Processing Machinery
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Degradation during processing caused by poor thermal stability of random copolymer polypropylene raw material
Fenómeno del problema
The product turns yellow or darkens in color, black spots or burn marks appear on the surface, and mechanical properties decline.
Material degradation is a manifestation of molecular chain breakage, and in severe cases large amounts of low-molecular substances are produced, affecting product quality.
Análisis de la causa
(1) Barrel temperature is set too high, exceeding the material's thermal stability temperature
(2) Material residence time in the barrel is too long, and thermal history accumulates degradation
(3) Screw speed is too fast, and shear overheating causes degradation
(4) Raw material antioxidant content is insufficient or has been consumed
(5) Regrind is used multiple times, and antioxidants are exhausted
Solución
(1) Control barrel temperature at a reasonable value within the 190-260°C range to avoid overheating
(2) Reduce material residence time in the barrel, avoiding prolonged high-temperature retention
(3) Reduce screw speed to 50-100rpm to reduce shear heat generation
(4) Select grades with good thermal stability, adding antioxidants if necessary
(5) Control the regrind proportion to no more than 20%, and regrind no more than 2 times
Conclusión clave
Thermal degradation is caused by high temperature, long residence time or excessive shear and needs to be solved from temperature control, rotation speed and regrind management.
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