The term ‘Plastic’ is used to refer to a wide range of semi-synthetic or synthetic organic polymers that are known to be malleable and, therefore, mouldable into differently shaped solids. Therefore, it is important to note that different types of plastics are known to possess different physical and chemical properties. Despite the fact that almost all plastics offer moldability as one of their key attributes, it can be noted that some types of plastics are remouldable and others are not.
What are the Varying Physical and Chemical Properties Exhibited By Plastics?
Different types of plastics are known to possess different physical properties, and are known to be classified based on the following physical properties:
- The hardness of the plastic
- The density of the plastic (or the mass-to-volume ratio of the plastic)
- The tensile strength of the plastic (or the maximum amount of stress that the plastic can handle without breaking or undergoing a permanent deformation)
- The resistance of the plastic to heat
- The glass transition temperature of the plastic (or the temperature at which the plastic is transformed from a hard, brittle substance to a soft, rubbery one)
The different chemical properties that different plastics exhibit varying degrees of are listed below. It can also be noted that different plastics can be classified into different categories based on these properties
The chemical structure of the polymer that makes up the plastic.
- The resistance of the plastic to certain chemical reagents or the chemical reactivity of the plastic
- The resistance of the plastic to certain chemical processes (which can, once again, be categorized based on the chemical reactivity of the plastic)
- The effect of ionizing radiation on the plastic, which is also dependent on the chemical structure and reactivity of the polymers that constitute the plastic.
- Effect of temperature on the chemical composition of the plastic (some plastics are known to undergo an irreversible chemical change when exposed to high temperatures)
Properties Exhibited by Thermoplastics and Thermosetting Plastics
The term ‘thermoplastic’ is used to refer to the plastics that do not undergo any chemical changes when subjected to high temperatures. These plastics do not undergo any changes in their chemical structures and chemical compositions when subjected to heat. Therefore, thermoplastics can be heated into a soft state and remoulded multiple times. Examples of thermoplastic polymers include polyethylene, polystyrene, and polypropylene.
Thermosetting plastics, sometimes referred to as thermosets, are the plastics that undergo an irreversible chemical change when heated. These plastics can only be moulded once. While moulding these plastics, an irreversible chemical change is known to occur. It is not uncommon for these plastics to undergo degradation and become damaged when exposed to large amounts of heat. An example of a process involving a thermosetting plastic is the vulcanization of rubber.
Properties Exhibited by Crystalline and Amorphous Solids
A majority of all plastics are known to be completely amorphous in nature. Common examples of completely amorphous plastics include polystyrene, polymethyl methacrylate, all copolymers of polystyrene, and all thermosetting plastics. However, it is important to note that not all plastics are 100% amorphous in nature.
Some specific plastics are known to have a partially crystalline nature. This implies that the molecular structures of these plastics have a partial amorphous nature and a partial crystalline nature. Such plastics are commonly referred to as semi-crystalline plastics. Common examples of semi-crystalline plastics include polyvinyl chloride (often abbreviated to PVC), polyethylene, polyesters, polypropylene, and polyurethanes. It can also be noted that the partial crystalline nature of these plastics is responsible for their specific melting points. Furthermore, the crystalline nature of these plastics also imparts a glass transition temperature to them.
Biodegradable Nature of Plastics
As is the case with several other properties of plastics, biodegradability is another property that different plastics exhibit varying extents of. For example, some plastics that are classified as biodegradable take relatively short durations of time to break down and decompose. Other biodegradable plastics are known to take a much longer duration of time to break down and decompose. Finally, certain plastics are known to be non-biodegradable in nature. These plastics cannot be broken down by bacteria and other organic processes.
Biodegradable plastics can be defined as the plastics that break down or degrade when exposed to ultraviolet radiation (or UV radiation, usually in the form of sunlight), water, and certain enzymes and bacteria. It is important to note that plastics that can break down as a result of wind abrasion can also be classified as biodegradable. The degeneration of plastics can occur at the surface (this type of degradation is referred to as aerobic degradation) and also in the absence of air (this type of degradation of the plastic is referred to as anaerobic degradation).
It can also be noted that some plastic materials can be produced from renewable sources of biomass. Such plastics are commonly referred to as bioplastics. Common examples of the substances from which bioplastics can be produced include vegetable oils, vegetable fats, straw, recycled food waste, corn starch, and wood chips. Furthermore, bioplastics can also be produced from many renewable plant materials, the most common of which include starch and cellulose.
Electrically Conductive Properties of Plastics
A vast majority of plastics are known to be electrical insulators. However, some plastics are known to have the ability to conduct electric currents. For example, intrinsically conducting polymers (often abbreviated to ICPs) are a specific class of organic polymers that have the ability to conduct electricity. A notable example of intrinsically conducting polymers is polyacetylene. However, it is important to note that the electrical conductivities of these materials are significantly lower than those of certain metallic conductors such as copper wires. The development of electrically conducting plastics is an upcoming industry. A good deal of research is going into the development of such plastics.
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