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Research status and application of properties of PBT engineering plastics

🕙 2023-07-27 👆

PBT engineering plastics.jpg

PBT is a crystalline linear saturated polyester prepared by condensation reaction of terephthalic acid (PTA) or dimethyl terephthalate (DMT) with 1,4-butanediol (BDO). It has good mechanical properties, its symmetrical molecular structure can achieve close stacking, has high crystallinity, and can rapidly crystallize at low temperatures. PBT parts are easy to flow and form during processing, with a short forming cycle, which can reduce production costs. Moreover, PBT has advantages such as moisture resistance, wear resistance, oil resistance, and low creep.

Due to the presence of crystalline and amorphous parts in PBT, adding other substances can easily modify it. However, PBT also has defects such as easy combustion, large precipitation of small molecules in contact with refrigerant, insufficient dielectric properties, and easy warping of thin-walled parts, which limit its application range. In order to compensate for the shortcomings of pure PBT resin performance, some modification studies have been conducted on PBT resin.

1. Research status of modification of PBT engineering plastics

In recent years, relevant enterprises have developed various new technologies and products for application, and PBT engineering plastics have developed towards high-performance, functionalized, and diversified directions. In response to the needs of the industrial field, the functionality of PBT has been improved through modification, which is favored by the market. At present, methods such as copolymerization modification, inorganic material filling modification, nanocomposite technology, and blending modification are mainly used domestically and internationally to improve the comprehensive performance of PBT. The research on the modification of PBT materials mainly focuses on high strength, high flame retardancy, low warpage, low precipitation, and low dielectric properties.

Mechanical properties

The tensile strength, bending strength and Flexural modulus of pure PBT resin are low, which can not be widely used in the industrial field. It needs to be modified to improve its mechanical properties. Glass fiber has the advantages of strong applicability, simple filling process, and low cost. The addition of fiberglass in PBT allows for the full utilization of the original advantages of PBT resin, and significantly improves the tensile strength, bending strength, and notch impact strength of PBT products.

In addition to glass fiber, other fibers can also be introduced to improve the mechanical properties of PBT. Zeng Deming et al. used short cut basalt to enhance PBT resin. After being treated with a coupling agent, basalt can be well compatible with PBT, effectively improving the mechanical properties of PBT composites.

In terms of flame retardancy

The vertical combustion level of pure PBT can only reach HB level, which is easy to burn and continuously drips during combustion. The flame is easy to spread, and its applications in automobiles, electronics, and textiles are limited. Halogenated flame retardants and halogen-free flame retardants are often added to modify the flame retardancy of PBT. Halogen flame retardants release toxic smoke containing Hydrogen halide when burning, which is harmful to human health and ecological environment. The EU has banned some halogen flame retardants. Phosphorus based flame retardants and inorganic flame retardants are mainly used for flame retardant modification of PBT.

When using inorganic flame retardants for modification, excessive addition can lead to a decrease in the mechanical properties of the material; However, phosphorus based flame retardants do not have this defect and have excellent characteristics of low smoke, low toxicity, and high flame retardancy. Phosphorus based flame retardants typically collaborate with nitrogen-containing compounds to achieve more efficient flame retardant systems. Phosphorus based flame retardants generate phosphoric anhydride during the combustion process to dehydrate and carbonize combustibles. The carbon layer can reduce heat conduction, delay or prevent the production of combustible gases, and the phosphoric anhydride forms a molten substance that covers the surface of combustibles after being heated, hindering the release of combustible gases.

In addition to traditional flame retardants, there are currently nano fillers added to PBT materials to improve their flame retardancy and anti dripping properties without damaging their processing performance. The commonly used nanomaterials are mainly nano metal oxide polymers and carbon group nanocomposites.

In terms of warping deformation

PBT material molecules are relatively prone to slip, orientation, and crystallization, resulting in a high shrinkage rate of the material and causing warping deformation of PBT parts, especially large thin-walled parts. For glass fiber reinforced PBT, due to the anisotropy of the added glass fibers, the shrinkage rate of the material varies in different directions during injection molding, increasing the warping deformation of the parts. This not only affects the surface quality and installation performance of plastic products, but also affects the strength of the plastic.

For the warping of PBT parts, in addition to improving the shape of the parts, mold design, and molding process parameters, PBT materials can also be modified to reduce warping deformation. In recent years, the warping deformation of PBT materials has been mainly improved through inorganic fillers and co mixed alloys. Inorganic filling includes single inorganic filling and combined filling with glass fiber. The inorganic materials used for filling mainly include talc powder, mica, Wollastonite, glass beads, kaolin, calcium sulfate whiskers, etc.

In addition, amorphous polymers such as polycarbonate (PC), acrylonitrile butadiene styrene copolymer (ABS), and styrene acrylonitrile copolymer (SAN) do not undergo crystallization during the injection molding process. Blending with PBT can also effectively improve the shrinkage of PBT.

In terms of precipitation performance

Due to the incomplete reaction of raw materials in the production process of PBT material, small molecules, oligomers, etc. are generated, and products made of unmodified PBT material precipitate under certain conditions, affecting the effectiveness of the product. When PBT material is applied to the silencer, motor coil framework, air conditioning insulation framework, etc. inside the refrigerator compressor, due to the special working conditions, a large number of small molecular substances are precipitated and dissolved in the refrigerant (Freon, Dichlorodifluoromethane), which is easy to block the refrigeration tube, making its refrigeration failure.

The precipitates of PBT mainly consist of small molecule oligomers of the resin itself and a small amount of additives inside. The use of glass fiber and high viscosity resin, filled with a certain amount of adsorbent, can reduce the precipitation of PBT. At present, the main methods for precipitation modification of PBT are the adsorption of inorganic porous materials and the addition of blocking agents, chain extenders, 1,4-cyclohexanedimethanol (CHDM) and other chemical methods.

In terms of dielectric performance

The dielectric properties of PBT materials play an important role in signal transmission speed, signal loss, and other applications in integrated circuits and electromagnetic shielding. In recent years, stricter requirements have been put forward for the dielectric properties of insulation materials, requiring the dielectric constant of insulation resin materials to not exceed 2.8. However, the dielectric properties of pure PBT materials cannot meet communication requirements. Developing a PBT material with low dielectric constant and low dielectric loss is of great significance.

At present, the dielectric properties of PBT are mainly modified by filling and blending low dielectric constant copolymers, with commonly used fillers being polytetrafluoroethylene powder and hollow glass microspheres. Carbon nanotubes also have a certain positive impact on the dielectric properties of PBT materials, but adding too much content increases the dielectric constant and dielectric loss of the material.

With the rapid development of electric vehicles, their high-voltage transmission requires higher Dielectric strength of connector materials. Although PBT has good arc resistance and is easy to realize high-speed molding, its Dielectric strength is low, which makes it impossible to realize high-voltage transmission on electric vehicles. The dielectric properties of PBT are modified by conductive or ceramic fillers to improve the Dielectric strength of materials to ensure the safety of electric vehicles.

2. The Application of PBT Modified Engineering Plastics

2.1 Automotive sector

With the gradual development of replacing steel with plastics, more and more non-ferrous metals and alloy materials are being replaced by plastics. PBT has good chemical corrosion resistance, stress cracking resistance, wear resistance, weather resistance, aging resistance and high strength performance, and is widely used in automotive external parts, such as wiper handle bracket, bumper, door handle, rear-view mirror shell, underbody, body side panel, radiator fan, radar penetration cover, corner grille and lighting components.

Due to its good processing and insulation properties, PBT has also been widely used in automobile parts, such as instrument panel, accelerator and clutch pedal, vehicle mounted Ashtray, endoscope bracing, etc. In addition, due to its excellent oil resistance, PBT is also used in automotive engine system accessories, such as fuel supply system components, spark plug plates, etc. PBT, which has been modified with alloys, has been applied in recent years to shock absorption sleeves, bearings, and other automotive shock absorbers. Modified PBT has been widely used in automotive engine equipment due to its excellent flame retardancy, dielectric properties, low warpage, and low water absorption.

2.2 Electronic and electrical field

PBT has been widely used in the field of electronic appliances due to its low dielectric, low warpage, high flame retardancy, high toughness, aging resistance, and environmental friendliness. Such as the shell of an electronic computer, igniter, electrical switch, copier, transformer frame, components of a baking machine, electric iron cover, etc. In addition, due to the excellent dielectric properties and easy processing of the modified PBT, it can be used for the bottom cover, shell, and spool of electrical appliances.

PBT is also widely used in communication devices, such as connection boxes, network cable ports, and middle frames for mobile phones and laptops. After modification, PBT is also used to manufacture the lamp head components of energy-saving lamps. The temperature in this area is high, and the flame retardancy of general plastics is difficult to meet the requirements. In the insertion industry, materials are required to pass ball pressure testing and have good flame retardancy.

2.3 Mechanical equipment field

PBT is widely used in the field of mechanical equipment, such as cams, gears, camera parts, Electric watch casings, mercury lampshades and various buttons, due to its high flame retardancy and heat resistance. Common coil frameworks require materials with high insulation breakdown strength to avoid Electrical breakdown during use; When it is applied to components such as refrigerators, it also needs to have low precipitation to prevent the precipitation of small molecular substances from causing mechanical components to fail.

PBT is widely used in the production of coil skeletons due to its excellent low dielectric and low precipitation properties. PBT can be used in the production of Computer fan, such as computer CPU, power supply, motor and other similar cooling fans, due to its excellent flame retardancy, good fluidity and easy molding.

2.4 Communication field

PBT has been widely used in the field of communication due to its good dielectric properties, processability, dimensional stability, and low linear expansion coefficient. In wireless communication, Fe3O4 nanoparticles are added to PBT composite materials to increase their consumption of electromagnetic waves and achieve magnetic shielding function, reducing the harm of electromagnetic radiation to the human body. They are used as plastic substrates for basic components of high-power communication equipment.

PBT is also used in the production of connectors that transmit signals. After modification, PBT not only has the required insulation, flame retardancy, and weather resistance, but also has excellent price and formability, making it suitable for the production of connectors. It is widely used in the interface of television and network cables, as well as the connection and transmission between various unit components of new energy vehicles.

The main components of flame-retardant PBT fiber optic sleeves include flame retardants, toughening agents, coupling agents, light stabilizers, etc. They have advantages such as low shrinkage, UV resistance, high modulus, and flame retardancy. The mechanical properties, flame retardancy, and aging resistance of the optical cable were tested, and the PBT optical cable met the standard requirements. This optical cable is a weather resistant cable with excellent performance and strong applicability to the environment.

2.5 Textile field

Due to the long flexible part on the basic chain of PBT, PBT fibers exhibit superior flexibility and elasticity. At room temperature, their elasticity is comparable to that of rubber, and they are not affected by the surrounding environment. They have fine three-dimensional curls and are suitable for the production of high elasticity and good hand feel textiles such as elastic fashion (such as elastic denim clothing) and elastic composite fabrics (such as elastic yarn for clothing).

In addition, the loose internal molecular structure of PBT and the easy entry of dye molecules make the PBT fiber have good dyeing performance, good fastness, bright color, good chlorine resistance, low price and easy processing, which are widely used in the manufacture of swimwear, Sportswear, home fabric fillers and tufted carpets. The blended fabric composed of PBT and PET has good tensile and compressive elasticity, and its elasticity is not affected by changes in ambient temperature. Due to its low cost, it can be used as a substitute for spandex.

3. Conclusion

There are several different modification methods available to address certain performance defects in the application of PBT engineering plastics in specific fields. Through modification methods such as filling, blending, and preparing nanocomposites, PBT has excellent high strength, high flame retardancy, low warping, low precipitation, and low dielectric properties, which can meet its requirements in fields such as automobiles, electronics, optical fibers, textiles, etc.

In the future, PBT materials that meet the requirements of low-carbon environmental protection and high-quality materials from various industries should be developed. By improving modification technology to accelerate the development of functional PBT products, multiple modification schemes can be comprehensively used to avoid the drawbacks of a single modification method, and to develop PBT materials with high additional functions. Focus on expanding the application of PBT materials in thermal conductivity, biological fields, and electromagnetic shielding, so that PBT materials can be applied in more and more fields.