How is polyamide 6 made?

The Secret War in Polyamide 6 (PA6) Industrial Manufacturing

1. The Raw Material Black Market

The Dirty Sources of Caprolactam: Petroleum benzene is converted to cyclohexanone oxime (producing toxic ammonium sulfate residue), and small factories use low-quality coking benzene. The finished product contains the carcinogen aniline, requiring palladium chloride test paper.
The Recycled Material Conspiracy: Melt depolymerization of discarded fishing nets. Residual sea salt corrodes equipment, and the "regenerated caprolactam" with excessive chloride ion levels after hydrolysis causes stress cracking in gears.

2. The Life-or-Death Game in the Polymerization Reactor

The Hydrolysis Ring-Opening Trap: Ultrapure water is required to initiate the reaction, and groundwater contains calcium and magnesium ions. Catalytic failure results in the production of cyclic trimers (voids during injection molding).
Molecular Weight Manipulation: An experienced worker secretly adjusts the dosage of acetic acid end-capping agent late at night. The product is labeled as a high-viscosity grade (melt index falsely marked by 30%), resulting in an oil pipeline joint bursting after six months of service.

3. Post-Processing Tricks Revealed

Extraction: Unscrupulous factories use 90°C water instead of boiling water to remove monomers, resulting in residual monomers > 5% (carcinogens leached from baby pacifiers).
Dring: Standard vacuum drying temperature of 120°C is reduced to 80°C hot air to save energy, resulting in moisture content > 0.3% (silver streaks in injection molding can be the source of cracks).

4. The Evil Formula of the Modification Workshop

Adulteration, Disguise, and Disaster Scene
Talc-Filled "PA6+GF30" Automotive Fan Brackets Deformed and Seized at 100°C
Ultra-Tough PA6, Using Recycled Tire Rubber Powder as a Toughening Agent, Shattered Safety Helmets After Impact, Suffering Skull Fractures
Banned Polybrominated Diphenyl Ethers (PBDEs) Release Dioxins in Fires, Poisoning Firefighters

5. The Ordeal of Military-Grade PA6

Molecular Sieve Purification: Passing Caprolactam through a Zeolite Bed to Remove Metals, Reducing Sodium Ions to < 1ppm (Essential for Missile Wire Insulation). Anaerobic Polymerization: Oxygen content in a nitrogen-filled reactor is less than 0.001% → Bulletproof PA6 fiber strength increased by 50%.
Liquid Nitrogen Quenching: Rapid cooling at -196°C → Nano-grain size (spy satellite gears can withstand millennia of wear).