polyethylene (LDPE, Low density Polyethylene)

Basic Information

Chemical Name: Low-Density Polyethylene

Abbreviation: LDPE

CAS No.: 9002-88-4

Chemical Structure: A linear polymer of ethylene monomers (C₂H₄) with a high degree of long and irregular branching, resulting in a lower crystallinity compared to other polyethylenes.

Physical Properties

Appearance: Typically translucent to opaque white solid; available in pellets, sheets, films, or molded forms.

Density: 0.910–0.925 g/cm³ (lower than high-density polyethylene, HDPE, due to its branched structure).

Melting Point: 105–115°C (varies slightly by grade, depending on branching density).

Tensile Strength: 7–20 MPa (lower than HDPE, reflecting its more flexible nature).

Elongation at Break: 100–600% (high ductility, allowing significant stretching before failure).

Flexibility: Highly flexible and impact-resistant, even at low temperatures (down to -60°C).

Transparency: Semi-transparent in thin films; opacity increases with thickness.

Water Vapor Barrier: Moderate resistance to water vapor permeation, making it suitable for moisture-sensitive packaging.

Chemical Resistance: Resistant to dilute acids, alkalis, and many organic solvents; swells in strong solvents like aromatic hydrocarbons or chlorinated solvents.

Chemical Properties

Stability: Chemically inert under normal conditions; resistant to oxidation at room temperature but may degrade under prolonged exposure to UV light (requires additives like antioxidants or UV stabilizers for outdoor use).

Non-reactivity: Does not react with most food substances, making it safe for food contact applications (complies with FDA and EU food safety standards).

Thermal Behavior: Softens when heated above its melting point; can be melted and reshaped (thermoplastic nature).

Manufacturing Process

LDPE is produced via high-pressure polymerization of ethylene gas (1000–3000 bar, 150–300°C) using free-radical initiators. This process induces extensive branching in the polymer chain, which reduces intermolecular forces and results in the material’s low density and flexibility.

Key Characteristics

Processability: Easy to melt, extrude, blow-mold, or film-cast due to its low melting point and fluidity in molten form.

Cost-Effectiveness: One of the most affordable polyolefins, making it ideal for large-volume applications.

Recyclability: Classified as resin identification code #4; recyclable into products like garbage bags, liners, or plastic lumber.

Applications

Packaging: Dominantly used in flexible packaging, including plastic bags (grocery bags, produce bags), shrink wraps, squeeze bottles (for sauces, detergents), and food packaging films (due to its non-toxicity and sealability).

Agriculture: Greenhouse films, mulch films, and irrigation tubes (benefiting from its flexibility and weather resistance with additives).

Consumer Goods: Toys, squeeze bottles, disposable gloves, and flexible containers (leveraging its impact resistance and ease of molding).

Industrial Uses: Cable and wire insulation (due to its electrical insulating properties), liners for tanks and pipes, and protective covers.

Packaging & Storage

Packaging: Available as pellets (25 kg bags or bulk containers) for manufacturing, or as finished products (films, sheets, molded items) in custom packaging.

Storage: Store in a cool, dry area away from direct sunlight and heat sources to prevent degradation. Pellets should be kept in sealed containers to avoid moisture absorption (though LDPE is inherently moisture-resistant).

LDPE is valued for its unique balance of flexibility, processability, and cost, making it a staple in packaging and consumer goods industries worldwide.

其纯度是多少？

The purity of Low-Density Polyethylene (LDPE) can vary depending on its grade and intended application. Generally, commercial LDPE products are highly pure, with polymer content typically exceeding 99%.

This high purity is achieved through the polymerization process, which minimizes residual monomers (ethylene) and other impurities. For most industrial and consumer applications (such as packaging, films, or molded goods), the remaining trace components (less than 1%) are usually:

Small amounts of unreacted ethylene (well below regulatory limits, often less than 0.1%).

Trace additives (e.g., antioxidants, UV stabilizers, or processing aids) used to enhance performance or stability, which are added in very low concentrations (typically 0.1–1% total).

For specialized applications requiring ultra-high purity (e.g., medical-grade LDPE for pharmaceutical packaging), the purity can be further refined to 99.5% or higher, with strict control over additive levels and residual contaminants to meet stringent regulatory standards (such as FDA or EU 10/2011).

Always check the specific product datasheet from the manufacturer for exact purity details, as it may vary slightly based on production processes and grade specifications.