Polybutylene terephthalate (PBT) is a polyester made by the condensation of terephthalic acid and 1,4-butanediol. It is an important thermoplastic polyester and one of the five major engineering plastics.
Polybutylene terephthalate is a milky white, translucent to opaque, semi-crystalline thermoplastic polyester with high heat resistance. It is not resistant to strong acids and alkalis, but is resistant to organic solvents, flammable, and decomposes at high temperatures.
Polybutylene terephthalate is widely used in automobiles, mechanical equipment, precision instrument parts, electronic appliances, textiles and other fields.
Abbreviation: PBT
Special properties: High heat resistance, toughness, fatigue resistance
Appearance: Milky white translucent to opaque, semi-crystalline solid
Chemical formula: (C12H12O4)n
CAS Number: 26062-94-2
Melting point: 233℃
Use
Most of the PBT resin is processed into compounding materials. After being modified with various additives, it can be blended with other resins to obtain good comprehensive properties such as heat resistance, flame retardancy, electrical insulation and good processing performance. It is widely used in industries such as electrical appliances, automobiles, aircraft manufacturing, communications, home appliances, transportation, etc. For example, after being modified with glass fiber, PBT can be used to manufacture electronic components that require long-term operation at high temperatures and high dimensional stability.
PBT has a high breakdown voltage and is suitable for making high-voltage resistant parts. Due to its good fluidity in the molten state, it is suitable for injection processing of electrical parts with complex structures, such as integrated circuit sockets, printed circuit boards, computer keyboards, electrical switches, fuses, temperature control switches, protectors, etc. Automobile bumpers, carburetors, spark plugs, fuel supply system components, igniters, etc. In the field of communications, PBT is widely used in integrated modules, wiring boards, power tools, etc. of programmable telephones.
Preparation
There are two main production methods for PBT : ester exchange and direct esterification polycondensation. The catalysts used include tetraisopropyl titanate, tetrabutyl titanate, zirconium alkoxide, tin alkoxide, etc.
(1) Ester exchange method : The ester exchange method uses dimethyl terephthalate (DMT) as raw material, and first undergoes ester exchange with 1,4-butanediol to produce dibutylene terephthalate, which is then polycondensed to produce polybutylene terephthalate. The ester exchange method uses an excess of 1,4-butanediol, with a molar ratio of DMT to 1,4-butanediol of 1ː1.3~1.7, and a reaction temperature of about 200°C, which is conducive to the reaction balance in the direction of producing dibutylene terephthalate and can reduce the occurrence of side reactions. The second step of polycondensation reaction temperature is about 250~260°C and is carried out under reduced pressure of 0.1~1mm Hg. The ester exchange method can be carried out intermittently or continuously. Its advantages are that the equipment is relatively simple, the reaction conditions are relatively mild, and it is relatively easy to control the ester exchange and polycondensation reactions in steps, but batch production has low efficiency.
(2) Continuous direct esterification polycondensation method: Continuous direct esterification polycondensation technology is relatively complex. Since the process materials are all carried out in a high-temperature, high-vacuum molten state, the equipment material, equipment structure, material transportation, and reaction condition control are relatively complex. Therefore, a variety of patented technologies have been developed. The more famous ones are: Lurgi Zemmer technology, which is characterized by the use of three reactors for esterification, pre-condensation and polycondensation. The polycondensation reactor is a horizontal disc reactor, and a single production line can reach a scale of 120,000 tons/year. The product quality is high, and the by-product tetrahydrofuran can be directly used in the production of polytetrahydrofuran; Japan’s Hitachi technology has four different types of reactors, which can simultaneously produce high-viscosity and medium-viscosity products. The scale of a single production line can reach 60,000 tons/year. Uhde Inyenta Fischer technology uses a tower reactor. Esterification and polycondensation can be completed in one reactor, and PBT products with a degree of polymerization of 20-35 can be produced. If products with a degree of polymerization of 80-150 are to be produced, they can be moved to another horizontal polycondensation reactor called DISCAGE.
(3) Solid-phase polycondensation process: The above process can only produce PBT products with a degree of polymerization of about 100 and a molecular weight of 20,000-35,000, which can meet the needs of textile and membrane products. For some engineering plastic products that require PBT with a degree of polymerization of 150-200 and a molecular weight of more than 40,000, the solid-phase polycondensation process is required. The solid-phase polycondensation process is complex and is carried out in a solid-phase polycondensation reactor. It mainly includes four main process steps, namely pre-crystallization, annealing, reaction and cooling. It can be carried out intermittently or continuously.
Toxic effects
PBT is non-toxic and non -irritating to the skin. The production process has adverse effects on the environment and needs to be managed.
Packaging, transportation and storage
PBT resin is packaged in plastic or woven bags with plastic lining. The storage place should be dry, ventilated, away from rain, exposure, high temperature and open flame, and avoid mixing with strong acids, strong alkalis and strong oxidants.
