HDPE plastic raw material performance

2019-09-23  417

HDPE plastic raw material is a high crystallinity, non-polar thermoplastic resin. The original HDPE has a milky white appearance and a semi-transparent shape in a thin section. PE has excellent resistance to most of the characteristics of living and industrial chemicals. Certain types of chemicals can cause chemical corrosion, such as corrosive oxidants (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 excellent electrical properties, especially high dielectric strength, making it suitable for wire and cable. Medium to high molecular weight grades have excellent impact resistance, both at ambient temperatures and even at low temperatures of -40F. The unique characteristics of various grades of HDPE are the appropriate combination of four basic variables: density, molecular weight, molecular weight distribution, and additives. Different catalysts are used to produce custom specialty polymer. These variables combine to produce HDPE grades for different applications; achieving the best balance in performance. This is the main variable that determines the characteristics of HDPE, although the four variables mentioned do interact.

Ethylene is the main raw material of polyethylene. A few other comonomers, such as 1-butene, 1-hexene or 1-octene, are also often used to improve polymer properties. For HDPE, the content of the above monomers is generally not more than 1% - 2%. The addition of comonomer slightly reduces the crystallinity of the polymer. This change is generally measured by density, which is linear with crystallization. The US general classification is in accordance with ASTM D1248, and the density of HDPE is 0.940 g/. Above C; medium density polyethylene (MDPE) has a density ranging from 0.926 to 0.940 g/cc. Other taxonomies sometimes classify MDPE as HDPE or LLDPE. Homopolymers have the highest density, maximum stiffness, good barrier properties and the highest melting point, but generally have poor resistance to environmental stress cracking (ESCR). Higher densities generally improve mechanical strength such as tensile strength, stiffness and hardness; thermal properties such as softening point temperature and heat distortion temperature; and barrier properties such as gas permeability or water vapor transmission. The lower density improves its impact strength and E-SCR. The polymer density is primarily affected by the addition of comonomers, but to a lesser extent by molecular weight. A high molecular weight percentage results in a slight decrease in density. For example, homopolymers have different densities over a wide range of molecular weights.

The development of new catalysts contributes to improving the performance of new grade HDPE plastic materials. The two most common types of catalysts are Phillips' chromium oxide based catalysts and titanium compound monoalkyl aluminum catalysts. The HDPE produced by the Phillips type catalyst has a medium width molecular weight distribution; the titanium monoalkyl aluminum catalyst produces a narrow molecular weight distribution. Catalysts used to produce narrow MDW polymers using a duplex reactor can also be used to produce wide MDW grades. For example, two series reactors producing significantly different molecular weight products can produce bimodal molecular weight polymers having a full broad molecular weight distribution.