Reviewed by Raghvendra GopalCheckmark
Last updated: April 10, 2019

What Does Hygroscopic Mean?

The term hygroscopic refers to a matter's ability to hold, adsorb and attract water from the surrounding environment. This process of absorption usually occurs near ambient or room temperature. This term originates from a 1790s device called a hygroscope, which was made to measure humidity. It did this by measuring changes in hygroscopic material, such as wool.

Hygroscopic substances are hydrophilic, which means they like water. Supporting hydrogen bonding and being polar are some of the chemical properties of hygroscopic matter. Hygroscopic substances are sometimes capable of dissolving in water and do so readily, but some do not, such as nylon.

During the hygroscopic absorption process, there are four components that work together to achieve this phenomenon. These are: polarity, absorption, adsorption and capillary action.

  • Absorption: A liquid substance enters the body of a material.
  • Adsorption: Molecules are held on the surface.
  • Capillary action: Water is pulled in through pores and narrow spaces due to the adhesive and cohesive properties of water.

Some common examples of hygroscopic substances include:

A good number of fibers and porous materials tend to be hygroscopic. Some of these you might encounter on the daily:

  • Table salt (sodium chloride).
  • Ethanol.
  • Methanol.
  • Caramel.
  • Brown sugar.
  • Paper.
  • Wool.

Hygroscopic substances are capable of causing corrosion in metals and other materials.


Corrosionpedia Explains Hygroscopic

Hygroscopic substances are capable of adsorbing and absorbing water from the surrounding area, eventually leading to damage and failure in various systems, equipment and machinery. Therefore, proper measures should be developed in order to inhibit corrosion. One method to analyze this is to accurately measure the humidity or the water vapor content present in the air using a hygrometer.

A hygrometer can gauge not only the dimension of substance changes through water vapor absorption, but also things such as physical and chemical property changes and vapor condensation.

Moreover, tests such as static loss of mass can be conducted in order to investigate the corrosive behavior of hygroscopic matter. With such, the hygroscopic substance is exposed to various corrosion inhibitor environments or solutions to determine the best way to inhibit hygroscopic corrosion. Finding the best inhibitor can significantly reduce the corrosive effects of hygroscopic substances.

Hygroscopic substances are useful for keeping products dry or removing water from an area. It may be necessary to add hygroscopic materials to products because of their ability to attract and hold moisture.

Rust, mold, mildew, rot, decay, warping, stretching, lumping, caking, agglomeration and decomposition are all common problems stemming from the presence of moisture or humidity.

The storage, manufacturing and transportation of materials often takes place in a humid environment not conducive to the moisture sensitivity of the materials. This issue can lead to the deterioration of stored materials, machinery and equipment, resulting in reduced product output and increased costs.

Improperly controlled moisture levels can trigger rusting behaviors in steels and coatings, as well as cause complications, in the pharmaceutical Industry. Decomposition and difficulty in tablet compression are common issues. Improper moisture levels can lead to the dry powders in tablets breaking, lumping and caking. It can even prevent the drying of gelatin capsules.

Hygroscopic materials, along with moisture measurement and control, are some of the ways to help regulate humidity and moisture issues in manufacturing.


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