Which Substance is Important in Making Plastics

Author: Dr Payal Baheti

Plastic tin can either be ‘synthetic’ or ‘biobased’. Synthetic plastics are derived from crude oil, natural gas or coal. Whilst biobased plastics come from renewable products such equally carbohydrates, starch, vegetable fats and oils, bacteria and other biological substances.

The vast majority of plastic in utilize today is synthetic considering of the ease of manufacturing methods involved in the processing of crude oil. However, the growing demand for express oil-reserves is driving a need for newer plastics from renewable resources such every bit waste material biomass or fauna-waste material products from the industry.

In Europe, merely a small proportion (about 4 – 6%) of our oil and gas reserves goes towards the product of plastics, with the balance used for transport, electricity, heating and other applications (Ref)

Most of the plastic in utilize today is derived by the following steps:

1. Extraction of raw materials
(largely crude oil and natural gas, merely also coal) – these are a circuitous mixture of thousands of compounds that then need to be processed.

2. Refining process
transforms crude oil into different petroleum products – these are converted to yield useful chemicals including “monomers” (a molecule that is the bones edifice blocks of polymers). In the refining procedure, rough oil is heated in a furnace, which is then sent to the distillation unit of measurement, where heavy crude oil separates into lighter components called fractions. 1 of these, chosen naphtha, is the crucial chemical compound to brand a large amount of plastic. However, there are other ways, such as using gas.

Figure i. Pictorial representation of how plastics are fabricated (Figure is adapted from ref)

iii. Polymerisation
is a procedure in the petroleum industry where low-cal olefin gases (gasoline) such as ethylene, propylene, butylene (i.e., monomers) are converted into higher molecular weight hydrocarbons (polymers). This happens when monomers are chemically bonded into chains. There are ii different mechanisms for polymerisation:

1. Addition polymerisation

The addition polymerisation reaction is when one monomer connects to the adjacent one (dimer) and dimer to the next one (trimer) and so on. This is achieved by introducing a goad, typically a peroxide. This procedure is known as concatenation growth polymers – as it adds ane monomer unit at a time. Common examples of add-on polymers are polyethylene, polystyrene and polyvinyl chloride.

2. Condensation polymerisation

Condensation polymerisation includes joining two or more than different monomers, by the removal of small molecules such as water. It likewise requires a catalyst for the reaction to occur between next monomers. This is known as pace growth, because yous may for example add an existing chain to another concatenation.  Common examples of condensation polymers are polyester and nylon.

iv. Compounding/Processing

In compounding, various blends of materials are melt blended (mixed by melting) to make formulations for plastics. By and large, an extruder of some blazon is used for this purpose which is followed by pelletising the mixture. Extrusion or a different moulding process and then transforms these pellets into a finished or semi-finished product. Compounding often occurs on a twin-spiral extruder where the pellets are and then processed into plastic objects of unique design, diverse size, shape, colour with accurate properties according to the predetermined conditions set in the processing machine.

…

More than detailed information on how plastic is fabricated is provided in the following sections below:

1. Polymer vs. plastic
2. What are hydrocarbons?
3. How is synthetic plastic created from crude oil?
4. How is plastic created from naphtha?
5. What is the main ingredient in plastic?
6. Which was the first human made plastic?
7. What was used before plastic?
8. Tin can y’all make plastic without oil?

1. Polymer vs. plastic

All plastics are essentially polymers, just non all the polymers are plastics.

The term
polymer and monomer
are derived from Greek words: where ‘poly’ ways ‘many’, ‘mer’ ways ‘repeating unit’ and the word ‘mono’ means ‘one’. This literally means a polymer is made from many monomer-repeating units. Polymers are larger molecules formed by covalently joining many monomer-units together in the form of bondage similar pearls on a cord of pearls.

The discussion
plastic
comes from ‘plasticus’ (Latin for ‘capable of moulding’) and ‘plastikos’ (Greek for ‘fit for moulding’). When we say plastics, we are referring to organic polymers (synthetic or natural) of loftier molecular weight which are mixed with other substances.

Plastics are high molecular weight organic polymers equanimous of various elements such equally carbon, hydrogen, oxygen, nitrogen, sulphur and chlorine. They can too be produced from silicon cantlet (known as silicone) forth with carbon; a common example is silicone chest implants or silicone hydrogel for optical lenses. Plastics are made up of polymeric resin often mixed with other substances chosen additives.

‘Plasticity ‘is the term used to depict the property, feature and aspect of a material that can deform irreversibly without breaking. Plasticity describes whether a polymer would survive the temperature and pressure level during the moulding process.

Chemistry allows us to vary different parameters to tune the properties of polymers. Nosotros can use different elements, change the type of monomers, and rearrange them in different patterns to change the shape of polymer, its molecular weight or other chemical/concrete backdrop. This allows plastics to be designed to accept right properties for a specific application.

2. What are hydrocarbons?

Most plastic in use today comes from hydrocarbons derived from rough oil, natural gas and coal – fossil fuels.

What is a hydrocarbon?

Hydrocarbons are organic compounds (tin can be aliphatic or aromatic) made up of carbon and hydrogen.

Aliphatic hydrocarbons
have no cyclic benzene rings while the
aromatics
have benzene rings.

Carbon (C, diminutive number = vi) has a valency of four, meaning it has 4 electrons in the outermost trounce. It is able to pair up with 4 other electrons from any element of the periodic table to make up chemical bonds (for hydrocarbon, it will pair up with hydrogen). Hydrogen on the other hand (H, with atomic number = one) has only i electron in the valence shell so four of these H-atom are ready to be paired up with C-atom by forming a single bail to give a C-H_four
molecule. CH_iv
molecule is called methane, which is the simplest hydrocarbon and the offset member of the Alkane family. Similarly, if two C-atoms would bail together they tin can link with up to six H-atoms with three existence on each C-atom to give a chemical formula of CH₃-CH₃
(or C_iiH₆) known as ethane and the series goes on as follows.

Methane series family unit: Methane (CH₄), ethane (CH₃-CH₃
or C₂H_vi), propane (CH_three-CH₂-CH₃), butane (CH₃-CH_two-CH₂-CH₃), pentane (CH_three-CH_ii-CH₂– CH₂-CH₃), hexane, heptane, octane, nonane, dodecane, undecane and so on.

Note that this type of bond with carbon and hydrogen is a
saturated bond
(sigma bond denoted as σ-bond). There can also exist
unsaturated bond
where a pi bond (π-bond) is present along with sigma bond giving carbon-carbon double bonds (alkenes) or have two π-bonds with a sigma giving carbon-carbon triple bond (alkynes), which very much depends on the type of hybridisation betwixt the elements.

Alkene family unit: Ethylene (CH_two=CH_ii
or C_twoH_four), propylene (CH₂=CH-CH₂), 1-butylene (CH_two=CH-CH₂-CH_iii), two-butylene (CH_iii-CH=CH-CH₃) and and then on. (Note that the 1-butylene and 2-butylene are isomers of butylene).

Alkyne hydrocarbons: Ethyne (CH ≡ CH or C₂H₂), propyne (CH≡C-CH_three), 1-butyne (CH≡C-CH₂-CH₃), 2-butyne (CH_three-CH≡CH-CH₃) and so on.

What are fossil fuels and where practice they come from?

Fossil fuels are mainly rough oil, natural gas and coal that are made upwardly of carbon, hydrogen, nitrogen, sulphur, oxygen elements and other minerals (Effigy 1, ref). The mostly accepted theory is that these hydrocarbons are formed from the remains of living-organisms called planktons (tiny plants and animals) that existed during the Jurassic era. The planktons have been buried deeper below the heavy layers of sediments in the Globe’s mantle, due to pinch from an enormous corporeality of heat and pressure level. Dead organisms decomposed without oxygen, which transformed them into tiny pockets of oil and gas. Rough oil and gas then penetrate in the rocks that ultimately accumulate in reservoirs. The oil and natural gas wells are found at the bottom of our oceans and beneath. Coal mainly originated from dead plants (ref).

Figure ii. Elemental limerick of fossil fuels (ref).

Scientists accept too questioned this theory. A recent study inNature Geoscience from Carnegie Institution in collaboration with Russian and Swedish colleagues revealed that the organic matter may not be the source of heavy hydrocarbon and that they could be existing already deep down in the Earth. Experts discovered that ethane and other heavy hydrocarbons could exist made if the pressure-temperature conditions can exist mimicked with those present deep within the Earths cadre. This is to say that hydrocarbons tin can exist made in the upper mantle that is the layer of World betwixt the crust and the core. They demonstrate it by subjecting marsh gas to laser heat-treatment in the upper layer of the Earth that and so transformed into hydrogen molecule, ethane, propane, petroleum ether and graphite. The scientists and then exposed ethane to the aforementioned conditions which reversibility produced methane. Above findings indicate that these hydrocarbons might be created naturally without the remains of plants and animals (ref).

3. How is synthetic plastic created from crude oil?

Constructed plastic comes from petrochemicals. When the source of oil below the surface of the Globe is identified, holes are drilled through the rocks in the ground to extract oil.

Extraction of oil
– Oil is pumped from underground to the surface where tankers are used to transport the oil to the shore. Oil drilling can as well accept place under the ocean using back up from platforms. Unlike size pumps can produce between 5 – xl litres of oil per stroke (Effigy i).

Refining of oil
– Oil is pumped through a pipeline that can be thousands of miles long and transported to an oil refiner (Figure 1). Spillage of oil from the pipeline during transfer can accept both immediate and long-term environmental consequences just safety measures are in identify to prevent and minimise this risk.

Figure 3: Fractional distillation of crude oil

Distillation of crude oil and product of petrochemicals
– Rough oil is a mixture of hundreds of hydrocarbons that also contains some solids and some gaseous hydrocarbons dissolved in information technology from the methane series family (mainly it is CH_four
and C_iiH₆, only it tin can be C₃H₈
or C₄H₁₀). Crude oil is first heated into a furnace so the resultant mixture is fed as a vapour to the fractional distillation belfry. The fractional distillation column separates the mixture into dissimilar compartments called fractions. There exists a temperature gradient in the distillation tower where the elevation is cooler than the base of operations. The mixture of liquid and vapour fractions gets separated in the tower depending on their weight and boiling bespeak (boiling betoken is the temperature at which the liquid phase changes into gaseous). When the vapours evaporate and meet a liquid fraction whose temperature is beneath the humid point of vapor, it partly condenses. These vapours of evaporating crude oil condense at unlike temperature in the tower. Vapours (gases) of the lightest fractions (gasoline and petroleum gas), flow to the elevation of the tower, intermediate weight liquid fractions (kerosene and diesel oil distillates), lingers in the centre, heavier liquids (called gas oils) carve up lower down, while the heaviest fractions (solids) with the highest boiling points remain at the base of the tower. Each fraction in the column contains hydrocarbons with a similar number of carbon atoms, smaller molecules are towards the summit and longer molecules nearer the bottom of the column (Ref). In this style, petroleum is decomposed into petroleum gas, gasoline, paraffin (kerosene), naphtha, light oil, heavy oil, etc.

Afterwards the distillation step, the obtained long chain hydrocarbons are converted into hydrocarbons that can and then be turned into many important chemicals which nosotros utilise for the training of a broad range of products applicable from plastic to pharmaceuticals.

Smashing of hydrocarbon is the principal process that breaks down the mixture of complex hydrocarbons into simpler low relative molecular mass alkenes/alkanes (plus by-products) by the means of high temperature and pressure.

Swell can be performed into two ways: Steam cracking and catalytic not bad.

Steam corking uses high temperature and pressure to break the hydrocarbons long chains without a catalyst, whilst catalytic neat adds a catalyst which allows the process to occur at lower temperatures and pressures.

The raw material used by the petrochemical industry is mainly naphtha and natural gas from oil refining operation in the petrochemical feedstock. Steam cracking uses the feedstocks from hydrocarbons mixture from diverse fractions such as reactant gases (ethane, propane or butane) from
natural gas, or liquids (naphtha
or
gas oil) (Figure 4).

Figure 4: Diverse chemicals obtained from fossil fuel later oil refining.

(Naphtha
is a mixture of C₅
to C₁₀
hydrocarbons obtained from the distillation of crude oil).

For instance, decane hydrocarbon is cracked down into products such as propylene and heptane where the erstwhile is then used to make poly(propylene) (Figure five).

Figure 5. Representation of Smashing of decane to convert into propylene and heptane.

Raw materials molecules are converted into monomers such as ethylene, propylene, and butene and others. All these monomers comprise double bonds so that the carbon atoms can afterward react to grade polymers.

Polymerisation
– hydrocarbon monomers are then linked together by chemical polymerisation mechanism to produce polymers. Polymerisation process generates thick, viscous substances as resins, which are employed to brand a plastic product. If nosotros look at a instance of ethylene monomer hither; ethylene is a gaseous hydrocarbon. When it is subjected to heat, pressure level and a certain catalyst, information technology joins together into long, repeating carbon bondage. These joined molecules (polymer) is a plastic resin known as polyethylene (PE).

Production of PE based plastic
–poly(ethylene) is processed in a manufactory to make plastic pellets. The pellets are poured into a reactor, melted into a thick liquid to cast into a mould. The liquid cools down to harden into a solid plastic and produce a finished product. Processing of polymer besides includes the addition of plasticizers, dyes and flame-retardant chemicals.

Types of polymerisations

Synthetic plastic is fabricated by a reaction known as polymerisation, which tin be performed in ii dissimilar means:

Improver polymerisation: Synthesis includes adding together monomers in a long chain. One monomer connects to the adjacent and and then on, when a catalyst is introduced, in a procedure known as chain growth polymers, adding one monomer unit at a time. Some addition polymerisation reactions are considered to create no side-products and the reaction can be performed in the vapour stage (i.east. gas phase) dispersed in a liquid. Examples: polyethylene, polypropylene, polyvinyl chloride and polystyrene.

Condensation polymerisation: In this case, 2 monomers combine to course a dimer (ii units) by releasing a byproduct. Dimers can then join to form tetramers (4 units) and and then on. These byproducts are necessary to be removed for the success of the reaction. The virtually mutual byproduct is water, which is treated and disposed of easily. Byproducts can also be valuable raw materials that are recycled dorsum into the feedstream.

Examples: Nylon (polyamide), polyester and polyurethane.

iv. How is plastic created from naphtha?

Plastic is often created from naphtha. Ethylene and propylene, for example, are the main raw material for oil-based plastic coming from Naphtha.

What is Naphtha?

There are different types of naphtha. It is a term used to draw a group of volatile mixtures of liquid hydrocarbons, obtained by the distillation of crude oil. It is a mixture of C_v
to C₁₀
hydrocarbons.

Naphtha is decomposed thermally at high temperature (~800 °C) in a steam cracker in presence of h2o vapor where it splits into light hydrocarbons known as major intermediaries. These are olefins and aromatics. Among the olefins, there is C₂
(ethylene), C_three
(propylene), C₄
(butane and butadiene). The aromatics consist of benzene, toluene and xylene. These small molecules are linked together by into long molecular chains called polymers. When a polymer comes out of the chemical mill they it is still not in the form of plastic – they are in the class of granules or powders (or liquids). Before they can get an everyday use plastic they need to undergo a series of transformations. They are kneaded, heated, melted, and cooled into objects of diverse shape, size color with precise properties according to the processing tubes.

For instance, for polymerisation of ethylene into polyethylene (PE), initiators are added to start the chain reaction, but after the germination of PE, it is sent for processing by improver of some chemicals (antioxidants and stabilisers). Later which an extruder convertsn PE into strings, thereafter grinders convert information technology into PE pellets. Factories and so cook them into final products.

5. What is the chief ingredient in plastic?

The main ingredient in most plastic textile is a derivative from crude oil and natural gas.

There are many different types of plastics – clear, cloudy, solid colour, flexible, rigid, soft, etc.

Plastic products are often a polymer resin which is then then mixed with a blend of additives (See polymer vs. plastic). The additives are of import as each of them are used to provide plastic with targeted optimum properties such as toughness, flexibility, elasticity, colour or to make them safer and aseptic to use for a detail application (ref).

What type of plastic a product is made from can be sometimes be identified by looking at the number at the bottom of plastic containers. Some of the primary types of plastic and the parent monomer is given below (Table i). This table shows the types of plastic and the monomers that make up the plastic.

Table 1. Principal polymer types, monomers and its chemic structures

Resin identification code	Polymers	Monomers
♳ PETE	Polyethylene terephthalate (PET)	Ethylene glycol and Dimethyl terephthalate
♴ HDPE	High-density polyethylene (HDPE)	Ethylene (CH2=CHii) *(lesser branching between polymer chains)
♵ PVC	Polyvinyl chloride (PVC)	Vinyl chloride (CH2=CH-Cl)
♶ LDPE	Low-density polyethylene (LDPE)	Ethylene (CHtwo=CH2) *(excessive branching)
♷ PP	Polypropylene (PP)	Propylene (CH3-CH=CH2)
♸ PS	Polystyrene (PS)	Styrene
♹ Others	Other plastics including acrylic, polycarbonates, polylactic acid (PLA), fibres, nylon	Unlike monomers are used for a detail polymer. For instance, PLA made from Lactic acrid

*The monomer used in LDPE and HDPE is ethylene but there is a difference in the degree of branching.

6. Which was the commencement human made plastic?

Meso American cultures (Olmec, Maya, Aztecs, 1500 BCE) used natural latex and rubber to brand containers and clothes water-resistant.

Alexander Parkes (UK, 1856) patented the first man-made bioplastic, called Parkesine, made from cellulose nitrate. Parkesine was a difficult, flexible and transparent plastic. John Wesley Hyatt (US, 1860s) made a fortune with Parkes’ invention. The Hyatt brothers improved plastic’due south malleability of cellulose nitrate by adding camphor and renamed the plastic as Celluloid. The aim was to produce billiard balls, which until and so were made from ivory. The invention is considered as the earliest example of homo-made bioplastic by many (ref).

The first truly synthetic plastic was Bakelite made from phenol and formaldehyde resin. Leo Baekeland (Kingdom of belgium, 1906) invented Bakelite that was coined as a ‘National Historic Chemical Landmark as it completely revolutionized every manufacture present in modern life. It has the property of high resistance to electricity, estrus, and chemicals. It has non-conducting backdrop, which is extremely essential when designing electronic devices such as radio and telephone casings. (ref).

seven. What was used earlier plastic?

Before the nascency of plastic, we were using wood, metallic, glass and ceramic, and animal derived materials such as horn, bone and leather.

For storage purpose, mouldable clays (pottery) mixed with glass were used which meant the containers were often heavy and fragile.

Natural materials from the bark of the safe tree – gum (latex resin) came into existence, the mix was sticky and mouldable but not useful for storage.

In the 18th century, Charles Goodyear accidentally discovered rubber – he added

In the 18th century, Charles Goodyear accidentally discovered rubber – he added sulphur into hot crude safe that reacted and made prophylactic resilient which upon cooling became elastic i.e., it had the property to snap dorsum into its original shape (ref).

8.  Can y’all make plastic without oil?

Yep, it is possible to create plastic from sources other than oil.

Although crude oil is the master source of carbon for moden plastic, an array of variants are manufactured from renewable materials. Plastic fabricated without oil is marketed every bit biobased plastic or bioplastics. These are made from renewable biomass such as:

• Lignin, cellulose and hemicellulose,
• Terpenes,
• Vegetable fats and oils,
• Carbohydrates (sugars from saccharide cane etc)
• Recycled food waste
• Bacteria

However, information technology should be noted that bioplastics are not automatically a more sustainable alternative in every case. Bioplastics differ as per the ways in which they break down, and bioplastics too, every bit any material, require resource in their production.

Bioplastics such every bit PLA, for example, represent a biodegradable material that will dethrone in certain environmental conditions, but may non bio-degrade in all sorts of climates. Therefore a waste stream of PLA based plastic is required. In the case of PLA it is a sensitive polyester that begins to dethrone during the recycling procedure and tin end up contaminating the existing plastic recycling stream (ref).

But bioplastics can accept many uses when designed with a proper waste stream in mind.

Bioplastics are potential materials for the fabrication of single-use plastic such as that required to make biodegradable bottles and packaging films. For example, in 2019, a researcher from the Academy of Sussex created a transparent plastic movie from fish-skin waste and algae; called MarinaTex (Ref). Biopolymers have also been investigated for medical applications, such as controlled drug release, drug packaging, and absorbable surgical sutures (ref, ref).

Maurice Lemoigne (France, 1926) discovered the first bioplastics made form bacteria, polyhydroxybutyrate (PHB), from bacterium Bacillus megaterium. Every bit bacteria consume sugars, they will produce the polymers (ref). The importance of Lemoigne’s invention was disregarded until the oil crunch hit in the mid-1970s spurred interest in discovering substitutes of petroleum-based products.

Henry Ford (US, 1940) used bioplastics fabricated from soybeans for some auto parts. Ford discontinued the use of soy plastics after World War II because of the surplus inexpensive oil supply (ref).

The developments in metabolic and genetic engineering accept expanded the research on bioplastic and applications for numerous types of bioplastics had become established specially PHB and polyhydroxyalkanoate (PHA), although at that place are many other interesting developments occurring all the time.