I. Highly Degradable Materials
PVC (Polyvinyl Chloride)
Degradation Trigger Temperature: Rapid decomposition occurs above 180℃. When the temperature in a localized area of the hot runner exceeds 200℃, a large amount of corrosive hydrogen chloride gas will be released within minutes.
Degradation Hazards: Decomposition products corrode the inner wall of ordinary stainless steel runners in hot runners, causing yellow streaks and black spots on injection molded parts. In severe cases, a large amount of fumes will be produced.
POM (Polyoxymethylene)
Degradation Trigger Temperature: Chain depolymerization will occur when the processing temperature exceeds 240℃, or when the temperature remains above 220℃ for more than 30 minutes.
Degradation Hazards: Rapid decomposition releases formaldehyde gas; a sudden increase in pressure within the runner may cause material spraying; injection molded parts will show obvious silver streaks and bubbles.
II. Medium-High Easily Degradable Materials
PET (Polyethylene Terephthalate)
Degradation Triggering Conditions: When the material's moisture content exceeds 50 ppm during heating, and the temperature reaches above 280℃, high-temperature hydrolytic degradation will occur.
Degradation Hazards: Molecular chain breakage leads to a significant decrease in melt strength, resulting in insufficient transparency, surface haziness, and a sharp drop in mechanical properties in injection molded parts.
TPU (Thermoplastic Polyurethane)
Degradation Triggering Temperature: When the temperature reaches above 230℃ and the residence time exceeds 20 minutes, molecular chain breakage degradation will occur.
Degradation Hazards: The melt turns yellow, and bubbles and surface pitting appear on injection molded parts, with a significant decrease in elasticity.
III. Medium Easily Degradable Materials
PC (Polycarbonate)
Degradation Triggering Conditions: When the material is not fully dried during heating, resulting in excessive moisture content, and the temperature exceeds 330℃, hydrolytic degradation will occur.
Degradation Hazards: Silver streaks and yellowing appear on the surface of injection molded parts, transparency decreases, and in severe cases, black spots may appear. PA66 (Nylon 66)
Degradation Triggering Conditions: Thermal oxidative degradation will occur if the temperature exceeds 320℃ during the heating process or if the material remains at high temperatures for an extended period.
Degradation Hazards: A sudden drop in melt viscosity leads to embrittlement and a significant reduction in mechanical strength in the injection-molded parts.
IV. Common Characteristics of Degradation Risks
For this type of easily degradable material, if localized hot spots occur during the hot runner heating process, if the melt remains in dead zones for extended periods, or if the material is not sufficiently dried, the degradation trigger time will be significantly accelerated. Strict control of the heating curve and holding time is essential.
