength is lower than HDPE, the anti-seepage coefficient, the heat resistance and the anti-sun aging property are poor, and it is easy to aging and decolorize under sunlight or high temperature. Therefore, LDPE is added with an antioxidant and a UV absorber to improve the plastic film. Inadequacies.
2, high density polyethylene (HDPE)
HDPE is non-toxic, tasteless, odorless, with a density of 0.940~0.976g/cm3, crystallinity of 80%~90%, softening point of 125~ l 35°C, temperature of use up to 100°C. It is in Ziegler catalyst Catalyzed under low pressure conditions, so high density polyethylene is also known as low pressure polyethylene.
advantage:
HDPE is a kind of thermoplastic resin with high crystallinity and non-polarity formed by copolymerization of ethylene. The original HDPE has a milky white appearance and a certain degree of translucency in a thin section. It has excellent resistance to most domestic and industrial chemistry. The properties, hardness, tensile strength and creep are better than low density polyethylene; wear resistance, electrical insulation, toughness and cold resistance are good; chemical stability is good, insoluble in any organic solvent at room temperature Corrosion resistance to acids, alkalis and various salts. It is resistant to corrosion and dissolution of strong oxidants (concentrated nitric acid), acid-base salts and organic solvents (carbon tetrachloride); the membrane has low permeability to water vapor and air. Low water absorption, the polymer is non-hygroscopic and has good water vapor resistance, and can be used for moisture and anti-seepage purposes.
Disadvantages:
The shortcoming is that its aging resistance is poor, and the environmental stress cracking resistance is not as good as LDPE. In particular, thermal oxidation will reduce its performance. Therefore, HDPE needs to add antioxidants and UV absorbers when making plastic coils. Improve the shortcomings in this regard.
3, linear low density polyethylene
LLDPE is a kind of ethylene and a small amount of high-grade α-olefin (such as butene-1, hexene-1, octene-1, tetramethylpentene-1, etc.) under high pressure or low pressure polymerization under the action of a catalyst. Copolymer, non-toxic, tasteless, odorless, density between 0.915~0.940g/cm3, milky white granules.
Compared with LDPE, LLDPE has the advantages of high strength, good toughness, rigidity, heat resistance and cold resistance. It also has good resistance to environmental stress cracking, tear strength, acid resistance, alkali, organic solvents, etc. Currently LLDPE Almost infiltration into all traditional polyethylene markets, the main application areas are agricultural film, packaging film, wire and cable, pipe, coated products and so on.
In summary, the above three materials play different tasks in different fields. Although all three have good insulation and moisture proof and anti-seepage properties, their non-toxic, tasteless and odorless properties make them in agriculture. Aquaculture, artificial lakes, reservoirs, and rivers are widely used. From the aspects of strong acid, strong alkali, strong oxidant and organic solvent, HDPE anti-seepage and anti-corrosion coils have been fully utilized in chemical and environmental protection industries. Look at LDPE, LDPE has good acid resistance, alkali, salt solution characteristics, and has good extensibility, electrical insulation, chemical stability and low temperature resistance, so it is in agriculture, aquaculture, packaging, especially Low temperature packaging and cable materials are widely used.
After reading this article, in the face of variety selection in various fields, have you chosen the right one?