Thursday 20 March 2014

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.

Thursday 13 March 2014

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.

Saturday 8 March 2014

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.

Tuesday 4 March 2014

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.