My Science School

           You might be using silicone brushes or spoons in your kitchen. Though they have a soft texture, they are used for cooking which generally involves high temperatures. Ever wondered why?

           Silicone is resistant to heat. It is a non-toxic substance that shows resistance to water and chemicals as well. Because of these reasons, silicone is preferred to make kitchen ware.

           Silicone is a polymer made of the repeating units of siloxane – silicon and oxygen atoms-, carbon and hydrogen. Sometimes, other elements like methyl or benzene are also used with these.

          Silicone has a wide range of uses. It is used as a solvent for dry-cleaning as an alternative to chlorine because it has less impact on the environment. Many of the electronic appliances have cases made of silicone. It is also used in the aerospace industry because of its various desirable qualities.

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           Have you seen the blood and urine bags used in hospitals? They are flexible and waterproof at the same time. These bags can only be used once and are made of medically approved PVC.

           PVC is cost-effective, transparent and light in weight. It is soft and tear resistant at the same time. All the IV bags and medical tubings are made of medically approved PVC. It is also used to make other products like bags to collect blood, catheters, heart-lung bypass sets and dialysis sets. Almost one third of plastic-based medical devices are made from PVC.

            In fact, 85,000 tonnes of PVC are used for medical purposes in Europe alone.

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           Polyester is a popular choice of clothing. All of you might have at least one polyester outfit. It has a bright colour and a silky touch. The cloth is very slippery as well.

          Polyester fabric is extremely strong. It is durable and won’t shrink. Polyester does not wrinkle easily which solves the problem or ironing. Polyester does not get stained easily. It is easy to wash and quick to dry. What more is needed for a fabric for rough use?

           The most popular and one of the earliest uses of polyester was to make polyester suits. It can also be folded into permanent pleats and decorative shape.

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           You might have seen petri dishes in your biology lab. When you see a petri dish again, remember that it is made of a polymer known as polystyrene. Polystyrene is a plastic that is used to make a variety of consumer goods. It is hard and is usually used to make laboratory equipment and food packaging.

           Several additives are added to polystyrene to make it suitable for the production of things like electronic appliances, automobile parts, toys, gardening pots and surf boards.

           Polystyrene is made by polymerizing styrene monomers. Some amount of styrene is present in nature as well: in strawberries, cinnamon and coffee. It is easy to sterilize polystyrene. Therefore, it has a wide range of medical applications, including tissue culture trays, test tubes and medical devices.

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           The first thing that comes to our mind when we hear the name PVC is the water pipes in our house. But, PVC is used to make a lot of other things as well.

           PVC shows good resistance to water. Because of its waterproofing traits, it is used to make rain-coats, shower curtains and water pipes. Its weather resistance is the reason why it’s used to make coats, jackets and sports bags. PVC also shows good flame resistance because of its chlorine content. When PVC catches fire, the chlorine atoms present in it are released and these atoms block burning. PVC is available in two forms- rigid and flexible. The rigid form of PVC is used to make doors, windows, and ATM cards. Flexible PVC is mainly used for plumbing and insulation.

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           HDPE and LDPE are two grades of thermosetting plastics made of ethylene monomers, whose properties differ from one another based on their structure.

           HDPE has a higher density. Therefore, it is harder, has a higher chemical resistance and can withstand higher temperatures. It has little branching resulting in higher strength and stronger intermolecular forces. It is used to make things like bottle caps, corrosion protection for steel pipes, folding chairs and tables, chemical resistant pipes, plastic bags and water pipes.

           On the other hand, LDPE is softer, more flexible and melts at a lower temperature than HDPE. Its strength is lower compared to that of HDPE.

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           Take a look around and you would find at least ten things made of low density polyethylene (LDPE) toys, utensils, films, bottles, pipes, insulating wires, plastic wraps, juice cartons and so on.

           Low density polyethylene is class of flexible thermoplastic depending on how they are being made. As the name suggests, it has a lower density and the force of attraction between the molecules is weak. LDPE is cheap and can be easily processed. It is generally not reactive at room temperatures. It is flexible and quite tough. These qualities make it a desirable polymer for making a lot of things.

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           Most of us have plastic food containers at home. These food containers are airtight and do not absorb moisture easily. A material called polypropylene is used to make such food containers. It is a thermoplastic polymer made of propylene monomers and is also known as PP. Polypropylene doesn’t absorb water and dries quickly. It is an effective insulator and does not transfer heat. PP is also resistant to acids and alkalies.

           A range of other products like bottles, various parts of automobiles, plastic hinges, carpets and clothing use polypropylene.

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           None of us will compromise when it comes to buying a backpack. It should be strong, durable and should not tear off easily. But, have you ever thought of the materials that are used for making a quality backpack?

           Long ago, backpacks were mostly made of cotton canvas with wax coating. The coating waterproofed them. But, these bags were prone to damage. Today, most of the backpacks are made of synthetic fibres like nylon and polyester. Though nylon has better waterproof traits than many other fibres, it can be easily damaged. But nylon can be strengthened using different techniques.

           Ripstop nylon is thicker and can be sewn close to get a tightly stitched fabric. It is used to make hiking backpacks. Your school-bags are often made of polyester. It is cheap and can be dyed into any attractive colour.

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           Mountaineering is not an impulsive activity. It requires proper planning and preparation which would not be complete without certain polymers.

           You need breathable clothes in which you can easily move around. Most of these clothes are made of nylon. You need strong ropes made of synthetic fibres and shoes with a firm grip. Hiking and mountaineering shoes are often made of materials like rubber with laces made of fibres like kevlar.

           You need a good backpack and that is made of a set of polymers. The bottles that you carry water in are yet another thing made of polymers.

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           Nomex suits have saved the lives of many race car drivers. Here is what Jeff Gordon, veteran racer, says about Nomex.

           “I’ve been racing for a lot of years and I’ve been wearing a Nomex suit for many of those, starting out in the go-cart days. Nomex is an amazing material. I have, unfortunately, had the opportunity to test this product in my racing.”

           “I was in a midget several years ago and (the car) did catch fire, which is pretty scary because you can’t see the flames. You don’t know you’re on fire until it’s almost too late. I was actually running through a practice and a fuel line came loose and I noticed my steering wheel was on fire and that’s why I knew I was on fire. I felt some heat, but nothing ever touched me, no flames ever got to me, no burns ever got to me.”

           “Of course in the midget cars we’re wearing three layers plus a Nomex underwear lining underneath it and that’s the reason why I certainly wouldn’t get in a race car and do my job without having Nomex on.”

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            Du Pont developed Nomex in the 1960s. This polymer is used to make the masks of firefighters, racing vehicles and to build aircraft for military use. Race car drivers and wildfire fighters wear suits made of nomex. It is used to reinforce the insides of helicopters and tail fins of aeroplanes. Needless to say, Nomex is a fireproof material.

            Nomex resists heat, chemicals and several radiations. The monomers of Nomex have a ring-like structure held together in a strong bond. It is sold as fibres and sheets.

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