Polyurethanes: Definition, Preparation, Properties and Application

What is Polyurethane?

Polyurethane (PU) is a polymer having organic units joined by urethane (also known as carbamate). Urethane is a compound that has an O-R group and an NH-R group bonded to the same carbonyl carbon.

Structure-of-Polyurethane

Polyurethanes are thermosetting polymers but their thermoplastic variants are also available in the market. Polyurethanes are prepared by the polymerization of toluene-2,6-di-isocyanate and ethylene glycol. If the reaction is carried out in the presence of a blowing agent, the product is polyurethane foam.

Preparation of Polyurethanes

Polyurethanes are formed by reacting a polyol (an alcohol with more than two reactive hydroxyl groups per molecule like ethylene glycol) and di-isocyanate or a polymeric isocyanate in the presence of suitable catalyst and additives.

Preparation-of-Polyurethane

Properties of Polyurethanes

1. Polyurethane has high load capacity in both tension and compression that may change shape under heavy load but will return to its original shape once the load is removed with little compression.

2. Polyurethanes possess high fear resistance along with high tensile properties.

3. Polyurethane material will remain stable with minimal swelling in water, oil, and grease.

4. Polyurethanes exhibit good electrical insulating properties.

Applications of Polyurethanes

1. Polyurethane foam is used for furniture stuffing, carpet backings, and insulation.

2. One of the most important uses of polyurethanes is in fabrics with elastic properties, such as spandex.

3. Polyurethane materials are commonly formulated as paints and varnishes for finishing coats t protect or seal the wood.

4. Polyurethane is also used in making solid tires and garments.

Popular Posts

Conducting Polymers: Definition, Examples, Properties and Applications

Image
What are Conducting Polymers? As the name suggests organic polymers that conduct electricity are known as conducting polymers. They are also known as intrinsically conducting polymers (ICPs) and they have alternating single and double bonds along the polymer backbone (conjugated bonds) or that are composed of aromatic rings such as Phenylene, naphthalene, anthracene, pyrrole, and thiophene which are connected through carbon-carbon single bonds. Examples: Polyacetylene, Polypyrrole, Polyaniline, etc What is the reason behind conducting nature of these polymers? Conducting polymers comes in two forms that are doped conducting polymers and non-doped conducting polymers. The conductivity of non-doped conjugated polymers is due to the existence of a conductivity band similar to a metal. In a conjugated polymer, three of the four valence electrons form strong sigma bonds through sp² hybridization where electrons are strongly localized. The remaining unpaired electron of each carbon atom re
Read more

Crime Scene: Definition, Types and Characteristics

Image
What is a Crime Scene ? A place where the crime is committed or where the maximum physical evidence related to crime is found is known as a crime scene. A crime scene is a starting point of the investigation which provides information about the suspect and the victim. This helps to reconstruct the crime and fast resolution of the case. It is noted that the crime scene is not limited to a single place but may extend to a wider area depending upon the nature of the crime committed. For example, In a murder case where murder is done at one place and the body is disposed on another place. In this case, we have two crime scenes that give information about the crime. Types of Crime Scene Based on evidence found on the crime scene: 1. Primary Crime Scene The crime scene where the actual crime occurred or where more usable pieces of evidence were found is known as the primary crime scene. For example, A murder scene, theft, assault, etc. 2. Secondary Crime Scene The crime scene which is some
Read more

Documentation of the Crime Scene: Step by Step

Image
What is documentation of the crime scene and Why it is done? After securing the crime scene, the next most important step is documentation of the crime scene because documentation permanently records the crime scene and its physical evidence. Documentation should be done without any wastage of time as the scene and its evidence may get altered over time. The documentation should be done innovatively and the originality of the crime scene should be maintained and documentation should not have pauses or breaks, it should remain constant till the whole crime scene is documented. There are four main tasks of documentation that is note-making, photography, videography , and sketching . It should be noted that all four tasks are necessary and none is a substitute for another. For example, notes are not substitutes for photography, video is not a substitute for sketching, etc. Following are the sequence for crime scene documentation: 1. Note making Documentation of crime scene in the f
Read more