PBT Performance Improvement Strategy

PBT Performance Improvement Strategy

Among numerous engineering plastics, Polybutylene terephthalate (PBT) is widely used due to its unique advantages. However, in order to further expand its application areas, it is crucial to enhance the heat resistance and impact strength of PBT. The following elaborates on effective methods to improve the performance of PBT from three dimensions: material modification, process optimization, and synergistic strategies.

I. Routes to enhance the heat resistance of PBT

1. Introduction of reinforcing agents:

Glass fiber (GF) and carbon fiber (CF) are common reinforcing materials for improving the heat resistance of PBT. When 15-30% of GF or CF is added, the heat deflection temperature (HDT) and mechanical strength of PBT will significantly increase, with GF being able to raise the HDT from about 60℃ to over 200℃. In addition, mineral fillers such as talc, mica or wollastonite, with an addition amount of 5-15%, can effectively improve the thermal stability of PBT and reduce its thermal expansion coefficient, thereby enhancing its heat resistance.

2. Blending with high-temperature-resistant polymers:

Blending PBT with high-temperature-resistant polymers like PC (Polycarbonate), PPS (Polyphenylene sulfide), and LCP (Liquid crystal polymer), can balance its heat resistance and toughness. For example, after the PBT/PC alloy is blended in a ratio of 70:30, the HDT can reach 130 - 150℃. Meanwhile, by introducing a small amount of epoxy resin (1 - 3%) or peroxide-induced crosslinking modification, the thermal stability of PBT can be improved, thereby enhancing its heat resistance.

3. Chemical modification methods:

By introducing heat-resistant groups into the PBT molecular chain through copolymerization or grafting, such as aromatic rings (like PBT-PET copolymer) or siloxane structures, the thermal decomposition temperature of PBT can be effectively improved, and its stability in high-temperature environments can be enhanced.

II. Measures to increase the impact strength of PBT

1. Addition of elastomers or toughening agents:

Core-shell elastomers (such as MBS, ACR) are commonly used toughening agents. Adding 5 - 10% of MBS can increase the notched impact strength of PBT from about 5 kJ/m² to 15 - 25 kJ/m². The addition of thermoplastic polyurethane (TPU) or ethylene - methacrylic acid copolymer (EMA), with a dosage of 10 - 20%, can significantly enhance the low-temperature toughness of PBT without unduly affecting its processing properties.

2. Blending with tough polymers:

By optimizing the ratio of PBT/PC alloy, such as 60:40, both HDT and impact strength can be well balanced. Moreover, after PBT/PET blending and ester exchange reaction to improve compatibility, the interfacial defects can be reduced, and the overall impact strength can be enhanced.

3. Interfacial optimization treatment:

Using silane coupling agents (such as KH - 550, dosage 0.5 - 1%) to treat glass fiber or fillers can enhance the interfacial bonding strength between PBT and these reinforcing agents, effectively reduce stress concentration, and thereby increase the impact strength of PBT.

III. Synergistic optimization strategies

1. Composite reinforcement and toughening:

Combining glass fiber reinforcement with elastomer toughening, for example, 20% GF plus 8% MBS, can achieve a HDT of 210℃ for PBT and increase the impact strength to 20 kJ/m². In addition, adding 2 - 5% of nanofillers, such as nano-clay or carbon nanotubes, and optimizing their dispersion can simultaneously enhance the heat resistance and toughness of PBT.

2. Crystallinity regulation methods:

The use of nucleating agents (such as talc, sodium phenylphosphate, etc.) can accelerate the crystallization process of PBT and increase the crystallinity to 40 - 50%, thereby enhancing the HDT. Meanwhile, toughening agents can offset the brittleness issue caused by increased crystallinity. In terms of processing technology, increasing the mold temperature to 80 - 100℃ and reducing the cooling rate can help reduce internal stress in PBT products, thereby improving their impact strength.

IV. Experimental verification and process adjustment

1. Formulation design:

Orthogonal experimental design can be employed to test different combinations of glass fiber, elastomers, fillers, etc., to determine the optimal formulation combination for achieving the best balance between PBT's heat resistance and impact performance.

2. Performance testing:

Devices such as thermogravimetric analyzer (TGA), heat deflection temperature tester, and impact tester can be used to evaluate the performance of modified PBT, accurately measuring changes in its heat resistance and impact strength, and providing data support for the optimization of formulations and processes.

3. Process parameter optimization:

The injection molding temperature should be controlled at 240 - 260℃, and the holding pressure should be maintained within the range of 60 - 80 MPa. By optimizing these process parameters, the degradation and porosity generation of PBT during processing can be reduced, thereby further enhancing its performance.

V. Application case references

1. In the automotive connector field:

Using PBT reinforced with 30% glass fiber and modified with 5% TPU can achieve a HDT of 220℃ for automotive connectors and an impact strength of 18 kJ/m², ensuring reliable performance in the complex conditions of high temperature and vibration in automobiles.

2. For electronic casing applications:

A PBT/PC alloy (ratio 70:30) combined with 2% nano-clay, when used for the production of electronic casings, can achieve a good balance of performance with an HDT of 150℃ and an impact strength of 25 kJ/m², meeting the requirements of electronic devices for the heat resistance, impact resistance, and dimensional stability of casing materials.

VI. Flame retardant modification expansion

On the basis of enhancing the performance of PBT, the optimization of flame retardancy is also an important requirement in the automotive and electronic fields. YINSU's PBT flame retardant, PBT-WL-20M, has excellent flame retardant effects and can meet the requirements of different flame retardant grades, and is widely used in the interior and exterior parts of automobiles. Its red phosphorus flame retardants 950-1 and 750A also perform well, not only with good flame retardant effects, but also maintaining the mechanical properties of the materials, and are suitable for products in the electronic and electrical fields. In addition, antimony trioxide substitutes, as environmentally friendly flame retardants, have good thermal stability and synergistic flame retardant effects, and can replace traditional antimony trioxide, providing more options for the flame retardant modification of PBT and further expanding the flame retardant solutions of PBT in various application scenarios, comprehensively improving its comprehensive performance to meet the increasingly strict regulations and market demands.