Phase Behavior and Its Effects on Crystallization in a Poly(trimethylene terephthalate)/Phenoxy Resin Blend
Phase behavior and its effects on crystallization in an extruded poly(trimethylene terephthalate) (PTT)/phenoxy resin blend were studied with time-resolved light scattering (TRLS), optical microscopy (OM), differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS). During annealing in the molten state, a two-phase structure with unique periodicity and phase connectivity was developed by liquid–liquid phase separation. After the formation of the phase-separated structure, the blend was homogenized by the interchange reactions between the two polymers. The crystallization behavior of PTT predominantly depended on the phase morphology developed during annealing. The pre-existing phase structures disturbed the lamellar orientation, resulting in a poorly ordered spherulitic superstructure.
Simultaneous liquid–liquid demixing and crystallization and its effect on the spherulite growth in poly(ethylene terephthalate)/poly(ether imide) blends
Abstract Poly(ethylene terephthalate) (PET)/poly(ether imide) (PEI) blends were miscible in the melt, but exhibited simultaneous liquid–liquid phase separation and crystallization over a wide range of temperature and composition. The interplay between these two processes is expected to dominate the morphological formation in the blends. In this study, the phase diagram of PET/PEI blend was determined to evaluate the envelop within which liquid–liquid phase separation was operative with crystallization. A UCST phase diagram below 240°C was identified for this system. The effect of liquid–liquid phase separation on the growth of PET spherulites was studied by small-angle light scattering (SALS). Nonlinear spherulite growths were observed for the blends at higher crystallization temperatures of 210°C and 220°C, while the growths were basically linear below 210°C. The nonlinear growth behaviour was discussed based on the competition between spherulite growth and spinodal decomposition.
Experimental study on bond behavior between high-strength grout and deformed steel bars
Abstract Engineers use high-strength grout to connect precast concrete members for its low shrinkage and good fluidity. This paper designed 87 central pull-out specimens using the control variable method to investigate the influence of factors on the rebar-grout bond property such as compressive strength, steel grade, bar diameter, transverse stirrups, and bond length. The test result showed that improving grout compressive strength (85.8 MPa–122.7 MPa) cannot improve the bond strength, which was different from the previous conclusions of concrete pull-out tests. Simplified formulas were presented for calculating the characteristic values of bond strength, residual strength, peak slip, and relative slip of load-holding platform based on parameter analysis. Then, a constitutive model was proposed to predict the full-range bond stress-slip curve of high-strength grout and steel bar specimens from bearing to failure. Finally, FEA models were established to evaluate the applicability and accuracy of the constitutive model.