Effect of molecular weight and concentration on gel-spun UHMWPE fibers with polybutene as a new spin solvent

Ultrahigh molecular weight polyethylene (UHMWPE) fibers have been investigated for years to improve performance with gel spinning process for wide applications in industry. Various spin solvents have been attempted including paraffin oil, decahydronaphthalene (decalin), kerosene etc. However, more work still needs to be done because of environmental issues or long extraction process of the aforementioned solvents. Recently, polybutene was found to be an effective spin solvent for UHMWPE fibers, which is environmentally friendly and widely available on the market. Besides producing high strength fibers, compared to paraffin oil, polybutene can form a gel with UHMWPE showing stronger phase separation behavior at room temperature. Because of this property, more extraction solvents can be saved. It was also demonstrated with experiments that the extraction efficiency is higher than that of the gel fiber formed with paraffin oil. Thus, polybutene has high potential to be used in large-scale production of UHMWPE fibers, which deserves further study. In this work, polybutene with different molecular weight was used to form spin dopes with UHMWPE. The dope concentration for each type of polybutene was also varied to check the effect of molecular weight and dope concentration on fiber properties. Viscoelastic properties of the spin dopes were obtained with parallel plate rheometry while thermodynamic properties of the dopes were characterized with differential scanning calorimetry (DSC) and thermal gravitational analysis (TGA). With optimized processing conditions, high strength fibers were collected and the crystalline structure was examined with wide angel X-ray diffraction (WAXD). DSC and TGA data also provided support for the effect of molecular weight and concentration of polybutene. It can be found that stronger fibers are obtained with lower concentration spin dopes. The viscosity of the dopes and corresponding spinning conditions are significantly affected by molecular weight of polybutene. Extraction efficiency is affected by both molecular weight and dope concentration. To obtain cost-effective superstrong UHMWPE fibers, an optimized design is needed based on the molecular weight of polybutene and the spin dope concentration.