Special engineering plastics! What is modified plastic?
Modified plastics refer to the addition of small molecule inorganic or organic substances to polymers (resins), which impart certain properties (mechanical processing properties) or improve certain properties through physical or chemical reactions.
Technologies and products of modified plastics
Modified plastic main product - inorganic powder filled modified plastic
China's inorganic powder filled modified plastics are in a leading position internationally in terms of production, variety, processing technology, and basic theory. Common inorganic powders include calcium carbonate, talc, kaolin, precipitated barium sulfate, wollastonite, brucite, tremolite, mica, and calcium oxide. According to relevant statistics, the total amount of inorganic powder used for filling modified plastics in China each year reaches 7-10 million tons, of which more than 70% is calcium carbonate (heavy calcium, light calcium), followed by talc powder.
The greatest function of inorganic powder filled modified plastics is to save petroleum resources. China's petroleum resources cannot meet the needs of rapid economic development, and a large amount of petroleum and resin need to be imported every year. Only the five major general-purpose resins (PE, PP, PVC, PS, ABS) have an annual import volume of over 24 million tons. The price of inorganic powder is less than 1/20 of the price of general resin, and for plastic products, raw material costs account for nearly 70% of the total cost. For plastic product manufacturing enterprises, reducing raw material costs without affecting the appearance and performance of the products not only increases the economic benefits of the enterprise, but also enhances market competitiveness.
Inorganic powder filled modified plastics also play an important role in controlling white pollution and environmental protection. Experimental results have shown that for packaging materials and tableware that are not easily recyclable, under the conditions of ensuring performance and hygiene, when the filling amount of inorganic powder (especially calcium carbonate) reaches 30% or more, they are more easily digested by nature after disposal. If used as an energy recovery product with high filling capacity, it is easy to burn, has a high heat recovery rate, and is less likely to cause secondary pollution. Inorganic powder filled modified plastics are not simply used to reduce resin usage, save oil resources, lower raw material costs, and minimize environmental pollution. More importantly, they can endow or improve certain functions of the material, which is irreplaceable by other methods.
1、 The most representative ones are as follows:
(1) Talc. Filling into resin can increase the rigidity of the material and is widely used in PE and PP pipes, which can improve the ring stiffness of the pipe and increase its compressive strength.
(2) Kaolin. Plastic is generally made of calcined kaolin, which can improve the insulation and block infrared radiation of the material. It is widely used in cables, greenhouse films, and plastic films to improve the insulation of cables and increase the temperature inside and on the ground.
(3) Inorganic powders with needle like structures, such as wollastonite, tremolite powder (also known as composite needle like powder), and certain crystal whiskers. The masterbatch produced by increasing material strength and toughness is usually referred to as reinforced or reinforcing masterbatch.
(4) Mica. It can significantly improve the rigidity, heat resistance, and electrical insulation of the product. Its increased rigidity is better than talc powder, and its insulation is better than kaolin.
(5) Magnesium hydrate. It is a cheap natural inorganic flame retardant, which is increasingly favored when the use of halogen series, especially decabromodiphenyl ether, is restricted. The higher the purity of brucite, the smaller the particle size, and the better the flame retardancy. In addition to flame retardancy, brucite also has smoke reducing properties.
(6) Precipitation of barium sulfate. Prepared by chemical methods, the purity can reach 99%, the whiteness can reach over 98%, the particle size is generally above 10000 mesh, the particle size distribution is narrow, the particles are relatively regular and round, and the chemical and heat resistance is good. In recent years, studies have found that the oil absorption value of precipitated barium sulfate is much smaller than other inorganic powders, only about 16, making it difficult to agglomerate and easy to disperse. Filling it into plastics has little effect on its mechanical properties and can significantly increase the brightness of the product. The brightening effect is better than ordinary brightening agents, with long-term no overflow. When filled into building drainage pipes, it can increase the density of the pipes and have good sound insulation effect.
(7) Natural zeolite. It has strong adsorption ability, can remove the odor of the product, and has little impact on the strength of the product. As a deodorizing masterbatch applied in recycled materials, it has a good effect.
2、 Modified plastic processing equipment
The basic principle of modified plastics, whether it is filling modification, blending modification or reinforcement modification, is to break the interface boundaries of materials with different properties with the help of additives through mechanical methods, and mix them into a uniform body. The more evenly mixed, the tighter the interface bonding, and the better the material's performance. The performance of processing machinery plays a very important role in the performance and strength of modified plastics.
Driven by the rapid development of modified plastics, in order to meet the market demand for modified plastics, China's plastic machinery processing industry has also achieved rapid development in modified plastic processing equipment in the past 20 years. In the early 1980s, when calcium carbonate filled masterbatch was introduced, there were no twin-screw extruders in China, and only single screw extruders could be used to produce calcium carbonate masterbatch. So far, the level of twin-screw extruders in China has reached the international advanced level, which can not only meet domestic production needs, but also export a large amount every year.
In addition to continuously updating and transforming twin-screw extruders to meet the demand for modified plastics, the plastic machining industry has also successfully researched and developed reciprocating single screw extruders and triple screw extruders. For the modification of crash powder filling, the surface activation treatment of the powder directly affects the product quality. At present, enterprises producing filling masterbatch mainly use high-speed mixers for surface activation treatment of inorganic powders. In recent years, enterprises producing high-speed mixers have successfully developed continuous production equipment specifically for surface activation treatment of inorganic powders.
In recent years, many enterprises have successfully applied the internal mixer originally used in the rubber industry to the production of filling masterbatch, and have achieved good results. Its advantages are high production efficiency, saving electricity, manpower, and additives, and reducing dust pollution. The specific method is to add all materials together into the internal mixer according to the formula, without heating. The temperature is automatically raised by the pressure and strong shear force of the internal mixer itself, and it is molded for about 12-15 minutes before being pressed into a single screw or twin-screw extruder for granulation. Material mixing and plasticization are completed in the internal mixer, where the single screw or twin-screw only plays a granulation role, so the structure is much simpler than ordinary single screw or twin-screw. Using the internal mixer process to produce filling masterbatch of the same specifications can save costs of 150-180 yuan per ton.
According to relevant reports, a new type of granulation equipment similar to the internal mixer process has recently been developed, which uses a dual rotor continuous mixer instead of the internal mixer. The plasticized material is directly fed into the single screw granulation through a dual stage method, and the entire equipment is integrated.
3、 Modified plastic processing aids
Additives are essential raw materials for the production of modified plastics, whether it is filling modification, blending modification, or reinforcement modification, all of which rely on additives. There are many types of additives used in modified plastics, including coupling agents, dispersants, lubricants (internal and external lubrication), plasticizers, compatibilizers, nucleating agents, and fluorescent whitening agents. The development of modified plastics has driven the development of additives. When initially producing calcium carbonate filled masterbatch, there were no coupling agent products on the market, but stearic acid was used instead. Aluminum ester coupling agents were first introduced in 1984 and were quickly promoted due to their low price, light color, non toxicity, good thermal stability, and easy use. The application of aluminum ester coupling agents plays an important role in improving the performance and quality of inorganic powder filled masterbatch. After aluminum ester coupling agents, a series of new coupling agent products with excellent performance, such as silane coupling agents, titanium ester coupling agents, rare earth coupling agents, acid phosphite coupling agents, aluminum/titanium composite coupling agents, and polymer coupling agents, have been developed successively for different modified products. Coupling agents play a crucial role in the performance and quality of inorganic powder filled modified plastics.
With the continuous progress and development of scientific theories, in order to better meet market demand, some multifunctional coupling agents have emerged in recent years, such as reinforcing, toughening, amphiphilic water suppressing, UV resistant, and brightening new coupling agents.
Although there has been significant progress and development in the use of processing aids for modified plastics, there is still a certain distance from practical needs, such as solving the problem of aggregation of nanoscale inorganic powders in plastics.
4、 The development trend of modified plastics
1. General plastic engineering plasticization, despite the continuous increase in new products of engineering plastics and the exploration of application fields, and the continuous reduction of costs due to the expansion of production equipment; However, with the continuous development and maturity of modification equipment and technology, general-purpose thermoplastic resins have become increasingly engineered through modification and have seized some of the application markets of traditional engineering plastics.
2. With the booming development of the domestic automotive, electrical, electronics, communication, and machinery industries, the demand for modified engineering plastics will significantly increase, and various high-strength and heat-resistant engineering plastics will be widely used.
3. Low cost special engineering plastics, such as polyphenylene sulfide (PPS), polyetherimide (PEI), polyimide (PI), polyetheretherketone (PEEK), imide (PAI), polysulfone (PSU), and polyphenylene sulfone (PPSU), have become increasingly important applications in cutting-edge technology fields such as electronics, automotive, aviation, instrumentation, petrochemicals, rockets, and aerospace due to their excellent electrical properties, high temperature resistance, and dimensional stability. Some also have good flame retardancy, radiation resistance, chemical resistance, and mechanical properties.
4. Nanocomposite technology will bring new opportunities for modified plastics, and the manufacturing and application of polymer nanocomposites will be an important topic in the future. Nowadays, the development of nanotechnology is advancing rapidly, and nano polymer materials, as an important branch, are showing new trends in research and development. The potential benefits of nanotechnology drive scientists from many countries to constantly explore and research, and the competition is fierce. For nano polymer materials, due to the small particle size, large surface area and easy agglomeration of nano powder particles, it is difficult to obtain nano structured composites by conventional blending methods when preparing nano powder modified polymer composites. In order to increase the interfacial adhesion between nano additives and polymers and improve the uniform dispersion ability of nano particles, surface modification of nano powders is required. Mainly to reduce the surface energy state of particles, eliminate the surface charge of particles, improve the affinity between nanoparticles and organic phases, and weaken the surface polarity of nanoparticles.
5. Developing new and efficient additives is also an important direction for the development of modified plastics. In addition to commonly used additives in plastic processing such as heat stabilizers, antioxidants, UV absorbers, nucleating agents, antistatic agents, dispersants, and flame retardants, toughening agents, flame retardant enhancers, alloy compatibilizers, and other additives are also crucial for modified plastics.
6. Developing efficient reactive functional intercalation agents to generate nano scale dispersed phases in situ through chemical bonding, thereby connecting the nano dispersed phases to the main chain of polymer molecules through chemical bonding, forming a seamless polymer/layered silicate nanocomposite material. With existing plastic film, sheet, and bottle forming equipment and processes, new plastic packaging products can be efficiently and low-cost manufactured, which can be recycled and reused, recycled and granulated for reuse. It is a new type of high barrier plastic packaging material with green environmental protection concepts.
PRES focuses on the production of special engineering plastic particles, modification production, sheet production, and bar production. The special engineering plastics produced by PRES have good strength and toughness, strong resistance to oxidation and aging, and great value in use. They enhance the hardness, rigidity, compression and wear resistance, and are suitable for processing bars, sheets, profiles, etc., thereby reducing production costs for enterprises.
