Physical properties of HDPE

Basic properties of high-density PE

Among the factors controlling the physical properties of HDPE are MFR, density, molecular weight, molecular weight distribution, crystallinity, double bonds, branched species, etc. But the three basic physical properties (factors) that regulate physical properties are molecular weight, molecular weight distribution and density. Various grades are manufactured by controlling these physical properties.

1. Molecular weight
As molecular weight increases (lower MFR), mechanical strength generally increases, but on the other hand, melt viscosity increases, making flowability (moldability) lower.

2.Molecular weight distribution
Molecular weight distribution affects the flowability and mechanical properties of the polymer significantly. As molecular weight distribution becomes wider, non-Newtonian properties increases, causing an improvement in flowability (moldability). Further, as the distribution becomes narrower, mechanical properties such as tensile strength and impact resistance become better.

As density increases, tensile strength and rigidity, among other things, increases, but impact strength, transparency, stress cracking resistance, etc. decline.

Relationship between molecular structure and physical properties

As shown below, the general physical properties of HDPE trend in accordance with a fall in molecular weight, an expansion of molecular weight distribution and a rise in density.

Basic physical propertgie
General physical properties
Lower molecular weight
(higher MFR)
Higher crystallinity
(higher density)
Wider molecular
weight distribution
Drawdown resistance
Melt tension
Surface hardness
Creep resistance
Stress cracking resistance