Non-conventioanl Nonwovens The Nonwovens Institute North Carolina State University 2401 Research Drive Raleigh, NC 27695-8301 Phone: FAX: URL: EMAIL: 919-515-6551 919-515-4556 http://www.thenonwovensinstitute.com [email protected] Copyright - NWI, NC State University 1 Why We Need Nano Fibers For Mechanical Filtration SVF=1.7%; 10 nm< dp<150 nm Copyright - NWI, NC State University nanofibers do not significantly affect the air flow filed B Maze, HV Tafreshi, Q Wang, & B Pourdeyhimi, J. Aerosol Sci., 38, 550 (2007) 2 How Do We Produce Micro & Nano Fibers? Meltblowing Spunbonding Reducing throughput Smaller capillary size & compensating with higher hole density Higher air attenuation Lower viscosity polymers … Copyright - NWI, NC State University Smaller capillary size Higher air attenuation … Bicomponent Islands-in-the-sea Splittables Other emerging technologies 3 Classical Bico Classification Side-by-side Sheath-core Segmented-pie Islands-in-the-sea Tipped Segmented-ribbon Copyright - NWI, NC State University 4 Segment-Pie: Splitting by Carding Card-splittable fiber after carding Card-splittable fiber before splitting Ref: Middlebrooks, M. C. Copyright - NWI, NC State University 5 Split Fiber Diameter Segmented Pie • 24 segments is probably the limit for this technology. 6 Diameter (Micron) 5 • The fibers form thin wedges and pack tightly when hydroentangled leading to low permeability 4 3 2 1 0 8 16 24 32 40 48 56 64 Number of Segments Copyright - NWI, NC State University 6 Bicomponent Fibers: Segmented Pie – Freudenberg’s Evolon • High surface area (microdenier fiber) • Improved barrier properties • … • Not good for an aerosol filter media… highly consolidated and low air permeability results in high pressure drops Copyright - NWI, NC State University 7 Islands-in-the-Sea • Consist of a sea component and an island component (many fine strands of polymer). • With the sea component dissolved away in subsequent processing, one may obtain micro and nano- fibers Copyright - NWI, NC State University 8 300 Islands-in-the-sea As-spun Fiber Islands: PLA Sea: Co-PET Copyright - NWI, NC State University 9 Island Fiber Diameter – I/S • 7 islands yield similar N. Fedorova, , NCSU, 2005 50/50 Sea-Island Ratio 2.00 • Commercially proven 0.87 technology in filament spinning Number of Islands Copyright - NWI, NC State University 60 0 12 00 24 0 37 0.34 0.22 0.15 7 Diamter (m) 7.00 diameter as 16 segmented pie • NWI has successfully spun 360 islands with fibers down to 300 nm 10 Alternative to I/S – With Sacrificial Sea Assumption: If sea can be fractured/fibrillated, several problems are overcome. Process becomes GREEN Cost can be lowered – no weight loss Two polymers will remain in the fabric. This can be problematic for dyeing and finishing… Copyright - NWI, NC State University 11 Fibrillating I/S Fibers: The Process Process will include mechanical shearing and hydroentangling in one step Spunbond web is passed through a calender cold to cause mechanical shear Web is then passed to hydroentangler and bonded sequentially and fractured simultaneously Copyright - NWI, NC State University 12 The Mechanism… Nylon Core, Polyethylene Sheath • The sheath or the sea is completely fragmented/fractured/fibrillate d. • The fibrillated/fractured elements wrap around the core or the islands providing better cover and higher strength Copyright - NWI, NC State University 13 Fracturing Caused by Shear Note the onset of fibrillation Copyright - NWI, NC State University 14 Onset of Fracturing by Hydroentangling The web was subjected to one manifold. Note the start of fibrillation Nylon/PLA 108 Islands Copyright - NWI, NC State University 15 Fully Fractured Mechanically on a 40 Mesh Belt The fabric fully fibrillated on a 40 mesh hydroentangling belt. The “holes” are the result of the open mesh causing the open areas. Nylon/PLA 108 Islands Copyright - NWI, NC State University 16 Fractured and Calendered The fabric fully fibrillated on a 100 mesh hydroentangling belt. There are no “holes”. The fabric was subsequently thermally bonded as well. Nylon/PE 108 Islands Copyright - NWI, NC State University 17 Mechanical Properties: Influence of Island Count structures result in superior strength making them ideal for a number of critical applications. Burst Strength (kgf) The I/S fibrillated 100 80 60 40 20 0 0 20 40 60 80 100 120 Number of Islands Copyright - NWI, NC State University 18 Air Flow (CFM) 60 50 40 30 20 10 0 0 20 40 60 80 100 120 Mean Pore Diameter (µm) Mechanical Properties: Influence of island count 40 30 20 10 0 0 Number of Islands Air Permeability Copyright - NWI, NC State University 20 40 60 80 100 120 Number of Islands Mean Pore Size 19 Non-conventional Shaped Fibers Applications: Filtration, wipes, artificial leather, … Copyright - NWI, NC State University 20 Is it All About Surface Area… ?? Photo courtesy of Fiber Innovation Technology Surface area α P m 4 L 11304000 Specific Surface Area L Denier Specific Surface, m2/g Diameter (Microns) where, is shape factor defined by, Lis total fiber length 9 105 cm , 100 0.1 1 10 100 1000 10 1 0.1 0.01 0.0001 0.001 0.01 0.1 1 10 100 1000 Denier Per Filament is fiber density 1.38 g / cm3for PET , Denier is linear density defined by 9000 A, Pis perimeter andAis cross sectional area. Copyright - NWI, NC State University 21 What are the limits of Shaped Fibers by Extrusion? Specific Surface, m2/g Diameter (Microns) 100 0.1 1 10 100 1000 10 Ro un 1 4D G d Photo courtesy of Fiber Innovation Technology 0.1 Smallest 4DG ~ 6 dpf 0.01 0.0001 0.001 0.01 0.1 1 10 100 1000 Denier Per Filament Copyright - NWI, NC State University 22 What is Possible? The shaped fibers available are Large > 6 dpf Are used in some filtration applications… Can shaped fibers be formed < 6 dpf Copyright - NWI, NC State University By bicopmonent spinning …. 23 New Shaped Fiber with Wings & Backbone Sheath-Core Configuration Core (Residual) Sheath (Sacrificial) PP PET PA PLA PLA EastONE CoPET Copyright - NWI, NC State University 24 What Are the Limits of Shaped Fibers? Specific Surface, m2/g Diameter (Microns) 100 0.1 1 10 10 Photos courtesy of Allasso Industries. Inc. 100 1000 4D G Ro un 1 W ing ed d 0.1 0.01 0.0001 0.001 Photo courtesy of Fiber Innovation Technology 0.01 0.1 1 10 Denier Per Filament Copyright - NWI, NC State University 100 1000 B. Pourdeyhimi and Walter J. Chappas, High surface area fiber and textiles made from the same, 20080108265, May 8, 2008. 25 Polymers Sheath: Sacrificial PLA Core: PA, PET, PP, PLA Sheath/Core Ratio: 50:50, 60:40 No. of Wings: 8, 16, 32 Basis Weight: Copyright - NWI, NC State University 50, 100, 200 gsm 26 The Process Spunbond Bico Hydroentangling 5 manifolds – 250 bar Post-process 6 – 10 % Caustic solution 90 °C, 2 – 4 min Untreated Winged Media Drum dryer NaOH bath Copyright - NWI, NC State University Water bath Treated Winged Media Neutralization bath 27 Typical nylon Winged Fibers Aspect Ratio = 0.54 Copyright - NWI, NC State University 28 Typical PP Winged Fibers Aspect Ratio = 0.34 Copyright - NWI, NC State University 29 Core-Modified Trilobal Micro Fibers & Fabrics Copyright - NWI, NC State University 30 Modified Tipped Trilobal Tipped tri-lobal Both the core and the tips are exposed on surface. Spinning can be difficult for incompatible polymers. Modified tipped tri-lobal The core is wrapped by the tips. Spinning is easy. This can also be done by a trilobal sheath-core structure but splitting is harder. Modified tipped tri-lobal The core is wrapped by the tips The fibers can be fractured to produce 4 separate fibers. This SEM micrograph shows the process of fracturing the tips or the sheath by hydroentangling. Copyright - NWI, NC State University 31 Modified Tipped Tri-lobal – PLA/PA6 Thermally bonded only Copyright - NWI, NC State University Hydroentangled and fractured. Note the curl and crimp – this leads to better “hand” 32 Challenges with Modified Tipped Trilobal The Core has to solidify quickly to allow fiber morphology development If using a removable/dissolvable polymer, low ratios are not possible It is not possible to use high tip ratios High tip ratio is desirable – to reduce core component Copyright - NWI, NC State University 33 Conclusions for Modified Tipped Trilobal Spinning can be problematic for exotic polymers, elastomers, etc. High percentage of tip polymer not easily achieved Fabric is similar to I/S Fibrillated Copyright - NWI, NC State University 34 New Proposed System Place a core in the tipped trilobal with the same composition as the tips. This way, we can control the ratios and be able to produce ratios below 25 % easily. Higher ratios are also possible. The lowest threshold is believed to be about 5%. This may require modifications to the pump and metering systems. Copyright - NWI, NC State University 35 Cored Trilobal Examples Polymer B Polymer B Copyright - NWI, NC State University 36 Hollow Cored Trilobal Polymer B Polymer B Copyright - NWI, NC State University 37 Cored Trilobal – Core is non-round Polymer B Polymer B Copyright - NWI, NC State University 38 New Pack Designed Critical features: Tips (A) wrap the core The core (A) can be: Hollow Contain another fiber configuration of the same polymer as tips The separator polymer (B) can be a very small percentage (< 50% and > 5%) of the overall fiber Copyright - NWI, NC State University 39 PP/PP (with pigment) 80/20 Ratio Results: July 14, 2007 Copyright - NWI, NC State University 40 PLA/PA6 80/20 Ratio Results: July 14, 2007 Copyright - NWI, NC State University 41 PLA/PA6 70/30 Ratio Results: July 14, 2007 Copyright - NWI, NC State University 42 Tensile strength (kgf) Some Results – 100 gsm fabric 30 25 MD CD 20 15 10 5 0 25/75 50/50 75/25 Core/Tip Polymer Ratio Nylon/PLA Copyright - NWI, NC State University 43 Conclusions for Core Modified TT – Fibrillated Properties Applications • • • • • • • • • • • • • • Extremely flexible, Strong High MVTR High Absorbency Excellent hand High Pilling Resistance Copyright - NWI, NC State University Intimate Apparel Various Forms of Apparel Outdoor Fabrics Hunting/Sports Wipes Bedding Automotive … 44
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