Poster in Oct 18, 2023 14:57:04

NONWOVEN TECHNOLOGY FOR UNCONVENTIONAL FABRICS

NONWOVEN TECHNOLOGY FOR UNCONVENTIONAL FABRICS

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(1.) INTRODUCTION TO NONWOVENS 

We know that nonwoven fabrics are one of the oldest and simplest textile fabrics. Its classic example is felt. The first well-documented discovery of felt dates back 3500-3000 BC. It was made from the hairs of various animals. The term Nonwoven fabrics was applied to new modern techniques, which were totally based on new principles, by the U.S.A. in 1965. "Non-woven fabrics" is being defined in different ways by different literatures; the term defined by "Textile oregano" in 1965 is as follows: 

"Nonwoven fabrics are products made of parallel laid, cross, or randomly laid webs bonded with the application of adhesive or thermoplastic fibers under the application of heat and pressure."

In other words, nonwoven fabric can be simply defined as a fabric that can be produced by a variety of processes other than weaving and knitting. The nonwoven fabric properties depend on the following particulars to a great extent, 

1. The choice of fibers 

2. Technology which determines how the fibers are to be arranged

3. The bonding process and the bonding agent

Fabric properties of nonwovens range from crisp to soft-to-touch to harsh, impossible-to-tear to extremely weak. This leads to a wide range of end products such as nappies, filters, teabags, geotextiles, etc. some of which are durable and others are disposable. The first stage in the manufacturing process of nonwoven fabrics is the "production of the web" and another is the "bonding of the web by using several methods". Some of those (binding methods) are felting, adhesive bonding, thermal bonding, stitch bonding, needle punching, hydro-entanglement, and spin laying.

 (2.) RAW MATERIALS 

(2.1.) FIBROUS MATTER 

The definition of nonwoven fabrics states that fibers are held together by a bonding agent to form a fabric. The art of choosing the right fiber to combine with the right binder by the most efficient process to obtain a desired fabric is the absolute goal of nonwoven manufacturing. Virtually all types of fibrous material can be used to make nonwoven bonded fabrics, the choice being dependent on: 

* The required profile of the fabric 

* The cost/ use ratio (cost-effectiveness) 

* The demands of further processing

Since nonwoven bonded fabrics are almost always developed to meet specific requirements, the correct choice of fiber is of supreme importance. It is not only a question of finding the best kind of fibers, but of taking special properties of the fiber concerned into consideration. It is essential for the development and production of nonwoven bonded fabrics for a comprehensive study to be made of the properties of different fibers. This can be done by comparing the requirements to be met by the particular fabric with results obtained from the various individual fibers. The fibers used in the greatest volume in nonwoven fabrics today are cotton, rayon, acetate, nylon, and wool. Synthetics, such as polyesters and acrylics, are being used increasingly, not necessarily to replace cheaper fiber but in fabrics intended for new and more exacting applications. Finally, the very newest fibers are modifications of standard types to make them especially adaptable to nonwovens, e.g. self-bonding viscose rayon and the synthetic polymeric fibers known as "fibroids". 
Cotton 
Although the early cotton nonwoven made exclusively from low-cost, low-grade cotton waste has almost disappeared from the market, cotton in various forms is still used extensively in nonwoven fabrics. The cotton used today may be a waste, such as a comber, and will produce a soft, absorbent nonwoven fabric with good bulk and bonding properties. The practice of blending various fibers affords the opportunity to use clean inexpensive grades in blends with the more uniform man-made fibers. The principal uses for cotton are in disposables and medical textiles, which together absorb about 30% of the total poundage, although many other fibers are now used in these fields along with cotton. 
Rayon 
Of the man-made fibers rayon (viscose) has been the leader in bringing about changes in the industry and today finds practical use in a wide variety of fabrics. This popularity is due to the following factors: 
* Low cost. 
* Ease of processing on all types of web-forming and bonding equipment. 
* A wide variety of descriptions, i.e., range of deniers, range of lengths, range of finishes, crimped and uncrimped, bleached and unbleached. 
Where added softness, dull whiteness, high bulk, and absorbency are essential, as in surgical and sanitary applications, the low-denier, dull, bleached, crimped fibers are generally used. For filtration of fine particles, one denier finds application, while deniers as coarse as 40 or more may be used in air filters where the semi-rigid, coarse open structure is desired. Blending of a variety of deniers is often necessary in a single product. 
Acetate 
Prior to the use of rayon in nonwovens, a plasticized acetate had been developed as a bonding fiber for cotton webs, and it is still used in this way with both rayon and cotton. However, is in the unplasticized form in both fine and coarse deniers as regular, bright, or dull crimped fiber. Its low price, good dimensional stability, thermoplasticity, mildew resistance, and low moisture absorption combine to make this fiber particularly attractive for many dry-processed nonwovens where strength is not a major factor. 
Wool 
The use of wool in nonwovens has been limited by its price and by the inability to utilize its characteristics to the best advantage in the early types of nonwovens. Now wool is being used in applications where bulk, warmth, and loft retention are important. Usually, either a waste or a reworked staple is blended with synthetics to reduce fabric cost. 
Polyamides and polyester 
25-50% of polyamide or polyester may be used in nonwoven fabrics for interlinings, particularly where wash-and-wear characteristics are important. Applications requiring exceptional resistance to flexing, abrasion, or chemicals, with price only a secondary factor, may use 100% of these fibers in blends of low and high-softening type to form both structure and bonding media, e.g., nonwoven polyester tapes for electrical applications. The heat setting properties of these fibers can be employed with advantage in the manufacturing of nonwoven fabrics by needle punching. 
Acrylic 
In spite of the comparatively high price of acrylics they are being used extensively in high-grade fabrics, especially those made by spray bonding, because of the high bulk of the fibers, good recovery, comfortable cushioning effect, resistance to moisture and chemicals, washability and suitability for dry cleaning. Produced in coarse deniers with high crimp, the acrylics are especially good for furniture and automotive cushioning. In needle looms they are showing promise in apparel applications. The heat-setting properties of these fibers can be employed with advantage in the manufacturing of nonwovens by the needle punching technology. 
Other fibers 
Fibers that are finding limited use for special products or on specially adapted machinery are glass fibers for reinforcing mats for lamination, ceramic fibers, thermoplastic vinyl resin type for bonding with heat and pressure, and asbestos and sulfite used in blends. Most of these fiber uses are too specialized to be within the scope of this book and are not in the range of products marketed as nonwovens, although they are nonwovens further processed and fabricated. 
(2.1.1.) FIBER DESCRIPTION CONSIDERATIONS
In selecting fiber for use in nonwoven fabrics the fiber description, i.e. the crimp, length, deniers per filament, and finish, is fully as important as fibers. 
Crimp 
It is almost impossible with most equipment to produce a nonwoven fabric from a completely straight fiber. The natural fibers have varying amounts of crimp and, just as the cut filament must be crimped for spinning, a crimp is necessary for the formulation of manageable web for nonwoven fabric production. Curly fibers are better than straight and usually curlier the better. Highly crimped fibers tend to form a more uniform web which will retain its original structure during the subsequent process. The amount and type of crimp may be determined by the requirements of the finished product. For example, a nonwoven intended for padding or cushioning in automobiles or furniture applications where loft and resiliency are required must be made from fiber having a permanent crimp. In the spray process, the penetration of a binder is directly dependent on the crimp and the relationship between crimp and denier. 
Denier 
The choice of denier per filament for fiber to be used in nonwovens is governed primarily by the requirements of the end product. The use of the finer fibers results in great density, strength, and softness and at the same time a more opaque sheet (fine fiber has more "covering" power). Heavy deniers are easier to open for the production of a uniform web at higher speeds than fine deniers. The adjustment of the processing equipment of the denier of the fiber used is a very important factor in successful nonwoven fabric production. 
Length 
The staple length of the fibers to be used depends on the type of web-forming equipment selected for the production line in most cases longer fibers can be used in cards and garnets better than in air lay machines, but there is no advantage in fabric strength derived from longer fiber. In any type of web-forming nonwoven fabrics, manufacturers have learned through experience that low production rates and poor-quality fabrics usually result from the use of fibers that are too long. Another result of long fibers may be excessive breakages. 
Finish 
The finish on the fiber surface is usually designated as "bright", "dull", or "semi-dull" and the selection is arbitrary depending on the luster or appearance desired in the end product. See details.

Source: Online/NNA

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