What Is a Polyolefin?
A polyolefin is the generic term for polyethylene and polypropylene. These materials are formed from monomers known as olefins, which are compounds containing double bonds between carbon atoms and are also referred to as alkenes.
Both polyethylene and polypropylene, as polyolefins, possess unique characteristics. However, they have the following in common: (1) lightweight due to their low density, (2) excellent moisture resistance, which prevents the permeation of water vapor in the air, and (3) only carbon dioxide and water are produced when burned because they are composed of only carbon and hydrogen atoms. Only carbon dioxide and water are produced when polyolefin is burned.
Types and Uses of Polyolefins
Polyolefins are a generic term for resins whose raw material compounds are olefins.
Polyethylene is classified into low-density polyethylene (LDPE), high-density polyethylene (HDPE), and ultra-high-molecular-weight polyethylene (UHMW-PE). UHMW-PE is used in separators for lithium-ion batteries.
Polypropylene is a milky white resin used in a wide range of industries, including food trays, home appliance parts, and automotive parts.
Structure of Polyolefins
The raw material for polyethylene, which is classified as polyolefins, is ethylene, while the raw material for polypropylene is propylene. Both of these raw materials have double bonds. Hydrocarbons with such double bonds, or alkenes, used to be called olefins. As a remnant of this name, polyethylene and polypropylene made from olefins are called polyolefins.
LDPE and HDPE are manufactured in different ways. Due to the difference in manufacturing methods, the number of molecular chains with branches and molecular weight differs, resulting in LDPE and HDPE having different physical properties. In the case of polypropylene, physical properties vary depending on the stereo-regularity of the methyl groups in the side chains, with higher stereo-regularity resulting in higher hardness and strength.
Characteristics of Polyolefins
The following are some characteristics common to both polyethylene and polypropylene, also known as polyolefins.
The first characteristic is that they are lightweight. Polyolefins have a density of less than 1 g/cm3, which is small among resins.
The second feature is excellent moisture resistance. Polyolefins have a low water absorption rate, so they are used to prevent the permeation of water vapor from the air, such as in lids.
The third characteristic is that no harmful compounds are produced when they are burned. Since polyolefins are composed of only carbon and hydrogen atoms, only water and carbon dioxide are produced when they are burned. However, it should be noted that if the polymer is partially modified or additives are added, other compounds may be produced during combustion.