• Polypropylene, polyester and cotton prices correlate well with oil-price over long periods of time.
• Hollow nanofibers have been obtained by sheath-core electrospinning of polymer on oil. Titania loaded versions have been calcined into tubular anatase fibers and aligned into bundles.
• Cellulose acetate has been electrospun from acetone/water solution and deacetylated to make pure cellulose microfibers.
• Nanofibers of polyethylene-oxide loaded with titania or magnesium oxide nano-particles have been electrospun. Chitosan/silver nanofibers are being developed.
• Nano-clay dispersions in aqueous polymers allow submicron coating to achieve barrier properties without affecting texture.
• Printing with functional “inks” can add local absorbency, odor control, differential drainage, hydrophilicity or hydrophobicity to a nonwoven.
• Freudenberg is commercializing Novolon®; deeply embossed microfiber fabrics made possible by spun-laying and entangling unoriented bico fibers.
• Hills Inc is testing an 8000 holes/m meltblowing dye for high productivity.
• Elastic spunbonds are now being sold by BBA in Germany , but not for diaper components.
The main INDA-TAPPI conference was preceded by a 1 day Nonwoven Enhancements conference organized in conjunction with the American Association of Textile Chemists and Colorists. Both Conferences are reported below, but the main INTC conference comprised 3 simultaneous sessions and only those attended are reported. The full set of papers will appear on www.inda.org/papers/intc2005 for a limited period and can be accessed by means of a password provided to attendees.
This was the largest and busiest nonwoven conference of recent years comprising 98 full presentations, 14 Poster presentations, 12 Supplier showcase presentations, 18 award presentations and a fashion show.
In this keynote speech, Ian Julian of Chemical Market Associates Inc., explored how oil price fluctuations occurred and how they affected the prices of polyester, polypropylene and cotton. Crude oil price is driven by supply and the demand from the transport (95%) and petrochemicals (5%) industries, and by emotion. The USA supplies 10% of world demand but uses 25%. OPEC supplies 40% but consumes 10%. Saudi Arabia produces more than half the OPEC total and is the flexible producer who normally adjusts output to meet total demand. However since 2004 production has run very close to capacity with little spare. Contracts for oil on the futures market run at 10 times the level of the physically available oil. China 's demand is up from 6.3% of global supply (2001) to 8% in 2005 driven not only by vehicle use, but also by the more prosperous population installing air-conditioners. Currently the Chinese electricity supply industry is using diesel-powered generators to cover demand surges in the summer months. Overall, oil is in short supply and prices will stay high for some time.
Natural gas follows crude oil pricing and 95% (methane) goes into fuel while 5% (ethane and propane) goes into petrochemicals. All the USA 's easily accessible natural gas has gone and imports of liquefied natural gas are needed. Shipments of LNG are currently limited by environmental issues associated with cooling and warming-up the gas.
Polypropylene chip price is now 81% raw materials (67% in 2001) and the correlation with oil price is good. From the graphs presented, fiber grade PP chip price in cents/lb is ~15% more than the WTI oil price ($/barrel) was two or three months previously, spikes in oil price excepted.
Polyester shows a similar correlation, the polycondensation chip price being ~35% above the WTI oil price in $/barrel. However in June 2005 polyester came down to 62c/lb while oil continued to rise to 60 $/b, but according to Mr Julian, polyester prices will get back into step if the crude oil price stays high.
Cotton too has tracked oil closely, the cotton A index (c/lb) historically being roughly double the WTI oil price ($/b). Cotton yield reflects the amount of petrochemical-based fertiliser and pesticide use, and the harvesting/transportation oil consumption is significant. Cotton is also tied to polyester price. However the good correlation broke in May 2004 when an unexpectedly high cotton crop revealed itself, cotton declining from ~70 c/lb to ~60c/lb while oil price doubled. This “hiccup” will be corrected over the next 12 months as the supply/demand balance corrects itself.
Alfred Watzl of Fleissner GmbH said the world capacity for producing spun laced fabrics was 435,000 tonnes in 2004 , this being broken down by laying process as follows:
All staple fiber – 220-260,000 tonnes
Staple/tissue composites – 50-55,000 tonnes
Staple/air-laid pulp – 90-130,000 tonnes
Wetlaid – 21-26,000 tonnes
Spunlaid - <5,000 tonnes
The most important end-use was wipes, and here Dr Watzl foresaw growth in the pulp-containing variety, especially the SPS trilaminate using two thin skins of PP spunbond to contain the air-laid pulp, or if one absorbent surface was needed, an SPC trilaminate (card web hydroentangled onto one face.) For the SPS product the raw material cost savings compared with the current polyester/viscose staple wipe substrate would be 50%. (€1.52/kg for the 70%CV/30%PET down to €0.76/kg for a 25%PP/75% pulp trilaminate product). Total cost comparisons suggested a 35,000 tonne spunbond/airlaid line would produce substrate at 65% of the cost of a current 12,000 tonne 2-card line using CV/PET staple. There was the additional low-cost option of buying commercially available diaper topsheet spunbond and laminating it either side of a commercial tissue on an Unwind/HE bonder/dryer/winder combination.
For durables, the hydroentanglement of polyester spunbond for roofing applications was now feasible, and HE was shown to give double the MD and CD strengths of needling. The additional cost of energy to achieve this is negligible now that bonding was possible at 200 m/min.
Jared Austin of BBA Fiberweb reviewed the advances in spunbond technology from the first attempts to adapt multi-jet continuous filament yarn production using draw-guns to stretch and lay the fibers through the Lurgi, Dupont, and K-C systems to the advanced draw-nozzle/vacuum Reifenhauser bico process. The BBA/Dow Chemical JV – Advanced Design Concepts – has now produced “Dreamex” elastic bicomponent spunbonds on a heavily-modified Reifenhauser line at a commercial scale at BBA's Linotec subsidiary in Germany . 13,000 filaments of thermoplastic elastomer (95%) are coated with a thin sheath of polyethylene (5%), laid, incrementally stretched in both the machine and cross directions, and finally heat set by through-air bonding. The stretching process drops the fabric basis weight by 50% and the fiber deniers by 30% - a valuable increase in area-yield for a disposable fabric.
If the fibers are “tipped trilobal” bicomponents with PP tips on a PU trilobal, the stretching process splits off the tips to give three sub-denier microfibers of PP for every triobal elastomer. The resulting fabric has an interesting suede-like texture.
For the future Dr Austin saw
• the commercialization of versions using the more economical elastic polypropylene
• the production of durable dyeable fabrics with polyester or nylon sheaths
• the evaluation of styrenic elastomers
• spunlaced elastomeric spunbonds (done off-line initially because BBA does not have HE and spunbond on the same line.)
Diaper side-panels will not be made using this technology until the quality of elastic PP polymers improves.
Dr Stephen Michielsen of NC State has investigated the structure and properties of a series of melt-blown polyether-based thermoplastic polyurethanes . Three hardness grades with hard segment chemistry based on 4,4-diphenylmethane diisocyanate and 1,4-butanediol were used. Because none of the polymers were available with rheology suitable for melt-blowing they had to be extruded at temperatures of 244, 267 and 280C (respectively for each hardness level) and these temperatures caused degradation such that the fabric molecular weight was half the chip MWt. The fabrics were produced at 14, 20 and 30 cms Die-Collector Distances and at two basis weights.
Mean Fiber diameters were typically around 5 microns (0-20micron range) i.e. similar to polypropylene. Using the “dogbone” tensile method (preferred for samples which otherwise break at the clamps of the Instron), best results were obtained at the short DCD and with the harder polymers. Increasing DCD gives weaker and less extensible fabrics suggesting that the inter-filament bond strength is insufficient at the higher DCD's. This in turn could be due to the extra time allowing the polymer to crystallize more completely. Did the orientation of fibers in the web change with DCD? Dr Michielsen said it did not.
Dr Alberto Lorioli of Meccaniche Moderne SpA ( Italy ) described the development of spun-laid needlepunched PET for applications requiring anisotropic, uniform fabrics of high tensile and tear strength and high thermal stability. Key variables affecting the fabric properties were:
• PET polymer rheology, Molecular Weight Distribution, and oligomer content
• Controlled moisture and crystallinity on entering the extruder
• Extruder screw profile, and the resulting melt temperature profile
• Polymer filtration prior to spinning
• Spinneret hole diameter, L/D, number of holes and the hole pattern
• Quenching/fume removal
• Stretching ejector details (geometry, no of fils, air pressure, temperature)
• Draw ratio
Unlike typical PP spunbond, the MM SpA PET system uses small round spinnerets fed from individual spin pumps, the “yarn” from each jet being stretched in its own oscillating air-gun prior to laydown.
A correctly set up process could produce PET filaments of 32 cN/tex tenacity with extensions less than 100%, whereas “narrow distribution” PP filaments used for coverstock had 20 cN/tex tenacity and 350% extension. Metallocene PP gave 31 cN/tex and 200% extension. Fiber laydown pattern is determined by the setting of the “flappers” which oscillate the ejectors to control filament direction and distribution at the conveyor. High stability fabrics require “real” (as opposed to flat calendar) heat setting where the web is held to width in hot air on a tenter frame.
Chunhui Xiang of Cornell University has electrospun both cellulose acetate and PLA and used dye uptake and release as a measure of their potential to deliver chemicals. A 17% solution of acetate in an acetone-water (17/3) mixture was electrospun and then deacetylated with 0.05M NaOH in ethanol to give what FTIR proved to be a 100% regenerated cellulose microfiber. PLA was electrospun from an 8% solution of the polymer in a chloroform/acetone mixture. Direct dye uptake by the cellulosic was about 3 times that of cotton. She concluded that high surface areas allow higher levels of chemical uptake and release. (Student presentation – paper not available)
Jesse McCann of the University of Washington ( Seattle ) has co-spun sol-gel precursors with an ethanol soluble polymer , and has extended this system to spin composite fibers with excellent size control down to tens of nanometers. Using a coaxial spinneret, he has been able to manufacture porous, hollow and core-sheath nanofibers and control the surface chemistry of those resultant fibers by tuning the core and sheath solutions. Patterned collectors have allowed the parallel alignment of arrays of nanofibers. These arrays could be readily be crosslaid into intriguing woven-like structures.
Metal-alkoxide precursors in polyvinylpyrrolidone were dissolved in ethanol or isopropropanol and spun, and when the PVP was dissolved porous nanofibers of the conjugated polymer remained. Burning off the organic matter yielded metal-oxide fibers (Tin or Titanium). Calcination of fibers made with amorphous titania for 3 hours at 500C yielded polycrystalline anatase fibers . Perfect hollow tubes of these oxides were obtained if the coaxial spinneret extruded viscous mineral oil down the centre. The oil can be a carrier for other materials, iron oxide being an example. Fibers with a titania/PVP sheath had also been made on a polystyrene core. Barium titanate nanofibers had piezoelectric properties.
If the collector had an insulating gap between two plates, the fibers bridged the gap forming a parallel alignment. If the insulating gap was created as a square between 4 electrodes, and opposite pairs of these electrodes were switched on and off alternately, a woven-looking mesh can be obtained. Dr McCann concluded that patterned collectors would enable the assembly of nanofibers into a variety of patterns.
Dr Sheshadri Ramkumar of Texas Tech. University ( Lubbock ) has shown how electrospun polyurethane nanofibers form in a unique honeycomb pattern on the collector and postulated applications in drug-delivery, protective clothing and tissue scaffolds. He has also added titania and magnesium oxide nanoparticles to a polyethylene oxide solution and spun composite nanofibers with distinct nodes of oxide which more than double the fiber diameter every micron or so. Here a 400,000 MWt PEO was dissolved in water at 4% and extruded at 50 microlitres per minute through a 16 kv field at 20C and 40%RH. When loaded with an unspecified amount of magnesium or titanium oxides, improved toluene absorbtion and UV protection factors were observed. An unspecified weight of nanocomposites were tested on an unspecified active carbon fabric, which also provided the control. Toluene absorbtion increased from 31% to 33%(sic) when the MgO composite was used and to 37% when the TiO 2 composite was used. The TiO 2 composite increased the UV protection factor from 15 to around 500. More detailed testing was promised, and Dr Ramkumar was now looking at Chitosan nanofibers loaded with silver for wound healing.
Harris Goldberg of InMat Inc described their barrier coatings which use nano-sized clay platelets dispersed in an aqueous polymer dispersion. These platelets allow very thin coats to have very high impermeability, and thus allow the development of barrier properties without substantially affecting the other physical properties of the substrate. The technology was developed by Hoechst and used in 1996 by Michelin to coat the inside of tires to reduce air loss while using less butyl rubber to make lighter tyres. In 1999 Dupont bought the technology from Hoechst and InMat is a buyout from Dupont. InMat is developing it for NBC suits which use neoprene and nitrile rubber rather than butyl rubber. They see a big market in packaging due to its ability to reduce oxygen pass through of polyester films to hitherto unachievable levels.
Coating nonwovens with the barrier is impractical because it would be too expensive to fill the large pores. The substrate has to be very smooth and pin-hole free. Nevertheless a 30 micron coat of the barrier is equivalent to 1mm of butyl rubber and can be stretched by up to 30% without rupture, this being enough for most practical applications. Data presented showed that coated PP film performed as well as PET film coated with the same weight. Acrylic films, normally even more porous, were similarly sealed, giving a 150,000-fold reduction in oxygen permeability, compared with the 1000-fold reduction achieved with the same weight on PET.
The main market is currently a coat on the inside of Wilson 's top of the range tennis balls.
In response to questions:
• The coating process currently works at 200 ft/min and applies a 0.2 to 0.5 micron layer.
• Multiple layers are needed if thicker coats are required.
• Normally the nano-coat is protected by a further coat of PE.
• Some customers find the adhesion to this protective PE coat is too low and this needs further funding to solve.
• The coat makes a normally clear PET film very slightly hazy.
• Cost: only pennies per tennis ball!
Mr H Geus of Reifenhauser GmbH pointed out that making a submicron web out of PP resin involved converting a quarter of a gram of polymer into a filament 1400 kilometers long. Reifenhauser's new meltblown technology gives many more filaments of this size and therefore allows the production of more retentive filters and higher – hydrohead barrier fabrics. Unfortunately patent issues prevented him from telling us how this was achieved. However the emphasis seemed to be on achieving high air speeds (> Mach 1) and filament speeds in the resulting turbulence of 6-10 times the air speed for much of the die-to-collector distance (DCD). Air temperatures were above the melting point of the polymer, and the extra draw-down was achieved close to the exit from the air-knives. Using a higher quality resin was also mentioned.
Dr Hassan Badaghi of Nordson Corp. listed the types of bicomponent fiber and their advantages. In addition to the bonding reasons for using sheath core bicos he added the ability to use virgin sheath polymers over recycled polymer to reduce costs, or to use expensive “functional” sheaths over cheaper cores to make high value products. Side-by-side bicos could, after hydroentanglement be heat treated to create permanent crimp and extra bulk in the final product.
Bico meltblown webs can be split to yield a high percentage of ~1 micron fibers, allowing an SMS structure to have the same hydrohead as an SMMS structure. Direct extrusion of finer fibers is now possible through engineering which allows melt-blown heads to operate either with double the polymer throughput or, to make “NanoPhase” products by reducing the throughput to get finer fibers. True nanofibers can be obtained by splitting melt-blown segment-pie fibers.
Asked what throughputs were possible when melt blowing to get an average fiber diameter below a micron, Dr Badaghi said the die in question used 50 holes/inch and passed 0.17 gms of polymer per minute per hole. The segmented bico MB's were split by using higher pressure air at the die. Did the Nordson process infringe the K-C patent in this area? No, but Nordson were concerned about another companies patents!
Finer Melt Blown Fibers
Arnold Wilkie of Hills Inc mentioned the
non-traditional (i.e. not using the original Exxon system) melt-blowing systems
before promoting the latest Hills technology :
• Biax-Fiberfilm uses a sheath of hot air around each die orifice.
• Nanoval uses a Laval nozzle to explode the filaments after extrusion thereby achieving higher throughput and finer, fully oriented microfibers.
• Nonwoven Technologies uses a pair of engraved plates to form the die holes and achieves good back pressures from the very high hole-lengths possible.
• Nordson Nanophase (no details)
• NanoTechnics (no details)
• Rieter EMBLO technology. (no details)
Instead of the almost universal “coathanger” polymer distribution, the latest Hills technology uses a multi-pump system to deliver the polymer to segments of the die thereby achieving higher uniformity of polymer flow and temperature while allowing the use of a wider range of rheologies. The die can be either electrically heated or, preferably vapor heated to get exact temperature control. The Hills spinnerets are not drilled but formed from 6 photochemically etched plates, fusion bonded to prevent leakage. This system allows the full range of Bicomponent fibers to be made, thereby allowing true nanofiber production at economical production rates. 4000 holes/metre has been commercialized and 8000 holes/metre is being tested. The plate system allows holes of 0.1mm diameter and 50:1 L/D – this being impossible with drilling methods. Together these innovations allow very low polymer flow per hole yielding finer fibers.
5 of the new lines are now on order – all for Asia . For the future Mr Wilkie mentioned the use of elastic polymers.
Dr John Hagewood of NCRC has made a 6 ounce spunbond which meets the grab strength and tongue tear specifications for a 20 ounce woven canvas . Nylon islands in a polyethylene sea were spunlaid at 0, 25, 50 and 75% PE, and 0,1,18, and 108 islands. Of these the 100% nylon and the 75% nylon in 108 islands were judged worth taking into a detailed bonding study using combinations of needling, hydroentangling, calendering and through-air bonding. Thermal bonding after mechanical bonding brought out the best results with calendering at 145C being equivalent to through-air bonding at 160C. Hydroentanglement (two passes) was the best form of mechanical bonding. The bico fabrics outperformed the 100% nylon and the polyethylene content appeared to be crucial to getting the best strengths after thermal bonding. Thermal bonding proved more important than hydroentangling. Attempts to use other bico structures (TPU/PP, PET/CoPET, Nylon/CoPET, TPU/NYLON, and PET/PE gave inferior results, the PET/PE being the best of these and worth further optimization.
Dr Benham Pourdeyhimi of the Nonwovens Co-operative Research Center has studied the effect of segment number on the properties of nonwovens made from these bicomponent fibers after they had been split in hydroentanglement. The microfibers could also be released by chemical, thermal or other mechanical means, but hydroentanglement had been of most interest to the industry recently. Freudenberg's Evolon® fabrics for instance used spun-laid segment-pie fibers and bonded the webs with high pressure HE, attempting to split and bond the fibers in one step. (Here entanglement restricts the opening up of the fibril bundles so some post-processing of the fabrics e.g. jet-dyeing is needed to achieve the desired softness.)
In this study fibers with 8, 16, 32 and 64 segments were spun from both 50/50 and 75/25 PET/Nylon into fibers with a diameter of 80 microns and nonwovens with a basis weight of 175 gsm and a thickness of 0.8mm. The segment sizes were equivalent to diameters of 4.5, 2.5, 2, and 1 microns respectively. The results of nonwoven testing showed smaller effects than expected, SEM's clearly indicating that the first fibrils liberated were twisted around the main fiber bundle preventing further opening. In the case of the 64 segment fiber, there was clearly a “cuticle” around the circumference of the bundle which also hindered splitting. Washing the fabrics did not improve matters and clearly some very vigorous treatment would be needed to achieve the properties expected from the segment sizes. Overall conclusion? You can't split segment-pie fibers properly using hydroentanglement alone, but the 16 segment products gave the best looking fabrics. Asked if the fibers could be split by needling, Dr Pourdeyhimi said they could not, but needling prior to hydroentanglement appeared to be beneficial to greater fibril liberation, maybe by damaging the fibers and maybe by creating spaces into which the fibrils could move. Short fibers ought to be easier to split (Wet-laid HE) but this had yet to be tried.
Dr Sandra Schmitt reviewed the methods available to alter the surface properties of a PP Spunbond:
• Modify the polymer chain
• Melt additives
• Coating or finishing the nonwoven
• Grafting new chemistries onto the surface.
Chain modification can be achieved by the addition of suitable co-monomers (but the examples given did not apply to PP). Maleic anhydride can be chemically linked to PP to make masterbatches showing carboxyl functionality. Acrylic acid and other reactive molecules can be grafted onto the surface of PP after its activation by plasma treatment, but the resulting hydrophilicity tends to diminish with time. Surface finishing or coating can also give transient hydrophilicity. Overall, the durable effects were obtained with chemistries unlikely to appeal to the hygiene products producers.
Dr Gang Sun of UCAL (Davis) made the case for antimicrobial textiles and polymers. One in twenty in-patients attending US hospitals develop infections and 88,000 of these 1.8 million nosocomial infections prove fatal. 97% of the infections are caused by “medical materials surfaces” such as nurses uniforms, stretchers, beds, tables chairs etc. SARS in particular survives longer on surfaces than other microbes, and has been seen to infect staff wearing full protective kit. Staph.aureus and MRSA infections doubled between 1987 and 1997 and the % of MRSA also doubled to account for 50% of the total.
A successful antimicrobial must be fast acting, broad spectrum, non-selective, unable to encourage the development of resistant organisms and non-toxic to higher life forms. Simple inorganic biocides such as hypochlorites, and peroxides are contenders, but halamines were, in Dr Sun's, view the best possibility for fabrics because they released chlorine slowly and could be regenerated by bleaching with hypochlorite. Halamines could be created from the usual permanent-press finishing chemicals such as DHDMEU and these could be grafted or cross-linked onto cellulose. Data showed the treated textiles as effective against a wide range of organisms and while the efficacy deteriorated on washing, it could be regenerated if hypochlorite was used in the washing process. Another compound (ADMH – the acronym not being explained) could be grafted onto any polymer and allow halamine functionality to be created on the surface.
Dr Sun is now exploring adding halamines to extruders making spunbonds. Asked if the halamines had been registered as pesticides he commented that it is the chlorine not the halamine which is the active ingredient and this is registered (so the halamine is not?) Did the effect work at high humidities? Yes, socks using halamines had been continuously worn by troops for 5-days without any fungal infections – or any other problems – developing.
Matthew Gande of CIBA Speciality Chemicals described their new additive “FRG-1”, a hydroxylamine based polymer degrader which can be added to the extruder to increase the melt-flow rate of polypropylene. Although their old additive “Irgatec CR 76” was not mentioned, FRG-1 appeared to be the same material, several of the graphs being the same as those used by CIBA's Paul Shields for his paper on Irgatec CR 76 at Insight 2004. Mr Gande however presented more detail.
The effects of the additive on a 35 MFI PP could be varied by altering its concentration, the extrusion temperature or the dwell time (throughput). Fiber diameter reductions appeared most sensitive to the peak temperature used in extrusion. Using 2% FRG-1 below 270C had no effect but at 275C the mean diameter had fallen to 2 microns (from 3), and by 285C the mean diameter was down to 1 micron. Reducing the throughput from 1 to 0.4 gms/hole/min reduced the mean diameter from 3 to 2microns (2% additive at 275C). At 0.6 gms/hole/min and 275C, increasing the additive concentration from 0 to 3% also reduced the mean diameter from 3 to 2 microns. Hydrostatic head graphs suggested the addition of 2% FRG-1 could raise this barrier property from 200 to 700mms when starting with a 35 MFI PP at 275C and 0.6g/h/m. (Air permeability fell from 1 to 0.36 m/s)
Using the additive on line to reduce the viscosity of a spunbond grade to that of a melt-blowing grade was said to offer cost-savings compared with the use of conventional melt-blown polymers. Waste reprocessing is improved. Furthermore, the system has no safety problems according to cytotoxicity, skin irritation and sensitisation testing.
FRG-2 was mentioned as a much faster acting degrader which appeared to be based on peroxides.
Dr Randall Bresee of the University of Tennessee considered the factors which determine fiber diameter development during melt-blowing:
• The air velocity at the die tip causes uniform draw.
• As the air-flow becomes turbulent irregular draw occurs as still-plastic fibers collide
• If filaments stick together in the turbulence, diameter increases
• Web shrinkage at the collector increases diameter.
The mean fiber diameter continues to fall even 20-80 cms from the die and this must be due to effect 2, but the maximum fiber diameter also increases so this has to be due to effect 3. The increasing variability of fiber diameter can also be measured in the same region. As the air flow at the die tip increases up to 550 cuft/min, the diameter falls, but above this flow it increases for a given die-collector distance. An interaction with DCD means that this optimum flow increases as DCD increases.
Overall, fiber diameter seemed to be affected significantly by die temperature, moderately by resin throughput rate and primary airflow rate, slightly by DCD, and insignificantly by collector speed. As DCD was increased, mean fiber diameter decreased and fiber diameter distributions shifted to finer fibers but the maximum fiber diameter and diameter CV increased. Fiber diameters became significantly less uniform when primary airflow rate was increased, especially when DCD was large. This result was viewed as evidence that diameter reduction occurred by fiber contact/entanglement when DCD was increased.
Dr Bresee thought that fiber diameter variation across the web would almost certainly be due to die temperature variations. Asked if the effects of air temperature had been studied, they hadn't but Dr Bresee thought that air temperature would be the same as the die temperature.
Alan Meierhoefer (Consultant) focused on techniques which rearranged the fibers in a web rather than simply printed or embossed bonded structures. Patterning made nonwovens more textile-like, improved some physical property or offered branding possibilities. This could be done before, during or after bonding the web. The water marking techniques of the speciality paper industry used patterned or knuckled wires which encouraged short fibers to congregate in the “valleys” and form a mirror-image of the wire pattern. Hydroentanglement achieved the same effect after web forming with high pressure water jets forcing longer fibers to move into the valleys, or into the holes of perforated collection plates. Higher water pressure still could be applied to the surface of bonded webs through patterened screens to modify the structure of a bonded nonwoven, this being the best way to add logos to hydroentangled fabrics. Examples given were perforated tea-bag papers with company logos, the original J-cloth wipes from Chicopee and the Miratec or Apex technology from Chicopee which PGI used to make textile like nonwovens. The latter used deeply 3D forming zones and could mimic most textile weaves. The original pyramid Apex pattern actually twisted the fibers together as they were washed down the sides of the pyramid by the high pressure water.
Asked why these techniques had had little success replacing woven textiles, Dr Meierhoefer said the fabrics lacked durability to abrasion and probably cost more to make than imported wovens.
Carol Clemens, the Director of Business Development for Freudenberg introduced Novolon™. Whilst this looked like a deeply embossed nonwoven (or fibrous version of bubble- wrap film) she was at pains to point out that conventional embossing would puncture the nonwoven if depths achieved with Novolon ™ were attempted. The key to Novolon™ was the use of unoriented thermoplastic fibers which could stretch by 200-300% when deeply embossed, the fibers being oriented and set in the process. Fibers with all deniers and shapes, bicomponent or otherwise would work in the process provided the webs were random laid. Crimp was desirable. Technical data for Evolon™ and spunbond fabrics showed that the spunbond gave dramatically higher compression resistance, especially when two layers of the moulded sheet were combined either with the domes “nested” or glued dome to dome. Here the use of twice the nonwoven gave treble-quadruple the compression resistance.
Freudenberg were targeting the foam market with these products, presumably the rigid foam market in view of the likely low resilience of Novolon™. Advantages over foam were listed as:
• Very high water/air permeability
• No water absorption
• Could use half the weight (c.f. foam) to achieve a given resistance to compression
• Lower flammability
• 1000 times the tear strength of the equivalent foam.
• Quick drying
• Aesthetically pleasing texture and appearance.
On the other hand it was more expensive than foam, could not easily be shaped and could not easily be made very thick. Markets under development were acoustic and thermal insulation panels, filters, upholstery and automotive padding and concrete reinforcement.
In response to questions, Freudenberg had licensed the process from NC State University, having supported its development. Thermal bonded nonwovens could not be used because they punctured. Lightly hydroentangled, needled or spunbonded webs were best. Blends of up to 50% with cellulosics could be processed. The line runs at 50 m/min with basic spunbond but has to slow down for coarser fibers. The depth of embossing is limited by the extensibility of the fibers in the web – currently 50mm with undrawn synthetics.
Dr Dick Aspland of Clemson reviewed textile dyeing and finishing technology with special emphasis on its application to nonwovens. Dyeing uses colored chemicals in solution, the uptake of which by fibers depends crucially on the fiber forming conditions and their thermal/chemical history. Different fibers need different dye-types and the process of dyeing is often at done slowly at elevated temperatures with vigorous agitation of the fabric. In short it's next to impossible to dye nonwovens to uniform shades without adversely affecting the structure.
Pigments can be added to the fiber forming polymer – erroneously known as dope-dyeing, and pigments can be bonded to the surface of a nonwoven (“printing”). Here there are pigment penetration issues, wicking effects, migration of pigment and the removal of additives from the nonwoven to contend with, and the pigment binders need heat curing. Transfer printing using heat to sublime disperse dyes from a printed paper on to the nonwoven is possible at temperatures of around 350F but this is probably too hot for most nonwovens.
Asked if he was aware of any further research being carried out to improve nonwovens coloration, Dr Aspland thought not. The whole subject was just too complex and uniquely dependent on the wide and variable range of nonwoven constructions.
Steven Dalbey, of Polytex Environmtal Inks thought gravure and flexographic printing techniques work well with nonwovens while the offset litho and silk screen methods were good but too expensive. Gravure uses a single roller etched with the mirror-image of the pattern to be printed. The ink or pigment is “doctored” into the etching on one side of the roll and the fabric is squeezed against the other side to pick up the color. Flexography is similar but the ink-pattern is transferred to a second smooth roller and from there to the fabric. Flexography runs fastest and can easily be retrofitted to a nonwoven production or conversion line. (“easily” applies to single color printing, the complexity increasing as the color range increases.) Nowadays, inks can be water-based and applied from sealed “doctor chambers” to allow a system with easy clean-up, and negligible liquid effluents or hazardous air pollution. Such systems are in use on baby products, medical nonwovens, food service wipes and are proving invaluable as a means of differentiating your product. Mr Dalbey said that printed diapers could be recognized by toddlers who now begged Mum to buy their favorite designs. Prints can also affect perception of performance, identical products being judged to perform very differently if the user liked or disliked the printing (in this case of the packaging)
“Inks” which add functionality such as extra absorbency, odor control, odor, hydrophilicity or which can add special effects such as differential drainage were now possible. For instance a topsheet could be printed invisibly on the diaper line with both hydrophobic and hydrophilic inks to localise strikethrough into predetermined regions.
In response to questions, any polymer could be printed with aqueous inks once the correct binder had been identified, and different fabric types (e.g. HE, SB, MB) could be printed to the same color by adjusting the inks. For baby wipes, the lotion formulation would affect the choice of ink for acceptable color fastness.
Dr. Mary Ann Moore of Florida State University said whiteness was a key factor in consumer perception of a product and the texture of that product will affect the apparent whiteness. Whiteness, being the absence of color, communicates a purity and freedom from contamination to the user, and surfaces appear whiter the more uniformly smooth they are. She provided data from CIE Lab assessments of nonwovens where the ‘L' value measures the greyness of a fabric (0=black, 100=white), the ‘a' value the red-green balance (with zero being neutral, -ve values green and +ve values red), and the ‘b' value measures the blue-yellow balance ( with zero being neutral, -ve values being blue and +ve values yellow)
The data provided did not really illustrate the main theme but a comparison of 16 spunbonds with 7 meltblowns yielded the following conclusions:
• Meltblowns appeared (to the CIE Lab instruments) whiter, greener and yellowier than the spunbonds.
• Higher bonding temperatures gave whiter, bluer nonwovens
• Higher bonding pressures gave greener fabrics.
Unfortunately the melt-blown and the spunbond had been made from different polymers, so the main conclusion to be drawn was that Florida SU could measure whiteness on a wide range of nonwovens and were looking for support to do a proper study.
Barry Byrd of BASF reported how pigment printing of color-fast finishes has improved:
• Compatiblizers now keep the emulsions in better condition
• Application is more uniform
• Clean-up is easier
• Migration is more under control
• There is a better understanding of how ambient temperature and pH affects the process.
• Wide-width padding or foaming techniques work well.
• Masterbatches are now prepared with everything but color and color is added last in a small header tank close to application.
An initial pre-dry where the temperature is rapidly raised to above 125F is needed to fix the pigment before normal drying and curing. No after washes are needed so there is no effluent. Resination is possible in the same bath and color fastnesses are excellent. Superfine powder pigments are becoming available and these can penetrate the fiber structure.
Melanie Jones of Precision Fabrics Group Inc described the new AAMI Standard PB70:2003 which guides health care workers to choose the appropriate level of protection. Garments must be labelled to indicate the level of protection offered on a scale of 1-4.
Level 1 must pass the AATCC42 water impact penetration test with a level of penetration below 4.5 gms.
For Level 2 the penetration must be less than 1 gm, and the fabric must also pass AATCC127 with a hydrostatic head better than 20 cms.
Level 3 is as for Level 2 but with the hydrohead standard increased to better than 50 cms.
Level 4 is based on two completely different tests. ASTM F1671, a microbial assay of viral pass through, and ASTM F1670, a blood barrier test.
Coatings which can be used to meet these standards include fluorochemicals which repel both water and alcohol but are expensive, or waxes which repel water and are cheap but not durable. Foam coating of fluorochemicals is needed to meet the highest standards.
Larry Wadsworth of the University of Tennessee introduced the thermally bonded tri-laminate , a combination of his “Cotton Surfaced Nonwoven” ( a PP spunbond with a cotton/PP blend thermally bonded to one surface) and Noveon™ monolithic barrier film. The CSN layers were coated with various fluorochemicals and antimicrobial latexes both before and after lamination to the film. Numerous variations on this theme had been evaluated against the new Level 4 barrier standard (above). Most could pass the blood-barrier test but failed the viral penetration test. The film coated tri-laminates, which were first foam coated with fluorochemical on the outer spunbond side and with antimicrobial latex on the cotton side passed ASTM 1670, and had a virtually 100% kill rate to bacteria. Some of these complex constructions also passed the viral barrier test. The work is supported by Cotton Incorporated.
Ron Dombrowski of TechTex Solutions Inc has compared nonwovens with wovens as flame barriers and finds that needled nonwovens give longer flame hold-out times than wovens of the same weight and chemistry. Interestingly on his test there was no difference between FR treated cotton or rayon (cheap and relatively comfortable) and Nomex (expensive and uncomfortable). It is of course the bulk of the nonwoven that makes the difference; if they are compressed to the same thickness as wovens the performance is the same. What FR agents were used on the cellulose? The usual phosphorous/halide-containing chemicals.
Atul Dahiya of the University of Tennessee Knoxville described their work with the Kimberly-Clark melt-blown elastomer process. K-C had intended to use this process for diaper components but had found it too expensive and had donated the technology to UTK for further work. The Arnitel EM400 copolyether-ester resin had been subjected to a full factorial experiment to identify the main effects and interactions of die temperature, throughput, and die/collector distance. Highest tear strengths came from low die temperature and high DCD while highest elongations came from high die temperature and low DCD. (Student presentation – paper not available)
Nagendra Anantharamalah of North Carolina State University has obtained excellent correlation between the computer model and the observed performance of a single nozzle over a range of water pressures. Best water column integrity is obtained when a hydraulic flip occurs and the water passes through the nozzle without touching the sides. This is achieved only with cone-down nozzle arrangements. Cone-up trials gave 50% higher discharge coefficients. (Student presentation – no paper available. The same data was presented at INTC in 2003 and is fully covered in that summary)
Michael Cunningham of EGS Gauging Inc reviewed the methods available for continuous on-line measurement of fabric properties. Infra-Red was preferable to beta, gamma, laser or X-ray. Ratiometric beamsplitter IR – which could quantify a component of the web by measuring the peak-to-background difference in IR absorption at a single wavelength was good but pigments or additives caused problems and any change of fiber needed “weeks” for recalibration and software upgrades. The latest single-sensor Full Spectrum IR gets round these issues and allows calibration for a variety of components with and without pigments. This uses an online spectrophotometer which can assess multiple components in the web including fiber blend ratio, pulp content, water content, binder content and basis weight. Users of this system report significant cost savings from 3-5% raw material savings, and 60-70% reductions in MD and TD property variability.
Kevin Marrick of PCMC covered the variety of ink types and curing technologies, arguing that water-based – which need more drying but are simple to use and free of VOC's - is the way forward for nonwovens . They are usually emulsions and require coalescents to soften the polymer binder and enhance its ability to fuse on curing. The use of expandable polymers allows the creation of texture for improved wiping, or exfoliation. They are applied from Anilox rolls comprising a steel core with a ceramic coat, laser engraved with the required pattern, to a depth to get the required capacity. Ink capacities are measured in BCM's – Billion Cubic Microns. The engraved plates can be in the form of sleeves, and the surfaces need continual cleaning to remove any fiber or residual ink. Drying needs to occur very quickly and with water-based inks the required time, temperature and turbulence are hard to achieve for high speed processes where more than one color is applied. Compressed air at supersonic speeds is used. Asked about coverage, Mr Marrick said solid colors could be obtained with the system. He could not share information on the costs of the process and inks.
Vasantha Datla of NC State has investigated the effect of melt additive chemistry on the hydrophobicity of polypropylene using 4 different groups of additives:
• Nonyl Phenol Ethoxylates,
• POE(n)-Stearyl Alcohol,
• Melt additives with C18 chain but different hydrophilic group, and
• Melt additives with similar hydrophilic-lipophilic balance (HLB), but different molecular sizes.
The conclusions were as follows:
• Melt additives concentrate at the film surface (proved using X-ray photo-electron spectroscopy).
• Melt additive migration leads to a hydrophilic surface by reducing the water contact angle over several days following fiber extrusion.
• Smaller molecular size and lower HLB leads to immediate melt additive enrichment yielding extra oxygen at the surface by day 2.
• Additional migration occurred between day 2 and Week 3 for most melt additives.
• Soaking the films in water changes surface properties further to an extent dependent on the type of the melt additive and the immersion time.
Asked if the conclusions would be valid for fibers, Mr Datla confirmed they would. He has yet to check the levels of surfactant in the water in which the films were soaked but agreed that the additive would probably be leaching out. Effects of additive concentration and the temperature during migration remain to be studied.
You-lo Hsieh of UCal (Davis) described the measurement of liquid wetting and absorption on several nonwoven materials with different manufacturing methods and
fiber contents, and on ultra-fine fibers generated by electrospinning of polymer solutions. The identified nonwovens were 2 filter papers (glass and aramid) and 2 hydroentangled cotton fabrics. The nanofibers were electro-spun from cellulose acetate in acetone and dimethylacetamide mixtures and were deacetylated to varying degrees of substitution down (down to 0, or pure cellulose) using caustic soda. He has also studied the effects of grafting “polymer brushes and gels” for controlled release and “stimuli-responsive” properties.
Holly Krutka of the University of Oklahoma has simulated 6 different multi-hole die geometries in 3 dimensions, calibrating the simulation against experimental results in the published literature. The flow fields from the multi-hole simulation were very different from the earlier single hole simulations. Velocity maxima occurred closer to the die face and the spreading rates for air jets in the center of the array was much less than for a single jet. Orifice spacing was shown to have a significant effect on the interaction between inner and outer jets. (The Schwarz die has a hot air “sheath” around each die hole rather than the air knife slot across the entire die width)
Roy Bamford of Aurora Textiles Finishing Co reviewed the multiplicity of mechanical and chemical methods used by textile manufacturers to affect the look and feel of durable fabrics. The only “new” process mentioned was a softening machine which used beaded rolls to “massage” the fabric against soft rubber to locally stretch and soften. This could be an alternative to compressive shrinking (Micrex) which was also mentioned.
Basis Weight Uniformity Studies
Dr Randall Bresee of the University of Tennessee showed how automatic optical scanning of a nonwoven on a light table could yield detailed information on the basis weight uniformity. The instrument scans a large full-width sample and uses different “pixel” sizes to generate a “uniformity spectrum”. Images are acquired from a 640x480 8-bit monochrome (256 gray levels) camera using autofocus but fixed aperture and exposure time. Uniformity is expressed as the CV% for different areas ranging from the 40 micron square individual pixels up to the 25mm square “whole images”. A plot of CV% versus area viewed provides the unique uniformity spectrum for that sample. Data can be analysed to separate out MD and CD variations.
Dr Behnam Pourdeyhimi of NCRC appeared to be using a similar optical technique to Dr Bresee to characterize a 400 cm 2 sample in 400 x 1cm 2 regions and used the Poisson test to determine the spatial uniformity of the images obtained. The “quadrant” method was used to divide the sample into n=4, 9, 16….equal squares and the variance for each value of n could be calculated along with the dispersion index and the chi-square value. A uniformity index was then obtained. ( Unfortunately neither the presentation nor the written paper allowed more clarity than this. The conclusions, reproduced here in full, were as follows: “The findings of this current study indicate that appropriate strategies can be developed to characterize nonwoven fabrics”.)
Dr Rita Salvado of the Universidade da Beira Interior ( Portugal ) has studied the visual uniformity of a large number of spunbond nonwovens and compared it with air permeability measurements. As expected the more uniform the fabric the lower the air permeability. The standard deviations of the air permeability results were observed to correlate well with the apparent uniformity, so Dr Salvado proposed the use of air permeability variation as a measure of fabric uniformity.
29 th September 2005