Investigation of environmental degradation of biodegradable and conventional plastics by microscopic and instrumental

Plastics, low cost, light weight, easy workability; They are polymers that are widely used in daily life, thanks to their properties such as little or no conduction of heat and electricity. Due to all these features, the use of plastic on a global scale; it is increasing even more with the increasing population and the advances in industrial and technological fields. The resulting wastes, on the other hand, remain intact for centuries in nature and can accumulate in the environment. Today, when it is understood that conventional plastics can cause irreparable problems in the environment and biota, biodegradable plastics that can be decomposed in nature have begun to be produced and used as an alternative to conventional plastics. Regardless of whether they are biodegradable or conventional, the processes of starting to decompose and completely disappearing in nature of plastic material types that may contain many additional additives still remain unclear. In general, fragmentation, aging or structural changes of plastic materials; It occurs through natural environmental factors such as UV radiation, humidity, temperature, salinity, oxygen exposure and biological processes and/or various anthropogenic factors. Examples of conventional plastics used in daily life are polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyethylene terephthalate (PET), polystyrene (PS) and polyurethane (PU). The most used ones in daily life are PP and PE. In particular, the use of disposable products such as plastic packages made of plastic of different densities and water bottles made of PET plastic is quite high. The usage time of disposable products can vary from a few seconds to a few hours. Approximately 50% of single-use plastics, which we can define as disposable plastics, turn into waste after a single use, and unfortunately, these plastics constitute a large part of the garbage found in sea and land environments. Plastic waste can reduce the productivity of farmland by inhibiting the nutrient uptake of plants in the soil. Likewise, lakes, rivers and oceans are polluted by single-use plastic waste. Biodegradable plastics and oxodegradable plastics have been shown as alternative solutions in plastic waste management. The term biodegradable; Biobased but non-biodegradable plastics, biodegradable but non-biobased plastics, and biodegradable and bio-based plastics. Plastics that are obtained with bio-natural raw materials (eg; starch-based, cellulose, chitosan) and disappear without leaving any residue in the nature are called biodegradable plastics and are relatively expensive. Plastics produced by adding additives that accelerate the deterioration of plastics are called oxo-bio-degradable plastics. The biodegradation of a plastic is due to the action of naturally occurring microorganisms such as bacteria, fungi and algae. Plastics obtained from plant products such as sugar cane, potato and corn starch are expressed as biodegradable plastics. It is possible to collect the factors affecting the degradation of plastics under two separate headings, physicochemical processes and biological processes. Physicochemical processes; It covers the effects of UV radiation, humidity, temperature, salinity and oxygen. Photo-oxidation by solar UV is generally considered the most important mechanism of environmental degradation. Because UV radiation is necessary to initiate the degradation of most plastics, it advances the pathway of polymers causing bond cleavage and a reduction in molecular weight. High humidity levels have a positive effect on decomposition, accelerating decomposition. Degradation of plastic occurs more slowly in hot and dry climates than in hot and humid climates. In sea waters with high salinity, the degradation rate of plastics is low, but there are opportunities to work on improving this rate. Likewise, oxygen can be added to the carbon chain of the polymer to increase degradability. Biological processes take place with the help of various microorganisms. These; plastic degradation originating from bacteria and fungi, biofilm originating and microbial origin. Microbial settlement and biofilm formation takes place on plastics, which is called the plastisphere. Environmental factors such as salinity, pressure, oxygen and current velocity differ in different parts of the sea, leading to differences in plastispheric communities in different parts of the sea. There are many techniques and devices that study the breakdown of plastics. In the visual observations made, the deteriorations on the surface of the plastic are discussed. Upon examining the plastics with an optical microscope, it is understood whether they are deformed by looking at the presence of pits or holes on the surface. Optical microscopy is used as the first step in plastic scanning for all samples or, in a way, as a pre-scan technique to reduce the number of plastic particles to be analyzed by SEM. More complex surfaces can be observed using scanning electron microscopy (SEM) or atomic force microscopy (AFM). Other techniques; weight loss measurements, changes in mechanical properties and molar mass, and CO2 formation/O2 consumption. Respirometric test for carbon dioxide production and sturm test for oxygen consumption are performed in laboratory environments. By using ATR-FTIR (Attenuated Total Reflectance-Fourier Transform Infrared), besides particle size and distribution, chemical structures such as polymeric basis of the sample are determined. The aging studies of plastics are done in natural environments and in laboratory environments where results can be obtained in a shorter time. The aim of the study is to follow the change in different natural environments of biodegradable and conventional type disposable plastics, which are formed and accumulate excessive amounts of waste in the environment due to excessive use today. For this purpose, real-scale research findings that we can evaluate about the degradation of different types of plastic materials in film form in environmental environments have been tried to be evaluated. As conventional plastics in studies; polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC) and polystyrene (PS) etc. disposable products such as bags, cardboard cups, examination gloves produced from raw materials, and polylactic acid (PLA) type disposable plates and sachet film were used as bioplastics. The materials used were placed at points determined in three different environments by choosing real soil, sea and lake environments around Sakarya province in order to simulate the change of plastic waste in fresh water, salt water and soil environments and its fate in the longer term. The samples, which were placed in the nets separately for each medium, were buried in the soil medium. For marine and lake environments, the nets in which the samples were placed were placed in the cage and released into the water. Then, they were treated in certain monthly periods (12 months in the sea and soil environment and 4 months in the lake environment. They were treated at regular intervals of one month from the date they were first left in the first place, that is, in the 1st month, 2nd month, 3rd month and 4th months) the changes in the surface and structure of the samples were examined with microscopic and spectroscopic techniques. The results obtained by using optical microscope, SEM (Scanning Electron Microscope) and ATR- FTIR(Attenuated Total Reflectance-Fourier Transform Infrared) devices were evaluated and recorded in order to form a basis for further scientific research. It is seen that the bio-based plastics used in this study, which compared the aging and degradation of bioplastics and conventional plastics, do not show a tendency to decompose faster than conventional plastics. Neither PE, UV-stabilized-PE, PP, PS, XPS plastics, including PLA type bio-based plastic and oxo-degradable-PE plastic in the form of film, were neither in the fresh-salt water (sea and lake) environment during a period of about 1 year. It has been determined that it does not degrade in the terrestrial (soil) environment. It was observed that the PLA plate started to shrink at a low level only from the morphological samples taken from the aquatic environment, and this shrinkage progressed more heavily in the samples taken from the soil. In the microscopic and spectroscopic examinations, it was understood that there was no remarkable change in a one-year period. These and other studies show that biodegradable, oxo-biodegradable and conventional plastic formulations remain functional in soil and marine environment for many years.