A Paper for Insight 2004 Austin, Texas, USA Oct. 10-14, 2004 Stretching the Value of Melt Blown with Cellulose Microfiber and Elastic Resins Rongguo Zhao Biax Fiberfilm Corporation, Greenville, Wisconsin Abstract The melt blowing (MB) process has been popular in making fine fibered articles, such as filter media, protective clothes, absorbent products and many others. Currently Polypropylene (PP) is the most used resin. The advantages of MB process attributes to its simplicity in converting a polymer resin to a variety of fibered products in a single step. The products of cellulosic microfiber and elastic resins will provide many additional values for special properties. This paper focuses on the process/property of products made from wood pulps and elastic resins. The potential applications of these products will also be discussed. Introduction Melt blowing (MB) process has been popular in making fine fibered articles, such as filter media, protective clothes, absorbent products and many others. Many thermoplastics can be used in a MB technology, although polypropylene (PP), polyethylene (PE), poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT), poly(cyclohexane dimethylene terephthalate) (PCT), co-polyesters and polyamides are among the preferred polymers. The MB technologies today can be roughly classified into 1
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A Paper for Insight 2004 Austin, Texas, USA
Oct. 10-14, 2004
Stretching the Value of Melt Blown with Cellulose Microfiber and Elastic Resins Rongguo Zhao
Biax Fiberfilm Corporation, Greenville, Wisconsin
AbstractThe melt blowing (MB) process has been popular in making fine fibered articles, such as
filter media, protective clothes, absorbent products and many others. Currently
Polypropylene (PP) is the most used resin. The advantages of MB process attributes to
its simplicity in converting a polymer resin to a variety of fibered products in a single
step. The products of cellulosic microfiber and elastic resins will provide many additional
values for special properties. This paper focuses on the process/property of products
made from wood pulps and elastic resins. The potential applications of these products
will also be discussed.
IntroductionMelt blowing (MB) process has been popular in making fine fibered articles, such
as filter media, protective clothes, absorbent products and many others. Many
thermoplastics can be used in a MB technology, although polypropylene (PP),
Extruder T zone 1 =165F; T zone 2 =198F; T zone 3 =230F; T clamp = 230F
Screen changer T Sc Ch = 230F
Metering Pump T pump =230F
Die block T melt =230F; P melt =650 psi; T air =250F; P air =14 psi
Water jet P=150psi
DCD 29 ~ 51 cm
Fiber size 4 ~ 25 m
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1 2 3 4
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1: extruder2: screen changer3: gear pump4: air manifold5: die block6: spinnerette7: air inlet8: coagulant inlet9: collector10: hydro-jets11: nip rollers
Figure 1. Experimental set-up for making microfiber cellulosic nonwovens
Figure 2 shows the effect of water spray on web structure. Since the attenuated
filaments (strands of cellulose-NMMO solution) are in a sticky state, without water spray
during MB, the filaments merge into one another at any contact points. Several fibers
may combine together to form big segments, as shown in Figure 2a. The resulting
products are stiff and brittle due to over bounding among fibers and incomplete
regeneration of the big fibers/segments.
Having water sprays in both sides of the MB filament stream at a proper location
of the spin line is proven essential for making valuable products. Spraying water on to
the web forming area on the collector surface helps the filaments to reduce bonding,
which results in softer products. Although the amount of combined big segments of
multiple fibers is reduced, the fused intersections remain, as shown in Figure 2b.
In a typical melt blown process, the fibers diameter reduces dramatically within
the first few centimeters from the spinnerette. It continues to decrease in the next few
centimeters with a much lower attenuation rate [1, 2]. The length of this attenuation
distance varies depending on the type of polymer, processing conditions, and
spinnerette settings [8]. Having this in mind, one will carefully apply water spray to a
location in the spin line where filament interactions are still not significant. At the
processing conditions listed in Table 1, the two-sided water spray is applied to the fiber
stream at 18 cm from the spinnerette. As shown in Figure 2c, the fibers are much
smaller and the merged segments of several fibers are considerably decreased.
Comparing Figure 2a, 2b, and 2c, one may reach a conclusion that water spray at a
proper location enhances fiber attenuation and prevents fibers from combining into big
fiber segments.
Figure 2d is a SEM microphotograph of cellulosic microfibers made from the
same equipment with coagulant jets instead of water spray. The coagulating jets have
the following major functions: (1) regenerating the cellulose from its NMMO solution into
Lyocell microfiber, (2) attenuating the filaments, and (3) entangling the microfibers to
form nonwoven web. These powerful jets minimize inter-fiber fusion and reduce the
formation of big fiber segments. The fiber size ranges from 4 m to 25 m with an
average of 14 m. The webs exhibit nice softness, good strength, and excellent
wetability.
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1.2.3 Potential ApplicationsThe cellulose microfiber nonwovens have the following unique properties, (1)
based-on renewable natural recourses, such as woods and some annual plants, (2)
biodegradable, (3) high temperature endurance, (4) excellent strength, (5) antistatic, and
(6) to be colored readily. They will find various applications in a broad spectrum. The
following are some examples of these potential applications
Baby diapers
Feminine hygiene napkins
Adult continental products
Bandages
Air filters
Liquid filters
Household wipers
Shop towels
Battery separators
Vacuum cleaner bags
Cosmic pads
Cabin Air Filtration in Cars and Planes
Food Packaging
Apparels
Disposable underwear
1.2.4 Future Research Plans
Based on our previous research, a new prototype spinnerette has been
designed. It will be fabricated and assembled with other processing components to
develop a complete MB pilot line. By using this pilot line, at least three wood pulps with
degrees of polymerization (DP) of 400~1000 and different solutions will be thoroughly
investigated.
Great efforts of the present project will focus on productivity and efficiency. The
other issues include interactions among air, filaments, and coagulation solution, and
their effects on the properties of fibers and the nonwoven web. Specifically, we will (1)
identify the operation windows for given solution compositions, (2) improve the melt
blowing process, (3) establish the processing/property relationships (4) identify key
issues requiring resolution during the technology commercialization.
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Figure 2 Cellulose MB microfibers
(a) Without water spray during MB; (b) Spray at the point of web-forming;
(c) Spray onto the spin line; (d) water-jetting during MB
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a b
c d
2. Microfiber nonwovens with elastic resinsAlthough thermally treated and stretched PP nonwoven web can achieve one
dimensional elasticity, nonwovens from a elastic resin are attracting more interests for a
variety of applications, including hygiene, medical, apparel, and personal care products.
Via a bicomponent spunbond technology, elastic nonwoven fabrics have been produced
with an extreme low sheath/core ratio [16]. The very thin sheath layer of non-elastomer
is activated during fiber attenuating process and form a corrugated fiber surface after lay
down, which is important to achieve the elasticity of the core. This thin layer of non-
elastomer covers the rubbery sheath to ensure a superior hand. Elastic MB nonwovens
are also under investigations by different researchers [17,18].
Thermoplastic polyurethane (TPU) elastomer is one of the popular resins to
make elastic fibers. Melt blown grade TPU is available in the market from a few
manufacturers. Other examples of resins available for MB process include polyether-
ester (PEE) elastomer, polyolefin elastomer and thermoplastic rubber.
Spinning these elastomers into fibers by a MB process is challenging in
comparison to PP melt blowing. Our experience taught us that drying is a critical step for
a successful TPU MB production. However, the selection of MB machine has a
significant impact on the web quality and their performances. Figure 3 shows the major
difference between a Biax design and a conventional design of MB technologies. Biax
MB technology features multiple rows of spinning nozzle with individual concentric air
jets to attenuate the fibers. It also tolerates high melt pressures at the spinnerette with a
wide operation window ranged from 300 PSI to 2000 PSI. A conventional MB technology
has a single row of spinning holes with impinging air streams from both sides of the die
tip to draw the fibers. The safe operation pressure of this process is about 300 PSI. This
will set the two technologies apart when trying to melt blow elastomers. Currently
available elastomers have melt flow rates mostly lower than 100 compared to common
MB grade resins that have melt flow rates higher than 300. In other words, one will
expect high melt pressure during melt blowing of these elastomers. Therefore, the
advantage of Biax MB technology is obvious over the other type.
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Figure 3, A comparison between two major MB technologies
The elasticity of the extruded filaments increases the filament turbulence during
MB process, which increases the tendency to produce merged fiber bundles. Figure 4
are the scanning electron microscopy images showing the PEE fiber bundles made from
a conventional MB process. Although fiber bundles or ropes are commonly observed for
MB PP and other semicrytalline polymers, under proper processing conditions, the fibers
are individual fibers in the bundles. In case of elastomer, fibers in a bundle are combined
and partially fused to each other, as shown in Figure 4b. As noted above, currently
available elastomers have relatively low melt flow rates. For a conventional MB line, high
temperature profiles are frequently used to reduce the high melt pressure at the die tip.
The heat from both melt and air keeps the attenuating and elastic filaments tacky for a
longer time, which causes a significant amount of fusion of entangled fibers.
With a Biax MB line, a lower temperature profile is normally employed and the
operation pressure at the spinnerette can be above 1500PSI. This allows the fiber
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surface cool enough before significant fiber entanglement occurs. The individual
concentric air jets apply friction forces on to filament surfaces parallel with the air
blowing direction, which permit filaments to travel longer distance without touching one
another. In addition, the spacing between Biax spinning nozzles is inherently bigger than
that in a conventional die. Therefore, the elastic web made from a Biax MB line exhibits
a structure similar to a normal PP MB web. The fused fiber bundles are significantly
reduced, as shown in Figure 5. This web structure allows the best fiber coverage,
enhances barrier properties, and ensures good elasticity in all directions, which are
critical for many end applications, such as protective apparel, medical and hygiene
products.
Conclusions:
With the increased environmental concerns on thermoplastic disposable
products, the nonwovens industry starts making efforts to develop fully biodegradable
products from biodegradable PLA, biodegradable polyester to biodegradable Lyocell.
Although Lyocell fibers are commercialized and the output increased lately, the cost of
this fiber is still too high for nonwoven disposable products. Making Lyocell nonwoven
roll goods from a one-step MB type process with high throughput and high efficiency will
open a door of hope for the industry to use this excellent fiber. Our R&D efforts in this
area are getting financial support from the Wisconsin Department of Commerce [19]. A
15-inch MB-type pilot line equipped with a multiple-row-spinning-hole spinnerette will be
built for extensive investigations focusing on operation windows,
process/structure/property relationships, and economic models of the process.
The nonwovens industry can also take good advantages of Biax MB technology
to produce elastic microfiber products. The concentric multiple-row-nozzle spinnerette
offers the industry high productivity, effectiveness, flexibility and energy saving. We have
made elastic microfiber webs from several elastomers, including TPU, PEE, EVA
polyolefin elastomer and thermoplastic rubber. Resulting products from a Biax MB line
showed superior web properties with higher productivity.
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Figure 4. Microphotograph of PEE fibers made from a conventional MB process
(a) fiber bundles, 200X; (b)cross-section of a fiber bundle, 700X
Figure 5. Microphotograph of elastic fibers made from a Biax MB process
(a) PEE elastomer, SEM, 500X, (b) Polyolefin elastomer, Optical, 100X
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b a
References:
1. Hong Yin, et. al. “Experimental study of melt blowing process”, International Nonwovens Journal, 8(1): 60 (1999)
2. Zhao, R. and Wadsworth, L. C. “Attenuating PP/PET Bicomponent Melt Blown Microfibers” Polymer Engineering and Science, 43(2), 463-469 (2003)
3. Shambaugh, R. L., “A macroscopic view of the melt blowing process for producing microfibers” Ind. Eng. Chem. Res. 27: 2363-2372 (1988)
4. Zhao R., Wadsworth, L. C., Zhang, D., and Sun, C. “Polymer Distribution during melt blowing PP/PET and its improvement”, J. of Applied Polym. Sci., 85 (14): 2885-2889 (2002)
5. Schwarz; E. C. A. "Apparatus and process for melt-blowing a fiber forming thermoplastic polymer and product produced thereby" US Patent 4,380,570 (04-19-1983)
6. Schwarz; E. C. A, “Apparatus and process for uniformly melt-blowing a fiber forming thermoplastic polymer in a spinnerette assembly of multiple rows of spinning orifices" US Patent 5,476,616 (12-19-1995)
7. Nonwovens Industry magazine Vol34, No.11, Page: 18.8. Zhao, R. “Melt blowing polyoxymethylene copolymer”, Book of Papers, TTSNA,
Atlanta, GA, March. 30-April 1, 2004 9. Zhao, R., Brown, D., Schwarz, C. A. E., Rong, H., Wadsworth, L. C., “Web
Structure/Performance/Property relationships of Melt Blown Microfiber Nonwovens”, Book of Papers, INTC 2002, Sept.24-26, Atlanta, GA, 2002
10. Zhao, R. “Bicomponent melt blown technologies today” Book of Papers, 13th TANDEC International Nonwovens Conference, Knoxville, TN, Nov. 2003
12. Woodings, C., “New Developments in biodegradable nonwovens” Http://www.technica.net/NF/NF3/biodegradable.htm
13. Petrovan, S., et. al., “Rheology of Cellulosic N-Methylmorpholine Oxide Monohydrate Solutions of Different Degrees of Polymerization”, Journal of Applied Polymer Science, 79:396-405 (2001)
14. Zhang Y., et. al. “Formation and Characterization of Cellulose membranes from N-methylmorpholine-N-oxide Solution”, Macromol. BioSci., 1(4): 141-148 (2001)
15. Liu, R., et. al. “The online Measurement of Lyocell fibers and Investigation of Elongational viscosity of Cellulose N-Methylmorpholine-N-oxide Monohydrate Solutions”, Macromol. Mater. Eng., 286(3): 179-186 (2001)
16. http://www.advenceddesignconcepts.com/brochure.pdf17. Wadsworth, L. C., “Melt Blown Thermoplastic Polyurethane for Elastic Military
Protective Chemical Liners”, Book of Papers, INTC 200218. Srinivas, S., “VISTAMAXX TM –Novel Polyolefin Specialty Elastomers from
ExxonMobil Chemical “ Book of Papers, ANTEC 2004, Chicago, IL, May, 200419. “Biax Fiberfilm advances MB cellulosic fabric manufacturing” Nonwovens Markets,