What is hdpe?


Eric has always been interested in construction materials research, and he has been working in this domain for over 5 years now. Currently, he studies at Stanford University, and he is also an experienced geosynthetic expert.

Table of Contents

What is hdpe?

High-density polyethylene (HDPE), a white powder or granular product. Non-toxic, tasteless, crystallinity of 80% to 90%, softening point of 125 to 135°C, service temperature up to 100°C; HDPE hardness, tensile strength and creep are worse than low density polyethylene; hdpe plastics wear resistance, electrical Good insulation, toughness and cold resistance; good chemical stability, insoluble in any organic solvents at room temperature, corrosion resistant to acids, alkalis and various salts; recycle hdpe the film has low permeability to water vapor and air, and water absorption Low.

HDPE poor aging resistance, environmental stress cracking resistance is not as good as low-density polyethylene, especially thermal oxidation will reduce its performance, so antioxidants and ultraviolet absorbers must be added to the resin to improve this deficiency. HDPE film has a low heat distortion temperature under stress, so care should be taken when applying it.

Plastic raw materials can be roughly divided into two categories

HDPE is an environmentally friendly material that can be recycled and reused when heated to the melting point of HDPE. It should be noted that plastic raw materials can be roughly divided into two categories: “thermoplastics” and “thermosetting plastics”. “Thermosetting” means solidification after heating to a certain temperature. Even if you continue to heat it, it cannot change its state. Therefore, the products with environmental protection problems are “thermosetting plastic” products, not “thermoplastic” products, so not all “thermoplastic” products “plastic” are not environmentally friendly.


What are the advantages of hdpe bottles?

hdpe containers has good heat resistance and cold resistance, good chemical stability, high rigidity and toughness, and good mechanical strength. Dielectric properties, environmental stress cracking resistance is also good.

Hardness, tensile strength and creep are better than low-density polyethylene; wear resistance, electrical insulation, toughness and cold resistance are better, but slightly worse than low-density insulation; chemical stability is good, at room temperature Under certain conditions, it is insoluble in any organic solvent, resistant to acid, alkali and various salts; the film has low permeability to water vapor and air, and low water absorption; poor aging resistance, environmental cracking resistance is not as good as low-density polyethylene, In particular, thermal oxidation will reduce its performance. Therefore, the resin needs to be added with antioxidants and ultraviolet absorbers to improve this deficiency.

HDPE film has a low heat distortion temperature under stress, which should be paid attention to when applying.

Purpose of hdpe material

HDPE resins can be molded into plastic products by injection, extrusion, blow molding, and rotational molding. Various types of containers, industrial accessories, medical supplies, toys, shells, bottle stoppers and shields can be formed by injection molding. Blow molding can be used to form various hollow containers, ultra-thin films, etc. Extrusion can be used to form tubing, stretch tape, strapping, monofilament, wire and cable jacketing and more.In addition, it can also form architectural decorative panels, shutters, synthetic wood, synthetic paper, synthetic film and formed calcium-plastic products, etc.

hdpe cutting boards geotechnical material manufacturers

Established in 2002, Tinhy’s teams are focusing on manufacturings, marketing, installations, applications, and R&D of geosynthetics. We now have 300+ experienced staff and operate 25+ advanced production lines and provided services to customers from 30+ countries.

Tinhy has four manufacturing facilities, covering an area of 100,000 square meters. We currently have 5 geomembranes (3 flat-die, 2 blown), 3 non-woven geotextiles (2 short-fiber, 1 continuous-filament), 3 MDS® drainage boards (up to 6 meters wide), 3 geocomposites (with geonets, GCL, and composite geomembranes), double-locking edges GCL, geonets, geogrids, and water-stop belt production lines. With the varieties of products and professional installation team, Tinhy always puts the integrity of the projects first by providing superior products and cost-effective solutions.

Recycling and utilization of density of hdpe

HDPE is the fastest growing segment of the plastic raw material warehouse recycling market. This is mainly due to its ease of reprocessing, minimal degradation characteristics and its wide application in packaging applications. The main recycling is where 25% recycled material, such as post-consumer recycled content (PCR), is reprocessed with virgin HDPE to make bottles that do not come into contact with food.

In this process, the polymerization reaction solvent is n-hexane, the catalyst is a high-activity z-N catalyst, ethylene and hydrogen are mixed and enter the first reactor, and the polymerization reaction occurs after mixing with the catalyst, and the polymer in the reactor is suspended in hexane in the form of slurry In the process, the polymerization temperature is about 80°C and the polymerization pressure is less than 10 bar. This process can produce products with a density range of 0.942-0.965 g/cm3 and a melt index range of 0.2-80. The comonomers are propylene and 1-butene. Production Traditional HDPE and bimodal HDPE have excellent high-density pipe performance and are suitable for making pressure pipes, reaching PE100+.

The characteristics of the continuous polymerization process of the slurry tank reactor are

low operating pressure and operating temperature; double tank reactors can produce unimodal and bimodal products by adopting different forms of parallel connection and series connection; high process operation flexibility, product grade conversion It is fast and does not require high purity of raw materials; propylene and 1-butene are used as comonomers; hexane is used as solvent, and the recovery unit is simple. A feature of this process is that the polymerization is carried out in an inert hydrocarbon diluent.

The technological process is as follows: polymerized ethylene (99.9% ethylene, 0.1% ethane) is sent to the drier and then enters the tank reactor together with the circulating diluent composed of n-hexane. The catalyst adopts a carrier containing titanium, manganese, triethyl The base aluminum is the grade of the cocatalyst. Add a small amount of hydrogen to control the molecular weight. The polymerization reaction forms polyethylene particles. The reaction temperature is 90°C and the pressure is 1.8MPa. The reaction can be carried out in two polymerization tanks in two steps, and the production concentration is 34% (mass fraction) The slurry solid, the monomer conversion rate can reach 97%.

The polymer is flashed from the second reactor to a pressure of 0.14MPa, and the flashed unreacted ethylene, ethane in the effluent and 2% cyclohexane diluent are compressed and cooled to 2.5MPa twice, and degassed The stripper recovers the ethane for recycle. The slurry left after flash evaporation is centrifuged to recover most of the diluent, and the solid filter cake is sent to the dryer to reduce the volatile component content to about 5% (mass fraction). The dryer operates in a closed cycle under nitrogen protection.

The dried polymer powder is sent to the fluidized bed for drying to remove all hydrocarbon diluents.the polymer particles are sent to the mixing section to add various additives, and then granulated.process uses isobutane as a diluent and uses chromium-based catalysts. The catalyst must be activated before use. The activated catalyst powder forms a catalyst slurry with high-purity isobutane under nitrogen protection, and then enters the loop reactor. After the raw material ethylene monomer is refined, it is pre-mixed with hydrogen and comonomer hexene-1, and then injected into the loop reactor, and ethylene generates polyethylene under the action of a catalyst.

The axial flow pump keeps the high-speed flow and very uniform mixing of the materials in the reactor, and the heat of reaction is evenly withdrawn by the jacket cooling water. The range of MI produced by this process is 0.15-100, and the density is 0.936-0.972 g/cm3.

The characteristics of the loop reactor process are

less equipment, short process, low investment cost; no wax and oligomers, no sticking to the wall; good powder shape, easy to transport; reaction heat is taken out by the reactor jacket cooling water , It is easy to remove heat and easy to adjust; the raw material requirements are high and need to be purified; the comonomer uses hexene; and isobutane is used as the solvent, which is easy to remove the residual solvent.

The process flow is as follows: fresh polymer grade ethylene is mixed with the prepared molecular weight regulator hydrogen, antifreeze and circulating diluent isobutane after drying, and then sent to the multi-loop continuous process reactor, and the catalyst is supplemented with isobutane to fill the reactor. into the reactor. The reaction temperature is 106.7°C and the pressure is 3.9MPa. The polymer and diluent slurry was passed through the loop reactor at a speed of 6 m/s by means of an axial flow pump.

The water cooling in the reactor jacket controls the reaction temperature, and the polymer solids are discharged from the vertical settling port in the loop reactor. So that the slurry concentration can reach 55%, and the conversion rate is 98%-99%. After the polymer is discharged, it is flashed to discharge the isobutane and residual monomers to the diluent recovery unit. Other solid polymers are mixed with additives and pelletized. 2. Gas-phase polymerization: gas-phase polymerization (gas-phase fluidized bed method) is typically represented by the univation technology of DOW Chemical Company and the Innovene technology of INNOS Company.

Catalyst, purified raw materials are injected into the reactor, and polymerization reaction occurs under the action of catalyst storage. The reaction is carried out under the conditions of 85-110 °C and 2.41 MPa. The single-pass conversion rate of ethylene is about 1%-2%, and the removal of reaction heat Mainly through the cooling of the circulating stream, the MI range of the produced product is 0.01-150, and the density range is 0.915-0.970 g/cm3.

The characteristics of the gas phase fluidized bed polymerization process are: low operating pressure and low temperature; full density polyethylene can be produced; the catalyst system includes titanium series and chromium series; metallocene catalysts; the requirements for the purity of raw materials are high, and all raw materials must be refined; No solvent, low energy consumption, low maintenance and operating costs. The production process is: the dry monomer is added to the reactor system together with hydrogen, and the raw material is added to a large circulating steam flow loop, and enters the bottom of the large fluidized bed reactor through gas distribution.

According to the design of the reactor, the raw material has 69.57 % ethylene (ethylene content is 99.9%, 0.1% is ethane), 10.43% hydrogen, 7.56% ethane and 12.44% nitrogen. This feed gas composition produced a product with a melt index of 8 g/10 min and a density of 0.964 g/cm3.

The catalyst is a mixture of magnesium dioxide with titanium trichloride and tetrahydrofuran as promoters, and the cocatalyst is triethylaluminum. The catalyst enters the reactor in solid form along with the nitrogen gas from the painless reactor site. The operating temperature is 105°C, and the specific temperature depends on the product grade.

The operating pressure of the reactor is 2.0 MPa, and the reaction gas comes out from the top of the reaction, and the catalyst containing solid matter is separated by a cyclone separator and sent back to the reactor. The gas from the cyclone is then compressed and circulated to the bottom of the reactor after recirculation cooler.

The reactor discharge intermittently sends product pellets to the tank through an airlock system. Part of the gas entering the discharge tank enters the compressor circulation system through the upper buffer tank, filter, gas cooler and separation tank. The polymer comes out from the lower part of the discharge tank and enters the purge tank and post-treatment system. The post-processing system includes adding various additives to the polymer, melting, pelletizing and packaging.

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