Jeff Dugan of Fibre Innovation Technology Inc. on Bicomponent Fibres
Conventional splittable fibres are made from (say) 8 segments of nylon and 8 segments of PET in a "pie-wedge" or "Citrus" configuration. The two different polymers have a low affinity for each other and therefore split easily into microfibres when stressed. They are used for synthetic suedes and leathers, wipes and filters. Problems with this long-established variety included difficult (2 step) dyeing needed for the textile end-uses, a tendency for nylon to fade easily, and to offer inferior chemical stability for some filters or indeed, some wipes.
To solve these problems, FIT were investigating fibre
shape effects and different
polymers. Round fibres with their mimimum surface/volume ratio had
the least appropriate shape for splitting and this placed greater demands on
using very different polymers in alternating segments.
- Flat fibres made up of alternating polymers across the width were the easiest to split.
- Y-shaped fibres with limb-tips made from different polymer from the core were easily cardable, harder to split, but much better than round fibre.
- The segmented X-shape was a good compromise between flat and Y. (but in questions he admitted this was theory: the fibre had not been made.)
- Tubular round fibres with a citrus configuration were more splittable than a solid round fibre.
With shape adjusted to reduce the demands on polymer
incompatibility, one could contemplate the ideal all
polyester or all polyolefin splittables.
- For a start, the problems caused by nylon could be minimised simply by minimising the nylon fraction in a round citrus fibre. Nylon could be used to do no more than isolate the polyester segments from one another.
- Using the renewable, crop-based Poly-lactic acid polyester (PLA) instead of nylon gave a surprisingly good all-polyester citrus fibre. The aliphatic PLA with its helical crystal structure has a very different surface energy to the aromatic, linear crystallised PET, and splits from it easily. Here the PLA gave other advantages related to its inherent absorbency, dyeability and comfort, all this without significant loss of strength, resilience or economy c.f. nylon.
- Poly-methyl pentene (PMP) is a true polyolefin with chemical properties between PP and PE but melting at 240 oC. It splits from PP readily and makes a technically superior all-polyolefin citrus fibre. It's high cost (~$4/lb) is a problem which can be minimised by using it as no more than a coating on the PP segments.
A PP/poly acrylonitrile (PAN) splittable
fibre looks both practicable and surprisingly advantageous:
- BP's "Amlon" thermoplastic acrylic is cheaper than PMP and gives an excellent splittablity/chemical stability balance with PP.
- PP and PAN are at opposite ends of the triboelectric series and develop opposite charges in needling. This give a more permanent electret effect than is possible with just PP where the opposite charges are on opposite sides of the same fibre.
Micro-Binder fibres can be
made by having polymers with widely differing melt temperature:
- PET/PE citrus fibres can be split in hydroentanglement and thermally bonded. The PE micro-fibres, intimately dispersed among the non-bonding PET fibres give many small areas of bonding and a nonwoven with an unusually good strength/softness balance.
- PMP/PP citrus fibres would have thermal bondability with even better chemical resistance.
Elastomeric Splittable Fibres
arise from segmenting PP or nylon and a thermoplastic polyurethane:
- These had excellent chemical resistance and could be split using heat alone.
- Because the spinning process orients and crystallises the PP and not the PU, the heating causes bulking and yields a self-bulking yarn for textile uses. However in staple form, the PU makes them hard to card.
- If a Y-shaped fibre with a PU centre and nylon tips is made, carding is straightforward, and the fibre still splits spontaneously to give a high bulk nonwoven on heating.
Wet-laying splittable fibres
is of course possible, but the dramatic increase in length/diameter ratio as the
fibres split means that they have to be cut very short.
This FIT paper dealt only with re-engineering the
pie-wedge or citrus section fibres. Similar thinking is already being applied to
concentric and sea-island bicomponents.
Prof. Abhiraman of Georgia Tech on the Fundamentals of Polymer Extrusion
If you spin and anneal fast enough in a spun-bond or
melt-blown process, even the unstretched fibres will crystallise to give strong
high-modulus products. For instance the normally amorphous random copolymer of
PET and polyethylene isophthalate, when spun at 6000m/minute with rapid
annealing gives a highly birefringent crystalline fibre as evidenced by X-ray
crystallograhy. Also, melt blowing PP from dope at 240 oC, with high veolcity
air at 177 oC gives crystalline melt-blown microfibres. (This interesting
lecture was unavailable in hard-copy and accompanied by minimalist overheads
which the author had no intention of sharing with members of the audience.)
Professor Charles Beatty ( University of Florida ) on Polymeric Alloys
Insight into the growing possibility of making valuable
products from post-consumer plastic waste, (but not available in print.)
The very properties of incompatibility necessary in
splittable bicomponents prevented mixed polymers from being recycled into usable
fibres or sheets. The problem lay with the molten blend being a collection of
phase-separated domains with little interfacial adhesion. The solution was to
reduce the size of these domains by more vigorus mixing and to increase the
interfacial adhesion by grafting on reactive groups to bond the dissimilar
polymers together. This was now being in a twin-screw extruder-reactor where the
molten polymers were mixed and injected with the chemicals needed to achieve
in-situ grafting. Maleic anhydride for condensation coupling or free-radical
precursors were used to attach graft-compatible side groups to each polymer.
These then reacted together in the extruder.
- Trials with this equipment had successfully made PVC/PP, PVC/PE and PP/PE alloys extrudable as interconnected phases rather than as discreet domains.
- The approach could also be used to form a PVC skin on PP. At 20% PVC or more in the blend, PVC accumulates at the surface of the PP due to the "surface excess" phenomena, and is firmly attached by the grafting. Could this be a way to make bicomponents with better dyeing and FR properties?
- The reactive extrusion of the PP/PE mixture gave an almost ten-fold improvement in impact strength compared with normal extrusion of the same mixture.
- SEM's showed a polystyrene/HDPE/polymethyl methacrylate mixture where the interface between domains appeared to contain micro-fibre bonds between the dissimilar polymers.
- Polyester/PP alloys with useful mechanical properties heralded the recycling of the ubiquitous polyester pile, polypropylene backed carpet.
Dale Gregory (Consultant) on 30 years experience in Improving Melt-Spun Fibres.
He had just retired from Eastman. His rather theoretical
paper led to the conclusion that further PET fibre improvements will result from
the quest for ever greater uniformity of orientation per filament and the
resulting denier per filament. This could be attained by reductions in
variability of melt viscosity, temperature and dwell time within the spin-pack.
Outside the spin-pack, along-the-filament variations could be reduced by
developing less variable quenching systems.
Dennis Tavernetti (BBA). Keynote Address:"Failure: The Mother of Invention"
He sought to demonstrate that failure, as part of a
systematic "trial and error" development process, is essential to progress. With
the nonwovens industry in a period of consolidation, with supply exceeding
demand, with selling prices and margins falling, it was natural to move to
reduce costs. However if investment and R&D were cut, the nonwovens industry
would fall into the same trap as the US textile industry.
The correct response was to try to add more value
through invention, and to make sure that the inventions provided real
tangible benefits without adding more cost than value. The
perceived value much loved by "Marketing" led at best to too many
"inventions", and hence high patenting and marketing costs for products which
would only ever have a short life-cycle before the consumer realised they
offered little real value. Edison did not develop electric lighting without
numerous failures.
It was important to recognise a failure, to stop wasting
time and money pushing ahead on products with dubious tangible benefits and to
redirect the limited development resources to more fruitful areas.
Panel Discussion
Dennis also presented a review of the US nonwoven scene
for the introduction to the panel discussion:
- The only growth in North America diaper sales was in Mexico (13% p.a.).
- Nonwoven use per diaper had increased due to core-wrap, acquisition and distribution layers, and cloth-like backsheet developments.
- However while demand for these coverstock-type fabrics was running at 200,000 tonnes/year, the supply was 270,000 tonnes/year.
- Card/latex was massively oversubscribed in 1998 despite its resurgence in acquisition layers.
- Card/thermal was 30% oversubscribed but had special properties (more textile-like than spunbond) and was expected to be back in balance by 2003.
Frank Harris, CEO of Fibre Innovation Technology gave his view of the next 5 years.
- He saw further industry consolidation but expected an upsurge of new small companies making unique high-value products.
- Textile replacement would gather pace, with home furnishings and automotive textiles being vulnerable to hydroentangled nonwovens.
- Alliances between nonwoven and textile companies could be expected as the textile industry registered the new opportunities for nonwovens.
- Environmentally driven products and processes would gain ground, but global competition would prevent any significant increases in raw material prices.
- In the fibre industry he saw increasing demands for bicomponent fibres (F.I.T.'s speciality) and not just for thermal bonding.
- He was expecting 10-15% p.a. growth for these fibres mainly in the personal care market and in automotive products.
- Perhaps surprisingly, he saw the emergence of 2 major new fibre types, both polyesters: PTT (poly-trimethylene terephthalate) and crop-based PLA (Poly Lactic Acid). Both would gain ground in conventional textiles before becoming available in nonwovens.
- Short-cut fibres for airlaying (3-4mm) would grow at 15-20% over the 5 year period.
- Spunbonded nonwovens based on the newer fine denier, bicomponent, multibeam technologies would grow.
- Splittable fibres would be used in needling to make new home-furnishing and automotive "textiles".
Lee Sullivan of Freudenberg-Spunweb
expected to see 30,000 tonnes of lightweight PET
spunbonds produced in the USA in 2000, and a further 4000 tonnes to be imported.
Overcapacity was evident in PP spunbonds, and while PET was broadly in balance,
the two new announcements amounting to an extra 6000-8000 tpa capacity would
create an imbalance. Heavyweight PET spunbonds, especially in the roofing
sector, were facing strong competition from needlefelts and it was in this
market that overcapacity was most evident.
Tom West of Dupont Nonwovens
pointed out that sustained growth over many years only
arises from constant re-invention of the company. Dupont had been an explosives
company in the 19 th C., a chemicals and energy company in the 20 th and was
expected to become a Chemistry, Biology and "Knowledge intensive solutions"
company in the 21 st C. Furthermore while the 20 th C. had relied heavily on raw
materials from oil, next century would see a switch into raw materials from
agricultural crops (PLA again).
Like Dennis he was concerned that the US nonwovens
industry was not reinvesting enough in new technology and R&D to stand up to
the global competition now emerging. Like Frank, he saw growth opportunities in
textile replacement and felt elastic nonwovens could hold the key to faster
progress. (N.B. Dupont's "Xymid": Lycra overstitching of a spunlaced nonwoven.)
- How much is Dupont investing in R&D?
A. 5-6% of sales overall and up to 10% in new technology
areas.
Q. Why was crop-based polylactic acid figuring
relatively strongly in these forecasts?
A. The panel listed:
- It has a cost-point between nylon and polyester.
- It has a very cotton-like handle.
- It is easily dyeable, and has excellent UV stability
- It is from a renewable resource.
- It is inherently absorbent and comfortable next to the skin.
- Dow-Cargill are contemplating a several hundred million pound per year plant.
- At 300million lbs/year capacity, the costs will be below $2/lb.
- How big a role would crop-based polymers play in the Dupont of ten years hence?
A. We already have a pilot plant.
Q. Why the investments in China?
A. Not for short-term profit. China might just become
the world's largest nonwoven market and being in at the start was good strategy.
Michael Tierney of Morgan, Lewis & Bockius: "Protect yourself!"
US patent law sets certain requirements for the
patentability of an invention and the information needed for a patent
application. Familiarity with these requirements is important to avoid "patent
pitfalls" and to provide sound patent protection for strategic research and
development. This presentation gave an overview of the property rights provided
by a patent, discussed the standard for patentabililty, and provided various
strategies for obtaining commercially effective patents.
"Measuring and Predicting Planar Absorbency Rates", by Bernie Miller of TRI
In Bernie's eyes, Washburn had earned his fame by simply
substituting La Place's equation into Poisseules equation. Bernie used the
equation, suitably corrected for the effects of gravity, to show that whenever
porous structures start to wick fluid, those with the larger pores will
always outperform those with the smaller pores. However, past a certain wicking
height and time, the smaller pore structures overtake and continue to absorb
faster and further than the larger pore structures. So, conclusions drawn from
wicking tests over say 2 minutes could be the opposite of those from tests
conducted over an hour.
Ram Shet of Technology Forecast Int. ( Neenah ) on the importance of proteins in Femcare:
Both soluble proteins and glycoproteins have a negative
impact on the performance of feminine hygiene products. Utilizing the knowledge
of protein-polymer interaction in biomedical products, a large increase in
absorbency can be achieved by engineering the molecular architecture of
superabsorbents in feminine hygiene pads
- Real urine contains enzymes which breakdown CMC superabsorbents so that even products with good retention under pressure with saline are degraded by urine.
- Real Menses contain proteins which spontaneously absorb onto any hydrophobic surface. It sticks due to charge, polarity, and increasing hydrophobicity as the protein unfolds.
- Hard proteins (lysoyme, ribonuclease) absorb under all conditions onto hydrophobic surfaces, but onto hydrophilics if electrostatically attracted.
- They can be displaced by soft proteins (myoglobin, albumin) which have lower structural stability and unfold much more readily. They absorb despite some hydrophilic dehydration and electrostatic replusion.
- Whenever blood contacts a foreign material, it coats it with plasma proteins which then dominate all subsequent absorbtion.
- Experiments studying the interaction of amphoteric polyamide membranes (made from 19.8 micron particles) with Bovine Serum Albumin (BSA) were described
- The membranes were treated with 0.1 Molar NaOH for times ranging from 5 to 30 minutes to give samples with differing carboxyl levels.
- Absorbtion of BSA onto the membranes is reduced by the increasing negative charge due to carboxyls.
- Absorbency of menses on cross-linked polyacrylic acid polymers can be improved by the use of surfactants, amido compounds, organic and inorganic salts.
- If SAP's are neutralised with K + rather than Na + and to a lower degree of neutralisation, blood absorbency is substantially increased. (The opposite is true of saline absorbency)
- K + neutralised SAP's give dramatic increases in free swell at 5 minutes immersion but slightly less free swell at 30 mins (c.f. Na +)
- K + SAP's from the relatively hydrophobic methacrylic acid monomer absorb blood faster (twice the volume in 5 mins) and have only slightly lower free swell at 60 mins (c.f. K + polyacrylic acid SAP's)
- Kimberly Clark's US Patents 5,241,009 and 5,346,485 (1993-4) were referenced.
Amy Morgan of Fibervisions on Visualising Fibre Finish:
Finish distribution is a key parameter in the
absorbency, processability and uniformity of roll goods.
- Finishes are applied to lubricate, to control fibre-to-metal and fibre-to-fibre friction and to allow liquid management.
- Finish is applied to PP before and after crimping, the latter to make up for losses caused by heat and steam in crimping.
- Finish uniformity has proved very hard to quantify with none of the following methods being satisfactory:
- Web uniformity measurement on the assumption that more even webs result from more even finish. (effected by many factors other than finish)
- Dynamic absorbtion testing. (multiple water drop test on webs: not good for fast absorbing fibres.)
- Tow wicking rate and pattern. (Not good for absorbent fibres)
- Single filament wicking - contact angle measurement. (too small a sample)
- Friction testing on a running tow. (factors other than finish can effect it)
- Optical microscopy to see the finish globules. (Better for hydrophobics than hydrophilics)
- Microfluorimetry, but the need to add fluorescent tracers to the finish is often impractical on production machines.
- Conventional SEM: sample preparation and high voltages can remove finish globules.
- Replica SEM: taking a silicone cast of the fibre surface. (Too fiddly and can remove finish also.)
- Environmental SEM: too expensive.
The proposed solution was not totally convincing but the
pictures from the technique were excellent.
She had used a "state of the art" R.J.Lee PSM-300 which
is much cheaper than environmental SEM, uses low accelerating voltage, and does
not need the sample to be in high vacuum. After easy sample preparation, the
finish droplets are clearly visible. Samples taken through processing show the
finish being smeared out over the fibre.
In response to questions, she confirmed positive
identification of the finish droplets using elemental X-ray spectra on the drops
as seen, and that she had done no work on cellulosics.
Airlaid Composites and Superabsorbent Polymers: by Edgar Herrmann, Stockhausen.
Absorbent polymers are one key component in absorbent
airlaid cores. By varying SAP types in "modular based constructions", the
targeted end-use products can be simply achieved through a combination of
different prefabricated constituents. These experiments with their SXM4750 and
SXM9100 SAP's in 32 different three-layer composites furnished predictable
overall conclusions:
- The more permeable SAP gave the fastest acquisition and transport.
- Diaper rewet is better for the most retentive SAP.
- Densification of air-laid pulp/SAP composites slows their acquisition rate.
- Densification improves rewet.
Conclusions regarding the layer combinations and
mixtures of SAP were less easy to draw, but were said to demonstrate ways of
solving individual design problems.
Dr Thomas Fechter of Fleissner on High Pressure Spunlacing
The application of high-pressure hydroentangling systems
has opened up new possibilities for product optimization and development.
- He showed photo's of two of Fleissers installations:
- A 1.8 metre 5 step (4 drums and a belt) machine with 7 injectors to make 600gsm fabrics.
- A 2.5 metre 3 step (2 drums and a belt) machine with 7 injectors for lightweights.
- The water system is cleaned by froth floatation followed by self cleaning sand filters. The sand filters are static-bed unlike (he said) the more fluidised system which Perfojet found leaked fine sand and eroded jet strips at an alarming rate.
- The froth floatation unit was said to remove fibre finish from the water system as well as fibre debris.
- They need to use antifoams to prevent foam from some finishes disrupting the sand filters.
- They use one piston pump per injector.
- They reduce the hole size to 0.1mm for heavyweights (>200gsm) to avoid flooding.
- Graphs of strength v speed showed strength reductions in the 100 to 200m/min range which could be corrected by pressure increases. (Below 100 m/min, speed and strength were unrelated.)
- On heavyweights, an energy input of 200 KW/metre is regarded as the economic limit for HE. Above this, the economics favour needlepunching.
- The key area for development was nozzle design and perfecting the hole profile to get longer coherent columns of water. (no fanning out)
- They are working with water additives to improve entanglement efficiency. (Viscosifiers??)
- They predict being able to install a 5.5metre wide line working at 600 m/min and 600 bar for spunbond. (n.b. This would make spunbonds much more textile-like and could be regarded as the two-dimensional analogue of yarn texturising.)
- He commented that jet life on viscose was 6 months compared to 1 year on polyester. This was due to 1 micron particles coming off the viscose. Questioning him afterwards revealed that he was unaware of the difference between matt and bright and didn't know which lustre had been used. (The particles were most likely titania from matt viscose being damaged by too high a pressure)
Steve Russell of Leeds Univ. on Structurally-Engineered Air Laid Webs
They had used a high speed camera to observe fibre
motion in the 20-year old Kroyer machine donated by BFF. The only interesting
observation was that as the web thickness increased, an increasing number of
fibres tended to stick vertically in those already laid down. The fact that he
had used straight rather than crimped fibres made the observations less
valuable.
Advanced Airlaid Composites Based on Superabsorbent Fibers by Ian Cheyne of Camelot.
He showed how product and process simplification coupled
with "a superior absorbent fibre" (Fiberdri™) can yield lower cost, more
absorbent and more flexible feminine hygiene products. The 3-layer Fiberdri™ pad
was compared with 3 commercial pads for cost, acquisition time, capacity,
retention, spreading and rewet using saline, synthetic menstrual fluid and
bovine blood:
- The air-laid composite with fibrous SAP had a materials cost no more than the lowest cost commercial product of comparable performance. (he said)
- Potential for lower capital and operating costs had been demonstrated.
- Potential existed for distribution cost savings. (30% thinner product)
- Despite lighter weight, the fibrous composite was ranked first for absorbency
- The fibrous product was more fabric-like in texture than the competitors.
- SA Fibres give more uniform air-laying than powders, with less dusting, migration and fallout, better performance on compression and better wet integrity.
Karla Garner of Kosa on Bicomponent PET for airlaying:
They had studied the effects of fibre denier (3, 15 and
32), shape (round, trilobal, pentalobal and High Void), and concentration
(12-52%) on the tensiles, bulk and compression resistance of air-laid pulp webs.
6mm fibres with 8-10 crimps/inch had been used throughout.
- 12% PET doubles the total capacity, doubles the web thickness and nearly doubles the wicking height.
- 15 dpf appeared to be the optimum denier.
- Wicking improves with shape:
round
- Absorbency decreases with PET contents above 12%.
- The more PET fibres (numerically) the weaker the web. (32 denier had least effect at any given concentration.)
Henning Skov-Jensen on the prospects for an Air-Lay Super-Site:
He defined a super-site as a single plant air-laying
100,000 tonnes per year and festooning the output to feed on-site diaper
production. The air layer would have a calender to densify the output to 0.4
gms/cc and bond it. He thought it possible that the super site could even be
built at a pulp-mill to achieve further integration.
The paper was notable for it's comprehensive breakdown
of the manufacturing costs of the super-site revealing the M&J machine would
cost $58M. 6000 tonnes of short-cut bico. reinforcing fibre would be needed at
an assumed price of $2/kg. The pulp would cost 55c/kg and the superabsorbent
(45,000 tonnes/year) would cost $2/kg.
The Regulation of Anti-microbials in Europe by Mike Baldry of MGCB Associates
He reviewed the changes to be expected when the
harmonised system replaces a plethora of national regulations.
The new Biocidal Products Directive (BPD), published on
April 24 th 1998 is now in force and has to be adopted into the laws of European
states by May 13 th 2000. It introduces a 2-layer approval system based on risk
assessment for the many active substances and biocidal products which are
outside the regulations for chemicals, human and veterinary medicines, medical
devices, cosmetics, food, food-contacting materials and plant protection
products.
There are many uncertainties for manufacturers and
users, however:
- Biocides used simply to protect a product from
microbial attack will be exempt.
Biocides intended to sanitise surfaces will need BPD approval. - The BPD will reduce incentives to research new biocides and their uses.
- There will be higher costs for data generation, fees and manpower to comply with the directive.
- There will be higher barriers to entering or remaining in the anti-microbials business in Europe.
- The Biocides business is likely to become concentrated among the larger companies.
- Biocides businesses will be similar to agro-chemicals and pesticides businesses.
- Results from risk assessments under the BPD could affect similar products in other regions of the world.
- The BPD will represent a much higher hurdle to obtaining regulatory approval than FDA/EPA.
- The BPD could prove to be a deterrent to imports, and for those products with approval, an incentive to export into regions with lower regulatory barriers. (e.g. Approval in the USA would be cheaper to obtain for BPD approved products)
Roy Broughton of Auburn University on Textiles with Antimicrobial Functionality.
He concluded that the ideal textile anti-microbial - one
which kills all microbes which come into contact with it, while being non-toxic
to higher life forms and not persistent in the textile-waste environment, does
not exist. Developing the ideal is getting increasingly costly thanks to ever
tightening regulations.
- Triclosan, is now widely used in fibres from Hoechst Celanese (acetate), Synthetic Industries (olefin) and Sterling Fibres (acrylic), but is now thought to be resulting in triclosan-resistant bacteria.
- Biguanides from Zeneca were reported
to be available in cellulosic fibres from Acordis® (sic)
With regard to whether the biocide should be spun-in fibres or added topically to fabrics he commented that it depended on the rate of leaching in the application. (Fast leachers better within the fibre, slow leachers better applied topically)
Saul Schapiro of Textile Biocides Inc. on Dealing with Current EPA regulations.
You can apply for registration by the EPA, but:
- It will take at least 9 months.
- The EPA has no protocol for the registration of treated textiles.
- Much expense, patience and persistence needed to succeed.
- Have to demonstrate that your product is effective at the 99.9% kill standard. However he commented that this could be relaxed in the interests of assisting the control of current "problem" organisms such as E.Coli, Staph., and Strep., for instance, on cutting boards.
- AATCC method 100 proves acceptable to the EPA, method 147 does not.
- Test data has to be from a GLP certified laboratory.
- There have not been many successful registrations due to the instability of the EPA positions.
You can apply for exemption from the regulations if:
- The biocide is only to protect the product and,
- If you imply no benefits to the user.
This exemption route could be a good start, allowing you
to market the product while persisting with full registration or "waiting for
the law to change!". (A four-page document clarifying the "Treated Articles
Exemption" is available appended to the paper.) With regard to terminology,
"Antibacterial" is no-longer allowed in a non-public health context, an while
"Antimicrobial" is OK, it must be qualified by a statement of what it is active
against. For example the FTC are currently "going after" Vaseline Intensive Care
Antibacterial Hand Lotion. "Unqualified anti-microbial/bacterial claims will not
be tolerated".
Confusion regarding the jurisdiction of the FDA and the
EPA is now being sorted out:
- EPA are dealing with cutting-boards, toothbrushes etc.
- FDA are dealing with mattress covers in hospitals (but not domestic?)
Processing and Property Studies of Cotton-surfaced nonwovens by Christine Sun of Tandec
She described a Cotton Inc. sponsored project on
stretching spunbonds to which PP/cotton blend webs had been thermally bonded.
The bonded webs had been stretched to 1.4, 1.5 and 1.7 times their original
length, the most notable effect being an almost proportionate increase
in thickness and basis weight.
In response to questions she admitted that they had been
allowed to shrink in the CD. The other conclusions were therefore less valuable.
"Carding of Microfibres" by Abdelfattah Seyman of NCSU
presented data on processing Wellman's 0.9 dtex
polyester on a conventional flat-top card.
The neatly designed and statistically analysed
experiments showed that nep and broken fibre levels in card-web could be reduced
to acceptable levels by increasing drafting, minimising the fibre recycling (by
reducing the doffer/cylinder setting) reducing the feed-roll speed (i.e.
throughput), and reducing the fibre length (38 to 30mm). Unfortunately, web
uniformity tended to deteriorate, and the only suggestions for improving this
were to use a highly opened fibre, and to pay more attention to feed-lap
uniformity.
An old textile hand in the audience commented that he
used to process 9-10 micron cotton into 120's CC yarns, but only on cards with
flexible wire clothing. Clearly many more carding points than were available on
modern metallic wire (saw-tooth) clothing were necessary for microfibres.
Thermal Bonding Session
This ran concurrently with the air-laid nonwoven session
and was not attended. The papers were as follows:
Doing It With Hot Air by Don B. Gillespie, Fleissner, Inc.
Although bonding is not the only influencing factor in
creating a nonwoven product, it is the key element providing strength and
performance to a nonwoven. Compared to other bonding processes, thermal bonding
provides manufacturers with numerous benefits ranging from economic efficiency
to uniformity. (paper absent from the proceedings)
Continuous Ultrasonic Bonding by Frank Simonetti, Herrmann Ultrasonics
The latest technology of continuous high speed
ultrasonic welding for nonwovens. This session covered the facts and fictions of
ultrasonic bonding and its relationship to other thermal bonding processes.
Heat Generation During Ultrasonic Bonding by Z. Mao & B.C. Goswami, Clemson University
A method for the prediction of heat generation during
ultrasonic bonding and its effects on fabric properties.
Nonwovens from Cotton/Cellulose Acetate Blends by Kermit E. Duckett, UTK.
Continued interest in biodegradable/compostable
nonwovens has led to the production and evaluation ofproducts containing cotton/
cellulose acetate fibers. By modifying the bonding process suitable fabrics can
be produced.
The printed paper indicates that acetone vapour
treatment, and aqueous acetone padding prior to calendering improve the strength
of the nonwoven, but not as much as triacetin.
CRW 30/9/99
