Deniz Duran1, Hatice Aktekeli2
1Ege University – Faculty of Engineering – Textile Engineering Department.35100 Bornova, İzmir/TÜRKİYE
2Ege University – Faculty of Engineering – Textile Engineering Department., 35100 Bornova, İzmir/TÜRKİYE
Elastic Nonwovens and Application Areas
Nonwoven surfaces have become one of the fastest-growing textile branches in recent years, which significantly stems from the practical use of disposable products, and awareness on its importance in terms of hygiene. It is desired that nonwoven surfaces used in some areas should have high flexibility in terms of comfort and ease of use and maintain this flexibility. For this reason, there is a day-by-day increasing interest in flexible nonwoven surfaces. In this study, the definition of flexible nonwoven surfaces, methods for obtaining flexible nonwoven surfaces and their application areas are specified.
Key Words:Nonwoven surface; Flexible nonwoven surface; Elastic nonwovens; Thermoplastic elastomer.
In the globalizing world, it has become a necessity to manufacture innovative products for the development of our industry and economy. Cost and speed are two of the most important factors in the production phase. In this area, nonwoven surfaces allow us to find fast, easy, effective and economical solutions to problems with their wide use at every stage of modern life. Nonwoven surface products offer manufacturers the advantage of simplicity in the manufacturing process and the ability to apply desired qualities (absorbent/retaining, soft/stretched etc.) to nonwoven surface products as they require a manufacturing process simpler than the conventional textile fabrics. 
Nonwoven surface products, which are manufactured in a fashion both faster and cheaper, are being used more ever day in new areas. Especially the increase in the practical use and usage habits of disposable products allow mobility in the nonwoven surface industry and caused the market to grow. When examining Turkey’s 22 main product groups in the technical textiles export, it is observed that nonwoven surface products constitute the most exported product groups of Turkey’s technical textile exports. Nonwoven surface products which form 30,9% of Turkey’s total exports of technical textiles (nonwoven) exports in 2017 were valued at approximately 479 million dollars, increasing by 9,5%. When examining the technical textiles imports in Turkey’s 22 basic product groups, it is seen that nonwoven surface products are the second imported products with 11,5% after glas fiber and their products. In 2017, imports of nonwoven surface products increased by 12% to approximately $ 220 million. [1, 2]
Demand for nonwoven surface products is increasing day by day and it is predicted that over the coming years the numbers will exceed today’s value. 
In the field of nonwoven products, products with a high degree of flexibility at low cost is constantly needed. these nonwoven products are being produced especially for disposable diapers, sick cloths and also areas such as lining, and filtration. They are preferred for flexibility, softness, durability, good stretch-backing properties and high tearing elongation features. 
There are also literature studies on elastic nonwovens –an important issue in innovations which have taken place in the nonwoven surface area in recent years.
In a study by Srinivas et al., they treated polypropylene homopolymer and thermoplastic elastomer (TPE) under the same conditions and observed a marked difference in elongation properties. The polypropylene homopolymer is only 35% elongated, while the surfaces produced with thermoplastic elastomer (TPE) can be elongated up to 360%. According to Srinivas et al., molecular parameters such as molecular weight, molecular weight distribution, composition, melting temperature and crystallinity grade affect the elastic behavior of the polymer. The elasticity of the web is related to the molecular weight and the specific elastomeric composition. As expected, low crystallinity requires high elasticity. As the level of crystallinity increases, the mechanical behavior of the polymer changes from an elastomeric character to a plastic one.
Zhao states in his work that the industry focused on the meltblown process to develop unique fiber and surface properties using special polymers, and that many factors are needed to develop high-value meltblown products, among which polymer properties, targeted areas of use of the product, and properties and capabilities of meltblown equipment are mentioned. Polypropylene nonwovens produced with the meltblown method have attracted more attention in areas such as hygiene, medical and personal care products with high flexibility of nonwovens made of elastic raw material, although they may have one-sided stretching properties. 
Dharmarajan et al., used the meltblown method in their work for surface preparation and have blended thermoplastic elastomer (TPE) and classical polypropylene on some samples. Inclusion of polypropylene thermoplastic elastomer increases the elongation of the nonwoven surface. Surface elasticity increases with increasing TPE ratio. Even 30% weight of TPE content makes the surface softer and drapery than polypropylene. In the light of these results, they have stated that meltblown elastic nonwovens containing TPE polymers have offered a new elastomeric product, which can be used in hygiene, personal care, medicine and industrial applications. 
Li et al. used the thermoplastic elastomer in their study to produce a surface with the meltblown method. According to Li et al., the elastic meltblown nonwovens have incomparable advantages over ordinary meltblown surface. Therefore, they have stated that this material is the new favorite in the nonwoven industry and elastic nonwovens produced with the meltblown method using TPE are high elastic materials which can solve the low elasticity problem of the conventional nonwovens. 
- ELASTIC NONWOVENS
Materials imposed to deformeation under pressure (elongation/ change of form) and reverted to its original state when unpressured are called elastic materials, and such deformations are called as elastic deformation. Mechanical creep (almost) does not occur. 
Elastic nonwovens are products, which exhibit superior elongation/reversibility compared to conventional nonwoven surfaces. While the elasticity on the conventional nonwoven surfaces is around 30%, it can reach 300% on elastic nonwoven surfaces. 
The limited resilience of the surfaces produced using conventional synthetic raw materials causes limitations in their usage and application. On surfaces produced using special thermoplastic elastomers (TPE), this problem can be avoided and highly elastic surfaces can be created (Figure 1). This will allow limitations and combine with the advantages of meltblown method to find a more common and convenient area of use. 
Elastic nonwoven surface before stretching Elastic nonwoven surface after stretching
Figure 1. Elastic nonwoven surface before and after stretching 
2.1. Elastic Nonwoven Production Methods
Elasticity can be achieved in the texture in different ways. The most important ones are:
2.1.1. Customized voluminous design for nonwoven web structure
Voluminous web structure can be achieved by needle method in particular. In this method, the fibers are laid smoothly on top of each other to form a surface and fixed with special needles to form a web surface. However, the surfaces produced in this method can be too thick and show little flexibility.
2.1.2. Achieving elasticity in materials using crimp fibers
As the crimp fibers on surfaces produced by using crimp fibers are opened under pressure, the surface will stretch and revert to its original state when unpressured. However, the flexibility obtained by this method is very insufficient.
2.1.3. Production using special meltblown method with raw materials
The meltblown method does not require a special preparation process to form the surface, nor does it need to prepare any solution to draw fibers. Fibers are taken directly from the polymers.
In the meltblown method, the special thermoplastic material (TPE) is heated in the extruder and melted up to the temperature and viscosity to provide the fiber formation. The melt is sprayed through the nozzle holes at high speed with a flow of hot air, and these micro-sized fibers become cool and solidify as they move towards the pick-up cylinder. The solidified fibers randomly orientated in the picking cylinder create the elastic nonwoven surface. 
2.1.4. Production with finishing operations such as coating
The nonwoven surface is created by covering one or both sides of the surface with a chemical substance. The chemical materials are applied on the surface in the form of powder, paste or foam to form a film layer on the ground. 
2.1.5. Production with composite technology
Composite materials are a group of material, which are created by bringing together at least two different materials for a specific purpose. The purpose in this three-dimensional assembling feature is to create a feature, which is not present in any of the components alone. In other words, it is aimed to produce a material with superior properties for the desired components. 
The elasticity of the web produced with the first two methods is limited while they have excessive thickness. Flexibility of the web obtained with the coating method is not at the desired level. It has been seen that problems are solved in the web produced using TPE chips. 
- THERMOPLASTIC ELASTOMER (TPE) – RAW MATERIAL FOR ELASTIC NONWOVENS
Crosslinked rubbery polymers, or rubbery webbands, which exhibit very high elongation under tensile force and revert to their original initial length when the force is lifted, are called elastomers. The most commonly used and known elastomers are polyisoprene (or natural rubber), polybutadiene, polyisobutylene and polyurethane.
Thermoplastic elastomers (TPE’s) are polymers that exhibit elastomer behaviors, even though they do not have chemical cross-links between their molecules.
The physical cross-links in the TPEs constitute the webbing structure by interlocking the flexible molecules together. They can be processed as thermoplastics at high temperatures and exhibit elastomeric behavior when cooled (Figure 2). The transition from thermoplastic behavior to elastomeric behavior is completely reversed, i.e. unlike conventional elastomers, thermoplastic elastomers can be processed repeatedly, so they can be recycled. 
Thermoplastic elastomers contain two distinct phases in their texture:
- Elastomeric phase with rubber features
- Rigid phase with thermoplastic features. 
Figure 2. Temperature change in the thermoplastic elastomer structure 
- APPLICATION AREAS OF ELASTIC NONWOVENS
Elastic nonwovens find use in the fields of filtration, medicine and hygiene as soft protective cap, lining and gloves.
- Medicine and Hygiene
Research and development studies in both fiber types, in which materials used in medicine and hygiene applications are produced, and in the production techniques of such materials, cause the increase in the use of medicine and hygiene textiles in all technical textiles every day. 
The fastest developments in medicine and hygiene textiles have occurred after the discovery of synthetic fibers. Rapid developments have been achieved with the invention nonwoven products in the 1960s, and improving a 56% reduction in the risk of infection transmission with the use of disposable products in 1985. 
The most important use of nonwovens is the hygiene industry. In a report published by EDANA – European Nonwoven Producers Association, 35 billion products have been sold in the European hygiene market in 1997, 90 billion in 2004 and 211 billion in 2013 (Figure 3). 
Figure 3. The number of nonwoven products sold in the European hygiene market
Especially the elastic nonwoven medical bandages exhibit excellent stretching, wrap the wound well, hel healing quickly and leave only a small trace. Patients using them feel comfortable and at ease.
Its porous structure allows skin moisture to penetrate and the skin to breathe. Its elastic structure easily conforms to body folds and joints.
In addition, these elastic nonwoven materials also find use in areas such as patients and diapers (Fig. 4), menstrual pads, and in hospital equipment such as surgical disposals and gowns that require disposability, non-slipperiness and elasticity. 
Figure 4. Patient diaper with elastic nonwoven materials 
- Soft Stretching Caps
It significantly increases comfort, safety and work efficiency for workers. It is non-irritant, soft-textured and has high tensile strength with low shrinkage force. They have a breathable structure for perfect comfort and ease. It provides excellent barrier treatment and filtration performance (Figure 5).
- For use in construction, mining, health and waste management to prevent dirt, dust, airborne particles and airborne liquids,
- For protection against dust, bacteria and harmful chemicals in laboratories and factories,
- For shielding against outdoor activities, wind and rain,
- In order to provide good bacteria and particulate filtration in medical use,
- It can be used for undercoating in hard caps, emergency respiratory masks and other face protection equipment. 
A study conducted by researchers at the University of Tennessee, USA, of Materials Science and Engineering reveals that the use of elastic nonwoven as a primer in military apparel shows better filtering features against chemical and biological threats.
Also, undercoating made of such structures in sportswear and women’s clothing helps show the body better. 
These structures, produced using microfiber fibers, have great market share thanks to their superior filtration performance.
These elastic nonwovens, which can also be used in production of masks, provide protection against gas, dust and bacteria in the medical field by preventing harmful granules (Figure 6). Also these filters can be used in AC units, automobiles and engines.
Figure 6. Mask with elastic nonwoven material 
Elastic nonwoven gloves are used in pharmaceutical factories and research laboratories, where high protection is required thanks to their excellent stretching, absorbing and filtering features. 
Elastic nonwovens provide balanced mechanical features thanks to better elongation for increased flexibility, higher impact strength, higher melt flow rate for easier machining, lower cost and higher performance in comparison with conventional nonwovens. Especially on machine applications, they exhibit better breaking resilience and tearing prolongation. 
Thanks to these features, the application area for elastic nonwovens is growing day by day. The studies conducted in this area is also increasing every day. Interest and researches in the elastic nonwovens, which is considered to be one of the important branches in nonwoven industry, are increasing thanks to the improvements in living standards rising with awareness on the importance of disposable products especialy for health, advanced level of improved product performances and the R&D activities conducted by the leading companies to grow their market domination.
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