Polypropylene is a thermoplastic polymer (thermoplastic): refers to a material that can be hardened after being heated and cooled, and can be repeatedly processed; polymer: refers to a natural or synthetic compound whose molecule is formed by a series of simple monomeric children. Repeated macromolecules are widely used, and even Australian banknotes are made of PP. PP has an unusual resistance to chemical solvents, acid and alkali resistance.
Can produce high-purity PP for the semiconductor industry. It is also antibacterial and suitable for disposable syringes and medical equipment. Can be used for injection molding or machining and welding. Can be used for pipes, filter materials, horns and other plastic products with higher quality requirements than polyethylene products. The banknote is made of biaxially stretched PP (BOPP) so that its durability is improved.
Polypropylene was discovered by Italian chemist Giulio Natta in the early 1950's. In modern science, inventing something that may be invented in different places at the same time. Polypropylene is such an extreme example that it was independently invented about nine times. It was a script that the patent attorney dreamed of was a good show. The lawsuit ended in 1989.
Polypropylene has been trying to perpetuate this legal series. Two American chemists J. Paul Hogan and Robert Banks who worked for Philippe Petroleum are now considered to be the "official" inventors of this material. Polypropylene is also like its cousin, polyethylene, which is very cheap and well supplied. Products from plastic bottles to carpets, plastic furniture, in the automotive industry is also very large.
Polypropylene is a highly rigid material and belongs to the same polyolefin as PE. The homopolymer density is as low as 0.90. Glass fibres and minerals (eg calcium carbonate) can be added. PP is not suitable for use below 0oC. If it is to be used at sub-zero temperature, copolymerization with butadiene is necessary, so that copolymer PP is produced. The operating temperature of homopolypropylene is 90oC, and its resistance to chemicals (acid, alkali) is very good. Parts produced with homopolymer PP have very low moisture absorption, but shrink large during injection molding. The electrical performance is very good, but the UV rotation resistance and other penetration resistance are poor.
Common methods for chemical modification: one is that the modified resin monomer is a single element, the modified monomer is another element, and the graft copolymerization is performed in the reaction vessel to obtain a new copolymer; the second method is to As the main raw material, the modified resin is effectively modified by increasing the polar elements in the resin molecules.
Polypropylene is widely used in the production of plastic pipes, but PP is a material with poor aging resistance. In order to improve the performance of PP, PP-B and PP-R resins were invented through chemical modification methods.
PP-B resin is a block copolymer of propylene and ethylene. Two polymerization reactors are used to synthesize propylene-ethylene block copolymers. One is used to polymerize monomer propylene into homopolypropylene, and the other is to introduce the homopolymer PP produced in the first reactor into ethylene to form a propylene-ethylene block copolymer, ie, to form an ethylene-propylene elastic segment. PP-B resin is essentially a copolymerization modification of homopolymer PP and ethylene. The modified PP-B resin combines the performance advantages of PE and PP.
PP-R is a random polypropylene modified with ethylene based on copolymer PP. The random molecular weight of PP is only tens of thousands, the cohesion is small, the melting point is low, and the mechanical properties are poor. Only ethylene-modified random PP has practical application value. The modification process is to vaporize propylene and send it into the reaction vessel by gas phase method, and send the material from the first reaction vessel to the second reaction vessel with an air lock system, and add ethylene to the second reaction vessel. A high-activity, highly-selective propylene catalyst was added to the upper part of the reactor and dispersed uniformly on the powder layer by stirring, and a random copolymer was formed by controlling the ratio of ethylene and propylene. This polymer changes the configuration of the PP molecular chain and causes ethylene to randomly and uniformly polymerize on the PP molecular chain.
Compared with ordinary PP, the stress cracking resistance of PP-R material is greatly improved. Under the effect of temperature and internal and external pressure, its performance decay is very slow. It is one of the most ideal materials for the production of hot and cold water pipes. .
Chemical modification to create new materials Chemical modification can not only change the properties of a resin, but also create new resin materials. Some of the most commonly used resin materials are modified, such as UHMPE, which is a chemically modified product. This UHMWPE greatly improves the mechanical properties of HDPE materials. Its wear resistance and self-lubrication are superior to those of other engineering plastics. Its mechanical properties and corrosion resistance are no less than those of polytetrafluoroethylene (PTFE).
LLDPE is also obtained by chemical modification. It is a copolymer formed by introducing a small amount of a-olefin monomer such as butene, hexene and octene into ethylene polymerization. It has a similar molecular configuration as HDPE but reduces the density and crystallinity. LLDPE has good resistance to environmental stress cracking, and its mechanical properties are also superior to LDPE. Therefore, its application range has been correspondingly expanded. Chlorinated polyethylene (CPE) is also a chemically modified product. It is the product of HDPE after chlorination. Chlorine (CL) partially replaces hydrogen (H) in the HDPE molecule, causing the crystal to be destroyed by the crystal, making it more flexible and somewhat elastic. It can be processed into CPE products not only by extrusion or injection molding, but also widely used in construction, electrical appliances, etc. Moreover, CPE itself is an excellent modifier and can improve the flame retardancy of PE materials through physical blending methods. Impact resistance of PVC materials.
Physical Modification Blend Modification The resin is blended with one or more other materials by mechanical means to achieve certain special requirements. This method is physical modification of the blend. Blend modification does not change the molecular configuration but can impart new properties to the material.
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