Welcome to world of PLASTICS!!!

Look around you, how many things do you see made from plastic? You will realize that plastics are everywhere. There are numerous plastics items such as: toys, pens, food or drink containers and plumbing pipes.  

What are Plastics?

Plastics are any synthetic or semi-synthetic organic polymer, which means that they are artificial or manufactured. So, synthetic materials are made of building blocks that are put together. Plastics are made of carbon. The main material used in the production of man-made plastics is oil(petroleum) and natural gas, but other natural materials like cellulose also can be also used to made plastics. Plastics are large carbon-containing compounds, called polymers which are composed of repeating units of shorter-carbon containing compounds, called monomers.

Plastics are grouped into two main polymer categories:

• Thermoplastics (which melt on heating and then harden again on cooling)
• Thermosets (which never melted when they have been formed but will cracked/charred when exposed to enough heat )

Examples of Thermoplastics       Acrylonitrile butadiene styrene – ABS       Polycarbonate - PC       Polyethylene - PE       Polyethylene terephthalate - PET       Poly(vinyl chloride) - PVC       Poly(methyl methacrylate) - PMMA       Polypropylene - PP       Polystyrene - PS       Expanded Polystyrene - EPS

Examples of Thermosets Epoxide (EP) Phenol-formaldehyde (PF) Polyurethane (PUR) Polytetrafluoroethylene - PTFE Unsaturated polyester resins (UP)

80% of the plastics produced are thermoplastics while Polyethylene, Polyvinylchloride(PVC), Polypropylene and Polystyrene are among the most commonly used thermoplastics (70%). 

6 Main types of plastics: 

• Polyehylene terephthalate(PET/PETE)

Common uses: soft drink bottles, cooking oil bottles, peanut butter jars, products containing essential oils, some fruit juices, alcohol beverage bottles, space blankets.

• Low-density polyethelene (LDPE)

Common uses: dry-cleaning bags, produce bags, trash can liners, food storage containers, bread bags, squeezable containers, six pack soda can rings, food storage.

• High-density polyethelene (HDPE)

Common uses: milk jugs, distilled water, large vinegar bottles, grocery bags, liquid laundry and dish detergent, fabric softener, motor oil, antifreeze, bleach and lotion.

• Polypropylene (PP)

Common uses: bottle caps, drinking straws, hinged containers, battery cases, dairy tubs (e.g. sour cream, cottage cheese), cereal box liners.

• Polyvinyl chloride (PVC)

Common uses: chemical spray bottles, pipes, electrical wire insulation, clothing, bags, upholstery, tubing, flooring, waterbeds, pool toys, bottles.

• Polystyrene (PS)

Common uses: bottle caps, drinking straws, yogurt cups, clear carryout containers, vitamin bottles, fast food, spoons, knives and forks, hot cups, meat and produce trays, egg cartons, food containers.

The chemistry behind plastics:

All plastics are polymers, but not all polymers are plastics. Plastics are formed by a process called polymerization. Polymerization occurs when individual monomers bond together. Identical monomers that combine together form homopolymers while different monomers that combine together form copolymers. Most plastic are usually created with several types of plastics, so they will not break down. 

The properties of a plastic are determined by:

• The type of monomers that made up. Homopolymer 1, Copolymers and Homopolymer 2 will have different chemical properties.
• The arrangement of monomers within the polymer. Straight polymers will have different chemical properties than branched polymers.

The monomers that can be found in plastics include organic compound like ehylene, propylene, styrene, phenol, formaldehyde, ethylene glycol, vinyl chloride and acetonitrile.

Due to the different combination of monomers, different kind of plastics with different chemical properties can be produced.

There are 2 ways which monomers can bond together to form polymers of plastics.

• Condensation reaction.

Two small molecules, monomers bind with the loss of a smaller molecule, usually water, alcohol or acid. As in the above picture, both monomer #1 and #2 have hydroxyl groups (OH) and hydrogen group (H). When the two monomers come together, one monomer lose a hydrogen while the other lose a hydroxyl group. The hydrogen and hydroxyl form water (H2O), and the remaining electrons form a covalent chemical bond between the monomers. The resulting compound is the basic subunit of copolymers #1 and #2. 

• Addition reaction.

Addition reactions involve rearranging electrons of the double bonds within a monomer to form single bonds with other molecules. The two molecules then formed polymer and the process repeated until polymer chains are formed. The various polymer chains can interact and cross-link by forming strong or weak bonds between monomers contribute to the physical properties of plastics (soft/hard, stretchy/rigid, clear/opaque, chemically inert). 

Today most plastics are made from petrochemicals(oil and natural gas). Oil is a carbon rich raw material. 

How Plastics formed?

The general way of plastics formed

1. Crude oil and natural gas are refined into ethane, propane or other petrochemical products. As in above figure, ethane undergoes cracking process into ethylene under high temperature furnaces. Ethylene is a small hydrocarbon consisting 4 hydrogen atoms and 2 carbon atoms. Various ethylene is chemically processed to make hydrocarbon monomers or carbon monomers used in plastics.

2. The ethylenes carry out polymerization reactions. The reaction produce polymer resins. Resin is the mass of polymers and usually in the form of powder or tiny granules. 

3. Resin is added with plasticizers, dyes and flame-retardant chemicals. The polymer is melted at first and cooled after that. The final polymer resins are formed usually in the forms of pellets. Finally, the polymer resins are processed into final plastic products by the main three processes, extrusion, injection and blow molding. 

• Extrusion: Pellets are heated and mechanically mixed in a long chamber, forced through a small opening and cooled with air or water. This method is used to make plastic films.
• Injection molding: The resin pellets are heated and mechanically mixed in a chamber and then forced under high pressure into a cooled mold. This process is used for containers like butter and yogurt tubs. 
• Blow molding: This technique is used in conjunction with extrusion or injection molding. The resin pellets are heated and compressed into a liquid tube, like toothpaste. The resin goes into the chilled mold, and compressed air gets blown into the resin tube. The air expands the resin against the walls of the mold. This process is used to make plastic bottles.

In our daily life now, it is almost impossible to live without plastics. Yes, plastics are very convenient to use because of their malleability and plasticity. They can be easily moulded by heating. But, did you know plastics take about 300 years to decay? Did you know almost a billion tons of plastics have been discarded since the 1950s? So, what happens to the plastic tossed out in the garbage? Lets us take the initiative by reducing the usage of plastics, only with that we perhaps can reduce and stop the harm to our planet, and in turn, benefit to ourselves. "Say No To Plastic Bags" please!

     Examples of Thermoplastics
      Acrylonitrile butadiene styrene – ABS
      Polycarbonate - PC
      Polyethylene - PE
      Polyethylene terephthalate - PET
      Poly(vinyl chloride) - PVC
      Poly(methyl methacrylate) - PMMA
      Polypropylene - PP
      Polystyrene - PS
      Expanded Polystyrene - EPS

Examples of Thermosets
Epoxide (EP)
Phenol-formaldehyde (PF)
Polyurethane (PUR)
Polytetrafluoroethylene - PTFE
Unsaturated polyester resins (UP)