About 100 delegates, mainly staff and students from Europe’s technical institutes and universities attended this now bi-annual conference. Two thirds of the papers presented were from technical institutes and universities and provided interesting updates on progress made on numerous EU-funded initiatives in nonwovens.
Ryan McEneany, Research Scientist, Kimberly Clark, USA described the outcome of a 10 year development programme on biopolymers. This was part of a strategy to cease being the world’s largest single user of polypropylene and become a major user of sustainable materials. Their PP use was mainly in SMS processes and while PLA worked well in spunbond, it was difficult in melt-blown due to the non-availability of the right Melt-Flow Rate.
Commencing with Natureworks 6201D PLA resin (MFR = 80g/10min at 210oC), quite apart from the viscosity problem, they experienced slow crystallization due to its high Tg (~60oC), high fibre shrinkage, biased orientation in the web and poor thermal bonding when draw ratios were high. They looked at flow modifiers, higher process temperatures and lower molecular weight polymers and it was the latter, obtained by processing undried resin, which showed the most promise...They therefore bought a Custom Humidification Unit from AEC to allow the PLA’s moisture content to be raised to 1000ppm in a controlled manner without risk of condensation. They processed it through a 40:1 L/D twin screw extruder at shear rates in excess of 1000 per second to maximise chain scission, vented the extruder prior to repelletising and finally dried the resin ready for melt-blowing. The final MFR ranged from 10 when sheared at 87ppm moisture to 116 at 1226 ppm moisture. This still proved too viscous in MB, but when 10% of an 8000 molecular weight polyethylene glycol was added a final satisfactory MFR of 310 was obtained.
As received, the PLA 6201D had a molecular weight of 107,800. After the high-scission processing and 10% PEG addition this had dropped to 58,400, sufficiently above the 40,000 danger level where Natureworks report PLA to be too brittle to use.
A further benefit of adding PEG is that it acts as a nucleus allowing PLA to crystallise more like PP. Furthermore by using PEG-PPG block copolymer additives they could tailor the crystallisation to suit their needs and reduce the hygroscopicity of the final MB web. Quench and draw temperatures could be adjusted to maximise crystallisation rate and to obtain higher crystallisation levels at lower draw force. The final MB process used a single screw extruder with limited blend capability running at 190-210oC to feed a single die tip at 90 degrees to the web direction, 8-12” above the web conveyor.
Fibre formation was good, and while the PLA fibres are tackier than PP there were no wire-release issues. Throughputs could be raised into the commercial range, but was still limited by high die-tip pressure. Using the best PEG-PPG random copolymer additive, stronger webs with much higher extensibility were obtained than possible with PP. Without the additive, both MD and CD strengths of the PLA webs were slightly lower, but the extensibilities were halved in the MD and quartered in the CD.
Remaining challenges were listed as:
· Ageing of the webs further dropping the molecular weight towards the brittle zone.
· Phase separation from PEG crystallization
· Improving the tensiles and crystallization further
· Web shrinkage
· Increased hydrophilicity.
There were more questions than time available:
· Were the monomers created in the hydrolytic degradation removed? No, but the fabrics smelled OK. (no burnt sugar smell)
· Why not source low molecular weight PLA? It would be a special product requiring very large orders and it would be more expensive.
· Does the more hygroscopic degraded PLA still need a spin finish? Yes, but not for rewet.
· Have any ageing studies been done? Yes: the PEG crystallises out and the brittleness increases so the meltblown webs have a reduced shelf-life. New formulations are being evaluated to overcome this.
· Is biodegradation rate affected? No: PEG is fully biodegradable.
Claudio Ermondi, Senior VP, Ahlstrom, Italy was replaced by Ray Volpe, Food & Medical Business, USA. He gave a somewhat different paper to the one advertised, preferring to major on a general introduction to the Ahlstrom Group and its successes in reducing its environmental impact.
With regard to the new PLA spunbond production, Mr Volpe thought the process needed more work to remove the “black art”.
· Standard PP spunbond machinery had had to be adapted to suit PLA.
· Temperature control had to be tightened throughout the process, especially in calendering.
The resulting BioWeb™ nonwovens were nevertheless being used in ultrasonically sealed teabags, diaper leg-cuffs, topsheets and backsheets, plant root wrap and soft-furnishing constructions.
In response to questions about capacity and bottlenecks, he said progress had been slowed by the recession during the last two years, but should pick up in the next year or two. They hoped to be using 2x to 3x more PLA by 2015, and needed another nonwoven producer to “take the jump” into PLA spunbonds.
Dr Josef Innerlohinger, Project Manager, New Applications, Lenzing (Austria) described various ways of making cellulose particles commencing with the well-established micro-crystalline cellulose made from pulp by dissolution of the amorphous cellulose in acid.
· Tencel®FCP was made by grinding short-cut Tencel tow and therefore could have diameters down to 0.9 micron and lengths of around around 0.4 mm. They were intended as fibrous fillers for plastics reinforcement but may also find uses in paper, board and construction materials.
· Tencel® CP appeared to be 5-250 micron particles made by precipitation of the NMMO solution of cellulose in a high-shear mixer, followed by grinding. It has found an application as filler in PU foam mattresses where the absorbency of the Tencel particles provides a drier sleeping environment than is usual on foam.
· Tencel® Fibrids are made by fibrillating short-cut Tencel® in a refiner until nothing but the fibrils remain. These are a few microns long and sub-micron in diameter. They have high absorbency (WI = 600%) arising from their high surface area (200m2/gm if solvent dried) and make film-like paper when sheeted.
· Additional functionality can be achieved using dope additives and a myriad of possible uses emerges. Lenzing are looking for partners to help develop applications.
Annabelle Legrix of Imerys Minerals (UK) described their experience with film production using resins loaded with calcium carbonate. Plastic bags made with 15% CaCO3 content required 10% less production energy, due to a more homogeneous melt arising from faster heating (10x increase in melt thermal conductivity), lower die-tip pressure, and faster cooling. The latter gives better bubble stability for blown film and faster cycle times in bottle moulding. (10% CaCO3 addition gives an 8% output increase for PE film. 40% CaCO3 addition gives a 40% reduction in bottle production cycle time.)
For fibre production, CaCO3 with finer particles, no particles near the jet hole size, and easy dispersion without agglomeration is needed. Fiberlink™ 101S is such a filler, and has been successfully added directly to PP for meltblowing and to masterbatches for spunbond production. In these spunlaid processes, the energy savings arising from faster heating and lower bonding temperatures have been observed and the increase in density means area output can be increased to maintain constant basis weight.
While 40% filler levels have been processed into meltblown, 20% is the maximum recommended level in both meltblown and spunbond. In spunbond, deniers down to 1.5 have been processed without fibre breakage.
Environmental effects are being evaluated. So far the carbon-footprint has been shown to be reduced c.f 100% PP at the same basis weight. Other environmental impacts and process energy impacts are being studied, as are the possible spin-offs from substantial increases in opacity arising from the filler. (Opacity of a 25gsm web goes from 28% to 33% for a 0 to 20% filler increase.)
Oil absorbency of filled MB PP is higher than 100% PP on a fabric volume basis, and filtration efficiency rises from 86% to 89% as 10% filler is added. This is thought to be due to the higher surface area and surface roughness of the filled fibres.
Testing of filled and unfilled PP in a wipe blend with rayon showed that the filler increased opacity and strength while panel testing of the same wipes showed consumers preferred the wet texture of the CaCO3 filled wipes.
In response to questions
· the particle size for fibre production was 1.4 micron with 98% below 8 microns,
· no trials with waste recycling had been done,
· Filler did reduce fibre strength but this had been made up by alterations of other process conditions.
· Different finishes would be needed, and these would also depend on polymer (PP, PET, PLA etc)
Jean Ruiz of the Paper Technical Center (CTP - France) described an experiment with 13 market pulps, refined at 3 different intensities and converted into 20gsm handsheets for evaluation of bulk and surface softness by expert panels. 5 panels were used each with 7 women and 8 men, 1 being from CTP the others being from the companies supporting the project.
· Softwood and deinked pulps were harshest
· Softness decreased with refining intensity
· Hardwood pulps, especially eucalyptus, were the softest
However the comparisons were made at similar refining conditions whereas in reality the optimisation of refining for each pulp could alter its softness potential relative to the others.
Mathematical modelling of the results showed excellent agreement (r2=0.86) between actual and predicted softness levels. The model was based on MorFi analysis of pulp fibre characteristics such as mean kink angle, mean curl index, broken fibre content, and fines content, both by length and area. It also showed that 60% of the perceived softness was due to the fibres used, and 34% was due to the effect of process conditions on the paper surface state.
On-line assessment of softness was attempted by using the output of an on-line fibre analyser fed through the mathematical model to predict the “softness potential” of the tissue in something close to real-time. The model was validated during one week of industrial trials, where 189 reels of tissue were produced.
SCA, Ahlstrom, Scott Paper, Botnia, BTG, and Fibria were listed as partners.
Dr Elaine Durham, Research Fellow, Nonwovens Research Group, Leeds University (UK) listed the requirements for nonwovens in tissue culture:
· The nonwoven scaffold should provide a template to allow the 3D organisation of the cells being cultured.
· It’s shape and strength will be tissue specific (ligaments need very different scaffolds to bone)
· It should be highly porous with a pore size to suit the cells and to allow transport of nutrients, oxygen and waste products.
· It has to appeal to the surgeon and appear strong enough for implantation.
· It should be biocompatible, biodegradable and non-toxic, because...
· ...it must be absorbed by the body as the tissues regrow.
Scaffolds could be made from synthetic sponges (“porogen-fused scaffolds”), electrospun webs, hydrogels and nonwovens. They could also be made by 3D printing and laser-sintering.
The internal architecture of the nonwoven is thought to be key to its success. Cell growth tends to occur at the surfaces and the resulting films prevent further growth in the deeper pores. So, Leeds have adapted their hydroentanglement process to make nonwovens with fine capillaries running down the MD by hydroentangling two pre-needled 60gsm PLA webs together either side of 0.2mm diameter high tenacity filaments spaced 0.4mm apart. These filaments can be pulled out leaving capillaries down which cells can travel into the interior. X-ray micro tomography has been used to show where the cells are within the scaffold after 14 weeks of culture. They still appear to be concentrated at the surface of the scaffold, and on the internal surfaces of the micro capillaries.
Dr Durham concluded that the scaffolds with microchannels have the potential to improve cell distribution and infiltration. In response to questions:
· The microchannel scaffolds were 2.5mm thick
· Dynamic cell culture had been tried and did give more penetration.
· The cells were only growing on the surface of the capillaries
· The cell-broth had been pipetted into each microchannel.
One questioner observed that other labs don’t have this problem and can grow cells throughout standard nonwoven webs.
Annahit Arshi of the Institute for Technical Textiles, RWTH, Aachen (Germany) reviewed RWTH’s development of a medical grade, quality assured production line for nonwovens for tissue culture.
She observed that the change from supplier to client dominated health care would result in the need for a whole spectrum of artificial organs and tissues to extend the lives of tomorrows old people. Nonwovens provide excellent scaffolds for cell growth, having a porous structure similar to collagen, while being strong, absorbent, drapable, and capable of being made from a wide variety of fibres with different surface structures.
At the microstructure level, fibre shape and surface texture are adjustable: at the meso-structure level crimp and texturing of fibres or filaments is important, and at the macro level, pore size and shape along with wettability and absorbency are key. All these factors could affect the adhesion, proliferation and differentiation of the cells to be grown on them.
With funding from the EU and support from Freudenberg, RWTH were therefore examining design and development concepts for the production of medical grade nonwovens and Ms Arshi was focussing on Failure Mode Effect Analysis to get a cumulative risk value for all possible failure-in-use mechanisms. This RPZ value ought to be below 125, but on the current machinery it was running at over 1000 due to high levels of contamination, including metals, from the fibre preparation and needleloom in the new line. So, RWTH is developing a new needleloom with complete mass-force compensation (no vibration), totally encapsulated lubricants, and clean-room quality bearings. They are also developing a new staple fibre cutter with novel tow-traction system and new blade geometry, and a new carding system.
Asked about the importance of fibre orientation in the web, Ms Arshi said it depends on the cells to be cultured. Adipose tissue needs random laid to give roundish pores and muscle tissue needs parallel-laid to give tubular pores. Wouldn’t other nonwoven process which gave less metal contamination than card/needle be better? Maybe.
Dr Karen Wiensch, Head of Regulatory Toxicology, BASF (Germany) defined nanotechnology as the intentional generation of structures smaller than 100nm where properties (mechanical, optical, chemical, biological etc) differ from those at a larger scale. Nanomaterials in powder form are easily dispersed as aerosols and can penetrate the skin or be deposited in the lungs and intestines where they can be further distributed around the body causing inflammation, catalysing the formation of reactive compounds and directly interacting with cells.
Recent studies include:
· The effects of titanium and zinc nanoparticles used in sunscreens on UVB-damaged skin.
· The distribution of nano-TiO2 in tissues following intravenous introduction into rats.
· The development of a test for assessing the effects of inhalation of nano-TiO2 by rats.
· Effects of nano-TiO2 and nano-ZnO on the mobility and reproduction of fresh water Daphnia magna
· The effects of inhaling carbon nanotubes.
In the latter study, during a 5 day exposure study, all the carbon nanotube samples induced inflammation in the lungs of the animals, and granulomas formed at high concentrations. The “no observed adverse effect concentration” (NOAEC) was less than 3mg nanotubes per cubic metre of air. In the 90 day exposure study, 0.5 and 2.5mg/m3 of nanotubes in air caused absolute and relative increases in lung weight, mild to severe inflammation, multifocal granulomas and lipoproteinosis in all animals, with a severity clearly related to nanotube concentration. Here 0.1 mg/m3 was regarded as the Low Observed Adverse Effect Concentration (LOAEC)
Dr Martin Dauner of ITW Denkendorf (Germany) reported on the breakthrough arising from the collaboration of ITV with Rieter OFT GmbH to develop centrifugal spinning for nanofibre production. ITV now has a 1m wide pilot line which can use the same polymers and solvents as nozzle electrospinning but at levels of productivity approaching that of melt blowing.
At the same time, progress to produce submicron fibres from meltblowing was made by Hills Inc (USA), Irema (Germany) and Hollingsworth and Vose (Germany), and all these had to address the problem of how to handle the fragile webs and control their performance in filtration. There are now several other projects underway:
· “Nablo” is a joint project between Freudenberg Filtration Technologies, Neumag Oerlikon Textiles GmbH, ITWM and ITV which targets developing melt blow technology to produce 0.1 micron fibres. This has already achieved 0.2 microns in the lab and 0.4 microns on the pilot line.
· “Nanoseparator” brings together Hengst GmbH, Junker GmbH, Nano-X, LFG Erlangen and ITV (all Germany) to produce nanofibres by centrifugal spinning. In one application the finest PP is performing best and for this melt-blow technology is now used.
· “Nanofatex” is a collaboration between Freudenberg Household Products, Polman GmbH, TransMit, and the Research Centres at the University of Marberg and ITV to develop nanofibres for use in cleaning towels.
Dr Ralf Taubner of the Saxony Textile Research Institute (STFI - Germany) introduced Hycospun®, their registered name for hydroentangled nonwovens containing fine-fibre meltblown webs. These were part of a project aimed at developing functional multilayer structures for technical applications.
Hydroentanglement was now the most important nonwoven bonding technology for staple fibre webs. Their 1m wide pilot line used an Adritz-Küsters hydroentanglement unit fed by a Reicofil 4 SMS with bico capability and a Küsters thermal bonding calendar was ideally suited to this sort of experimentation. (It also had in-line Dilo needlepunching and a Fleissner through-air bonder-drier before the Celli winder.)
Numerous data tables provided the properties of many laminates and illustrated Dr Taubner’s main point: using hydroentanglement to laminate a wide range of nonwovens together offered excellent possibilities for manufacturing high performance nonwoven composites.
Has STFI tried laminating spunbonds made of crimped bico-fibres to get more volume? Yes.
Dr Francois Rault, Associate Professor – ENSAIT (France) defined noise as unpleasant, undesirable and unwanted sound which has adverse health effects such as deafness, sleep deprivation, auditory tiredness, stress and increased risk of accident. He reviewed sound absorbtion theory and recent work on the Normal- incidence sound Absorbtion Coefficient (NAC) of fibrous absorbents concluding that:
· Finer fibres absorb more sound (higher NAC)
· Irregular fibres absorb more sound than round fibres, so natural fibres are generally better absorbers than man-made.
· The 4DG “deep-grooved” polyester absorbs as much sound at 6.7 dtex as round fibre does at 1.7 dtex.
· Flax fibres give the best NAC
· Multilayer structures absorb more sound than the equivalent thickness and weight of a monolayer.
For the multilayer structures, needlepunching and hydroentangled materials were used, and the best performance was with hydroentanglement when the sound approached from the hydroentangled side. Furthermore, alternating layers of HE and NP fabrics in a 4-ply structure absorbed more sound that the same fabrics arranged in pairs.
Dr Simone Gramisch of the Fraunhofer Institute for Industrial Mathematics (Germany) showed how the needle-hole pattern in a needlepunched nonwoven could be computer-derived from the needle layout and knowledge of the web properties, its feed rate, and the drafting forces applied. If this pattern looked unacceptably non-random it was possible to calculate which needles to move to which free holes in the needle-board to correct the problem, without ever making any nonwoven fabric. An intriguing spin-off of the technique was the potential to set up a needleboard with an apparently nonsensical arrangement of needles which in production, after multiple punches and drafting, produced a nonwoven with holes in the form of whatever letters or logo had been pre-programmed into the board set-up. However in practise, a 1% change in the theoretically required feed rate would result in the logo being unacceptably blurred.
Dr Amit Rawal, Associate Professor of Textile Technology, Indian Institute of Technology, (India) used the theory of fibre contacts to model the mechanical properties of thermally bonded nonwovens. The mathematical approach proved inscrutable, but the following conclusions were gleaned:
· Tensile failure occurs due to fibre pull-out from the bonds.
· A simple 2D micromechanical model can predict the behaviour in compression.
· Classic Freeston and Platt modelling overestimates bending rigidity, but Dr Rawal’s modification of the procedure gets nearer the truth.
Work continues on the modelling of nonwovens hydraulics, shear, tear, permeability, wetting and wicking using the same theory of fibre contacts.
Dr Philippe Vroman, Associate Professor, ENSAIT (France) focussed on the potential of long vegetable fibres as substitutes for glass in composites. Of the vegetable fibres considered, flax, hemp, ramie, jute, kenaf, coir, sisal and cotton, flax showed the greatest potential especially when specific (i.e. corrected for fibre density) tensiles and elastic modulii were considered. However, the incorporation of natural fibres into polymer matrices is fraught with problems:
· Lack of adhesion to the polymer. Compatibilisers or coupling agents need to be added to the fibre surface.
· Poor thermal stability can cause not only a deterioration of mechanical properties but also odours, fogging, dust and colour changes. Fibres need to be coated or grafted with monomers to improve stability.
· Moisture sensitivity can lead to dimensional instability. Again grafting with monomers helps.
· Biodegradability and photodegradability need correcting and here again; monomer grafting could be the solution.
· Variation in fibre properties with harvest, region grown etc leads to variation in composite properties.
In trials to date, the best results have been obtained using a 70/30 flax/PP needled nonwoven faced with lightweight webs of the same blend hydroentangled onto each surface. This laminate, with a 1650 gsm basis weight was thermo-compressed at 200oC to make a 2mm thick bar for testing.
Mohit Raina, Head of Spinning Technology, RWTH Aachen (Germany) has been working on new methods for non-destructive characterisation of the structure of nonwovens.
· Fibre orientation was assessed by scanning an A3 size sheet and using image analysis to quantify the fibre directions. The resulting fibre orientation vectors could be overlaid onto the original image to give a visualisation of the variations in orientation.
· The capacitance and hence the permittivity coefficient of the web was measured over a wide range of frequencies (1000 to 600,00 Hz). Results from this dielectric analysis have been correlated with basis weight, and fibre blend ratio. However the results are not absolute and relative humidity must be tightly controlled.
· A micro CT scanner has been used to visualise the 3D structure of a porous nonwoven. Fibre positioning and the resulting pore size and volume can be analysed.
Christoph Hacker of the Institute for Technical Textiles at RWTH Aachen, (Germany) described the RWTH development of multi-jet electrospinning of commodity polymer melts to make fibres of less than 0.5 micron diameter under conditions which could be operated on an industrial scale. The procedure involves:
· Using a reduced melt viscosity (PP with 190,000 molecular weight was mentioned).
· Blending it with a “slipping agent”.
· Spinning it from a charged 64-nozzle spinneret block fed from a piston pump at a throughput of 0.2ml/hr/nozzle.
· The conveyor collected filaments with 552 ± 260nm diameter.
· 18 m2/hr of 0.5 gsm “nonwoven” results.
This nano-nonwoven is very fragile and must be bonded to the surface of a substrate. Early trials with calendering, needling or hydroentanglement of webs spun from a single nozzle destroyed the nano-nonwoven. Spray bonding looks possible but has the disadvantage of reducing the porosity and thickening the filaments. Applications in filtration and tissue engineering are anticipated.
Kay Grinneback, Senior Scientist, SWEREA (Sweden) is developing carded/bonded nonwovens which are highly resistant to penetration by nails, high pressure water jet cutters, or knife-stabs. This market is currently dominated by wovens made from para-aramids or ultra high molecular weight polyethylene yarns where the force taken to prise apart the warp and weft accounts for much of the penetration resistance. SWEREA is concentrating on developing nonwovens for two specific applications, one being a shoe liner to prevent nail penetration through the sole and the other being protection from the water jets used in hydro-demolition and rust removal.
Water jets at the highest pressure used in industry can penetrate the woven protection and cause serious injuries. The energy released in 0.1 second hit from a 3000 bar water jet at a distance of 7mm is equivalent to a direct hit from a hunting rifle. The new nonwovens made by carding Dyneema fibres (UHMWPE from DSM) and bonding with a special polymer can now offer protection against these jets.
Ina Sigmund of STFI (Germany) has been using the new extrudable melamine resins from Borealis Agrolinz in an innovative lab-scale meltblown process to make 35 to 350 gsm self-bonded nonwovens containing fibres from 1 to 12 microns in diameter. These are inherently flame retardant (LOI=32), don’t melt or shrink in a flame and also offer high thermal and acoustic insulation. They have high filtration efficiency and are resistant to alkalis and organic chemicals. Acid resistance is only fair however. Applications in hot gas filtration and protective clothing are envisaged.
Thomas Broch Nielsen of Fibertex (Denmark) has developed super-hydrophobic, self cleaning nonwovens by coating with isotactic PP nanospheres and here the repellency arose from the so-called “lotus effect”. He now has a permanently hydrophilic coat for topsheet which can be applied from a kiss roll and this has been shown to give a constant strikethrough time of 2 seconds over 20 insults where the normal hydrophilic finishes fail after 6 insults.
For geotextiles production, a modification of the polymer with UV absorbing nano-particles improved their stability according to EN12224 from 14 days to 4 months, and this material is now commercially available.
Fibertex also have an Elmarco Nanospider 0.5m electrospinning pilot line and are using this to coat various substrates with various polymers in the form of fibres below 1 micron diameter. They see the resulting products as filling the gap in the purification market between traditional nonwoven filters and membranes.
Dr Gunter Scharfenberger, Manager, Fibres and Finishing, Freudenberg R&D Services(Germany) reviewed the progress on the government funded project to make “bio-inspired nonwovens on the base of recombinant silk proteins.” Here, Freudenberg (nonwoven production) along with BASF (raw materials), and Lohmann & Rauscher (converting and retail), are collaborating with the University of Bayreuth and RWTH Aachen on the development of wound dressings and anti-allergenic surfaces. The recombinant protein being electrospun is composed of well-known sequences of spider silk and resilin insect protein and is produced by “white biotechnology” and expressed by bacteria. 10% aqueous solutions of the protein stabilised with polymeric detergents and electrospun yield webs with too-many beads, but at 20% the yield of nanofibres increased dramatically. Further improvements followed from the use of polyethylene oxide additives at up to 1.5%.
The process is now being scaled up and the laboratory samples are being subjected to medical tests to evaluate performance.