**2. Multilayer nonwoven structures for acoustic insulation**

Combinations of different nonwovens, fiber combinations, and integration of process tech-

The definition of nonwovens by EDANA (The European Disposables and Nonwovens Associations) and INDA (The North American Association of the Nonwoven Fabrics Industry), two leader associations in nonwovens market, "A nonwoven is a sheet of fibers, continuous filaments, or chopped yarns of any nature or origin, that have been formed into a web by any means, and bonded together by any means, with the exception of weaving or knitting." Nonwovens are engineered fabrics that can form the products that are disposable, for single or short-term use or durable, with a long life depending on the requirements and

Multilayer or multicomponent nonwovens, also called as composite nonwovens, are the structures of various combinations of materials and processes providing great advantages. There are an increasing number of combinations of spunbonded (S) and meltblown (M) processes as SM, SMS, SMMS, SSMMMMSS, etc., where weaker meltblown fabrics are sandwiched between the stronger spunbonded fabrics. SMS (Spunbond + Meltblown + Spunbond) type multilayer nonwovens, has commercially success, are the best known products. These materials are produced continuously in a single line as well as a discontinuous line is also available. Nonwovens with their bulky, fibrous, and porous structures, one of the most common textile materials, have an important role on sound absorption within the automotive, construction and a variety of industrial uses. Because of the porosity of the structure and the fibers interlocking in nonwovens are the frictional elements that provide resistance to acoustic wave motion. When sound enters into fibrous materials, its amplitude is decreased by friction as the waves try to move through the tortuous passages. Thus, the acoustic energy is converted

In multilayer nonwovens, in accordance with the layers' structural parameters, different fiber intersections and fiber orientations occur. Pore connection and distribution become an important factor in determining acoustic properties because of the flow of sound wave through the material has been affected. Additionally as the number of layers increases or with different layer combinations in multilayer nonwovens, tortuosity and pore geometry will vary and

Many researchers studied and reported sound absorption characteristics of nonwovens/multilayer nonwovens in the literature. Ulcay et al. investigated sound absorption properties of spunbonded nonwovens produced from fibrillated islands in the sea bicomponent filaments with the various numbers of islands 1, 7, 19, 37, and 108. The results, as the effect of the number of islands on acoustical absorptive behavior, showed that spunbonded webs with 108 islands were better acoustic absorbers. Spunbonded nonwovens with the island in the sea bicomponent fibers were also compared with some high loft nonwovens; it has been reported that multilayer nonwovens with 108 islands have better sound absorbing performance [2].

Liu et al. studied the acoustic characteristics of dual-layered nonwovens by analyzing experimentally and theoretically. In experimental analysis, it was defined the sound absorption coefficients of 20 dual-layered nonwoven fabrics with four types of meltblown polypropylene

nologies are an increasingly beneficial option for new product developments.

the intended product life [6, 7].

42 Engineered Fabrics

into heat resulted with sound absorption [1].

different sound absorptions will be provided.

Nonwoven industry had growth substantially for decades prior to the global recession between 2008 and 2010. The worldwide production of nonwovens was primarily based in Europe, North America, and Japan until the last decade. Now, nonwovens are produced on thousands of lines around the world. Asia is now the dominant nonwoven producing region, accounting for 42% of the world's production in 2014 [8]. Nonwoven production by region is shown in **Figure 1**.

The production of nonwovens is carried out in three stages as seen in **Figure 2**. Web formation is the major determinant of the characteristic of final product. The choice of methods for forming webs is determined mainly by fiber type and fiber length. The methods for the web formation from staple fibers were based on the drylaid and wetlaid processes, as well as in spunmelt processes, polymer chips are converted into webs by filament laying.

**Figure 1.** Nonwovens production by region (bubble size in tones of production) [8].

perforated panel, the friction between the moving molecules of air and the internal surface of the perforations dissipates the acoustical energy into heat. The perforations are usually holes or slots, and as with a single resonator, porous material is usually included in the airspace to

Acoustic Insulation Behavior of Composite Nonwoven http://dx.doi.org/10.5772/intechopen.80463 45

In this research chapter, it has been examined that the sound absorption characteristics of SMS type composite nonwovens. SMS structure is a spunmelt structure where the middle layer is the meltblown, sandwiched between the two top and bottom spunbonded layers.

Spunbonded and meltblown methods are both melt spinning method basically, with the shortest textile production line from polymer chips to a web. In the spunbonded method, continuous filaments are extruded directly from thermoplastic polymer chips. The formation of a web of continuous filaments deposited on the conveyor belt is assisted by air suction. Some residual temperature creates a weak bonding effect on the filaments but this is not considered as bonding. The web is then bonded directly by various means, normally thermal bonding. The web obtained is anisotropic. As thickness ranges from 0.2 to 1.5 mm, basis weights from

Meltblown method is similar to spunbond. The hot, molten, low viscosity polymer is forced through nozzles to form a stream of polymer. At the nozzle tip, the filaments are picked up by hot, high velocity air streams that stretch the filaments by drag forces into very fine diameters. The filaments gradually cool as they travel across to the collector, a conveyor band or drum. The use of suction at the collector assists in web formation. The main typical characteristics for meltblown nonwovens are weak tensile properties, porous and capillary structure, isotropic formation, large surface area, etc. As the basis weight of the meltblown webs varies between

Spunbonded structures have a number of advantages as fabric's durability and lower cost in comparison to other nonwovens and woven and knitted fabrics. Meltblown nonwovens are made from microfibers that are much finer than in the spunbonded process. The fibers' fineness makes fabrics that are softer but much weaker than spunbonded materials. Due to the larger volume of fiber per unit weight, meltblown materials have improved fiber distribution and are important to a broad range of functional applications. For example, meltblown fabrics have good barrier properties and high insulating values and thus are used in filtration, barrier materials for medical and disposable apparel and apparel insulation. So together, the combination of spunbonded and meltblown structures can create a strong product which can also offer functional applications. Spunbonded layers act as protective layers for meltblown layers [10–12].

As the bonding method of spunmelt nonwovens, thermal bonding is usually available. Thermal bonding is the process to heat the web where heat is treated with hot rollers, hot air or sound waves. It can be carried out by means of heated calender rollers even after web formation in spunmelt systems. In these methods, fusing fibers act as thermal binders. Important process parameters affecting the web properties are roller temperature, roller speed or contact time and pressure applied to web. Additionally, roller pattern (flat, pointed, etc.) controls the fabric strength, drape, stiffness, and softness. Heating temperature of rollers should be suit-

10 to 200 gsm. Filament thicknesses are between 10 and 80 μm [6, 13, 14].

10 and 350 gsm, the fineness of the fibers ranges from 0.5 to 30 μm [9–11].

able for melting point of the polymer consisting of web [9–11].

introduce damping into the system [30].

**Figure 2.** Nonwovens production stages.

Multilayer or composite nonwovens are produced by a modern and innovative industry that have numerous applications including, but not limiting to, hygiene, medical, filtration, insulation, automotive, agriculture, home furnishing, and packaging. Hygiene is the basic usage of multilayer nonwovens used in numerous products including baby care, feminine care, and adult products. The automotive industry also represents a significant market for application. Also breathable composite nonwovens are available for agriculture market. These materials offer engineering solutions by creating multifunctional products as well as economic solutions [14].

Sound absorbing materials are used in almost areas of noise control engineering to reduce sound pressure levels. They are used in a variety of locations—close to sources of noise, in various paths, and sometimes close to receivers. To use them effectively, it is necessary to:


Synthetic fibrous materials made from minerals and polymers are used mostly for sound absorption and thermal isolation. However, since they are made from high-temperature extrusion and industrial processes based on synthetic chemicals, often from petrochemical sources, their carbon footprints are quite significant. Although polyurethane and melamine foams are probably the cellular porous sound-absorbing materials currently most in use, other types of foams have been designed for environments where heat or corrosion resistance is required. Perforated panel absorbers have been used for many years in noise control usually to confine porous absorbing materials. When spaced away from a solid backing, a perforated panel is effectively made up of a large number of individual Helmholtz resonators, each consisting of a neck, comprised of the perforated panel and a shared air volume formed by the total volume of air enclosed by the panel and its backing. When the sound waves penetrate the perforated panel, the friction between the moving molecules of air and the internal surface of the perforations dissipates the acoustical energy into heat. The perforations are usually holes or slots, and as with a single resonator, porous material is usually included in the airspace to introduce damping into the system [30].

In this research chapter, it has been examined that the sound absorption characteristics of SMS type composite nonwovens. SMS structure is a spunmelt structure where the middle layer is the meltblown, sandwiched between the two top and bottom spunbonded layers.

Spunbonded and meltblown methods are both melt spinning method basically, with the shortest textile production line from polymer chips to a web. In the spunbonded method, continuous filaments are extruded directly from thermoplastic polymer chips. The formation of a web of continuous filaments deposited on the conveyor belt is assisted by air suction. Some residual temperature creates a weak bonding effect on the filaments but this is not considered as bonding. The web is then bonded directly by various means, normally thermal bonding. The web obtained is anisotropic. As thickness ranges from 0.2 to 1.5 mm, basis weights from 10 to 200 gsm. Filament thicknesses are between 10 and 80 μm [6, 13, 14].

Multilayer or composite nonwovens are produced by a modern and innovative industry that have numerous applications including, but not limiting to, hygiene, medical, filtration, insulation, automotive, agriculture, home furnishing, and packaging. Hygiene is the basic usage of multilayer nonwovens used in numerous products including baby care, feminine care, and adult products. The automotive industry also represents a significant market for application. Also breathable composite nonwovens are available for agriculture market. These materials offer engineering solutions by creating multifunctional products as well as economic solutions [14].

Sound absorbing materials are used in almost areas of noise control engineering to reduce sound pressure levels. They are used in a variety of locations—close to sources of noise, in various paths, and sometimes close to receivers. To use them effectively, it is necessary to:

• Identify the important physical attributes and parameters that cause a material to absorb

• Provide a description of the acoustical performance of sound absorbers used to perform

• Develop experimental techniques to measure the acoustical parameters necessary to measure the acoustical parameters of sound absorbing materials and the acoustical perfor-

• Introduction of sound absorbing materials in noise control enclosures, covers, and wrap-

Synthetic fibrous materials made from minerals and polymers are used mostly for sound absorption and thermal isolation. However, since they are made from high-temperature extrusion and industrial processes based on synthetic chemicals, often from petrochemical sources, their carbon footprints are quite significant. Although polyurethane and melamine foams are probably the cellular porous sound-absorbing materials currently most in use, other types of foams have been designed for environments where heat or corrosion resistance is required. Perforated panel absorbers have been used for many years in noise control usually to confine porous absorbing materials. When spaced away from a solid backing, a perforated panel is effectively made up of a large number of individual Helmholtz resonators, each consisting of a neck, comprised of the perforated panel and a shared air volume formed by the total volume of air enclosed by the panel and its backing. When the sound waves penetrate the

pings to reduce reverberant build up and hence increase insertion loss.

sound.

44 Engineered Fabrics

specific noise control functions.

mance of sound absorbers.

**Figure 2.** Nonwovens production stages.

Meltblown method is similar to spunbond. The hot, molten, low viscosity polymer is forced through nozzles to form a stream of polymer. At the nozzle tip, the filaments are picked up by hot, high velocity air streams that stretch the filaments by drag forces into very fine diameters. The filaments gradually cool as they travel across to the collector, a conveyor band or drum. The use of suction at the collector assists in web formation. The main typical characteristics for meltblown nonwovens are weak tensile properties, porous and capillary structure, isotropic formation, large surface area, etc. As the basis weight of the meltblown webs varies between 10 and 350 gsm, the fineness of the fibers ranges from 0.5 to 30 μm [9–11].

Spunbonded structures have a number of advantages as fabric's durability and lower cost in comparison to other nonwovens and woven and knitted fabrics. Meltblown nonwovens are made from microfibers that are much finer than in the spunbonded process. The fibers' fineness makes fabrics that are softer but much weaker than spunbonded materials. Due to the larger volume of fiber per unit weight, meltblown materials have improved fiber distribution and are important to a broad range of functional applications. For example, meltblown fabrics have good barrier properties and high insulating values and thus are used in filtration, barrier materials for medical and disposable apparel and apparel insulation. So together, the combination of spunbonded and meltblown structures can create a strong product which can also offer functional applications. Spunbonded layers act as protective layers for meltblown layers [10–12].

As the bonding method of spunmelt nonwovens, thermal bonding is usually available. Thermal bonding is the process to heat the web where heat is treated with hot rollers, hot air or sound waves. It can be carried out by means of heated calender rollers even after web formation in spunmelt systems. In these methods, fusing fibers act as thermal binders. Important process parameters affecting the web properties are roller temperature, roller speed or contact time and pressure applied to web. Additionally, roller pattern (flat, pointed, etc.) controls the fabric strength, drape, stiffness, and softness. Heating temperature of rollers should be suitable for melting point of the polymer consisting of web [9–11].

One of the applications in thermal bonding in spunbonded process is producing web consisting of bicomponent fibers. Bicomponent fibers contain two different polymers extruded together from the same spinneret to compose a single fiber cross section. The properties and applications of bicomponent fibers depend on both the properties and distribution of the polymers in the cross-sectional area. Accordingly, typical configurations are side by side, core/sheath, island in the sea, sliced, pie slice, etc. The most commonly used in nonwovens and well-known binding bicomponent fibers is sheath/core type. When a bicomponent nonwoven web is heated sufficiently to melt the sheath, polymer melts and flows to the nearest adjacent fiber and binds the structure. It is recommended that the melting temperature difference between the components should be at least 40°C for proper bonding. Lower bonding temperature is provided by bicomponent fibers than in a typical thermal bonding application. Additionally, with this method, some structural parameters of a nonwoven fabric, such as fabric density, fiber diameter, tortuosity, porosity, etc., will be affected [15, 20].
