Table of Contents

What is LDPE
Low Density Polyethylene is a branch of polyethylene with a density of 0.910–0.940 g/cm3. What fundamentally separates LDPE from its HDPE counterpart, is the structure of their polymer chain. Despite both being constituted by ethylene monomers, LDPE possesses a polymer chain with side branches. There branches are responsible for LDPE's low density as they have an irregular shapes and causes gap in-between each polymer chains. LDPE have a melting point of 105-115°C [1].

Figure 1: Polymer chain of polyethylene [2]

Advantages and Disadvantages
LDPE Advantages
LDPE Disadvantages
Electrical Insulator [1]
Low water absorption
Transparent in thin film form
High impact strength at low temperature, good weatherability
Low cost
Vulnerable to stress cracking [1]
Limited usage under extreme temperature
High gas permeability
Highly flammable

LDPE Chemical Compatibilities
When not exposed to strong oxidizing agents, LDEP remains unreactive at room temperature. It is able to withstand a temperature of 80°C - 95°C under a short operation time. While the nature of LDPE being tough and flexible, it can still break under high pressure condition. Comparing to HDPE, LDPE shows lower tensile strength yet higher resilience [3].
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Table of LDPE's chemical properties [3]
Element LDPE's corresponding resistance Chemical reaction with LDPE
Acid Excellent None
Base Excellent None
Ester Excellent None
Aldehydes
Good Low
Ketones Good Low
Vegetable oil Good Low
Aliphatic Limited Significant
Aromatic Limited Significant
Hydrocarbons Limited Significant
Mineral oil Limited Significant
Oxidizing agent Limited Significant
Halogenated hydrocarbons Poor Violent

LDPE Pipes Applications and Fitting
Common LDPE piping have a outer diameter ranging from 12mm to 75mm. with a maximum pressure of up to 10 bars. When compared to HDPE pipes, LDPE pipes are much smaller in size, therefore LDPE pipes are often used to transport solvents such as water in low quantities. It sees most frequently applications in: drainage, agriculture, gardening, and irrigation systems [4].
Some applicable methods of joining LDPE pipes[4]:
Mechanical Connectors
Inside Welding
Electro Fusing
When fitting LDPE pipes, the inner diameter of the pipe is measured for the fitting.

Figure 2: A sizing chart of LDPE [5]

LDPE Recycling
Despite both being polyethylene, LDPE must be recycled separately from its high density counterparts, giving it a recycling number of 4. Although it was not accepted for most recycling programs in the past, more communities starts to adopting the progress as LDPE is one of the most produced plastic. During recycling, processors melts down LDPE to eliminate its contaminants and then form them into thin resalable plastic sheets.

Figure 3: Recycling symbol of LDPE [6]

References

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Faculty Advisor: Mary Robinson

Element	LDPE's corresponding resistance	Chemical reaction with LDPE
Acid	Excellent	None
Base	Excellent	None
Ester	Excellent	None
Aldehydes	Good	Low
Ketones	Good	Low
Vegetable oil	Good	Low
Aliphatic	Limited	Significant
Aromatic	Limited	Significant
Hydrocarbons	Limited	Significant
Mineral oil	Limited	Significant
Oxidizing agent	Limited	Significant
Halogenated hydrocarbons	Poor	Violent

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