Sheet Plastic | Sheet Plastics

Sheet plastic - polymers changing our lives

Towards the end of this millennium, various new materials were developed, that were previously unknown. They are plastic (polymers), carbon fibre, use of different new metals like palladium, titanium etc. This affected our lives profoundly. Plastics played an important role in the transformation of our lives. Plastics are of three types – based on its internal structure (i) linear

(ii) Sheet

(iii) 3D structure

Among all these, sheet plastics play a vital role in the things of our daily use.

Sheet plastics are called so because the formation of this type of polymers is just like numerous sheets of paper stacked upon one another. This gives it some characteristic features that one would expect in sheets. It can be moulded to form very thin yet strong sheets used where plastic sheets are large strong durable sheets are required. But when moulded to form 3D structure like a stack of papers, its strength falls if force is applied along its length and it may break. It is also more easily possible to recycle a sheet plastic than a 3D plastic.

Plastic sheets have a dynamic range of applications.

•  Plexiglas or polymethyl meta-acrylate was first marketed in 1936. It is a very cost effective, strong light durable where heavy force is not implied. It is somewhat brittle and more prone to scratches than glass. In the Second World War it was extensively used in windshields, submarine periscopes, gun turrets etc. It also lacks the harmful bisphenol found in polycarbonates. It has a wide range of implementation. It is used in making spectator protection in ice hockey. It is used in making large aquariums. It is used in motorcycle helmets and riot control vehicles. It is also used in making certain lenses. PMMA also has a high degree of compatibility with human tissue and sometimes used as a replacement of intraocular lenses of the eye in cataract patients. It is used to make bone cement that is used to remodel lost bones and affix implants. It is used in dentures with proper colouring. Acrylic paints are also made from this polymer.

•  PVC (poly-vinyl chloride) sheets are a good durable alternative to normal steel and other substances where transparency is not a factor. It is heavily used in various household items like chairs, tables, kitchen accessories, water pipes etc. It has a unique property of low permeability to ware vapour and other gases which make it ideal in food processing industry. Its low inflamability and rigidity is used to make pipes, floor tiles window frames etc. The state of California is considering to put a ban on the polymer as it is dangerous for human health and also is a threat to the recycling system. The main constituent of PVC is vinyl chloride is a carcinogen. Even recycling cost is much higher than forming PVC from raw materials because of the extensive grinding and recompounding required. But still many governments are thinking this as the only way to stop the pollution caused by this polymer.

•  Polystyrene (PS) is another kind of polymer that is put to heavy use both in house-hold as well as industrial purposes. It is much tough and can withstand strong impact. Its commercial applications began as early as 1930. It is actually an inexpensive, strong thermoplastic i.e., it is softened by the application of heat. It can resist attack of strong alkalis, acids and may other solvents. It also good electrical insulator and does not absorb water. After 1960's even better forms of poly styrene were put to use in manufacturing equipments like refrigerator. Majority of the polystyrene is not recycled. Instead it is more used in other polymer applications where it is used as fillers in products that will not be recycled. It is also used in making insulating sheets in concrete foundations.

•  Polycarbonate plastic is made from Bisphenol A. It is expensive but many times stronger than other alternatives and many forms of glass. It has low resistance to scratches and so a hard transparent coating is required to make special eyewear lenses, compact disks, drinking bottles and other exterior automotive components. With a coating it can be also used to make bullet proof or rather “bullet resistant” glass which is widely used in military as well as industrial purposes. Polycarbonate is very attractive to manufacturers due to its unique properties, but it has many hazards also. Bisphenol is a toxic substance and constant long exposure can serious health damages to even cancer.

•  Teflon or tetrafluoroethylene is another sheet plastic that is has some unique properties like high heat resistance (inert up to about 300 degrees centigrade), corrosion resistant material. It can withstand the highest temperature among organic substances. It is appreciably soluble in acetone but not in water. It is used in making fine cooking materials like non-stick cookware and heating iron. It was also used in coating substances of equipment used in radioactive materials to prevent corrosion in World War II. It also finds uses in temperature resistant seals, gaskets, o-rings etc.

•  Chlorotrifluoroethylene is a fluorinated elastomeric used in space applications as it can withstand temperatures up to about 250 degrees centigrade.

•  Polyvinyl fluoride shows transparency as well as extreme weather ability. So it is used in making laminated coatings like insulating electrical equipments and wires. It also finds uses in piezo-electric substances and thus in making some modern sensors.

Most of the polymers used are not much recyclable. This is because of the inherent cross linking that initially gives them the sheet structure. This also makes them hard to biodegrade, which are causing an increase in the pollution levels in our environment. Bio-degradable plastic is much difficult to make due to economic reasons and the instability caused during production. Most of these go to dump under the ocean beds where they are disturbing the natural eco-cycle, which eventually after some years will affect the whole food chain and destabilize the whole ecosystem.