Energy efficiency implies reducing energy consumption without reducing comfort or quality of life, protecting the environment and ensuring the supply of future generations. This means meeting the needs of the present without compromising the future.
On the other hand, noise pollution is a very present environmental problem in modern society due, among other things, to the development of industrial activities and transportation. For the World Health Organization , noise is one of the factors that causes more diseases and has to be considered a health problem.
All these aspects must be taken into account in the design and operation of buildings. To protect them as much as possible from aggressions due to noise and as a first step to achieve their energy efficiency, it is essential to provide them with good acoustic and thermal insulation .
Natural fibers used as insulators
A porous material between two partitions improves acoustic and thermal insulation. Porous synthetic materials, such as rock wool or glass wool, are common solutions.
A promising and eco-friendly alternative can be porous nonwovens made from natural or recycled fibers . These fibers are not harmful to health and are available in large quantities, often as waste products from other production cycles.
In some countries, the use of natural fibers such as fique or coconut represents a great economic interest for the agricultural sector. By promoting the use of natural fibers, the growth of demand is favored and, therefore, an increase in the income of the producers and the countries that produce these fibers. In addition, society is increasingly aware of the need to reuse waste and to use what nature provides, avoiding the growing consumption of scarce raw materials.
A second life for textile waste
Another example of these porous natural materials is that made from the fibers obtained from the fraying of recycled cotton garments, which serves to dispose of textile waste that ends up in landfills. Some companies and organizations use this textile fraying technique to convert the fibers obtained into products such as blankets and rags for the automotive industry.
In a recent study, a group of researchers used material made from cotton fibers obtained by shredding recycled jeans using a blade mill.
The fibers are intertwined to produce a fabric using the punching technique. In the punching machine, the fibers pass through a board of needles provided with projections that move up and down at high speeds, intertwining them. In this way, a network of mechanically bonded fibers is achieved without using any type of binder.
The performance of the resulting material varies depending on its density. For a density of 80 kg / m³ and a thickness of 2.5 cm, the material has a thermal conductivity of 0.038 W / mK. This figure is less than 0.05 W / mK, a value below which a material is classified as thermal insulator, and is comparable to traditional materials.
To describe the acoustic behavior of the material, the acoustic absorption coefficient is used, whose value ranges between 0 and 1. For each frequency, a value close to zero indicates that the material reflects almost all the incident sound energy and a value close to one, that most of the incident sound energy is dissipated in the material. The material is then said to be absorbent. The porous structure of the manufactured material favors this absorbent behavior.
The NRC ( Noise Reduction Coefficient ) index calculated as the arithmetic mean of the absorption coefficient values for the frequency bands between 250 and 2000 Hz is 0.51 for the material based on textile fibers. A figure comparable to the 0.53 that results for mineral wool.
It is also possible to verify the improvement in acoustic insulation that the use of the designed material would entail, paying attention to the changes in the global acoustic reduction index to airborne noise. This variable represents the difference between the insulation of the basic structural element with the additional layer of material and without that layer. Again, the improvement introduced by the material designed with textile fibers is comparable to that obtained with mineral wool.
If we compare the manufacturing process of the product from textile waste with that of other insulators used in construction, the CO₂ emissions that are generated are lower.
However, the environmental impact caused by a process or product must be analyzed objectively and scientifically, including all its stages: acquisition of raw materials, product manufacturing, distribution and transportation, use and maintenance, and waste management. On many occasions, the emissions generated during the management of textile waste depend on how it is carried out and are lower in those processes that require less transport.
The ideal situation would be to have the center that provides the textile waste and the one that generates the material together, that is, to make sustainable products, production and consumption should be local and avoid long-distance transport.
Urban waste is of increasing concern due to its exponential increase in recent years. The regulations establish that from 2025 the selective collection of textile waste will be mandatory , which will facilitate the development of solutions of this type. From 2030, no waste that can be reused or recycled can be thrown into landfills. The panorama that opens before us is impressive and research on new materials is a key option to contribute to the fulfillment of these objectives.
María Ángeles Navacerrada Saturio , Associate Professor of the Department of Structures and Physics at ETSAM. Head of the architectural acoustics research group, Polytechnic University of Madrid (UPM)