Roles of phase separation and crystallization in the structure formation of new segmented polyurethane ureas and their nanocomposites with single-walled carbon nanotubes

Abstract

Crystal structure and supramolecular organization of new segmented thermoplastic polyurethane ureas and their nanocomposites with ultra-small additives (less than 0.1 wt.%) of single-walled carbon nanotubes (SWCNTs) have been been investigated using DSC and X-ray diff raction analysis. Taking into account the Avrami model, eff ects of physical aging and thermal history of the samples on the crystallization rate was described. It was demonstrated that the introduction of ultra small amounts of SWCNTs does not decrease the crystallinity, but decreases the crystallization rate.

Optimization of Structure of Soft Block for Design of Adaptive Polyurethanes

“…As we have shown earlier, the crystallization rate of PCL in diblock copolymers has maximum at 5 °C [9]. Crystallization rate of PBA is the highest at 25 °C and slowly decrease at decreasing temperature [10]. Thus, by varying the crystallization temperature, it is possible to change both the overall degree of crystallinity and the relative content of each phase, obtaining materials with two independent physical networks of the soft block.…”

“…where ΔHm -total melting enthalpy measured from DSC curves, ΔHºmPBA = 95 J/g and -HºmPCL = 243 J/g equilibrium melting enthalpy of PBA and PLC, respectively; wPBA and wPCL -mass fraction of polyols in TPU. These values we have calculated previously from DSC and X-ray diffraction data of as-received polyols [6,[8][9][10].…”

“…The studied TPUs have been synthesized according to three-stage method described in our earlier publications [6,[8][9][10]. Two crystallizing polyols with similar molecular weight 2000 Da were taken in different in weight ratio PBA/PCL (in %): 0/100 (TPU 0/100), 50/50 (TPU 50/50), 60/40 (TPU 60/40), 80/20 (TPU 80/20), 100/0 (TPU 100/0).…”

A review on microphase separation measurement techniques for polyurethanes

“…Increased phase separation usually augments the PU mechanical properties including the ultimate strength, modulus, and elongation at break. In this regard, increased hard segment content, [26][27][28][29] using aromatic and symmetric isocyanates [30][31][32][33] and including nanofillers like carbon nanotubes (CNTs) [34][35][36] increase the phase separation and positively influence the PU mechanical properties. It has to be noted that the positive relation between phase separation and mechanical properties is not ubiquitous.…”