Polymers are very large molecules, or macromolecules, formed by the union of many simple structural units, which usually are derived from monomers. These molecules are a product of hydrocarbons, compounds composed mainly of hydrogen and carbon, joined together in a chain structure. Additionally, they are much more analysed by scientists nowadays compared to the past as they are very important and there is no other molecule that can replace it. This is due to the fact that they have a huge application in different aspects of sciences, technologies and industry (Namazi, 2017). The vast application of these polymers has resulted in many environmental issues and concerns and is also threatening everyone’s health as a result (Santos, 2011).
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Almost all objects that surround us are composed of polymers and examples include clothing, automobile parts, medication coating, transportation and buildings construction. In addition, polymers play a significant role in the development of pharmaceuticals, biomedicine, molecular biology, biochemistry, and biophysics (Sald´ıvar-Guerra and Vivaldo-Lima, 2013). The main aim of this essay is to analyse and evaluate how the chemistry of polymers results in useful properties and leads to environmental issues.
- How polymers are created
Polymers are synthesised from monomers, known as small molecules able to form larger molecules, through polymerisation. This process is restricted by chemical, mechanical and thermodynamic conditions; these conditions must be optimal for the reaction to take place. These factors are capable of creating an enormous amount of polymer varieties (Reimschuessel, 1975). As a result of these factors, a number of polymers with different structural possibilities can be synthesised. The various structural possibilities enable polymers to have diverse properties, allowing for the many applications of polymers in day-to-day life.
The diagram below shows how the polymerization is represented by the reaction of a few monomer units:
Figure 1: Polymerisation(Polymers and polymerisation reaction, 2019)
- Two types of polymerisation
Polymerisation reactions have been divided into two basic types: polyaddition and polycondensation. Polyaddition, otherwise known as addition polymerisation occurs in a free radical process involving high pressure, high temperature and a catalyst. An example of a catalyst that can be used is organic peroxide, which readily breaks up to form radicals, in turn initiating a chain reaction. The physical and chemical properties vary with reaction conditions such as pressure or temperature, as well as functional groups in their structure. The reaction conditions determine if the polymer will become resistant to chemical attack and non-biodegradable. An example of addition polymerisation is poly(propene), whereby the addition process is random so the polymer appears with different structural arrangements of CH3.
The second type of polymer formation is through condensation. Condensation polymerisation takes place when monomers join together with the expulsion of small molecules such as water or methanol. In this reaction, not all the original atoms (molecules) are present in the polymer. Additionally, each monomer must have at least two reactive sites, which usually are two functional groups therefore the condensation polymer consists of functional groups instead of double bonds (Shukla, 2018).
The diagram below illustrates an example of condensation polymers:
Figure 4: CondensationEmeritus, 2017).
Useful properties of polymers
Examples of polymers and their usefulness in daily life are: Polyvinyl chloride and polyethylene. Polyvinyl chloride or PVC, which has a chemical formula of CH2=CHCl, is one of the most widely used polymers in the world. This material makes up a large amount of synthetic or semisynthetic polymer products, such as window fames and shutters, product packaging and toys. Its name comes from the fact that in its semi liquid state it appears malleable or to have plasticity nature. Polyvinyl chloride is a thermoplastic material and therefore can be melted more than once and as it cools down it hardens.
Figure 5 and 6: Poly(ethylene) is used to make large up to small water pipes (The essential chemistry industry, 2017).
Polyvinyl chloride is derived from salt and oil. The first synthesis step involves the formation of chlorine by the electrolysis of sodium chloride. Secondly the chlorine is then combined with ethylene that is obtained from oil. The resulting product, which is ethylene dichloride, is converted to vinyl chloride monomer in high temperature conditions. Finally these monomer molecules undertake polymerisation to form the polyvinyl resin. There are many properties, which make polyvinyl chloride appropriate for lots of applications in daily life. The strength and toughness of PVC makes it useful during bad weather conditions, it is also flame resistant, easily in bent and processed, and has high compatibility with other additives. It also has good electrical insulation abilities and chemical stability, which means it not de-polymerise (Gilani, 2017).
Some of polyvinyl chloride plastic’s most important characteristics include its tensile strength and resistance to environmental degradation, as well as to chemicals and alkaline. It is very dense and thus very hard and resists impact deformation very well compared to other plastics. It is widely available, commonly used are it is relatively inexpensive and easily recyclable. Its low cost and the long lasting characteristics of most plastics make it an easy choice for many industrial applications, for example in construction (Creative mechanisms staff, 2016).
The other polymer, which is known for its useful properties, is Polyethylene. It is a durable thermoplastic long chain hydrocarbon polymer with a crystalline structure, which is created through the polymerisation of ethylene monomer (C2H4) n . This polymer can be created from three different types of polymerisation reactions: Free radical polymerisation, anionic polymerisation and cationic polymerisation. All there reactions consist of two chemical components hydrogen and carbon. The properties of polyethylene that make the molecule popular include the inexpensive cost of production, the non-standing nature of the plastic and the non-toxic content. During the formation process, it can be combined with other materials, such as rubber, to develop other properties. The features of polypropylene, which make the plastic an appropriate choice are its good resistance to organic solvents, its low water permeability, its high electrical resistance and impact strength. This makes the plastic a very useful for use in products like food packaging, plastic parts such as tubing and laminating (Batra, 2014). Polypropylene also is resistant to cracking under stress and high level of impact resistance or under high temperature conditions. The high temperature resistance enables polyethylene to be used in dishwashers and microwaves, due to the fact that they are considered as a microwave-safe plastic. The properties of polypropylene that make the plastic a popular option to use for products include the lightweight nature of the material and its high tensile strength, thus naming it as one of the most abundant plastics in the world with around ten tons being formed per year. Additionally, another important property is the ability to recycle polypropylene products, as 100 percent of polypropylene can be recovered for other uses in the future. The plastic can be combined with other chemicals and materials, such as rubber and antioxidants, to form products such as PVC piping.
Figure 8: Plastic found in rainbow fish guts. Full stomach, no nutrition(Marine, 2017).
However, the manufacturing of PVC often creates huge amount of toxic chemical pollutants such as vinyl chloride, dioxin and hydrochloric acid. These pollutants pose several health risks to both humans and the environment. Some harmful human effects include things such as increased risk of cancer, birth defects, neurological damage, reproductive problems and diabetes. PVC degrades very slowly, therefore making it extremely harmful to the environment as it accumulates. The only options for disposal are through recycling, incineration and landfill. PVC is a thermoplastic material, despite the fact that the material degrades with each reuse cycle. Recycling however is costly and also a labour intensive process that requires several processes involving the sorting of plastics and the separation of the different additives and compounds that form the plastics therefore is sometimes not a viable option (Gilani, 2017).
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Likewise the usage of polyethylene for packaging of materials has negative environmental impacts on land, water, air and ecosystem health. The accumulation of this polymer waste in the soil will lead in poor soil aeration and increase in soil temperature. Polyethylene products can last up to 1000 years in the soil preventing the break down of biodegradable materials around it (Batra, 2014).
Moreover, the sea creatures, which mistake these polyethylene wastes for food or get entangled in it suffer from painful injuries, or even death. Ship debris, which also consists of polyethylene waste have a bad impact in the tourism economy as they contaminate the sea. During the polyethylene waste combustion harmful particles such as paraffin, olefins and dioxins are emitted into the air. In addition, plastic ingestion by animals can cause decreased feeding stimuli. Over 80 species of seabirds with plastic bags in their stomachs face painful death (Godfrey, 2014).
Environmental problems overcome
In order for us as a human population to have a cleaner environment there needs to be raised awareness about the dangers of non-biodegradable polymers. With the increased awareness around global warning, industries are now actively taking responsibility to find solutions to replace environmentally harmful polymers with those that are degradable or easier to recycle and re-use. An important focus for the future is finding ways to produce biodegradable plastics, which will limit carbon dioxide emissions during synthesis and degrade to organic matter after disposal (Future Scope of Polymer Science, 2018).
Researchers in India have developed a relatively low-temperature process to convert certain kinds of plastic waste such as polypropylene into liquid fuel as a way to re-use discarded plastic bags and other products. The purified polypropylene would turn into oil after the process, with the conversion process taking less than an hour at 850 degrees Fahrenheit. This is a key development as polypropylene is said to make up approximately a quarter of the world’s 5 billion tons of plastic waste and based on the predictions, their new process could convert 90% of polypropylene into fuel. There’s no date as to when this conversion process might be widely implemented however it might motivate some industries to consider the concept, as not only it is a good alternative to prevent the polypropylene build up but the fuel itself can be sold for profit (Westlake, 2019).
Another suggestion is to exchange plastic bags into paper bags, in order to reduce the amount of plastic used in daily life. Paper Bags Research shows that paper in landfills does not break down or degrade at a considerably faster rate than plastic does. Actually, nothing totally degrades in modern landfills because of the lack of light, water, oxygen and other important elements that are necessary for the degradation process to be completed. It can take between 400 and 1000 years for plastic bags to decompose.
UK retailers for have recently introduced degradable carrier bags, which are made from plastic and can degrade under certain conditions or after a predetermined length of time. Another way in which retailers have tried to prevent the overuse of plastic bags is by adding a 5p fee whilst purchasing a bag, this defers people from wanting one and even encourages them to use a reusable bag. Those bags can be composed by two types of degradable plastic: bio-degradable plastics, which means they have the ability to degrade by themselves as they contain a small percentage of non oil-based material, such as corn starch; and photodegradable plastics, which will break down when exposed to sunlight (Bell and Cave, 2011).
The world will not be the same if we run out of polymers, as they are very a highly useful and convenient material. Although they are one of the world’s biggest environmental problems, yet both industry and society still heavily rely on its usage. Processes such as reducing, reusing and recycling of biodegradable polymers, prevents the accumulation of plastics in the environment. However this is not enough, several new developments are still needed to ensure that biodegradable polymers and PLA can replace all existing plastics. In order for plastics to be successfully substituted, cost needs to ignored and not considered a roadblock, moreover disciplines such as climate science, chemistry, engineering, material science and biochemistry must collaborate to allow us to evolve into a biodegradable polymer society which in turn will allow us to make positive changes to protect the environment.
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