HDPE is a highly crystalline, non-polar thermoplastic resin. The appearance of the original HDPE is milky white, and the thin section is translucent to a certain extent. PE has excellent resistance to most domestic and industrial chemicals. Certain types of chemicals can cause chemical corrosion, such as corrosive oxidizers (concentrated nitric acid), aromatic hydrocarbons (xylene) and halogenated hydrocarbons (carbon tetrachloride). The polymer is non-hygroscopic and has good water vapor resistance, and can be used for packaging purposes. HDPE has good electrical properties, especially the high dielectric strength of the insulation, making it very suitable for wires and cables. Medium to high molecular weight grades have excellent impact resistance, even at room temperature and even at low temperatures of -40F.
PE has many uses, 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 a diameter of 48in for industrial and urban pipelines. The use of large-diameter hollow-wall pipes as a substitute for rainwater drainage pipes made of concrete and other sewer pipes is growing rapidly.
Sheet and thermoforming
The thermoformed lining of many large picnic refrigerators is made of PE, which has toughness, light weight and durability. 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 the 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 bottles are automatically trimmed, without the need for post-finishing steps like general blow molding. Although some narrow MWD grades are used to improve surface finish, medium to wide MWD grades are generally used.
Injection molding
HDPE has countless applications, ranging from reusable thin-walled beverage cups to 5-gsl cans, which consume 1/5 of domestically produced HDPE. Injection molding grades generally have a melt index of 5-10. 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.
Rotomolding
The materials used in this processing method are generally crushed into powders, which are melted and flowed in a 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 is generally in the range of 3-8. Higher MI grades are generally not suitable because they do not have the impact and environmental stress crack resistance expected of rotomolded products.
High-performance rotational molding applications utilize the unique properties of its chemically cross-linkable 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. Crosslinkable 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.
