In the hygiene field, nonwovens are sometimes considered articles of everyday use without distinctive characteristics. Feminine hygiene products, baby diapers, adult incontinence products and wet towels are just some examples of the numerous applications of nonwovens that enter every phase of our daily lives.
Peter Meijer, BBA Nonwovens
What are nonwovens? Nonwovens are products that are all around us and yet only very few people are aware of them. In the September issue of the Perini Journal, Colin White gave a definition of what nonwovens are and he described the development of these versatile products. His article closes with a description of the key end-uses of nonwovens and he remarks that the wonderful world of nonwovens touches every phase of our lives. And touching every phase of our lives is, quite literally, exactly what happens: most people in the western world use nonwovens from very young until they are very old and even beyond!
During birth, doctors, nurses and midwives probably wear head-covers, gowns, shoecovers and face masks made from nonwovens. The equipment that is used for the birth came, quite possibly, wrapped in nonwoven fabrics; bed sheets and absorbent materials can also be based on nonwoven technology. And immediately after birth nonwovens fulfil several important functions: the soft inside layer of the disposable diapers that the vast majority of children use in the western world is made of polypropylene nonwoven. Feminine hygiene products and adult diapers, too, are large applications using nonwovens. And nonwovens are even used in coffins.
Truly, "cradle to grave". Bodyworn absorbent hygiene articles are important users of nonwoven fabrics. In the statistics published by the European Disposables and Nonwoven Association (EDANA) Personal Care and Hygiene represented 36% by weight (about 390,000 mt) and more than 56% of the total m² produced (almost 16.5 billion m²2) of the total Western European production of nonwovens in 2001. It is easy to see that hygiene is the largest segment of the nonwovens business. The hygiene market, as defined by Edana, consists of the following main products: baby diapers, adult incontinence products, feminine hygiene products, dry and wet wipes and some smaller applications. The following table shows the nonwoven deliveries of all Western European suppliers to the hygiene business, split by application and manufacturing technology: A short review of the how and why of the nonwoven usage in these market segments follows.
BABY DIAPERS.
Topsheet has traditionally been the largest application for fabrics in diapers. The function of the topsheet is to provide a soft layer that gives integrity to the diaper and allows moisture to pass into the diaper core. Topsheets have to be skin friendly, for which reason virtually all topsheets today are made from polypropylene, either from short (staple) fibres that are carded or from continuous filaments in spunbonded fabrics. Both these technologies have advantages and disadvantages. Carded webs are made from crimped fibres and are more bulky than spunbonded fabrics. Carded fabrics also have a different touch or hand-feel than spunbonded fabrics that have a silky softness. Spunbonded fabrics usually are stronger, mainly in the cross-machine direction, for which reason lower basis weights, and hence lower priced, fabrics can be used for any given need. It is mainly for this, cost related, reason that spunbonded fabrics have recently gained market share at the expense of carded thermalbond.
In Western Europe and North America virtually all topsheets are thermally bonded using a calendar. In Asia and particularly in Japan, the consumer needs are different and even softer fabrics are used. In addition to carded thermalbond and spunbonded fabrics other technologies such as through-air bonding and hydroentangled (spunlaced) webs are often found in diapers. But back to Europe where most topsheets are made from homopolymer polypropylene. Because PP is a hydrophobic polymer, surface treatments are needed in order to allow moisture to pass, preferably in one direction. Good liquid strike-through and low re-wet are the objectives. These treatments are becoming increasingly sophisticated with a trend towards permanent hydrophilicity. The treatment should not wash off the surface of the fibres, so that multiple gushes (insults) can pass into the core.
Another important feature of diapers is the standing leg gather. This was introduced in order to further improve diaper performance and to prevent both urine and faeces from leaking out of the side of the diaper. These gathers are hydrophobic and need to have good barrier properties. Since it is easier to make high barrier spunbonded fabrics and spunbond-meltblown composites than hydrophobic carded webs, the spunlaid is the technology of choice. Directly below the topsheet is quite frequently a layer of lofty fabric. The purpose of this layer is to briefly store and distribute the urine. After acquiring and distributing the moisture away from the point of the insult, this layer ideally releases its moisture to the core, where it can be "locked away". Bulk and the capability to remain bulky, both under pressure or when wet, are important properties of such acquisition-distribution layers. They are usually made of carded staple fibre, bonded in a variety of ways, with resin (adhesive) bonding the most widely used. Depending on the diaper design, other technologies such as through-air bonding, needle punching and even thermally bonded spunbonds are also used. New diaper designs are being developed and introduced to the market all the time. A recently introduced diaper has an apertured topsheet (a fabric with regularly spaced holes or apertures).
The advantage of this fabric is that it can also aid in managing runny bowel movement, a typical phenomenon for young babies that are breast-fed.
Other nonwovens are sometimes found in the absorbent structure of a diaper, for example fabrics replacing diaper tissue with very light weight nonwovens or an isolation layer close to the backsheet. Important is that all components having to do with diaper absorbency, including the topsheet, leg gathers, acquisition-distribution layer and the diaper core work together to form a high performance system. A lot of properties have been standardized, but a need for close cooperation between the suppliers of the raw materials and the converters of diapers remains. Nonwovens are not only used in the absorbent structure of diapers.
Very noticeable was the introduction of textile-like backsheets, in which a layer of fabric (either carded PP or spunbonded) is laminated to the film backsheet of the diaper. The purpose is to give the diaper a more garment-like appearance and with the introduction of breathable backsheets, the nonwoven fabric also gives additional integrity to the diaper. onwovens are used in the diaper closure system, both in adhesive tapes and in hook-and-loop closures. Complete side-panels can even be made with nonwovens, incorporating elastic features for improved fit. How well diapers fit the users, particularly after extended use, is, obviously, important and further improvements in diapers will target this feature. Stretchy and elastic nonwovens are likely to become much more important in the future. Development centres also on aesthetics; to make diapers more fun to wear and to further differentiate the various brands, printing and colored diaper components are likely to become more important than was the case so far. This may represent a new market opportunity for novel technologies, as printing of Nonwovens is not trivial.
All the descriptions above have concentrated on the functionality and the looks of fabrics in the diaper. An additional important performance aspect of nonwovens in diapers is the ease with which the fabrics can be used on modern high speed diaper machines. The all-important aspect of economics is a function of performance in use, price and convertibility. Web handling and the question how best to deliver all the materials to the diaper machine, whether as individual components or as sub-assemblies, will keep us busy for a while and the likely solutions will also change over time.
FEMININE HYGIENE.
The bodyworn absorbent products for feminine hygiene can be broadly divided into: menstrual pads, panty liners and tampons.
There are some new products that are slotted between pads and tampons, but that market is still very small. In baby diapers, where the products are relatively large and cores are often three dimensional with a density gradient to improve the handling of large quantities of liquid, the cores are made on the diaper line from fluff-pulp and superabsorbent polymers. In feminine hygiene, whether pads or liners, the finished product is much smaller and the amount of liquid that needs to be absorbed is also smaller. For this reason, cores are often made from airlaid nonwovens. These fabrics can either directly contain superabsorbers or the SAP is sandwiched between two layers of the airlaid fabric. If powder loads that exceed the amount that can be directly handled in the airlaying process are needed, the SAP can be introduced in the core by putting the powder between two layers of airlaid that are subsequently laminated together, or by folding one airlaid web onto itself with powder between the layers. To deliver the absorbent core to the converting machine is a major challenge: because the fabric is lofty and the widths are typically narrow, delivery on rolls is not efficient. For this reason prefabricated cores (or core components) are likely to be festooned into boxes.
There is another, proprietary technology that delivers the fabric in a type of bales. The topsheet of feminine products is often made from carded nonwoven. A large part of the market uses an apertured film and apertured nonwovens are also used extensively.
The properties of topsheet in the feminine hygiene business are quite different from those in baby diapers. The surface tension of the fluids, the quantities and the pressure with which the fluids are released are, naturally, very different from diapers. For this reason, the fabrics need to be more hydrophilic and the entire construction needs to wick fluids away from the user. An important requirement in feminine protection is the ability to hide stains; the pads should look clean and fresh even during and after use.
This means that topsheet materials need to have good opacity. Below the topsheet, nonwovens can provide further improved re-wet properties and can prevent powders and cellulose-particles from coming back through the apetured top layer. Nonwovens are also used as the fluid barrier or backsheet. Meltblown and spunbond-meltblown composites with their very fine fibres can provide sufficient barrier properties. But here, too, it is the design of the entire product that determines the properties of the individual components. All materials need to work together, when properly designed, panty liners and even pads can do without film as a backsheet.
ADULT INCONTINENCE.
In this market we can distinguish between body worn products, similar to baby diapers, and underpads, absorbent products that are put directly into beds to protect the mattress and sheets. The applications for nonwovens are very similar to those in baby diapers. Topsheets, barrier leg cuffs, distribution layers, airlaid cores, nonwoven closure systems and textile backsheets are all used. The successful marketers of incontinence products develop products that are increasingly specialized to meet needs of the various types of incontinence.
A product needed for completely incontinent (and sometimes bed-ridden) users is very different from a product designed for occasional urinary "accidents". The materials are, therefore, very different and often unique to the application. Another distinguishing feature of the market for nonwovens to the AI business is that some products are sold to the institutional market, where the needs are quite different from the consumer, or retail, business. Adult protection is a market that has been growing at fast rates. The versatility of nonwovens are contributing to this development.
CONCLUSION.
Nonwovens in hygiene are sometimes seen as commodities, without distinguishing features. It is, however, clear that nonwovens can offer solutions to the producers of hygiene articles that can allow them to further differentiate their products and to develop products that deliver improved value to the end-user.