Friday 7 November 2003

Insight - Nashville 19th – 23rd October 2003

More than 500 of the great and good of the nonwoven industry, 50 having travelled from Europe, assembled for 5 days in gloriously sunny Nashville for a conference of 27 sequential papers arranged to allow ample time for questions and networking.

It was the 25th event in this independent series of conferences organised by Marketing Technology Services of Kalamazoo Michigan, and marked a quarter of a century of top-class programmes, always up to the minute and often controversial, arranged by Jim Hanson and his team.

The Evolution of Diapers

Donald Sheldon, VP Absorbent Products of the Tyco Healthcare Retail Group Inc. reviewed the US development of diapers from the 1950’s cloth diaper services through Victor Mills development of Pampers to the present day. He argued that current diapers were too complex, the complexity arising from the limitations of the Pulp/SAP core structure which absorbed too slowly requiring ADL’s and leg cuffs to manage the unabsorbed volume until the core caught up.
He thought future diapers would have a core of SAP and filaments with built in odor management and an SMS backsheet, the whole structure allowing all-over stretch. They would prevent heat build-up and discomfort and would look and feel like textile underwear. Furthermore they would be free of surfactants, lotions and antimicrobials to avoid creating future allergy or resistance problems.
Asked if there was any patent coverage on the SAP/Filament core Mr Sheldon said there were 26 patents* with more to come. What about air-laid cores? They gave no real advantages and required a massive investment to use: maybe $1m/diaper line. Filaments would prove cost-effective compared with pulp, and a training-pant design would gain share in the main diaper market as it had done in Japan.

Absorbent Hot Melts

Pat Kellogg of H B Fuller pointed out the deficiencies of current SAP powders:
  • Most diapers are discarded with some SAP unused.
  • Airborne SAP is a safety hazard.
  • SAP gel on baby’s skin is a concern for mothers.
  • Backsheets are easily punctured by SAP.

    A number of ways of fixing the SAP in place had been evaluated:

  • Mixing SAP with hot melt polymer.
  • Coating SAP with fine hot melt powder and fusing it to the pulp.
  • Adding hot-melt powder to the drum former.
  • In-situ polymerisation of SAP monomers to give a SAP bonded core.

Of these simply mixing SAP with hot-melt looked best if the carrier, application and performance issues could be solved:

  • Water soluble hot melts failed because they competed with the SAP for fluid.
  • EVA was not good.
  • Thermoplastic elastomers didn’t work.
  • But, hydrophilic versions of TPE did.

The form of SAP to be added to this carrier was clearly important:

  • Big particles caused problems.
  • Fines seived from the process were better than normal SAP.
  • Especially ground and sifted powder was best but still not right.
  • So, Fuller developed a new form of SAP.

The resulting “Hydrolock®” hot-melt absorbs 30 g/gm of water in one minute and 30/gm/gm 0.9% saline in 8 minutes. Saline absorbency under load is 28.4 and the lubricity (ASTM D-2266) is <1mm so it should not wear out the nozzles. Flow-rate versus metering pump speed is linear, and when applied by the usual hot melt equipment it sticks to whatever it lands on and stays put.

The benefits: No dusting or sifting, lower waste, faster line speeds possible, lower loadings possible, can apply it where its most needed i.e. leg gathers, thinner backsheets can be used, and super thin pulp-free products become possible.

In response to questions, Mr Kellogg added:

  • It’s not designed to be flushable but it would help design of flushable products.
  • Results with synthetic blood have been variable, but consumer testing has been very positive.
  • No special nozzle filters are needed.
  • Application should be at 250 0C. The product is unstable at 300 0C.
  • SAP/Adhesive ratio? The performance is not based on SAP content alone.
  • Could the SAP separate out? No.
  • The acquisition rate may be too slow for diaper use, except maybe as a leakage barrier
  • It is not recommended as an adhesive. The cohesion is lost in water.
  • %SAP? Not a valid question. It’s a 100% absorbent hot melt.

Polyester for Airlaid

Keith Carnes of Wellman Inc described how the absorbency/retention of air-laid core materials is affected by additions of polyesters of different deniers and in differing concentrations. The studies were carried out on a 12” DanWeb pilot line, the control diaper core being 40% Sumitomo Aquakeep SA55S, 50% Weyco NB416 fluff pulp and 10% KoSa T255 PE/PET bico fiber at 600 gsm and 0.12 g/cc density. An adult incontinence control had the same structure at 250 gsm.

  • Replacing SAP with PET fiber whilst maintaining fabric weight improves absorbency, retention and acquisition time over a range of differing constructions and densities.
  • Reducing the PET denier from 11 to 3 improved absorbency (rate and capacity). The optimum denier may be lower still.
  • Hydrophilic finishes on the PET were better than hydrophobic finishes.
  • If core weight is reduced by substituting PET for pulp, absorbency generally improves.

Mr Carnes concluded that further studies with finer PET fibers, different finishes and higher PET levels were now needed. He also mentioned a new absorbent polyester, a copolymer with polyethylene glycol, which had a contact angle of 54 0 compared with rayon’s 58 0 (his measurement) and regular polyester’s 76 0 . It also showed a diameter swelling of 20% on wetting and was now being patented.

Hydrogen bonded Airlaid

Krishna Kumar, Manager of R&D for Novathin at Rayonier Corp. sought to dispel concerns about the stiffness, strength and absorbent rate of their hydrogen bonded air-laid cores.

  • The compression modulus of a 200 gsm core with 25% SAP could be reduced from the normal 5.5 N/mmto 2.5 by changing the process options and to 1.3 by changing the raw material options. (Gurley stiffness down from 350 to 255 gf.)
  • Third insult acquisition time could be reduced from 45 to 19, 14 or 11 seconds by three separate approaches to improving on the control.
  • Elongation could be increased from 3% to 11% and tenacity from 19.5 to 23.5 N/5cms while reducing density from 0.33 to 0.27 g/cc by two other approaches.
  • For a 400gsm core with 55% SAP, thickness could be increased by 50%, strength by 15%, and third insult acquisition time reduced from 33 to 23 seconds.

In summing up, Mr Kumar said that Novathin was now available in weights from 80 to 700 gsm, with densities of 0.1 to 0.45 and containing 0 to 70% of SAP. Novel forms of pulp were now being investigated. What about pre-formed diaper cores? The current value proposition was better performing cores at the same cost as the on-line cores.

Bico Fibers for Airlaid

Ida Pittman, a Senior Development Engineer with Kosa showed how their Type T255 PET-Core, Co-PE sheath bico gives the highest strength bonds to woodpulp while T254 with its Co-PET sheath gives best bonding to polyester. When bico contents are below 15%, pulp-bico bonds predominate in defining the strength, whereas above 15% bico, the bonds between the bico fibers predominate. 15% is therefore the concentration of bico which in these trials gave the most variability in web strengths, so 20% or above is recommended. Interestingly, this “transition concentration” was different for different fiber types, and so needed to be determined for every web type. Other conclusions from the study:

  • Tensile strength of the pulp/bico blends is affected most by basis weight, then by bico concentration and bico length; bico denier being least important.
  • 20% 4mm bico gives the same strength as 10% 8mm bico.
  • Reducing the bico denier from 2.8 to 1.5 increases strength by 50%
  • Replacing a sixth of the bico with solid PET fibers yields a softer more resilient web without loss of tensile.
  • Hollow PET gives more bulk.

In response to questions, crimp effect had not been studied, some hydrophilicity is lost as the sheath polymer melts, but Kosa use finishes designed better to stay on the surface. Asked if density had been held constant throughout the trials, Ms Pittman said it had not been deliberately varied.

Agricultural Airlaid

Annette Skyt of Dan-Web Holding’s Dan Core division argued that there may be a case for smaller air-laid lines than those that had created the global oversupply situation. Lines of 1000 to 4000 tpa output in widths from 250 to 1200 mms would be good for a variety of niche products and would be cheaper to install and more flexible in use. For instance, Kinsei ( Japan) use a narrow Dan Web line to:

  • Incorporate orange-juice manufacturing waste into an air-laid web for use as an agricultural mulch.
  • Incorporate green tea leaves, bean curd or bamboo into air-laid for use as cat and dog litter. (These bio-wastes all have a natural absorbency and ability to control bacterial growth and odor.)
  • Make 8gsm 100% synthetic fiber nonwovens for roofing lining and tea-bags. Make 700 gsm synthetic fiber nonwoven from 72 denier fiber.

Also in Japan cheese, bread and milk packaging is being made containing natural moulds to inhibit bacterial growth, and sushi trays are made to inhibit the odor of fish.
In Denmark, wood fibers reinforced with longer natural fibers (e.g. coir or straw) are air-laid and bonded with glue and/or bico fibers to make moulded furniture components. Air-laid wallpaper is also made using 76% Weyco NB416 bonded with 10% Trevira 255 bico and 14% Airflex EP 1188 latex at 118 gsm. The same product is selling as an air-filter, and a lightweight version makes an interesting Oshibori.

Patterned wires from Cofpa allow the forming of individual meat-pads which avoid the problem of SAP in the seams.

Dan-Web’s new inverted air-former lays onto a small transfer conveyor above the main conveyor and allows air-laid to be combined with impervious layers such as film. It can also be configured to lay dry pulp ontop of wet laid pulp above the forming wire of a wet-lay machine.

Absorbing liquids, odors and gases

Steven Bullock, an R&D Section Head with Procter and Gamble’s Babycare and Femcare division , responsible for out-licensing P&G’s technology introduced the absorbent laminate structures (ALS) developed to provide ultra thin femcare cores with built in odor control. This technology, developed in Pescara Italy, sandwiches a core of SAP, odor absorbent and hot melt particles between two nonwovens or tissues, bonds the core and seals the powder-free edges. The bonding powder does not affect the functional powder’s absorbency, and the resulting pads are soft, thin, flexible and easily made at high speed. Powder-free edges are achieved by laying the powder in stripes or rectangular pouches on a nonwoven, followed by heat treatment and hot-melt gluing the top layer of nonwoven in place.

The resulting pads can be 25-1500mms wide and filled with 8-700 gsm of up to 6 different powders of 50-600 microns diameter. The strips can be festooned or reeled. Functional absorbents could be SAP’s, active carbon, zeolite, baking soda, silica gel, potassium permanganate etc. Fruit preservation was mentioned as a novel new possibility. Tomatoes and bananas stayed fresh longer on ALS sheets containing permanganate and zeolite.

Femcare aside, P&G’s consumer testing had shown that the top 5 potential applications would be in fridges, garbage cans, shoe cupboards, shoe insoles and in gym-bags, and all those whose opinions were sought expressed a wish to buy such products. P&G had however decided that such products were too “nichy” and were therefore looking to licence the technology.

In response to questions:

  • BBA were already producing the material for P&G panty liners and “special negotiations” would be needed for any licences in the femcare area.
  • Active carbon is not used as an odor absorbent for femcare.
  • Particle size was not too critical a factor in performance.
  • The products did not have FDA approval for direct food contact, but because the actives would not be in direct contact with food, this was not perceived as a problem.

Hydroentangled Spunbond

Frederic Noelle of Rieter Perfojet having recently shown how hydroentanglement could improve the bulk and softness of a fully bonded spunbond now described how hydroentanglement at a very early stage in the process could give fabrics similar to staple products. Previous attempts to HE spunlaid products had taken the consolidated (but unbonded) web from the forming conveyor into the HE bonding unit on a second conveyor. The new Spunjet system positions the HE bonder above the forming conveyor allowing the unconsolidated web to be bonded. The result is efficient bonding at much lower water pressures, and hence thicker fabrics with a better softness/strength balance.

Hydroentangling Spunbonds: Water Pressure versus Strength

Compared with conventional thermal-bonded spunlaid, degradation of fiber strength at the edges of the bond-points is eliminated and the bulk and porosity of the fabric is improved by the absence of the ~20% film-like bond area. Compared to needlebonded spunlaid, finer fibers can be bonded at much lighter weights. Compared to any carded products, spunlaying allows the production of nonwovens with square properties (MD=CD) at higher productivity.

The new process has worked on a commercial scale, i.e. 3.2 m width, running at 400 m/min to give 12,000 tpa output. The machine could spin PP or PET containing additives or colors in deniers between 1 and 6 and in weights between 15 and 600gsm. Patterning of the bonded webs with logos etc. was possible. The line will be commercially on-stream by the end of 2003.

Asked if woodpulp or rayon could be incorporated, Mr Noelle said they were working on this. The high strengths from low water pressures are possible because the web had very low cohesion when it was bonded. The bulk arose because the filaments were effectively crimped by the looping action of hydroentanglement. Water filtration was not an issue, the filaments being perfectly clean and finish free.

Global Diaper Survey

Blake Kuster of Absorbent Technologies Inc reported results from a Sumitomo Seika Chemical Co. study of 110 diaper types from around the world. In addition to core structure, static absorbency/rewet testing of the products had been carried out:

  • % SAP ranged from 42% in Japan down to 23% in the Middle East with North America (36.5%), Europe (29.3%), South America (26.8) and the rest of Asia (26%) in between.
  • US diapers are the fastest absorbers, the Japanese products appearing to have been designed to give a slower uptake.
  • US diapers have the lowest rewet on average, but a UK private label product was best of all in this regard. Asia-Pacific products had the highest average rewet on these lab. assessments.
  • The newer perforated film ADL’s look good especially with lower SAP levels.
  • SAP containment is still an issue with dusting and pinhole problems especially in private label products containing more than 35% SAP.
  • Best performers are not necessarily those with most SAP. 25% SAP efficiently blended and positioned can more than satisfy absorbency demand.
  • From a briefly shown master chart of Rewet v %SAP, a Japanese sandwich-type diaper coded DSG4 with 3gms rewet at 16% SAP looked the most remarkable. At the other end of the scale a product coded KC2 with 25% SAP gave a 39 gm rewet. Heavier (>30gsm) ADL’s are needed to get the best out of ultrathin or low SAP cores.
  • >70% SAP Possibilities? Only if the current SAP structure changes. Current SAP’s are too coarse and harsh for comfort.

Hygiene Products Material Changes

Pricie Hanna of John R Starr Inc reviewed recent changes in the construction of selected hygienic absorbents:

  • K-C’s “Convertibles” used wide-stretch side tabs sonically bonded, and a stretch laminate waistband on a product which could be used either as a pant or as an open diaper.
  • K-C’s “GoodNites” with “Trimfit” discreet youth incontinence underpants used a highly densified core with increased SAP and a lofty carded, through air-bonded ADL.
  • P&G’s “Pampers Easy-Ups” now had wetness indicators to facilitate potty training and the child’s awareness of wetting.
  • Kao’s “Merries” had a versatile mechanical fastening system which could be fastened at the front or the back.
  • P&G’s “Always Maxi Pad” now had an extra absorbent layer, an airlaid ADL which reduced leakage.
  • SCA Hygiene’s “Libresse Goodnight” pad has an elastic band extended lengthways under the core for better body fit. The core is wide in front, narrow at the crotch and split in half at the (wide) back.
  • SCA’s “Libresse with Invisible Wings” is an ultra-thin pad with transparent film barrier, backing and wings for maximum discretion.
  • SCA’s “Libresse 2 in 1” is an ultrathin panty liner with the absorbency of a napkin.
  • SCA’s “Libresse So Slim” is an ultrathin panty liner daily alternative to extra panties when travelling.
  • SCA’s “Libresse Micro” is a very small oval liner in a hard plastic container for everyday use in most panty styles.
  • Walmart’s “Assurance Refastenable Underwear” can be pulled up like underwear or changed like an open diaper without removing clothes. It uses an apertured film ADL.

For improved leakage prevention, fluid transport and absorbtion systems are being optimised, extra leg cuffs are being added and improved elastics and elastic fabrics are being developed.

For increased convenience and ease of use, look out for pull-ups with openable sides, adjustable side panels, and easy-to-grip tabs.

For increased comfort, softer spunmelts and lighter nonwoven/film laminates are being used, elastics are getting gentler and cores are getting thinner and hence better fitting due to >50% SAP and improved ADL’s. New film/nonwoven laminates are being used to improve air-flow and hence skin health. For discretion, quietness (softer films) and odor absorbency (modified SAP’s) are being added to the above material changes.

Asked if the pharmaceutical companies would win over disposables, Ms Hanna said that John Starr Inc had helped them understand the market. Pharma solutions appeared to very specific to each of the many causes of incontinence, whereas the disposable products could be applied to all.

She felt that the 8-hour, $5 diaper proposed by Ms Ericksen would be too specialised for the major producers but may be developed by an entrepreneur.

The average SAP content in diapers was now 48%. Next year premium products with 70% SAP would appear.

The wipes market continues to grow as fabric qualities are upgraded. Some of the newer household wipes are showing impressive staying power.

Pharmaceuticals threaten Disposables?

Helena Engqvist (Consultant) warned that the pharmaceutical industry with its massive R&D capability and desire for double-digit growth was beginning to develop products which could reduce the need for hygienic absorbents.

  • The Seasonale® drug now on the market reduced the number of periods a woman had per year from 13 to 4. If generally used this would have a dramatic effect on the $18bn disposable femcare industry.
  • Adult incontinence, a $6.3bn market in 2002 is being targeted with oxybutylene patches which now have approval for over-the-counter sales.

The pharmaceutical industry has been successful in redirecting its marketing effort from healthcare professionals to consumers and this will continue.

No child left behind - given 8 hour diapers

SusanEricksen, a Special Needs Educational Co-ordinator highlighted the problems of coping with the incontinence of handicapped children in schools in the USA. The time and costs of diapering were significant. Handicapped children attended either Center Based Programs or Public Schools:

  • For the Center Based Programs she had calculated that it costs about $7000 to equip one room with the tables, lifts and bolster to allow 2 assistants to change the diapers of the 12 children in the class. Monthly cost of disposables amount to $256 (paid by the parents of each child) and staff time required amounts to one full-time person, or $2120/month. Furthermore, each child loses 40 minutes of education per day to diaper changing.

  • The 30,000 multiply-handicapped incontinent students in mainstream US schools change their own diapers, but this takes longer, so they lose 80 minutes per day of educational time or 40 days/year. With each change costing $3.18, the cost per day amounts to $763,200 in the US.

Ms Ericksen made a case for diapers specially designed for these students, a key target being a product which would keep them dry and odor free for the full 8-hour school day. Such a product would be worth at least $5 per diaper, and would, as a much-improved training pant, command a larger market than she had calculated for this paper.

In response to questions: Yes, reusable products would be acceptable. They would have to be sized to fit students up to the age of 26. They could be distributed with the other “special care” needs of the educational system or over the internet.

Chlorox Wipes Case Study

Andrew Kilkenny and Garry Embleton of Chlorox Services Co. pointed out that the early antimicrobial wipes, Dow “Spiffits” and Chlorox “Spruce-Ups” failed because they overpromised and underperformed at a time when consumers were not so aware of the benefits of disinfection and convenience as they are now. So Chlorox reformulated and relaunched in Jan 2000, a week ahead of the competition, the resulting demand exceeding all expectations. The key to their success was collaboration with suppliers:

  • They ran 32 wipe constructions in consumer tests to ascertain aesthetic and performance preferences.
  • Nonwoven type, Embossing and Binder levels were among the variables studied.
  • Cleaning, Disinfection, Absorbency and Dispensability were among the attributes monitored.
  • The suppliers who provided the fabrics were allowed direct access to the consumers used for the panel testing.

Contract packers are used for their speed and flexibility compared with in-house converting. These were most helpful in dealing with early complaints related to roping, excess wipe left out of the canister, and fallback into the canister. They reoptimised the perforation pattern and developed a new closure system which allowed storage of excess wipe. Problems with the “logs” collapsing in transit and storage were dealt with by a move to a stiffer substrate.

The success of the relaunch was sustained by introduction of new varieties:

  • Thicker/larger wipes
  • New Fragrances
  • Flushability (for toilet wipes)

Chlorox are looking for new partnerships with suppliers and this appeared to be the main motivation behind the presentation. They feel their “both parties win” approach gives the supplier a proper return for providing a “total value package”, i.e. innovation, low costs, service and high quality. They look for two types of supplier:

    • Cost and service driven (Low R&D%)
    • Innovative suppliers (High R&D%)

Most suppliers are somewhere between these extremes.

Their “Technology Brokerage” manages the R&D relationship with suppliers, and R&D pervades all aspects of the collaboration. An “R&D relationship owner” works with procurement and the supplier to ensure Chlorox is exposed the suppliers full capabilities. They have also developed a quantitative supplier performance assessment and use this to push opportunities towards the high performing suppliers.

In response to questions:

  • Should these relationships with suppliers be exclusive? Yes, and furthermore Chlorox would like a share in any intellectual property they develop.
  • Their flushable product is pulp based, and the flushability claims are based on a dispersion test.
  • Wipes account for 10% of Chlorox turnover, but Chlorox now have 16-17% of the wipes market.
  • They have developed their own wiping tests and “soils”.

The Wipes Market

Susan Stansbury of Arketype Inc provided the latest data on the wipes market:

  • INDA put the 2002 North American market at $2.2bn whereas Paperloop estimated a $1.5bn demand.
  • Baby wipes were 55% of the total, the rest being 14% Personal and skin care wipes and 31% household wipes.
  • North American demand for spunlace was now 100 – 120,000 tonnes/year. Half of this was for wipes, and ~35% for medical.
  • The key US producers of spunlace were Dupont, BBA, Green Bay Nonwovens, PGI and Ahlstrom. K-C made it primarily for their own use.
  • Airlaid capacity in North America was ~250,000 tonnes, some of this underutilised.
  • 60% of the airlaid is in wipes, with Georgia Pacific Nonwovens having the strongest position.
  • The wiping sector is set to grow at 6-7% pa for the next 5 years, with 15% pa growth in some niches.
  • New wipes continue to emerge, e.g. pet-care, body wipes, antibacterial wipes, and insect repellents.
  • Dry wipes typically compete in Food service and in the $1.5bn industrial sector, 32% of which is now disposable rather than reusable products. Most growth is expected for spunlace replacing the reusable shop towels.
  • Dry wipes have about 30% of the total nonwoven wiping market and do not grow as quickly as wet wipes.
  • Chemically treated versions (delivered dry for wet use) are set for above average growth and could take share from their wet counterparts. (Easier to make and cheaper to deliver. No bioburden issues)

Asked to name some fast-growing niches, Ms Stansbury said many were auto-related. New players , probably contract manufacturers teaming up with marketing companies to make private label products, would enter the field.

PP for Wipes

John Wolhar, Americas Sales Manager for Fibervisions made a case for replacing the viscose in wet-wipes with their newly developed HyEntangle WA fiber. PP has the inherent benefits of low density (more fibers/gm), low melting point (easy embossing), whiteness c.f viscose, cheapness, softness, and excellent chemical resistance. Their older HyEntangle fiber had a specially low dtex, higher tenacity and a low-foam finish and has now been optimised to improve production economy and wiping performance.

Because PP fabrics do not collapse when wet, the 100% PP wipe stays bulkier and maintains a higher wet CD strength. Absorbency and wettability tests carried out with 0.5% detergent solutions looked good. Furthermore because the absorbtion was entirely inter-fiber, 100% PP gave better lotion release than viscose containing wipes.

Does the finish survive hydroentanglement? Yes, for the newer WA fiber.

Is the wiping efficiency as good as the rayon containing products? “It should be OK in wet-wipes”.

IR, RF and Hot Air

Ben Wilson, Sales Manager of PSC Inc pointed out that both radio frequency and infra-red drying needed air-flow to carry the evaporated water away from the drying zone, so combination dryers would be the best solution to most drying problems.

  • Hot air dryers were best for holding a product at a temperature for a long time without overheating.
  • IR was best for rapid heating of the whole web.
  • RF heats the center of a fabric before the outside, while IR does the opposite.
  • RF also heats the water preferrentially and dries the wettest parts of a web or fabric first. It therefore removes damp spots and can be used to reduce the variations in moisture content at the end of a hot air or IR system.

RF heating depends on the loss factor of the material in the dryer, but loss factors change on heating. So PP is not sensitive to RF until its temperature goes above 250 0F and then runaway heating leads to meltdown. RF with cool through air drying would be best for such products.

Ultrasonic bonding revisited

Torsten Brieger of Hermann Ultrasonics Inc described how their micro-gap control system is making sonic bonding consistent enough for the most demanding welding and bonding applications. Stepper motors are now used to change the weld-horn position in 0.4 microns steps to compensate for thermal expansion of the titanium horn or variations in thickness of the webs or fabrics. The stepper motors respond to signals from load cells in the actuators allowing constant welding force to be maintained over widths up to 3m and at speeds up to 500m/min. Compared with calendering the ultrasonic approach is a low energy cold process which gives full bond strength instantly, allowing webs or multiple layers of prebonded fabrics to be welded with precise bond points.

Speciality Meltblowns

Mr Soichi Obata of Kuraray Saijo Co Ltd said that his company makes meltblowns from PP, elastics, adhesives, PBT, nylon and composites in the form of a spunlace/meltblown/spunlace laminate. They have now added two new polymers, a polyarylate and a novel polyamide to their range.

The polyarylate is a liquid crystal aromatic polyester (“Beltron®”) made from 2-hydroxy-6-naphthoic acid and 4-hydroxybenzoic acid. A filament version has been used to make the airbags of the Mars Lander, but the meltblown version comprises 4 to 7 micron continuous filaments with a melting point of 300 0C, or 340 0C - for a “heated” version. Other properties to note:

  • 100% strength retention over 72 hours at 200 0C
  • Better than 84-94% strength retention in Normal solutions of hydrochloric, nitric and sulphuric acids over 100 hours at 90 0C.
  • Uniform 15gsm fabrics are possible c.f. a 22 gsm minimum for aramid papers. 10 gsm is targetted.
  • Fabric water absorbtion of 0.1% after 170 hours at 90%RH c.f. 2.5% for aramid papers.

The second new polymer was a polyamide based on nonanediamine and terephthalic acid. Standard meltblown from this had 2-5 micron fibers and a soft handle, whereas a high density version used 9-11 micron fibers calendered into a paper-like sheet. It had a high resistance to caustic, the tensile strength increasing by 20% after 50 hours in N NaOH at 90 0C.

In response to questions:

  • They expected applications in heat and chemical resistant filters.
  • They would not sell the polymer pellets for others to convert.
  • Polyarylate meltblown would cost ~$90/kg, the cost of the polyamide was not available.

Hygiene Market in Eastern Europe

Krystyna Jozefowicz, Manager of the Foreign Trade Dept. of Poland’s TZMO SA described how the company had evolved from a state-owned surgical dressing manufacturer into the leading producers of hygiene products in Poland. In 1991 the 800 employees bought the company and have since grown to employ 4000 people today. They have 67% of the Polish market (P&G ~20%) and have successfully expanded into the Ukraine and Russia. She was concerned that European Integration would leave Russia, Ukraine, Kazakhstan and Belarus out and predicted that these countries would form a new economic block of 205 million people because they would not accept “waiting list” status.

Surprisingly, she claimed that the hygiene markets in Eastern Europe were now mature and saturated.

Cytotoxicity Testing

Eleanor Sun (Consultant, recently retired from PGI) explained the test methods and their current importance.

  • Cytotoxicity arises from biologically harmful extractibles in the materials.
  • The test is suitable for detecting subtle changes in raw materials, vendor differences or process deviations.
  • It correlates well with animal testing and reduces the need for such testing.
  • It is now mandated for all medical devices such as menstrual pads, tampons and incontinence products.

The most commonly used version of the test is the MEM (Minimum Essential Medium) Elution test where the the medium contacts the material for 24 hours and the any change in the mediums ability to culture cells is visually assessed. Mammalian cell culture medium is preferred as this extracts substances which are not soluble in water. Antibiotics can be added to suppress the effects of microbes.

L929 mouse fibroblast, rabbit cornea or human embryonic lung cells are grown in a flask and challenged with the extract. Changes in the layer of cells are observed over three days and damage rated on a 0-4 scale. Dyes such as tryphan blue stain dead cells blue and live cells yellow to help the rating process.

0 – no visible effects
1 – Slight changes, <20% of rounded cells and some lysis (cell walls destroyed)
2 - Mild effect, <50% rounded but no holes in the layer
3 - strong effect <70% rounded or lysed: holes appearing in the layer
4 – Severe effect >70% destruction of the layer.

0 and 1 would pass, and the product would be worth more thorough safety testing using more costly techniques. 2 would be borderline and require further cytoxicity study. A result of 4 would be followed by repeating the test with progessively diluted extract to define the “no-effect” level.

Hydrophilic finishes, lubricants, antistats, wetting agents, colorants and antimicrobials can all cause cytotoxicity.

A cytotoxicity test costs about $100 (24hr) to $300 (72hr)

New Airlaid Pilot Line

Jim Hanson of MTS Inc has a new air-laid pilot line under construction:

  • It is 0.6m wide with 5 DanWeb heads and space for other formers.
  • The 5 forming zones each have their own hammermill, fiber and SAP feeders.
  • One of the spaces could take a head capable of laying 30mm fibers at high throughput.
  • Latex (one side only) and thermal bonding options will be available from the start.
  • Calender lamination of film to the airlaid will be possible.

Clearly a very wide variety of multi-component multi-layer composites will be possible on this machine which will be available for hire in the new year.

Thursday 25 September 2003

INTC Baltimore: 15th - 18th September 2003

450 delegates attended a programme of 73 papers in 17 sessions, plus student papers, table-top displays and a new technology showcase
Renaissance Hotel - Baltimore. Venue for INTC 2003
Hurricane Isabel did her best to dampen spirits and many delegates were forced into early or late departures by flight cancellations. However about 100 remained through the last morning, and those who failed to get out at all that day had the unusual experience of watching Chesapeake Bay trying to check into the conference hotel on Friday morning.
Nevertheless, it was one of the best technical conferences of recent years, the highlight, for your correspondent at least, being the informative and coherent sessions on nanofibers.

Keynote Speech

Thomas Kehl, the New MD of Freudenberg implored the nonwovens industry to speed up new product development to allow faster growth. He was critical of the whole development process:
  • Current investment tended to be focussed on extending the life of products rather than discovering new breakthrough products and markets.
  • Heavy investments by big companies were often the least productive.
  • Methods used for prioritising projects were unreliable (“sporadic”)
  • Major projects which failed to live up to expectations developed a life of their own and were not terminated quickly enough.
  • Unfocussed budgeting criteria led to long pay-back times.
However in a word of encouragement for the smaller companies he observed that external sources of ideas tended to deliver better returns.
There were several traps for an unwary management board trying to grow a new business:
  • The Denominator Trap: overstatement of the market share potential.
  • The Sustainability Trap: an inability to support marketing at the required level past the launch budget.
  • The Substitution Trap: too much cannibalisation of profitable products occurs.
  • The Uniformity Trap

Industry Trends - Panel Discussion

Ted Wirtz, the retiring President of Inda opened the discussion with a presentation of 2002 industry statistics:
  • North American nonwovens usage was 1.05 million tonnes, worth $4.4bn.
  • Two thirds were destined for “short-life” end-uses and one-third for “long-life”
  • 14% of production was exported, up from 10% of production in 1992.
  • 104,000 tonnes of nonwovens were imported.
  • Total production would rise from 1.25 million tonnes in 2002 to 1.710 million tonnes in 2007 (includes exports)
In the 2000 to 2002 period 302,000 tonnes of new capacity have been added in NA:
Polymer to fabric processes now accounted for 37% of world capacity and would continue to grow at 6-8% per annum. New composite structures would drive this growth (“SMXMS” - the X being unspecified but pulp is likely to be important.)
Fiber to fabric processes accounted for the remainder and would grow at 3-5% per annum. This growth would be driven by spunlace wipes and air-laid absorbent cores.
Other key trend drivers would be:
  • Reducing barriers to international trade.
  • Overcapacity in air-laid, spunlaid and spunlace.
  • Migration of R&D to the consumer product producers. (The rest of chain has been “milked” and can no longer afford R&D).
  • Technology being dedicated to end-uses. (More wipes lines than general purpose spunlace lines).
  • China, Turkey, Saudi Arabia and the Middle East growing at 10% pa.
  • Latin America growing at 8% pa.
In future the flow of new products would be the reverse of the traditional, i.e. the consumer product makers would develop the ideas and specify the nonwovens and raw materials to be used.
In conclusion, Mr Wirtz observed that too many nonwoven producers and raw material suppliers were too ready to accept commodity supplier status and cut back new product development. R&D really did pay off in this industry.
Lee Sullivan of Freudenberg Nonwovens focussed on the importance of the automotive market to the US economy in general - “35% of GDP is auto-related”, and to a polyester spunbond producer in particular. He stressed the highly technical nature of PET spunbond production c.f. PP spunbond and related Freudenberg’s continued success in this sector to the difficulty competitors had in meeting the ever-tighter requirements of the auto and carpet markets. For the future he saw a resurgence of use of carpet tiles, this time shaped to prevent the fact that they were tiles being so obvious.
Chuck Moestra of Rohm and Haas provided an outlook from the viewpoint of a binder and additive supplier. Opportunities for growth would come from
New performance requirements:
  • Need to work over a broader temperature range
  • Flame retardency becoming more important
  • More antimicrobial products.
  • More environmentally-friendly products
  • Low formaldehyde products
  • Better barrier performance
And new market opportunities in:
  • Automotive
  • Medical
  • Filters
  • Wipes
  • Building
  • Insulation (acoustic)
- But not in apparel or home furnishing.
The panel provided answers to some audience questions:
  • Environmental issues will drive nonwoven wipes development. Too many are getting into the sewage system and blocked drains are now causing concern in local authorities. Biodegradation is needed and flushable products that really work will have to be developed.
  • Biodegradable spunbonds are too expensive for use at present. They are about twice the price of regular polyester, but R&D is underway (CDP-PLA) and they could be important in future.
  • There’s no evidence that antimicrobial chemicals in wastewater are killing fish.
  • About 80 companies claim to be specialist finishers of nonwovens. In reality most of these just slit roll-goods: only a few really add new functionality and value.
  • Nonwovens and Textiles companies should begin working together for mutual benefit in recognition of end-user needs. (Witness INDA’s invitation to Technical Textile producers to exhibit at IDEA 2004)

Measuring fiber size on- and off- line

Chris Fandrey of Powerscope Inc introduced the Ensemble Diffraction method for scanning nonwoven webs to obtain real-time information on fiber diameters. The technique uses a laser beam which, after scattering on passage through the web, is analysed by a “ring detector” which measures the scattered beam’s intensity at various distances from its original axis.
Fraunhofer scattering equations are applied, suitably corrected to compensate for:
  • Multiple scatters (scattered light passing through another fiber)
  • Scattering due to fiber crystallinity
  • Refractive index effects
Results can be obtained every second, and the beam can be up to 12mm wide. It can be traversed across the web to give a full width fiber diameter profile.
Correlation with SEM measurements of fiber size is excellent, the scattering technique giving slightly higher diameter values due to fiber bundling. Used on-line in a melt-blowing process it picks up the diameter changes with distance from the nozzle and can detect shot levels as an anomalous scatter at small angles.
The technique is currently limited to webs with >35% light transmission, and this means webs lighter than about 4 gsm. Practical fabrics have to be “thinned out” for off-line measurement, but melt-blown fibers can be measured on-line in the nozzle-to-drum region.
In response to questions:
  • The technique is very insensitive to fiber orientation (due to ring detection of scatter)
  • Additional data on fiber crystallinity, refractive index and bicomponency may be obtainable.
  • Non-round fibers will be interpreted as round, and an average diameter given.
  • It works best on glass fiber.
  • The kit costs $70,000

Nonwoven Spacer Fabrics

Dr Steve Russell of Leeds University (UK) described small-scale work on a hydroentanglement analogue of the Laroche - Napco “3D needlefelt” technology. Water jets had been used to bond two prebonded webs together either side of spacers, which, if tubular, could simultaneously be used to fill the spaces with powders. He thought the powder could be a superabsorbent if it were possible to dry the web in the space between the last HE zone and the end of the spacers.
Photo’s of single and two-side entangled products were shown, although any continuous operation on existing HE machines would not allow two sided entanglement without collapsing the tubes. One sample had a PU coat on the inside of the tube, presumably made by using an annular spacer.

Spun Lace Composites/Nanoval

Alfred Watzl of Fleissner GmbH & Co offered spunlace lines 7 m wide operating at 600 bar water pressure and running at 250m/min on carded products (200 if aperturing required) or 400m/min on spunbond. Composite manufacturing capabilities were based on Fleissner’s exclusive licence to use Georgia-Pacific’s 3 layer hydroentanglement technology, the key example being the spunbond/pulp/spunbond composite with 75% pulp and 10 gsm spunbonds produced at 400m/min.
The paper also mentioned the unique Nanoval “melt-blown” technology that uses a Laval nozzle and ambient air to draw and explode the forming filaments into a bundle of continuous microfibers of 0.03 to 0.35 dtex. The technique gives much higher throughput than conventional melt-blown (~100gms/min/hole) and produces stronger more oriented nonwovens.
Asked what the relationship between Fleissner and Nanoval was, Mr Watzl said there was no formal relationship but the technique was interesting and they were collaborating on its development. The process was not yet commercial.
(NB Since the conference, Neumag has acquired the Nanoval technology)

Structure/Property relationships for HE nonwovens

Dr Benham Pourdeyhimi of NCRC is running a series of experiments to investigate structure, process and property relationships in hydroentanglement. First results indicate that increasing hydroentanglement energy from 0.3 to 2.2 Kwh/kg does not affect MD/CD orientation in the web. However, in production processes, high pressures tend to stick the web to the forming belt, and the force needed to remove it would tend to increase the MD orientation. MD tensile strength and bending rigidity increases with bonding energy up to about 1.5 Kwh/kg, and then declines. Fabric elongation increases linearly with energy for nylon webs and is unaffected for polyester webs.
Fabric thickness decreases to a minimum around 1.5 kwh/kg and then increases, appearing to be roughly the inverse of the tensile trend.
Asked if the way the energy is applied affects the results, Dr Pourdeyhimi said it would. However, in practice it would not be possible to use either hundreds of nozzles at low pressure or one nozzle at very high pressure to investigate the effects.

Pore structure in Nonwovens

Dr Krishna Gupta of Porous Materials Inc showed how their Water Intrusion Porosimeter (WIP), designed for use on hydrophobic structures, could be used in conjunction with the standard Mercury Intrusion Porosimeter (MIP) to give extra detail of pore structure in fabrics made of mixtures of hydrophilic and hydrophobic fibers. In the WIP test, the water spontaneously fills hydrophilic pores but only fills hydrophobic pores under pressure, while in the MIP test all pores require pressure to fill them. (Hg is universally non-wetting). So, in the WIP test the uptake/pressure curve is a measure of hydrophobic pores only and the MIP test uptake/pressure curve relates to all the pores. The difference relates to the hydrophilic pore structure. For an unspecified “fibrous paper”, 82% of the pore volume was found to be due to hydrophilic pores with an average size of 60 microns, and 18% of the pore volume was due to hydrophobic pores with an average size of 9 microns.
Asked about the pore size ranges detectable, Dr Gupta said 20 microns was currently the largest detectable by WIP, but a new technique was being developed to measure pores up to 1mm in diameter. MIP worked from 30 angstroms up to 400 microns but needed very high pressures. The advantage of WIP was its relative simplicity on hydrophobic materials.

Cavitation in HE nozzles

Dr Hooman Tafreshi of NCRC has compared observations of water jets using high speed cameras with theoretical expectations based on fluid dynamics. When the cone-shaped nozzles have the high pressure water entering at the base (“cone-up”) the calculated Reynolds number (10,600 to 36,000) predicts that the jet should atomize over a wide pressure range, but in practice, this only occurs at pressures above 2000psi. If the nozzle is inverted with respect to the water flow - “cone down” – atomisation does not occur even at pressures above 2000psi. This has been shown to be due to the water riding on a cushion of air throughout the cone-down nozzle.
This cannot happen in the cone-up configuration for any practical nozzles, but does occur if the cone angle is greater than 60 degrees.
At pressures above 2700psi the water jet appears unstable, the atomisation point varying with time under apparently constant process conditions. Modelling suggests that this is caused by cavitation, the onset of which allows air into the nozzle and creates a “hydraulic flip”.

Designing Nozzles for Better Water Jets

Asli Begenir now with Sara Lee, collaborated with Pourdeyhimi and Tafreshi at NCRC to produce this paper. They studied the effect of water pressure and nozzle design on the discharge coefficient, the water jet profile and its breakup length. One cone-shaped nozzle with an L/D of 7.65 was used both cone-up and cone-down relative to the high pressure side of the injector, and compared with a second cylindrical nozzle with an L/D of 1. Water pressure was varied from 100 to 5000 psi.
The conclusions were:
  • Water column break-up length varied from 0 (for cone-up at pressures above 2000psi) to 200mm’s (for cone-down at 2000 psi)
  • Cone-up generally gave significantly shorter breakup lengths than cone-down or cylindrical.
  • Cone-up gives a discharge coefficient of 0.9 c.f 0.63 for cone down and cylindrical (over the whole pressure range)
  • Cone-up gives a higher rate of energy transfer to the fabric at pressures below ~2000 psi due to the higher discharge rate (mass flow)

Dynamic wiping efficiency

Marshall Oathout of Dupont Inc. presented new procedures for investigating the factors involved in wiping a wet surface clean whether liquid is present to assist cleaning or as the result of a spill. The factors were:
  • Dynamic wiping efficiency, i.e.rate of absorbtion of the liquid
  • The number of particles present in the liquid
  • The number of particles on the wipe which may be left behind on the surface.
The dynamic wiping efficiency test was developed using 9 commercial clean room wipes. 5 were hydroentangled nonwovens containing cellulose, one was woven cotton, two were knitted polyester fabrics and one was a PP spunbond. Each fabric had its maximum absorbent capacity checked and dry samples were then used to wipe up a range of spill volumes (up to 130% of this capacity) on a stainless steel surface. The wipe was attached to a sled pulled at 25 cm/sec over the surface. Unsurprisingly, the hydrophilic wipes outperformed the hydrophobic ones, with the 100% lyocell HE wipe appearing best when used both dry and pre-wetted to close to its saturation point. In the pre-wetted test, woodpulp/PET HE fabrics performed almost as well as the lyocell.
The wet particle removal test was in essence the above dynamic wiping test, the spill being contaminated with 10million 1.6 micron latex particles. After the wiping test, the surface was rinsed and the resulting liquid passed through a particle counter to establish how many particles were left behind. In this test, the 100% lyocell HE fabric did best both dry and prewetted. Interestingly every wipe removed more particles than expected from the % of spill left behind, so the particles appear to preferentially stay with the wipe. This effect was most apparent for lyocell and least apparent for the knitted fabrics.
The “particles contributed by the wipe” test was the wet particle removal test using an uncontaminated spill. Particles in any spill left on the surface would therefore have come from the wipe. 1-3 micron particles were counted. Here the knitted Polyester and the 100% polyester HE appeared best with the 100% lyocell HE being good up to about 90% of its capacity. Particle release from all fabrics was much lower than expected from earlier static particle release testing.
Comparisons of wiping stainless steel, polyethylene and glass surfaces showed that glass was much more retentive to particles. Stainless and PE were similar.
Testing with 0.6 micron particles gave results very similar to the 1.6 micron particles.
Wiping iso-propyl alcohol spillages proved difficult on this rig because the spill spread out beyond the sled width for all but the smallest spill.
The bottom line: It’s necessary to wipe dry to wipe clean.

New Lyocell Fibers for Nonwovens?

Nick Simpson of Tencel Ltd reviewed 10 years of lyocell development and summarised the attributes of the fiber across the whole range of nonwoven products.
Wipes had proved to be the most successful nonwoven end-use. Hydroentanglement and needling were the most used conversion technologies. Nonwovens using lyocell were better than viscose nonwovens for strength, especially wet strength, for aperturing clarity, softness (at comparable strength), basis weight range in spunlacing, and low-linting. In air-laying the low cohesion of the fiber gave good results, and in needlepunching the ability to use a 1.7 dtex fiber led to softer products.
In response to questions, Mr Simpson said available Tencel fiber types were restricted to between 1 and 3 denier, but any length from 0.5mm upwards could be supplied. Prices could not be discussed, but it was comparable with viscose and hence more expensive than polyester staple. Wicking and water retention properties were similar to viscose. The dissolution process did not degrade wood-pulp so fiber and pulp had similar degrees of polymerisation.

Partially-Oriented Hollow Polyester for Nonwovens?

Ivo Edward Ruzek of Industrial Consulting estimated that worldwide use of polyester in nonwovens was now around 500,000 tonnes and felt that future growth needed a fiber specially tailored to the needs of the nonwoven producers. The traditional cotton-type fiber as sold to the nonwoven industry was no longer good enough:
  • For hydroentanglement, the fiber should be 1-2denier with low modulus and strength, and with a low foam finish.
  • For thermal bonding the fiber could be as for HE but would need blending with a low melt fiber such as co-polyester or PLA.
  • Latex bonding would need a high modulus fiber because here the main market was roofing felt.
  • Needling would need high denier fibers.
  • Many end-uses, especially distribution layers, would need a permanently hydrophilic fiber.
So Mr Ruzek proposed a partially oriented fiber with a strength of about 4.2 gpd and 65% extension made from PET with ethylene or propylene glycol blocks to get better moisture management or with PLA to lower the melting point. Furthermore, if it could be made with a hollow core, weight and cost savings could follow while the hollow fiber would give improved resilience.

Hollow Polypropylene Fibers

Diana Ortiz of the University of Oklahoma gave Robert Shambaugh’s paper on producing PP fibers with 50% hollowness, this being defined as (ID/OD) 2 where ID is the diameter of the hole, and OD is the outside diameter of the fiber. In a low-speed, short-spin (0.5 m threadline) spunbond process this could be achieved by injecting nitrogen into the core of a bicomponent jet. The fiber spun with 0.5 g/min polymer per hole at 1500m/min showed a 0.3 birefringence suggesting full orientation. Even at 1g/min/hole full orientation appeared to be achieved at only 1900m/min spin speed.
Questioners suggested that the birefringence measurements were affected by the hollowness, and that the fiber was not really fully oriented. Why did the hollow fiber have such a low tenacity and high extension? Ms Ortiz said that both solid and hollow fiber made on their machine had similar extensions, so the hollow result was not unusual. Why had nitrogen, rather than air been used to fill the core? She agreed air could be used in future.

Splitting Meltblown Bicomponents?

Yanbo Lui of TANDEC gave Christine Sun’s paper. TANDEC made a 50/50 nylon/PP meltblown web and hydroentangled it. The fibers broke up into shorter fibers without splitting. The main conclusion was that basis weight reduces with increasing water pressure (due presumably to fiber loss), and that the adhesion between the two polymers in the bicomponent was too high.

Electrospun Biodegradable Nanofibers

Dr Gisela Buschle-Diller of Auburn University defined nanofibers as fibers with a diameter below 0.5 microns. When electrospun such fibers are invisible and when spun onto a black background it takes some time before the web begins to appear.
Polymers suitable for electrospinning should melt without decomposition or dissolve in a solvent and reform on solvent evaporation. In this study PVA, polycarbonate, biopolyester, poly-hydroxybutyrate, and poly(DL-lactide-co-glycolide) were spun through 5-25 Kv electric fields to a collector 5-25 cms away. Both voltage and distance were varied in 5 unit intervals.
Increasing the voltage gave finer fibers while increasing the nozzle-to-collector distance gave coarser ones. Melt-spinning polymers gave better results than solvent-spinning. Attempts to make a bicomponent sheath-core nanofiber resulted in side-by-side bicomponency.
Testing electrospun nanofibers proved difficult. However the coarser PLG fibers (1.8 micron or 0.03 denier/fil) gave a yield stress of 12 g/denier at a yield strain of 16%.
In response to questions, they have yet to try hot-drawing the nanofibers to improve strengths.

Fiber Charging Effects on Target coverage in Electrospinning

Peter Tsai of the University of Tennessee defined nanofibers as having diameters below 0.1 microns. Electrospun nanofibers can carry the spinning charge and Dr Tsai wanted to know what happened if electrically different polymers were spun, both separately and together. A variety of polar and non-polar polymers had therefore been spun and their charge-retention abilities had been monitored to see if useful electrets could be obtained.
No charge was retained on polar polymers but the non-polar materials had a potential of above 100volts for over 100 hours after production. Negatively charged polystyrene appeared best, retaining 250 volts for 250 hours.
The spread of fibers from the nozzle depended on fiber diameter, nylon (78nm) giving a 24” wide pattern while polyurethane (656nm) gave an 8” pattern. If 3 nozzles were used to spin the same polymer onto the same collector, the central web was narrowed by the repulsion of the outer webs, and the webs could not be made to overlap into a single sheet. If however alternate nozzles were oppositely charges the webs attracted one another and mingled, but tended to form ropes.
If 2 layers of oppositely charged polystyrene were spun on top of one another, the charges are not destroyed. Each surface maintains its own charge.

Patterned Electrospun Fiber Structures

Phil Gibson of the US Army Natick Soldier Center was hoping to develop electrospinning to produce fabrics and filters to protect against chemical and biological warfare agents. He pointed out that electrospinning was really very simple technology and illustrated a hand-held device powered by 2x9volt batteries which could spray fibers. He envisaged such devices being used to overspray battledress garments to protect against spores and contaminated micro-dust when required. The fibers would have to be very elastic (nylon was too brittle!) and polyurethane appeared to be favoured. Enzymes could be added to the polymer to give them a specific reactivity.
If the PU was sprayed onto a woven wire, the fibers bond where they contact the wire and the resulting patterning provides a rip-stop effect which increases the tear resistance. Pore size was not affected.
A questioner thought that spraying onto a net would give a suitably reinforced structure. Dr Gibson agreed and said that this was still to be done. The net could be a nonconductive polymer, because it could be wetted to provide temporary conductivity.
Why not use polyurethane membranes in battledress? Because nanofibers were much better for comfort. Their porosity allowed convective as well as diffusive heat and moisture transport.

Nanofiber sandwiches

Kristine Graham of Donaldson Co. Inc. said that nanofiber webs were impossible to handle and so had to be directly applied to the product. Donaldson already spray them directly onto commercial filter materials, and are now trying to attach them to wearable fabrics for the same reasons as Natick.
  • They target 98% retention of 2 micron particles but test according to ASTM 1215 with 0.8 micron particles. They have established that 80% retention of this size is equivalent to their target.
  • As a check on durability, this performance has to be maintained through 1500 Gelboflex cycles and a military laundry cycle.
  • They would also like to demonstrate a nanofibers ability to carry active chemicals.
When 0.25 micron fibers are sprayed directly onto a nylon shell fabric, the nanofiber layer tends to be punctured by any loose fiber ends. So Donaldson sprayed them onto 0.6 and 1.0 oz/yd 2 spunbond. To protect this layer, a top layer of similar spunbond was added to create a nanofiber sandwich. However better results were obtained by laminating two of the nanofiber-coated spunbonds together – nanofibers inside.
They now tried to attach this laminate to a shell fabric carrying activated carbon. Here beetter results were obtained if the two nanofiber layers were not bonded together, but allowed to float freely.
Washing showed up a fundamental problem. The nanofibers filtered out the detergent particles and after washing the fibers were therefore more contaminated than before. The filter proved too good to clean, but this did demonstrate the potential for attaching particles to the surface of the nanofibers
To demonstrate active chemistry potential, polyoxymettalate, a mustard gas adsorbent was added to a solution of thermoplastic polyurethane. This worked, and in fact there was evidence that the nanofiber enhanced the chemicals reactivity rather than diminishing it, as expected.
Asked how “heavy” the nanofiber coats were, Ms Graham said they don’t try to measure this. It would certainly be less than 0.1lb/ft 2. Could the detergent carrying effect be used to carry other useful chemicals. Yes.

Stretching Nanofibers

Kevin Kit of the University of Tennesse, working with nylon 6,6 in a Dupont-funded project, was trying to align nanofibers to allow some drawing-down and to understand their properties.
He was spinning the fibers onto the sharp edge of a rapidly rotating meat-slicer to obtain aligned-bundles of nanofibers to be removed and tested.
The meat slicer had a critical rotational speed defined as the polymer extrusion velocity, and when running faster than this it stretched the emerging fibers. The nylon fibers were spun from a 10% solution in formic acid under 15 or 30Kv applied charge onto the blade of the slicer positioned 10 cm away. This gave 0.3micron fibers at a 0.8gms/day production rate.
Samples were collected by spinning for 8 hours at 5 speeds, from the critical speed (233m/min) up to 2833 m/min. At the critical speed, orientation was measured at 0.5 (i.e. none) and at the highest speed 0.86 (high). Molecular orientation went from 0.1 to 0.3 and crystalline orientation remained constant at 0.3. With high voltage extrusion mechanical properties increased only at the highest speeds, peaking at 120mPa for a 10% strain.
At 15kV the extrusion speed is lower so more orientation results and the strength increases more progressively over the collection speed range.

Quality Control in Nanofiber Production

Dmitry Luzhansky of Donaldson Co Inc. thought fibers needed to be less than 0.25 microns in diameter to earn the nanofiber title. Donaldson make 10,000m 2/day of nanofiber webs on the surface of filters e.g the self-cleaning air-filter of the Abrams M1A1 battletank used in Iraq, and the combustion gas filters on gas-turbine engines.
Their quality control testing involves:
  • For Uniformity/Efficiency:
Continuous on-line non-contact monitoring of aerosol filtration efficiency uses laser particle counters upstream and downstream of the web. Measurements are taken at 5 positions across the web and the results are computer-analysed and printed out within 1 second of measurement. This is adequate for up to 200 m/min line speed.
  • Fiber size: SEM photograph and image analysis every 5 seconds.
  • “Environmental factors”: samples are challenged with the heat, oil or solvents they are likely to experience in use and their efficiency is measured before and after the challenge.
  • Bending test:the composite is bent under a microscope and the angle where the nanofiber layer begins to break is noted.
What level of efficiency is targeted? 98% removal of 0.8 micron particles.

Disc-electrodes for controlling nanofibers

Samira Farboodmanesh of Lowell University described how adding a disc-shaped electrode to the nozzle could change the pattern of fibers on the collector. She had electrospun a 10% solution of polyethylene oxide in ethanol from a normal “needle” nozzle and from the same nozzle through a hole in various charged metal discs. Without the disc, a 20 cm spread of web was observed on the collector. With a 10 cm disc at the same voltage as the nozzle, the spread dropped to 10 cm and the diameter of the formed-fiber decreased. She did not know why the diameter decreased, but a member of the audience later suggested that it might be due to the increasing field strength created by the focussing effect of the disc.
If the charged disc is tilted at an angle to the needle-nozzle, it directs the web in that direction. If a charged plate is arranged parallel to the stream of fibers between nozzle and collector then the plate attracts or repels the fibers depending on charge.
The fibers can also be collected as a yarn in the gap between two charged needles. If one of these needles is rotated a small sample of twisted nanofiber yarn can be collected.

Small fibers – Big thinking

Kevin White of Physical Sciences Inc. is developing a process to reinforce the gossamer-thin films intended for NASA’s solar-sails. When you plan to use solar photons to push a spacecraft up to speeds approaching that of light itself, there is, to say the least, a great need to reduce the mass of the sail that does the pushing. NASA’s calculations show that a film has to be less than 15 micron thick to stand a chance of working, and at this thickness it is too fragile to be packed into and unpacked from the shuttle. Physical Sciences Inc is therefore trying to electrospin bands of nanofiber onto a 7.5 micron colorless polyimide film to reinforce it.
Their new (and subject to a patent application so it could not be shown) focussing system sprays on 1 metre lengths of a 2mm wide band of nanofibers, and this is repeated every half-metre. The total application is 0.2gms/metre and this increases the tear resistance of the film from 1gm to 28 gms.

Remediation of Electret Charge Decay

Peter Tsai of the University of Tennessee(TANDEC) reviewed the ways of creating charged webs under the headings:
  • Polarisation
  • Induction
  • Corona treatment
  • Tribo-electrification
  • Hydrocharging (tribo-electrification using water to create friction - USP 5,496,507)
The best approach, and so the one used at TANDEC was corona treatment, and this could increase the filtration efficiency of a 90gsm 2-micron meltblown from 77 to 99.995%. However the charge dissipated under ambient conditions and dissipated more rapidly as particles (NaCl or Oil) built on the surface, or as temperature increased. The dissipation rate on PP could be reduced by use of a novel – but unspecified – “charge additive”, while the oil-induced dissipation could be reduced by the use of a fluorocarbon treatment.
Oil particles increased the filter efficiency of uncharged PP or nylon meltblowns, but did not affect uncharged PU or glass media.

Melt-blown Nanofibers?

John Hagewood of Hills Inc defined nanofibers as fibers less than a micron in diameter and pointed out that the Hills Inc thin-plate technology used to spin islands-in-a-sea fibers could, after extraction of the sacrificial sea polymer, yield very fine fibers.
A melt-blowing head with 100 holes per inch making IIAS bico at low throughput yields a spread of fiber diameters with a modal diameter in the 0.7 to 0.9 micron range.
In response to a question Mr Hagewood said they were now developing a 200 hole/inch head to allow higher productivity.

Surface coating using Atmospheric Plasma

Rory Wolf of Enercon Industries Corporation explained how plasma enhanced chemical vapour deposition (PECVD) can now be used at atmospheric pressure to add high performance coatings to a variety of nonwovens, films and papers.
Successes claimed included:
  • Acetylene in the plasma carrier gas enabled aqueous-ink printing of the treated surface of a metallized LDPE film
  • The same treatment improved the water wettability of a clay-filled paper without affecting its breathability.
  • The same treatment improved the water drop spread time of a polyester fabric from >30 seconds to <1 second.
  • A substituted silane treatment applied a 0.07micron coating to a modified polystyrene film, thereby reducing its oxygen transmission rate from 7,238 to 387 mls/m 2/day.
  • “Cleaning the fiber structure” of a range of melt-blown air-filters to improve “filtration performance” by up to 10x without creating pinholes.

Wet-laid Feather Fiber

Dr Todd Bullions of Virginia Polytechnic Institute and State University was looking for ways of using the 2-4 billion lbs of feathers produced by the US poultry industry. The cleaned and short-cut feathers had insufficient cohesion to be wet-laid on there own so Kraft pulp and kenaf had been evaluated as carrier fibers to get the feathers into sheet-form where their low density and good insulation properties could be utilised. Pulp proved to be the best carrier, but a kenaf enthusiast in the audience felt that the kenaf used here may have been a bad sample. Dr Bullions was advised to try again with a new one.

A Burning Issue

Dr D V Parikh, of USDA’s Southern Regional Research Centre described laboratory experiments involving the carboxymethylation of woven cotton gauze followed by treatment with silver nitrate to create an antimicrobial burn dressing. The silver nitrate was shown to be effective against staph. aureus, klebsiella pneumoniae and aspergillus flavus. However, if the silver nitrate concentration rose above 0.5%, e.g. by drying out, the burn dressing could burn you, so it had to be wetted regularly.