Recycled Polyester Content Held as Mass Balance against Segregated Stock
Customs compliance requires physical composition testing while brand claims rely on audited mass balance ledgers, forcing buyers to manage separate verification streams.
Antimony Catalyst Residue
Polymer Composition
Inorganic trace elements remaining in polyester polymers after the polymerization process has reached completion. Antimony catalyst residue originates from the use of antimony trioxide or antimony acetate to accelerate the reaction between terephthalic acid and ethylene glycol. It persists in the final fiber at concentrations typically ranging from 150 to 300 parts per million.
Detection Protocol
Laboratory testing identifies these metallic traces through inductively coupled plasma mass spectrometry or atomic absorption spectroscopy. Small quantities of antimony catalyst residue are often found in standard polyethylene terephthalate because the metal is an efficient and cost-effective catalyst for large-scale production. The analysis requires the dissolution of the fiber in a strong acid before the concentration of the metal is measured against a set of calibrated standards.
Quality Impact
Thermal stability during downstream processing depends on the management of these metallic inclusions. High levels of antimony catalyst residue can cause graying or dullness in the yarn, particularly during high-temperature dyeing or heat-setting stages. This effect is most visible in bright white or pastel-colored fabrics.
Regulatory Limit
Safety standards for apparel and footwear often restrict the migration of heavy metals to protect the wearer. Some brands demand antimony-free polyester, which requires the use of titanium-based or germanium-based catalysts during the synthesis of the polymer. The presence of the metal is a standard industry benchmark.