Polyethylene is the most widely produced and used plastic in the world and is an integral part of the urban lifestyle of a person. The high demand for PE is given to its mass use as a packaging material due to flexibility, heat and electrical insulation and barrier properties, chemical and thermal stability, ease of processing and, most importantly, accessibility and low cost. More than 35% of all PE produced is used to make the package. Other areas of its application are electronics, mechanical engineering, construction, light industry. Another side of scientific and technological progress is the problem of waste accumulation and its negative impact on the environment and human health. With the development of industry in Ukraine, the amount of waste is growing. Conversely, the amount of recycled, i.e. reused plastic articles, is reduced.
Polyethylene is an ethylene polymerization product and it is hardly naturally occurring. This is non-biodegradable plastic, the decay of which lasts at least 200 years, releasing harmful substances into the environment. To reduce the negative effect of the used polyethylene, it is disposed of by burial or by external exposure to physicochemical or biofactor. Some fungi and bacteria can contribute to the biodegradation of PE by releasing chemicals that can break down long chains of polymers.
The problem of plastic waste accumulation is related to the limited shelf life of many plastic products and the complexity and high cost of plastic recycling processes. Plastic recycling is the process of collecting plastic waste and processing it into useful products. There are several types of PЕ processing processes. This is primary, secondary, tertiary and quaternary processing. Primary processing - reuse of the product, as a rule, for the same purpose. Secondary processing - pellet production. Thermoset polymer cannot be recycled into granules, so they are depolymerized into oligomers by chemical reaction. This is tertiary processing. One of the methods of recycling the polymers is pyrolysis. This is the thermal scheduling process of the organic substances that the polymers consist of. For polyethylene, this temperature is about 450 C. To increase the efficiency of the process, for example, to accelerate it or reduce the temperature in the reactor, a variety of catalysts can be used.
Pyrolysis products depend on the degree of branching of PE, its molecular weight, temperature and type of reactor, catalyst, which is used and is characterized by high quality and environmental safety, since the feedstock does not contain phosphorus, sulfur and nitrogen compounds. The simplest example of recovery (quaternary processing) is the burning of PE. Incineration releases a significant amount of energy from polyethylene, the heat of combustion of which is about 47 MJ/kg. This method is environmentally dangerous because the thermal degradation of PE in the presence of oxygen releases cellular compounds that are dangerous to human health. The cleaning of the combustion gases is expensive, resulting in the lowest economical combustion efficiency among all recycling methods.
Waste reduction can be achieved by introducing a cyclical economy based on the principle of 3-R: Reduce (reducing the use of resources and providing the advantage of renewable materials), Reuse (maximum possible product efficiency), Recycle (recovery of by-products and waste for their reuse). The use of PE waste as alternative materials for urban development programs will reduce gas emissions and fossil fuel consumption. Dematerialization, the use of goods as a service instead of the traditional model of sale, the use of waste from one production as a raw material for another contribute to the reduction of waste volumes too.
An example is the use of PE waste to strengthen the soil in geotechnical schemes of retaining walls, foundations, road foundations, embankments, and slope stabilization. As a result of including strips of polyethylene bags in the soil, soil resistance to landslide increases, bearing capacity and soil subsidence characteristics are improved. Another area is the construction of roads where plastic waste is used to increase the life of roads. The life of roads built from plastic-modified asphalt is growing several times. Such a coating is more resistant to damage, reduces the cost of raw materials and industries, is much safer for the environment than ordinary asphalt. The use of plastic waste instead of specially made additives will help significantly improve the environmental situation in the country.
The best waste reduction strategy in Ukraine is measures to reduce the quantity of materials for the production of plastic products, extend the service life of products by reusing them in order to postpone disposal where possible.
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