High Density Polyethylene Resins

The linearity of the chains and consequently the highest density of HDPE make the orientation, alignment and packing of the chains are more efficient; intermolecular forces (Van der Waals) can act more intensively and, as a consequence, the crystallinity is higher than in case of LDPE. Being higher crystallinity, the merger may occur at higher temperature. Because of crystallinity and the difference in refractive index between the amorphous and crystalline phases, HDPE films (obtained via Ziegler-Natta or Phillips) are thin translucent, less transparent than LDPE (obtained via free radicals), and less than crystalline. While the electrical properties are little affected by the density and the molecular weight of the polymer, the mechanical properties suffer a strong influence on the molecular weight, the content of branches, the morphological structure and orientation. The orientation of the polymeric chains applies a strong effect to the mechanical properties of the polymer. Materials manufactured with highly oriented HDPE are about ten times more resistant than those made from polymer not oriented since the orientation increases packaging chains and consequently increases the stiffness of the polymer. In general, the HDPE has low chemical reactivity. At enviroment temperature, HDPE is not soluble in any solvent , although many solvents such as xylene, for example, cause a swelling effect. At high temperatures, dissolve in some HDPE aliphatic and aromatic hydrocarbons. HDPE is relatively heat resistant. HDPE is appliable in different segments of the plastics processing industry, covering the processing of blow molding, extrusion and injection molding.

• Injection : Through the injection process, the HDPE is used for making buckets, trays, bathtubs, toys, food containers, toilets seats, trays, lids and bottles, crates, water tanks, among others.
• Blow : For blowing process Lotte HDPE resins offer an excellent combination of stifness and enviroment stress crack resistance, making them the materials for several application in industrial containers, household, bottles, drums, etc.
• Extrusion : For extrusion, the HDPE is recommended for wire and cable insulation, freezer bags, metal pipe coating, pipe for sewerage and gas distribution, sanitary sewage, trash bags, grocery bags,etc. Some Brazilian industries are already exploring a new market, developing a specific HDPE grade for blow molding of fuel tanks. HDPE and LDPE has many common applications, but in general, HDPE is harder and resistant and LDPE is more flexible and transparent. An example of the relationship of hardness and flexibility is the fact that HDPE is used to make threaded caps (rigid) and LDPE threadless caps (flexible).