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Difference Between HDPE and PP

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Key Difference – HDPE vs PP
  

HDPE is high-density polyethylene while PP is polypropylene. Thus the key difference between HDPE and PP is that the HDPE is made with ethylene monomer whereas PP is made with propylene monomer.

Polymers are macromolecules formed from a number of small molecules known as monomers. There are many different forms of polymer compounds based on the type of monomer and the way of these monomers bind to each other.

CONTENTS

1. Overview and Key Difference
2. What is HDPE
3. What is PP
4. Similarities Between HDPE and PP
5. Side by Side Comparison – HDPE vs PP in Tabular Form
6. Summary

What is HDPE?

HDPE is high-density polyethylene. It is a form of polyethylene. HDPE is also a thermoplastic material which is made from petroleum. The chemical formula of a repeating unit of this compound is –C2H4-. HDPE is very popular due to its high strength-to-density ratio. This means HDPE has a lightweight, but is very strong. The density of HDPE is equal or higher than 0.941 g/cm3. The reason for this high density compared to usual polyethylene is the low degree of branching and thus, the polymer chains pack tightly.

Properties of HDPE

Some of the important properties of HDPE are listed below.

Figure 1: Repeating Unit of HDPE

Applications of HDPE

There are many applications of HDPE. The major application is the production of plastic bottles, plastic bags, bottle caps, boats, fireworks, fuel tanks of vehicles, etc.

What is PP?

PP is polypropylene. It is a thermoplastic polymer built from propylene monomers. PP is formed via the addition polymerization of propylene monomers.

Properties of PP

The important properties of PP are listed below.

Figure 2: Tacticity in PP; isotactic PP (top two chains) and syndiotactic PP (bottom chain).

When a polymer chain of PP is considered, it has methyl groups on one side of the polymer chain. These side groups are known as pendant groups. Based on the structure of polymer chains, there are three types of PP named as isotactic, atactic PP, and syndiotactic PP. Isotactic PP has pendant groups on the same side and atactic PP has pendant groups in a random manner whereas syndiotactic PP has pendant groups in an alternating pattern.

What are the Similarities Between HDPE and PP?

What is the Difference Between HDPE and PP?

HDPE vs PP
HDPE is high-density polyethylene. PP is polypropylene.
 Density
HDPE has a very high density (0.941 g/cm3). PP has a low density (0.905 gcm3).
Degree of Branching
HDPE has a low degree of polymer chain branching. PP has a high degree of polymer chain branching compared to HDPE.
 Transparency
The transparency of HDPE is low. The transparency of PP is high.
Tacitiy
Tacticity is absent in HDPE. Tacticity is present in PP.
Temperature Tolerance
HDPE cannot withstand autoclaving conditions. PP can withstand autoclaving conditions.

Summary – HDPE vs PP

HDPE and PP are polymer compounds which are thermoplastic. The term HDPE stands for high-density polyethylene. The term PP stands for polypropylene. The key difference between HDPE and PP is that the monomer used to make HDPE is ethylene whereas the monomer used to make PP is propylene.

Reference:

1. “High-Density Polyethylene.” Wikipedia, Wikimedia Foundation, 28 Feb. 2018, Available here.
2. Johnson, Todd. “Learn About the Basics of the Plastic Resin Polypropylene.” ThoughtCo, Available here.
3. Lazonby, John. “Poly(Propene) (Polypropylene).” The Essential Chemical Industry Online, Available here.

Image Courtesy:

1. “Polyethylene-repeat-2D-flat” (Public Domain) via Commons Wikimedia
2.”Polymers Tacticity V.1″ By Jü – Own work (CC0) via Commons Wikimedia

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