A Comprehensive Guide to the Comparison and Selection of HDPE and LDPE

The most commonly used polymers include polyethylene, and it has two major versions: high-density polyethylene (HDPE) and low-density polyethylene (LDPE). The two materials are highly different in molecular shape, physics, and applications. To choose the right material for the right purpose, it is important to understand these differences.

HDPE

HDPE is the third-largest commodity plastic material in the world, after polyvinyl chloride and polypropylene.

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LDPE

LDPE is a kind of high branched polyethylene. In the late 1940s, it was the first plastic to be commonly used commercially in packaging.

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HDPE vs. LDPE: Molecular Structure

HDPE molecules are long linear molecules with few branches, which is why its molecular chain is very well ordered and dense. This is why it is very crystallised (between 80 and 95%) and dense (0.941 and 9.65 g/cm³). LDPE, on the other hand, is branched with a high number of side chains that upset packing and drop crystallinity to 55-65%. The density of LDPE is therefore lower-from 0.910 to 0.940 g/cm³.

Figure 1: Molecular structure for different types of polyethylene^[1].

HDPE vs. LDPE: Properties

HDPE's density and crystallinity will be higher, and hence it will be very strength and stiff, perfect for structural applications. The lesser crystallinity of LDPE, the higher the flexibility and impact resistance, but the lower the tensile strength and stiffness.

HDPE is chemically stable, resistant to acids, alkalis, and organic solvents, and environmentally resistant to stress cracking. LDPE is chemically stable, less resilient to stress cracking, and more transparent and elastic, which is good for consumer packaging and flexible film.

Property	HDPE	LDPE
Density	0.941-0.965 g/cm3	0.910-0.940 g/cm3
Tensile Strength	24-40 MPa	7-14 MPa
Melting Point	120-136 °C	105-115 °C
Crystallinity	80-95%	55-65%
Heat Resistance	Higher, continuous use temperatures up to 80-100°C	Weaker, continuous use temperature around 60-80 °C
Softening Point	125-135 °C	90-100 °C
Hardness	60-70 Shore hardness	41-45 Shore hardness
Processing Temperature	180 °C	160 °C
Low Temperature Performance	Still maintains some performance at low temperatures, but the specific low temperature embrittlement temperature is not explicitly mentioned.	Good low-temperature properties, able to maintain properties at temperatures as low as -70 °C.

What are HDPE and LDPE Used for?

The distinct properties of HDPE and LDPE lead to varied applications.

HDPE Applications

• Structural Uses - HDPE's high strength and rigidity make it suitable for pipes, containers, and industrial parts.
• Thermal Resistance Applications - Products such as hot water pipes and chemical storage tanks benefit from HDPE's superior thermal and chemical resistance.

LDPE Applications

• Flexible Packaging - LDPE's flexibility and toughness are ideal for plastic bags, shrink wraps, and squeeze bottles.
• Low-Temperature Performance - LDPE remains functional at -70°C, making it suitable for frozen food packaging and insulation.

HDPE vs. LDPE: Selection Guide

It's also depending on the application that you choose between HDPE and LDPE.

• Select HDPE if you need high tensile strength, rigidity, and thermal resistance.
• Select LDPE when you need impact resistance, strength, and visibility, like film on packages and soft bags.
• HDPE is for the extreme environments of high stress and high temperature. LDPE is for use in low temperatures and light chemical exposure.

Conclusion

HDPE and LDPE are very different and suit many industrial and consumer applications. When producers and engineers have the full range of molecular properties, physical characteristics, and applications to which they can relate, material decisions can be made to optimize product performance and profitability.

Related Hot Products from Alfa Chemistry

View a wide range of our products to find the best option for your application:

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Reference

1. Ragaert, K.; et al. Microstructural Foundations of the Strength and Resilience of LLDPE Artificial Turf Yarn. J. Appl. Polym. Sci. 2016, 133, 1-12.