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Introduction to Plastic Wastes: Processing Methods, Environmental and Health Implications

Ali Mahmoudnia1, Behnam Nejati2, Mahsa Kianmehr3, Masood R. Deiranloei1, and Farshad G. Kootenaei1

1Faculty of Environment, University of Tehran, 16th Azar St., Enghelab Sq, 1417466191, Tehran, Iran

2Department of Renewable Energies Engineering, Science and Research Branch, Islamic Azad University, Hesarak blvd, Daneshgah Square, Sattari Highway, 1477893855, Tehran, Iran

3Faculty of Medicine, Mashhad University of Medical Sciences, Knowledge and Health Town, Shahid Fakouri Blvd, 9919191778, Mashhad, Iran

1.1 Introduction

The term "pliable," which means "easily formed," has been the origin of the word plastic [1]. The word "plastic" was first used in the 1630s to refer to a material that could be shaped or molded. This word is obtained from the Latin word "plasticus," meaning to mold or shape, and the Ancient Greek word plastikos, which describes something that may be molded. Leo Hendrick Baekeland initially used the term "plastic" in the current sense in 1909, and it is now a general term that is used to describe a wide range of materials [2]. Moreover, plastics are referred to as long chains of monomers called monomers, joined to different indistinguishable subunits to create a polymer. Depending on the type of plastic, commercial plastics typically include between 10,000 and 100,000,000 monomers per chain. Polymers in which each monomer is the same as the following monomer in the sequence are called "homopolymer." Nevertheless, polymers may be made up of various alternating monomers, named "copolymers." Polymers can also be made from branched chains in different architectures, different from a simple and basic linear polymer chain. Two polymers may also be blended to create a plastic mix that concurrently demonstrates the features of each polymer, subsequently giving both advantages. Moreover, combining two polymers can comprise a blend with improved features compared to either polymer alone. Polymers can have originated by nature, namely cellulose, which serves as the primary the components of plant cell walls and aids in the adaptation of cellular activities [3, 4]. Cellulose is known to be one of the most prevalent bio-based polymers on the globe. However, synthetic plastics created by humans are the vast majority of polymers of the modern age. John Wesley Hyatt was the inventor of the process for making celluloid, the first artificial plastic. John Wesley created a synthetic plastic that could be molded into many shapes and made to replicate natural materials namely horn, tortoiseshell, and linen that could be used in the manufacture of plastic by correctly processing cellulose polymers formed from cotton fibers with camphor [5].

The invention of synthetic polymers utilized to produce plastic materials has extended their application in varieties of products from packaging to cosmetics. Nevertheless, the majority of these polymers are not biodegradable, and after they are utilized and destroyed, they pose significant problems for waste management. Nevertheless, the usage of plastics can also have unfavorable externalities, including increasing atmospheric greenhouse gases (GHGs) or harm to the environment. It often is not biodegradable, which means that it might stay around as garbage for a very long period and possibly endanger both the environment and public health.

In the current chapter, we draw on existing knowledge about plastic to be an introduction to plastic waste management. We discuss plastics' environmental and health effects and show how plastic materials contribute to climate warming from cradle to the grave. We also present that the widespread use of plastic materials is a fix that backfires archetype. Then appropriate strategies to deal with plastic waste are discussed.

1.2 Plastic materials: Composition and Classification

The bulk of plastics consist of fillers, binders, plasticizers, pigments, and additional ingredients. Plastic's main characteristics are determined by the binder, and frequently, the plastic's name is derived from binder molecules. Binders might be synthetic or natural, including milk protein, casein, or a derivative of cellulose. It is also noted that most binders are made of synthetic resins [6]. For the most part, plastics are made from polyethylene. In accordance with the required properties of the finished product, it can alternatively be described as an ethylene polymer with the molecular and empirical formulae CH2-CH2 and (-CH2-CH2-)n, respectively. The majority of organic solvents, acids, alkalis, and water have no effect on polyethylene [7]. Thermoplastics and thermosets are two categories of plastic that may be distinguished depending on their chemistry and physical features. Thermoplastics are a form of plastic that can be heated up, melted, and molded, then cooled down to become rigid. Additionally, these three steps are repeatable for thermoplastics. This feature of the plastic also makes them suitable for mechanical recycling, which is an effective means of waste management. The internal structure of thermoplastics, which including chemical bonding, as well as other structural characteristics and properties, can be used to categorize them.

1.2.1 Thermoplastics

Since 1940, the thermoplastic polyethylene terephthalate (PET) has been made based on fossil feedstock. Currently, it is utilized in the packaging of bottles and the textile industry. PET still enters the environment in substantial amounts even though it was developed for industrial purposes. A type of thermoplastic polymer known as high-density polyethylene (HDPE) is created from ethylene monomers. Similar ethylene molecules undergo a polymerization event to create polyethylene. According to this empirical formula (C2H4)n, polyethylene is an unsaturated organic alkene formed of structurally organized hydrogen and carbon. HDPE is an inexpensive thermoplastic having a linear structure with minimal branching in comparison with other thermoplastics. It is made at a low pressures of 10 to 80 bar and low temperatures of 70-300°C environment. HDPE is frequently used to make soap containers and liquid cleaning product packaging, freezer and shopping bags, food and drinks storage, faux wood planks, bottle caps, pipelines, protective helmets, insulation, and vehicle fuel tanks [8].

The production of polyvinyl chloride (PVC) is the world's biggest use of chlorine gas. In total, human activities consume 16 million tons of chlorine or 40% of global production annually. Organochlorine, which can be referred to as a massive class of compounds that have recently come under regulatory and scientific investigation due to their widespread use and negative impact on public health and also the environment, is most commonly produced in PVC. The majority of plastic wastes with chemical compositions devoid of chlorine are more harmful to the community than plastic trash produced by plastics [9]. Vinyl manufacture, the creation of hazardous compounds, and excessive energy and resource consumption during various production stages all have negative consequences on the environment.

Ethylene is made from natural gas, oil, or chlorine gas, which is mostly made from sea salt through high-energy electrolysis. These are the two essential ingredients used to create vinyl [10]. Chlorine gas and the organic molecule ethylene are joined in chemical reactions to produce ethylene dichloride (EDC), also known as 1,2-dichloroethane in science. The term "chlorination" refers to this manufacturing procedure. A by-product of this process is organic HCl, which is mixed with more ethylene to make additional EDC via the chemical manufacturing technique known as oxychlorination. By a process known as pyrolysis, the generated EDC is simultaneously further transformed into chloroethylene (VCM - vinyl chloride monomer). A lengthy chain of PVC known as white powder is created by joining the VCM monomers created during the pyrolysis process. Stabilizers, plasticizers, colorants, and different essential additives, which can provide any particular attribute for the desired plastic working, are added with pure PVC. Because of its stiffness, brittleness, and ability to progressively accelerate its disintegration with intensity from UV radiation, PVC in its pure state is not terribly beneficial. PVC is made usable by adding additives to the polymer to boost its moldability and flexibility. [11]. PVC is frequently utilized in vinyl records, sewage and water pipes, garments, water bottles, and medical containers. It is also utilized in furniture, flooring, electric conductors, and other utilitarian wires [12].

In contrast to HDPE that has an extensive branching structure and contains both short-chain and long-chain monomers, LDPE is a long chain of identical subunits that is transparent and semirigid. Free radical polymerization is used to produce LDPE, which requires very particular circumstances including high pressure and temperatures ranging from 80 to 300 degrees Celsius. A total of 4000-40,000 carbon atoms with numerous short branches and subbranches are used in the LDPE's synthesis. Two alternative processes, stirred autoclaving and tubular methods, can be used to create LDPE. Presently, tubular reactors are utilized more frequently...