Dry, wet and polymer-laid nonwovens

Generally, in dividing nonwovens into three major areas – drylaid, wetlaid and polymer-laid (encompassing the spunmelt technologies of spunbond, meltblown and flashspun), it can be said that drylaid materials have their origins in textiles, wetlaid materials in papermaking, and polymer-laid products in polymer extrusion and plastics (remembering that there is always at least one exception to the rule).

1 Drylaid nonwovens

The first drylaid systems owe much to the felting process known since medieval times. In the pressed felt industry, cards and web lappers were used to make a batt containing wool or a wool blend that is subsequently felted (hardened) using moisture, agitation and heat. Some of the drylaid webforming

technologies used in the nonwovens industry, specifically carding and garnetting, originate from the textile industry and manipulate fibres in the dry state. In drylaid web formation, fibres are carded (including carding and cross-lapping) or aerodynamically formed (airlaid) and then bonded by

mechanical, chemical or thermal methods. These methods are needlepunching, hydroentanglement, stitchbonding (mechanical), thermal bonding (sometimes referred to as thermobonding) and chemical bonding. Airlaid pulp web formation originated from the paper industry. Fabrics are formed by converting wood pulp in blends with man-made fibres into random-laid absorbent webs, using air as the dispersing medium and as the means of transferring fibres to the web-forming zone. In the traditional airlaid process, synthetic resin bonding agents were applied to the pulp web using a spray process. 

2 Wetlaid nonwovens

Paper-like nonwoven fabrics are manufactured with machinery designed to manipulate short fibres suspended in liquid and are referred to as ‘wetlaid’. To distinguish wetlaid nonwovens from wetlaid papers, a material is regarded by EDANA as a nonwoven if ‘more than 50% by mass of its fibrous content is made up of fibres (excluding chemically-digested vegetable fibres) with a length to diameter ratio greater than 300, or more than 30% fibre content for materials with a density less than 0.40 g/cm3’. This definition excludes most wetlaid glass fibre constructions which sectors of the industry would class as nonwovens. The use of the wetlaid process is confined to a small number of

companies, being extremely capital intensive and utilising substantial volumes of water. In addition to cellulose papers, technical papers composed of highperformance fibres such as aramids, glass and ceramics are produced.

Drylaid,wetlaid and Polymer-laid

3 Polymer-laid nonwovens

Polymer-laid or ‘spunmelt’ nonwovens including spunbond (spunlaid), meltblown, flash-spun, apertured films as well as layered composites of these materials, are manufactured with machinery developed from polymer extrusion. In a basic spunbonding system, sheets of synthetic filaments are

extruded from molten polymer onto a moving conveyor as a randomly orientated web in the closest approximation to a continuous polymer-to fabric operation. Global spunmelt demand has grown on average by 11% per annum in recent years and it now has an estimated 25% share of the global nonwovens industry. Hygiene product components such as coverstocks, backs, distribution layers and leg-cuffs account for around 62% of spunmelt production, of which spunmelt materials account for around 65% of hygiene product components, and this is expected to rise still further to at least 72%

in the coming years.

Definition and classification

In defining what a nonwoven is, there is always at least one exception that

breaks the rule. This is perhaps fitting, since while being now recognised in

its own right, the nonwovens industry has drawn on the practices and knowhow

of many other more well-established fields of polymer and materials

manufacturing with a piratical disregard and an eye to the most diverse range

of end-use products. For this reason, it is possible for companies with almost

nothing in common, with vastly different structures, raw materials and

technologies, areas of research and development and finally, customers to be

grouped together under the nonwovens ‘umbrella’. Many would define

themselves by the customers they serve, as being in the medical, automotive,

hygiene or civil engineering industries, for example.

The term ‘nonwoven’ arises from more than half a century ago when

nonwovens were often regarded as low-price substitutes for traditional textiles

and were generally made from drylaid carded webs using converted textile

processing machinery. The yarn spinning stage is omitted in the nonwoven

processing of staple fibres, while bonding (consolidation) of the web by

various methods, chemical, mechanical or thermal, replaces the weaving (or

knitting) of yarns in traditional textiles. However, even in the early days of

the industry, the process of stitchbonding, which originated in Eastern Europe

in the 1950s, employed both layered and consolidating yarns, and the parallel

developments in the paper and synthetic polymer fields, which have been

crucial in shaping today’s multi-billion dollar nonwovens industry, had only

tenuous links with textiles in the first place. Therefore, the nonwoven industry

as we know it today has grown from developments in the textile, paper and

polymer processing industries. Today, there are also inputs from other industries

including most branches of engineering as well as the natural sciences.

Certainly today, the nonwovens industry is reluctant to be associated with

the conventional textile industry and its commodity associations nor would

it want its products to be called ‘nonpapers’ or ‘nonplastics’. The term‘nonwoven’, then, which describes something that a product is not, as opposed

to what it actually is, has never accurately represented its industry, but any

attempts to replace it over the years have floundered. The illusion created by

this misnomer has been for some to think of nonwovens as some kind of bulk

commodity, even cheap trade goods, when the opposite is often true. The

nonwovens industry is highly profitable and very sophisticated, with healthy

annual growth rates in double digits in certain sectors and parts of the world.

It is perhaps one of the most intensive industries in terms of its investment

in new technology, and also in research and development.

EDANA, (The European Disposables and Nonwovens Association) defines

a nonwoven as ‘a manufactured sheet, web or batt of directionally or randomly

orientated fibres, bonded by friction, and/or cohesion and/or adhesion’, but

goes on to exclude a number of materials from the definition, including

paper, products which are woven, knitted, tufted or stitchbonded (incorporating

binding yarns or filaments), or felted by wet-milling, whether or not additionally

needled. To distinguish wetlaid nonwovens from wetlaid paper materials, the

following differentiation is made, ‘more than 50% by mass of its fibrous

content is made up of fibres (excluding chemically digested vegetable fibres)

with a length to diameter ratio greater than 300’. Other types of fabric can be

classified as nonwoven if, ‘more than 30% by mass of its fibrous content is

made up of fibres (excluding chemically digested vegetable fibres) with a

length to diameter ratio greater than 300 and its density is less than 0.40g/

m3. This definition, which forms ISO 9092:1988 and EN 29092, was most

likely coined prior to the enhancement of plastic film layers which have

become broadly indistinguishable from fabrics in modern multi-component

or composite nonwovens.

INDA, North America’s Association of the Nonwoven Fabrics Industry,

describes nonwoven fabrics as ‘sheet or web structures bonded together by

entangling fibres or filaments, by various mechanical, thermal and/or chemical

processes. These are made directly from separate fibres or from molten

plastic or plastic film.’ Nonwovens are engineered fabrics that can form

products that are disposable, for single or short-term use or durable, with a

long life, depending on the application. In practice, the life of a nonwoven

product can be measured in seconds, minutes, hours or years but the design

and engineering requirements of these fabrics are often complex and challenging

regardless of the intended product life (Table 1.1).

Nonwovens are engineered to provide specific functions to ensure fitness

for purpose. These properties are combined to create the required functionality,

while achieving a profitable balance between the expected product life and

cost. Nonwoven technology also exists to approximate the appearance, texture

and strength of conventional woven and textile fabrics and in addition to flat

monolithic fabrics, multi-layer nonwoven composites, laminates and threedimensional

nonwoven fabrics are commercially produced. In combination