Thermoset Plastics Easy Definition Fun Facts About Plastic
Thermosetting plastics are also known as thermosetting polymers or thermosets. They are produced by the process of condensation polymerization and consist of long molecular chains that are cross-linked together by covalent bonds. These materials can be molded into any desired shape upon heating, but once they are cooled, they permanently get settled and become very rigid and can not be reformed or recycled again because of their increased tensile strength and melting point. They do not melt even at higher temperatures. This rigidity is because of the increase in the cross-linking of polymer chains present inside the thermosetting materials due to the energy gained by the heat. In many cases, the rate of cross-linking can also be increased by adding a catalyst or by applying external pressure.
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Properties of Thermosetting Plastic
- Thermosetting materials have a three-dimensional crosslinked molecular structure due to which they are much stronger than thermoplastics materials.
- The higher the density of cross-links, the higher will be their ability to maintain their rigid shape.
- Thermoset plastics are chemical resistant and can survive against both organic and inorganic acids.
- The density of thermosetting materials depends on their constituent components.
- These materials lose their elasticity upon heating and become brittle in nature.
- Thermosets can't be reformed and recycled once they set their shape.
- Thermoset materials maintain their stability at both high and low temperatures.
Examples of Thermosetting Plastic
Thermosetting plastics are widely used in various industries due to their high thermal stability and chemical resistance properties. We can mold them into any shape, and once they set, they do not lose their stability even in extreme temperature conditions. Many manufacturers have switched to thermosets as they are cost-effective and are a great replacement for some metal components. Here are some examples of thermosetting plastics.
1. Vulcanized Rubber
Vulcanized rubber is a type of thermoset plastic as once it is molded, it retains its shape and can't be recycled again. The untreated rubber is converted into the vulcanized rubber through a process called vulcanization. In this process, the natural rubber is treated with Sulphur and various activators like Zinc fatty acid esters at the temperature of 140-160°C. Vulcanized rubber is more hardened than natural rubber. It is used in the manufacturing of various goods as it has both electrical and thermal insulation properties. Moreover, it has good abrasion properties and is inexpensive. It is used in manufacturing tires of vehicles because it has high tensile strength, hence it reduces the chances of tire punctures. Other uses of vulcanized rubber include seat belts, toys, conveyor belts, rubber hoses, and shoe hoses.
2. Bakelite
Bakelite was the first thermoset plastic that was synthesized from synthetic components. The chemical name of Bakelite is 'Polyoxybenzyl Methylene Glycol Anhydride,' and its chemical formula is ({C}_{6} {H}_{6}O.C{H}_{2}O)n. Commercially, it is also known as phenol-formaldehyde resin as it is synthesized by the condensation process between phenol and formaldehyde, under high pressure with HCl as a catalyst. However, other catalysts like ammonia and zinc chloride are also used sometimes, as per the requirement of the reaction. The product obtained from this reaction is further heated slowly till a hard substance called Bakelite is obtained. Bakelite is easily moldable in its liquifiable state, hence it is used in the manufacturing of various products. To increase the strength of the bakelite, various fillers like gypsum, mica, asbestos are also used. Bakelite has a wide application in the electrical industries for making switches, boards, sockets, and wire insulation because of its electrical insulation properties. The unique property of Bakelite is that it can be produced in different colors that is why it is widely used in the manufacturing of colorful bangles, bracelets, and artificial jewelry. The application of Bakelite is also found in various kitchenware products.
3. Duroplast
Duroplast is a composite thermoset material that is similar to Bakelite except for the fact that it is reinforced with cotton or wool fibers. One of the most significant properties of Duroplast is that it is lightweight and strong. Due to this property, Duroplast is used in making car bodies, which reduces the cost of using steel for making various car parts. It is also used in the manufacturing of toilet seats. However, it has a major disadvantage, which is its difficulty to decompose. If we burn them, they release highly toxic fumes that are harmful to the environment.
4. Urea-Formaldehyde Resins
Urea-Formaldehyde is also known as Amino plastic or carbamide-methanol. As the name itself suggests, they are synthesized by the reaction between the Urea and Formaldehyde in the presence of water, and at a PH value higher than 7. These Thermosets are highly cross-linked and have a semi-crystalline structure. They become rigid very rapidly if the temperature is elevated. They have wide applications in wood product industries and are used as an adhesive for particleboard. Their other applications include laminating decorative items, coating, air filtration, and fiberglass mats.
5. Melamine-Formaldehyde Resins
They are synthesized by reacting Melamine with Formaldehyde under low alkaline conditions. Like urea-formaldehyde resins, it is also widely used in wood industries. Melamine polished boards have better heat and chemical resistance properties than natural boards. Melamine-Formaldehydes are fully compatible with Urea-Formaldehyde resins and are often reacted with each other for reducing the emission of formaldehyde from particleboards, and this blend of resins is called melamine-urea-formaldehyde. Melamine resins are fire-retardant that is why they are used as additives in the manufacturing of papers, paints, plastics, and flame-resistant textiles. Many other products that are manufactured using these resins are particleboards, laminates, kitchenware, and floor tiles.
6. Epoxy Resins
Epoxies are reactive thermosetting resins and are also known as polyepoxides. Epoxy resins contain at least one epoxide group. The most commonly used epoxies are 'Diglycidyl Ether of Bisphenol A' (DGEBA) and 'Diglycidyl Ether of Bisphenol F' (DGEBF). However, DGEBF is somewhat on the expensive side. Epoxy resins are widely used in aerospace industries because of their heat and corrosion-resistant properties. These resins also find use in structural adhesives, metal coatings, and encapsulations of electrical components.
7. Polyimides
Polyimide resins are produced by the condensations reaction of aromatic primary diamines with aromatic tetracarboxylic dianhydrides. Because of the presence of aromatic rings in them, they have excellent thermal and chemical properties, and they can withstand high temperatures. They are widely used in the production of sockets, bushings, and bearings as they exhibit high mechanical strength and are water-resistant. They are also a great replacement for high-performance materials like metals and ceramics. However, their one shortcoming is that they are quite expensive.
8. Silicon Resins
Silicon resins have many applications due to their strong 3D network structure. They have the general formula RnSiXmOy, where R is usually Methyl or Phenyl, and X is the functional group (H, OH, Cl) or Alkoxy group (OR). These resins form very hard, heat and water resistance films, and show outstanding dielectric properties. They also provide very good UV rays resistance films. Silicon resins are available in different consistencies from a range of highly viscous liquids to solids. They find their applications in paints, coatings, sealants, silicone fluids, and electrical industries due to their reliability and durability. Silicon resin is widely used in art and craft for making various silicon items. They are also used in the healthcare sector because of their biocompatible nature.
9. Cyanate Esters
Cyanate esters consist of -O-C=N group attached to a phenyl ring. They show low water absorption, low dielectric loss, and high-temperature stability than Epoxies. Cyanate esters are usually found in brittle form, which is why they are often blended with epoxy resins or other thermosetting resins to get better-toughened products of enhanced properties. They are mainly used in aerospace industries due to their high structural and mechanical properties. Moreover, they are also used for electronic chip adhesives and encapsulation of various electronic equipment.
10. Polyurethane
Polyurethanes are produced by the reaction between the organic diisocyanate and a diol compound. They can also be produced in the foamed structure if water is used in their manufacturing process. This foamed structure is used in the manufacturing of cushions, carpets, armrests, and mattresses. Polyurethane has a rigid foam structure, and they are used as insulation for various buildings. Their elastomeric structure finds applications in making car bumpers, steering wheels, windshields, gaskets, door panels, and other automotive and electrical components. However, their main disadvantage is that they are prone to microbial attacks and often get yellow underexposure to UV light.
11. Furan Resins
Furan structure consists of a five-membered aromatic ring having four carbon (C) atoms and one Oxygen (O) atom. Furan resins have thermoset oligomers (Oligomers are the polymers whose molecules have similar repeating units), these oligomers are cross-linked together when heated in the presence of a catalyst. These resins are highly volatile, having boiling points near to room temperature, and they are soluble in some organic solvents like ether, acetone, and alcohol. Furan resin is widely used in cement and binders to make them chemical resistant. Their other uses include wood adhesives, coatings, and explosive binders. The main disadvantage of furan is that it is highly toxic to human beings.
12. Vinyl Ester Resins
Vinyl ester resins are prepared by the process of esterification of epoxy resin with vinyl acids; the vinyl acid group is responsible for the cross-linkage in them. It is ideal for the vacuum infusion process as it has low viscosity, hence it is easy to pour. Vinyl ester resins are often called the hybrid of Epoxy resins and polyester because their properties or other characteristics lie between them. It is widely used in the marine industry because of its high water-resistant and corrosion-resistant properties. They are widely used for corrosive-resistant coatings in tanks and pipes. They also find their application in chemical plants and petrochemical industries because of their high heat resistance level.
13. Polyester Resins
Unsaturated Polyester resins are formed by the reaction of difunctional organic acids (phthalic, maleic, fumaric) with polyhydric alcohol (Ethylene glycol, propylene glycol, halogenated glycol) in the presence of a catalyst. They are resistant to water and various chemicals and can withstand very high temperatures. They are used in boat building industries for making various parts of yachts and workboats because of their high strength and durability. Nowadays they are also used for flat roofing because they provide seamless and easy to maintain flat roofs. These resins also find application in making various electrical components, pipes, tanks, and ducts because they are lightweight, easy to handle, and have a longer shelf life.
Source: https://studiousguy.com/thermosetting-plastic-examples/
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