High density polyethylene (HDPE) is synthesized in a very different way compared to LDPE granules. Thus linear chains are created. In fact, HDPE is generally the result of polymerization with a small amount of comonomers, which ultimately forms a series of short-chain branches that are mainly aligned with the main chain to produce a polymer with easy processability. A high degree of linearity increases the percentage of crystallinity (density increase). The density of HDPE is generally in the range of 0.96-0.96 g / cm. The production of HDPE film is somewhat different from the production of LDPE film. Due to the higher degree of crystallinity and stronger molecular structure, HDPE melts at higher temperatures (F “275-265, C” 135-130) and has a more limited performance. Also, the screw in HDPE process requires more torque and therefore more motor power. To enhance solid feed, due to the high friction between the granules and the barrel, the feed section is often grooved. One of the most obvious differences between HDPE and LDPE film production is the high freezing line height in the HDPE process. The height of the freezing line is usually 8 to 10 times the diameter of the die. Also in HDPE process, the strength of molten material is less than LDPE. So it is difficult to keep the bubble stable. Delaying the bubble tension in the TD direction until the molten material cools (increasing the freezing line height) increases the bubble stability. HDPE film has higher tensile strength and toughness than other types of polyethylene. Therefore, continuous efforts have been made to reduce the thickness of HDPE films (downgauging). In addition, HDPE has good barrier and protection (resistant to gas penetration), which is due to the high degree of crystallinity.
