High temperature thermoplastics are melt processable plastics. High temperature thermoplastics have a long-term stable structure at temperatures above 150 ° C. Their short-term use temperatures can also be above 250 ° C. The excellent temperature capability of these polymers is in the plastics market. It has a very high appeal and its market share has maintained a high growth rate in recent years. Sometimes high temperature thermoplastics are also called 'high performance plastics'. Therefore, the cost of high temperature thermoplastics is on average 10% higher than that of general purpose plastics. Times!
High temperature thermoplastics typically achieve their temperature resistance by introducing a rigid aromatic ring into their molecular structure rather than an aliphatic group. This limits the movement of the backbone and requires the breaking of two chemical chains (with one of the fatty structures) In comparison, the chain breaks (Fig. 1). Therefore, the mechanical properties, high temperature properties and chemical resistance of high temperature thermoplastics are greatly improved. Compared with crosslinked thermosetting polymers, the properties of high temperature thermoplastics are generally better.
Figure 1: Degradation of aromatic and linear polymers due to heat aging
In practical applications, high temperature thermoplastics often need to be compounded and modified to meet specific application properties. By using special reinforcing materials such as glass fiber, the heat deformation resistance and rigidity can be further improved compared with the base polymer. Additives such as fluorocarbon or graphite particles will significantly improve the sliding friction characteristics, adding conductive fillers will provide improved conductivity, and the addition of boron nitride and other thermally conductive fillers will provide good heat transfer, which is important in many high heat applications. .
Figure 2: Plastic Performance Pyramid
Currently, the high temperature melt processable thermoplastics market includes many polymer families, each consisting of several types of polymers. The plastics industry typically uses such things as 'high performance', 'engineered polymers' and 'standard' or 'commodities ' Plastic terminology describes the application of these materials. Figure 2 above illustrates the location of high performance or high temperature thermoplastics.
High temperature thermoplastics (such as all polymers) contain two molecular structures: amorphous (random ordered) and crystalline (highly ordered). For practical purposes, thermoplastics are amorphous polymers or have amorphous and crystalline regions. Semi-crystalline polymers. One of the main differences between the two types is how they respond to temperature (see Figure 3). Amorphous and crystalline high temperature thermoplastics are used in automotive, aerospace, medical and electrical applications that require high performance. /Electronic industry.
Figure 3: Characteristics of amorphous and semi-crystalline high temperature thermoplastics
Automotive lightweighting is a topic that is often mentioned today. High temperature plastics are often seen as a substitute for metals. Figure 4 summarizes some of the advantages and disadvantages of high temperature plastics compared to metals.
Figure 4: Advantages and disadvantages of high temperature plastics compared to metals