Plastics are a type of synthetic and semi-synthetic organic material. They are malleable and they can be used for making solid objects.
Plastics are organic polymers and they have a wide range of applications. They can be used in packaging, in making pipes for plumbing purposes, or vinyl siding. They are also used in making toys, automobiles, and furniture. You can learn more on this here.
Although plastics are regarded as insulators meaning that they do not conduct electricity, they can still store electric charges and transmit it at higher frequencies.
The DK (Dielectric constant) of an insulator material is a measurement of how effective the material is as an insulator. For plastic, it is the comparative level of charges stored in it when it is placed in the middle of two metal plates as compared to when air or a vacuum replaces the plastic.
That is, it is the ratio of capacitance that is induced by two metallic plates that have an insulator present between them compared to the capacitance of these plates when there is air or vacuum.
Furthermore, it can also be referred to as the permittivity of electric, relative permittivity or to put it simply, permittivity. It is usually measured comparatively based on the permittivity recorded in a free space. A Dk of 2 therefore means that the material can absorb two times more electrical charges than when it is in a vacuum.
Several variables can affect the dielectric constant of plastic. They can include factors such as
- The frequency that is used. As the frequency increases, the dielectric constant reduces.
- The thickness of the material
- Presences of additives in the material.
- Voltage.
- Environmental conditions like temperature and moisture.
- The structure and morphology.
Polar and Non-polar Plastic
The dielectric property of plastic will depend on its structure. The structure is what determines if it is polar or non-polar.
Dipoles are created in polar plastics such as nylon, PC, PVC, etc. because of the imbalance in the way electrons are distributed. The dipoles will align when there is an electric field making the material an average insulator. These kinds of polymers have the tendency to absorb moisture which in turn increases their dielectric constant and lowers their resistivity.
Non-polar plastics on the other hand have molecules that are symmetrical and covalent. They do not have polar dipoles meaning when there is an electric field the dipoles are not aligned making them quite highly resistive with a very low dielectric constant. These polymers are not affected by moisture or temperature.
Importance and Use
The dielectric constant of plastic applies to the production of capacitors. A capacitor is a component used in storing electrical energy in an electric field. Capacitors have at least two electrical conductors that are separated by an insulator.
Capacitors come in various forms but they all work in the same way. They are useful as a component in making electronics. They are also used by circuit board designers to compare various printed circuit boards.
Furthermore, it is used in developing materials for energy storage.
Calculating the Dielectric Constant of Plastic
For electrical and electronic applications, an insulating material that has a higher dielectric is used as there is a need for higher capacitance.
The formula for calculating it is:
K = Em/E0
Where k = dielectric constant, Em = permittivity of the plastic or insulator, and E0 is the permittivity vacuum.
Or
E = C/C0 , C0 = E0A/t
Where
C = capacitance using the insulator as the dielectric capacitor
C0 = Capacitance utilizing vacuum or air as dielectric
E0 = Permittivity of the vacuum (8.85 x 10-12 Farad per meter).
A = Cross-section area of a sample
t = the sample thickness.
To use this, the plastic is put between two metallic plates and the capacitance is measured. The capacitance is measured a second time, but without the sample at this point. The Dielectric constant is the ratio between the two measured values. You can see more on this here https://passive-components.eu/what-is-dielectric-constant-of-plastic-materials.
Conclusion
The dielectric constant of an insulator determines the level of energy that a capacitor it is used in can store when an electric voltage is applied. The material becomes polarized when exposed to an electric field and this results in the reduction of the electric field. This makes it good for use in increasing the capacitance of a capacitor.
