How to Select the Right Plastic Material? | Mechanical Properties | Special Properties

In our previous articles, we’ve discussed the manufacturing and processing of plastics. We got into the details of injection and blow molding plastic manufacturing processes, and your response to those posts was quite phenomenal. Today, we will discuss the selection of the plastic material process to manufacture excellent quality products with great productivity.

Let’s dive into the infamous world of plastic selection –

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Selection of Right Plastic material –

Plastic material selection in itself is not a very difficult process. Still, it requires adequate knowledge about characteristics of different plastic materials and their suitability with the supposed end product and familiarity with the specialty of individual plastics.

Clearing out the purpose and function of the end product is very important to choose the right material. Then one has to assess the suitability of the range of candidate materials.

The following are the most essential and regarded characteristics for consideration of mostly all engineering products –

Mechanical Properties – Strength, stiffness, specific kind of strength and stiffness, fatigue, and influence of high and low temperature on these following properties;
Corrosion vulnerability and Degradation
Wear Resistance and frictional properties
Special properties like thermal, electrical, optical, and damping capacity
Molding and other methods of fabrication
Costs attributes

Let’s have a detailed discussion on all the characteristics mentioned above –

#1 Mechanical Properties –

Strength and Stiffness:

Thermoplastic materials are viscoelastic, meaning that their mechanical properities show signs of both viscous liquids and elastic solids. When a thermoplastic is stressed or pressured, it responds by exhibiting viscous flow.

This conventional stress-strain method is regularly used to describe the mechanical properties of plastics.

However, the stress-strain method should only be used for the initial sorting of materials. For long terms tests, the results will not be accurate.

There is always an elastic region for low strain, whereas, on high strains, stress and strain are parallel to each other. In the absence of specific information related to particular plastics, design strains should be kept at 1%.

Lower values are recommended for more fragile thermoplastics such as acrylic polystyrene, and values 0.2- 0.3% should be used for thermosets.

To make the material more flexible, the temperature should be increased until it starts to deform more. Strain rate is another significant behavior of plastic that needs to monitor.

The plastic materials with different grades come with different mechanical properties. If we take the example of polypropylene for each 1kg/m3 change in density results in a 4% change in modules.

When it comes to stiffness in plastics, it is expressed in terms of modulus of elasticity.

Fatigue:

Because of cyclic stresses, plastics are prone to be affected by fragile cracks, just like metals. There high damping and low thermal conductivity results in thermal softening. Plastics like polypropylene, ethylene-propylene copolymer, and PVDF.

Fatigue is usually classified into brittle and ductile. Brittle fractures are comparatively more dangerous as the damage can’t be observed before it ruptures the surface.

In polymeric material, fractures can be both brittle and ductile depending on variables like the nature of additives, strain rate, processing conditions, stress systems, and temperature.

The fatigue with damage usually occurs in aggressive environments like the continuous application of steady stress.

Corrosion vulnerability and Degradation:

Corrosion vulnerability or resistance is one of the main features of plastics that attracts people to use plastics for manufacturing many products; however, plastics are also susceptible to chemical strike and degradation.

The breakdown of chemical structure is one of the prime reasons for degradation. It mostly occurs because of concentrated acids and solvents, but sometimes can also be affected by hydrolysis and oxidation. In some were instances, heat, radiation, and stress are also responsible.

Hydrolysis and oxidation can be prevented or delayed for a long time by incorporating antioxidants and stabilizers to keep the properties of plastic materials intact.

If you go by the behavior of polymers, it has been proven many times that crystalline plastic materials (e.g., Nylon 66 ) are more dependable than amorphous plastics when it comes to environmental vulnerability.

Wear Resistance and frictional properties:

The Popularity of plastic materials for manufacturing bearing structures is on the rise, e.g., gears, pistons, cams, seals, etc.

Such demand is the tremendous ability to absorb shock and vibration; negligible wear in the absence of conventional lubricants also plays a crucial role for plastics.

Another advantage is the high load carrying ability and strength.

The friction and wear of molding materials are strictly dependent on the application and the properties of the material. Even reinforced plastics have much lower modulus values than metals.

The mechanism that controls plastics’ wear rate is adhesive wear, which is defined by the fine particles of polymer being removed from the surface.

Interesting Read – What is PEEK Material? | Properties of PEEK | Limitations of PEEK | How PEEK is Manufactured? | Applications of PEEK

#2 Special Properties –

Thermal Properties:

The conventional thermal properties like conductivity are derived by the effect of temperature on plastics’ mechanical properties. A key role here is played by temperature.

As the plastic material will be heated, a noticeable increase in the relative movement can found because the molecules start receiving more energy. As a result, the material becomes more flexible, and when it is cooled down, the material becomes stiffer.

The temperature for amorphous plastics and crystalline plastics differ a lot from each other. However, the introduction of electrical conduction for plastics is a game-changer for plastic engineering as it offers many advantages for designing using static electricity and shielding computers from electromagnetic interference (EMI).

Mainly two approaches are used called coating or compounding. In coating, the surface of the plastic is treated with a conductive coating. For compounding, fillers like brass and steel are incorporated into the plastic.

Optical Properties:

Four optical properties are important for plastics – refraction, transparency, gloss, and light transfer. Certain plastics are optically clear, e.g., acrylic, cellulosic, and ionomers.

Certain plastics are purposely made transparent for few applications, e.g., polyethylene, polycarbonate, polypropylene, epoxy, polystyrene, and PVC.

Interesting Read – What is TPR Material? | Advantages of TPR material | Disadvantages of TPR Material | Properties of TPR | Difference Between TPR Material and TPE Materia

Final Thoughts –

Everything which is mentioned above about selecting the right plastic material is my finding over weeks of research. Those were my thoughts on the selection of plastic materials.

Feel free to write your reviews and thoughts in the comment box.

How to Select the Right Plastic Material? | Mechanical Properties | Special Properties | Types of Plastics