Polymers Used in Daily Life

 

polymer-chemistry

From the stone age to the age of computers, a significant development in the materials that make our daily life comfortable is self-evident. One of the most revolutionary materials in the modern world are polymers. It is a material containing large molecules made by bonding (chemically linking) a series of building blocks called monomers. Polymers are present in almost every aspect of modern-day lives because of their vast spectrum of properties. Natural polymers like wool, cotton, and silk are present in our society long before the notion itself. The first synthetic polymer was invented in 1869 by John Wesley Hyatt, who made the first substitute for ivory billiard balls. It was not until 1907 when polymers entered the industrial sector with the invention of Bakelite, the first fully synthetic plastic, meaning it contained no molecules found in nature. These inventions emerged as a field of macromolecular chemistry, a field closely associated with the name of Herman Staudinger, who received the Nobel Prize in 1953 for first proposing the idea of polymerization (a process of reacting monomer molecules together in a chemical reaction to form polymer chains). Since then, there have been several developments in the synthesis of various polymers, contributing to six more Nobel prizes associated with the field of polymeric sciences. Let’s take a look at some of the most commonly used polymers in everyday life.

1. Polyethylene

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Polyethylene, also known as polythene, is one of the most prominent plastic polymers, accounting for 34% of the total plastic market in the world. It is a lightweight and durable thermoplastic with a crystalline structure and the general chemical formula ({C}_{2}{H}_{4})_{n}. It has excellent physical properties such as high ductility, high impact strength, and very great chemical resistance. Although there are different types of polyethylene classified by their density and branching, the most common types that we encounter in our daily life are:

  • Low-Density Polyethylene (LDPE):  It is a semi-rigid and translucent polymer with a high degree of long and short side-chain branching, which lowers the density of the polymer. It is produced at high pressure (1000-3000 bar; 80-300°C) via the free radical polymerization process. The average polymer molecule contains 4000-40 000 carbon atoms, with about 20 branches per 1000 carbon atoms. This makes them a useful plastic for molding and extruding in any desired shapes. The most common use of LDPE is in the manufacturing of plastic bags that we use to carry items; however, certain governments around the globe have banned the use of plastic bags due to rising environmental concerns. LDPE is also used for manufacturing various containers, dispensing bottles, wash bottles, tubing, plastic parts for computer components, and various molded laboratory equipment.
  • Linear Low-Density Polyethylene (LLDPE): LLDPE is produced by polymerization of ethylene (or ethane monomer) with 1-butene and smaller amounts of 1-hexene and 1-octene, using Ziegler-Natta or metallocene catalysts. The structure of LLDPE has a linear backbone with short, uniform branches. These short branches can slide against each other upon elongation without becoming entangled like LPDE. In recent years, LLDPE has infiltrated almost all traditional polyethylene markets. It has replaced the use of LDPE for plastic bags and sheets, allowing for lower thickness and almost equivalent efficiency. Other items made of LLDPE include transparent film, stretch packaging, bags, toys, lids, caps, pipes, cables, geomembranes, and mainly flexible tubing.
  • High-Density Polyethylene( HDPE): It is a cost-effective thermoplastic with linear structure and no or low degree of branching. It is manufactured at low temperature (70-300°C) and low pressure (10-80 bar). Due to the absence of branching, HDPE has a strong tensile strength with a temperature tolerance ranging up to 120 °C for a short period of exposure. HDPE is a preferable choice for piping because of its extremely high chemical resistance. Thanks to its high malleability, rigid strength, and corrosion resistance, HDPE is the perfect combination of strength, cost-efficiency, and environmental friendliness.

2. Polyester

Polyester is the category of polymers that contain an ester group in the monomer subunit. In daily life, it is most commonly referred to as a form of fiber called Polyethylene terephthalate (PET). Depending on its processing and thermal history, polyester may exist both as an amorphous and as a semi-crystalline polymer. Polyester fibers are often mixed with natural fibers to create a fabric with aggregate properties. As compared to plant-derived fibers, synthetic fibers made of polyester have superior water, wind, and environmental resistance. Its hydrophobic property makes it ideal for garments and jackets that are to be used in wet or damp environments by coating the fabric with a water-resistant finish intensifies this effect. Besides clothing and fabric, PET is also used as a substrate in solar cells, a waterproof barrier for cables, and also as an oxygen barrier for type IV composite high-pressure gas cylinders.

3.  Acrylics

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Acrylics, also known as acrylate polymers, are a group of polymers prepared from acrylate monomer ({CH}_{2}{=}{CHCOO}^{-}). These materials are commonly known for their transparency, resistance to breakage, and elasticity. These properties make acrylic extensively useful for applications requiring high transparency and impact resistance. Some of the common uses include acrylic nails, acrylic paint, security barriers, LCD screens, and acrylic home decors. Another acrylic includes cyanoacrylate resins, made into fast-acting adhesives, such as superglue, pressure-sensitive adhesive, etc. Poly-2-hydroxyethyl methacrylate, abbreviated poly HEMA, is acrylic used in the medical sector to make contact lenses.

4. Polyvinyl Chloride (PVC)

Polyvinyl Chloride (PVC or Vinyl) is a high-strength thermoplastic material that comes in two basic forms, rigid and flexible. It is produced by the polymerization of vinyl chloride monomer. It’s a white, brittle solid that comes in powder or granule form. PVC is now replacing conventional building materials such as wood, metal, concrete, rubber, ceramics, and others in a variety of applications due to its versatile properties such as lightweight, durability, low cost, and ease of processing. PVC pipes have replaced the metal pipes used for household distribution of water, thereby reducing the risk of contamination via corrosion. It is commonly used as an insulating cover for electricity wires network throughout the house. PVC is used in the manufacturing of sliding doors and window frames that are extremely durable, affordable, and help conserve energy when heating and cooling homes. In fact, vinyl windows have three times the heat insulation of aluminum windows. It also plays a critical safety role in dispensing life-saving medicine through IV bags and medical tubing. Almost one-third of plastic-based medical materials are made from PVC.

5. Polypropylene (PP)

Polypropylene ({C}_{3}{H}_{6})_{n} is one of the most versatile and cost-effective thermoplastic polymers in all plastics. It is a rigid and partially-crystalline polymer produced via chain-growth polymerization of propene (or propylene) monomer. It has several properties that make it a better choice of plastic than polyethylene, e.g., higher melting point makes it employable in the manufacture of microwave-safe containers, and higher resistance to cracking and stress, even when flexed, makes it less vulnerable to daily wear and tear. Polypropylene’s characteristics make it ideal for tough and robust products ranging from protective car bumpers to life-saving medical tools and cold-weather gear for soldiers. Moreover, it can also be engineered into a wide range of packaging that helps protect products we rely on every day, from medicine to yogurt and baby food. A large volume of PP is utilized in the fabric industries. PP fiber is utilized in a host of applications including slit-film, tape, strapping, bulk continuous filament, staple fibers, spun bond, and continuous filament. For marine applications, PP ropes and twines are used as they are very strong and moisture resistant.

6. Rubber

Rubber is an elastomer, i.e., a polymer that is primarily characterized by its ability to regain its original shape after being deformed. There are many different kinds of rubber, but they all fall into two broad types: natural rubber and synthetic rubber. Natural rubber is harvested mainly in the form of the latex from the rubber tree (Hevea brasiliensis) or other plants. In chemical terms, it is a polymer of isoprene, also known as 2-methylbuta-1,3-diene, with the chemical formula ({C}_{5}{H}_{8})_{n}. Synthetic rubbers are made in chemical plants using petrochemicals as their starting point. One of the most commonly known synthetic rubber is neoprene, chemically known as polychloroprene, made by reacting together acetylene and hydrochloric acid. Neoprene has good chemical stability and maintains elasticity over a wide temperature range, which makes it a preferred material for the manufacturing of wetsuits, wrist and orthopedic knee braces, surgical gloves, laptop sleeves, mousepads, and gaskets. Another popular family of synthetic rubbers is styrene-butadiene rubber (SBR), which is derived from the copolymerization of two monomers: styrene and 1,3-Butadiene. This rubber is widely used for the manufacturing of tires all around the world.

7. Teflon

Many of us come across this material when we make our food on a non-stick pan. Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer of tetrafluoroethylene and is known by its common brand name Teflon. It is one of the most slippery man-made materials. Apart from its use in the kitchen, PTFE is used as a cost-effective solution for industries ranging from oil & gas, chemical processing, industrial to electrical/electronic and construction sector because of its extensive properties such as exceptional heat and chemical resistance, good electrical insulating power in hot and wet environments, low dielectric constant, strong anti-adhesion, flexibility, and low water absorption. These properties make Teflon employable in several automotive parts such as gaskets, valve stem seals, shaft seals, linings for fuel hoses, power steering, transmission, etc. In the chemical industry, it can be used as coatings for heat exchangers, pumps, diaphragms, impellers, tanks, reaction vessels, autoclaves, containers, etc. Due to its electrical properties, it is widely used in insulation, flexible printed circuit boards, semiconductor parts, etc.

8. Nylon

Nylon

Most of us are familiar with the term ‘nylon’ as a superstrong silky fiber that is generally found in umbrellas, socks, and ropes. In chemistry, nylon is a generic designation for a class of polyamides (polymers with repeating monomer units linked by amide bonds).  Nylons are generally produced by reacting difunctional monomers containing equal parts of amine and carboxylic acid so that amides are formed at both ends of each monomer. There are different types of nylon depending on the nature of the monomer units. Two of the most commonly used nylons are:

  • Nylon-66: It is one of the most commonly used polyamides in the textile industry. Nylon 66 is synthesized by the copolymerization of two monomers each containing 6 carbon atoms, which gives nylon 66 its name: hexamethylenediamine ({H}_{2}{N}({CH}_{2})_{6}{NH}_{2}) and adipic acid (({CH}_{2})_{4}{COOH}_{2}). Nylon 66 is frequently used when materials with high mechanical strength, rigidity, good stability under heat, and chemical resistance are required. Typical applications of nylon 66 include fiber for textiles, carpets, molded parts, pipes, zip ties, conveyor belts, hoses, polymer-framed weapons, and the outer layer of turnout blankets.
  • Nylon-6:  It is another popular polyamide that we may come across in our daily life.  Unlike nylon-66, nylon-6 is produced by the ring-opening polymerization of a single six-carbon monomer called Caprolactam (({CH}_{2})_{5}{C(O)NH}. Nylon 6 fibers have high tensile strength, elasticity, and a lustrous finish. They’re wrinkle-free and immune to abrasion as well as chemicals like acids and alkalis; however, they may lose their tensile strength when soaked with water. Most of the nylon-6 is produced in the form of filament yarns for the manufacturing of apparel, hosiery, upholstery, seat belts, parachutes, ropes, and industrial cords.

9. Silicone

Silicone, also known as polysiloxane, is a high-performance elastomer made of polymerized siloxanes (chains made of alternating silicon and oxygen atoms). By varying the lengths, side groups, and crosslinking of −Si−O− chain, silicones can be synthesized with a wide variety of properties and compositions. These properties range from high-temperature performance to durability, excellent electrical insulation properties as well as varying transparency. With these unique characteristics, silicone rubber is widely used in industries such as aerospace, automotive, construction, medical, electricity, food processing, etc. For instance, sealants and adhesives made of silicone are used to seal and protect doors, windows, wings, and electrical components in the aviation and construction sectors. Due to their non-toxic properties, silicones are often used in the medical sector for implants and drug delivery systems. Advances in silicone technology enable today’s exterior paints and coatings to last longer and stand up to the sunlight and pollution. Paints made with silicones offer exceptional adhesion, pigment dispersion, and chemical, weather, and stain resistance

10. Hydrogel

A hydrogel is a three-dimensional (3D) network of hydrophilic polymers that can absorb and hold a substantial amount of water while maintaining the structure due to the chemical or physical cross-linking of individual polymer chains. Physical crosslinks consist of hydrogen bonds, hydrophobic interactions, and chain entanglements, whereas chemical cross-linkage involves covalent bonds between polymer strands. The polymers used to create hydrogels usually have monomers containing hydrophilic groups such as –{NH}_{2}, –{COOH}, –{OH}, –{CONH}_{2}, –{CONH}, and –{SO}_{3}{H}, which is why they are so efficient in absorbing water. Hydrogels appear in various everyday products such as hair gel, toothpaste, and cosmetics. Some superabsorbent hydrogels are acrylate-based materials, which are mainly used to absorb fluids in disposable diapers. The high-porosity structure of hydrogels allows drugs to be loaded and then released, making long-term transdermal drug delivery easier and allowing for a controlled drug delivery system. Another important use of hydrogels in the medical sector involves tissue engineering (a set of methods that can replace or repair damaged or diseased tissues with natural, synthetic, or semisynthetic tissue mimics). Both synthetic and naturally derived materials can be used to form hydrogels for tissue engineering scaffolds.

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