1. What is modified plastic
Modified plastics refers to the addition of small molecular inorganic or organic substances to polymers (resins), through physical or chemical actions, to endow them with certain properties (machining properties) or to improve certain properties.
2.Technology and products of modified plastics
1. The main product of modified plastics is inorganic powder filled modified plastics
Our country's inorganic powder filled modified plastics are in the leading position in the world in terms of output, variety, processing technology and basic theory. Commonly used inorganic powders include calcium carbonate, talc, kaolin, barium sulfate, wollastonite, brucite, tremolite, mica and calcium oxide. According to relevant statistics, the total amount of inorganic powder used to fill modified plastics in my country reaches 7-10 million tons every year, of which more than 70% is calcium carbonate (light calcium, heavy calcium), followed by talcum powder.
The biggest role of inorganic powder filled modified plastics is to save oil resources. my country's petroleum resources cannot meet the needs of rapid economic development, and a large amount of petroleum and resins need to be imported every year. Only five general-purpose resins (PE. P. PVC. PS. ABS) import more than 24 million tons of inorganic powder each year, and the price of inorganic powder is not enough for general-purpose resins. 1/20 of the price, for plastic products, the cost of raw materials accounts for nearly 70% of the total cost. For plastic products manufacturing enterprises, the cost of raw materials is reduced without affecting the appearance and performance of the products, which not only increases the economic benefits of the enterprise, but also improves market competitiveness.
Inorganic powder filled modified plastics also play an important role in the control of white pollution and environmental protection. Experiments have shown that for packaging materials and tableware that are not easy to recycle. Under the condition of ensuring the use performance and sanitation, when the filling amount of inorganic powder (especially calcium carbonate) reaches more than 30%, it is easier to be absorbed by nature after being discarded. If it is used for energy recovery, it is a product with high filling capacity, which is easy to burn, has a high heat recovery rate, and is not easy to cause secondary pollution.
Inorganic powder filling modified plastics is not only for reducing resin consumption, saving petroleum resources, reducing raw material costs, and reducing environmental pollution, but more importantly, it can endow or improve certain functions of materials, which are irreplaceable by other methods. The most representative ones are as follows:
▶ Talc. Filling into the resin can increase the rigidity of the material, and it is widely used in PE and PP pipes, which can improve the ring stiffness of the pipe and increase the compressive strength.
▶ Kaolin. Calcined kaolin is generally used for plastics, which can improve the insulation of the material and block infrared rays. It is widely used in cables, greenhouse films and mulch films to improve the insulation of cables and increase the temperature inside the shed and on the ground.
▶ Inorganic powders with acicular structure, such as wollastonite, tremolite powder (also known as composite acicular powder) and some whiskers. To increase the strength and toughness of the material, the masterbatch produced with it is usually called tower strength or reinforcing masterbatch.
▶Mica. It can significantly improve the rigidity, heat resistance and electrical insulation of the product. Its increased rigidity is better than talcum powder, and its insulation is better than kaolin.
▶Brucite. It is a kind of cheap natural inorganic flame retardant. When the use of halogen series, especially decabromine ether, is restricted, inorganic flame retardants are becoming more and more popular. The higher the purity of brucite, the smaller the particle size, the better the flame retardancy. In addition to being flame retardant, brucite also has the function of eliminating smoke.
▶Precipitate barium sulfate. Prepared by chemical methods, the purity can reach 99%, the whiteness can reach more than 989%, the particle size is generally above 10,000 days, the particle size distribution is narrow, the particles are relatively regular and round, and the chemical resistance and heat resistance are good. In recent years, studies have found that the oil absorption value of precipitated barium sulfate is much lower than that of other inorganic powders, only about 16, 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 tower light effect is better than that of ordinary brightening agents, and it will not overflow for a long time. It can be filled into the sewage pipes for construction, which can increase the density of the pipes and has a good sound insulation effect.
▶ Natural zeolite. It has strong adsorption, can remove the peculiar smell of the product, and has little effect on the strength of the product. As a deodorizing masterbatch, it works well in recycled materials.
2. Modified plastic processing equipment
Modified plastics, whether it is filling modification, blending modification or reinforcement modification, the basic principle is to mix materials with different properties, with the help of additives, through mechanical methods to break the boundary of the interface and mix them into a homogeneous body , The more uniform the mixing, the tighter the interface is combined, and the better the performance of the material. The quality 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, my country's plastics machinery processing industry has also achieved rapid development in modified plastics processing equipment in the past 20 years. In the early 1980s, when calcium carbonate filled masterbatches came out, there was no twin-screw extruder in China, and only single-screw extruders could be used to produce calcium carbonate masterbatches. So far, the level of twin-screw extruders in my country has reached the international advanced level, which can not only meet the needs of domestic production, but also have a large number of exports every year.
In the plastic machinery processing industry, in addition to the continuous upgrading of twin-screw extruders to meet the needs of modified plastics. It has also successfully researched and developed a reciprocating single-screw extruder and a three-screw extruder. For dead powder filling modification, the surface activation treatment of the powder directly affects the product quality. At present, enterprises that produce filler masterbatch mainly use high-speed mixers for surface activation treatment of inorganic powder. In recent years, enterprises producing high-speed mixers have successfully developed continuous production equipment specially used for surface activation treatment of inorganic powders.
The mixed flower of biological science is in the province of Baoguang Neike, and Yu Zhengsheng's drunken chapter commission quality construction only has the most effect on super-making, and the super-junction set up is more than general-type development. Some of the open ones use the Xixihang process to reduce the date and the dance light, and the pass number is sold out in 1, 10, and the materials are added to the removal machine together without heating. Those who pass the exercise will automatically open up Changchang through their own pressure and strong deduction force. About 12~15in, press into a single-screw or double-bar extruder for regulation. According to relevant reports, a new type of granulation equipment similar to the internal mixer process has been researched and developed recently. The double-rotor continuous mixer is used instead of the internal mixer. The plasticized material directly enters the single-screw granulation through a two-stage method. become one.
3. Modified plastic processing aids
Auxiliaries are indispensable and important raw materials for the production of modified plastics. No matter it is filling modification, blending modification or reinforcement modification, additives are inseparable. There are many kinds of additives used in modified plastics, commonly used are: coupling agent, dispersant, lubricant, plasticizer, compatibilizer and fluorescent whitening agent. The development of modified plastics has led to the development of additives. When calcium carbonate filled masterbatches were initially produced, there were no coupling agent products on the market, but stearic acid was used instead. Aluminate coupling agent first came out in 1984, because of its low price, light color, non-toxic, good thermal stability, easy to use and other advantages, it was quickly popularized and used. The application of aluminate coupling agent plays an important role in improving the performance and quality of inorganic powder filled masterbatch. Following aluminate coupling agents, silane coupling agents, titanate coupling agents, rare earth coupling agents, acid phosphite coupling agents, aluminum/titanium composite coupling agents, polymer coupling agents, etc. A series of new coupling agent products with excellent performance and available for different modified products have been developed one after another. For inorganic powder filled modified plastics, the coupling agent plays a vital role in the performance of the product.
With the continuous progress and development of scientific theories, in order to better meet the market demand, some multifunctional coupling agents have emerged in recent years, such as enhanced type, toughened type, amphiphilic water-suppressing type, anti-silent external line Type, brightening type and other new coupling agents.
Although the processing aids used in modified plastics have made great progress and development, there is still a certain distance from the actual needs, such as solving the problem of nano-scale inorganic powder agglomeration in plastics.