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World of polymers; a glimpse into the classification of polymers

On November 17, 2020 | By KVN Impex Management

Polymers are everywhere. We can find polymers in almost all the products that we use daily. No one can even imagine a world without polymers. Do you know exactly what this polymer that has become so entrenched in our daily lives is? Polymers, material or substance composed of macromolecules which are essentially a combination of many small molecules called monomers. Monomers, the small building blocks of polymers, have the ability to chemically linked together to form long chains with other molecules through a process known as polymerization. The word polymer is actually derived from the Greek word “polus meros” which means “many parts”. These polymers become the raw material for nearly every product from mere plastic bags to the valuable silicone heart valve. It will amaze us that our genetic code, DNA, and the plastic we throw away are basically polymers. Plastics are polymers, generally derived from petrochemicals. The diversity in the molecular structure of plastics yields a wide range of different properties and characteristics. The polymers that are plastics can be categorized into two major types “thermoset“ and “thermoplastics” based on their molecular bond and their behavior
while the application of high temperature. Let’s dig into more details of this classification.

Thermoplastic and thermosetting polymers

Thermoset or thermosetting polymer and thermoplastic, or thermo softening plastic are two major categories of polymers that are subjected to diverse manufacturing procedures and offer a variety of properties based on their reaction to heat and characteristics of their chemical bond. A thermoplastic is a polymer with sharp melting points that can be molded and remolded by applying the precise amount of heat to weaken the intermolecular bonds. While the thermosetting polymers cannot be remolded or reshaped because they form an irreversible bond due to the strong covalent bonds along with the formation of cross-links of molecules during the curing process.

Thermoplastic: An overview

The thermo softening plastic will be softened, melted into liquid form by reheating without losing the physical properties, hence the name, and can be reshaped into any desired shape that makes it highly recyclable. The unshaped thermoplastic polymers also referred to as thermoplastic resins yield many benefits like chemical resistance, high strength, lightweight, flexibility, versatility, etc. Thermoplastics are formed by either addition polymerization (linking monomers by chain addition without the formation of by-products) or condensation polymerization (monomers react with each other to form polymers, releasing small molecules as by-products). There are many types of thermoplastic resins with a variety of properties, and they can be recast into various shapes upon processing through different procedures such as injection molding, compression molding, thermoforming, rotational molding, extrusion molding, blow molding, transfer molding, laminating and calendering process.

Types of Thermoplastic polymers

There is a variety of thermoplastics available in the market with different characteristics.
Some common thermoplastics are listed below:

  • Polycarbonate: The transparent thermoplastics with carbonate groups linked in their chemical structure offering high impact resistance, strong, tough, and versatile properties. Polycarbonates are widely used in the manufacturing of storage containers, CDs, lightweight eyeglass lenses, drinking bottles, shatterproof windows, etc.
  • Polyethylene: The most common thermoplastic polymer, having a very simple structure, comprises a long chain of carbons while each carbon atom is bonded with two hydrogen atoms. This economical polyethylene is loaded with a wide variety of properties such as good impact resistance, outstanding resistance to chemicals, excellent stability in low-temperature environments, etc.
  • High-Density Polyethylene (HDPE): HDPE is one of the most versatile, affordable thermoplastics polymers which are human-made and is prepared under low temperatures and pressures through a catalytic process with the aid of an active catalyst. The great strength-to-density ratio, high chemical resistance, good low-temperature resistance, and excellent tensile strength are the well-known advantages of HDPE. This is mainly used in the manufacturing of bottles, food, and beverage containers, 3-D printing filament, toys, snowboards, ice boxes, ropes, nets, etc.
  • Low-Density Polyethylene (LDPE): LDPE is a translucent polymer made from gaseous ethylene under controlled conditions and is famous for the production of plastic bags.
  • Polyethylene terephthalate (PET): Polyethylene terephthalate (PET or PETE) is a transparent, semi-crystalline, strong, lightweight, and biodegradable thermoplastic polymer classified among the polyester family. Higher-strength, outstanding electrical insulation, good gas barrier properties, and moisture resistance are counted as some of its major merits, and PET is widely used in packaging applications.
  • Acrylic: Poly (methyl methacrylate) or Acrylic is also known by various trade names like Plexiglas, Acrylite, Acrylic Plastic, Altuglas, Perclax, Astariglas, Perspex, etc. This transparent polymer has high strength, stiffness, excellent clarity, good impact resistance, etc and is used in the manufacturing of lenses, roof windows, LCD screens, sales displays, etc.
  • Nylon: Nylon is a member of the synthetic polymer family, a tough, strong thermoplastic with excellent abrasion resistance. Nylon exhibits high-temperature resistance owing to the high melting point. Due to the outstanding wearing properties, it is used to make vehicle parts, screws, machine parts, gears, etc.
  • Polyvinyl chloride (PVC): PVC is the third most widely produced synthetic plastic polymer in the world. This versatile polymer comes in two basic forms: rigid PVC that is used in the manufacturing of tanks, valves, pipes, etc and flexible PVC that possess good resistance against many chemicals, UV, acids, alkalis, oils, etc, electric insulation properties which makes it suitable for producing wire and cable insulation.

The long list of thermoplastics does not end with the types mentioned above. Polybutylene terephthalate (PBT), Polypropylene, Polystyrene, Teflon, Vinyl, Polyetherimide (PEI), etc are just some of the other common polymers in the thermoplastics category.

Pros of Thermoplastics

  • Thermoplastics are highly recyclable as they can be easily melted and reshaped.
  • The outstanding toughness and durability provides high impact resistance.
  • Thermoplastics have high dimensional stability in humid and other harsh environments.
  • They are lightweight and possess high strength.
  • The resistance to chemicals of thermoplastics makes it suitable for many industrial applications.
  • Imparts excellent aesthetics and a great finish.

Cons of Thermoplastics

  • Thermoplastics are relatively more expensive than thermoset polymers.
  • Some of the low-quality thermoplastics can easily melt in direct sunlight due to the low melting point.

Thermosetting polymers: An overview

Thermoset is a polymer that attains high strength when the heat is applied and undergoes a chemical reaction during curing that forms an irreversible structure of cross-linked molecules which makes this polymer impossible to remold. The irreversible chemical bond obliterates the threat of re-melting while exposing to heat, that makes thermosetting polymer well-suited for high-heat applications like kettles, plugs, laptop chargers, circuit breakers, insulators, motor components, etc.

Types of Thermosetting polymers

The main types of thermosetting plastics are epoxy resin, melamine-formaldehyde, polyester resin, and urea-formaldehyde.

  • Epoxy Resin: These are also referred to as polyepoxides, a long chain structure of the basic monomer unit, i.e., bisphenol A diglycidyl ether (BADGE or DGEBA), formed by the reaction of bisphenol A (BPA) and epichlorohydrin (ECH). Epoxy resin has good resistance to water, excellent adhesive properties, hardness, chemical resistance, and good electrical insulating properties. The principal uses of this thermosetting polymer are in making adhesives, castings, encapsulation, sealers, cardiac pacemakers, etc.
  • Melamine formaldehyde: Thermosetting polymers, made from the condensation polymerization of melamine and formaldehyde, are melamine- formaldehyde, also known as melamine resin or melamine. Melamine is a stiff, hard, and versatile polymer that possesses good chemical and heat resistance, which is used in the manufacture of crockery items, decorative laminated panels, tableware, coatings, etc.
  • Polyester resin: Polyester resins are unsaturated resins that have good electrical insulating properties, low creep, great strength, chemical resistance, and adequate resistance to water. These resins are utilized in the production of fiberglass laminations, boat hulls, coating, and bonding of other materials.
  • Urea-formaldehyde: Urea-formaldehyde or urea-methanal is a highly cross- linked opaque thermosetting polymer formed by mixing urea and formaldehyde in an acidic or neutral condition which undergoes a further condensation reaction. These resins exhibit excellent tensile strength, fast curing, abrasion resistance and are used in making adhesives, table lamps, handles, control knobs, and casing of electrical appliances.

Pros of Thermosetting polymers

  • Good resistance to high temperature and chemicals.
  • Suitable for the manufacturing of permanent, large and solid shapes.
  • Ability of thick and thin wall formation.
  • Outstanding resistance to deformation.
  • Cost effective and offer an attractive finished product appearance.
  • High dimensional stability and high structural rigidity.
  • Excellent resistance to corrosion effects.
  • Better dielectric strength.

Cons of Thermosetting polymers

  • Thermoset cannot be recycled.
  • Repairing is much more difficult.
  • Hard to achieve good surface finish.
  • Inability to be reshaped or remolded.

The polymer industry is a dynamic field with rapid transformations. The ubiquitous polymers are undergoing ceaseless innovations, and the arrival of new technologies has taken the global polymer market to a whole new level. Polymers are permeated our daily life and play decisive roles in each and every sector of the world. Polymer producers can thrive in the future by focusing more on the further production of sustainable polymers to embrace environmental protection.

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