Optimizing polybutene-1 pipe performance through rotational shear: A study on crystalline structure, mechanical strength, and thermal conductivity

To meet the demand for high-performance pipe materials in complex working environments and high-load conditions, this study investigates the relationship between structural regulation and performance enhancement of polybutene-1 (PB-1) under rotational shear conditions. The study focuses on the effects of mandrel rotational speeds (0, 4, 8, 12, and 16 rpm) on the condensed state structure, crystalline phase transitions, and macroscopic properties of PB-1 pipes. Tensile test show that the hoop mechanical properties of the pipes were significantly enhanced, especially at 8 rpm, where the tensile strength of the pipes increased from 14.98 MPa in static conditions to 29.99 MPa. Differential scanning calorimetry (DSC) revealed that rotational shear accelerates crystalline phase transitions, while scanning electron microscopy (SEM) confirmed the formation of a dense shish-kebab structure in PB-1 pipes. The shish-kebab structure parameters were analyzed using two-dimensional small-angle X-ray scattering (2D-SAXS) and two-dimensional wide-angle X-ray diffraction (2D-WAXD). The results indicate that rotational shear leads to grain refinement, increases in the size of both shish and kebab structures, a reduction in crystalline region thickness, and a shorter long period. Crystalline orientation analysis revealed that, for all rotational speeds, the degree of orientation of the pipes' inner and core layers was higher than that of the outer layer. Additionally, thermal conductivity tests showed that the in-plane thermal conductivity of PB-1 material nearly doubled at 8 rpm, reaching 0.3006 W/(m·K), whereas the out-of-plane thermal conductivity of the pipes marginally improved within the range of 0–8 rpm.