EFFECTS OF PLASTIC WASTE TO THE ENVIRONMENT

INTRODUCTION

Environmental pollution due to plastic wastes is a global phenomenon today, the disposal of waste plastics has become a major environmental problem all over the world.  USA, Europe and Japan generate about 50 million tons of post consumer plastic waste material. Saudi Arabia is one of the major producers of plastic in the world with total production capacity of around six million metric tons per year. The amount of plastic wastes in Saudi Arabia is about 15-wt% in the composition of domestic municipality waste. 

Recycling waste plastics into reusable plastic products is a conventional strategy followed to address this issue for years. However this technique has not given impressive results as cleaning and segregation of waste plastics was found difficult but indispensible in this technique. It is estimated that approximately 10 thousand tons of plastics waste per day is generated. Plastic wastes include different types of Low Density Poly Ethylene (LDPE), High Density PolyEthylene (HDPE), Poly Ethylene Terephthalate (PET), Polypropylene (PP), Polystyrene (PS), Poly Vinyl Chloride (PVC) etc. As the plastic waste segregation is difficult it was essential to have novel technologies for plastic waste disposal.

Today, sophisticated technologies are available for plastic waste management. Pyrolysis is one such technique used not only for waste disposal but to produce useful products like industrial diesel, gaseous fuel, carbon black etc.

Many varieties of materials used on daily basis are made from petroleum derivatives called plastics. The term ‘plastic’ can be broadly defined as a polymeric material that has the capability of being molded or shaped, usually by the application of heat and pressure. A plastic material is any of a wide range of synthetic organic solids that are mouldable. Plastics are typically organic polymers of high molecular mass, but they often contain other substances. They are usually synthetic, most commonly derived from petrochemicals, but many are partially natural.

Plastic materials made up of large, organic (carbon-containing) molecules that can be formed into a variety of products. The molecules that compose plastics are long carbon chains that give plastics many of their useful properties. In general, materials that are made up of long, chainlike molecules are called polymers. This property of plasticity, often found in combination with other special properties such as low density, low electrical conductivity, transparency, and toughness, allows plastics to be made into a great variety of products. These include tough and light weight beverage bottles, flexible garden hoses, insulating food containers e.t.c.

 Plastics can be made hard as stone, strong as steel, transparent as glass, light as wood, and elastic as rubber. Plastics are also lightweight, waterproof, chemical resistant, and produced in almost any color. More than 50 families of plastics have been produced, and new types are currently under development.

Like metals, plastics come in a variety of grades. For instance, nylons are plastics that are separated by different properties, costs, and the manufacturing processes used to produce them. Also like metals, some plastics can be alloyed, or blended, to combine the advantages possessed by several different plastics. For example, some types of impact-resistant (shatterproof) plastics and heat-resistant plastics are made by blending different plastics together.

Plastics can be classified by the chemical process used in their synthesis, such as condensation, polyaddition, and cross linking.  There are two types of plastics: thermoplastic and thermosetting polymers.  Thermoplastics are the plastics that do not undergo chemical change in their composition when heated and can be molded again and again. Examples include polyethylene terepthalate (PET), high density polyethylene (HDPE), polyvinyl chloride (PVC), polypropylene (PP), polystyrene (PS), low density polyethylene (LDPE).

Thermosets can melt and take shape once after they have solidified, they stay solid. In the thermosetting process, a chemical reaction occurs that is irreversible. The vulcanization of rubber is a thermosetting process. Examples include unsaturated polyester, epoxies, phenol formaldehyde, polyurethane, and urea and melamine formaldehyde.

Plastics have unique properties because of their strong chemical bonds which make them adequate for many applications; however, these bonds are not biodegradable. Plastics have revolutionized quality of life and more and more many new life saving devices are and will be made of them. Plastics in different forms are one of the most widely used materials due to their diverse benefits and many applications to daily life.

Carrying plastic bags (CPB) is the main mode of transportation of goods in daily shopping. Consumers and retailers have accepted the CBP for their benefits because of its light-weight, strength, inexpensiveness, practical, and as a sanitary way of transporting goods and foods. The bags used in grocery stores to carry foods and goods are made of high density polyethylene (HDPE), and the bags usually used in department and fashion stores are made of low density polyethylene (LDPE). Polyethylene is a product of petroleum, a non-renewable resource which takes many centuries to break down when put in a landfill.

 Enormous volumes of plastic materials composed of bags, dishes, packing materials e.t.c after daily use, generate billions of tons of non biodegradable waste. These commodities quickly become pollutants; they pollute the environment (air, land and water), exhaust the landfills, and endanger wild and human lives. The number of landfill sites is decreasing. Also landfilling could result in plastic additives such as phthalates and various dyes polluting ground water. Incineration is an alternative to landfill disposal of plastic wastes, but this practice could result in the formation of unacceptable emissions of gases such as nitrous oxide, sulfur oxides, dusts, dioxins and other toxins. The option of secondary recycling or mechanical recycling which is the reprocessing of plastic waste into new plastic products with a lower quality level is not showing any signs of growth in the recycling industry. Tertiary recycling, this returns plastics to their constituent monomers or to their higher value hydrocarbon feed stock and fuel oil, is gaining momentums as an alternative method.  Tertiary recycling includes all those processing which attempt to convert the plastic wastes to basic chemicals by the use of chemical reactions such as hydrolysis, methanolysis and ammonoloysis for condensation and to fuels with conventional refinery processes such as pyrolysis, gasification, hydrocracking, catalytic cracking, cooking and breaking of addition polymers excluding PVC.

Waste plastics can be reused as valuable resources according to the treatment technologies. The mechanical recycles for the production using the same material can be recommended as a desirable technology because this makes no more pollution problems. But it is very difficult to separate various waste plastics with dust and metals into one-component raw material which can be recycled without any problems. So, thermal recycle technologies are the objects of interest as alternatives for the mechanical recycle technologies.

In these technologies, Pyrolysis and catalytic conversion of plastic is a superior method of reusing the waste. The distillate product is an excellent fuel and makes Thermo Fuel one of the best, economically feasible and environmentally sensitive recycling systems in the world today. Thermo Fuel diesels can be used in any standard diesel engine, trucks, buses, trains, boats, heavy equipment and generators.

 With heavy consumption of fossil energy and fuels, the world will be faced with shortage of energy and environmental concerns in the near future if no other solutions are to be found. On the other hand, renewable energy sources and waste streams can be processed for production of energy and fuels.