Processing of High-Strength Polymer Fibers

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1 Processing of High-Strength Polymer Fibers Donggang Yao, Professor School of Materials Science & Engineering Georgia Institute of Technology Atlanta, GA Phone:

2 Fiber Spinning Research in Our Group Solution spinning Bicomponent melt spinning line Mixing and formulation Single-component melt spinning Flow & deformation Wet spinning - Amides - Protein - Polyacrylonitrile - Cellulose and its derivatives Gel spinning - Fast solvent removal - High-strength PE fibers - New high-strength POM fibers - New high-strength PEO fibers - Gel spinning of polyketone Melt spinning Blends spinning Elastomeric fibers Special drawing and heatsetting techniques 2

3 Processing of High-Strength Polymer Fibers Our research in fiber spinning focuses on development of new processes to improve fiber strength and fiber spinning economics. We have a great interest in solving grand challenges from the polymer/fiber industry. The approaches we take involve both chemical and mechanical processing to address various aspects in new fiber products development. The engineering component of our work is supported by deep materials science, advanced characterization, theoretical analysis and modeling. In the past 10 years, our work has primarily focused on 1) Formulate new spin dopes suitable for gel spinning 2) Improve the economics of the gel spinning process 3) Improve strength of wet-spun fibers 4) Heat setting of natural and regenerated fibers Our fiber research has been funded by federal agencies (including NSF and National Textile Center), the Georgia State, as well as by various industrial supports. 3

4 Recent Accomplishments in Wet/Gel Spinning Oligomer-polymer spinning Spinning of molecular or physical blends (rather than classical solution) with controllable phase miscibility and separation - A compatible or miscible blend or solution above the polymer Tm - A largely phase-separated blend below the polymer Tc Mechanical removal of solvents To remove solvent mechanically rather than by evaporation/extraction To produce more drawable fiber precursors To allow direct drawing in a continuous setup To enable a process similar to melt spinning Gel spun high-strength fibers for several new polymers including PEO, POM and other more polar polymers 4

5 Twist Gel Spinning (TGS) Process I II C III I: Mixing II: Gel extrusion & twisting III: Extraction (optional) IV: Hot drawing a: Gel fiber b: Undrawn fiber c: Drawn fiber A: Solution or blend B: Quenching bath C: Extraction bath D: Heated bath A a Twisting b IV c B D Wyatt, Deng and Yao, Polym. Eng. Sci., 55 (4): (2015) Wyatt, Fang and Yao, Polym. Eng. Sci., 55(6): (2015) 5

6 Example UHMWPE Fiber Properties Sample Strength (GPa) / (g/denier) Error Modulus (GPa) Error Elongation Error GA Tech Fiber 4.68 / % % 4.8% 2% Dyneema SK90 yarn 3.69 / % % 6.7% 3% Spectra S2000 fiber 3.56 / % % 4% 5% Stress (GPa) GA Tech Fiber Spectra 2000 Dyneema SK Strain (mm/mm) Stress (g/denier) Ga Tech fibers are ~ 30% stronger and stiffer than the top-notch commercial fibers. Ga Tech fibers are available at large fiber diameter up to 100 µm while commercial fibers have diameter typically smaller than 25 µm. 6

7 New High-Modulus, High-Strength POM Fibers Polyoxymethylene (POM) Strebgth ~ 2 GPa Modulus ~ 50 GPa High resistance to creeping, fatigure, solvent and salt. Comparing: Nylon fibers:strength < 0.9 Gpa; Modulus < 5 GPa Ph.D. Thesis by Xudong Fang, April

8 New High-Strength PEO Fibers PEO fibers nearly 10 times stronger than traditional melt-spun ones were produced. Wyatt, Chien, Kumar and Yao, Polym. Eng. Sci., 54 (12): (2014) 8

9 Strengthening of Natural Silk Fibers Developed a special hot drawing process for strengthening of silk by rapid heating and localized drawing. Increase in fiber strength of ~40% was achieved. Natural silk yarn dr=1.067 dr=1.13 PEG bath Feed roller Heated roller Averaged strength (MPa) Collection roller Temperature ( C) X. Fang, T. Wyatt, and D. Yao, Fibers and Polymer, 16(12): (2015) 9

10 Melt Spinning Example: High-Strength Fiber from Low MW PP PP with high MFI or low MW, although desired in melt spinning for enhanced productivity, is difficult to be spun into high-strength fiber using the standard process where extensive jet stretching is applied. In this work, a processing route involving minimal jet stretch and a two-stage hot drawing procedure in the solid state was able to produce fibers with tensile strength and Young s modulus of ~ 600 MPa and 12 GPa, respectively. Intensity /041 second stage first stage precursor θ [degrees] Stress [MPa] frist stage second stage Strain Q. Mao, T.P. Wyatt, J. Chen, and D. Yao, Polym. Eng. Sci., 56(2): (2016). 10

11 New Spin Dope Formulation Example: Binary/Ternary or multi-component Spin Dopes Spinning Single phase blend/solution Gelling Phase separated Control and optimization of miscibility, compatibility, phase separation, transport, and sequence of extraction through thermodynamic and kinetical calculations. 11

12 Design of Pilot Fiber Spinning Lines for Industry 12