Melting, Solidification, and Crystallization of a Thermoplastic Polyurethane as a Function of Hard Segment Content

Polymorphic microstructure of MDI/BD-block polyurethane as determined by temperature-sensitive conformation variation

MDI/BD-block thermoplastic polyurethanes (TPUs) crystallized at different isothermal temperatures and different cooling rates were investigated using multiple techniques. The MDI/BD blocks crystallized in form II when the isothermal temperature was equal to or higher than 150 °C, and in form I at lower isothermal temperatures. Form II had a higher crystal elastic modulus of 6.75 GPa than form I of 1.31 GPa. Form I exhibited contracted conformation, while form II exhibited an extended conformation when viewed from the length of the c-axis in the crystalline state. Based on an analysis of the second derivative in FTIR spectroscopy and simple modeling, the conformation differences were considered to stem from the urethane group's internal bond rotation concerning the phenyl ring and the opening bond angle of phenyl-CH₂-phenyl. The generation of form II above 150 °C may be due to the activation of urethane and the flexible methylene elevated by the high temperature. Overall, it was seen that the crystallization of MDI/BD blocks involved a physicochemical change.

Multiblock Thermoplastic Polyurethanes: In Situ Studies of Structural and Morphological Evolution under Strain

The structural evolution of multiblock thermoplastic polyurethane ureas based on two polydiols, poly(1,4-butylene adipate (PBA) and poly-ε-caprolactone (PCL), as soft blocks and two diisocyanites, 2,4-toluylene diisocyanate (TDI) and 1,6-hexamethylene diisocyanate (HMDI), as hard blocks is monitored during in situ deformation by small- and wide-angle X-ray scattering. It was shown that the urethane environment determines the crystal structure of the soft block. Consequently, two populations of crystalline domains of polydiols are formed. Aromatic TDI forms rigid domains and imposes constrains on the crystallization of bounded polydiol. During stretching, the TDI–polydiol domains reveal limited elastic deformation without reorganization of the crystalline phase. The constrained lamellae of polydiol form an additional physical network that contributes to the elastic modulus and strength of the material. In contrast, polydiols connected to the linear semi-flexible HMDI have a higher crystallization rate and exhibit a more regular lamellar morphology. During deformation, the HMDI-PBA domains show a typical thermoplastic behavior with plastic flow and necking because of the high degree of crystallinity of PBA at room temperature. Materials with HMDI-PCL bonding exhibit elastic deformation due to the low degree of crystallinity of the PCL block in the isotropic state. At higher strain, hardening of the material is observed due to the stress-induced crystallization of PCL.

Synthesis of antibacterial polyurethane film and its properties

Polyurethane (PU) is a polymer widely used in the biomedical field with excellent mechanical properties and good biocompatibility. However, it usually exhibits poor antibacterial properties for practical applications. Efforts are needed to improve the antibacterial activities of PU films for broader application prospect and added application values. In the present work, two PU films, TDI-P(E-co-T) and TDI-N-100-P(E-co-T), were prepared. Silver nanoparticles (AgNPs) were composited into the TDI-N-100-P(E-co-T) film for better mechanical properties and antibacterial activities, and resultant PU/AgNPs composite film was systematically characterized and studied. The as-prepared PU/AgNPs composite film exhibits much better antibacterial properties than the traditional PU membrane, exhibiting broader application prospect.