Should the Use of Plastice Be Banned?

Introduction:

It is vital to understand the chemical composition and production of plastics to decide whether or not they are harmful to the environment. The following report will go into depth about how plastic is made, how industries use plastic and the implications it has on the environment. This report will also ultimately answer if plastics should be banned, suggest alternative products to use instead of plastic, and the importance of organic chemistry as a whole.

The Chemistry Behind Plastics:

People today use hundreds of plastic products each day. Plastics are made from crude oil, which is a naturally found, finite, non-renewable fossil fuel that is made up of a mixture of hydrocarbons. This crude oil is found underground, which then gets extracted and transferred to oil refineries. Fractional distillation is used to refine crude oil into its main fractions, including naphtha, kerosene and gas. These substances contain hydrocarbons which can either be “cracked” into smaller molecules or monomers, or go through a process of polymerisation. The molecules that are to be cracked are usually the hydrocarbons with longer chains, and the molecules that are polymerised are usually the molecules that are already small such as ethene, propene or butene.

FLOW CHART

Fractional Distillation:

Crude oil is a mixture of hydrocarbons. Firstly, it is heated in a furnace, then pumped through as a vapour into a fractionating tower. The shorter hydrocarbons have a lower boiling point, so they condense at the top of the tower shown in figure 1. The longer hydrocarbons have a higher boiling point so they condense at the bottom of the tower. This process occurs continuously in each tray, producing different fractions (different chain length) with different uses as shown in figure 2.

Figure 1. Fractional distillation of crude oil.

The reason that oil refineries conduct fractional distillation is to transform crude oil into industrially demanded substances such as naphtha, ethene, gas and kerosene, for example.

In order to make more useful fractions ethene, one of the most important and sought-after substances by industries, the chemical, naphtha, must go through the process of cracking.

Figure 2. Major fractions from the primary distillation of crude oil.

Cracking:

For the longer chain hydrocarbons, most oil refineries will crack the molecules into shorter and more useful chains. There are two types of cracking catalytic cracking and thermal cracking. These processes both occur at high temperatures.

Catalytic cracking is the process where the substances extracted from the fractional distillation with long hydrocarbon chains and therefore, molecules with high boiling points, from the crude oil are broken into more useful, shorter hydrocarbon chains – molecules with lower boiling points. The equipment used to undertake this chemical process is called a cat cracker, as shown in figure 3, the reaction is typically carried out at 500°C and in the absence of air, with pressures above atmospheric. Alkenes with 15 to 25 carbon atoms per molecule are broken into two smaller molecules where one is an alkane and one is an alkene, such as the breakdown of pentadecane into decane and pentene:

Figure 3. Catalytic Cracking Process

C₁₅H_32(l)           C₁₀H_22(l)      +     C₅H_10(l)

The catalysts used for cracking alkenes are inorganic compounds called zeolites, which are crystalline aluminosilicates. This alkene further splits into smaller alkenes until either ethene, propene, or both are formed. These ethene/propene products formed are the starting materials for making plastics – monomers.

Thermal or “steam” cracking is a non-catalytic process in which a mixture of alkanes with steam is passed through very hot metal tubes at 700-1000°C, and at just above atmospheric pressure, in order to decompose the alkanes completely into the smaller alkanes such as ethene and propene. The reactant ethane, propane or butane gases or the liquids (naphtha or gas-oil) are preheated and vaporised, mixed with steam and then heated to 750-850°C in a tubular reactor shown in figure 4. This is how they get converted into shorter chain hydrocarbons without a catalyst. One example is the thermal cracking of undecane into ethene and propene:

Figure 4. Thermal Cracking Process

C₁₁H_24(l)           4C₂H_4(g)      +     C₃H_6(g)     +     H_2(g)

Similarly to catalytic cracking, the products of thermal cracking are also further broken down into ethene, propene and/or butene.

Polymerisation:

Polymerisation is the chemical process of monomers forming together to form polymers. Often, it takes thousands of monomers to make a single polymer. There are two different ways to polymerise molecules depending on the complexity of the monomers, which are known as addition polymerisation and condensation polymerisation.

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Addition Polymerisation:
Addition reactions involve the rearranging of electrons of double bonds within a monomer, to form single bonds with other similar molecules. Contrary to condensation polymerisation, this process loses no atoms. (do I put an explanation of PVC here too?)

Low density Polyethene Using an Initiator Molecule:

The stages in the production of polyethene are:

1. Initiation – an initiator chemical starts the reaction by opening the double bond of the ethene monomer. This forms the free radical which has an unpaired outer shell making it very reactive.
2. Propagation – the free radical then breaks the bond of another ethene monomer and connects the monomer to the chain. This reaction repeats forming a polyethene chain.
3. Back biting – LDPE free radicals at the end of chains tend to “bite back”. This means that the radical curls up to one of the middle hydrogens and takes it, forming branches from the middle of the chain.
4. Termination – when two free radicals collide and join, the process stops. A complete polyethene molecule is formed and the process stops for that chain.

High density Polyethene Using Zeolite Catalyst:

When changing ethene into high density polyethene, a zeolite catalyst provides one active site for the growing polyethene chain resulting in no back biting.

Condensation Polymerisation:

The monomers used to form condensation polymers do not have a double bond. Instead, the functional groups of the monomers react and as a small molecule such as water is produced as a by-product. (do I put an explanation of nylon here as well?)

Polyester:

The carboxyl functional group of benzene – 1,4 – dicarboxylic acid reacts with the hydroxyl functional group of ethane – 1,2 – diol to form water. Then this continues to form polyester.

Global Uses of Addition and Condensation Polymers:

Polyeth(yl)ene:

Each year, over 80 million tonnes of polyethene is manufactured, making it the world’s most industrially demanded plastic. Over 60% of the ethene found in crude oil after distillation each year gets manufactured into polyethene. Polyethene is produced in two main forms: low density/linear low density and high density.

Low Density (LDPE) and Linear Low Density (LLDPE)

The LDPE/LLDPE forms are often used for film packaging and for electrical insulation because they are flexible, tough and relatively transparent. LDPE is also used to produce some flexible lids and bottles as well as in wire and cable applications. LDPE also has an excellent resistance to acids, bases and vegetable oils, which makes it handy for food packaging as it won’t react with the food. Figure 5 shows which industries use LDPE the most.
The advantages of LDPE include that it is low cost, it resists moisture & good chemicals and it is readily processed by all thermoplastic methods. The disadvantages of LDPE are that it has high thermal expansion, poor weathering resistance, difficulty to bond, is flammable and they are not biodegradable.

Figure 5. Division of low density polyethene amongst industrial uses

Dispersion forces between chains

Amorphous structure

High branching

High Density Polyethene (HDPE)

Linear/Crystalline Structure

Weak dispersion forces between chains

Low Branching

Figure 6. Division of high density polyethene amongst industrial uses

HDPE is useful where a moisture resistance and a low-cost material is needed. The advantages of HDPE include that it is low cost, moisture resistant, chemical resistant and impact resistant from -40°C and 90°C. However, its disadvantages include that it has high thermal expansion, it is subject to stress cracking, it has poor weathering resistance, it is difficult to bond and it is flammable.

Polyvinyl Chloride

Polyvinyl Chloride is made by reacting ethylene with oxygen and hydrogen chloride over a copper catalyst. PVC is a naturally white and brittle plastic which is produced in two general forms, rigid or flexible. Rigid PVC is used in pipes and vinyl, whereas flexible PVC is used for insulation on electrical wires and in flooring where a there needs to be a sterile environment such as a hospital or school. The advantages of PVC include

Figure 7. Division of PVC amongst industrial uses

that it is abundant, it is cheap, it is dense so it resists impact deformation, it has tensile strength and it is resistant to chemicals and alkalis. The disadvantages are that it has poor heat stability and that it emits toxic fumes when melted.

Nylon

Nylon is a synthetic thermoplastic material which is classified as a polyamide, and is a condensation copolymer. The structure of nylon in figure 8 is called nylon 6, as each unit of the polymer chain has two lots of six carbon atoms. This number changes depending on the number of carbons in this chain. The advantages of nylon include that it is lightweight, strong, abrasion resistant, easy to wash, fast drying and resists oil and chemical damage. However, the disadvantages include that it has poor resistance to sunlight, low absorbency and is heat sensitive.

Strong hydrogen bond

Amide functional group

One of 6 carbon atoms

Carboxyl functional group

Figure 8. Structure of Nylon 6

Polyester

Polyesters are polymers formed from a diol and a  dicarboxylic acid. These components are melted and squeezed through holes which are then spun to form a fibre.  This fibre is widely used in clothing either alone or in blends with other fibres. The advantages of polyester include that it is stain resistant, strong, flexible, cheap and dries quickly, whereas the disadvantages are that it is very temperature sensitive and low absorbency.
 

Advantages and Disadvantages of the Production of Plastic:

The above information about structure, properties and uses of different polymers is necessary for scientists to know so the effects of the production and use of polymers on society can be thoroughly examined. Many people believe that polymers only have negative effects on the environment, however there are also benefits of using these materials.

Advantages:

Aside from the advantages of polymers that they are used in almost every single man-made product, polymers also have other advantages in society.

These advantages include:

     Plastics have aided aeronautics since WWII. The ability of plastics to withstand heat lead to it being an important material in aerospace technology as it is also lightweight and strong, which makes the weight of the aircraft lighter. This resulted in improved aerodynamics, which lead to improved fuel efficiency and performance.

     The building and construction industry has also greatly benefitted from using plastics as plastics are used for products such as valves and pipes. Plastics’ resistance to corrosion makes it an excellent material for decorative elements that are found in bathroom units such as plumbing, flooring, windows, doors and insulation.

Plastic used in plumbing

     Plastics are used in house wiring due to its thermal and insulating properties. For this reason, it is also good for the production of small appliances such as can openers, microwave ovens, coffee makers, shavers, irons, and hair dryers.

     Because plastic is rigid and tough, it is ideal to be used for packaging. On top of this, it has the ability to be shaped or coloured anyway desired by the company.

     Plastic is the main material used to make modes of transportation due to its properties of being tough, resistant to corrosion, durable, lightweight, and easy to colour. Through the use of plastic, the average weight of a car is around 300 kg lighter since 1988. This lighter weight means the fuel is more efficient and has relies on less oil.

Disadvantages:

Apart from the following disadvantages, it is important to note that fossil fuels, including crude oil, take an extremely long time to form in the earth, so they are labelled as non-renewable.

     Most plastics are improperly disposed of after their use such as synthetic, lightweight plastic products like packaging. These man-made plastics are nonbiodegradable which means that they tend to persist in natural environments.

How plastic affects local wildlife

     At the current rate that fossil fuels are being extracted, the CIA is predicting that oil deposits will run out in just over 46 years.

     Landscapes are littered and polluted by plastic products, often plastic packaging (low density polyethene), which affects the wildlife of that environment and possibly even making animals endangered through getting suffocated by or ingesting the plastic.

     In the ocean, plastic pollution can kill wildlife through entanglement in objects such as plastic bags, but it can also kill through ingestion, by being mistaken for food. 

     Polymers are using up non-renewable resources like petroleum which is not sustainable.

     Many raw materials used to make polymers are toxic, which means workers in factories are exposed and at risk to these toxins, as well as the environment and general public if there is a leak.

     When factory workers drill in the ground for the crude oil, carbon emissions are released, which are the cause of global warming.

Global Sustainability:

Through comprehending and accepting the information about industrial uses, chemical processes and the impact of polymers on the environment, it is gathered that it would be in the best interest for the planet, the environment, animals and the general quality of life if the use of plastics were banned. This would not only significantly reduce the amount of carbon emissions released into the atmosphere, as plastic producing industries will have to stop manufacturing them, but less wildlife would die each year due to plastic ingestion of suffocation.However, as plastics are a fundamental material of manufacturing products and most products contain large amounts of plastic, it is not realistic to ban the use of plastics at this time as there are already so many products that are manufactured with plastic.

However, biopolymers have been produced and tested, which are polymers made from plant materials rather than non-renewable fossil fuels. Biopolymers are produced by living organisms, some occurring naturally and some from biomass. Natural occurring biopolymers include starch and cellulose which are composed of long chains of glucose molecules and proteins which are made of chains of amino acids. Environmental benefits of biopolymers include that they are carbon neutral, they are renewable and they are compostable which means less environmental pollution. This new discovery would be a good substitute for regular polymers and would affect the carbon emissions in the atmosphere significantly. However,if the production and use of plastics was to be banned it should be done gradually to avoid conflicts between governments and businesses as well as to control the prices that the general public would have to pay, in order live sustainably.

Conclusion:

As mentioned previously, in order for a scientist to make an educational judgement on whether or not all plastics should be banned, relies heavily on the background knowledge of that scientist on polymers. Hence, organic chemistry is crucial to understand and acknowledge in order for scientists to understand the extensive damage that the oil refinery processes of fractional distillation and cracking, as well as plastics themselves have on the environment and humanity.

Put bonding description into each type of polymer

Molecular structure

Explore reasons for reactivity

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