Plastics account for about 70% of all marine litter and have a great capacity to adsorb persistent organic pollutants, toxic chemical compounds, present in seawater. Therefore, to analyze the marine litter issue, basic information is needed on the characteristics of plastics and persistent organic pollutants.
What is plastic?
The Greek word plastikos has the meaning “moldable”. Plastic is a synthetic material, made from organic polymers that can be easily molded due to their plasticity under certain conditions of temperature and pressure. They later become rigid according to the intended end use of the material. This material has been used since the 20th century and its intensive use is currently considered an environmental problem due to the amount of waste it generates annually. The materials used in the production of plastics are as diverse as cellulose, coal, natural gas, salt and crude oil (crude oil). Crude oil is a complex mixture of hundreds of compounds, and needs to be refined to produce plastic.
The production of plastics begins with a distillation process at an oil refinery, which involves separating the crude into lighter groups called fractions. Each fraction is a mixture of hydrocarbon chains (chemical compounds made up of carbon and hydrogen), which differ in terms of the size and structure of their molecules. One of these fractions, naphtha, is the crucial element for the production of plastics. The two main processes used in plastic production require specific catalysts. In a polymerization reactor, monomers such as ethylene and propylene aggregate to form long polymer chains. Each polymer has specific properties, structure and sizes depending on the various types of basic monomers used.
There are different types of plastics, which can be grouped into two families of polymers:
• Thermoplastics (whose structure changes with temperature). When the temperature rises and exceeds the respective softening point, it is possible to plastically mold, returning to a solid state when it cools. Theoretically thermoplastic resins are recoverable indefinitely. They are formed by polymeric chains that establish non-covalent intramolecular bonds between the chains. When heated, these bonds become weaker and the polymer can be shaped, the bonds re-establishing when the polymer cools, becoming rigid. Examples: Polyolefins, polyurethanes.
• Thermosets, thermosetting or thermosetting (whose rigidity does not change with temperature) – In the hot manufacturing process, or even at room temperature, they solidify into a mass forming a solid and stable body, by adding certain chemical agents, not returning to soften. They take the shape of the mold when they are prepared and then when heated, they do not change the consistency and cannot be re-moulded. When heated to high temperatures, they decompose. This type of materials presents more difficulties in the recycling process. Examples: Polyester.
Plastics production can be divided into four categories:
1. Acquisition of raw material or monomer;
2. Synthesis of the basic polymer;
3. Adjustment of polymer characteristics for manufacturing;
4. Inserting the plastic into the mold for the final shape;
There are chemical additives that can be used in the production of plastics so that they acquire different properties. Examples of these actives are antioxidants (which protect the polymer from degradation by ozone and oxygen), ultraviolet radiation stabilizers (which protect them from extreme weather conditions), plasticizers (increase polymer flexibility), lubricants (reduce friction problems), pigments (they give color to polymers), flame retardants and antistatic agents. Plastics are generally manufactured as composites, and these materials are made by adding reinforcements such as fiberglass or carbon fiber to the plastics, increasing the strength and stability of the material.
The properties that make plastic so useful, such as stability and resistance to degradation, are the causes that make it dangerous for the environment. Plastic polymers have the advantages of lightness, transparency, impermeability, thermal, acoustic and electrical insulation, inalterability and elongation. Disadvantages include ease of combustion, toxicity of gases resulting from combustion, poor heat resistance and high static electricity.
plastic identification code
The Plastics Identification Code (PIC) for plastics was created in 1988 by the Society of Plastics Industry (SPI) in the United States of America and introduced in Australia in 1990. This identification code has been a key element in the management of used plastics in Australia. In 2001, the Plastics and Chemicals Industries Association (PACIA) recognized that the guidelines for the use of symbols needed to be updated to match the changing needs of the market, and a revision was made to the PIC developed with funding from EcoRecycle.
In Europe, its application is voluntary by the manufacturers, but it has to respect a precise codification, according to the European Commission decision 28/01/1997 (97/129/EC), which creates the material identification system pursuant to Directive 94/62/EC of the European Parliament and of the Council on packaging and packaging waste. The latest update in the European context was the amendment of Directive 94/62/EC on packaging and packaging waste by Directive 2005/20/EC.
This code is based on a numerical classification system ranging from 1 to 7 depending on the resins that make up the polymers, and which also serves for recycling. The following table shows the main uses for each type of plastic and associated polymer.
Biodegradable Plastics, Bioplastics and Oxo-biodegradable Plastics
In addition to recycling and waste recovery, the industry has been focusing on new solutions and alternatives to existing plastics, having developed research into biodegradable plastics, bioplastics and oxo-biodegradable plastics. But what are these plastics? Could it be that this type of polymer does not pose threats to the environment?
The concept of biodegradable plastic comes together with the research efforts developed by the industry, due to efforts to minimize the pollution generated by their industries. Biodegradable plastic has the ability to decompose in natural aerobic (compost) and anaerobic (landfill) environments, and biodegradation is done through microorganisms that metabolize the molecular structures of plastic films to produce a humus-like substance ( biomass) which is less harmful to the environment, along with water and carbon. Since all plastics are biodegradable, this type of concept is more a question of marketing than proper properties that distinguish the materials so labeled.
The concept of bioplastics refers to a plastic made from an organic polymer, ie, produced from a biological source. such as, for example, cellulose films, such as wood cellulose, or corn-based polymers. All plastics (bio or crude) are biodegradable, which means they have the ability to be degraded by environmental (ultraviolet radiation, sea salinity) and biological (microorganisms) conditions. Some plastics have very slow rates of degradation and are sometimes considered non-degradable, a concept that is misused, as they are actually degradable but very persistent in the environment. Most plastics have degradation rates on the order of decades or hundreds of years, which vary with polymer stability, temperature and available oxygen content. Thus, most bioplastics will only degrade at high rates of velocity under extremely controlled conditions in industrial composting plants.
You oxo-biodegradable plastics are one of the new bets of the plastics industry, due to its accelerated degradation in environmental conditions. Oxo-biodegradable plastics are plastics that contain in their composition an additive that works as a catalyst for degradation reactions, and that increases the speed of the natural degradation process, so that the products resulting from degradation are water, carbon dioxide. carbon and biomass. The technology used in these polymers causes degradation to occur in about 18 months, depending on the environmental conditions and the microorganisms involved in the process. Through this process it is possible to reduce the period of degradation, in some cases from hundreds of years to 18 to 20 months. Since this technology is new, it is not yet possible to estimate the environmental consequences, since other plastics such as polyethylene or polypropylene are used in the manufacturing process of these plastics. However, it is a significant advance by the industry regarding environmental concerns.
Persistent Organic Pollutants (POP)
According to the Stokholm Convention on Persistant Organic Pollutants, Persistent Organic Pollutants (POP) are organic chemicals, ie carbon-based. As an example we can mention PCB, DDT and PAH (polycyclic aromatic hydrocarbons). These chemical compounds have a particular combination of physical and chemical properties such that, when released:
• remain unchanged for long periods of time;
• They are widely distributed throughout the environment (soil, water and air) as a result of natural processes;
• They accumulate in the adipose tissues (fatty tissue) of living organisms, including the human beings;
• They are toxic to both humans and all wildlife.
POPs are widely distributed around the world as a result of their use in recent decades, especially for pest control in agriculture. These toxic chemical compounds have the ability to focus on living organisms in a process called bioaccumulation. Although they are not soluble in water, they are soluble in lipids, where their concentration can be increased. up to 70000 times ambient levels. The most affected species are fish, predatory birds, mammals, that is, consumer groups in food chains. When these species travel, they carry pollutants with them, hence it is possible to find POPs in regions such as the Arctic, hundreds of kilometers from the nearest source of these pollutants.
This extensive contamination of the environment results in continued exposure to various species, including humans, for periods of time that can span generations. O contact with these toxic chemical compounds can result in acute or chronic effects. The effects of POPs can include cancer, allergies, hypersensitivity, central nervous system damage, reproductive disorders, and immune system disruption. Some POPs are also considered endocrine disruptors, which affect and alter the hormonal system, causing damage to the reproductive and immune systems of exposed individuals and their descendants.