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The Fiber Society

New Frontiers in Fiber Science

Spring Meeting ­ May 23-25, 2001

Book of Abstracts ­ Posters and Presentations

Organized by: Nonwovens Cooperative Research Center

Part I

Image Studies in Electrospinning Process Han Xu, Darrell.H.Reneker Preparation of oriented nano- and mesotubes by electrospun template fibers (TUFT-process) H. Hou, M. Bognitzki, J. H. Wendorff, A. Greiner Electrospinning of Polycarbonates and their surface characteristics Changmo Sung, Heidi Gibson & Ravi Varma N.K Electrospun Fibrous Membranes of Photovoltaic and Conductive Polymers David Ziegler, Kris j. Senecal, Chris Drew, Lynne Samuelson Development of Electrospinning from Molten Polymers in Vacuum Ratthapol Rangkupan and Darrell H. Reneker Branched and Split Fiber from Electrospinning Process Sureeporn Koombhongse and Darrell H. Reneker

Part II Changes in Porosity and Transport Properties of Microporous Elastomeric Electrospun Nonwoven Membranes Under Biaxial Strain Conditions Phillip Gibson and Heidi Schreuder-Gibson Objective Evaluation of Hydroentangled Nonwoven Fabrics Omer B. Berkalp, Abdelfettah Seyam & Behnam Pourdeyhimi Fabrication of Electrospun and Encapsulation into Polymer Nanofibers Woraphon Kataphinan, Sally Dabney, Daniel Smith, and Darrell Reneker On the Measurement of Contact Angle of Droplets on Fibers E. Shim, M. Srinavassarao and B. Pourdeyhimi Prediction of Performance in Thermally Pointed Bonded Nonwovens H. S. Kim and B. Pourdeyhimi The Influence of Fiber Crimp and Process Variables on Needle Fabric Properties Vasantha M Datla, William Oxenham, Behnam Pourdeyhimi

Part III: Composites from Hydrontangled Webs N. Vaidya, B. Pourdeyhimi and M. Acar A Study of Spin Finish Application on Fibers E. Shim, M. Srinivasarao & B. Pourdeyhimi The Effect of Anisotropy on In-Plane Liquid Distribution in Nonwovens Amy Konopka and Behnam Pourdeyhimi Evaluation of Textile Structure of Arterial Endoprosthesis after Implantation in a Canine Model Ruwan Sumanasinghe, Johnathan Beaudoin, Martin King, Ze Zhang, Yves Marois, Yvan Douville and Robert Guidoin Reorganization of the Structures, Morphologies, and Conformations of Bulk Polymers via Coalescence from PolymerCyclodextrin Inclusion Compounds Min Wei and Alan E. Tonelli Atmospheric Pressure Helium Plasma Treatment of High Strength Polyethylene Fibers Qiu, Y., Zhang, C., Anantharamaiah, N., Xie, S., and Vaidya N. P. Evaluation of Meltblown Nonwoven Structures Yogeshwar Velu, Tushar Ghosh and Abdelfattah Seyam Contribution from the Fibrous Materials Research Center Department of Materials Engineering, Drexel University

Image Studies in Electrospinning Process

Han Xu, Darrell.H.Reneker Department of Polymer Science, The University of Akron, Akron, OH 44325-3909

Fibers with a diameter in the nanometer range to achieve larger surface volume ratio and uniform fiber diameter are in demand for different applications. Electrospinning is an effective method to produce microfibers and porous sheets. A series of efforts 1,2 has been made to understand the nature behind this process. The goal is to take a better control of the final product. Video images were used to study the elongational relaxation time, a key parameter in a comprehensive computer model1 of the electrospinning process. Analysis of the development of the "envelope cone" composed of a slowly developing jet was also described. Elongational Relaxation of Polymer Fluids A mechanical stretching apparatus for polymer fluids, simulating the stretching that occurs in the electrospinning process, was used to study the elongational relaxation of polymer fluids. The elongational relaxation time is a parameter in the computer model of the electrospinning process1, which can be described in the following way. A cylindrical column of fluid was created by lifting a flat-faced cylindrical tip, at a speed of 350mm/s for a distance of 21mm, out of a pool of fluid. The decrease of the column diameter as a function of time was observed with a high-speed camera. Poly(ethylene-oxide) with a molecular weight of 400,000 g/mole in a concentration range from 2% to 10% in water was studied. Surface tension and intermolecular forces dominate this thinning process. The inertial and gravity forces can be neglected. The relaxation times were calculated from the change of the diameter with time3,4. The relaxation times for the solutions were in the range of ten to a hundred milliseconds. The logarithm of these relaxation times decreases linearly with polymer concentration. Degradation of poly(ethylene-oxide) decreases the elongational relaxation time and results fibers with smaller diameters and a"beads on string" morphology. Envelope Cone Development --- A Slowly Developing Spinning Jet A solution of 1% poly(isobutylene) (MW: 2.4x106 g/mole) dissolved in a mixture of paraffin based mineral oil and acetone was electrospun. The path of the jet was a well-developed expanding spiral that moves with a downward speed of 0.2m/s and radical velocity of 0.1m/s, which are both five times slower than PEO/water system reported1. The vertical distance between the first and second fully developed coil are twice larger than that of the poly(ethylene oxide)/water system. First and second orders of bending instability were recorded at 30 frames per second. The growth of the bending instability clearly demonstrated its self-similar, fractal nature. The bending instability occurs through out a large range of time scales, from half of a second, when the first turn of the spiral develops, down to milliseconds, the time scale for the second or third orders of bending instability. The spiral character of the jet path shown in the images (Fig. 3) is also observed at a scale of 1mm in the jets on the grounded collector.

700

0. 14

Relaxation Time(s)

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0.1

y = 0.0051e0.3066x R2 = 0.9854

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10% 2%

0 50

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4%

100 150

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200 250

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300 350 400 450 500

y = 0.003x 1.4454 R2 = 0.8846

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t(ms)

Concentration(%)

(a) Fig. 1 PEO(MW: 400,000)/water solution with different concentrations, (a)The diameter decrease of the cylindrical column during stretching. (b)Elongational relaxation time measured by image studies.

(b)

Fig. 2 The development of first and second orders of bending instability observed in poly(isobutylene) (MW: 2.4x106 g/mole) / paraffin based mineral oil / acetone system. Time intervals between two neighbor frames are 0.1 second. ________________ 1. D. H. Reneker, A.L. Yarin, H. Fong, S. Koombhongse, J Appl. Phys. 87, 9 (2000). 2. A.L. Yarin, S. Koombhongse, D.H. Reneker, J. Appl. Phys. to be published. 3. M. Stelter, G. Brenn, A.L. Yarin et. al., J. Rheol. 44, 3 (2000). 4. Yarin, A.L., Free Liquid Jets and Films: Hydrodynamics and Rheology (Longman, Harlow, and Wiley, New York, 1993), 71-73. Harlow, and Wiley, New York, 1993 Back to Top

Preparation of oriented nano- and mesotubes by electrospun template fibers (TUFT-process)

H. Hou1, M. Bognitzki, J. H. Wendorff, A. Greiner Philipps-Universität Marburg, FB Chemie, Institut für Physikalische Chemie, Kernchemie und Makromolekulare Chemie, Hans-Meerwein-Str., D-35032 Marburg, Germany [email protected]

Nano- and mesotubes made of a variety of materials including polymers, metals, and composites were prepared by the so-called TUFT-process (tubes by fiber templates) (1). The concept of the TUFT-process is processing of degradable or extractable template fibers by electrospinning, to coat them by any material, and finally to develop tubular structures by selective removal of template fibers. Electrospinning of polymers yields dense nonoriented polymer webs. Consequently, tubes prepared from such webs by the TUFT process yields also nonoriented webs of tubes. However, for a variety of applications related to transport, separation, or optics oriented tubular structures are desired. Unfortunately, post-processing orientation of tubes prepared by the TUFT-process requires more prerequisites due to intertubular film formation upon coating by polymers. Therefore, the preparation of oriented structures has to be accomplished in the template fibers, which requires the preparation of webs of oriented template fibers by electrospinning or by postprocessing orientation. Well oriented electrospun fibers were obtained by usage of metal devices or by postprocessing orientation which will be presented in detail on the poster. Polymer or metal deposition on oriented electrospun fibers, for example based on poly-L-lactide or polyamide 66, resulted in oriented composite fibers which were converted into corresponding tubular fibers by removal of poly-L-lactide by extraction or thermal decomposition. 1) M. Bognitzki, H. Hou, M. Ishaque, T. Frese, M. Hellwig, C. Schwarte, A. Schaper, J. H. Wendorff, A. Greiner, Adv. Mater. 12, 637 (2000) Back to Top

1

Presenting author

Electrospinning of Polycarbonates and their surface characteristics

Changmo Sung, Heidi Gibson & Ravi Varma N.K Center for Advance Materials, UMass, Lowell, MA US Army labs, Natick, MA UMass, Lowell, MA

The aim of this study is to electrospin a BisPhenol-A based polycarbonate and to study the nature of the fiber surface. Preliminary results have indicated that the polycarbonate electrospun fibers have a "raisin like", wrinkled structure. The appearance of such a surface is very much related to the relative rates of to evaporation of the solvent from the surface of the polymer solution droplet and the rate of evaporation at the core. Rapid evaporation of the solvent on the outer surface of the polymer solution droplet could result in formation of a thin, dry polymer layer on the outside, while on the inside evaporation is incomplete. Thus the polymer sphere possesses a fixed surface area even before it has completely lost its solvent content. Further loss of the solvent from the inside of the sphere by diffusion into the ambience, causes the polymer sphere to `warp', thus forming the `raisin like structure'. The same effect is also believed to cause the cylindrical fibers to warp into almost flat bands. More work on this aspect is expected to reveal more answers. Back to Top

Electrospun Fibrous Membranes of Photovoltaic and Conductive Polymers

David Ziegler1, Kris j. Senecal1, Chris Drew2, Lynne Samuelson1 1 U.S. Army SBCCOM, Natick Soldier Center, Natick, MA 01760 2 Center for Advanced Materials, UMass Lowell, Lowell, MA 01854

The pace and development of electrospinning has been rapidly increasing in the past few years. One of the most interesting developments has been the development of a hybrid solar cell utilizing electrospun conductive polymers and "doped" with photovoltaic dyes and nano-crystalline semiconductor particles. The simplistic electrospinning technique yields a flexible photovoltaic membrane that has tremendous application potential. The photovoltaic membrane has been characterized using electron microscopy to image both the surface of the material (using scanning electron microscopy (SEM)) as well as the interior of the nanofibers using transmission electron microscopy (TEM). In conjunction with the electron microscopy, energy dispersive X-ray spectrometry (EDS) work was used to visually ascertain the location of the dyes in the polymer fibers by using X-ray mapping. Recent data from photoresponse testing show microamp and millivolt production levels from the electrospun photovoltaic solar cells and calculations have been made on the membrane growth rate and fiber-charge calculations. Figure 1 shows an ESEM photomicrograph of the copper phthalocyanine dyed electrospun polyacrylonitrile (PAN) fibers. Figure 2 is a TEM photomicrograph of the same sample and shows the nano-crystalline TiO2 semiconductor particles embedded within the fibers.

Figure 1: ESEM photo of copper phthalocyanine dyed electrospun PAN fibers.

Figure 2: TEM photo of the same copper phthalocyanine dyed PAN fibers clearly showing the embedded TiO2 nano-crystalline semiconductor particles. Back to Top

Development of Electrospinning from Molten Polymers in Vacuum

Ratthapol Rangkupan and Darrell H. Reneker Department of Polymer Science The University of Akron, Akron, OH 44325-3909, USA The electrospinning process utilizes the influence of an electric field on the behavior of polymeric fluids. For polymer solutions, when the electrical force overcomes surface tension, a charged jet is created. The jet typically develops a bending instability and then solidifies to form fibers, which are in the range of nanometers to around 1 micron (1). Most studies were done with polymer solutions. Larrondo and Manley (1981) studied the electrospinning process from polymer melts (2). In this study, pellets of polypropylene, polyethylene, poly (ethylene terephthalate) (PET) or poly (ethylene naphthalate) (PEN) were held either in a copper cup or a flat copper sheet and then melted in a vacuum with a radiant heat source. Charges were supplied by a metal wire connected to the cup. A collector plate made of an aluminum sheet was placed 5-15 cm away from the cup and maintained at an attractive electrical potential. The electric field strength between the cup and the collector sheet was varied from 0-10 kV/cm. A video camera was used to observe the spinning process. The morphology of the fibers was examined with an optical microscope and a scanning electron microscope (SEM). The vacuum process was used because the magnitude of the electric field in a vacuum is not limited by the low dielectric breakdown strength of air (3). This enables us to obtain high electric field strength over large distances. When the electric field strength reached about 3-4 kV/cm a droplet of molten polymer was pulled out, trailed by a jet that became thin and soon broke. When the electric field strength was increased, a steady charged jet flowed toward the collecting plate. Higher electric field strength produced a bending instability. At very high electric field strength, multiple jets were created. These jets also showed the bending instability. Jets solidified either in flight or after reaching the collector. The diameters of the fibers produced ranged from 300 nanometers to 10 microns. A variety of fiber morphologies were observed, including flat fibers, coiled fibers, bent fibers, sinusoidal fibers and helical fibers. SEM images indicated that the charged jet of molten polymer underwent several cycles of bending instability similar to those observed in solution electrospinning. In some cases, the fibers were fused together at crossing points. This fusing may be useful to self-reinforce a non-woven sheet. The electrospinning process is an attractive and easy route to produce nanofibers. The electrospinning process from polymer melts under vacuum in particular has a potential to be used in manufacturing nanofibers in the space. This will allow fabrication and repair of a strong yet very light structure, such as solar sail or a large aperture mirror. A better understanding of several aspects of the process, for example roles of processing parameters and fluid dynamics of polymer melt, is being developed.

References: 1. D. H. Reneker, A. Yarin, H. Fong and S. Koombhongse, J. Appl. Phys., 87, 9, 4531 (2000) 2. L. Larrondo and R. St. J. Manley, J. Polymer Science, Part B, 19, 909 (1981) 3. Chang, J. S., Kelly, A. J. and Crowley, J. M., Handbook of Electrostatic Process, M. Dekker, New York, 1995, Chapter 4

10 µm

10 µm

Fig.1 Non-woven sheet of PET electrospun fibers.

Fig. 2 Bent PEN nanofibers.

20 µm 10 µm

Fig. 3 Coiled PEN electrospun fibers at a crossing point.

Fig. 4 PEN fibers fused together

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Branched and Split fiber from Electrospinning Process

Sureeporn Koombhongse and Darrell H. Reneker Department of Polymer Science, The University of Akron, Akron, Ohio 44325-3909

The electrospinning process use electrical force as a driving force. As the potential different is applied between the surface of polymer droplet and the collector, the surface of the polymer droplet becomes cone shaped and a charged jet is ejected from the vertex of the cone. After the charged jet emerges from the polymer droplet, it moves as a straight jet for some distance then begins a spiraling path. The spiraling path of the charged jet is triggered by the electrically driven bending instability.1,2 The development of the electrically driven bending instabilities shows a self-similar, fractal-like process. Nanofibers are formed by the elongation of the charged jet due mainly to the repulsive interaction between charge carried by adjacent segments of the jet. As the solvent evaporates, the surface charge density of the charged jet increased. The surface charge density eventually reaches a limit value at which electrical force overbalances the force from surface tension. The elongation of the jet can reduce charge per unit surface area since elongation increases the surface area of a particular mass. In some case, the charged jet can reduce its charge per unit surface area by ejecting a smaller jet from the surface of the primary jet, or by splitting apart to form 2 smaller jets. A branched fiber results from the initiation of a smaller jet on the surface of the primary jet. A split fiber results when the primary jet splits apart into 2 smaller jets. The smaller secondary jet ejected from the surface of the primary jet was observed in the electrospinning of poly(2-hydroxyethyl methacrylate) (HEMA). The thinner branch was usually perpendicular to the axis of the primary jet. The small jets, pointing out of the primary jet, are observed both on straight part of the primary jet (see figure1a), and on the bending part (see figure 1b). Figure 2 shows scanning electron micrographs of branched fibers collected on the aluminum foil (a) 16% HEMA in ethanol, (b) 20% PVDF in a mixture of 50:50 dimethyl formamide : dimethyl acetamide and (c) 30% PS in dimethyl formamide.

(a) (b) Figure 1: (a) Jet branches on the bending part of the jet in electrospinning of 12% HEMA in a mixture of 50:50 ethanol : formic acid and (b) jet branches on a nearly straight part of a jet in electrospinning of 20% HEMA in ethanol.

20 µm

10 µm

10 µm

Figure 2: Branched fiber of (a) 16% HEMA in ethanol, (b) 20% PVDF in a mixture of 50:50 dimethyl formamide : dimethyl acetamide and (c) 30% PS in dimethyl formamide.

Splitting of the charged jet is another way for the jet to reduce its charge per unit surface area. Jet splitting can happen in two ways, (i) the primary jet splits apart into 2 smaller jet or (ii) the primary jet splits apart in the middle and forms a loop.

20 µm Figure 3: Split fiber of HEMA. This fiber shows the splitting of the primary jet into 2 smaller jets. The charged jet can split apart in the middle and form a hole (see figure 4a) The formation of loop or hole by splitting of the jet is also confirmed by the presence of looped fibers captured at the collector (see figure 4b).

100 µm (a) (b) Figure 4: (a)The charged jet split apart in the middle to form hole in electrospinning of 20% HEMA in a mixture of 50:50 ethanol : formic acid. (b) Looped fiber of 20% HEMA in ethanol.

1. 2

D. H. Reneker, A. L. Yarin, H. Fong and S. Koombhongse, J. Appl. Phys. 87(9), 4531 (1999). . A. L. Yarin, S. Koombhongse and D. H. Reneker, submitted to J. Appl. Phys.

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