Полибутилентерефталат

Description

Polybutylene terephthalate (PBT) is a crystalline thermoplastic from the group of engineering plastics, a polycondensation product of terephthalic acid (or dimethyl terephthalate) with 1,4-butanediol. It differs from the related polyethylene terephthalate in the more flexible four-carbon diol fragment: the chain crystallizes faster, which gives a short injection molding cycle and stable dimensions of the castings.

Basic Attributes

• CAS No.: 26062-94-2
• Molecular weight on card: 148.23
• Material class: semi-aromatic polyester, engineering thermoplastic
• Melting point: 224–227 °C
• Relative density: 1.31–1.55 depending on filling
• Water absorption: 0.07%
• Heat resistance by deformation: 60 °C at a load of 1.82 MPa; over 120 °C at a load of 0.45 MPa
• Mechanics: tensile strength and modulus of elasticity at the level of polyoxymethylene and polyamides
• Friction: low coefficient of friction, self-lubricating properties

The original product card did not contain any numerical data other than the molecular weight of 148.23; other indicators are taken from reference sources by CAS number. Brands differ in melt viscosity and type of filler - most often it is chopped fiberglass, less often mineral fillers and fire retardants.

Scope of application

• electrical engineering and electronics: coil frames for television and radio equipment, connectors, housings, terminal blocks, device bases
• automotive industry: parts under the hood, sensor housings, ignition system elements
• mechanical engineering and instrument making: gears, plain bearings and other components where lubricity and corrosion resistance are required
• products operating in humid environments: water absorption of 0.07% prevents sizes from floating

Properties during operation

PBT maintains dielectric properties over a wide range of temperatures and humidity, and is resistant to oils, fuels, dilute acids and most organic solvents. The weak point of polyesters is alkaline hydrolysis and prolonged exposure to hot water and steam. Glass-filled grades increase heat resistance and rigidity, but require strict adherence to the drying regime before casting.

Storage and handling

The granulate is hygroscopic: it is dried before processing, otherwise residual moisture causes hydrolysis of the melt and a drop in molecular weight. Store in a closed, moisture-proof container in a dry place. Take the GHS classification and transport codes from the supplier's safety data sheet - they are not listed in the product card.