Chemical vs Mechanical Recycling
Mechanical recycling degrades polymer chains over multiple lifecycles, limiting true circularity. Chemical (Advanced) Recycling seeks to solve this by breaking plastics down into their basic molecular building blocks (monomers or hydrocarbon feedstocks), allowing them to be rebuilt into virgin-quality materials regardless of initial contamination or color.
Advanced Methodologies
Pyrolysis
The dominant process for mixed polyolefins (flexible films, mixed PE/PP). Waste plastic is heated in an oxygen-free reactor to temperatures between 400°C and 600°C. Because there is no oxygen, the plastic does not burn; instead, the long hydrocarbon chains fracture, yielding a synthetic crude oil (pyrolysis oil), synthetic gas (syngas), and solid char. The oil can be fed into traditional petrochemical crackers to synthesize new plastics.
Depolymerization (Solvolysis/Glycolysis)
Primarily targeted at PET and Polyurethanes. Using specific solvents and catalysts, the bonds connecting the polymer chain are unzipped. This reduces PET back into its constituent monomers: PTA (purified terephthalic acid) and MEG (monoethylene glycol). These monomers are purified and re-polymerized, yielding virgin-equivalent PET suitable for direct food-contact and medical applications.
Energy Economics & Yield
The primary hurdle for chemical recycling is energy intensity. The thermodynamic cost to break molecular bonds is substantially higher than the energy required for simple mechanical melting. Life-cycle assessments (LCA) demand that chemical recycling facilities optimize their syngas capture to power their own reactor heating to remain environmentally viable.
Processing Complex Feedstocks
Mechanical systems fail when faced with multi-layer packaging (e.g., a pouch containing layers of PE, aluminum, and nylon). Chemical recycling approaches, particularly solvent-based dissolution, offer a pathway to separate these multi-material architectures by selectively dissolving one polymer type at a time, leaving the other substrates intact for secondary recovery.