Description
Polybutylene terphthalate (PBT; Poly(butylene terephthalate)) is a semicrystalline thermoplastic polyester considered as a medium performance engineering polymer. It is produced industrially in a two-step batch or continuous process. The first step involves the transesterification of dimethyl terephthalate (DMT) with 1,4-butanediol (BDO) to produce hydrobutyl terephtlate (bis-HBT) at a temperature of 200°C. The second step consists to the polycondensation of bis-HBT at 250°C to yield PBT. It exhibits both excellent electrical properties and chemical resistance. When reinforced with glass fibers, it has improved stiffness and mechanical strength. Typical uses include connectors, capacitors and cable enclosures. PBT is also used in hot appliances such as iron and kettles.
Chemical Properties
Poly(butylene terephthalate) is prepared in a condensation reaction between dimethyl terephthalate and 1,4-butanediol and its repeating unit has the general structure:
This thermoplastic shows good tensile strength, toughness, low water absorption, and good frictional properties, plus good chemical resistance and electrical properties.
Uses
Polybutylene terephthalate (PBT) resin is widely used in the automotive, electronics, electrical, machinery, and instrumentation industries to manufacture various structural parts and components. It is also used to produce filaments and films. Glass fiber reinforced PBT with added flame retardants is extensively used in flame-retardant components for televisions, such as output transformer frames and bases, various electrical connectors and switches, potentiometers, strip connectors, and color picture tube sockets. PBT can be blended with other polymers to create plastic alloys, with the largest market being the automotive industry, such as for car bumpers and ignition components. These alloys are also increasingly being used in the food industry, for example, to create microwave oven heating containers that can withstand temperatures above 160°C. Additionally, it is used in mechanical parts and fiber modification.
Synthesis
PBT preparation methods are: dimethyl terephthalate and 1,4-butanediol as raw materials for the ester-exchange method; high purity terephthalic acid and 1,4-butanediol as raw materials for the direct esterification method. The former is generally used in the industry, firstly, the ester exchange reaction is carried out in the ester exchange reactor at atmospheric pressure and 160-190, and then the polycondensation reaction is carried out at pressurized and elevated temperature. The continuous method process can be used to produce low, medium and high products with different viscosities.
