• Diffuse Coplanar Surface Barrier
Discharge Plasma treatment allows faster, safer and cheaper activation of PP
spunbonds. Permanent hydrophilicity is claimed from a 0.27 KWh/kg application on
a 17gsm fabric. The treatment also allowed chitosan to be grafted onto the
surface of the PP.
• Dissolving cellulose in ionic liquids allows the production of lyocell-like fibers, but the solvents tried so far are unlikely to yield cheaper fibers.
• Pore size distribution can be measured, albeit laboriously, with a scanning light microscope.
• Hydroentangled fabrics exhibit 2-3 times the dye uptake of equivalent woven or knitted products.
• The atomic force microscope has been adapted to measure the surface friction of PP fibers and hence the effects of spin finishes.
• Dissolving cellulose in ionic liquids allows the production of lyocell-like fibers, but the solvents tried so far are unlikely to yield cheaper fibers.
• Pore size distribution can be measured, albeit laboriously, with a scanning light microscope.
• Hydroentangled fabrics exhibit 2-3 times the dye uptake of equivalent woven or knitted products.
• The atomic force microscope has been adapted to measure the surface friction of PP fibers and hence the effects of spin finishes.
The first EDANA Nonwoven Research Academy was the conference
component of last year's INDEX in Geneva . This second NRA was the first
“stand-alone” meeting, the first to encourage student participation with a
special registration fee of €25, and the first to feature EDANA grants to cover
fees, travel and accommodation expenses for 11 selected MSc and PhD students of
nonwovens.
Held in the lecture theatre of the Ecole Nationale Su p é rieure
des Arts & Industries Textiles (ENSAIT) in Roubaix , France and with the
majority of papers being given by Research Institutes, this conference was as
academic as the organisers intended. From the delegate list, of the 135 people
present, 36 had registered as students (21 from ENSAIT). With a few exceptions,
companies (59 attendees) were represented by their R&D personnel, and the
remainder were from the Research Institutes and Universities. As well as a full
day of lectures, the programme included optional visits to the ENSAIT GEMTEX (Engineering and Textile Materials)
laboratory, IFTH (Institute Francais
Textile-Habillement) and CENT (Centre
Européen des Nontissés). Summaries of the papers presented follow.
Novel approach to fibre recycling
Dr Andreas Bartl , Assistant Professor –
Vienna University of Technology, Institute of Chemical Engineering (Austria)
reviewed fiber production in 2004 and observed that cotton (26 million
tonnes), depending where grown, required between 70 and 500 billion tonnes of
water, between 6 and 19 million tonnes of oil, between 150,000 and 250,000
tonnes of pesticides and between 3.4 to 5.3 million tonnes of fertilizers for
its supposedly eco-friendly production. Thermal energy recovery from its
incineration was only 17 Mj/kg, less than that of the oil needed in its direct
production and far less than the total oil requirement once that used to produce
the pesticides and fertilizers was included. Recycling of such fiber was
therefore urgently recommended. Sources of fibrous waste ranged from predictable
fiber and textile production waste to the unpredictable output of carpet and
tyre shredders via apparel waste with its unwanted contamination of buttons and
zips.
In addition to ecological worries about cotton, legislation, e.g
the vehicle end-of-life regulations and the need for economy drove the need for
increased levels of fiber recycling so Dr Bartl and his colleagues had hit on
the idea of using short fibers from shredders as viscosity modifiers. To test
the idea they had started with well characterized 0.3 to 2 mm viscose fibers,
typically 1.7dtex, guillotine cut by Casati ( Italy ). Sieving trials showed
that sieving was incapable of separating the fibers into well defined lengths
and diameters, but an optical image analyzer (Morfi – which works on suspensions
of fibers in water) could separate a mixture into the component lengths. Next
they took lyocell fiber ground up in an Alpine cutting mill, and fiber reclaimed
from tyres, both ground and as-received, characterized them on the Morfi
analyzer and investigated their influence on the viscosity of glycerol in 1% w/w
suspensions. All trials showed increased viscosity and the ground fibers changed
the flow behaviour from Newtonian to thixotropic. The unground tyre-derived
fibers caused pseudoplastic flow.
Real applications for fibers obtained by grinding waste needled
and spunlaced nonwovens are expected in reinforcing bitumen as used in asphalt,
roofing and sealants and these are now being investigated. Lacquers, cements and
adhesives could be other outlets for recycling such fibers.
A skeptical questioner wondered whether or not the project had
industrial support – maybe from the paint industry. It didn't. Maybe the method
would work for bituminous paints using tyre-derived fibers,
Ionic liquids for man-made cellulose fibres
Dr Thomas Röder , Project Manager –
Lenzing AG, Pulp Research ( Austria ) surveyed the literature on ionic
liquids for cellulose dissolution. Ionic liquids are salts that melt below 100C,
the most valuable being those that are liquid at room temperature (RTIL's).
RTIL's generally comprise a bulky and asymmetric organic cation e.g. 1-alkyl
3-methylimidazolium with anions ranging from simple halides to large organics,
the larger ones tending to give lower melting points.
To replace NMMO in lyocell production the required solvent should:
• Melt below 20C and boil above 200C.
• Dissolve 15%+ of cellulose without excessive degradation.
• Allow cellulose to be reprecipitated in water.
• Be easy to recycle at high efficiencies.
• Be non-toxic and odourless.
• Yield cheaper fibers than lyocell.
• Yield better fibers than lyocell
• Dissolve 15%+ of cellulose without excessive degradation.
• Allow cellulose to be reprecipitated in water.
• Be easy to recycle at high efficiencies.
• Be non-toxic and odourless.
• Yield cheaper fibers than lyocell.
• Yield better fibers than lyocell
The chlorides tend to be good cellulose solvents,
1-butyl-3-methylimidazolium chloride (BMIM-Cl) yielding a spinnable 10% solution
at 100C and a 25% solution given pulses of microwave energy. Unfortunately the
latter was extensively degraded and non-fiber-forming.
The WO 2006/0000197 A1 patent from TITK suggested the use of
BMIM-Cl in a 10-45% solution in water to dissolve wet pulp (50% cellulose) to
give a 16.5% cellulose (DP=530) solution when stabilized with sodium hydroxide
and propyl gallate. This could be air-gap spun at ~50 m/min through ~100micron
holes at ~110C into water. Fibers were stronger than lyocell with similar
elongations, but the proposed solvent recovery system looked expensive.
Lenzing's work with the same solvent and with
1-allyl-3-methylimidazolium chloride (AMIM-Cl) has used dry pulps and achieved
similar fiber properties albeit from lower concentrations of cellulose in
solution (11%). AMIM-Cl gave a slightly lower modulus fiber from solutions of up
to 12% cellulose. Key areas for further work are:
• Optimisation of spinning parameters
• Investigation of degradation and the development of better stabilizers
• Developing a commercially viable recovery system
• Investigation of other RTIL systems
• Investigation of degradation and the development of better stabilizers
• Developing a commercially viable recovery system
• Investigation of other RTIL systems
In response to questions, Dr Röder did not think either of the two
RTIL's worked on to date would yield a cheaper fiber than lyocell. The solvents
are very expensive and corrosive, and residues in effluent would have an aquatic
toxicity equivalent to many other problem solvents.
Fire retardancy using intumescence
Sophie Duquesne , Lecturer – Ecole
Nationale Supérieure de Chimie de Lille ( France ) said intumescence
arises when a carbon source (polyurethane) mixed with an acid (ammonium
polyphosphate) and a blowing agent (melamine) is heated. The resultant foamed
char provides a physical fire barrier. Intumescent mixtures can be applied by
any of the usual coating systems, using masterbatches by extrusion, or in powder
coating of bulky nonwovens.
A laboratory investigation of padding versus backcoating methods
onto a PP nonwoven yielded the following observations:
• Padding allows fast development of the protective foam and
delays fiber melting. However the fibers still ignite
• Back-coating is more effective but if the face is exposed the PP quickly melts and burns
• Extrusion of inherently flame retardant articles could be best but the technique now has to be confirmed on fibers.
• Back-coating is more effective but if the face is exposed the PP quickly melts and burns
• Extrusion of inherently flame retardant articles could be best but the technique now has to be confirmed on fibers.
Improved textile coating after nap-raising needling
Dr Barbara Schimanz , Project Leader –
Saxon Textile Research Institute (STFI-Germany) has tried needling a
stitchbonded nonwoven to create a hairy surface in order to increase the
adhesion of any coating applied to that surface. Adhesion of the coating did
improve by 15-20% but the needling operation almost halved the nonwoven's MD
strength, presumably as a result of breaking the stitching yarns. CD strengths
were however more than doubled. Less aggressive ways of improving adhesion were
not discussed.
Penetration and spreading of liquids in layered nonwovens
Dr Ningtao Mao , Senior Research Fellow –
Nonwovens Research Group, Centre for Technical Textiles, University of Leeds (
United Kingdom ) pointed out that while liquid absorbtion and
penetration in homogeneous single layer materials is well understood, the
performance of multilayer composites is complicated by the effects of the
interface between layers. This interface region is now being studied
theoretically and practically at Leeds University , but these first attempts at
developing a mathematical model to predict composite absorbency behaviour have
concluded that “work is required to elucidate the structure of this region”.
Difficult questions about fluid flow against gravity in diaper cores and the
absorbency of non-Newtonian fluids such as menses were probably meant as helpful
indications of a possible future direction.
Structuring of spunlaced nonwovens
Dipl.-Chem Wolfgang Schilde , Department
Manager – Saxon Textile Research Institute (STFI) ( Germany ) has been
using their state-of-the-art pilot line with Fleissner Aquajet to investigate
creating 3-D effects (dimples) in spunlace nonwovens. After basic
experimentation to optimize the process, factors affecting the thickness of a
3-D structure were explored, line speed proving the most important for a given
fibre. At 25 m/min well defined dimples were obtained. Measurements of heat
insulation properties led to the suggestion that 3-D nonwovens made from FR
fibers could be used in the insulation layer of fire-brigade clothing where the
extra thickness would allow savings of 30-50% in weight of fiber used.
An expert system for needlepunched geotextiles
Dr Amit Rawal , Post-doctoral Researcher
– CSIR, Materials Science and Manufacturing ( South Africa ) has
measured the effects of feed-rate, stroke frequency and depth of needle
penetration on the properties of needlepunched geotextiles.
• Increasing needle penetration increases MD fiber orientation
• Increasing stroke rate reduces MD fiber orientation
• Permeability of geotextiles is reduced by increases in both needle penetration and stroke frequency
• Lower feed rates increase the permeability
• Increasing stroke rate reduces MD fiber orientation
• Permeability of geotextiles is reduced by increases in both needle penetration and stroke frequency
• Lower feed rates increase the permeability
The “expert system” developed from the mathematical model allows
the design of geotextiles with specific properties in a cost effective manner.
In response to questions, fiber orientation had been measured by
recording the angles of surface fibers relative to MD. Maybe there should be a
factor in the model for fiber properties, and maybe the model should now be
verified experimentally.
Nonwoven pore size distribution from optical profiling
Dr Philippe Vroman , Associate Professor
– Ecole Nationale Supérieure des Arts et Industries Textiles (ENSAIT) (France)
has used white-light interferometry with a CCD microscope stepping at 1
micron intervals in the X and Y directions and with 1 nanometer resolution in
the Z direction to build up multicoloured images of a nonwoven fabric. This
non-contact technique is commonly used for characterizing surfaces in the
metallurgical, optical and the paper industries. Here, vertical stepping allows
the nonwoven to be characterized in several slices through the thickness, each
slice being coloured differently. After acquiring the image it needs several
stages of processing prior to pore size distribution measurement, “thresholding”
– removing background fibers, and “binarisation” – to separate fibers from pores
being most important. Pore sizes are then measured one by one from the final
image and their distribution, mean, median and maximum sizes are calculated.
Correlations between the measured values and hydraulic properties and filtration
performance appear to be good. However the method only works well on thin
materials, is very time consuming – around 2 days for a result on a few square
millimeters - and is only suitable for use in a research environment. On the
plus side, the same equipment can be used to measure thickness (non contact),
fiber orientation, cloudiness, cover factors, roughness and the embossing ratio
of a calendared product.
Could a flat-bed scanner be used to get faster results? Yes, but
it would miss the 3-D information which allows the effects of the next layer of
fibers to be accounted for. Can surface roughness be correlated with hand-feel?
They are working on this. Could the method be made to work on-line? Yes, with
different sensors, but a confidentiality agreement prevents information sharing
here.
Nonwovens as potential vibration dampers
Dr Elaheh Ghassemieh , Lecturer –
Mechanical Engineering Department, University of Sheffield (United Kingdom)
has measured the vibration damping properties of nonwovens by bonding
them to a magnetically-excited cantilever beam in the ASTM E-756-98 standard
test. For fiber-glass nonwovens, damping ratio increased linearly with basis
weight, the rate of increase increasing with the amplitude of the vibration. If
the glass nonwovens were reinforced by stitchbonding, the damping ratios were
further increased, but only if the reinforcement aligned with the beam
direction. Aramid nonwovens proved less efficient dampers than glass, but had
much greater increases in damping with amplitude. Had Dr Ghassemieh studied
polyester nonwovens? Yes, but her applications were in aerospace where high
modulus and resistance to corrosion were required.
Dyeing performance of hydroentangled fabrics
Andrew D. Hewitt , Postgraduate
Researcher – Nonwovens Research Group, Centre for Technical Textiles, University
of Leeds ( United Kingdom ) has shown that in standardized conventional
textile dyeing operations, hydroentangled nonwovens exhibit 2-3 times the
dye-uptake of knitted or woven textiles made of the same fibers at the same
basis weight. This applies to cotton (direct dyes) and polyester and PLA
(disperse dyes). Furthermore the HE fabrics exhibited increased depth of shade
and higher wash-fastness. The effects were thought to be due to the lower
density and even fiber distribution in the nonwoven compared with the highly
densified yarn structures in the conventional textiles. However varying the
bonding pressure in HE to make denser fabrics (70 bar up to 190 bar, which
reduced the fabric thickness from 1.4 to 1.1 mm) had no effect on the dyeing
performance. If dyeing conditions were altered for the HE fabrics to restrict
dye-uptake to the levels obtained on wovens and knits, then savings in dye,
energy and wastewater treatments would be obtained, and the environmental impact
of the dyeing process could be reduced.
Questioners were concerned that the dyed HE fabric lightfastness
would be inferior and doubted the ability of HE fabrics to survive commercial
dyeing operations. Lightfastness remained to be measured. Dimensional stability
of the HE fabrics had been good in laboratory dyeing.
Plasma surface modification
Kenth Johansson , Area Manager Surface
Modification – YKI, Institute for Surface Chemistry (Sweden) said the
disadvantages of conventional plasma treatment included the need for long
treatment times, the costly Helium gas and the short life of the electrodes. A
new method called Diffuse Coplanar Surface Barrier Discharge Plasma treatment
overcame these problems by:
• By using 10x the usual power density (100 W/cm 3 ), speeds can
be increased
• By alternating the positive and negative electodes and embedding them in a single ceramic plate (treatment from one-side only). This arrangement created a “waste-free” localized plasma field with high homogeneity.
• Using nitrogen or carbon dioxide gases along with the reactive gases instead of helium.
• By alternating the positive and negative electodes and embedding them in a single ceramic plate (treatment from one-side only). This arrangement created a “waste-free” localized plasma field with high homogeneity.
• Using nitrogen or carbon dioxide gases along with the reactive gases instead of helium.
This process could activate the surface of a 17 gsm PP spunbond
using only 0.15 KWh/kg and could create a permanently hydrophilic surface with
0.27 KWh/kg. The embedding of the electrodes in a ceramic plate yields a safe
and robust system which incidentally allows the nonwovens to be pressed and even
laminated against the plate.
After plasma activation chitosan could be grafted onto the surface
of PP simply by dipping the fabric in a chitosan solution.
In what was really a second paper on a different subject, Dr
Johansson described the use of an atomic force microscope to measure the
frictional properties of polypropylene fibers with and without spin-finishes.
Here a short length of one fiber was glued to the cantilever of the AFM and this
was “scanned” across another single fiber. Plots of frictional response against
load and distance were obtained. These showed that spin-finishes (alkyl
polyether ethoxylates) tend to migrate to the crossover point of the two fibers,
reduce the static friction by a factor of 3 and prevent viscoelastic deformation
of the fibers.
Separation of Tencel fibres during airlaying
Dr Mohammad Osman , Researcher -
Nonwovens Research Group, University of Leeds ( United Kingdom ) has
used high speed photography to show that the main fiber-chip opening in an
air-lay head (M&J-Type) occurs by collision of the rotor blades with chips
on the screen. Effects of fiber morphology, pre-opening, fiber finish, fiber
crimp and cutting methods have been studied but, maybe for commercial reasons,
will not be reported for some time.
Calvin Woodings
26/4/2006
ENSAIT Founded in 1889, the
ENSAIT trains 47% of French textile engineers to post-graduate level. Research
at ENSAIT: The GEMTEX (Laboratory of engineering and textile materials) is a
university laboratory. It is structured around two main research areas, namely
processing and chemistry of materials and composites, (which include processing
of textile materials and properties) and automation and textile logistics,
(dealing with modelling, simulation and control of textile processes as well as
supply chain management).
IFTH performs Applied Research
and Development actions that are intended to make technology progress and to
improve production techniques. The Institute is also responsible for the Bureau
de Normalisation des Industries Textile-Habillement - BNITH (Textile-Apparel
Industry Standardisation Office). It participates actively in several French,
European and international standardisation commissions. Within the framework of
training and consulting actions, IFTH provides tools in decision making to
companies such as software and possibilities of interactive exchanges:
technological watch clubs, thematic days, distribution of useful information,
etc....
CENT is the European Centre for
Nonwovens, which is dedicated to innovation in the nonwovens sector. The Centre
offers well equipped, flexible facilities and laboratories, covering various
technologies. It provides a wide range of scientific and technical capabilities
covering different nonwovens areas and processes.