How to distinguish HDPE, LDPE and LLDPE

Polyethylene classification

(1) LDPE: low density polyethylene, high pressure polyethylene

(2) LLDPE: linear low density polyethylene

(3) MDPE: medium density polyethylene, bimodal resin

(4) HDPE: high density polyethylene, low pressure polyethylene

(5) UHMWPE: Ultra High Molecular Weight Polyethylene

(6) Modified polyethylene: CPE, cross-linked polyethylene (PEX)

(7) Ethylene copolymer: copolymer of ethylene-propylene copolymer (plastic), EVA, ethylene-butene copolymer, ethylene-other olefin (such as octene POE, cyclic olefin), ethylene-unsaturated ester copolymer ( EAA, EMAA, EEA, EMA, EMMA, EMAH)

At present, China is already the world's largest importer of polyethylene and the second largest consumer. Polyethylene is a mixture of ethylene monomers. Polyethylene plastic is a plastic product made of polyethylene resin as a substrate and added with a small amount of additives such as antioxidants and slip agents. Polyethylene is mainly divided into linear low density polyethylene (LLDPE), low density polyethylene (LDPE), high density polyethylene (HDPE) three categories, the following Jiuzhi plastic network details their respective performance characteristics:

HDPE (high density polyethylene)

HDPE is non-toxic, odorless, odorless, and has a density of 0.940 to 0.976 g/cm3. It is a product of polymerization under low pressure conditions catalyzed by Ziegler catalyst, so high density polyethylene is also called low pressure polyethylene.

(1) Advantages

HDPE is a thermoplastic resin which is copolymerized with ethylene to form a high crystallinity and a non-polarity. The original HDPE has a milky white appearance and a semi-transparent shape in a thin section. It is excellent in resistance to most domestic and industrial chemicals and is resistant to corrosion and dissolution by strong oxidizing agents (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 moisture barrier applications.

(2) Disadvantages

The shortcoming is that its aging resistance and environmental stress cracking are not as good as LDPE, especially thermal oxidation will reduce its performance, so high-density polyethylene is added with anti-oxidant and UV absorber to improve the plastic film. Inadequacies.

LDPE (low density polyethylene)

LDPE is non-toxic, odorless, odorless, and has a density of 0.910 to 0.940 g/cm3. It is polymerized by using oxygen or an organic peroxide as a catalyst under high pressure of 100 to 300 MPa, also called high pressure polyethylene.

(1) Advantages

Low density polyethylene is the lightest variety in polyethylene resins. Compared with high-density polyethylene, its crystallinity (55%-65%) and softening point (90-100 °C) are lower; it has good flexibility, extensibility, transparency, cold resistance and processability; its chemistry Good stability, resistant to acid, alkali and salt aqueous solutions; good electrical insulation and gas permeability; low water absorption; easy to burn. It is soft in nature and has good elongation, electrical insulation, chemical stability, processability and low temperature resistance (resistant to -70 ° C).

(2) Disadvantages

The disadvantage is that it is poor in mechanical strength, moisture barrier, gas barrier and solvent resistance. 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. It has poor anti-seepage coefficient, heat resistance and anti-sunlight aging. It is easy to aging and decompose and discolor in sunlight or high temperature, resulting in performance degradation. Therefore, low-density polyethylene is made into plastic coil. Antioxidants and UV absorbers have been added to improve their deficiencies.

LLDPE (linear low density polyethylene)

LLDPE is non-toxic, odorless, odorless, and has a density between 0.915 and 0.935 g/cm3. It is ethylene with a small amount of high-grade α-olefins (such as butene-1, hexene-1, octene-1, tetramethylpentene). -1, etc.) A copolymer of high pressure or low pressure polymerized under the action of a catalyst. The molecular structure of conventional LLDPE is characterized by its linear backbone, with little or no long chain branching, but containing some short chain branches. No long chain branching results in higher crystallinity of the polymer.

LLDPE resin products

Compared with LDPE, LLDPE has the advantages of high strength, good toughness, strong rigidity, heat resistance and cold resistance. It also has good resistance to environmental stress cracking and tear strength, and is resistant to acids, alkalis and organic solvents.

Differentiating method:

1LDPE

Sensory identification: soft to the touch: white transparent, but the transparency is average.

Identification of combustion: yellow and blue on the burning flame; smokeless when burning, smell of paraffin, melted and dripped, easy to draw.

2LLDPE

LLDPE and benzene can swell in prolonged contact and become brittle when exposed to HCL for extended periods of time.

3HDPE

The processing temperature of LDPE is lower, about 160 degrees, and the density is 0.918 to 0.932 g/cm 3 . HDPE processing temperature is higher, about 180 degrees, and the density is higher.

In summary, the above three materials play an important role in different types of anti-seepage engineering. HDPE, LDPE and LLDPE have excellent insulation, moisture and impermeability, non-toxic, odorless and odorless properties, making them extremely suitable for use in agriculture, aquaculture, artificial lakes, reservoirs and rivers. It is widely popularized and popularized by the Fisheries Bureau of the Ministry of Agriculture, the Shanghai Fisheries Research Institute, and the Fishery Machinery and Instrument Research Institute.

In the medium environment of strong acid, strong alkali, strong oxidant and organic solvent, the material properties of HDPE and LLDPE can be well utilized and utilized, especially HDPE is resistant 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 materials have been fully utilized in the chemical and environmental protection industries. Low-density polyethylene also has good resistance to acids, alkalis, and salt solutions, and has good elongation, electrical insulation, chemical stability, processability, and low temperature resistance. Therefore, it is widely used in agriculture, aquaculture, packaging, especially low temperature packaging and cable materials.