In recent years, the global engineering plastics industry has developed rapidly, and is expected to grow to US$113.7 billion by 2020. By then, the global demand for engineering plastics will reach 29.1 million tons annually. Developing regions such as Asia, South America and the Middle East will be the main driving force for the growth of Engineering plastics. Over the past 10 years, the annual output value of engineering plastics in China has increased by more than 20%. At present, the annual production capacity of engineering plastics in China has reached 600,000 tons, and the annual output of modified engineering plastics has exceeded 2 million tons. Some products processing technology has entered the international advanced ranks.
Polytetrafluoroethylene (PTFE) is a a kind of fluorinated materials with excellent comprehensive properties. Engineering plastics modified by PTFE are mainly used in high-end applications. With the continuous improvement of social demand, the market potential of these products is huge.
Polytetrafluoroethylene (PTFE) is a fluorinated polymer material invented by Dr. Plunkett in the 1930s. Because of its excellent comprehensive properties, PTFE has the reputation of “King of Plastics”. The excellent performance of PTFE comes from its unique molecular structure. The structure formula of PTFE is [CF2CF2] n. Hydrogen connected with carbon atom is replaced by fluorine atom. Under the protection of fluorine atom, PTFE has excellent properties of temperature resistance, radiation resistance, aging resistance, insulation, flame retardancy, adhesion resistance, self-lubrication and so on. It has been widely used in many fields.
Blending modification of engineering plastics by using the excellent properties of PTFE can complement each other’s advantages, further improve the properties of engineering plastics and expand their application fields. The modification of engineering plastics by PTFE blend modifier mainly concentrates on two aspects: anti-wear lubrication and anti-dropping flame retardant.
The chemical compositions of anti-wear lubricants and anti-dripping agents are both polytetrafluoroethylene. The difference is that the molecular weight of anti-wear lubricants is about 300,000, and that of anti-dripping agents is about 4-5 million. The addition of low molecular weight PTFE to plastics, rubber, coatings and other fields can significantly reduce the friction coefficient of the material surface, improve the wear resistance of the material itself, and play the role of internal lubrication and demoulding. Polytetrafluoroethylene (PTFE) with large molecular weight is fibrotic under the action of shear force of screw to form a network structure and play a role in anti-dripping.
1. Anti-wear lubricant
Most engineering plastics have high surface friction coefficient and need external lubricants in sliding friction situations, which limits the application of engineering plastics in situations where external lubricants are not allowed to be used. Polytetrafluoroethylene (PTFE) has very low surface energy and excellent self-lubricating properties. By blending PTFE with engineering plastics, oil-free lubricating composites with low surface friction coefficient can be prepared.
Polytetrafluoroethylene (PTFE) superfine powder with molecular weight of 30,000-200,000 and average particle size of less than 30 microns is used as friction reducing lubricant for engineering plastics modification, also known as PTFE micro powder. The properties of PTFE powder, such as wide working temperature range, weather resistance, chemical stability, self-lubrication and non-stickiness, are exactly the same as those of high molecular weight PTFE resin. While maintaining the original properties, PTFE powder has the advantages of good dispersibility and easy mixing with other materials evently. It is an excellent modifier.
2. Anti-dripping agent
There are three main types of anti dripping agents: Pure powder type, emulsion type and coated type.
1). Pure powder type
Pure powdered anti-dropping agent is pure PTFE particles. The dispersion and fluidity of PTFE can be improved by sintering the surface of the particles. When the anti-dropping agent is premixed with plastics, it has better dispersing function and avoids early fibrosis.
The advantage of pure powder anti-dropping agent is that the content of PTFE is 100%, and it can be added in a large amount without any other impurities.
2). Emulsion type
The emulsion type anti dripping agent is made of polytetrafluoroethylene dispersed in water under the action of dispersant and made into a polytetrafluoroethylene dispersion emulsion. Because the emulsion contains a lot of water, it has higher requirements for the equipment and technology when used.
3). Coated Type
Coated anti-dripping agent is a kind of polymer coated on the surface of PTFE particles, which makes it have better dispersion in the process of mixing plastic resin. The outer coated polymer is generally polyacrylonitrile, polystyrene and polymethyl methacrylate.
Compared with the pure powder and emulsion type anti dripping agents, the coated anti dropping agent has the advantages of good dispersibility, easy to use, no agglomeration at room temperature, easy to store, no crystal spots on the product surface, and high surface finish. However, the polymer coated on the outer layer of the final product belongs to impurities, which will have a certain impact on the performance of the product. In addition, the maximum dosage of coated anti dripping agent can only be 0.5%.