High-Density Polyethylene
The material used for blow-molded hollow plastic containers is low-pressure high-density polyethylene-specifically HDPE. High-Density Polyethylene (abbreviated as "HDPE") is a highly crystalline, non-polar thermoplastic resin. In its natural state, HDPE appears milky white; in thin cross-sections, it exhibits a certain degree of translucency. PE possesses resistance to most household and industrial chemicals. However, certain types of chemicals can cause chemical corrosion-examples include corrosive oxidants (such as concentrated nitric acid), aromatic hydrocarbons (such as xylene), and halogenated hydrocarbons (such as carbon tetrachloride). This polymer does not absorb moisture and exhibits excellent resistance to water vapor, making it suitable for packaging applications. HDPE possesses high dielectric strength and insulation properties, making it suitable for use in electrical wires and cables. Grades with medium to high molecular weights exhibit excellent impact resistance. The specific characteristics of various HDPE grades are determined by the combination of four fundamental variables: density, molecular weight, molecular weight distribution, and additives. Different catalysts are employed to produce polymers with customized, specialized properties. The interplay of these variables results in the production of various
HDPE grades tailored for specific applications.
High-Density Polyethylene consists of non-toxic, odorless, and tasteless white granules. It has a melting point of approximately 130°C and a relative density ranging from 0.941 to 0.960. It exhibits both cold and heat resistance; plastic containers manufactured from HDPE typically have a standard operating temperature range of -50°C to +70°C, with short-term temperature resistance reaching up to approximately 100°C . It demonstrates excellent chemical stability, high rigidity and toughness, and good mechanical strength. Furthermore, it possesses favorable dielectric properties and good resistance to environmental stress cracking.
The recommended melting temperature range for processing is 220°C to 260°C. For materials with higher molecular weights, a melting temperature range between 200°C and 250°C is recommended.
Polypropylene
Polypropylene (abbreviated as "PP") is another thermoplastic resin commonly used in the manufacture of plastic containers. PP features a high melting point-reaching up to 167°C-and is both non-toxic and odorless.
