As a group, polyethylene plastic is the most widely-used plastic in consumer goods. The range of polyethylene plastic materials is defined by density produced by crystalline branching within the material composition. The material grades include high-density polyethylene (HDPE), medium-density polyethylene plastic (MDPE) and low-density polyethylene (LDPE). Within the low-density polyethylene family, linear low-density polyethylene (LLDPE) is stronger and less flexible than LDPE.
High-density polyethylene injection molding results in products that are less flexible and stronger than products produced by injection molded lower-density polyethylene. With the fewest crystalline branches in its makeup, HDPE is defined with a density range of .941 to .960 g/cc. Although it has greater impact resistance, HDPE can sometimes be used in place of polypropylene, another commonly produced plastic found in commodity products.
At the other end of the polyethylene spectrum, LDPE has many crystalline branches in its composition for an end product that is softer, more flexible and less brittle than the polyethylene materials with higher density ranges. LDPE and LLDPE are often used for lower temperature injection molding applications and will not withstand the high temperatures tolerated by HDPE.
Polyethylene plastic is the common choice for high-volume, low-cost injection molded applications. It can also be overmolded onto tubing for surface smoothness or roughness. Polyethylene is also used to produce sheeting for food wraps and plastic film.
The characteristics of plastic injection molded polyethylene differ by the grade selected with HDPE having the greatest strength and rigidity and LDPE showing the most softness and flexibility. Polyethylene is:
While this material is a popular choice, under certain conditions, polyethylene can warp and suffer environmental stress fractures.
Within the broad industry of consumer goods, plastic injection molded polyethylene applications using grades from high density to low are found in many products, including: