The material selection platform
Plastics & Elastomers
The material selection platform
Plastics & Elastomers

Resin Selection for Thermoplastic Composites

That long-predicted future opportunity for thermoplastic composites seems to be materializing now as they have become increasingly important in various applications. But, nothing can be as challenging as a material selection to finally develop a final product. Are you looking for solutions for an easier resin selection? Find out here!

Apprise your knowledge with the various thermoplastics and learn how to select the correct thermoplastic resin considering different criteria.


Thermoplastic Resins Composition and Selection

Thermoplastic Resins Composition and Selection

The market share for thermoplastic resins is expanding within a growing composites market. For example, the automotive market is seeking new solutions for lighter vehicles and high volume production. Some applications of thermoplastic composites in the automotive industry include:

  • Seat frames
  • Battery trays
  • Bumper beams
  • Load floors
  • Front ends
  • Valve covers
  • Rocker panels, and
  • Under engine covers

In many cases, thermoset resins, such as epoxies, are not satisfactory for these applications and, thus, there is an increased interest in the use of thermoplastic materials.

Advantages of Thermoplastics over Thermosets in Composites

Advantages of Thermoplastics over Thermosets in Composites

Compared to thermoset resins, there are two major advantages of thermoplastics in composites. The first is that many thermoplastic resins have an increased impact resistance compared to comparable thermoset materials. In some instances, the difference is as high as 10 times the impact resistance.

The other major advantage of thermoplastic composites is the ability to reform. When heat and pressure impregnate a reinforcing fiber with a thermoplastic resin, a physical rather than a chemical change occurs. This allows the thermoplastic composites to be reformed and reshaped. Thus, the thermoplastic composite can be recycled at the end of its life.

Need to Select Right Polymers for Thermoplastics Composites

Need to Select Right Polymers for Thermoplastics Composites

One of the key factors that affects the performance of a thermoplastic composite is the polymer that is used as the basis for the composite material. There are many factors that need to be considered when selecting a matrix polymer for use in thermoplastic composites.

Need to Select Right Polymers for Thermoplastics Composites

Making the selection of the appropriate matrix material is complex, because, in general, the choices do not excel in every category. For example, one material might be inexpensive and have good corrosion resistance but has a very low glass transition temperature and is susceptible to creep. Another material might offer a very high glass transition temperature but be expensive and have relatively poor hydrolytic stability or solvent resistance.

Thermoplastics that have high mechanical properties and that can operate in more varied and aggressive environments tend to cost more. It is necessary to select the best candidate for the specific needs of the particular demanding application.

Thermoplastics Resins Used in Composites

Thermoplastics Resins Used in Composites

Thermoplastic are commonly used in composites but are not limited to the following:

Each of these resins provide certain advantages and disadvantages to the resulting final thermoplastic composite. In that regard, the final application is extremely important in defining the resin requirement for the matrix polymer.

Before discussing the features of these type of resins, it needs to be pointed out that the thermoplastic polymers that are used in thermoplastic composites can be divided into two general classes:

The classification is based mainly on the maximum service temperature of the polymers, which in turn is based on the glass transition temperature or Tg. This is the temperature at which the amorphous portion of the polymer changes from a glassy to a rubbery phase on heating. Semi-crystalline thermoplastic polymers may carry a load above the Tg, as only the amorphous phase of the polymer has become rubbery. The crystalline portion of the polymer remains solid until the melt temperature, or Tm, is reached.

The following Table summarizes the glass transition temperatures, Tg, melt temperatures, and processing temperatures, process of the thermoplastic polymers that are commonly used in thermoplastic composites.

Polymer Morphology Tg (°C) Tm (°C) Process (°C)
 PBT  Semi-crystalline  56  223  250  $$
 PA6  Semi-crystalline  48  219  245  $
 PA12  Semi-crystalline  52  176  224  $
 PP  Semi-crystalline  -20  176  190  $
 PEEK  Semi-crystalline  143  343  390  $$$
 PEI  Amorphous  217  --  330  $$
 PPS  Semi-crystalline  89  307  325  $
 PEKK  Semi-crystalline  156  306  340  $$
Common Thermoplastics Used in Composites

Based upon the definitions previously provided, PEEK, PEI and PEKK can be classified as high temperature thermoplastics while the other polymers can be categorized as engineering thermoplastics. In general, as can be seen from the information in the Table above, high temperature thermoplastics tend to have a higher relative cost than do the engineering thermoplastics. This is an important consideration for the selection of resins in certain applications.

Factors Influencing Thermoplastic Resin Selection

Factors Influencing Thermoplastic Resin Selection

In general, there are three categories that are regarded as the most important criteria:

  1. Cost
  2. Operating environment and the associated environmental resistance of the matrix, and
  3. Mechanical properties

Factors Influencing Thermoplastic Resin Selection
Factors Influencing Thermoplastic Resin Selection

For the operating environment, concerns are generally items like operating temperature and exposure to sun, water and chemicals. For mechanical properties, items like strength, stiffness, and toughness are important features. It does need to be noted that the mechanical properties of the thermoplastic composite are influenced not only by the choice of the matrix polymer but also by the reinforcing fiber and the interface between the matrix and the reinforcement.

The use of such resins is a requirement to make thermoplastic composites economically feasible in such applications.


For high volume applications, such as automotive uses, the cost of the thermoplastic resin is a key consideration. Thus, resins that have a low relative cost, such as polypropylene and polyamide are often the resin choice for these type of applications. However, the environmental considerations are also an important factor in making the decision as to which of the engineering thermoplastics should be used in a particular high volume application.

For example, polyamides are sensitive to moisture in the environment and can undergo degradation and a subsequent loss in mechanical properties if there is a large quantity of water present. Thus, if the use conditions present a situation in which moisture is an issue, polyamides would not be a good choice for the thermoplastic polymer to utilize. Instead, in that case, polypropylene, which is not sensitive to the presence of water, would be a better choice for the polymer in the thermoplastic composite.

Summarizing the information provided in this guide, then, the major driving force for the selection of a particular thermoplastic resin in thermoplastic composites is the desired application for which the final composite will be utilized.

Operating Environment

Even within the class of high volume applications, the operating environment for the thermoplastic composite is a significant factor in the choice of the the appropriate matrix resin. Thus, if moisture or solvent resistance is required in the desired application, the resin features in that regard must be considered. For example, polyamide resins are sensitive to moisture in the operating environment and the performance of such resins will be dependent on the surrounding conditions. For high volume applications that require a resin that is not sensitive to moisture effects, polyolefins, such as polypropylene and polyethylene are reasonable choices.

Related Read: Advancing polyolefin composites for new applications »


Another factor that will determine the choice of the correct thermoplastic resin to use in the thermoplastic composite is the intended use temperature for the finished part. Thus, while resins such as polypropylene and poly(butylene terephthalate) offer low cost, their temperature performance is quite low. Therefore, they would not be the resin of the choice for applications that involve temperatures above about 100°C.

On the other hand, the high temperature thermoplastics, such as PEEK and PEI, can be used for applications that require high temperature performance. The potential negative of the use of such resins, however, is their relatively high cost compared to resins such as polypropylene and polyamides. The high cost of these resins will limit their use to more specialty type applications such as aerospace uses.

As has been shown in this guide, different resins are useful over different temperatures. The selection of the appropriate resin for the desired use temperature will help guarantee the success of the product in its application.

The following Table summarizes some of the key current composite applications for several of the resins:

Resin Aerospace
Under the
Structural Medical
PP    x  x  
PA6      x  
PEI  x      x
PEKK  x      x
PEEK  x      
PA12      x  
PBT    x  x  
PPS  x    x  
 Composite Applications for Various Resins

The information contained in this Table shows that the lower cost resins, such as PP, are utilized in high volume automotive applications while the higher cost, high temperature thermoplastics find specialty applications in the aerospace and medical applications.

As additional applications are developed for thermoplastic composites, it will continue to be necessary to define the correct resin for utilization as the matrix material. The rules that have been provided here can be used as the basis for the selection criteria. In that way, there will be a greater likelihood of the successful implementation of the composite material in its desired utilization.

Reach Faster Higher Heat Resistance with your Thermoplastic Composite Materials

Talk to Mark DeMeuse where he will share how to reach higher heat resistance with your thermoplastic composite materials by learning to improve your filler/polymer interface properties. He will also help you tailor surface properties (fiber sizing, use of coupling agents, reactive functionalization…) for high-temperature applications (automotive, aircraft, electronics…) thereby improving HDT, strength & fracture toughness.

Thermoplastics Composites Interface Optimization for High Heat Applications

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