Heating and plasticization control strategies in the melt extrusion process of bottle flake raw materials

I. Characteristics and challenges of bottle flake raw materials
Although the basic chemical composition of recycled PET bottle flakes is the same as that of virgin PET, in actual applications, these bottle flakes often contain a certain amount of impurities, such as label residues, dust, additives, and other substances that may have been introduced during the previous processing. These impurities not only affect the purity of the bottle flakes, but may also change their melting behavior. For example, some additives may reduce the thermal stability of PET, causing it to begin to degrade at lower temperatures, resulting in problems such as gas, color changes, or decreased mechanical properties. Therefore, how to effectively deal with these challenges during the melt extrusion process has become the key to improving the quality of recycled PET.

II. Importance of heating and plasticization
The melt extrusion process is to heat the solid plastic raw materials to a molten state and plasticize them through the shearing action of the screw, and finally form a continuous and uniform melt for subsequent molding processing. For recycled PET bottle flakes, the heating stage needs to ensure that the bottle flakes can quickly and evenly reach the melting temperature, while the plasticization stage requires the melt to have good fluidity and uniformity to reduce internal stress and improve the mechanical strength and surface finish of the product.

3. Accurate control of heating temperature
Accurate control of heating temperature is the prerequisite for achieving efficient melting and plasticization. Too high temperature will accelerate the degradation of PET and lead to a decrease in melt quality; while too low temperature may cause the bottle flakes to not be completely melted, affecting extrusion efficiency and product quality. Therefore, it is crucial to reasonably set the heating temperature curve according to the impurity content of the bottle flakes, the type of additives, and the requirements of the target product. Usually, the temperature in the preheating zone is low and gradually transitions to the high temperature in the melting zone to ensure that the bottle flakes are gradually softened and finally completely melted. In addition, the use of advanced technologies such as infrared heating and hot air circulation can further improve the heating efficiency and uniformity.

4. Adjustment of screw speed
The screw speed is an important factor affecting the plasticization effect and extrusion rate. Higher screw speed can enhance the shearing effect and promote the mixing and homogenization of the melt, but it may also increase the temperature and degradation risk of the melt. On the contrary, although low-speed operation can reduce degradation, it may reduce plasticization efficiency and extrusion output. Therefore, according to the characteristics of the bottle flakes and production needs, flexibly adjusting the screw speed and finding the best balance between plasticization efficiency and degradation control are the key to achieving high-quality melt extrusion.

V. Optimization strategies and practices
In order to further optimize the melt extrusion process of recycled PET bottle flakes, the following strategies can be adopted: first, strengthen the pretreatment of raw materials, such as using advanced cleaning equipment to remove impurities; second, introduce intelligent control systems to monitor and adjust the heating temperature and screw speed in real time to achieve dynamic optimization; third, develop a special screw design suitable for recycled PET to improve plasticization efficiency and melt quality; fourth, explore the use of new additives, such as heat stabilizers and antioxidants, to enhance the thermal stability and degradation resistance of PET.