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What Are Thermoplastics

Posted on: October 4th, 2017 by byersbushblog

Did you know that the aircraft manufacturing and aerospace design industries have been benefiting from thermoplastics for over 15 years? The tough and durable material can be found in wide use in many commercial and military applications.

The interest in thermoplastics in these industries may be traced to its ability to deliver products with reduced weight and cost without relying on fasteners. As an alternative to metallic structural brackets, it also eliminates the hazards of galvanic corrosion allowing aircrafts to last longer. What else makes thermoplastics interesting and important?

Thermoplastics Definition

thermoplastics definition

What exactly are thermoplastics? These are basically organic materials that when subjected to heat will begin to melt allowing it to be processed. In general the thermoplastic material is melt processable and undergoes a viscous phase.

After cooling, the material can be molded into its final shape. Are you aware that thermoplastic resins are extremely common? In fact, you may not know it, but you come in contact with these materials regularly. The flexibility of this material allows it to be formed into shapes without needing any reinforcement to make it stronger.

Types of Thermoplastics

types of thermoplastics

There is more than one type of thermoplastic that you can come across. Generally, these polymers may be categorized either as amorphous or semi-crystalline. When we talk about amorphous thermoplastics, we are referring to materials that do not result in a crystalline structure and molded with temperatures that are near glass transition levels. Unfortunately, amorphous thermoplastics are known for its poor resistance to some types of solvents.

On the other hand, semi-crystalline polymers are characterized by areas that are amorphous combined with areas that are so closely packed with crystal lattice. The type of polymer used and the cooling rate applied will define the amount of crystallinity that a specific part will have. It is important to point out that with semi-crystalline polymers, there will be a melt temperature and a point where the crystalline structure can breakdown.

For semi-crystalline thermoplastic polymer materials, the property will be affected by the degree of crystallinity. When there is low crystallinity, you can expect the material to be tough, yet exhibits poor resistance to solvents. Most of the engineered thermoplastic materials you will find will have fast crystallization rates.

Usually, with composite structure, a key concern has to do with how to attach a piece to the other parts of the structure being formed. Welding to structures can be done by subjecting the bondline to heat until it reaches the processing temperature. Injection molding, thermoforming, and extrusion is the most common way that thermoplastics are processed. Did you know that there is more than one form of thermoplastic material?

Fabric prepregs is the first form where a carbon fiber woven or glass material along with thermoplastic resins will be integrated into fabrics. These are commonly called semi-pregs because aside from being slightly drapable and conformable, there is also the presence of the resin that can be found on the surface of the fabric. You will need high temperatures to ensure that impregnation will occur. PEEK, PPS, PA, and PEI resins can be used.

Reinforced Thermoplastic Laminates (RTL) is another form, which has better fiber bundle impregnation. This is made possible by the high pressure, temperature, and viscosity of the resins that undergo thermoforming.

Lastly, you may also find thermoplastic in tape form. It is used mostly for laying and fiber placement because of its efficiency. Automated solutions like these usually come in the form of fiber tape.

Thermoplastic Properties

thermoplastic properties

What are the common properties that you will see with thermoplastic products and materials? The wide usage of thermoplastic composites for several years have led to the discovery of its various properties and depending on its specific chemistry, it can exhibit characteristics that closely resemble rubber or can be as strong as any aluminum material.

With densities ranging from 0.9 to 2 gm/cc, it is safe to say that it is one of the lightweight materials we have today. You may even find some thermoplastic materials that have the capability to withstand temperatures going well beyond the 600 degrees mark. Most thermoplastic materials though retain their properties up to 100 degrees temperature on the average.

When applied at room temperature, many thermoplastic materials do not have any known solvents. Majority though can serve as excellent insulators either in thermal or electrical form. It is not farfetched for thermoplastic materials to be electrically conductive when it is merged with metal or carbon fibers. Many industries find great usage of thermoplastics because aside from its weight and strength, the cost of processing for various applications is comparatively low.

What other properties from thermoplastics?

  • Short thermoforming cycle time for part fabrication;
  • Low moisture acceptance;
  • High levels of toughness;
  • Resistant to damage;
  • Allows large structure fabrication;
  • Supports room temperature storage;
  • Retention of properties despite repeated heating and cooling;
  • Extremely low void content;
  • Alternative to part fabrication; and
  • Fire retardant.

Uses of Thermoplastics

uses of thermoplastics

source: commons.wikimedia.org

Carbon fiber and fiberglass are the most common materials used by thermoplastic products as reinforcement. Actually, it can use any type of short discontinuous fiber to increase its mechanical properties. Technically, it can be classified as a type of fiber reinforced composite material except for the fact that its strength is far from those of continuous fiber reinforced composites.

When we talk about FRP composites, we are referring to materials that user reinforcing fibers that have at least a fourth of an inch length. The use of continuous fiber and thermoplastic resins can be seen in various structural composite product manufacturing.

Higher performance or higher costing materials are commonly distinguished from basic commodities such as polypropylene, polyethylene, polystyrene, and PVC. The engineered plastic materials would usually include polyesters, nylons, and polycarbonates among others. The engineered materials commonly have tensile strengths of more than 7,500 psi and may have a market price of about $2.00 a pound.

The most common products that you may find today based on the type of thermoplastic resin being used can be:

  • Water and soda bottles from PET;
  • Packaging containers made of polypropylene;
  • Safety glass lenses that are polycarbonate;
  • Children’s toys made from PBT;
  • Vinyl window frames;
  • Polyethylene grocery bags;
  • PVC pipes and joints;
  • Airplane armrests made of PEI; and
  • Nylon footwear among others.

There are definitely more uses of thermoplastics to come. One of the widely and more popular usage of thermoplastics today is in the powder coating industry. And if you want to get the best powder coating service, call Byers Bush Powder Coating today.

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