Splittable Bico Fibres in Decorative Nonwovens

The final summaries from Roubaix...

Ralf Taubner of STFI (Germany) promoted STFI’s facilities mentioning their Reicofil spunbond, Hergerth carding, Fleissner hydroentanglement, Danweb air-laying and Küsters calendering.  He provided a wealth of data on nonwovens which could be made from the kit before concentrating on a current project for Duni (Sweden) intended to improve the lustre and colour intensity of their majority-pulp tableware range.  All composites where the pulp was sandwiched between spunbond and/or carded webs looked and felt better than those with a pulp surface, and surfaces of splittable PLA/PE fibres which had been hydroentangled were best of all.

Modelling Nonwoven Compression Behaviour

Amit Rawal of the Indian Institute of Technology, Delhi (India) has developed a two-step model to describe the uniaxial compression behaviour of thermally bonded nonwovens.  The results from this model have been compared with experimental data on the thickness under various pressures of parallel and random laid structures.  Good agreement was obtained.  It was concluded that fibre modulus, fibre volume fraction, Poissons ratio and the alignment of fibres are the key determinants of compression behaviour. The model could be applied to other porous networks such as those made from multiwalled carbon nanotubes.

Modelling the Spun-laid Nonwoven Process

Christian Leithäuser of the Fraunhofer Institute of Industrial Mathematics (Germany) described the modelling of melt-flow in the spin pack, of extrusion and drawdown, of turbulence in the drawing air and of fibre laydown.   By combining these models developed within 8 different doctoral theses undertaken between 2009 and 2013 the Fraunhofer ITWM has, in essence, created a virtual spunbond line.  The models are now being used to optimise or even completely redesign the spinning process and to evaluate and compare virtual nonwovens prior to their production.

A Viscose/Bico Air Laying Expert System

Tobias Maschler of DITF Denkenorf (Germany) presented an expert system for the development of air-laid nonwovens which is being constructed with funding from the Allianz Industrie Forschung programme.  It is a Web 2.0 client server application which can be accessed via a browser.  It contains all the important facts about the process, and how they relate to the Oerlikon Neumag air-layer and the Fleissner through-air bonder at STFI.  It also contains data on the fibres which might be used, allows input of the desired nonwoven properties (e.g basis weight, density, thickness, absorbency) and calculates the fibre blend and process parameters to obtain those properties.  It also calculates an initial estimate of the likely nonwoven production costs.

Recycling Carbon Fibre Composites

More from the EDANA NIA 2013 Conference in Roubaix...

Bernd Gulich of STFI (Germany) reminded us that all commercial carbon fibre composites use filament yarns or tows often in woven structures for maximum strength and stiffness.  Production of these structures results in short carbon fibre waste which can be converted into nonwovens with different but useful properties.  Furthermore, post-consumer carbon composites are now becoming available and these can be pyrolysed to release pure carbon fabrics which can be shredded and also converted to nonwovens.  Unlike the rigid woven structures these nonwovens can be moulded into complicated shapes.  While the composite strengths are low compared with virgin fibre products, the resulting mouldings are very lightweight compared with glass reinforced plastics and therefore suitable for use in non-structural components of cars and planes.  At present, long reclaimed carbon fibres are chopped to about 60mm length and carded into waddings for stitch-bonding or needling.  The technology is difficult because the dust created may well be harmful and is certainly capable of shorting out any unprotected electrical circuits.

Air-Laid Carbon fibre nonwovens

Mario Löhrer of RWTH Aachen University (Germany) was also using rejects from carbon fibre composite production but only in the form of staple fibre or rovings which could be short-cut and air-laid into nonwovens.  These would be used to produce back rests for the front seats of cars in order to demonstrate the usefulness of the technology.

So far, discontinuous air-laying of the output of a Trützschler fine-opener had been used to make isotropic waddings for impregnation and this was now being scaled up into a continuous process.  The system appeared to do little damage to the fibres and little dust was produced outside the air-layer. An in-situ polymerisation impregnation system was also being developed.  Here the carbon fibre nonwoven was coated with lauro-lactame monomer, an activator and a catalyst, and this was polymerised and cured with UV and heat to form the composite in one continuous operation.

New Glass Nonwovens

More from the EDANA NIA 2013 Conference in Roubaix...

Marjo Peeters of Owens Corning (Holland) reviewed the current uses of glass nonwovens.  High performance glass fibre with diameters of 6.5 to 23 microns and lengths from 6 to 18mm were wet-laid in very large quantities and bonded with thermoset or thermoplastic resins.  This nonwoven was used as a primary backing for tufted carpets where its dimensional stability, heat resistance and wet strength were second to none.  Unfortunately, the cheap and effective thermoset bonding  systems used for carpet backing  out-gassed traces of formaldehyde and this was becoming unacceptable indoors.

Sustaina™ formaldehyde-free glass nonwovens had therefore been developed and these were now being commercialised:

• ·         Tensile strengths of Sustaina™ were better than the Urea-Formaldehyde bonded glass nonwovens (dry) and the same when wet.
• ·         Hot-dry strength retention was triple that of UF.
• ·         Sustaina™ was the only product with a USDA certified-biobased bonding system.

·         It cost less than UF or competitive acrylic-based formaldehyde-free systems.

In response to questions, Ms Peeters could not reveal the chemistry used in Sustaina™ but said the USDA certificate was awarded because 49% of the organic component of the nonwoven was bio-based.  The resin itself is inherently flame retardant.

Eco-efficient Coatings for Textiles

More from the EDANA NIA 2013 Conference in Roubaix...

Frederik Goethals of Centexbel (Belgium) described new energy-efficient coating systems for finishing textiles involving UV curing of non-aqueous coatings and sol-gel coatings.  These methods provide surfaces with high abrasion resistance, high hydrostatic head water-proofing, flame retardency, easy care and UV-protective features. 

UV-cure was fast, energy efficient, low in volatile organics emissions, suitable for small production runs and could even be used on hard surface lacquers.  The coating is a non-aqueous mixture of oligomers, monomers, photoinitiators and additives and can be cured cold (no evaporation of solvents) in 4 seconds with UV light from a mercury lamp to give a stable surface.

Sol-gel coating uses metal-oxides, mainly silicon-based which are thermally polymerised with an organic polymer to give hard, durable, omni-phobic, abrasion resistant, antimicrobial and flame retardant surfaces.  UV cure and sol-gel could be combined for 100% coatings, water-based coatings and water-based finishes.  This could lead to highly hydrophobic fabrics.

Fabric treatments involve high-viscosity coats which can be non-aqueous or water-based, the latter requiring drying before UV curing.  The processes are continuous and attention must be paid to the thermal sensitivity of any thermoplastics in the fabric, to removing the ozone generated in curing, and to protecting the operatives from UV exposure. FTIR analysis is required to check the completeness of the curing, i.e the complete absence of any monomer.

Asked about the costs, Mr Goethals said the process machinery costs were lower than for conventional coating but the chemical costs were higher.  (A UV lamp for textile finishing would cost €200,000.)  Typical finished fabrics would be 50/50 fibre/coating.  The photoinitiator chosen must be matched to the frequency of UV radiation used.

Wound Care with Photo-active Collagen

More from the EDANA NIA 2013 Conference in Roubaix...

Giuseppe Tronci of Leeds University School of Dentistry described advanced wound care as a $2bn market currently led by hydrogel dressings such as Convatec Aquacel .  These dressings absorb wound exudate to form a protective gel but have several limitations.  They have poor strength when wet and any attempt to increase their strength reduces exudate absorbency.  
They are also based on cellulose which does not promote the healing process as well as collagen.  Unfortunately collagen loses its integrity on extraction from tissues and needs stabilising.  

This is done as follows:

•         Isolate type 1 collagen from rat’s tails.
•          Functionalise it using either 4-vinylbenzyl chloride (4VBC) or glycidyl methacrylate (GMA).  These functional groups attach to the surface of the collagen triple helix structure.
•          UV irradiation of the functionalized collagen causes cross-links to form between the triple helices stabilising the polymer, preventing dissolution and allowing gel formation.

These superabsorbent collagen gels have proved to have better swelling and compression properties than carboxymethyl celluloses, compression at a micro-level having been measured using an atomic force microscope. 

Cytotoxity according to ISO 10993-5 showed that mouse fibroblasts thrived on the gel. For fibre or nonwoven manufacture, the functionalised but unstabilised collagen can be dissolved in water at 4⁰C, wet spun into yarn in a coagulation bath of acetone or methanol, UV-irradiated and stabilized, washed and dried.

Composites from Flax and Bio-resins

More from the EDANA NIA 2013 Conference in Roubaix...

Prof. Philippe Vroman of ENSAIT (France) was working on making nonwovens and composites using flax, jute and bio-based materials to replace glass reinforced plastics with green composites.  He explained the terminology:

•        Biocomposites referred to oil based polymers reinforced with natural fibres, or bio-sourced polymers reinforced with oil-based fibres.
•          Bio-sourced polymers were those made from starch, castor oil or sugar-cane via ethanol such as PLA, PA11 and PE. 
•          Green composites were bio-sourced polymers reinforced with natural fibres.
•          Natural fibres suitable for reinforcement were flax, jute, hemp, sisal, bamboo and kenaf

Commercial examples were from the boating industry:

•          The “Gwalaz” trimaran based on cork, flax and balsawood reinforced with flax.
•          The “Araldite 6.5” yacht 50% of which was made from flax-reinforced composites.
•          The “Plasmor” kayak made from flax/starch-based composite.

Flax was also being used in conjunction with glass and carbon in a variety of sporting goods and automotive panels.

Green composite manufacture involved blending the natural fibres with bio-sourced thermoplastic fibres and compression moulding them to the desired shape.  Physical properties of the composites had been measured in comparison with glass/PP structures.  All the green composites had tensile strength and flexural moduli better than the glass/PP control, with Flax/PA11 proving to be twice as strong.  50/50 Glass/PP had the best impact resistance with the 70/30 flax/PP composite coming a close second.  70/30 Flax/PLA had the best sound absorbency.  However the density of the green composites was generally much higher than the control and the effects of humidity, temperature and UV on the ageing of the green composites had yet to be determined.  In response to questions the other issues in need of further research included “fogging” when used in car interiors, costs of the green composites c.f. current products, appearance of the composites in home furnishing applications, and optimisation of the interface between fibre and resin in each case.

Nanostructured Nonwovens with Self-Assembling Peptides

More from the EDANA NIA 2013 Conference in Roubaix...

Robabeh Gharaei of Leeds University (UK) said the materials of the title were being developed as nonwoven scaffolds for tissue engineering.  Such scaffolds had to be highly porous 3D structures which were biocompatible, bioresorbable, biodegradable and had an appropriate surface chemistry.  Examples given included naturally derived polymers such as collagen, chitosan, and elastin or synthetic polymers such as polycaprolactone, polylactic acid or  polyglycolic acid and its copolymers.  These could be 3D printed into the appropriate porous structure, spun into nanofibres, or even simply used as a hydrogel.  Improvements promoting cell attachment, cell proliferation, cell differentiation and extracellular formation were required, and the incorporation of self-assembling peptides within the polymer was thought to be a potential solution.

Electrospun nonwovens have therefore been made from 6% PCL in hexafluoro-2-propanol loaded with the peptides P₁₁-4 and P₁₁-8, both of which were bioactive and specially synthesised for use in nonwoven scaffolds.  Concentrations of 20 and 40g/l of the peptides in the dope were used and both caused the production of a biphasic structure (a mixture of filaments and short submicron fibres).  ATR-FTIR analysis of the fibres showed the presence of both monomeric and beta-sheet peptide structures. It was postulated that the peptides were self-assembling into “beta-sheet tapes” during spinning and causing this mixture. 

Asked if the biofunctionality of these nonwovens had been checked, Ms Gharaei said they hadn’t but she expected to see improvements over the current scaffolds.  The peptides did not self-assemble in solution so it must be happening during spinning.  Maybe the peptide is affecting the surface tension of the dope and thereby affecting the resulting fibres.

Nonwovens containing Methylglyoxal for Wound Care

More from the EDANA NIA 2013 Conference in Roubaix...

Sophie Bulman of Leeds University (UK) thought dressings which used Manuka Honey to increase the rate of healing of chronic wounds owed at least some of their success to the methylglyoxal content of the honey.  Infections in chronic wounds were resistant to antibiotics and while some treatment success was claimed for silver impregnated dressings, bacteria were now evolving with silver resistance also.  Alternative metals e.g. zinc and naturally derived antibacterials such as Manuka honey were therefore being evaluated.  Alginate nonwovens, knitted viscose and non-fibrous hydrocolloids were all being used as substrates for the honey but it was a difficult material to handle due to its stickiness, could cause skin rashes and was not suitable for use on the open wounds of diabetics.

Manuka honey was compared with the equivalent amount of methylglyoxal as an antimicrobial finish on textiles using ISO 20743:2007 and found to be similarly effective.  PP spunbond nonwovens samples were then coated either by electrospraying  a water-based solution of 8% PVA loaded with  11% MG, or electrospinning the same solution into a web of nanofibres.  Both methods were intended to give the maximum possible surface area.  FTIR and NMR analysis proved the PVA nanofibres contained MG. The samples were then tested using the zone of inhibition method on agar plates colonised with E. coli and S. aureus bacteria according to ISO 20645:2004.  The controls (spunbond with no MG) showed no zone of inhibition, whereas the spunbond electrosprayed with MG showed zones of 4mm for E. Coli and 6mm for S. Aureus.  The MG/PVA nanofibre coats were even more effective showing inhibition of bacterial growth up to 20 and 21mms respectively.  Asked how much MG was required to render the nonwoven antimicrobial Ms Bulman said 1mg/cm2.

PP nonwovens containing non-encapsulated PCMs

More from the EDANA NIA 2013 Conference in Roubaix...

Waclaw Tomaszewski of the Institute of Biopolymers and Chemical Fibres (Poland) described the uses of Phase Change Materials in regulating the temperature of buildings (in insulation) and people (in clothing).  These chemicals absorb heat on melting and release it again on freezing and can be tailored to work at specific temperatures, e.g 22⁰C for building insulation and 37⁰C for clothing.  Unfortunately the PCMs are normally supplied as microcapsules and these increase the costs of products made from them, restrict the concentration in fibre to about 10% and prevent their use in fine-fibre products such as meltblown.

In this project, 4 different PCMs (all paraffin waxes) were added to PP and pelletized.  Not all the wax co-crystallized with the PP: e.g. from a 30% addition only 20% remained fixed in the polymer.  Further losses occurred due to evaporation of some of the wax from some of the PCMs during melt blowing, but meltblown PP webs containing 20% PCM were produced and tested.  Thermal imaging and measurements of temperature regulation factors showed that the PCMs were working as expected although the rates of heating and cooling affected their performance.  They worked better with gradual temperature changes.  Thermal wave propagation measurements showed that for rapid temperature changes only the PCM in the layer close to the heat source was effective. 

In response to questions Mr Tomaszewski revealed that the PCM tended to be at the surface of the fibre and could be removed by washing.  One questioner proposed using the PP/PCM pellets for the core of a bico fibre.

Laser-bonded Electrospun Nonwovens

More from the EDANA NIA 2013 Conference in Roubaix...

Christoph Hacker of RWTH Aachen University (Germany) observed that the electrospun webs needed to improve the filtration efficiency of drinking water filters are very fragile and therefore hard to laminate to stronger meltblown or spunbond nonwovens.  They are easily destroyed by hydroentanglement, needlepunching or thermal bonding, and the use of lasers alone fails because the polymers do not absorb laser energy.  The solution is to electro-spray submicron droplets of an energy absorber onto the substrate before electrospinning the fibrous layer, and for the purposes of these experiments the droplets contained carbon black to indicate how uniformly the spot-bonds were distributed.

The beam from a 100watt diode laser was spread using a prism to 35mm wide and as the laminate containing the droplets – held under pressure beneath a glass plate - was illuminated by it, the droplets heated up and spot-bonded the layers together without destroying any of the electrospun filaments.

Microscopy and peel strength tests showed the bonding process was successful and filtration testing showed that the bond points did not affect filtration efficiency.

Work continues to convert this batch demonstration process into a continuous process with wider lasers, simultaneous electrospinning and electrospraying, and a search for improved energy absorbers.  Mr Hacker thought the process might ultimately run at 10m/min.

Hydroentangled Air-laid flax Nonwovens

More from the EDANA NIA 2013 Conference in Roubaix...

Philippe Mesnage of ITFH (France) is evaluating hydroentanglement as an alternative to needlepunching for making flax nonwovens for composite reinforcement. The raw flax contains ~70-75% cellulose with 10-15% of hemicellulose, 3-5% lignin and a similar proportion of pectins. Mechanically refined flax (MRF) tows were cut into lengths of 25-35mm for airlaying and compared with a more fully refined 45mm flax intended for spinning into yarns (SF). MRF was coarse – 34 to 90 on the IFS scale (Flax Standard Index) compared with 20-30 IFS for the SF fibres. These long fibres clogged the air-lay drums and further work was carried out with fibres chopped to 15mm which could be successfully laid into ~150gms sheets.

After hydroentanglement, nonwoven tensile strengths were highest for the SF fibres (358N/5cm) compared with 215N/5cm for the best of the MRF.  Tear strengths were however comparable, presumably due to the higher denier of the MRF.  The extra stiffness of the MRF samples was not just down to the coarser fibres.  Mr Mesnage thought the non-cellulose components of the fibre were being solubilised in hydroentanglement and acting as a chemical binder.  Asked what advantages this route might have over the needlepunched route he thought there was a potential for higher productivity from the faster laying and bonding machinery and added that the end product was completely natural, made in the EU and used no added binders.

EDANA NIA: New Hydroentanglement and Dry-Lay equipment at CETI

The EDANA Nonwovens Innovation Academy began 7 years ago as the ”Nonwovens Research Academy” also in Roubaix and it remains one of the few meetings to feature original technical papers mainly from the European technical institutes. This year it was hosted by the European Centre for Textile Innovation (CETI) and commenced with a tour of the recently opened €50m nonwoven pilot plant. This comprises state-of-the-art pilot lines for carding, cross-folding, spunlaying of mono, bi- and tri-component fibres, meltblowing, thermal bonding, hydroentanglement, and needlepunching. Machinery has been supplied by Andritz, Laroche, Strahm and Hills Inc. The layout allowed continuous production of laminates of carded and SMS webs with either calender or HE bonding.

Photos from CETI follow:

The hydroentanglement zone is in line with both the Hills Inc spunbond system and the dry-lay card...

...and feeds an Andritz through-air dryer/bonder

The full-size Andritz card can feed a crossfolder for felt and wadding development or feed a narrower lighter web through the spunmelt zone into hydroentanglement

The Laroche Flexiloft airlayer feeds webs under the crossfolder for combination with card webs.

The New Melt-spun Nonwoven Pilot Plant at CETI

EDANA's Nonwovens Innovation Academy was held last week at the European Textiles Innovation Centre in Roubaix France.  Here are some photos of the new spunmelt pilot equipment now available for hire.

 The Hills Inc spunlaying head (left) and meltblowing (right)

Meltblowing

  

 Spunlaying

 

Simom Fremeaux of CETI describing Tri-component yarn spinning

Go to CETI for more details