Plastics

Plastics are organic materials, like wood, paper, or wool. Natural products such as cellulose, coal, natural gas, salt, and, of course, crude oil are used as raw materials for the manufacture of plastics. 

 One of the earliest examples was invented by Alexander Parkes in 1855, who called his invention Parkesine. We know it today as celluloid. Polyvinyl chloride (PVC) was first polymerized between 1838 and 1872. A decisive breakthrough came in 1907 when Belgian-American chemist Leo Baekeland developed Bakelite, the first real mass-produced synthetic plastic. 

The term `` plastic '' is derived from the Greek word `` plastikos '', which means something like malleable. This refers to the malleability or plasticity of the material during manufacture, allowing it to be molded, pressed, or extruded into a variety of shapes, such as films, fibers, sheets, tubes, bottles, boxes, and much more.

 

The most common types of plastic we use are numbered according to their recycling codes. Plastic recycling numbers 2, 4, and 5 are the safest. While the plastic numbers 1, 3, 6, and 7 should be avoided. But that doesn't mean you can use safer plastic without fear. All plastic products can leak toxic chemicals when heated or damaged. Therefore, it is better to switch to other materials such as metal and glass if possible.

1) PET (Polyethylene terephthalate)

PET is a lightweight polymer and comes with varying degrees of rigidity. It is widely used in plastic beverage bottles and also in clothing fibers (where it is often referred to as "polyester"). It is also used in prepared food packaging and adhesive tapes. 

To make PET, terephthalic acid is reacted with ethylene glycol. This reaction is typical Fisher-type esterification in which an acid is reacted with an alcohol.

2) HDPE (High-Density Polyethylene) 

High-Density Polyethylene (HDPE) is a thermoplastic polymer made from monomeric ethylene. It is sometimes called "polyethylene" when used for HDPE pipe. HDPE is used in the manufacture of corrosion-resistant plastic bottles and pipes. 

Polyethylene is manufactured by the addition or radical polymerization of ethylene (olefin) monomers. HDPE is known for its high strength/density ratio. The density of HDPE can range between 930 and 970 kg / m3

3) PVC (polyvinyl chloride) 

PVC is available in rigid and flexible forms. In its rigid form, it can be used for door and window frames, pipes, and bank cards. By adding plasticizers, a more flexible shape can be achieved, which is used in electrical cable insulation and as a substitute for rubber.

 

The electrolysis of saltwater produces chlorine. The chlorine is then combined with ethylene extracted from the oil. The resulting element is ethylene dichloride, which converts to vinyl chloride monomer at very high temperatures. These monomer molecules polymerize to form polyvinyl chloride resin.

4) LDPE (Low-Density Polyethylene) 

LDPE is a soft, flexible, and lightweight plastic material. LDPE is known for its low-temperature flexibility, toughness, and corrosion resistance. 

It is not suitable for applications where rigidity, high-temperature resistance, and structural strength are required. It is widely used for orthotics and prosthetics. LDPE has good chemical and impact resistance and is easy to manufacture and mold.

5) PP (polypropylene) 

Polypropylene is particularly resistant to heat, physical damage, and corrosion. Therefore, it is widely used in food containers, rugs, ropes, plastic furniture, and pipes. It is also used to make items for medical or laboratory purposes.

 

Polypropylene can be synthesized from propylene by dehydrating 1-propanol using the H2SO4 catalyst and, as expected, cationic polymerization using the Ziegler-Natta AlCl3 catalyst can produce polypropylene. The molecular weight of polypropylene is 3900 g / mol.

6) PS (Polystyrene) 

Polystyrene is one of the most widely used plastics. In its solid form, it is used to make plastic cutlery, CD cases, and disposable razors, while it is used as a foam in packaging materials, building insulation, and foam packaging for food and beverages.

 

Polystyrene is made by polymerizing styrene, a petroleum-based liquid hydrocarbon monomer. In this three-step synthesis, styrene is formed by the radical bromination of ethylbenzene and the elimination reaction of (1-bromoethyl) benzene. The styrene produced in this first step is then polymerized to synthesize the final product from polystyrene.

7) Others like (PTFE, PA, PU) 

PTFE (Polytetrafluoroethylene) - The well-known brand is Teflon. It is a very low reactive polymer and is used in non-stick coatings on cookware. GoreTex fabrics also contain PTFE-based fibers. It also has uses as a lubricant and as insulation for electrical wires and cables. 

 

PTFE is polymerized from the chemical tetrafluoroethylene, TFE is synthesized from fluorspar, hydrofluoric acid, and chloroform. These ingredients combine at high temperatures, an action known as pyrolysis. TFE is a colorless, odorless, and non-toxic gas, but extremely flammable.

PA (polyamide) - actually refers to a family of polymers; Nylon 6.6 is shown here. It was originally intended as a replacement for rayon for military purposes such as parachutes. Today it is used in clothing, guitar strings, and fishing lines.

 

solutions of 1,6-hexane diamine and sebacoyl chloride are carefully poured into the same container. At the interface of the two layers, nylon polymer is formed, which can be continuously drawn out of solution in the form of a "rope" and wound around a cylinder. 

PU (Polyurethane) - Polyurethanes are also a family of polymers; the R group in the above structure varies. Its uses include foam seats for furniture and cars, latex-free condoms, shoe soles, football liners, wheels for scooters and skates, and some paints. 

 

The synthesis of flexible polyurethane foams often involves two main steps: puffing and gelling. The blowing reaction produces carbon dioxide and urea, which expand and become trapped in the reaction mixture, while the urethane bonds are formed by reactions of the isocyanate and hydroxyl groups of the polyol (ethylene glycol).

Recycle: 

There are different types of plastics. And that makes it impossible to recycle all plastics in the same way. However, there are two ways to recycle plastic.

Traditional recycling: 

This is the most widely used recycling method. Another word for traditional recycling is mechanical recycling. This process is suitable for recycling thermoplastic materials.

 

In the traditional recycling process, plastics are melted and processed into new plastic products. After recyclers melt the plastic, they process it into new products in a process called injection molding.

Advanced recycling: 

Advanced recycling is a process in which plastics break down through the action of chemicals. This method consists of three other techniques. These techniques include pyrolysis, chemical recycling, and gasification. 

 

Pyrolysis is a technique that recycles plastic waste into crude oil. In chemical recycling, a polymer is reduced to a monomer that can be used to create new products. For example, manufacturers use chemical recycling to make nylons.

Reference:

1) https://en.wikipedia.org/wiki/Polyethylene_terephthalate

2) https://www.acplasticsinc.com/informationcenter/r/common-uses-of-hdpe

3) https://en.wikipedia.org/wiki/Polyvinyl_chloride

4) https://www.curbellplastics.com/Research-Solutions/Materials/LDPE

5) https://www.creativemechanisms.com/blog/all-about-polypropylene-pp-plastic

6) https://en.wikipedia.org/wiki/Polystyrene

7) https://www.europur.org/applications/what-is-polyurethane-foam

8) https://en.wikipedia.org/wiki/Plastic_recycling