Causes of Brittle PET Plastic Sheet

A large part of the brittleness of the PET sheet is caused by internal stress. There are many reasons for the brittleness of products, mainly as follows:

Equipment

1. There are dead corners or obstacles in the barrel of the PET extruder, which easily promotes the degradation of the melt.

2. The plasticizing capacity of the extruder is too small, and the plastic is not fully plasticized in the extruder barrel. The plasticizing capacity of the extruder is too large, and the time that the plastic is heated and sheared in the barrel is too long, the plastic is easy to age, and the product becomes brittle.

3. The ejector device is inclined or unbalanced, and the ejector cross-sectional area is small or improperly distributed.

Mold

1. The gate is too small, you should consider adjusting the gate size or adding an auxiliary gate.

2. If the runner is too small or the configuration is improper, it should be arranged as balanced as possible or increase the size of the runner.

3. Poor mold structure causes an abnormal injection cycle.

Process

1. The temperature of the twin screw extruder barrel and nozzle is too low. If the material is easy to degrade, you need to increase the temperature of the barrel and nozzle.

2. Reduce the screw pre-plastic back pressure and speed to make the material looser and reduce the degradation of the plastic due to shearing overheating.

3. Mold temperature is too high, demolding is difficult; mold temperature is too low, the plastic is cooled prematurely, the weld seam is not fused well, and it is easy to crack, especially for high melting point plastics such as polycarbonate.

4. The cavity core must have a proper demolding slope. When the core is difficult to demold, increase the cavity temperature and shorten the cooling time; when the cavity is difficult to remove, reduce the cavity temperature and extend the cooling time.

5. Use metal inserts as little as possible. Brittle plastics with a large heat and cold specific capacity, such as polystyrene should not be used for insert injection molding.

Raw Materials

1. When the raw materials are mixed with other impurities or doped with excessive solvents, or other additives.

2. Some plastics, such as ABS, will undergo catalytic cracking reaction with water vapor when heated under damp conditions, causing large strains to the parts.

3. Too many times of plastic recycling or too high content of recycled materials, or too long heating time in the barrel will cause the parts to be brittle.

4. The quality of the plastic itself is not good, for example, the molecular weight distribution is large, and the components containing the uneven structure such as rigid molecular chains occupy too much. It may also be contaminated by other plastic adulteration, bad additives, dust, and impurities.

Product Design

1. The product has sharp corners, gaps, or parts with large differences in thickness that are prone to stress cracking.

2. The product design is too thin or too much hollow.