2. Polypropylene (PP), also known as polypropene – It is a thermoplastic polymer used in a wide variety of applications.
Example: Prolene. In Prolene sutures. Chemical formula (C3H6)n
Polypropylene plastic contains only carbon and hydrogen. Burning it produces only carbon dioxide CO2 and water H2O.
It is produced via chain-growth polymerization from the monomer propylene.
Polypropylene belongs to the group of polyolefins and is partially crystalline and non-polar. Its properties are similar to polyethylene, but it is slightly harder and more heat resistant. It is a white, mechanically rugged material and has a high chemical resistance.
Bio-PP is the bio-based counterpart of polypropylene (PP).
Polypropylene is the second-most widely produced commodity plastic (after polyethylene). In 2019, the global market for polypropylene was worth $126.03 billion. Revenues are expected to exceed US$145 billion by 2019. The sales of this material are forecast to grow at a rate of 5.8% per year until 2021.
Example: polypropylene rope, seats, tubes.
Polypropylene is liable to chain degradation from exposure to temperatures above 100 °C. Oxidation usually occurs at the tertiary carbon centers leading to chain breaking via reaction with oxygen. In external applications, degradation is evidenced by cracks and crazing. It may be protected by the use of various polymer stabilizers, including UV-absorbing additives and anti-oxidants such as phosphites (e.g. tris(2,4-di-tert-butylphenyl)phosphite) and hindered phenols, which prevent polymer degradation.
Microbial communities isolated from soil samples mixed with starch have been shown to be capable of degrading polypropylene. Polypropylene has been reported to degrade while in the human body as implantable mesh devices. The degraded material forms a tree bark-like layer at the surface of mesh fibers.
3. Polyvinyl chloride (colloquial: polyvinyl, or simply vinyl;[6] abbreviated: PVC) – It is the world’s third-most widely produced synthetic polymer of plastic (after polyethylene and polypropylene). About 40 million tons of PVC are produced each year. Chemical formula (C2H3Cl)n
Polyvinyl chloride is the only plastic that produces large amounts of dioxins when burned. So, incinerating it is contraindicated. Some dioxins are manifestly toxic. They contain chlorine, which is presented in PVCs.
4. Polyethylene terephthalate (or poly(ethylene terephthalate), PET, PETE, or the obsolete PETP or PET-P) – It is the most common thermoplastic polymer resin of the polyester family and is used in fibers for clothing, containers for liquids and foods, and thermoforming for manufacturing, and in combination with glass fiber for engineering resins. Chemical formula (C10H8O4)n
Polyethylene terephthalate plastic contains only carbon and hydrogen and oxygen. Burning it produces only carbon dioxide CO2 and water H2O.
Polyethylene terephthalate consists of polymerized units of the monomer ethylene terephthalate, with repeating (C10H8O4) units. PET plastic contains only carbon and hydrogen and oxygen.
In 2016, annual production of PET was 56 million tons. The biggest application is in fibers (in excess of 60%), with bottle production accounting for about 30% of global demand. In the context of textile applications, PET is referred to by its common name, polyester, whereas the acronym PET is generally used in relation to packaging. Polyester makes up about 18% of world polymer production and is the fourth-most-produced polymer after polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC).
Examples: plastic bottles.
Biodegradation – At least one species of bacterium in the genus Nocardia can degrade PET with an esterase enzyme. Esterases are enzymes able to cleave the ester bond. Also, the initial degradation of PET can be esterases expressed by Bacillus and Nocardia.
Japanese scientists have isolated a bacterium Ideonella sakaiensis that possesses two enzymes which can break down the PET into smaller pieces that the bacterium can digest. A colony of I. sakaiensis can disintegrate a plastic film in about six weeks. (To be continued)/PN
