The Reason and Solution for Whitening of PET Preform Bottom

The Reason and Solution for Whitening of PET Preform Bottom

PET preform is an essential component for producing plastic bottles, especially those for drinking water and beverages. However, some PET preforms may have a whitening phenomenon at the bottom, which affects the appearance and the quality of the final product. In this article, we will explore the causes of PET preform whitening and the solutions to prevent it.

First of all, what causes PET preform bottom to turn white? It is mainly attributed to the insufficient drying of the PET resin before injection molding. PET resin is highly sensitive to moisture, and even a small amount of water can cause degradation during processing. Moisture, in combination with heat and pressure, causes hydrolysis of PET molecules, leading to the formation of white dots or streaks at the bottom of the preform. Moreover, high-cavity injection molds with low cooling efficiency will increase the residence time of PET in the hot runner system, resulting in more exposure of the material to high temperature and moisture.

To solve the whitening problem, we need to take a series of preventive measures. First and foremost, it is recommended to source high-quality PET resin from reliable suppliers. The moisture content of the PET resin should be less than 0.02% before processing. Secondly, the drying process should be optimized to eliminate any residual moisture in the resin. Dryers with dew-point control are highly recommended, which can precisely monitor the humidity and temperature of the drying air. Thirdly, choose injection molding machines that have adequate injection pressure and cooling capacity to minimize the material's exposure to high temperature and moisture in the mold. Finally, regular maintenance of mold and hot runner systems is needed to prevent any water buildup.

In conclusion, PET preform whitening is a common issue in the plastic industry, but it can be prevented by taking appropriate measures. The key is to control the moisture level in the PET resin and control the processing conditions to minimize hydrolysis. With proper techniques and equipment, high-quality PET preform can be produced, contributing to the sustainable development of the plastic packaging industry.