Difference between low-density polyethylene and high-density polyethylene

Low Density Polyethylene (LDPE)
Polyethylene with a relative density of
0.9109.25 is called Low Density Polyethylene, while polyethylene with a density between low density and high density is called Medium Density Polyethylene On the contrary, polyethylene with a relative density lower than
0.910; It has also been released Becoming very low density polyethylene (VLDPE), and even having a relative density less than
0.900, it is also known as ultra low density polyethylene (ULDPE) in foreign countries. Although there are many varieties of polyethylene, low-density polyethylene and high-density polyethylene are still the main ones that dominate the polyethylene market Traditional low-density polyethylene is produced by free radical polymerization of polymer grade ethylene using oxygen or peroxide as initiators under high temperature and high pressure Therefore, low-density polyethylene is also known as high-pressure polyethylene
Low density polyethylene is a white resin with a wax like texture, characterized by a non-linear structure The molecular weight is generally between 1000 and 5000. Therefore, compared with medium density and high-density polyethylene, it has lower crystallinity and softening point, better flexibility, elongation, electrical insulation, transparency, and higher impact strength. Low density polyethylene has poor mechanical strength and heat resistance. In addition, another obvious weakness is poor resistance to environmental stress cracking
Low density polyethylene is mostly used as film products, while a large part of the film products are used for packaging and another part is used as agricultural film and construction film Low density polyethylene packaging film can be used for food packaging such as candy, vegetables, frozen foods, etc. It can also be used as an inner lining film, shrink wrap film, elastic packaging film, heavy packaging film, and other non food packaging films
High Density Polyethylene (HDPE)
Polyethylene with a density of 0.9410.965 is called High Density Polyethylene. High Density Polyethylene

is produced by low-pressure method, hence it is called Low Pressure Polyethylene.
There are two production methods: liquid-phase method and gas-phase method Liquid phase method includes solution method and slurry method
High density polyethylene can be classified into homopolymers and copolymers. The so-called copolymerization refers to the infiltration of a small amount of alpha olefin during polymerization, which can reduce the density and crystallinity of polyethylene. Therefore, compared to homopolymers, it has better environmental stress cracking performance, higher surface hardness, and better dimensional stability
High density polyethylene improves heat resistance and mechanical strength (such as tensile, bending, compression, and shear strength) compared to low-density polyethylene, and enhances its barrier properties against water vapor and gases High density polyethylene can be processed into pipes, sheets, sheets, profiles, as well as single filaments, flat filaments, and packing tapes using extrusion method; Blow molding can be used to produce large and medium-sized hollow containers Such as bottles, barrels, and large industrial storage tanks; Various parts, daily necessities, and industrial products can be produced by injection molding
LDP
E, LLDPE, and HDPE. The difference between these three types of PE:
LDPE [Chinese name:
Low density high-pressure polyethylene]:
Sensory identification:
Soft feel:
White and transparent, but the transparency is average. Combustion identification:
The combustion flame is yellow on top and blue on the bottom;
; When burned, it is smokeless, has a smell of paraffin, melts and drips, and is easy to draw. LLDPE [linear low-density polyethylene]: Linear low-density polyethylene is structurally different from ordinary low-density polyethylene because it does not have long branched chains The linearity of LLDPE depends on the different production and processing processes of LLDPE and LDPE LLDPE is typically produced by copolymerization of ethylene and higher alpha olefins such as butene, hexene, or octene at lower temperatures and pressures The LLDPE polymer generated during the copolymerization process has a narrower molecular weight distribution than general LDPE, and its linear structure gives it different rheological properties The melt flow characteristics of LLDPE are suitable for the requirements of new processes, especially the use of thin film extrusion technology, which can produce high-quality LLDPE products The traditional application of LLDPE in polyethylene has enhanced its resistance to elongation, penetration, impact, and tear, making it suitable for use as a film Its excellent resistance to environmental stress cracking, low temperature impact, and warpage make LLDPE attractive for pipe, sheet extrusion, and all molding applications
The latest application of LLDPE is as a lining layer for plastic film used in waste landfill and waste liquid tanks Higher tensile strength, penetration resistance, tear resistance, and increased elongation are the characteristics of LLDPE, making it particularly suitable for film production If hexene or octene is used instead of butene as a comonomer, even the impact resistance and tear resistance can be greatly improved For a given resin with the same melt index and density, the impact and tear properties of hexene and octene LLDPE resins are improved to 300% The longer side chains of hexene and octene resins act as "knot" molecules between the chains, improving the toughness of the compounds
HDPE [High Density Polyethylene]:
HDPE is a thermoplastic resin with high crystallinity and non polarity The original appearance of HDPE is milky white, with a certain degree of semi transparency in the thin section PE has excellent resistance to most household and industrial chemicals Certain types of chemicals can cause chemical corrosion, such as corrosive oxidants [concentrated nitric acid], aromatic hydrocarbons [xylene], and halogenated hydrocarbons [carbon tetrachloride]
This polymer is non hygroscopic and has good water vapor resistance, making it suitable for packaging purposes HDPE has excellent electrical properties, especially high insulation dielectric strength, making it very suitable for wires and cables The medium to high molecular weight grade has excellent impact resistance, even at room temperature and low temperatures of -40F.
The response above is already comprehensive. To add, HDPE is now mostly used in pipes, such as drainage pipes.
It is an ideal pipe material to replace traditional concrete pipes and clay pipes Nowadays, it is a new technology and the country is promoting the use of linear low-density polyethylene (LLDPE). LLDPE is almost inert to chemical reactions and does not undergo any chemical reactions with any substances. It only burns
LLDPE can swell when in contact with benzene for a long time, and become brittle when in contact with HCL for a long time, but it takes several years. It can be used to store these two things normally

Performance differences between LDPE and HDPE: Tensile strength: LDPE is 7-14 MPa, while HDPE is 24-31 MPa. Operating temperature: LDPE is below 100 degrees, while HDPE is below 120 degrees Shore hardness: LDPE is 41-45, while HDPE is 60-70 Low density polyethylene [LDPE] is a thermoplastic obtained by ethylene radical polymerization under high pressure The processing temperature of low-density polyethylene is lower, about 160 degrees Celsius, with a density ranging from 0.918 to 0.932 grams per cubic centimeter Mainly used as the outer sheath of telecommunications cables
High density polyethylene [HDPE] has a higher processing temperature, about 180 degrees, and a higher density
HDPE,LDPE, The difference between PE and PE is that PE is polyethylene HDPE is high-density polyethylene, also known as low-pressure polyethylene LDPE is low-density polyethylene, also known as high-pressure polyethylene HDPE and LDPE are both types of PE Polyethylene is mainly classified by density, and its properties vary depending on the variety and grade: ① High density polyethylene [HDPE]:
is an opaque white powder, which becomes milky white particles after granulation. The molecules have a linear structure and rarely show branching, making it a typical crystalline polymer.
The mechanical properties are superior to low-density polyethylene, with a melting point higher than that of low-density polyethylene, about 126-136 ℃. Its brittleness temperature is lower than that of low-density polyethylene, about -100 to -140 ℃
② Low density polyethylene [LDPE]:

It is a colorless, semi transparent particle with long branched chains in its molecules and loosely arranged between molecules
③ Linear low-density polyethylene [LLDPE]: Generally, only short branches exist in the molecule, and its mechanical properties are between high-density and low-density polyethylene. Its melting point is 15 ℃ higher than that of ordinary low-density polyethylene, and its low temperature resistance is also better than that of low-density polyethylene. Its stress cracking resistance is several times higher than that of ordinary low-density polyethylene
According to production methods, polyethylene can be divided into low-pressure polyethylene, medium pressure polyethylene, and high-pressure polyethylene. Different production methods of polyethylene result in different densities and melt indices (indicating fluidity) Density and melt flow rate are also key indicators for identifying and distinguishing different varieties and grades of polyethylene
Processing and application can be achieved through methods such as blow molding, extrusion, injection molding, etc., and are widely used in the manufacturing of films, hollow products, fibers, and daily necessities In actual production, in order to enhance the stability of polyethylene against ultraviolet radiation and oxidation, improve processing and usage performance, a small amount of plastic additives need to be added The commonly used UV absorbers are ortho hydroxybenzophenone or its alkoxy derivatives, and carbon black is an excellent UV shielding agent In addition, it also participates in antioxidants, lubricants, colorants, etc., expanding the application scope of polyethylene
More than half of the total production of low-density polyethylene film is blown into film, which has good transparency and certain tensile strength. It is widely used as packaging material for various foods, clothing, medicine, fertilizers, industrial products, and agricultural films It can also be processed into composite film using extrusion method for packaging heavy objects. Since 1975, high-density polyethylene film has also been developed, which has high strength, low temperature resistance, moisture resistance, and good printability and processability The biggest use of linear low-density polyethylene is also to make thin films. Its strength and toughness are superior to low-density polyethylene, and its puncture resistance and rigidity are also good. Although its transparency is poor, it is still slightly better than high-density polyethylene In addition, polyethylene coating can be extruded and coated on paper, aluminum foil or other plastic films to produce polymer composite materials
Hollow products made of high-density polyethylene have high strength and are suitable for use as hollow products Bottles, barrels, cans, tanks, and other containers can be made by blow molding, or large containers such as tanker tanks and storage tanks can be made by casting
The extrusion method of pipe sheet can produce polyethylene pipes. High density polyethylene pipes have high strength and are suitable for underground laying The extruded sheet can undergo secondary processing High density polyethylene can also be made into low foam plastics by foaming extrusion and foaming injection methods, which can be used as platens and building materials

LDPE [density 0.915-0.93], MDPE [density 0.93-0.94], HDPE [density above 0.94], the higher the density, the greater the film's ductility, heat resistance, oil resistance, chemical resistance, and waterproofing, but the transparency will decrease This is the difference between LDPE film and HDPE film Another characteristic that is not related to density is that the molecules of HDPE film are longitudinally arranged, making it easy for HDPE film to tear