Low-Density Polyethylene (LDPE) is a thermoplastic polymer derived from the monomer ethylene. Produced through a high-pressure polymerization process, its relative cost-effectiveness and desirable physical properties have secured its place as one of the most common and versatile polymers globally. Its applications range from thin, flexible packaging to thicker, molded industrial parts.
Key Characteristics of LDPE
LDPE’s functional properties stem from its highly branched molecular structure, which prevents the polymer chains from packing tightly together. This results in a low density, typically ranging between 0.910 and 0.940 grams per cubic centimeter. This lower density imparts the material’s signature flexibility and softness, distinguishing it from denser polyethylene variants.
The polymer exhibits excellent resistance to impact and tearing, maintaining toughness even at low temperatures, making it useful for frozen food packaging. LDPE provides a good barrier against moisture, though it allows gases like oxygen to pass through more easily than other plastics. Its relatively low melting point, around 115°C, makes it highly suitable for heat-sealing and easy processing during manufacturing.
Dominant Uses in Films and Liners
The high flexibility and transparency of LDPE make it the preferred polymer for thin, pliable sheets, accounting for approximately 60% of the global market. This category includes common consumer items, such as plastic bags used for groceries, produce, and dry cleaning.
Its superior moisture resistance and pliability are harnessed in protective packaging like shrink wrap and stretch film used for bundling and palletizing products. LDPE is also extensively used in the agricultural sector for making durable films, such as greenhouse covers and mulch films, which help retain soil moisture and protect crops. Beyond packaging, the material lines liquid containers, providing a protective barrier for substances ranging from milk to various chemicals.
Applications in Molded Items and Extrusion
While LDPE is most famous for thin-film uses, its pliability and chemical resistance also suit it for thicker, molded, or extruded products. It is frequently used to manufacture flexible lids and tops for rigid containers, requiring a tight seal and easy removal. Due to its inherent softness and stress-crack resistance, LDPE is the material of choice for pliable squeeze bottles used for condiments and personal care products.
In industrial settings, the material is extruded into tubing and piping, particularly for agricultural irrigation systems and transporting non-aggressive water or chemicals. A distinct application is its use as jacketing and insulation for electrical cables and wires. LDPE’s excellent dielectric properties—its ability to resist the flow of electricity—make it a reliable protective layer for conductive materials.
LDPE and the Recycling Stream
LDPE is classified under the Plastic Resin Code #4, marked by the chasing arrows symbol with the number four in the center. While technically recyclable, LDPE is not consistently accepted in all municipal curbside collection programs. This is often because thin films and bags can clog sorting machinery at recycling facilities.
Many grocery stores and retail chains offer specialized drop-off collection points for clean plastic films and bags. When successfully recycled, LDPE is often repurposed into non-container products, such as composite lumber, plastic furniture, or trash can liners. LDPE is also considered safe for food contact by the U.S. Food and Drug Administration (FDA) and is a common material for food packaging.