polypropylene

Polypropylene, also known as polypropene, is a thermoplastic polymer in the polyolefin family. Like other polyolefins, it is derived from the monomer propylene by addition polymerization. It exists in several stereochemical forms, with isotactic polypropylene (iPP) being the most common commercial grade. Atactic PP is amorphous and usually not used commercially; syndiotactic PP is also produced for specialty applications. Polypropylene is typically semicrystalline, with a melting point around 160–170 °C and a density of about 0.90 g/cm3.

Production and catalysts: polypropylene is produced by chain-growth polymerization using Ziegler–Natta or metallocene catalysts, often in slurry, gas-phase, or bulk processes. Polymer properties are tuned by comonomers (random or block ethylene to yield copolymers) and by additives and crystallinity.

Properties and applications: PP offers high chemical resistance, good fatigue endurance, and relatively high heat resistance for a plastic. It has low moisture absorption, good electrical insulation, and moderate barrier properties to gases. It is relatively lightweight and inexpensive. Common grades include homo-PP, random-copolymerized PP, and block-copolymerized PP (impact-modified).

Processing: PP is processed by injection molding, extrusion (films, pipes), blow molding, thermoforming, and nonwoven spinning. Packaging, films, automotive components, textiles, and consumer products are major uses. Medical and laboratory equipment also use PP for sterilizable components.

Recycling and safety: PP is widely recycled (resin code 5). It requires stabilizers for outdoor use to resist UV degradation. It is generally regarded as safe for food-contact applications when manufactured to applicable standards.