polyolefin

Polyolefin is a class of polymers produced by the polymerization of olefin (alkene) monomers, primarily ethylene and propylene. The most widely manufactured examples are polyethylene (PE) and polypropylene (PP), with grades ranging from flexible films to rigid plastics. Polyolefins are characterized by simple hydrocarbon backbones formed by addition polymerization, resulting in saturated polymers with variable branching and crystallinity.

Synthesis and structure: Polyolefins are formed by addition polymerization using catalysts such as Ziegler-Natta or metallocene systems, under low to moderate temperatures and pressures. Ethylene gives polyethylene, while propylene yields polypropylene. The tacticity of polypropylene (isotactic, syndiotactic, or atactic) strongly influences crystallinity and properties. PE is typically semi-crystalline, with density variations leading to high-density (HDPE) and low-density (LDPE) grades, and linear low-density polyethylene (LLDPE) as well. Copolymers and blends extend the service range.

Properties and processing: Polyolefins offer good chemical resistance, moisture barriers, electrical insulation, and a favorable strength-to-weight ratio. They are processable by extrusion, injection molding, blow molding, and film blowing, making them versatile for packaging, consumer goods, pipes, and automotive parts. Additives can tailor properties such as UV resistance, flame retardancy, or impact strength.

Applications and environmental aspects: Polyolefins are used in packaging films and bottles, grocery bags, piping, automotive interiors, and construction components. They are widely recycled, with mechanical recycling common in many streams, though different grades require sorting. Limitations include limited high-temperature performance, susceptibility to UV degradation without stabilizers, and environmental concerns related to plastic waste and energy use in production.