Current Status and Development of Plastic Modification Technology

Modified materials emerged in the 1990s. Thirty years of development have endowed them with advantages such as replacing steel, copper, wood, and traditional plastics, and offering lighter alternatives to heavier materials. They are widely used in household appliances, automobiles, high-speed railways, subways, aerospace, ships, office equipment, communication devices, machinery, and construction industries.

According to data from the National Bureau of Statistics, by 2020, the demand for modified plastics in China reached 22.5 million tons, with a modification rate rising to 21.7%. Of this, household appliances accounted for 34%, automotive applications for 19%, and other fields for 47%. By the end of 2022, the production of modified plastics in China reached 28.84 million tons, with a total output value exceeding 415.2 billion yuan. China is gradually becoming the world's largest market and growth driver for modified plastics.

Modified plastics have become a strategic emerging industry and a research hotspot in the field of petrochemical polymer materials in China. Therefore, research on the principles, equipment and processes, raw materials, formulations, key preparation technology challenges, and applications of plastic modification is of great significance for promoting the development of the entire plastics industry.

Figure 1: Plastic

1. Plastic Modification Technology and Characteristics

Plastic modification technology refers to the techniques used to obtain new materials during the processing of polymer resins into plastic products. This can be achieved through physical modification methods such as filling, reinforcing, blending, chemical modification methods such as block copolymerization and radiation cross-linking, or other modification methods like foaming, stretching, and compounding. This technology greatly enhances the flame retardancy, thermal conductivity, mechanical properties, wear resistance, and electromagnetic shielding of plastics. However, it may also reduce certain properties of the original plastics, such as insulation performance, corrosion resistance, and gloss. Suitable formulations and measures can be adopted to minimize these negative changes in performance.

2. Key Technologies in Plastic Modification and Molding

Polymer modification involves mixing and blending base resins with various modifiers using equipment such as premixing devices, batch melt mixing equipment, continuous rotor (FCM) mixers, and reciprocating screw extruders.

In the modification molding process, formulation design and preparation processes are particularly critical. The former includes the selection and principles of the form, dosage, and combination of the basic resin masterbatch and modifiers. The latter involves determining the appropriate modification process flow, selecting molding equipment, and drying plastic pellets. Both can significantly prevent cross-linking or degradation, improving product performance and quality. Additionally, the use of non-destructive testing techniques allows for the inspection and evaluation of the internal and external structure of modified plastics without compromising their structural integrity and performance, ensuring product quality, safety, and reliability, thereby improving production processes and extending product lifespan.

2.1 Key Points in Plastic Modification Formulation

2.1.1 Selection of Base Resin: The resin should be chosen based on its similarity in performance to wear resistance, heat resistance, etc. The viscosity of various resin materials should be close to ensure flowability; different production methods and modification requirements demand different flowability.

2.1.2 Selection of Additives: The selection principles for additives should achieve synergy, counteract undesirable effects, be processable, environmentally friendly, economical, and have minimal or no negative impact.

The shape of additives significantly affects modification. For example, fibrous additives enhance strength, spherical additives improve toughness, flowability, and gloss. Smaller particle size enhances mechanical properties, color strength, and conductivity but reduces monodispersity. The additive shape needs to be comprehensively considered to determine the amount and surface treatment method of additives.

2.2 Key Points in Plastic Modification Process Technology

2.2.1 Drying Treatment:

Plastic pellets containing moisture and volatile low-molecular compounds can easily undergo cross-linking or degradation at high temperatures, leading to defects such as silver streaks and bubbles in products, affecting quality. Preheating and drying treatment of plastics is necessary.

Drying temperature, time, and material layer thickness affect drying effectiveness. In actual production, direct or indirect drying methods should be selected based on the plastic's hygroscopicity, melting point, dew point, humidity, thermal conductivity, and production batch size. Combining these two methods is an effective drying approach.

2.2.2 Screw Combination and Feeding Technology:

In plastic modification molding equipment, the screw structure is the core component of molding. The molding cycle consists of stages such as feeding, melting, blending, and exhaust. Different materials, formulations, performance requirements, molding processes, and stages require different screw structures and combinations, which need systematic research and engineering practice validation.

2.2.3 Filler Surface Treatment Technology:

In the plastic modification process, various polar inorganic fillers need to be added. Since their compatibility with organic materials with very low polarity is poor, modification methods such as powder intercalation, mechanochemical, and chemical coating need to be used to improve compatibility, resulting in high-performance products.

2.2.4 Color Difference and Size Appearance Control Technology:

Combining scientific instruments like computers with the experience of operators for pigment mixing, whiteness and black spots detection, and using impurity filtration technology can produce high-quality, colorful products.

3. Plastic Modification and Non-Destructive Testing Technology and Its Application

In the 21st century, harmonious coexistence between humans and nature is a challenge that humanity must face together. With technological innovation and changes in development methods, all industries are moving towards green, energy-saving, environmentally friendly, recyclable, and reusable directions. High-performance material modification technologies continue to emerge.

3.1 Graphene Modification Technology

Graphene, discovered by Nobel Prize laureates Andre Geim and Konstantin Novoselov, is a new two-dimensional carbon crystal material composed of single-layer carbon atoms from graphite, with a thickness of about 0.335 nm, the thinnest material discovered so far. Polymers modified with graphene exhibit superior performance, such as high heat resistance, corrosion resistance, high hardness, barrier properties, high mechanical and electrical properties. Some scholars have conducted in-depth research on the processing methods, performance, and non-destructive testing of graphene-modified plastics.

Graphene Modified Plastics
Image Source: Xindao Technology

In addition, some scholars believe that graphene modification technology has many challenges to address, such as controllability of layer wrinkles, stacking, and agglomeration, good compatibility, high quality, and low cost.

Kamboj, Saurabh, and other scholars systematically reviewed the latest research results of graphene technology, including the preparation methods of graphene-based composites and their development applications in photocatalysts, supercapacitors, and lithium-ion batteries.

After forming a composite, the performance of nanometal oxide materials is significantly improved, which can effectively degrade organic pollutants in wastewater and be more widely used in photocatalysis. Graphene is also considered an excellent material for supercapacitors, providing great application potential for the development of high-performance electric vehicles. Lithium-ion batteries made from graphene composite materials as negative electrode materials have low self-discharge rates, high energy densities, and good cycle life.

Graphene modification technology also attracts researchers' interest in applications in energy storage, chemical sensors, electronics, and healthcare.

3.2 Carbon Fiber Modification Technology

Carbon fiber, known as the "black gold" of the 21st century, has excellent properties such as high elastic modulus, specific strength, creep resistance, and fatigue and corrosion resistance, making it an enhancing material for modified resin matrices. Thermoplastic reinforcing materials have characteristics like recyclability, fast molding, impact resistance, and easy repair, with promising application prospects in transportation, ships, aerospace, and medical devices.

Due to the different types of carbon fibers, their strength, modulus, interface bonding performance, and comprehensive properties vary. The surface functional groups of carbon fibers show inertness and non-polarity. Using modification techniques to enhance bonding with the resin matrix to improve performance and application fields is the focus of research at home and abroad.

Zhan Yikai, Li Gang, and other scholars reviewed domestic and international surface modification technologies for carbon fibers, divided into chemical methods and physical methods.

Chemical methods include surface oxidation and grafting, with advantages like fast reaction rates and significant effects, increasing surface roughness and microfeatures, thereby improving interface bonding strength. However, chemical modification processes may damage the internal structure of the fibers, leading to reduced strength, which is a challenge that needs improvement.

Physical methods include coating and plasma treatment. These methods are flexible, easy to control, and pollution-free but require high production equipment standards and cannot fundamentally improve surface properties, limiting their development.

3.3 Non-Destructive Testing Technology for Modified Plastics

Complex and unstable manufacturing processes and environmental changes in service can cause various types of damage such as delamination, porosity, fiber breakage, and wrinkling, severely affecting their mechanical properties. Ultrasonic non-destructive testing technology, with advantages like portability, simplicity, and high detection efficiency, is widely used in product design, damage detection, quality evaluation, and life assessment.

Yang Hongjuan and other scholars systematically reviewed ultrasonic non-destructive testing technologies, including C-scan based on body waves or guided waves, phased array, laser ultrasound, air-coupled, and fiber-optic ultrasound, as well as damage diagnostic imaging algorithms to achieve damage morphology imaging. Suitable non-destructive testing methods should be selected based on sample density, thickness, elastic constants, and transducer parameters, and research outlook should be conducted on constructing array sound field models of carbon fiber modified materials, damage imaging algorithms, intelligent monitoring imaging systems, damage quantitative evaluation standards, diagnostic evaluation, and life prediction.

4. Recommendations for the Development of Modified Plastics and Non-Destructive Testing Technology

Improve the industrial, standards, and intellectual property systems for modified plastics.
Promote mutual enhancement between theoretical research and engineering practice applications in plastic modification. Currently, research on modified materials mainly focuses on theory and general product fields, while applied research in production practices involving talent training, equipment manufacturing, formulation design, and process development needs strengthening.

Enhance the conversion rate of scientific research achievements into intellectual property and guide practical production. Strengthen research and production of high-performance modifiers, new materials, and products, guiding major domestic modified plastics enterprises like Kingfa Science & Technology, China Xinda, Silver Jubilee Technology, and Dawn Polymer to produce high-level products, promoting the plastic modification industry in China towards safety, green, environmental friendliness, lightweight functionality, and ecological intelligence.

In non-destructive testing technology and imaging algorithms, further construct array sound field models for carbon fiber modified materials, damage imaging algorithms, develop intelligent monitoring imaging systems, and make non-destructive testing equipment more portable, simpler to operate, and more accurate and efficient.

5. Conclusion

The vigorous development of modified plastics provides strong technical support for the diverse development of industries such as household appliances, automobiles, aerospace, high-speed rail, ships, office equipment, electric tools, and machinery construction. However, these industries also place higher technical requirements on the formulation design, modification molding processes, and equipment of modified plastics. Therefore, research on plastic modification molding technology has positive significance for promoting the development and transformation of the entire plastics industry.