📘 Six Causes of Plastic Yellowing
Part 2: Thermal Oxidation — Heat as the “Turbocharger” of Aging
🌡 Phenomenon
It’s not only sunlight that causes plastic to yellow—heat itself is also a powerful driver. If the processing temperature is too high, the material stays in the machine too long (“resin hold-up”), or recycled materials are repeatedly reprocessed, color darkening will gradually occur.
Even after products leave the factory, long-term exposure to high temperatures (for example, in server rooms or inside car cabins) will gradually lead to yellowing and embrittlement.
⚗️ Core Mechanism: When Heat Adds Fuel to the Fire
- Higher temperature accelerates reactions: Heat speeds up chemical reactions, promoting free radical formation and accelerating hydroperoxide decomposition.
- β-Scission: Free radicals break polymer chains, reducing molecular weight and mechanical strength.
- Crosslinking and Gelation: Some materials crosslink under heat, becoming harder and brittle, altering melt flow index (MFI).
👉 Like toasting bread—at first only the surface browns, then hardens as heat accelerates aging.
🧩 Common Materials and Scenarios
- PP / PE: Overheating or excessive shear leads to yellowing then brittleness.
- PET: Moisture-sensitive; insufficient drying causes hydrolysis and color deepening.
- PC: Narrow processing window; long residence time or heat causes yellowing unless stabilized.
🔍 Testing Insights
- DSC: Detects crystallinity or melting changes after oxidation.
- GPC: Measures molecular weight drop or crosslinking rise.
- MFI: Scission increases MFI; crosslinking decreases it.
👉 Thermal oxidation affects the full chain from molecular weight → melt flow → performance.
📘 There are four more articles in the “Plastic Aging Mechanism” series explaining yellowing, embrittlement, and gloss loss.
Further reading – Six Causes of Plastic Yellowing Part 1: Photo-oxidation
🔹Chitec Technology | The Expert in Anti-Aging Solutions for Materials
建議您使用以下瀏覽器觀看本網站，
要下載瀏覽器，請直接點擊以下:以獲得最佳瀏覽效果。