Surely many people have heard this word more than once and even, perhaps, wondered how exactly it is spelled and what it means. But not everyone is aware that knowledge about this physical property of materials can be useful in everyday life. That is why we will get to know him better.
Definition
Hygroscopicity is the property of any material to absorb and retain moisture from the air. The letter "r" in the first part of the word may confuse some, because we all know that complex terms related to water usually begin with the prefix "hydro". But here we are talking about something else. Hygroscopicity takes into account the absorption by materials of only the water that is sprayed in the air in the form of steam, which means that a completely different attachment is needed. "Hygro" means that the word has to do with humidity. It's simple.
We've sorted out the definition, and now it's time to find out what this word actually means. The air around us has a certain humidity - even the weather forecast says this. Some fibers are able to absorb this water, often changing their properties in the process. It is thanks to the hygroscopicity of clothes and shoescan get wet even without rain. In what cases it is good, and in what cases it is bad, we will find out below.
Which materials are hygroscopic?
This article will focus mainly on fabrics. But not only they know how to absorb moisture from the air. The indicator of hygroscopicity of a material is often necessary to know for builders, furniture makers, manufacturers of complex equipment and many others.
For example, we all know that wood has a porous structure, which increases its hygroscopic properties. Water, penetrating into the structure of the tree, deforms it. That is why wood furniture is practically not installed in rooms with high humidity. To reduce hygroscopicity, special impregnations can be used.
No less important are the hygroscopic properties of insulation used in construction. The air in the pores of the material retains heat in the room. But if the insulation gets wet, it will instantly lose its basic properties. Therefore, the materials used for these purposes must have a minimum hygroscopicity. The ideal indicator is 0%.
Hygienic properties of fabric
All materials have different physical characteristics, such as density, strength, etc. But for fabrics that should later turn into wardrobe items, other properties are also important - hygienic. They determine how comfortable clothing will be made from a particular material.
- Breathability. The name speaks for itself. High performance fabricsbreathability is able to "breathe", and with low - protect from the wind.
- Vapor permeability. The ability of a fabric to let moisture through to wick sweat and other fluids away from the body.
- Water resistance. Protects the body from fluids. This property of the fabric is increased with the help of various impregnations and polymer coatings.
- Dust capacity. This property allows the fabric to hold small particles on its surface. The looser the material, the higher the dust capacity.
Electrifying - the ability of a fabric to accumulate static electricity
Do not forget about the heat-shielding properties of the fabric. This is the ability to maintain a normal body temperature when it is cold outside. Let's talk about the last property in more detail.
Hygroscopic fabric
This indicator refers to the hygienic properties of textiles, which, in turn, determine the comfort of a particular material when worn. Moreover, the requirements for clothing largely depend on its purpose.
Hygroscopicity is the most important property of a sports uniform or summer clothing. Increased air and body temperature leads to profuse sweating, which, in turn, creates considerable discomfort for a person. It is the high hygroscopicity of the fabric that allows you to get rid of excess moisture. This property is also the most important indicator for manufacturers of everyday underwear.
What determines the ability of a fabric to absorb moisture from the environment? First of all, from the fibers from which it is made. In addition, the presence of protective coatings and impregnations is important.
Types and hygroscopicity of fibers
Materials from which fabrics are made can have different origins. There are natural fibers and synthetic ones. First, let's talk about the first. They are created by nature itself, although not without human participation.
Wool, sheared from various animals, is most often used to make warm clothes. It is she who is one of the leaders among natural fabrics in terms of the ability to absorb moisture. The hygroscopicity of wool fibers is approximately 15-17%. But the moisture absorption rate is relatively low.
This figure is much higher for many other fabrics. For example, the hygroscopicity of cotton is only 8-9%, but it is able to absorb moisture much faster than wool. Another natural material is flax, obtained from bast fiber. Its ability to absorb moisture can range from 12 to 30%.
Artificial and synthetic fibers
The first type includes materials obtained from natural compounds. A prime example is viscose. It is created using natural cellulose. Viscose fibers are characterized by strength, heat resistance, and high hygroscopicity, equal to almost 40%.
Synthetic fibers are made from oil and coal products. These include polyamides. Nylon, nylon and anide are made from these fibers. The hygroscopicity of such materials is quite low, only 3-4%, but they retain tensile strength andvery durable. Polyester fibers, from which lavsan fabric is made, have a high rate of heat resistance and light resistance. But their hygroscopicity is minimal - only 0.4%.
The polyurethane fibers that are the basis for lycra and spandex also do not have the ability to absorb moisture from the environment. From the foregoing, we can conclude that the hygroscopicity of clothes made from synthetic materials is much lower than things made from natural fabrics. But is it really a disadvantage?
Hygroscopicity - good or bad?
Everything in the world is relative. The same can be said about the topic we have raised. It cannot be unequivocally said that hygroscopicity is good. Yes, it allows people to survive the heat more easily, and athletes to perform exercises in more comfortable conditions. But for some fabrics, too much moisture can only hurt.
Using the example of insulation, we have already found out that water reduces the thermal insulation properties of materials. In addition, some fabrics are deformed by moisture - we all know how knitwear stretches after washing. The same fate, only on a smaller scale, can befall some materials at very high relative humidity. Therefore, it is not always possible to say with certainty that the hygroscopicity of the fabric is a plus. The question is the purpose of this or that material.
How is this indicator determined?
In the 80s of the XX century, GOST 3816-81 was created in the USSR. It contains a detailed description of the methodsdetermination of some properties of textiles, including hygroscopicity. Here's how it works.
Specialists take samples of fabric measuring 5 x 20 cm and each is placed in a separate cup for weighing. The main objective of the experiment is to find out how much water the material will absorb under certain conditions. To do this, a glass with a sample is placed in a desiccator, in which the humidity of the air is 97-99%. After 4 hours, the sample is weighed, and after that, at a temperature of 105-109 ° C, the material is dried and its new weight is determined.
The hygroscopic index (H) as a percentage is determined using the formula: H \u003d (Mv - Ms) / Ms x 100, where Mw and Ms are taken, respectively, for the mass of wet and dry tissue.
