Full analysis of physical property parameters of high-density polyethylene (HDPE)

As one of the five general plastics, high-density polyethylene has excellent mechanical properties and chemical stability, making it widely used in packaging, pipe, container and other fields. This article will systematically sort out the core physical parameters of HDPE to help engineering and technical personnel accurately grasp material properties.

Overview of Basic Characteristics of HDPE

High density polyethylene is a thermoplastic resin polymerized from ethylene monomers, with low molecular chain branching and high crystallinity (usually 85-65%), with a density range of 0.940-0.976g/cm ³.

. This special molecular structure endows it with significantly higher rigidity, tensile strength, and heat resistance than LDPE. Typical HDPE is milky white and semi transparent, with low surface glossiness and a hard touch. It can be used in a temperature range of -40 ℃ to 100 ℃, which can meet the requirements of frozen packaging and withstand boiling sterilization treatment.

Performance indicators: Density, Melt Flow Index (MFR), Tensile Yield Strength, Elongation at Break, Vicat Softening Point, Brittle Temperature. Typical physical property benchmark values for HDPE. Typical value range. Testing standards

0.940-0.976 g/cm³

ASTM D1505

0.1-20 g/10min

ASTM D1238

20-32 MPa

ASTM D638

300-1000%

ASTM D638

120-130

ASTM D1525


ASTM D746

Detailed explanation of mechanical performance parameters
The most significant advantage of HDPE is its excellent mechanical properties.
. Taking 25 μ m film as an example, the biaxial tensile strength can reach over 45MPa, which is more than twice that of LDPE film. This high-strength characteristic allows HDPE products to be made thinner in the same application scenario, thereby reducing material consumption. The bending modulus is usually between 1000-1400MPa, reflecting the good rigidity of the material. It is worth noting that the mechanical properties of HDPE exhibit significant anisotropy, with a difference of up to 1015% in tensile strength between longitudinal (MD) and transverse (TD) directions.
In terms of impact strength, HDPE performs well at room temperature, with a cantilever beam notch impact strength of up to 30110J/m. However, in low-temperature environments, the impact performance of some grades will significantly decrease, which requires special attention when selecting materials. The low-temperature toughness of HDPE can be significantly improved by adding elastomer modification, such as the brittleness temperature of some special grades can be as low as -90 ℃.
Thermal performance and weather resistance
The hot deformation temperature of HDPE (under a load of 1.8MPa) is usually between 60-80 ℃, with a Vicat softening point of about 120-130 ℃ and a melting point range of 125-135 ℃. These parameters determine the applicability of the material in high-temperature environments. It should be noted that although HDPE has good short-term heat resistance, its long-term use temperature should not exceed 60 ℃, otherwise creep and stress relaxation phenomena may occur.
In terms of weather resistance, HDPE itself has poor UV resistance, and materials that have not been stabilized will show significant aging after 6-12 months of outdoor use. By adding additives such as carbon black and ultraviolet absorbers, the service life can be extended to more than 5 years. Thermal oxidative stability is also a weak link in HDPE, and antioxidants (such as 1010/168 composite system) are usually added during processing to prevent degradation.
Chemical stability and permeability
As a non-polar material, HDPE has excellent chemical corrosion resistance. It can withstand the erosion of most acid, alkali, and salt solutions, including strong acids such as concentrated hydrochloric acid (30%) and sulfuric acid (50%), as well as alkaline solutions of various concentrations. In terms of organic solvents, HDPE has excellent resistance to alcohols and oils, but it can be swollen by halogenated hydrocarbons (such as carbon tetrachloride) and aromatic hydrocarbons.
In terms of permeability, HDPE has an extremely low water vapor transmission rate (0.3-0.4g · mm/m ² · 24h · atm), making it an ideal moisture-proof material. But the oxygen permeability is relatively high (about 500700cc · mm/m ² · 24h · atm), which is not suitable for packaging applications that require high oxygen resistance. This defect can be effectively improved by compounding with other materials such as EVOH.

Comparison of Typical Grade Performance

There are significant differences in the performance of HDPE grades produced by different production processes and catalyst systems.
. Here is a comparison of performance parameters for three typical grades:

Table 1 Comparison of physical properties of typical HDPE grades

Performance indicators

Blow molding grade (XL6500) Injection molding grade (8003) Film grade (BE0400)

Density (g/cm ³)

0.952

0.958

0.945

MFR (g/10min) 0.3

8.0


Tensile strength (MPa) 28

25

32

Tensile elongation at break (%)

800

600

900

Environmental stress cracking (hr)>1000

200

500

Main applications

Pressure pipelines

Industrial containers

Heavy packaging films

Processing and application suggestions
HDPE has various processing methods, including blow molding, injection molding, extrusion, and rotational molding.
. Melt flow rate (MFR) is a key parameter for selecting processing technology: MFR10g/10min is suitable for thin-walled injection molded products. The processing temperature is usually controlled between 180-240 ℃, and the recommended mold temperature is 40-60 ℃.

In terms of material selection, pressure pipelines should prioritize grades with excellent resistance to environmental stress cracking (such as F50>1000hr under the testing standard ASTM D1693); Food packaging should choose specialized materials that meet FDA standards; Outdoor products should choose models that contain UV stabilizers. It is worth noting that HDPE has a relatively high shrinkage rate (1.5-4%), and sufficient shrinkage allowance needs to be reserved during product design.
With the development of material modification technology, various types of reinforced HDPE continue to emerge. Adding glass fiber can improve rigidity and heat resistance; Blending with rubber can improve toughness; Adding nano fillers can simultaneously enhance mechanical properties and barrier properties. These modified materials are gaining increasingly widespread applications in high-end fields such as automotive components and medical devices.