bestcryptoplaytoearngames2022| Collection 丨 List of Differences between LDPE, HDPE, and LLDPE

Source: quick Molding Point of View

Polyethylene (Polyethylene) is one of the five major synthetic resinsBestcryptoplaytoearngames2022At present, China is the largest importer and second largest consumer of polyethylene in the world. Polyethylene is mainly divided into three categories: high density polyethylene (HDPE), low density polyethylene (LDPE) and linear low density polyethylene (LLDPE).

Table 1 comparison of properties of HDPE, LDPE and LLDPE materials

smell

Toxicity.

Non-toxic, tasteless, odorless

Density

0Bestcryptoplaytoearngames2022. 940~0.976g/cm3

0.910~0.940g/cm3

0.915~0.935g/cm3

Crystallinity

85-65%

45-65%

55-65%

Molecular structure.

It only contains carbon-carbon and carbon-hydrogen bonds, which requires more energy to break.

The molecular weight of the polymer is small and it needs less energy to break.

The linear structure, branched chain and short chain are less, and less energy is needed to break.

Softening point

125135 ℃

90-100 ℃

94-108 ℃

Mechanical properties

High strength, good toughness and strong rigidity

Mechanical strength

Poor

High strength, good toughness,

Strong rigidity

Tensile strength

High

Low

Higher

Fracture

Elongation rate

Higher

Low

High

Impact strength

Higher

Low

High

Moistureproof and waterproof performance

It has good permeability to water, water vapor and air, low water absorption and good impermeability.

Moisture and gas insulation are poor.

It has good permeability to water, water vapor and air, low water absorption and good impermeability.

Acid, alkali, corrosion and organic solvent resistance

Resistance to strong oxidant corrosionBestcryptoplaytoearngames2022Resistant to acid, alkali and various salts, insoluble in any organic solvent, etc.

Resistant to acid, alkali and salt solution corrosion, but poor solvent resistance

Resistant to acid, alkali and organic solvents

Heat / cold resistance

Good heat resistance and cold resistance, even at room temperature and even at-40F low temperature, excellent impact resistance

Low temperature embrittlement temperature <-90 ℃

Low heat resistance, low temperature embrittlement temperature <-70 ℃

Good heat and cold resistance, low temperature embrittlement temperature <-90 ℃

Resistance to environmental stress cracking

good

Better

good

I. High density polyethylene

HDPE is non-toxic, tasteless, odorless, and its density is 0.940~0.976g/cm3. It is polymerized under the condition of low pressure catalyzed by Ziegler catalyst, so high density polyethylene is also called low-pressure polyethylene.

Advantages:

HDPE is a kind of thermoplastic resin with high crystallinity and non-polarity formed by ethylene copolymerization. The appearance of the original HDPE is milky white and translucent to a certain extent in the thin section. It has excellent resistance to most domestic and industrial chemicals, and 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 waterproof and steam properties, and can be used for moisture-proof and anti-seepage purposes.

Disadvantages:

The deficiency is that the aging resistance and environmental stress cracking property are not as good as LDPE, especially the thermal oxidation will reduce its performance, so high density polyethylene added antioxidants and ultraviolet absorbers to improve its shortcomings.

HDPE double-wall bellows

2. Low density polyethylene

LDPE is non-toxic, tasteless, odorless, with a density of 0.910~0.940g/cm3. It is polymerized under the high pressure of 100~300MPa with oxygen or organic peroxides as catalysts, also known as high-pressure polyethylene.

Advantages:

Low density polyethylene (LDPE) is the lightest kind of polyethylene resin. Compared with HDPE, its crystallinity (55%-65%) and softening point (90-100 ℃) are lower; it has good softness, extensibility, transparency, cold resistance and processability; it has good chemical stability and can resist acid, alkali and salt aqueous solution; it has good electrical insulation and air permeability; low water absorption; easy combustion. It has soft properties, good extensibility, electrical insulation, chemical stability, processability and low temperature resistance (can withstand-70 ℃).

Disadvantages:

The deficiency is that its mechanical strength, moisture insulation, gas insulation and solvent resistance are poor. The molecular structure is not regular enough, the crystallinity (55% Mel 65%) is low, and the crystallization melting point (108126 ℃) is also low. Its mechanical strength is lower than that of high density polyethylene, and its impermeability coefficient, heat resistance and sun aging resistance are poor, and it is easy to age and decompose and change color in sunlight or high temperature, resulting in the decline of performance. therefore, low density polyethylene added antioxidants and ultraviolet absorbers to improve its shortcomings when making plastic coil.

LDPE Eye drop bottle

Linear low density polyethylene

LLDPE is non-toxic, tasteless, odorless, and its density is between 0.915~0.935g/cm3. Ethylene and a small amount of advanced α-olefins (such as butene-1, hexene-1, octene-1, tetramethylpentene-1, etc.) are polymerized under high pressure or low pressure under the action of catalyst. The molecular structure of conventional LLDPE is characterized by its linear main chain, with little or no long branched chains, but contains some short branched chains. The lack of long branched chains makes the polymer more crystallinity.

Compared with LDPE, LLDPE has the advantages of high strength, good toughness, strong rigidity, heat resistance, cold resistance, good environmental stress cracking resistance, tear strength resistance, acid resistance, alkali resistance, organic solvent resistance and so on.

LLDPE resin shopping basket

Fourth, the method of distinction

LDPE: sensory identification: feel soft; white and transparent, but general transparency.

Combustion identification: yellow and blue on the combustion flame; smokeless during combustion, with the smell of paraffin wax, melting dripping, easy to pull wire.

LLDPE:LLDPE can swell in contact with benzene for a long time, and become brittle in contact with HCL for a long time.

The processing temperature of HDPE:LDPE is lower, about 160C, and the density is 0.918-0.932 g / cu cm. The processing temperature of HDPE is higher, about 180CBestcryptoplaytoearngames2022The density is also higher.

V. Summary

To sum up, the above three materials play an important role in different types of anti-seepage engineering. HDPE, LDPE and LLDPE all have good insulation, moisture-proof and impervious properties, and their non-toxic, tasteless and odorless properties make them widely used in agriculture, aquaculture, artificial lakes, reservoirs and river courses, and have been popularized and applied by the Fisheries Administration of the Ministry of Agriculture, Shanghai Fisheries Science Research Institute and Fisheries 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 brought into full play and utilized, especially HDPE is much higher than the other two materials in resistance to strong acid, strong alkali, strong oxidation and anti-organic solvent, so HDPE impervious and anticorrosive coil has been fully utilized in chemical industry and environmental protection industry.

LDPE also has good resistance to acid, alkali and salt solution, and has good extensibility, electrical insulation, chemical stability, processability and low temperature resistance, so it is widely used in agriculture, aquaculture, packaging, especially low temperature packaging and cable materials.

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