It is a synthetic, thermoplastic polymer belonging to the polyolefin family, obtained through a reaction known as polyethylene polymerization, which is produced from ethane, a component of natural gas.
High-density polyethylene is semi-crystalline (70–80%), colorless, odorless, non-toxic, and milky in appearance; it is available in all transparent and opaque shades.
General Properties of High-Density Polyethylene
The properties of high-density polyethylene, like those of any other polymer, depend primarily on its structure—that is, essentially on its molecular weight and crystallinity.
Physical Properties
High-density polyethylene has a density, as shown in the table below, ranging from 0.941 to 0.965 g/cm³; it has a high degree of crystallinity, making it an opaque material with a waxy appearance: the light transmittance of this plastic ranges from zero to forty percent, depending on its thickness.
There are gas permeability tests for high-density polyethylene, in which the results depend on the sample's thickness, density, and temperature during the measurement.
In high-density polyethylene, the higher the density, the lower the permeability; due to its nonpolar nature, it absorbs very little moisture and provides an excellent vapor barrier against this substance.
High-density polyethylene has high permeability to certain substances in which it is soluble at high temperatures, such as aliphatic, aromatic, and chlorinated solvents.
It also exhibits some permeability to oils and fats, particularly pine oil, orange oil, peppermint oil, and camphor. When stored in bottles, these substances cause the material to soften slightly over time and may lead to cracks under stress, especially in the homopolymer type.
Source: UNIVERSITY OF SAN CARLOS DE GUATEMALA, FACULTY OF ENGINEERING, SCHOOL OF CHEMICAL ENGINEERING—ERNESTO ROCA GIRÓN