What are the difficulties faced in the manufacture of glass fiber reinforced nylon?

Nylon (PA) has a series of excellent properties such as high mechanical strength, chemical resistance, oil resistance, wear resistance, self-lubrication, and easy processing and molding. It has become one of the thermoplastic engineering plastics widely used at home and abroad.

However, in practical applications, the performance requirements of nylon are different under different service conditions or environments.

For example, components such as electric drills and motor casings, pump impellers, bearings, diesel engines and air-conditioning all-plastic fans require nylon materials to have high strength, high rigidity and high dimensional stability; Due to the poor low-temperature toughness of nylon, it needs to be toughened and modified at this time; in some outdoor applications, nylon materials must be modified for weather resistance in long-term outdoor environments.

The reinforcing materials used in reinforced nylon are mainly fibrous substances such as glass fiber, carbon fiber, and whiskers, among which glass fiber reinforcement is the most widely used. The rigidity and hardness of the material can be significantly improved by glass fiber reinforcement, and the dimensional stability and heat resistance of the material can be significantly improved.

Since nylon itself is not strong enough, its strength can be improved by adding 10-30% fiber. Especially 30% strength is recognized as the most suitable ratio. It can also be added to 40-50%. According to the specific requirements of different products, coupled with an appropriate formula, it can be successful.

Production Process of Glass Fiber Reinforced Nylon

Generally speaking, there are two production processes for glass fiber reinforced nylon: long fiber method and short fiber method.

The long-fiber method, that is, nylon and other components are pre-mixed and then added to the hopper, while the glass fiber is brought into the screw from the glass fiber inlet through the screw rotation, and then mixed with the nylon resin.

Short fiber method, that is, the chopped glass fiber is forced to be transported to the barrel through the side feeder, and then mixed with nylon.

 

Factors Affecting Properties of Glass Fiber Reinforced Nylon

First, the interfacial bonding between glass fiber and nylon resin is the most important influence on glass fiber reinforced nylon. If the combination between the two is not good, the strengthening effect will be greatly reduced. At this time, the surface treatment of glass fiber is particularly important. Today, fiberglass manufacturers have been able to produce fiberglass models with different surface treatments for different materials for use by modified plastic manufacturers, as long as they are selected properly.

Second, the length of the glass fibers in the nylon material is another major factor affecting its performance. In general, long glass fibers are superior to short glass fibers in terms of tensile strength, flexural strength and modulus, and notched impact strength.

At the same time, the dispersion of glass fibers in the material cannot be ignored. The dispersion of glass fiber mainly depends on the proper shearing action of the twin-screw and the kneading of materials, which involves the combination and speed of the screw. The choice of screw speed is related to the content of additives such as glass fiber in the formula. For flame retardant reinforced nylon, low speed is appropriate because the flame retardant has been thermally decomposed.

In addition, the processing temperature, glass fiber diameter, and glass fiber type will also affect the final performance of the material, so I will not repeat them here.

 

Thermo-oxidative aging of glass fiber reinforced nylon during processing

Taking glass fiber reinforced nylon 66 as an example, the glass fiber is easy to squeeze and rub against the material, the screw and the inner wall of the barrel in the barrel of the twin-screw extruder, and generates a lot of frictional heat. The actual temperature of the material in the barrel of the extruder is often much higher than the temperature displayed by the extruder. Such a high temperature can easily lead to thermo-oxidative aging degradation of nylon 66 and reduce the mechanical properties of the composite material. Table 1 shows the effect of different antioxidant systems on the initial mechanical properties of glass fiber reinforced nylon 66 composites.

 

Table 1  Initial Mechanical Properties of Glass Fiber Reinforced Nylon 66

 

It can be seen from the data in the table that the tensile strength, flexural strength and notched impact strength of the 1# sample without antioxidant are all lower than the corresponding properties of the 2# and 3# samples, this shows that the addition of antioxidants can effectively retard the thermo-oxidative aging degradation of nylon 66 during processing, and significantly improve the mechanical properties of the composite. It shows that a suitable antioxidant system can play a better role in stabilizing the initial processing.

 

Fluidity of Glass Fiber Reinforced Nylon

The fluidity of glass fiber reinforced nylon is poor. During the injection molding process, problems such as high injection pressure, high injection temperature, unsatisfactory injection, and poor surface quality are prone to occur, which seriously affects the appearance of the product and leads to a high defect rate of the product. Especially in the production process of injection molding products, it is not possible to directly add lubricants to solve the problem, but to improve the raw materials. Generally speaking, this requires adding lubricating ingredients to the modified formula.

 

Resistance to high temperature thermo-oxidative aging of glass fiber reinforced nylon

In some application fields such as bearings and diesel engine fans, glass fiber reinforced nylon often faces the problem of long-term high-temperature thermal-oxidative aging. Although the reinforced modification of nylon with glass fiber can moderately improve the heat resistance of nylon, it cannot solve the problem very well. However, better results can be achieved by adding suitable anti-thermal and oxidative aging additives to the glass fiber reinforced nylon composite material, or follow the above picture.

After the three samples were subjected to 1000h thermal oxygen aging, the tensile strength retention rate of 1# sample (without antioxidant) was 58.0%, and the tensile strength retention rate of 2# sample (commonly used antioxidant system) was 77.4%, and the corresponding performance of 3# sample (improved antioxidant system) is 88.0%. It can be seen that a suitable antioxidant system can effectively delay the thermal-oxidative aging degradation of glass fiber reinforced nylon, thereby exerting a better high-temperature thermal-oxidative aging protection effect.

 

Weather resistance of glass fiber reinforced nylon

Affected by external conditions such as sunlight, temperature changes, and wind and rain, nylon will undergo a series of aging phenomena such as fading, discoloration, cracking, chalking, and strength decline. Among them, ultraviolet rays are the key factor that promotes aging. Weather-resistant nylon is currently mainly black products, that is, to solve its weather resistance by adding carbon black and other UV-absorbing additives to nylon. However, in addition to black products, natural or light-colored nylon also often faces the problem of aging when used outdoors, mainly manifested in the yellowing of the parts.

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