Nylon (PA) has a series of excellent properties such as high mechanical strength, chemical resistance, oil resistance, wear resistance, self-lubrication, easy processing and molding, and 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, nylon materials are required to have high strength, high rigidity and high dimensional stability for parts such as electric drill and motor housing, pump impeller, bearing, diesel engine and air conditioning all-plastic fan; Due to the poor low-temperature toughness of nylon, it is necessary to toughen it at this time; In some outdoor applications, nylon materials must be weather-resistant in long-term outdoor environment.

The reinforcing materials used for reinforcing nylon are mainly fiberglass, carbon fiber, whisker and other fibrous materials, and glass fiber reinforcement is the most widely used. The rigid strength 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.

Because the strength of nylon itself is not enough, the strength of nylon can be improved by adding 10-30% fiber. In particular, the strength of 30% is recognized as the most appropriate proportion. There are also 40-50%. According to the specific requirements of different products, plus the appropriate formula, it can be successful.

Production process of glass fiber reinforced nylon

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

Long fiber method, that is, nylon and other components are premixed and then added into the hopper, while glass fiber is brought into the screw through screw rotation from the glass fiber inlet, and then mixed with nylon resin.

Short fiber method, that is, the chopped glass fiber is forced to be conveyed to the cylinder through the side feed, and then mixed with nylon.

Factors affecting the properties of glass fiber reinforced nylon

First of all, the interfacial adhesion between glass fiber and nylon resin has the most important effect 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, glass fiber manufacturers have been able to produce glass fiber models with different surface treatments for different materials for use by modified plastic manufacturers, as long as the selection is appropriate.

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

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

In addition, processing temperature, glass fiber diameter and glass fiber type also affect the final performance of the material, so it will not be repeated here.

Thermal oxygen aging of glass fiber reinforced nylon during processing

Taking glass fiber reinforced nylon 66 as an example, glass fiber is easy to extrude and rub with the material, screw and inner wall of the barrel in the twin-screw extruder, and generates a large amount of friction heat, which often makes the actual temperature of the material in the barrel of the extruder far higher than the displayed temperature of the extruder. Such high temperature is very easy to cause the thermal oxygen aging degradation of nylon 66 and reduce the mechanical properties of the composite. Table 1 shows the effect of different anti-oxygen systems on the initial mechanical properties of glass fiber reinforced nylon 66 composites.

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 easy to occur, which seriously affect the appearance of products, resulting in high product defect rate. Especially in the production process of injection molding products, lubricant can not be directly added to solve the problem, but can only be improved on the raw materials. Generally speaking, this requires adding lubricant ingredients into the modified formula.

High temperature thermal oxygen aging resistance of glass fiber reinforced nylon

In some applications such as bearings and diesel fans, glass fiber reinforced nylon is often faced with the problem of long-term high-temperature thermal oxygen aging. Although reinforcing and modifying nylon with glass fiber can moderately improve the heat resistance of nylon, it can not solve the problem well. It can be seen that adding appropriate anti-thermal oxygen aging additives to the glass fiber reinforced nylon composite can achieve better results. The appropriate anti-oxygen system can effectively delay the thermal oxygen aging degradation of glass fiber reinforced nylon, thus giving play to better thermal oxygen aging protection effect at high temperature.

Weatherability of glass fiber reinforced nylon

Under the influence of external conditions such as sunlight, temperature change, wind and rain, nylon will appear a series of aging phenomena such as fading, discoloration, cracking, pulverization and strength reduction, among which ultraviolet ray is the key factor to promote aging. Weather-resistant nylon is mainly made of black products, which is to solve its weatherability by adding carbon black and other UV-absorbing additives into nylon. However, in addition to black products, natural or light color nylon also often faces the problem of aging when used outdoors, which is mainly manifested by yellowing of products.