Research status and application of PBT engineering plastics modification

PBT is a kind of crystalline linear saturated polyester made from terephthalic acid (PTA) or dimethyl terephthalate (DMT) and 1,4-butanediol (BDO) by polycondensation reaction, with good mechanical properties, its symmetric molecular structure can realize close stacking, with high crystallinity, can be quickly crystallized at low temperature. With good mechanical properties, its symmetrical molecular structure to achieve close stacking, with high crystallinity, at low temperatures can be quickly crystallized.PBT parts processing is easy to flow molding and molding cycle time is short, can reduce production costs, and PBT has a moisture-resistant, abrasion-resistant, oil-resistant and other advantages, creep is also small.

Since PBT contains crystalline and non-crystalline parts, it is easy to modify it by adding other substances. However, PBT also exists easy to burn, and refrigerant contact with small molecules precipitation, dielectric properties of insufficient thin-walled parts prone to warping and other defects, limiting its scope of application. In order to make up for the lack of pure PBT resin performance, PBT resin has been some modification research.

1. PBT engineering plastics extrusion machine Current status of modification research

In recent years, the relevant enterprises to develop a variety of applications of new technologies and new products, PBT engineering plastics to high-performance, functional, diversified direction. For the needs of the industrial field, through the modification to enhance the functionality of PBT, favored by the market. At present, copolymerization modification, inorganic material filling modification, nanocomposite technology, blending modification and other methods are mainly used at home and abroad 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, low dielectric and so on.

Mechanical properties

Pure PBT resin tensile strength, flexural strength and flexural modulus are low, in the industrial field can not be widely used, need to be modified to improve mechanical properties. Glass fiber has the advantages of strong applicability, simple filling process and low cost, etc. The addition of glass fiber to PBT enables the original advantages of PBT resin to be brought into play, and the tensile strength, flexural strength and notched impact strength of PBT products have been significantly improved.

In addition to glass fiber, other fibers can be introduced to improve the mechanical properties of PBT. Zeng Deming et al. used short-cut basalt to enhance the PBT resin, after the coupling agent role of basalt can be better compatible with PBT, effectively enhance the mechanical properties of PBT composites.

Flame retardant properties

Pure PBTpelletizing machine vertical combustion grade can only reach HB level, easy to burn and burning continuous drip, the flame is easy to spread, its application in automobile, electronic appliances and textiles and other aspects are limited. Halogenated flame retardants and non-halogenated flame retardants are often added to PBT for flame retardant modification. Halogenated flame retardants release toxic fumes containing hydrogen halide when burning, which is harmful to human health and the ecological environment, and some halogenated flame retardants have been banned in the European Union. The flame retardant modification of PBT mainly uses phosphorus flame retardants and inorganic flame retardants.

When using inorganic flame retardant modification, adding too much content will lead to a decline in the mechanical properties of the material; but the phosphorus flame retardant does not have this defect, and has a low smoke, low toxicity, high flame retardant properties. Phosphorus flame retardants are usually synergized with nitrogen-containing compounds to achieve a more efficient flame retardant system. Phosphorus flame retardants in the combustion process to generate phosphoric anhydride to make the combustible dehydration carbonization, carbon layer can reduce heat conduction, delay or prevent the production of combustible gases, and phosphoric anhydride after the heat to form a molten material covering the surface of the combustible material, hindering the release of combustible gases.

Warp deformation

PBT material molecular relative slip is easy, easy to orientation, crystallization, resulting in large shrinkage of the material, causing PBT parts, especially large thin-walled parts of the warping deformation. For glass fiber reinforced PBT, due to the addition of glass fibers with anisotropy, resulting in different directions in the injection molding of the material shrinkage rate is different, increasing the warping deformation of the parts, not only affecting the surface quality of the plastic products and the installation performance, but also affect 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, can also be modified to slow down the warping deformation of PBT materials. In recent years, the warpage deformation of PBT materials is mainly improved by inorganic filling and co-mingling gold. Inorganic filling includes single inorganic filling and combined filling with glass fiber, and the inorganic materials used for filling mainly include talc, mica, wollastonite, glass beads, kaolin, calcium sulfate whiskers and so on.

Precipitation performance

As the raw materials of PBT material can not be fully reacted during the production process, small molecules, oligomers, etc. are generated, and the products made of unmodified PBT material produce precipitation under certain conditions, which affects the effectiveness of the parts. When the PBT material is used in the silencer inside the refrigerator compressor, the motor coil skeleton and the air conditioner insulation skeleton, etc., due to the special working conditions, the precipitation of a large number of small molecules in the refrigerant (Freon, dichlorodifluorodichloromethane) dissolved in the refrigerant tube is easy to block the refrigeration tube, so that its refrigeration failure.

PBT precipitates mainly the small molecule zwitterion of the resin itself and a small amount of additives contained within. The use of glass fiber and high viscosity resin, filled with a certain amount of adsorbent can reduce the amount of PBT precipitation. At present, the main inorganic porous material adsorption form and the addition of blocking agent, chain extender, 1,4 cyclohexanedimethanol (CHDM) and other chemical methods for PBT precipitation modification.

Dielectric properties

PBT materials in integrated circuits and electromagnetic shielding and other fields of application, the dielectric properties of the signal transmission speed, signal loss and so on play an important role. In recent years, the dielectric properties of insulating materials to put forward more stringent requirements, the requirements of the dielectric constant of the insulating resin material does not exceed 2.8. while the dielectric properties of pure PBT materials can not meet the requirements of communication, the development of a low dielectric constant, low dielectric loss of PBT materials is of great significance.

At present, the dielectric properties of PBT are mainly modified by filling and blending low dielectric constant copolymers, and the commonly used fillers are polytetrafluoroethylene powder and hollow glass beads. Carbon nanotubes also have a certain positive effect on the dielectric properties of PBT materials, but the addition of too high a content of the material's dielectric constant and dielectric loss increases.

With the rapid development of electric vehicles, its high-voltage transmission on the connector material dielectric strength requirements are higher, although PBT arc resistance is good, easy to realize high-speed molding but low dielectric strength, can not be realized in electric vehicles for high-voltage transmission. Through the conductor class or ceramic filler on the PBT dielectric properties of the modification to improve the dielectric strength of the material to ensure the safety of electric vehicles.