Difference Between Polyethylene and Polypropylene

Polyethylene vs Polypropylene
 

Polymers are large molecules, which has the same structural unit repeating. The repeating units are called monomers. These monomers are bonded to each other with covalent bonds to form a polymer. They have a high molecular weight and consist over 10,000 atoms. In the synthesis process, which is known as polymerization, longer polymer chains are obtained. There are two main types of polymers depending on their synthesis methods. If the monomers have double bonds between carbons from addition reactions, polymers can be synthesized. These polymers are known as addition polymers. In some of the polymerization reactions, when two monomers are joined, a small molecule like water is removed. Such polymers are condensation polymers. Polymers have very different physical and chemical properties than their monomers. Moreover, according to the number of repeating units in the polymer, properties differ. There are a large number of polymers present in the natural environment, and they play very important roles. Synthetic polymers are also used widely for different purposes. Polyethylene, polypropylene, PVC, nylon, and Bakelite are some of the synthetic polymers. When producing synthetic polymers, the process should be highly controlled to get the desired product always. Polyethylene and polypropylene have become a very controversial issue at the present day, due to their incapability of degradation. They make up a considerable percentage in our garbage; therefore, they keep on increasing on the earth surface. This problem has caught the attention of researchers, and recycled plastics have been synthesized.

Polyethylene

This is the most common plastic used in the world today. Polyethylene is a polymer made of ethylene. Ethylene has two carbon atoms bonded to each other with a double bond. Two hydrogen atoms are bonded to each carbon. When polymerizing, the double bond is broken, and new sigma bond between two carbons of two ethylene molecules takes place. In other words, polyethylene is produced by an addition reaction of the monomer ethylene. Its repeating unit is –CH₂– CH₂-. Thus, this has a very simple structure with long chain carbon atoms. Depending on the way it is polymerized, the properties of the synthesized polyethylene change. Sometimes they can be straight chain, or sometimes they can be branched. Branched polyethylene is easy to make and lot cheaper. However, its strength is much lower than straight chain polyethylene. Polyethylene is used in making bottles, bags, toys, etc.

Polypropylene

Polypropylene is also a plastic polymer. Its monomer is propylene, which has three carbons and one double bond between two of those carbon atoms. Polypropylene is manufactured from propylene gas in the presence of a catalyst such as titanium chloride. It is easy to produce and can be manufactured with high purity. Polypropylenes are light in weight. They have a high resistance to cracking, acids, organic solvents and electrolytes. They also have high melting point and good dielectric properties and are non-toxic. Polypropylenes have a high economical value. They are used for pipes, containers, house ware, packaging, and automotive parts.