It is a synthetic, thermoplastic polymer, a member of the polyolefins obtained from a reaction known as polyethylene polymerization, made from ethane, a component of natural gas.
High density polyethylene is semi-crystalline (70 - 80%), colorless, odorless, non-toxic, milky and 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 fundamentally on its structure, i.e. basically on its: Molecular weight and Crystallinity.
Physical properties
High Density Polyethylene has a density as shown in the table below of 0.941 - 0.965 g/cm3; it presents a high degree of crystallinity, thus being an opaque material with a waxy appearance: the transmittance of this plastic is from zero to forty percent, depending on the thickness.
There are gas permeability tests for high density polyethylene, where it depends on the thickness of the sample, the density, and the temperature during the measurement.
In high density polyethylene, the higher the density, the lower the permeability, due to its non-polar nature, it absorbs very little moisture and has a high vapor barrier quality.
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 shows some permeability to oils and fats, in particular to pine, orange, peppermint and camphor essence. In bottles, these substances induce a slight softening in the long term and the possibility of stress cracking, especially in the homopolymer type.
Source: UNIVERSIDAD DE SAN CARLOS DE GUATEMALA FACULTY OF ENGINEERING ERNESTO ROCA GIRÓN SCHOOL OF CHEMICAL ENGINEERING