PE can be manufactured in a wide range of different processing methods. Using ethylene as the main raw material, propylene, 1-butene, and hexene as the copolymer, under the action of a catalyst, the slurry polymerization or gas phase polymerization process is adopted, and the obtained polymer is flashed, separated, dried, granulated, etc. Process to obtain finished products with uniform particles. Including such as sheet extrusion, film extrusion, pipe or profile extrusion, blow molding, injection molding and rotational molding.
▲Extrusion: The grade used for extrusion production generally has a melt index less than 1 and a medium to wide MWD. During processing, low MI can obtain suitable melt strength. Wider MWD grades are more suitable for extrusion because they have higher production speeds, lower die pressures and reduced melt fracture tendency.
PE has many extrusion applications, such as wires, cables, hoses, pipes and profiles. Pipe applications range from small-section yellow pipes for natural gas to thick-walled black pipes with 48in diameter for industrial and urban pipelines. The use of large-diameter hollow-wall pipes as a substitute for concrete rainwater drainage pipes and other sewer pipes is growing rapidly.
Sheet and thermoforming: The thermoforming lining of many large picnic refrigerators is made of PE, which is tough, light and durable. Other sheet and thermoformed products include mudguards, tank liners, pan guards, shipping boxes and tanks. A large number of fast-growing sheet applications are mulch or pond bottom villages, which are based on the toughness, chemical resistance, and impermeability of MDPE.
▲Blow molding: More than 1/3 of HDPE sold in the United States is used for blow molding. These range from bottles containing bleach, motor oil, detergent, milk and distilled water to large refrigerators, car fuel tanks and canisters. The characteristics of blow molding grades, such as melt strength, ES-CR and toughness, are similar to those used for sheet and thermoforming applications, so similar grades can be used.
Injection-blow molding is usually used to make smaller containers (less than 16oz) for packaging medicines, shampoos and cosmetics. One of the advantages of this process is that the production bottle is automatically trimmed, without the need for post-finishing steps like general blow molding. Although there are some narrow MWD grades used to improve surface finish, medium to wide MWD grades are generally used.
▲Injection: HDPE has countless applications, ranging from reusable thin-walled beverage cups to 5-gsl cans, which consume 1/5 of domestic HDPE. Injection molding grades generally have a melt index of 5 to 10, and there are grades with toughness and lower fluidity and higher fluidity grades with processability. Uses include daily necessities and food thin-walled packaging; tough, durable food and paint cans; high resistance to environmental stress cracking applications, such as small engine fuel tanks and 90-gal garbage cans.
▲Rotational molding: The material using this processing method is generally crushed into powder material, which is melted and flowed in the thermal cycle. Rotomolding uses two types of PE: general-purpose and cross-linkable. General-purpose MDPE/HDPE usually has a density ranging from 0.935 to 0.945g/CC, with a narrow MWD, which enables the product to have high impact and minimal warpage, and its melt index generally ranges from 3 to 8. Higher MI grades are generally not suitable because they do not have the impact and environmental stress crack resistance desired for rotomolded products.
High-performance rotomolding applications utilize the unique properties of chemically crosslinkable grades. These grades have good fluidity in the first part of the molding cycle, and then crosslink to form their excellent environmental stress crack resistance and toughness. Wear resistance and weather resistance. Cross-linkable PE is only suitable for large containers, ranging from 500-gal tanks for transporting various chemicals to 20,000-gal agricultural tanks.
▲ Film: PE film processing generally uses ordinary blown film processing or flat extrusion processing. Most PE is used for film, general low density PE (LDPE) or linear low density PE (LLDPE) are available. HDPE film grades are generally used where superior stretchability and excellent impermeability are required. For example, HDPE film is often used for commodity bags, grocery bags and food packaging.