Environmental Impact of Plastic Waste

Environmental impact of plastic waste

Plastic waste has a huge negative impact impact on the environment and the animals living in it. A study that was completed in 2018 revealed that 8.3 billion metric tons of plastic has been produced in the six decades since plastic production began. Of that, 6.3 billion metric tons has become waste and only nine percent of this has been recycled. The waste that is not recycled, which is largely the majority of it, either ends up in landfills or loose in the environment as litter, it is thought that most of this will eventually end up in the ocean. According to figures published in a 2015 issue of the journal Science, between 4.8 and 12.7 million tonnes of plastic enter the ocean each year. If the present trends continue it is estimated that there will be more plastic than fish in the sea by 2050. It is estimated that over 500 marine species have come into contact with plastic debris. Animals will mistake the plastic for food and consume it. Research indicates that half of the sea turtles and over half of seabird species worldwide have ingested plastic. The ingestion of plastic can be detrimental to marine life, sometimes after consuming plastic, sea-life will mistakenly believe that they have eaten enough because their stomachs are full but then starve to death. Not only this but the plastic can harm the animals insides after being ingested, often leading to the death of the animal. Marine life doesn’t even need to eat plastic to be effected by it many fish, sea turtles, and seabirds are caught in netting or other forms of plastic, which can mean they starve or drown.

Petroleum based plastics

●       Production process of petroleum based plastics

●       LDPE (low density polyethylene)

The production of petroleum based plastics begins with the distillation of crude oil in an oil refinery. Crude oil is a naturally occurring, unrefined petroleum product composed of hydrocarbon deposits and other organic materials. During the distillation process the heavy crude oil is heated and separated into ‘fractions’, groups that contain a mixture of compounds which share similar boiling points. Another process is cracking, cracking breaks large molecules into smaller ones, some heat treatment occurs but most cracking uses catalysts. Smaller molecules are more useful, and therefore of greater value. An important chemical process involved in the production of petroleum based plastics is polymerisation, polymerisation is the process of joining monomers together into a chain. LDPE is produced by catalytic polymerisation of ethylene, monomers of ethylene are joint to form chains of polymers of LDPE. This process is operated under very high pressure (up to about 350 megapascals) and high temperatures (up to about 350°C). An initiator, such as a small amount of oxygen and/or an organic peroxide is used. Ethene is compressed and passed into a reactor along with the initiator, this is where the polymerisation process occurs. The chemical equation of the reaction is: nC2H4 →  [-CH2-CH2-]n  ΔH= -92 kJ mol-1. The structure of LDPE polymers has both long and short branches, which prevent that polyethylene molecules from packing close together, resulting in LDPE being a flexible material.

●       Degradation process of petroleum based plastics

●       LDPE (low density polyethylene)

Biodegradation is the decomposition of organic material by microorganisms. Wood, food scraps and other materials can be transformed by bacteria in the soil into other compounds, however petroleum plastic cannot, as the majority of bacteria are not interested in consuming petroleum based plastic as it holds no nutritional value for them. LDPE can be slowly broken down by photodegradation. When UV rays from the sun react with tertiary carbon bonds in the molecular chain structure, free radicals are formed. These free radicals will react further with oxygen, and carbonyl groups in the main chain will be produced. Essentially breaking the bonds of the long molecular chain structure of LDPE, which overtime will result in a piece of plastic being broken down into lots of tiny pieces of plastic, or micro plastics.

●       Environmental impact of the production and degradation process

●       LDPE (low density polyethylene)

Both the production and degradation of petroleum based plastic has a significant effect on the environment. The production of petroleum based plastic requires oil or gas from the earth. In the case of LDPE it is natural gas. This gas is extracted through hydraulic fracturing or ‘fracking’. The process of fracking has a significant negative effect on the environment. Fracking affects the air quality surrounding fracking sites, as one of the main chemicals released in the fracking process is methane, and it’s estimated 4% of it escapes into the atmosphere during extraction, also pollutants are released during the operation of fracking locations. Fracking also has an effect on water supply and quality. Millions of gallons of water are used during the fracking process, reducing the amount of clean water available for other uses. The chemicals used in fracking, which are left in the ground, can leak into and contaminant water sources. Toxic chemicals are released during the production of plastic. When petroleum based plastic is broken down into microplastics, these micro plastics contain and can both absorb and give off chemicals and harmful pollutants. If these micro plastics end up in the ocean they can be consumed by fish, which can then be eaten by humans, exposing us to these toxins.  

Bio based plastics

●       Production process of bio based plastics

●       PLA (polylactic acid)

To transform corn into plastic, corn kernels are immersed in sulfur dioxide (SO2) and hot water  (H2O), during this immersion its components break down into starch, protein, and fiber. The kernels are then ground down and the starch is separated form the corn oil. Starch is converted into dextrose (a type of sugar), through liquefaction and saccharification enzymes. This dextrose is turned into lactic acid in fermenting vats, the chemical equation for this reaction is: C6H12O6 → 2 C3H6O3. The lactic acid is then converted into lactide in a chemical plant. The lactide then undergoes the polymerisation process to form the lactide monomers into long chain molecules of polylactide acid (PLA).

●       Degradation process of bio based plastics

●       PLA (polylactic acid)

PLA can decompose into water and carbon dioxide in 47 to 90 days, in the right conditions. The degradation of PLA is due to three mechanisms, hydrolysis, thermal degradation, and photodegradation. Hydrolysis is when the ester groups of the main chain dissected, resulting in the molecule being divided into two parts, therefore reducing the molecular weight. The chemical equation for this reaction is: -COO + H20 → -COOH + OH-. Thermal degradation is the degradation of polymers through overheating. Photodegradation occurs when PLA is exposed to sunlight, the to low-wavelength and high-energy UV radiation in sunlight induces degradation of the plastic. PLA polymers can be broken down by microorganisms, after the initial breakdown of the polymere, the microorganisms will then take the remaining components and break them down further into simpler units. The enzymes within microorganisms will turn the polymer into ATP for energy through oxidation or hydrolysis, carbon dioxide, nitrogen gas, methane, water, minerals, and biomass will be by products of this reaction.

●       Environmental impact of the production and degradation process

●       PLA (polylactic acid)

The production and degradation process of PLA does not have a largely negative effect on the environment. Yes, the degradation of PLA produces small amounts of carbon dioxide, however the corn grown for the production of PLA would produce more than enough oxygen to combat this. A large amount of land is taken up by corn plantations to use in the production of PLA. The production of PLA is actually mainly positive for the environment as the process has low carbon emissions and low energy consumption is needed. The degradation of PLA provided microorganisms with an energy source.

Biodegradable plastics

●       Production process of biodegradable plastics

●       Polybutyrate (PBAT)

PBAT is a synthetic biodegradable polymer that is produced through non renewable resources. PBAT is produced by random copolymerization of 1,4-butanediol, adipic acid, and dimethyl terephthalate (DMT) monomers. First 1,4-butanediol and adipic acid are polymerized to create their polyester, this reaction can be represented by the chemical equation: 1,4-butanediol is also polymerized with DMT to create another polyester, this reaction can be represented by the chemical equation: .                       These two polyesters are then added together by using tetrabutoxytitanium as a catalyst, the result is a copolymer of the two previous polymers. This can be represented by the chemical equation:

●       Degradation process of biodegradable plastics

●       Polybutyrate (PBAT)

PBAT is able to decompose biodegrade as it is created to do so. The biodegradable PBAT polymers break down to form gases, salts, and biomass. There are two main mechanisms in which biodegradation can take place. One is through physical decomposition which is a result of reactions, such as photodegradation and hydrolysis, which have both already been explained. The other mechanism is through biological processes, such as aerobic and anaerobic processes. The  chemical equation for aerobic biodegradation is:        In which the polymer would be the PBAT polymer. The chemical equation for anaerobic biodegradation is:  In which the polymer would also be the PBAT polymer. Natural polymers can be broken down by numerous organisms, however microorganisms have not had time to adapt to break down synthetic polymers as they have not been around for long.

●       Environmental impact of production and degradation process

●       Polybutyrate (PBAT)

The production of the specific biodegradable plastic, PBAT, still requires the use of non-renewable resources. However manufacturing PBAT emits less carbon dioxide and requires less energy than the manufacturing process of petroleum-based plastics. The fact that can biodegrade means that the degradation process has a positive impact on the environment as no waste is left to harm water sources or animals.

Advantages & disadvantages of petrol, bio-based and biodegradable plastics

Discussion

Petroleum based plastic is an extremely convenient material. It is durable and light, and can be made into a diverse range of products, which can then be recycled into other forms. Petroleum based plastic is economically cheap to produce, therefor the products made from it are affordable. However the production and waste of petroleum based plastic comes at a high cost to the environment. The production process is energy intensive and releases significant amounts of CO2 into our atmosphere. The oil and gas required for the production of petroleum based plastics is extracted from the ground through fracking, this process is damaging to the environment as it causes air and water pollution. Furthermore the resources needed to produce this type of plastic are fossil fuels, therefore non-renewable. I believe the environmental impact of petroleum based plastic waste is the most significant issue to be considered. Because petroleum based plastic takes hundreds of years to break down, and even then it can never fully be gone, its waste has a large impact on the environment and its inhabitants. Plastic pollution is one of the largest and most serious problems we are facing today, there are especially calls for concern in regards to the plastic pollution of our oceans and its detrimental effect on sea-life. Because of the negative environmental consequences of petroleum based plastic I believe it should not be promoted in the future. We must act now to prevent the problem from getting worse, as we already have far too much on our plate. I would recommend that the supermarket food chain should consider changing the type of plastic packaging that they use to a mixture of bio-based and biodegradable plastics. For products that are either hot, wet, need to be contained for long periods of time, or are required to be durable I would recommend that they package them in biodegradable plastics. All other products should be packaged in bio-based plastics, which are also biodegradable. This action would be beneficial to the environment, as the production and degradation of bio-based and biodegradable plastic is not harmful for the environment, furthermore plastic waste will be then be reduced as these plastics can decompose. The change to alternative plastics would be more expensive than staying with conventional plastics, however as demand increases for bio-based and biodegradable plastics, as I’m sure it will as more make the change to these more renewable resources and the demand for them will increase, the plastics will become more affordable. I think it is a small price to pay for the earth’s health. One issue with changing to bio-based and biodegradable plastics would be the difficulty to dispose of the plastic as they need specific conditions to decompose and can only be processed in specific waste facilities. However as the use of these plastics increase it will become more accessible to decompose of bio-based and biodegradable plastics.  Another reason for changing from petroleum based plastics to bio-based ones is because petroleum based plastics are made from non-renewable resources, eventually these resources will run out. Bio-based plastics are made from renewable resources. Some of these resources are also food resources, so it wouldn’t be wise to exhaust all of these food resources also on plastic production. However there are bio-based plastics that are made out of materials that are not also a food source, and actually some that a waste, which would be advantageous to use for plastic production.     

Processing of 5 sources

References

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• All images are from wikipedia.org