High performance drives increased use of polyester and polypropylene nonwovens for filtration
media.Filtration is divided into two broad classifications gaseous filtration and liquid
filtration. The proper filtering medium must be selected based on the material to be filtered, the
operating environment and the actual operating conditions. There is no universal fiber for
filtration. Neither is there a single fibrous or textile form suitable for every type of
filtration.The food and beverage industry is diverse, offering many opportunities for filtration
products. Filtration is important in dairy, meat, poultry, alcoholic beverages, soft drinks and
bottled water. The largest single application for beverages is beer filtration. Filtration is one
of the key unit operations in the manufacture of most types of basic raw materials and in the
production of most industrial and commercial products. Choosing The Filter MediumFollowing are
some of the major criteria that must be met in selecting the proper filter medium for a specific
application:Which is the most valuable component the filtrate or the filtered streamWhat is the
particle size to be retained by the mediumWhat is the permeability of the clean filtration
mediumWhat is the solids-holding capacity of the filtering medium, and what is the resistance of
the filtering medium to the passage of the filtered streamWhat is the physical state of the
suspension to be filtered, and what is the chemical constitution and temperatureThe choice of a
filter design for a given process depends on some of the following factors:the properties of the
solids to be removed and their concentration;particle size and shape as well as the properties of
the fluid;the quantity of material to be handled;whether the solid or the liquid, or both, are to
be retained after filtration;whether the filtrate must be washed; andwhether the filtration process
should be batch or continuous. Bag Filters For Liquid FiltrationBag filters have become more
popular for liquid filtration for process filtration and for hydraulic and lubricating filtration.
Polypropylene is the favored material for most liquid filtration because of its chemical resistance
and competitive price. Nonwovens For Protecting Membrane FiltersThe use of reverse osmosis is
growing by about 12 percent per year, gas separation types are growing by about 12 percent per
year, and electrodialysis is growing by about 8 percent per year.Polymeric microporous membranes of
cellulose acetate, polysulfone, polyvinylidene fluoride, acrylonitrile polymers and nylon are used
in chemical, pharmaceutical, food processing and waste treatment operations. Submicronic particles
must be removed from fluid process streams in these operations.Membrane filtration is the
separation of the components of a pressurized fluid, effected by polymeric or inorganic membranes.
The pores of the membrane are so small that significant fluid pressure is required to drive the
liquid through them.The pressure required varies inversely with the size of the pores. These
membranes have pores so small that they will plug and blind off instantly unless they are run in
the crossflow mode.Unlike traditional filtration, in membrane filtration, all the influent does not
pass through the media, but instead is split into the permeate (filtrate) and concentrate streams.
The concentrate stream flows parallel to the membrane, hence the term crossflow.The crossflow
membrane is a pressure-driven process in which the semipermeable medium acts as a surface filter to
split the feed stream into two effluents a purified stream and a stream concentrated in solutes too
large to pass through the pores of the particular membrane.Moving from the smallest to the largest
pore sizes, there are four categories of membrane filters.reverse osmosis (RO)nanofiltration
(NF)ultrafiltration (UF)microfiltration (MF)Reverse osmosis effects separation of small solutes,
including salts with ionic radii in the Angstrom ( range. The exact mechanism of rejection in RO is
more complex than in UF and MF.Nanofiltration is a term that was coined in the late 1980s to define
membranes that were already in use and were referred to as loose RO. They have pores close to one
nanometer in diameter (1- and effect partial salt rejection.NF membranes pass a higher percentage
of monovalent salt ions than divalent or trivalent ions. Nanofiltration membranes span the gap
between RO and UF classes of membranes. Ultrafiltration standards have been developed under ASTM
Standard D-1129, but no such official definition yet exists for reverse osmosis or
nanofiltration.Microfiltration is understood as the fine end of particle filtration, with pores
from 0.1 to 1 micron in diameter. MF membranes have pores two to five orders of magnitude larger
than the other classes.MF media are actually membranes and can be run in the crossflow as well as
in the normal flow mode. This can provide longer media life. In order for the membrane filter
systems to work properly, membrane fouling must be prevented.In membrane filtration, nonwovens can
play an important adjunct role. Some of the functions of nonwovens in membrane filtration systems
follow.protection during manufactureprotection and support during testingpleat separation for fluid
distributionpleat support to prevent collapseprefiltrationThe membrane films used are usually thin
and often in the range of 4 to 6 mils in thickness. While many of these membranes have good
chemical resistance and tensile strength, they are susceptible to puncture, damage from abrasion
and fatigue failure from flexing.Also, the membranes must be protected during fabrication into
cartridges and other forms. To protect the membranes during fabrication, they are often sandwiched
between two or more layers of nonwoven material. The nonwovens are typically polypropylene or
polyester.Extruded nettings as well as spunbonds and meltblowns are used extensively as protective
media.Polypropylene is commonly used because of its broad chemical compatibility and low cost.
Polyester provides a better combination when used with nylon membranes because of the higher
melting temperatures of the two materials. Nonwovens made from virgin resins with minimal additives
are required in processes where materials must meet FDA requirements.Care must be taken when using
meltblown nonwovens to prevent shedding of particles, particularly with finer denier meltblowns.
Often meltblowns will be calendered to prevent fiber shedding.

 Downstream Nonwoven LayerA layer of nonwoven material adds structural support to the
folded membrane and must allow the fluid to move out of the pleat. This becomes more important as
differential pressure increases with contaminant buildup, increased fluid velocity or increased
fluid viscosity.Spunbonds are very suitable for the downstream layer because of their higher
strength and freedom from fiber shedding. Extruded nettings are also used, but they are thicker
than spunbonds. Upstream Nonwovens LayerIt is important to maintain proper fluid flow dynamics
above the membrane. The upstream nonwoven layer must keep the flow channels open between adjacent
pleats. Without support from a nonwoven layer, adjacent pleats may pinch together and impede fluid
flow. The upstream layer reduces the particle contaminant load on the final membrane filter. Proper
prefiltration greatly enhances the filtration performance of the membrane filter.The major
objective of the prefilter is to remove large, oversized particles so that the narrow pores of the
membrane filter do not become prematurely clogged. Important parameters for selecting a prefilter
are mean flow, pore size, pore size distribution and bubble point. The mean pore size correlates
well with filter retention efficiency. A narrow pore size is usually preferable. Generally, a
separate prefilter unit with nonwoven media is preferable. A separate prefilter can extend the use
of the final membrane filter by up to two times its normal life.There are some requirements for
nonwovens used with membrane filtration systems (See Figure 1). Benefit Of
Pre-FiltrationOsmonics SPIRALTEK® rolled filter medium with a spiral-wound design creates a
tangential crossflow motion that sweeps particulate across the medium and traps contaminants in
special nonpermeable sections, rather than in the medium itself. Rolled filters, much like pleated
filters, are made with different types of polymer membrane.Some of the following applications use
prefiltration systems based on the Osmonics SPIRALTEK rolled filter medium:Magnetic Media
Filtration Rolled filters provide the sharp cutoff to separate oversized particles from metal oxide
slurry. They also help to eliminate gel slugs.Specialty Inks Inks used for ink-jet printers,
ballpoint and roller pens and other specialty uses require highly efficient filters that can handle
viscous fluids and achieve the fine separation of contaminants from pigments. Rolled filters work
well in these applications.Biotechnology In processing blood serums, or biological extracts,
removal of unwanted bacteria, protein and other materials is essential. The ability of rolled
filters to hold a large volume of particulate is very beneficial. They also help to increase the
longevity of downstream sterilizing filters.Fermentation Broths In pharmaceutical and beverage
production, enzymes have to be removed once they have completed their work. Rolled filters, because
of their holding capacity, help to improve the efficiency of downstream membrane
filtration. Dry-Gas FiltrationFor many years, woven fabrics were the most typical media, but
during the last 20 years, nonwovens have become the dominant filtration media.A major advantage of
nonwovens is versatility, since almost all major types of nonwovens can be used alone or in
combination in some type of filtration application.For air and hot-gas filtration applications,
there was earlier acceptance of needlepunched nonwovens in Europe than in the United States. This
is no longer the case. Higher-speed needlelooms, improved needles, high-temperature resistant
fibers and specialized fabric finishes have broadened the uses of needlefelts in both dry and wet
filtration. Needlefelts can be engineered to provide varied pressure drops and dirt holding
capacity.Polyester fibers are important for dry-gas filtration for use up to 275°F (135°C). Where
higher temperatures are required, fiberglass, DuPonts Nomex®, PPS (polyphenylene sulfide) and
Inspecs P84® polyimide fibers are used.Polypropylene is limited in dry-gas filtration to areas
where only relatively low temperatures are encountered. This excludes its use from baghouse
installations for power generation plants, as well as asphalt-, cement- and metal-processing
installations.However, polypropylene use is growing in applications for clean rooms and hospital
operating rooms, for which polypropylene filter media are available in a wide range of types from
bulky to paper-like structures. Filters For Gaseous FiltrationClass A filters are for coarse
dust and can even retain 60-micron particles. Class A filters are not suitable for filtering
sub-micron particles.Class B filters cover a wide range of efficiencies for removing sub-micron
particles. They are often used in the form of bags supported on a metal framework, or as
cartridges. They are commonly used as filters for air conditioning systems or as prefilters for
Class C filters.Class C or HEPA (High Efficiency Particulate Air) filters are specifically designed
to deal with very fine particles at low loadings. They are typically used in combination with a
Class B filter as a prefilter.Typical applications for Class C filters are electronic and
pharmaceutical clean-room manufacturing and fermentation processing.

 Collection Mechanism In Dry-Gas FiltrationIn dry-gas filtration, particulates are
collected by three mechanisms direct interception, impaction and diffusion.In collection by
impaction, the particles have so much inertia that they cannot follow the streamline around the
fiber; thus they impact on its surface. The mechanism involves a collision of the particle on the
barrier. Another mechanism involves particle interception. In this case, the particles have less
inertia and can barely follow the streamlines around the obstruction. Even if it doesnt actually
touch the fiber, the particle is immersed in the viscous stream around the barrier, which will be
enough to slow it down so it will graze the barrier and stop. When this happens, the porosity of
the filter medium decreases and the true filtering surface begins to form.The third collection
mechanism is important for particles that are below 1 micron in aerodynamic diameter. Diffusion is
considered immaterial for particles with diameters smaller than 0.1 micron, which is in the
Brownian motion range. In this case, the particles are so small that their individual motion can be
affected by a collision on a molecular or atomic level.Other important factors are electrostatic
attraction and gravitational settling. As the particle loading in a filter increases, the
collection efficiency increases, but so does the pressure drop across the filtering unit. The
pressure drop is used to monitor the condition of the filter and to determine when it needs to be
cleaned or replaced. Baghouse FiltrationsOne of the most common uses of baghouses is in the
electric utility industry where coal is used. A baghouse is a large metal box divided into two
functional areas. One area, the dirty-air plenum, may be a part of the baghouse proper, or it may
take the form of a gas-distribution manifold.The function of the dirty-air plenum is to distribute
the incoming gas evenly to the filtering elements or bags. The clean-air plenum is part of the
baghouse where recombination of the air from each of the individual bags takes place. The interface
separating clean-air and dirty-air plenums is the filtering medium or bags. The baghouse hopper is
a receptacle for collected particulate materials and is part of the dirty-air plenum.As discussed
in the previous section, the filter mechanisms involved in removing particles from a fluidized gas
stream are impaction, interception and diffusion. These mechanisms are responsible for the
collision of a particle on a target (the filter fabric) and are of paramount importance when the
baghouse is first brought on-line and the filtering elements are still clean.After a short time,
however, the bags become caked with a layer of flyash, and the dust cake actually becomes the
filtering medium. No matter how vigorously the bags are shaken, collapsed or pulsed, a residual
dust cake is retained after each cleaning, and the bags now act mainly as a matrix to support the
flyash. Classification Of BaghousesBaghouses are characterized and identified by the method
used to remove flyash from the bags. The bags in shaker-type units are suspended from a structural
framework, which is supported in such a way that it is free to oscillate when driven by a small
electric motor. Periodically, a damper isolates a compartment of the baghouse so that no air flows
into it. The bags in that compartment are then shaken for about a minute, during which time the
collected dust cake is dislodged from the bags. The dust falls into the hopper and is later
removed.Reverse-flow baghouses are equipped with an auxiliary fan that forces air through the bags
in an isolated compartment with the airflow in the opposite direction to filtration. The backwash
action collapses the bags and fractures the dust cake. When the bag is reinflated by being brought
back on-line, the fractured dust cake is dislodged into the hopper. If the unit operates under
suction (that is, if the main process fan is located on the clean side of the baghouse), the
reduced pressure in the baghouse may eliminate the need for an auxiliary fan. Some units combine
shaking and reverse-flow cleaning in the same unit.Reverse-pulse baghouses use a short pulse of
compressed air directed from the top to the bottom of the bag. This primary pulse usually lasts
less than a tenth of a second and aspirates secondary air as it passes through a nozzle or venturi.
The resulting air mass expands the bag and casts off the collected flyash. Shaker and reverse flow
units collect flyash on the inside of the bags, while reverse-pulse units collect flyash on the
outside of the bags.Baghouses have some practical limitations. Most bags have rather
low-temperature capabilities, ranging from 180°F to 300°F and above. Thus a practical limitation
exists when using fabrics able to withstand air-preheater outlet temperatures of 300°F and above.
Abrasion is a natural phenomenon that results from contact with flyash-laden gases. Some wear on
the filter bags occurs when flyash strikes a bag tangentially.The destruction of a bag from
chemical attack is generally due to misoperation. Processes that evolve gases at elevated
temperatures frequently produce water vapor and acid radicals, which at the acids dewpoint will
concentrate into a liquid. The acid dewpoint depends on the concentration of the constituents in
the gas, and it is almost impossible to predict.The bags tend to wear out with age. After hundreds
of cleaning cycles, the fabric weakens and will ultimately fail. The better the bag maintenance and
the better the equipment design and materials selection, the longer the bag will last.

 Overall Trends In FiltrationNonwovens will continue to grow in importance. Higher
performance requirements for filtration systems are being driven by industry needs for improved
productivity and by stricter environmental requirements. The ability to engineer nonwoven materials
to meet these more stringent requirements is responsible for the growing use of all major types of
nonwovens in filtration applications. The use of automotive cabin filters is now a growing market
for nonwovens. Greater household use of drinking water filter systems and home air and household
cleaning devices present good growth potential for nonwovens. In wet filtration uses, polypropylene
will continue to be the dominant material because of its superior chemical resistance and
relatively low material cost.Meltblown nonwoven use in filtration is expected to continue to grow
by more than 8 percent per year over the next five years. Meltblown technology providing higher
strength webs is now under development and will further improve its versatility as a filtration
medium. Spunbond nonwovens will also show healthy growth in filtration, both alone and in
combination with meltblown materials. Needlepunch nonwovens continue to improve their performance,
particularly for more demanding dry-gas filtration applications based on improved manufacturing
technology.In wet filtration, needlepunched and meltblown combination fabrics are growing in
importance. Dry-laid nonwovens have lost some market share to spunbonds, but higher carding speeds
and improved thermal bonding techniques will help stabilize their position in filtration
applications.Use of specialty fibers will grow in filtration. Governmental clean air requirements
are boosting the use of high-temperature resistant fiber such as DuPonts Nomex, Inspecs P84, BASFs
Basofil® and PPS for industrial and utility systems. The use of fibers that incorporate additional
functions, such as antistatic and antifungal properties, is growing.There will be greater use of
fabric functional finishes. Use of additives and treatments is growing. The use of materials in the
form of finishes or microporous film laminates of silicone or fluorocarbons, which provide better
cake release properties, will continue to grow. The application of selective absorbents, such as
carbon and zeolite, to filter media is another important trend. The formation of electrets in
filter media to improve efficiency has now been widely commercialized.There will be major areas of
growth for nonwovens in filtration. Reverse osmosis is a growing industrial process for a wide
range of industries including food, pharmaceutical and microelectronics, and it will require
nonwoven filtration media for prefiltration of liquids. There is a growing need for nonwovens of
greater uniformity for use as casting support for membrane filters.Nonwoven use will not only grow
in automotive and household applications, but will become better known to the public because of
these growing uses.

August 2000

The Safety Equipment Institute (SEI), McLean, Va., recently adopted two new NFPA standards for
testing chemical splash and vapor protective clothing used by emergency responders for protection
against potential hazards. As a non-profit organization, were committed to making sure emergency
responders have confidence in the safety products they rely on for protection from unforeseen
hazards, said Patricia A. Gleason, president, SEI. The independent testing of hazardous materials
protective clothing will continue to be conducted through Intertek Testing Services (ITS), SEIs
contract testing laboratory, for all SEI protective clothing programs.

August 2000

Foss Manufacturing Co. Inc., Hampton, N.H., has begun construction on a new nonwoven fabric
facility in Pulvershiem, France, with expected completion by October. Located in the Alsace region,
the 62,500-sq-ft facility will employ more than 80 people in the first 12 months and eventually
employ 200 people within five years.We chose the Alsace region because it is located in the heart
of Europe at the intersection of France, Germany and Switzerland, said Stephen W. Foss, chairman,
president and CEO. There is excellent infrastructure and easy access to international container
services. The area has a highly skilled and well-educated workforce and is poised for further
manufacturing growth.The facility will be capable of producing fabrics up to 160 inches in width in
a weight range from 80 to 800 grams per square meter, utilizing all synthetic fibers. Sheet
extrusion equipment will also be installed, allowing for production of fabrics up to 78 inches in
width with film thickness ranging from 0.2 to 0.6 millimeters. Future plans include expanding the
facility to 225,000 sq ft to serve as a central distribution center to all of Europe for
FossFibres® specialty products including Healthshield antimicrobial and antifungal bicomponent and
binder fibers, high-ultraviolet, solution-dyed and fire-retardant fibers.

August 2000

A view into the vast field of manufacturing and application of industrial textilesThe
technical and technological application of textiles has become a rapidly growing field, especially
over the past two decades. For example, even though some textile seat belts for automotive
applications were installed before the 1960s, nobody imagined then how large a role textiles would
play in passenger safety. The demand for seat belts, as well as supplemental restraint systems such
as air bags, is huge. And while this is only the result of about two decades, we now have a better
feeling for how the market for such technical safety textiles will grow.

There are thousands of applications of textiles today for industrial and consumer usage.
Additionally, many potential uses have not been explored because end users arent aware that textile
fabrics and composites can effectively replace many traditional materials. Industrial textiles are
not in the spotlight like flashy brand-name apparel textiles and live almost a secret life, often
hidden from the eye of the end user. And the manufacturers of high-technology industrial textiles
are (understandably) very secretive about their manufacturing processes and the design of their
fabrics. The market for industrial fabrics and engineered textiles is growing constantly and
becoming increasingly significant. This leads to technical developments and innovations of advanced
textiles for new tasks. A growing awareness can be observed of environmental demands, e.g., methods
of filtration, or of the substitution of textiles for conventional materials. A great effort is
geared toward the development of cheaper, easy-to-install and lightweight textile components (in
the automotive industry, for example) based on textiles.Dream It, And It Will Be TextilesThe
following list of applications is based on a summary of fields that was compiled over the years by
Sulzer Textil Ltd., Switzerland. The company has been in the field of woven industrial applications
for many decades and set many of the original benchmarks for this sector with the introduction of
the Sulzer Projectile weaving machine. In geotextiles, woven industrial fabrics are selected for
their stability and strength, while nonwovens are often selected because of their cushioning,
damping and liquid filtration properties. Each individual manufacturing technology, in combination
with specific fibers, has certain advantages in a particular field. It seems that the nonwovens
technology has an even more impressive growth rate over the past years when compared to all other
industrial textile manufacturing technologies. Unlike consumer-oriented textile producers, the
industrial textile manufacturers face challenges presented by fibers that are extreme in nature and
chemical origins. Also, physical and mechanical properties of fibers and yarns are often very
different from those used in typical consumer textiles. The distinct design of fabrics for
industrial applications often requires special devices and setups on the production machinery.
Textile manufacturers are understandably very secretive about machine settings and installations.
Many of the nonwovens installations show a specific custom layout, and weavers have to purchase
expensive, wide, reinforced or specially equipped weaving machinery to be able to produce the
desired industrial fabrics. However, it seems to pay back when one compares the profit margins of
the industrial fabric segment with those of the rest of the textile industry.Industrial TextilesAs
already mentioned, woven textile products, nonwovens and knitted textiles share each segment of
industrial textiles, while the actual percentage assigned to each individual manufacturing
technology may vary from application to application. The technical specification profile,
cost-effectiveness and practical performance determine which manufacturing technology receives the
lions share. The following list provides a general overview of all major fields in which textiles
play a significant role.

• Protection and safety-related textiles
• Public services
• Medical and healthcare applications
• Agriculture, horticulture and fisheries
• Buildings and light structures
• Transportation
• Packing, transporting and shipping
• Filters and other industrial applications
• Miscellaneous applications of textiles
• Geotextiles

Following are some selected sub-categories of industrial textiles.Protection, Safety

These are mainly textiles that have a role in protecting the environment and humans from
leaks, spills, falling debris, fire, heat radiation and resulting accidents.

• Protective tarpaulins and netting (e.g., for scaffolding)
• Extinguishing blankets
• Safety nets
• Fire-resistant fabrics
• Fluorescent fabrics
• Insulating fabrics
• Reflecting fabrics
• Gas-proof fabrics
• Water-repellent fabrics
• Waterproof fabrics
• Microporous fabrics
• Oil-repellent fabrics
• Acid-resistant fabrics
• Fly screens
• Mosquito netting

Public ServicesThese textiles are used by the military, fire fighters, police and similar
institutions to camouflage, shelter and protect their forces.

• Camouflage netting
• Camouflage fabrics
• Army tents
• Fabrics for protection against projectiles and shrapnel
• Fabrics for peace-keeping and battlefield applications
• Fabrics for uniforms
• Nuclear, biological and chemical (NBC) protective fabrics
• Fire-fighting suits and fabrics
• Parachute fabrics
• Packing materials for defense applications (e.g., sandbags)

Medical, HealthcareThis is an ever-growing sector, especially for nonwoven applications,
because many textiles in this field are either one way or do not need to withstand high stress
levels and long-term cleaning cycles.

• Barrier fabrics for the operating theatre
• Fabrics for medical courtesy
• Fabrics for casts
• Orthopedic fabrics
• Stabile bandages
• Elastic bandages
• Cotton gauze bandages
• Fabrics as mattress and pillow protectors
• Diapers (babies, incontinence)
• Sanitary napkins
• Medical sutures

Agriculture, Horticulture, FisheriesThis sector is mainly dominated by knitted and woven
fabrics. In agricultural applications, very wide fabrics and vast square yardage especially find
their applications.

• Shade and energy-saving fabrics for greenhouses
• Ground cover fabrics
• Tie-ribbon and tape for fruit crops and similar applications
• Bags and nets for storage
• Fabric for root ball packing
• Netting for enclosures (e.g., grazing)
• Protective fabrics and nets
• Twine and cordage for enclosures
• Textile products for bagging and wrapping purposes
• Draw cloth for mushroom cltivation and rabbit breeding

Buildings, Light StructuresThis is a vast field of applications that often challenges the
highest standards of color fastness, UV resistance, strength and durability.

• Insulating and draining fabrics for buildings
• Roofing textiles
• Indoor sun screens
• Outdoor sun screens
• Awnings
• Shading fabrics
• Draught strip for doors and windows
• Reinforcing fabrics for plaster
• Tent fabrics and camper/trailer extensions
• Fabrics for marquees
• Fabrics for light-permeable structures

TransportationThere are thousands of individual applications when considering all forms of
transportation, such as motorcycle, car, bus, train, trolley, aircraft and ship. Besides the
comfort textiles (covers, decoration) for personal and industrial applications, there are many
technical textile applications hidden from the eye because of surrounding rubber or plastics.

• Passenger compartment linings
• Car trunk lining materials
• Mats
• Coated textiles (dashboard, door panels, etc.)
• Upholstery fabrics for car, bus, train, trolley, aircraft and ship seats
• Fabrics for decorative and sound-proofing applications in trains, trolleys, aircraft and
  ships
• Aftermarket seat covers
• Seat belts
• Air bag fabrics
• Tire cord fabrics
• Structural support fabrics for fan belts, timing belts and hoses
• Noise and heat damping/insulating materials

Packing, Transporting, ShippingThere are a host of applications in this arena. Applications
range from wrapping a piece of jewelry to wrapping an army tank. Following is a sampling of the
various applications.

• Cargo and container nets
• Mail bags
• Money bags
• Large textile bags
• Fabric for conveyor belting (coated and uncoated)
• Polyolefin fabrics for packing
• Fabrics for shopping bags, shoulder bags, backpacks, etc.
• Suitcase fabrics (outer shell and lining fabrics)
• Textile wrappings for car tires
• Industrial packing (bags in polypropylene, jute, etc.)
• Canvas and tarpaulin fabrics for shipping protection
• Container fabrics for silos (e.g., for water)
• Helicopter nets

Filters, Other Industrial Applications

An amazing technological area is the world of textile filters. Some high-tech filters are
used for blood filtration in the medical field. Workshop materials as well as polishing and sanding
tools often contain a textile core. Again, the array of potential applications is seemingly
endless. A partial listing follows.

• Filter fabrics from extremely fine mesh to coarse mesh
• Wet-filtration applications
• Dry-filtration applications
• Open-weave fabrics
• Tubular fabrics
• Felt fabrics
• Fabrics for polishing discs, cutting discs, abrasives
• Belts, etc.
• Technical textiles for electronic applications
• Technical textiles for heavy engineering
• Technical textiles for papermaking, printers, laundries and the cement industry
• Industrial pulley drive belts

Miscellaneous ApplicationsAgain, touching just the tip of the iceberg, the following listing
contains only a few textile applications that play important roles in their specific fields of
utilization.

• Woven primary carpet backing
• Secondary carpet backing
• Artists canvas
• Cinema screens
• Canvas for film sets and theatre scenery
• Umbrella fabrics
• Fabric for parasols, deck chairs and windbreakers
• Textiles for specific sports applications (e.g., judo mats, outdoor mattress covers, etc.)
• Fabric for sports shoes and slippers
• Base fabrics for coating
• Base fabrics for flexible lamination
• Fabrics for shower curtains

GeotextilesThis is a vast and rapidly growing field of applications. It is estimated that only
about 20 percent of all possible applications for textile products have been developed. It is
usually the end user who cannot imagine a textile product that could lead to significant
improvements and savings. However, for geotextile applications, it is often the textile
manufacturers drive to research and educate their customers that leads to new textile products.
Companies like Synthetic Industries, Chattanooga, Tenn., for example, offer a broad range of
geotextiles for civil and environmental engineering, as well as fabrics for erosion control and
storm water management. The company offers high-strength woven geotextiles for soil stabilization,
reinforcement and containment; and nonwoven geotextiles for drainage, separation, cushioning and
pavement overlay. Its geotextiles and erosion-control products are distributed in more than 50
countries. Following are more applications in geotextiles.

• Textiles for engineering water flow and road drainage
• Roadway separation and railroad stabilization
• Textile product reinforcement of earth, slopes and hills
• Erosion-control blankets
• Turf-reinforcement mats
• Fabrics for landfill rehabilitation
• Surface fabrics for sport grounds
• Protective fabrics for pond foils
• Engineered water-filtrationfabrics

August 2000

 first Internet chemical marketplace to provide a neutral market where buyers and sellers of
all sizes can conduct both large and small transactions.Covalex. com empowers buyers with pricing
and product information that helps them make smarter purchasing decisions, said Bob Steel, chairman
and CEO. The site exposes suppliers to new customers and reduces the costs and time associated with
completing a transaction all directly impacting the bottom line.The sites supply-chain management
offering will help companies to better manage costs and inventories by streamlining the evaluation,
purchase, tracking, distribution and procurement processes. Accurate, real-time global, national
and regional market information will also be available through Covalex.coms information
bureau.Conducting business on the Web will be a necessity for those who want to remain competitive
in their industries, said Steel. Covalex.com helps companies realize cost savings and operating
efficiencies today. Long term, it will help ease industry issues like price volatility and
imbalances in supply and demand.

August 2000

The multi-storied behemoths that dot the landscape of the American Northeast and South serve as a
reminder of days when companies built physical facilities to be viable producers for more than a
half-century.Today, however, many companies build plants with much shorter life cycles. Its not
uncommon to see plants built as late as the 1960s or early 1970s no longer in use, according to
industry engineering/construction consultants.Machinery changes so quickly now, said Wilson
Tillotson, division manager, manufacturing, Lockwood Greene, a Spartanburg, S.C.-based engineering
company. Buildings that were well-equipped for the latest manufacturing technology just a decade
ago are woefully obsolete today.Automated processes, such as new doffing mechanisms for roving and
spinning frames, require a different physical layout than older, more labor-intensive machinery.
High-speed rapier looms need stronger, more stable flooring with less vibration; air-jet machinery
taxes the capabilities of air compression systems; and temperature/humidity requirements stress the
air conditioning.It is not uncommon to see companies move more toward pre-engineered construction,
especially for some of the lighter processes, Tillotson said. You will likely see more and more
companies gravitate in this direction.Pre-engineered facilities are suitable for such functions as
cut-and-sew operations, Tillotson said. Heavier manufacturing, such as spinning and weaving,
however, still require substantially more structural strength.The two biggest obstacles that
confront most new facilities are environment and electronics, according to Neal E. Tonks, Ph.D.,
director of manufacturing, Bayer Corp.s Bushy Park plant near Charleston, S.C.Environment is, of
course, an old issue, one that textile companies have faced regardless of when and where theyve
built new plants. Electronic considerations, however, are relatively new to the industry so new, in
fact, that it is easy to overlook their importance until painful and costly experience teaches
otherwise.

The level of computerization in our operation is significant, Tonks said of the Bayer plant.
The Bushy Park plant, which manufactures Bayers Dorlastan® spandex fiber, recently underwent a
$60-million expansion. Computerization represents fully 25 percent of our total investment cost. We
have a sophisticated control system that monitors our processes to ensure exact tolerances. Just
the exercise of running cable trays was a major factor in the design of our facility of making sure
we had the right infrastructure in place to get power and computer control to where it was
needed.Tonks said it wouldve been a costly and time-consuming venture had electronic considerations
not been such a high priority with the Bayer design team. It wouldve been a nightmare if we hadnt
given thought to how we were going to design the electronic layout.In general, though, I believe
these considerations are still an afterthought a lot of times. We are so focused on reaching
economies of scale of fitting maximum production capability into minimum space that we overlook
having the infrastructure in place to make the most efficient use of what we have.Environmental
issues remain a primary consideration in new construction. Working with the EPA and the respective
state and local regulatory organizations is old hat for almost all U.S.-based companies in the
textile/apparel complex. But other than nonwovens and specialty applications, few new textile
facilities are being built in the United States.Thats one reason we dont design plants to be in
production for 50 years anymore, said one industry insider who preferred to remain unnamed. Despite
all the advances in automation and production speed, textile manufacturing is still a
labor-intensive process. The industry, to be competitive on a global basis, has to go to wherever
the labor is available. Years ago, it migrated from the Northeastern sector of the United States to
the South. Now it is moving to Mexico and Latin America. I believe we have a specific window of
opportunity there, however. In the not-too-distant future, basic manufacturing will move again,
essentially to wherever there is a ready supply of relatively skilled, inexpensive labor. So it
really doesnt make a great deal of sense to build a plant to last 100 years.Environmental factors,
depending upon location, might be less stringent in developing nations than in the United States,
but major U.S. mills tend to build plants in other countries to specifications similar to those for
domestic facilities.Air quality and wastewater treatment standards might be similar, but the
process of getting required permits and approvals can be substantially different.Mexico is
well-known for its bureaucratic, presentation-oriented approach, according to several mill
executives. One mill reported it took more than a year to get the environmental impact statement
approved, even though the mill used the same waste treatment, air abatement and hazardous waste
disposal procedures that generally win quick approval in the United States.In addition, the same
mill reports construction practices in Mexico that differ depending upon region.You find that
contractors in the northern part of Mexico generally work much the same way as you would expect in
the United States, using a lot of heavy equipment and mechanization, one executive said. The
further south in Mexico you go, however, the more labor-intensive construction becomes. In the
southern part of the country, if you need a ditch that is 10 feet wide and 40 feet long, you might
see people in the trench with shovels. Conversely, you would never see that in the United States or
in northern Mexico.Water is a particularly big issue in Mexico because all water is federally
owned. A company building a plant has to dig its own wells, pay for all water pumped out of the
well and then pay again when treated water is returned.From a cost perspective, U.S. mills say the
only significant difference is in labor. Materials cost about the same in the United States and
Mexico, and scheduling is very similar.Regardless of location, however, todays plants are built to
provide optimum conditions for high-quality manufacturing. High-speed equipment exponentially
increases dust and air pollution. Processes that might require one kilowatt of power a few years
ago might now require 10. More air exchanges per hour are necessary. Power delivery has to be
cleaner to provide uninterrupted operation of sensitive electronic controls.Infrastructure Tax
DeductionsOur tax rules go to quite some length to define and limit the tax deductions for the
infrastructure of your textile operation or business. Ordinarily, neither the buildings that house
the operation nor what tax rules refer to as structural components qualify for fast tax
write-offs.The term structural components includes such parts of a building as walls, partitions,
floors and ceilings, as well as any permanent coverings such as paneling or tiling, windows and
doors. It rarely includes machinery required to meet temperature or humidity requirements essential
for the operation of other machinery or for materials processing.Machinery will meet a sole
justification test even though it may provide employee comfort as well or serve, to an
insubstantial degree, areas where such temperature or humidity requirements are not essential. A
good example would be the air conditioning and humidification systems installed in many textile
plants to maintain temperature or humidity within the narrow optimum range that is critical in
processing particular types of yarn or cloth.Squeezing Faster Depreciation DeductionsUntil
recently, textile operations and businesses could choose faster or slower depreciation methods for
their machinery and equipment. Similar choices did not exist for buildings and their structural
components, which were required to be depreciated over 39 years using the slow, straight-line
method of depreciation.Today, the Internal Revenue Service (IRS), in IRS Legal Memorandum
199921045, provides guidance to building owners who want to maximize up-front depreciation
deductions. Now, some of the assets installed in a building can be written off via accelerated
depreciation over five or seven years (or even expensed immediately under the Section 179,
first-year expensing rules) if they are not structural components.MACRS DepreciationUnder the IRSs
basic depreciation system, MACRS (modified asset cost recovery system), nonresidential real
property is depreciated over 39 years using straight-line depreciation. By contrast, so-called
Section 1245 property is eligible for much faster depreciation (e.g., five years) using the
200-percent declining balance method.Under MACRS, a textile operation generally cannot break up a
plant building into components and write off each separately. However, according to the U.S. Tax
Courts decision in the case of Hospital Corp. of America vs. Commissioner (109 TC 21 (1997), if
property would have qualified as tangible personal property for investment tax credit purposes
under pre-1981 tax laws, it will also qualify as tangible personal property for MACRS purposes
today.Assets Eligible For Quick RecoveryThe Tax Court concluded that Hospital Corp. could
depreciate, over a five-year period, a percentage of the electrical systems, measured by electrical
load, that was allocable to hospital equipment as opposed to building operation and maintenance.
Also eligible for quick write-offs were many components, at least to the extent that they were for
a function or equipment unrelated to the operation or maintenance of the building, regardless of
the fact that the equipment was permanently installed.When a structure is built to house a
restaurant, for example, that part of the cost of its electrical distribution systems that is
allocable to the restaurants operation (e.g., refrigerators, freezers, food preparation equipment)
would be eligible for five-year accelerated depreciation. Similarly, the owner of a building
housing extensive computer operations should be able to claim a quick write-off for the portion of
the electrical systems relating to the computers. Obviously, an engineer would have to certify the
percentage of the electrical load allocable to non-building operation or maintenance.The IRSs legal
memorandum validates the Tax Courts central conclusion regarding whether assets installed in a
building should be eligible for fast recovery under MACRS. Unfortunately, that memorandum also
states no bright line test exists for determining if property is a structural component or tangible
personal property.The IRS doesnt have a test for separating structural components from the tangible
personal property supporting your textile operation. However, the faster write-offs now available
for that personal property make the effort of following the IRSs advice well worthwhile.By Mark E.
Battersby
Editors Note: Mark E. Battersby is a tax and financial advisor from Ardmore, Pa. He writes a
weekly farm taxes column syndicated in 45 newspapers and a topical tax column carried by several
trade magazines and more than 25 business publications.

August 2000

The Hosiery Associations (THA), Charlotte, N.C., annual convention in September will feature a
variety of seminars on issues affecting the legwear industry. The event will provide a forum in
which hosiery professionals legwear manufacturers, retailers, business lawyers, and e-commerce and
finance networks can share information and provide mutual support.Some questions that will be
addressed during the show include: How will my sourcing operations be affected by the removal in
2005 of textile quotas for the members of the World Trade Organization (WTO) Is my company prepared
to get involved in e-commerce What are the ready-to-wear fashion trends predicted for Fall 2001,
and how can my business capitalize on them What steps should I take to evaluate the worth of my
business for a sale, merger, acquisition or family transferFor more information on business
sessions and events scheduled for the convention, visit the associations site,
www.hosieryassociation.com.

August 2000

Synthetic Industries, Chattanooga, Tenn., and Shaw Industries, Dalton, Ga., were awarded a U.S.
patent for the invention of SoftBac carpet, a collaboration of both companies.The patent was given
for a composite fabric consisting of a woven scrim combined with a fiber batt. It also covers the
method for manufacturing the carpet. The object of the invention is to provide a modified secondary
carpet backing that will increase the delamination strength and dimensional stability of the
carpet, as well as block the latex or other adhesive from exuding out of the back of the carpet.The
physical properties of SoftBac carpet are second to none, said Carey Mitchell, director of
technical services, Shaw. To date, we have yet to find a carpet system that offers the same
dimensional stability, is as easy to work with and that is as consumer friendly as SoftBac.

August 2000

Industry InfrastructureBy Jim Phillips, Executive EditorCompact And Efficient
Air filtration developments save space, reduce dust and increase product
quality.Compliance with OSHA dust standards remains a major expense in both construction of
new textile plants and expansion and retrofitting of older ones, according to executives of air
filtration systems suppliers. The good news, however, is that the hit on space, cost and efficiency
is steadily declining.The trend in air filtration is toward smaller units that outperform their
gigantic predecessors, cost less to install and require less downtime for maintenance.In truth,
OSHA has probably done the industry a favor, said W. Brad Carr, vice president, textile engineering
sales, Luwa Bahnson. Modern air filtration systems eliminate so much particulate matter that
product contamination is not nearly the issue it once was. The efficiency of air filtration systems
in American textile plants has had a positive impact on product quality.Luwa Bahnson,
Winston-Salem, N.C., is one of the major companies in the United States that design and manufacture
complete turnkey air filtration systems, as is Pneumafil, in Charlotte, N.C.We are designing new
systems that offer up to 50-percent space savings over conventional systems, said John Stonestreet,
Pneumafils sales manager. These smaller systems provide greater efficiency than much larger,
older-style systems. We have some applications, for example, that outperform older systems that use
tandem design.Air Filtration ChallengesThe challenge before air filtration system design engineers
has not been solely to keep up with OSHA standards. New, faster production equipment high-speed
cards, spinning frames, looms has significantly increased the amount of particulate matter that
must be removed from ambient air.Its not a linear progression; its exponential, Carr explained. It
is amazing the amount of dust and waste produced by modern machinery. A rule of thumb is that a
typical mill 20 years ago would have required 20 air exchanges per hour (AC/H) to keep particulate
matter within limits. Ten years ago, the same mill would need 30 AC/H. Today, with current OSHA
dust level requirements and the speed of new production equipment, that same mill would need 45-55
AC/H.

OSHA requirements now allow a maximum respirable dust concentration in most workplaces of 133
micrograms per cubic meter, Carr said.We have to look at several things in accomplishing our goals,
he continued. How you supply the air can be as important to quality and cleanliness as how you
remove waste.For example, Luwa Bahnsons LoomSphere® system, a patented system designed to provide
optimum humidification for the weave room, establishes and maintains an exact and constant
environment around each loom. A precise airflow is designed to bathe each loom in a tightly
controlled environment of cool, humid and clean air. The conditioned air flows through the entire
warp sheet and preconditions the warp beam. As the air flows through and around the loom, the yarn
is strengthened by the moisture gain while the dirt and fly are carried to the return air openings
on the floor, where they are removed.Carr said the LoomSphere system results in reduced energy
costs, reduced maintenance, less capital cost and, most importantly, clean and precisely controlled
conditions at the loom.The advantage to this system is that it is a gentle flow of air over the
process, Carr said. It doesnt create turbulence, which would stir up the fiber fly and dust.For
ambient air filtration in large, open spaces, Luwa Bahnson, like Pneumafil, has developed efficient
systems that occupy a fraction of the space needed by conventional drum filters.We have our Sonic
Micro Filter, which is ideal in installations where space is at a premium, said Carr. It requires
less room than a conventional drum- and panel-type filter, requires less pressure drop, or energy
usage, than roll-media filters and automatically cleans itself, which eliminates labor required to
change disposable roll media.The ambient air return in the Sonic Micro Filter is conducted axially
to the rotary filter screen. The proprietary filter mesh and flow rate velocity are selected in
accordance with the type of application. A layer of fiber and dust is built up on the fine-mesh
screen, which increases filtration efficiency. At a selected pressure drop, the filters are cleaned
until the pressure drop is lowered to a selected set point. The waste deposited on the filter
screen/media is removed by means of a near-sonic velocity impact air nozzle in conjunction with a
catching suction nozzle. The high mass flow/high impact air nozzle dislodges the waste to
regenerate the filter screen/media.

Luwa Bahnson, as well, manufactures an Air Bell system for circular knitting applications,
which the company claims can eliminate fiber defects by as much as 50 percent. The Air Bell system
controls the airflow volume, condition and pattern to optimize efficiency. The distribution of air
provided by the Air Bell system, Carr said, sufficiently prevents fluff from entering the bell. The
air current at the feed wheel is strong enough to transport any free-flying fibers that develop.
The fibers are then carried off. This method of control prevents fluff from returning to the
knitting machine.Pneumafils Everclean Rotary Pleated Belt Filter, also a patented filtration
system, combines high-capacity pleated-membrane media with high-efficiency suction cleaning, said
Stonestreet.The Everclean filter consists of a number of filter cells, he said. Each cell comprises
an endless pleated media belt looped between two pulleys. Unfiltered air enters the unit parallel
to the filter cells and passes through the straight sections of the belt loop. Larger fibers
collect on the outer edges of the pleats, and smaller particles build up on the media surfaces
between pleats. The clean air continues between the two sides of the cell into a plenum in back of
the filter and then exits. Pressure drop across the media is constantly monitored. When the high
set point is reached, a cells belt begins rotating around the pulleys, and a stationary suction
plenum underneath the cell is activated. As the belt moves around the lower pulley, the pleats open
up and airflow through the media is blocked, allowing the pleats to be vacuumed clean.We have been
notified by two recent clients that the installation of this filtration system has allowed them to
exceed the OSHA dust test for the first time in history, said Stonestreet. One installation was a
plant expansion, and the other was a retrofit of an existing application.The Everclean system is
designed for production areas from opening through spinning. For weave-room applications, Pneumafil
offers its Automatic Panel Filter (APF).The APF is a self-cleaning filter that installs in a
fraction of the time required for installation of space and conventional drum filters, Stonestreet
said. Air is cleaned as it flows through an arrangement of parallel, hollow filter cells, each
formed by two sets of filter panels. A pressure differential switch or timer activates the cleaning
mechanism, which travels in and out of the space between filter cells. A shuttle device moves the
cleaning mechanism from cell to cell and returns it to the starting position when a complete pass
of the filter panels is accomplished. Filter panels are always cleaned in the same sequence,
ensuring that dirtier cells are cleaned before those with less accumulation. Stripper nozzles
vacuum the filter media until proper pressure is restored. Waste is pneumatically carried to a
disposal unit.Both companies have brought to domestic and export market preassembled filtration
systems that offer substantially reduced engineering, labor and installation costs.The Luwa Bahnson
Insta-Filter, a complete primary and secondary filtration unit, is used as part of a complete air
engineering solution. Contaminated air flows horizontally through a baffle system to equalize and
straighten air flow. Next, the air flows through a Sonic Micro Filter or Rotary Pre-Filter to
remove lint. The Rotary Pre-Filter provides preliminary filtration of air streams heavily charged
with waste. Air then passes through a Luwa Bahnson Multi-Drum Vac® (MDV) filter to remove
microdust. The MDV provides filtration of fine particles. Both lint waste and microdust waste can
be automatically removed and compressed for easy handling.This is a very simple filtration system,
said Carr. It is ideal for export because it doesnt require a lot of engineering and installation
expertise on-site. By assembling much of the system before it is shipped, a lot of add-on costs are
eliminated.The Pneumafil Rotary Pleated Belt Filter is preassembled on a steel base and prewired,
including controls, Stonestreet said.Both Pneumafil and Luwa Bahnson provide primary and secondary
filtration systems, as does Industrial Air Inc., Greensboro, N.C.Industrial Air offers filtration
systems, ranging from integrated air systems to air washers, fiber and waste separators, custom
HVAC systems, as well as bag, drum and roll filters.Our main focus, as is that of the entire
industry, is to provide our customers with the most efficient means to meet OSHA dust standards,
said Allen Hunter, president, Industrial Air. We offer complete, turnkey solutions to make this
happen.Among the newest offerings from Industrial Air is the S Series drum filter, according to
Hunter. The S Series filter is constructed of perforated steel panels bolted together to form a
cylindrical horizontal rotating drum. The arrangement, Hunter said, allows even air distribution
across the fabric filtering media. When bolted together in multiple sections, these panels form a
rigid cylindrical truss member that eliminates the need for a continuous center support shaft,
which facilitates maintenance. The drum is cleaned by a series of vacuum nozzles located on the
outside of the cylinder, allowing convenient media inspection. Industrial Air has also introduced a
new Hi-Vac sleeve receiver that has 400 percent more screen area than standard 30-inch flat screen
receivers, Hunter said.Replacement media for many filtration systems are proprietary, according to
Pneumafils Stonestreet. However, one new venture, FiltersRx.com, a division of Lifetime Industries,
now makes replacement filters available through the Internet.For More InformationLuwa Bahnson3901
West Point Blvd.Winston-Salem, NC 27103(336) 760-3111
www.luwabahnson.com Pneumafil
Corporation4500 Chesapeake DriveP.O. Box 16348Charlotte, NC 28297(704) 399-7441
www.pneumafil.com Industrial Air
Inc.428 Edwardia DriveGreensboro, NC 27409(919) 292-1030

August 2000

Wet Processing UpdateATI Special ReportpH Control In The Dyeing Of Polyamide
DyStars Optidye N program calculates optimum conditions for dye penetration and shade
stabilization.Uptake of acid and metal-complex dyes by polyamide is temperature-dependent. The
fiber takes up the dye at temperatures above the glass transition point because the segments in the
polymer chains become more mobile at higher temperatures. The fibers thus open and allow the dye,
which is attracted to the positive charge on the amino end groups in the fiber, to penetrate the
polyamide. It is then bonded to the fiber through intermolecular forces. At the end of the dyeing
process, a thermodynamic equilibrium is established between the dye dissolved in the liquor and the
dye that has diffused into the fiber. The relationship between the dye concentration in the liquor
and on the fiber is roughly described by the well-known Langmuir and Nernst isotherms.A finite time
is required to achieve this state of equilibrium. The time required depends on the substrate, the
dyes and the process parameters. This process can be described by the laws of dyestuff diffusion.
Applying these physical chemical principles in conjunction with practical experience shows the
dyeing process.Systematic OptimizationThere are two established methods of dyeing polyamide with
acid and metal-complex dyes: the constant-pH process and the pH-sliding process. While the
constant-pH process ensures that the dye exhausts onto the substrate by raising the temperature,
the pH-sliding process achieves exhaustion by a combination of raising the temperature and reducing
the pH.In the constant-pH method of dyeing polyamide (Polyamide S process), the aim is to produce
dyeings that are as level as possible from the outset and have good reproducibility.

Level application of dyes, particularly at the start of the dyeing process, can be ensured if
all of the dyes exhaust onto the substrate uniformly. This is what is referred to as their
combination behavior (See right). It can be achieved in two ways. The first is to select suitable
dyes with good combinability. If this is not possible on coloristic grounds or because of the
fastness properties required, a second method can improve the combination behavior of some dyes by
using an auxiliary with affinity for the dye. The optimum concentration of such auxiliaries depends
on the type of dye, dye concentration and the auxiliaries used. The combination behavior of the
dyes may deteriorate if the amount of auxiliary exceeds the optimum level.To ensure good levelness,
the dyebath must contain enough dye to allow sufficient migration. However, if bath exhaustion is
too low, too much dye is wasted. As well as raising dyestuff costs, which are relatively low
compared with the overall process costs, this alters the final shade and thus impairs
reproducibility. A low pH increases bath exhaustion and reduces migration, while an increase in the
concentration of an auxiliary with affinity for the dye has the opposite effect. The pH therefore
needs to be optimized to ensure optimum bath exhaustion. At the same time, the strike rate (i.e.,
kinetic properties) plays a major role in regulating the dyeing process. During the heating-up
phase, the dyes exhaust onto the fiber in a given temperature range. This is known as the critical
temperature range. The beginning and end of this range are indicated by TStart and TEnd (TStart
must not be confused with the temperature at the start of the dyeing process). The optimum heating
gradient depends primarily on the unit used.To ensure good penetration of the fiber and thus
stabilize the shade and improve fastness, a diffusion phase is required after exhaustion of the
dyes. The time required for this depends on the substrate and diffusion properties of the dyes. In
practice, the diffusion period is often unnecessarily long. This raises process costs and can
damage the goods. Optimum conditions can be calculated using DyStars Optidye N computer program,
which includes both the underlying theory and the necessary dyestuff data.The Optidye N ProgramThe
Optidye N program contains the formula required for systematic optimization of polyamide dyeing
(See below). It contains data on the properties of DyStar products and a number of auxiliaries.
Users enter details of the recipe, dyeing units and substrate for each batch. The program then
calculates the optimum dyeing profile, the pH required to achieve average bath exhaustion of
approximately 95 percent and the auxiliary concentration required to ensure optimum compatibility
of the dyes. Alongside the recipe data, details of the substrate are very important.

Two parameters are required to describe the dyeing properties of polyamide to be dyed in the
constant-pH process. The V value shows how quickly a standard dye exhausts onto the substrate. The
fiber saturation value (SF value) shows the maximum amount of dye that can exhaust onto the
substrate. Any dyehouse laboratory can determine these values by carrying out a few dyeings. Values
determined in bulk conditions vary between 1 and 3 for SF and 0.2 and 5 for V. For a typical recipe
with Telon A dyes, the following exhaustion ranges may be calculated on the basis of the SF and V
values given above.For V=0.2 a range of T
^Start=74°C and T
^End=102°C is calculated. To save time, the bath can be heated to 74°C as fast as the
equipment allows, without any risk of unlevelness. By contrast, for V=5, the final temperature T
^End=31°C, while T
^Start would be below the normal water temperature (theoretically below 0°C).
Consequently, heating the bath too quickly at the start would entail a risk of unlevelness. A dwell
time at the start of the process (e.g., 15 minutes at 20°C) can reduce this risk but not eliminate
it entirely. Moreover, a higher starting pH would be required. In other words, a pH-sliding process
would have to be used. Using a pH-sliding process, the bath could be heated rapidly from 31°C.
These examples show how effective optimization of the dyeing profile can be. The next section looks
at the progress made on the basis of these theoretical findings.Extending The Polyamide S ProcessAs
we have seen, it is necessary to regulate bath exhaustion to ensure the correct level of migration.
In the constant-pH process, the aim is to achieve final bath exhaustion of around 95 percent.
However, to increase reproducibility, bath exhaustion of nearly 100 percent would be ideal. This
can be achieved by reducing the pH. Similarly, if the V value of the substrate is very high and the
strike rate cannot be controlled solely via temperature, a modified version of the constant-pH
process is required. The pH-sliding process was developed from the constant-pH process specifically
for critical shades and problematic units and substrates. This process uses a combination of
temperature rises and a reduction in the pH during dyeing to control exhaustion of the dye. Under
standard dyeing conditions (pH 7), the amino end group and the carboxyl group are protonated. In
other words, viewed from a distance, this material has a positive electrical charge. A negatively
charged dyestuff molecule is therefore attracted to the PA and tries to react with it. Raising the
pH in other words, reducing the concentration of H
⁺ ions deprotonates the carboxyl group, leading to a negative charge. The fiber thus
takes on a neutral or negative charge, and the dyestuff molecules are not so keen to react with
it.Therefore, pH plays a major role in the exhaustion of the dye from the liquor onto the surface
of the fiber and in the diffusion of the dye in the fiber. The optimum pH range required for the
pH-sliding process depends to some extent on end groups in the fiber. Practical trials have shown
that a pH
^Start that generates bath exhaustion of around 70 percent is most suitable. Since the
reproducibility of a dyeing is best at 100-percent bath exhaustion, wherever possible the pH should
be reduced to a level where this is achieved. pH
^End thus depends on the substrate, dyeing recipe and auxiliaries used. This value can be
calculated using the Optidye N program. It is about 3 points below pH
^Start and 0.5 points below the pH used for the constant-pH process.

To optimize the pH-sliding process, we look at three different ranges in which the pH can be
reduced (See right).Depending on requirements (i.e., the level of difficulty), three different
points are recommended for the addition of the acid. In the process shown in Figure 4 as the most
rapid method, the pH is reduced as soon as the temperature reaches the start of the critical range.
This method is suitable for relatively uncritical conditions. The dyeing time at T
^max is then equivalent to the diffusion time in the constant-pH process. The critical
temperature range can be passed through faster because the pH at the start of the process is above
the level used in the constant-pH method, allowing for more level dye uptake.In the second method
illustrated here (the universal method in Figure 4), which has proved reliable in practical trials,
the pH is reduced when the temperature reaches the end of the critical range. This generally
ensures an optimum balance between dyeing time and reliability.The third method, which is shown in
Figure 4 as the most reliable method, should be used only for very difficult shades such as
turquoise. In this method, the pH is not reduced until the temperature reaches T
^max. The low level of bath exhaustion at the higher initial pH value is utilized for
migration of the dyes. Compared with the constant-pH method, the dyeing time at maximum temperature
is increased by the length of time required for dosing.Regrettably, the most suitable of these
three methods can only be determined empirically at present, as no mathematical formulae are
available. Alongside the migration properties of the dye, other major influences are the equipment
used and the composition and pH-dependence of the polyamide.Constant-pH Vs. pH-Sliding MethodsThe
two methods used to dye polyamide are the constant pH method and the pH-sliding method. The
parameters used in this illustration were calculated on the basis of the same recipe with the aid
of the Optidye N program. The unbroken curves show the temperature profile for each method (the
gray curve shows the pH-sliding process and the black one shows the constant pH method), while the
broken line shows the pH profile. The fiber saturation value of the substrate used in this example
is SF=2.0, and the strike rate is V=1.2. Both curves show that the liquor was heated as fast as
possible up to the critical range. Since virtually no dye is exhausted onto the fiber during this
heating phase, the highest possible heating gradient should be selected to save time. The critical
temperature range depends on the pH; it is slightly higher for the pH-sliding process than for the
constant pH process. A higher heating-up rate can be selected in the critical temperature range
when using the pH-sliding method than when using the constant pH method. Once the temperature has
reached TEnd, at which point exhaustion of the dyes is completed or the desired level of bath
exhaustion is achieved, depending on which method is being used, the heating rate is increased
significantly. The temperature is held at the maximum point until full penetration of the fiber is
achieved. This is necessary to stabilize the shade and achieve the desired fastness properties. The
dwell time at maximum temperature may be longer in the pH-sliding process if the maximum
temperature is used for part of the pH-sliding phase.The amount of auxiliaries needed to optimize
the combinability of the dyes varies in the examples shown here. Virtually no auxiliary is required
for the constant pH process (the optimum concentration is 0.2 percent), whereas 0.6 percent is
required for the pH-sliding process.Although the pH-sliding takes longer and requires buffers and a
control unit, it has proved effective, especially for shades where it is difficult to achieve level
dyeings. The process also improves reproducibility because it raises bath exhaustion. Setting The
pHChanging the pH during the dyeing process is a method that has been used since the 1970s to dye
carpets on winch becks, for example. Methods such as the Telomat and Dosacid processes are
well-established. Since the pH is an inverse logarithm of the concentration of H+ ions, it is often
difficult to regulate automatically. Methods used to control the pH during dyeing include pH
buffers, acid or alkali donors and automatic control and regulation units.While a pH buffer
maintains a constant, predefined pH, acid and alkali donors alter the pH as the temperature rises.
Automatic pH measuring and control units can be used for the constant pH and pH-sliding methods.
Moreover, they are often used to monitor the pH and thus control the process. However, in the past,
such units have not been stable enough to become established. A modern pH-control unit is expected
to meet the following requirements:

• robust technology with low maintenance requirements;
• user-friendliness;
• automatic calibration;
• long-lasting electrodes; and
• simple connection to dyeing units

pH-FiT, a pH measuring and control unit developed by Thies, SETEX and DyStar, has a modern
SETEX 737 control unit with integrated fuzzy logic to match the measurements taken to ideal values
using predefined rules. To make it easier to use, the unit has an automatic calibration device,
which contains buffer solutions and a KCl solution to protect the electrodes. pH-FiT is available
either as an integral system built into dyeing units or as a mobile unit, which can be connected
and operated in the same way as well-known alkali dosing units such as Adcon (automet).The pH
sensor (electrode) is built into a bypass parallel to the liquor pump. To prolong the life of the
electrodes, they are only placed in the liquor to take measurements. The bypass has a back cooling
system that cools the liquor to 80°C. This is also designed to prevent wear of the electrodes. In
the mobile unit, the acid or alkali is added via a dosing pump. If several pH-FiT units are
installed in the same plant, it makes sense to pump the chemicals in a closed-system circuit with a
dosing valve for each dyeing unit.To demonstrate how the Polyamide S process can be used to
optimize the pH-sliding process in conjunction with a pH-FiT unit, Figure 3 shows exhaust samples
taken from the dyebath after beam dyeing of a polyamide taffeta fabric with Supranol and Isolan
dyes. To achieve an optimum dyeing profile, the starting temperature for the critical range was
calculated at 48°C, while the final temperature was calculated at 88°C. Since the dyeing involved a
critical shade with high-molecular dyes, the reduction in pH was selected to ensure maximum
migration (i.e., the pH was reduced after the critical temperature range). The optimum pH range in
this case is 8.5 to 5.6. A statistical evaluation was made of the reproducibility of bulk dyeings
performed using the pH-sliding method and the Polyamide S process on the basis of approximately 300
batches dyed on the jet. After optimization of the process, the optimized and non-optimized batches
were compared.Process times were reduced by 27 percent per batch, mainly due to a 65-percent
reduction in the need to correct faulty dyeings. The use of acetic acid instead of an acetate
buffer cut chemical costs by 48 percent. Altering the chemicals used also reduced effluent
contamination, for example, but lowered the COD.

The Compudye SystemOptimizing the pH-sliding process through the Polyamide S process is only
one aspect of our approach to modern dyeing methods. Following successful application of the
Optidye N PC program, where certain data such as the recipe have to be entered manually, it is far
more effective for routine work to automate both these inputs and the transmission of the dyeing
parameters calculated to the control units. Dyehouses often have a host computer system on which
the servers and PCs depend and which is responsible for coordinating routine tasks. The Optidye N
program may use data already in the system. Alternatively, the host system may require data from
the Optidye N program. Once the dyeing recipe has been calculated, data on the recipe, substrate
and equipment are transmitted to the Optidye N program to optimize the recipe. In the simplest
case, this takes place manually. In a fully automated dyehouse, the data would be transferred
automatically via a network. The Optidye N program would then pass the relevant optimized recipe
parameters on to the control unit on the dyeing machine which needs data like T
^Start, T
^End, heating-up rate, pH range, pH reduction time, etc. and to the color kitchen, which
needs data on the dyes required and the optimized additions of auxiliaries.For more information on
pH control research, contact Karl-Heinz Michel, DyStar, at 49 69 2109 2734.

August 2000