Notes from the EDANA Nonwoven Research Academy Roubaix 20-21/4/2006

Key Points

• 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.

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

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

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.

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

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.

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.