Several common processing methods for plastic products
1. Extrusion: Grades used for extrusion production generally have a melt index of less than 1 and a medium to wide MWD. During processing, a low MI can achieve a suitable melt strength. Wider MWD grades are more suitable for extrusion because they have higher production speeds, lower die pressures, and a reduced melt fracture tendency.
2. 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, detergents, milk and distilled water to large refrigerators, automotive 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.
3. Injection: HDPE has countless applications, ranging from reusable thin-walled beverage cups to 5-gsl cans, consuming 1/5 of domestically produced HDPE. Injection molding grades generally have a melt index of 5 to 10, with grades with lower toughness and higher fluidity with processability. Applications include household and food thin-walled packaging; ductile, durable food and coating cans; high environmental stress cracking applications such as small engine fuel tanks and 90-gal trash cans.
Fourth, rotomolding: The materials used in this processing method are generally pulverized into powder materials to make them melt and flow during thermal cycling. Rotomolding uses two types of PE: general purpose and crosslinkable. General-purpose MDPE / HDPE usually has a density ranging from 0.935 to 0.945g / CC, with a narrow MWD, which gives the product high impact and minimal warpage. Its melt index range is generally 3-8. Higher MI grades are generally not suitable because they do not have the impact and environmental stress cracking resistance that rotomolded articles expect.
High-performance rotomolding applications take advantage of the unique properties of their chemically crosslinkable grades. These grades have good fluidity in the first stage of the molding cycle, and are then crosslinked to form their excellent resistance to environmental stress cracking and toughness. Abrasion 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 storage tanks.
5. Film: PE film is generally processed by ordinary blown film or flat extrusion. Most PEs are used in films, and both general-purpose low-density PE (LDPE) or linear low-density PE (LLDPE) are available. HDPE film grades are generally used where excellent stretchability and excellent barrier properties are required. For example, HDPE film is commonly used in merchandise bags, grocery bags, and food packaging.