In the process of plasticizing plastic raw materials, one or more of the following situations often occur, such as the rheology of polymers and changes in physical and chemical properties, which are usually characterized by the following properties:
1. Fluidity: The fluidity of thermoplastics can generally be determined from a series of indices such as molecular weight, melt index, Archimedes spiral flow length, apparent viscosity and flow ratio (process length/plastic wall thickness). analyze.
2. Crystallinity: The so-called crystallization phenomenon refers to the phenomenon that the molecules of the plastic change from free movement and completely disordered to the molecules stop free movement and are arranged in a slightly fixed position to form a molecular display model from the molten state to the condensation.
3. Heat sensitivity: Heat sensitivity means that some plastics are more sensitive to heat. When the heating time is long at high temperature or the shearing effect is large, the temperature of the material increases and it is prone to discoloration and decomposition. When heat-sensitive plastics are decomposed, by-products such as monomers, gases, and solids are produced. In particular, some decomposed gases are irritating, corrosive or toxic to human body, equipment, and molds.
4. Easy hydrolysis: Even if some plastics only contain a small amount of water, they will decompose under high temperature, high pressure, and this property is called easy hydrolysis. These plastics (such as polycarbonate) must be preheated and dried
5. Stress cracking: Some plastics are sensitive to stress, and are prone to internal stress during molding, which is brittle and easy to crack, or the plastic parts crack under the action of external force or solvent. This phenomenon is called stress cracking.
6. Melt fracture: The polymer melt with a certain flow rate passes through the nozzle hole at a constant temperature. When the flow rate exceeds a certain value, obvious transverse cracks occur on the melt surface, which is called melt fracture. When the melt flow rate is selected When producing high-quality plastic raw materials, the nozzles, runners, and feed ports should be enlarged to reduce the injection speed and pressure, and increase the material temperature.
References
[1] Zhong Shuheng. Color Composition. Beijing: China Art Publishing House, 1994.
[2] Song Zhuoyi et al. Plastic raw materials and additives. Beijing: Science and Technology Literature Publishing House, 2006.
[3] Wu Lifeng et al. Masterbatch User Manual. Beijing: Chemical Industry Press, 2011.
[4] Yu Wenjie et al. Plastic Additives and Formulation Design Technology. 3rd Edition. Beijing: Chemical Industry Press, 2010.
[5] Wu Lifeng. Plastic Coloring Formulation Design. 2nd Edition. Beijing: Chemical Industry Press, 2009
Post time: Jun-18-2022