An engineering discipline that studies the common laws of physical and chemical processes in plastic processing, as well as the various measures to achieve these processes. It is based on the theories of polymer chemistry, polymer physics and chemical engineering, and uses various advanced experimental techniques and calculation methods to explore the influence of plastic or synthetic resin structural factors and external factors on plastic processing processes and equipment, so as to solve the theoretical and methodological problems of plastic processing technology, plastic product design, plastic machinery design and operation.

The plastic processing industry has developed rapidly, the scale of production has continued to expand, and processing equipment has become increasingly large-scale, efficient and automated, resulting in the requirement to use engineering theory to solve production and application problems. At the same time, the theory and practice of polymer rheology and chemical unit operations have a good foundation, and the application of mathematical model methods and computers has provided advanced methods and means for theoretical research. In 1958, American E.C. Bernhardt first proposed the concept and main content of plastic engineering in the book "Thermoplastic Processing" edited by him, calling for further research on the principles of plastic processing. In 1960, HR Jacobi of the Federal Republic of Germany wrote "Principles of Extrusion Technology", which expounded the theory of melt extruders and was the first monograph detailing the extrusion theory of non-Newtonian fluids. In 1970, Z. Tadmore and I. Klein of the United States co-authored "Principles of Plasticizing Extrusion Engineering", summarizing the research results of plasticizing extrusion principles, which further promoted the development of plastic extrusion technology and equipment. Relying on these theoretical models, many extruder screws and die heads used in industrial production have been designed, and the extrusion process conditions have also been optimized. In terms of the injection molding process, through modeling research, software for mold design and product design has been developed, which greatly saves design time and costs, improves the design accuracy of injection molds and the quality of injection molded parts, and is a major progress in plastic injection molding technology. In 1974, BB Lapshin of the Soviet Union wrote "Principles of Thermoplastic Injection Molding", which summarized the research results of injection molding technology based on the modern concepts of polymer physical chemistry.

The main areas of plastic engineering research are: ¢Ù Plastic compounding: improving or giving plastic certain properties through chemical changes or adding plastic additives to adapt to specific uses and processing requirements. ¢Ú Plastic processing: designing and using various processing techniques and equipment to transform plastic into products with practical application value. ¢Û Plastic product design: selecting materials and structural design of various plastic products based on plastic properties and product use requirements. ¢Ü Other engineering issues in the plastic processing industry, such as quality control, testing technology, application development, cost analysis, market research and standardization.

The object of plastic engineering research is very complex. In the process of plastic processing, there are both physical changes and chemical changes, which often occur simultaneously and affect each other; the material system is also relatively complex, with both solids and melts, and often multiple phases coexist. Moreover, the melt flow behavior varies in many ways, such as Newtonian and non-Newtonian, isothermal and non-isothermal states, high viscosity and low viscosity, etc.; the equipment structure and geometric shape are diverse; the morphology and content of the components in the plastic are different, and the external conditions are unstable, which makes the flow boundary more complex and difficult to describe. Therefore, the analysis and research of plastic engineering often has to rely on practical experience and trial and error. Similarity theory and dimensional analysis are the most commonly used methods. Since the 1960s, mathematical model methods have been applied in plastic engineering research, and combined with experimental work, plastic engineering research methods have been innovated and improved.

The theoretical research on plastic engineering is becoming more and more in-depth and perfect, but the theory of the transfer law of multiphase systems and non-Newtonian fluids in the plastic processing process needs to be deepened. Combined with the determination of plastic properties, further research on the quantitative relationship between the structure and performance of synthetic resins, especially the research on the law of structure and performance changes during plastic processing and use, etc., all need to be continued.

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