Large-Scale Nanofiber Manufacturing| Ultrahigh-Molecular-Weight Polyethylene Fibers with ExcellentCreep Resistance Derived from an Online-Tailored Fish-Skeleton-likeMolecular Structure

Prof. Wang Dong (WTU): Online Melt Preparation of "Tailor-Made" Ultrahigh-Molecular-Weight Polyethylene Fibers with High Creep Resistance

Ultra-high molecular weight polyethylene (UHMWPE) fibers are among the world's top three high-performance fibers, exhibiting excellent properties including high specific strength/modulus, outstanding impact resistance, and superior wear resistance. They withstand corrosion from strong acids/alkalis, finding wide applications in military protection, aerospace, medical materials, radomes, and marine anchor ropes.

Despite these advantages, UHMWPE fibers suffer from low heat resistance, poor creep resistance, weak composite adhesion, and high melt viscosity causing processing difficulties. Creep formation is a critical issue - low creep resistance and Young's modulus lead to intermolecular slippage under stress. This significantly limits UHMWPE's civilian/military applications.Common solutions like filler modification, multi-stage stretching, silane/UV/radiation crosslinking show limited effectiveness in enhancing intermolecular forces. 

Fig. 1. (a) Online preparation process and (b) modification mechanism of high creep-resistant UHMWPE fibers.

 Prof. Wang Dong's team at WTU published "Ultrahigh-Molecular-Weight Polyethylene Fibers with Excellent Creep Resistance Derived from an Online-Tailored Fish-Skeleton-like Molecular Structure" in Macromolecules.

Research Objective:

To prepare ultra-high molecular weight polyethylene (UHMWPE) fibers with excellent creep resistance by customizing fishbone-like molecular structures online, providing new approaches and methods to solve the creep problem of UHMWPE fibers and expanding their application fields.

Fig. 2. (a, b) FTIR spectra of UHMWPE fibers, (c) Torque changes of UHMWPE with different monomers at high temperature, (d) Complex viscosity versus frequency for different samples, (e) Schematic of molecular structure changes before (I) and after (II) modification.

Experimental Methods:

1. Material Selection:   Appropriate ultra-high molecular weight polyethylene (UHMWPE) raw materials and potential additives are selected. Parameters such as the viscosity-average molecular weight and molecular weight distribution of the raw materials are precisely characterized.   2. Molecular Structure Design and Preparation:   Specific technologies or processes are employed to customize the molecular structure of UHMWPE online, forming a fishbone-like molecular structure. This may involve chemical methods such as copolymerization and grafting, or special physical processing techniques.   3. Fiber Preparation and Molding:    Materials with designed molecular structures are processed into fibers via processes such as gel spinning. Parameters during spinning, including solution concentration, temperature, and draw ratio, are strictly controlled and optimized.   4. Performance Testing:    Multiple testing methods are used to comprehensively characterize the properties of the prepared fibers, including:     - Mechanical Property Testing:** Measurement of tensile strength, elongation at break, etc.     - Creep Testing:** Measurement of creep behavior under different loads and time conditions.     - Differential Scanning Calorimetry (DSC):** Analysis of the fiber’s crystallization behavior and thermal properties.

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Fig. 3. Crystal structure analysis of fibers.







Fig. 4. (a) Schematic of molecular chain orientation evolution during UHMWPE fiber production. SEM images of UHMWPE fiber surface morphology after 10× thermal stretching: (b, c) 3 million MW UHMWPE and (d, e) 3 million MW UHMWPE with 5% 1-hexene. AFM images of UHMWPE fibers with different monomer ratios at same thermal stretching ratio: (f) 0%, (g) 1%, (h) 3%, (i) 5%.







Fig. 5. (a) Constant-force creep curves of different fibers under 10 thermal stretching cycles, (b) Constant-force creep curves of the same modified fiber at 5× and 10× thermal stretching ratios, (c) Dynamic thermomechanical analysis curves at -30°C, (d) Dynamic thermomechanical analysis curves and (e) creep strain values at 70°C, (f) Time-dependent creep strain values of different fibers at 70°C using constant-load suspension method, (g) Schematic of enhanced intermolecular forces evolution in different modified UHMWPE molecules.




Research Results:


1. Successful Construction of Fishbone-like Molecular Structure:
   Through various analytical methods such as nuclear magnetic resonance (NMR) and infrared spectroscopy (IR), the formation of the fishbone-like molecular structure was confirmed. The characteristics and parameters of the molecular structure, such as branch degree and branch chain length, were determined.
2. Excellent Creep Resistance:
   Compared with conventional UHMWPE fibers, fibers with a fishbone-like molecular structure exhibit significantly reduced creep deformation under the same load, demonstrating a notable improvement in creep resistance. This performance may reach or even exceed the level of commercially available fibers currently recognized as having superior creep resistance in the industry.
3. Synergistic Optimization of Other Properties:
   In addition to creep resistance, other properties of the fibers, such as mechanical strength and heat resistance, may have been improved to a certain extent or maintained at a good level. No obvious performance degradation was observed due to changes in the molecular structure.
4. Revelation of Structure-Property Relationship:
   An in-depth analysis of the internal relationship between the fishbone-like molecular structure and creep resistance revealed that this special structure effectively enhances the creep resistance of the fibers by mechanisms such as slowing down the mutual sliding between molecular chains and increasing the intermolecular forces.

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Fig. 6. (a, a') Macroscopic image and SEM of pilot-scale modified UHMWPE fibers, (b) AFM image of modified fiber surface morphology, (c, d) Optical microscope images of modified fibers. (e) Creep strain values of different fibers at 70°C environmental temperature (96 h test duration), (f) Stress-strain curves of different fibers, (g) Modulus of different modified fibers, (h) Creep strain values of different fibers measured by constant-load suspension method at -30°C.







Fig. 7. (a) Contour plots of process parameters and performance parameter optimization, (b) Response surface model showing the effect of monomer incorporation on fiber strength and creep resistance, (c) Response surface plots of various axial planes, (d) Molecular chain interaction mechanism, (e) Performance comparison between modified fibers and best-selling commercial products.





Research Conclusions:

The online-tailored fish-skeleton-like molecular structure represents an effective approach to significantly enhance the creep resistance of ultra-high molecular weight polyethylene (UHMWPE) fibers, providing novel strategies and technical pathways for producing high-performance UHMWPE fibers. The developed UHMWPE fibers with this distinctive molecular architecture demonstrate superior performance characteristics, showing promising potential for widespread applications in fields demanding exceptional creep resistance, including aerospace engineering and high-end cable manufacturing, with substantial application prospects and economic benefits.

This study provides new experimental evidence and theoretical support for deeper understanding of creep mechanisms and structure-property relationships in UHMWPE fibers, making significant contributions to advancements in polymer materials science. The online integrated grafting-spinning methodology remarkably improves intermolecular chain slippage resistance while maintaining spinnability, effectively overcoming the limitations of conventional modification methods regarding efficiency and durability. This innovative approach offers multiple advantages including simplicity, rapid processing, high efficiency, cost-effectiveness, and excellent versatility.