Dielectric Strength of Plastics | Electrical Properties of Plastics | The Definitive Guide

Hello people; I hope you’re all doing fantastic. Today, I will share a very engaging piece on plastics’ dielectric strength and dielectric properties. So without further ado, let’s get started.

Dielectric Strength of Plastics 

The dielectric strength of most plastics typically falls between 100 and 300 kV/cm, averaging at about 200 kV/cm. In contrast, specific chlorinated and additive-enriched polymers showcase dielectric strengths as high as 500 kV/cm. Teflon, renowned for its outstanding chemical and impact resistance, can achieve a remarkable 700 kV/cm.

Most plastics are poor conductors of electricity and resist a current flow, thus called dielectrics or insulators. That is one of the most valuable properties of plastic material and makes them applicable in making products utilized in our day-to-day lives, such as switches & switchboards, wire coatings, light fittings, and other electrical goods & Appliances.

As plastics are insulators when voltage is applied and steadily increased on them, It will eventually reach a point when the electrical properties break down—the breakdown increases an electrical arc across the electrodes, which causes a catastrophic reduction in resistance.

What is Dielectric Strength? 

The dielectric strength of plastics or any insulating material can be understood as the ratio of the charge deposited in an insulating material between two metallic plates to the charge stored when a vacuum or air replaces the insulating material. The phenomenon is called electrical permittivity. The dielectric strength of a material showcases its ability to store electrical energy.

The dielectric strength of plastic depends on its type and shape, the field increase rate, and the medium surrounding the insulator. Dielectric strength is derived by a unit kV by mm of thickness.

How to Calculate Dielectric Strength?

The most common standard tests to calculate the dielectric strength of plastic materials are ASTM D149 or IEC 60243-1. Below are the methods used for measuring dielectric strength:

1. Short time method
2. Slow rate of rise method
3. Step by step method 

Short Time Method

Here, the voltage is applied across the two electrodes and bumped up constantly at a uniform rate (500 V/sec) until the breakdown occurs. The meaning of breakdown is when the voltage punctures the sample or creates decomposition.

Slow Rate of Rise Method

The voltage is applied to the test electrodes at only 50% of the breakdown voltage until breakdown or decomposition happens.

Step By Step Method

The voltage is applied to the electrodes at a predetermined starting voltage in various steps and spans until the breakdown.

Interesting Read – 7 Best UV Resistant Plastics For Outdoor Applications 

Applications

• Dielectric material for capacitors used in radio and other electrical equipment.
• Development of material for energy storage solutions.
• Used by circuit designers to evaluate different printed-circuit-board (PCB) materials.
• Thin films in the high-speed digital microprocessor.

Factors Affecting Dielectric Strength 

• Hold on tight because things are about to get heated! The dielectric strength of plastics tends to drop as temperatures rise, roughly moving in an inverse relationship to absolute temperature. Yet, it’s fascinating that dielectric strength remains remarkably unaffected by temperature fluctuations.
• But wait, there’s more! Mechanical stress can significantly impact dielectric strength, as it introduces internal flaws in insulators, creating leakage pathways and weakening their dielectric fortitude.
• And here’s the twist: manufacturing quirks can significantly affect a plastic’s dielectric strength. Even the tiniest defects can pack a punch from weld lines in injection molding to flow lines in compression molding. These seemingly insignificant imperfections can slash an insulator’s dielectric strength by 30-40%!

Polar Vs Non-Polar Plastics 

A plastic material’s dielectric strength and electrical properties heavily depend on its structure. The structure of a polymer decides whether it is polar or non-polar, thereby determining its electrical properties.

Polar polymers (PMMA, PC, Nylon, PVC, etc.) are comprised of dipoles created due to the imbalance in the distribution of electrons. These dipoles align themselves in the presence of the electric field. Thus dipole polarization is designed for the polymer, making them average-performing insulators.

On the other hand, Non-polar polymers (PS, PTFE, PP, PE) have symmetrical molecules and are entirely covalent. There is no presence of polar dipoles in them, and thus the attendance of the electric field doesn’t align with the dipoles. However, the movement of electrons in the direction of the electric field will erupt in a slight electron polarization. These polymers have elevated resistivities and low dielectric constant.

Polar plastics have the propensity to absorb moisture from the atmosphere. Moisture has the ability to raise the dielectric constant and lower the resistivity. As the temperature rises, polymer chains move faster, and the dipoles are aligned more quickly.

Non-polar plastics do not affect the rising atmosphere and moisture.

Dielectric Strength Values of Polymers 

Engaging Read – What is the Glass Transition Temperature of Plastics?

Dielectric Constant Values of Mainstream Polymers 

Fascinating Read – What is the Density of Plastics? | The Complete Guide

FAQs 

Get ready to dive headfirst into the electrifying world of the dielectric strength of polymers! We’ve compiled a list of sizzling FAQs to quench your thirst for knowledge. Come on, let’s take a look!

What is the formula of dielectric strength?

M1L2T−2Q−1.

What is the dielectric strength of Bakelite?

300-550 Kv/inch

Why is plastic an electrical insulator?

In layman’s language, they don’t possess free electrons moving around, a phenomenon also called delocalized electrons. That makes them bad conductors of electricity and heat, which gives them the property of great insulators.

How can polymers be made electrically conductive?

The two main methods used to make insulators electrically conductive – Chemical synthesis and electro (co) polymerization. Chemical synthesis means connecting the carbon-carbon bond of monomers by placing the simple monomers under various conditions, such as heating, light exposure pressing, and catalyst.

Suggested Read 

• What is Compressive Strength of Plastics | The Complete Guide
• Mechanical Properties of Plastic Materials | The Definitive Guide
• Physical Properties of Plastic Materials | The Complete Guide
• Thermal Properties of Plastics | The Ultimate Guide
• What is Processing and Drying Temperatures of Plastics
• Mold Temperature in Plastics | A Complete Analysis
• Polystyrene Repeat Unit | Polystyrene Properties
• Polycarbonate VS Plastic Lenses | A Complete Analysis

Final Thoughts 

That is all I wanted to say about the electrical properties of plastics and the dielectric strength of plastics. Dielectric strength and dielectric const of any plastic material are essential properties that should not be neglected. The electrical properties of any plastic material make it applicable for making many types of products.

Have a wonderful day.