The key difference between aliphatic and aromatic polyurethane is that aliphatic polyurethane contains a chain structure whereas aromatic polyurethane contains a ring structure.
Polyurethane or PUR is one of the largest class of polymers having properties that can be changed depending on applications. These materials can be either thermosetting or thermoplastic. Also, they can be rigid, soft, or flexible, depending on the chemicals structure. A polyurethane polymer forms from the reaction between an organic diisocyanate and a diol compound.
CONTENTS
1. Overview and Key Difference
2. What is Aliphatic Polyurethane
3. What is Aromatic Polyurethane
4. Side by Side Comparison – Aliphatic vs Aromatic Polyurethane in Tabular Form
5. Summary
What is Aliphatic Polyurethane?
Aliphatic polyurethane or aliphatic acrylic polyurethane is a polymer material which has no aromatic structures. It is important as a coating in industrial and building applications. The chemical structure of this polymer material is important because this material is tough and flexible. Therefore, this material is an additive for many products to get a durable finish. Most commonly, this material is used for sealants and coatings that are intended for outside use.
When considering the chemical makeup of aliphatic polyurethane, it contains long chains of repeating molecules. Since these chain structures can be chemically manipulated to be more or less flexible and strong, this material is versatile. The term aliphatic refers to the composition of open-chain hydrocarbons.
Moreover, this material dries out to a tough finish, and it is highly resistant to water as well as UV rays. Therefore, this material does not turn yellow when exposed to sunlight. Also, this material has high tensile strength and flows slowly. Therefore, we can easily apply this material as a coating (as a thick film). Since this material easily binds with epoxy, we can easily apply it on epoxy as a sealant. Moreover, this material is commercially available in gloss or matt finish and in various colors.
What is Aromatic Polyurethane?
Aromatic polyurethane is a polymer material containing cyclic, aromatic structures. The structure of aromatic polyurethane differs from aliphatic polyurethane according to the structure of the isocyanate used in the production. If the isocyanate is aromatic, then the polymer material becomes aromatic. The most common aromatic isocyanates are toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), and naphthalene diisocyanate (NDI). Here, toluene diisocyanate is usually used as a mixture of two isomers. Often, TDI and MDI are used for the production of thermoplastic elastomers and foams, but their polymeric forms are used for coatings, sealants, and adhesives.
Figure 01: Synthesis of Aromatic Polyurethane
Aromatic polyurethane has a high glass transition temperature. They are rather brittle, whereas aliphatic polyurethane has a low glass transition temperature and is flexible.
What is the Difference Between Aliphatic and Aromatic Polyurethane?
The key difference between aliphatic and aromatic polyurethane is that aliphatic polyurethane contains a chain structure whereas aromatic polyurethane contains a ring structure. Therefore, aliphatic polyurethane does not contain aromatic rings while aromatic polyurethane contains aromatic rings. Furthermore, the aromatic polyurethane has a high glass transition temperature and is rather brittle, whereas aliphatic polyurethane has a low glass transition temperature and is flexible.
The following table shows more differences between aliphatic and aromatic polyurethane.
Summary – Aliphatic vs Aromatic Polyurethane
The key difference between aliphatic and aromatic polyurethane is that aliphatic polyurethane contains a chain structure whereas aromatic polyurethane contains a ring structure. Moreover, aromatic polyurethane has a high glass transition temperature and is rather brittle, while aliphatic polyurethane has a low glass transition temperature and is flexible.
Reference:
1. “What Is Aliphatic Acrylic Polyurethane?” Hunker, Available here.
Image Courtesy:
1. “Polyurethane synthesis” By Hbf878 – Own work, remade based on File:Polyurethane.png by zh:User:Cyfer (CC BY-SA 3.0) via Commons Wikimedia