A Spectroscopic Analysis of the Phase Evolution in Polyurethane Foams

Abstract

Infrared spectroscopy has been used to study the evolution of polyurethane foam structure, providing measures of relative reaction kinetics, hard segment growth, the onset of phase separation, the formation of order, and the development of final morphology. Changes in free, monodentate, and bidentate hydrogen-bonded urea groups dominate the organization of the entire ensemble. Hard segments formed by reaction of 2,6-toluene diisocyanate (2,6-TDI) and by a mixture of 80% 2,4-TDI and 20% 2,6-TDI displayed very different local segmental alignment, a factor crucial in the development of morphology. Phase separation occurred faster, with fewer and shorter hard segments, in the systems with well-ordered straight chains. The formation and time evolution of monodentate ureas suggest that phase development may be incomplete, or trapped, in systems with ill-defined urea structures. A low degree of spatial order exists in the systems containing these structures.

In situ Foaming Evolution of Flexible Polyurethane Foam Nanocomposites

“…[3] Hence, infrared spectroscopy is particularly useful to analyse the time-related aspects of foam evolution and morphology development. [1,[5][6][7] In PU foams, these analyses are carried out by studying four particular regions: (i) the NH stretching region, 3 500-3 200 cm À1 ; (ii) the amide I region or carbonyl region, 1 800-1 600 cm À1 ; (iii) the isocyanate absorbance band at %2 300 cm À1 ; and (iv) the amide II region, below 1 600 cm À1 . Here, the NH stretching and the amide II regions were not considered due to variations on the extinction coefficient with hydrogen bonding and the complex nature of the absorbance peaks, respectively.…”

“…[1,[4][5][6][7][8] Real time morphological changes during phase separation are monitored by SAXS. [1,6] Meanwhile, FT-IR spectroscopy has been used to understand the polymer structure development and the kinetics during foaming.…”

“…[1,6] Meanwhile, FT-IR spectroscopy has been used to understand the polymer structure development and the kinetics during foaming. [1,6,7] FT-IR enabled monitoring both the sequence of chemical reactions and morphological changes by analysing the decay of isocyanate and the evolution of H-bonded bands. In situ rheology measurements have provided information on the foaming evolution through changes in the modulus or viscosity profile using a modified parallel-plate rheometre under forced adiabatic conditions.…”

Estudio de Nanocompuestos de Espumas de Poliuretano Reforzadas con Nanocargas en Base Carbono

“…[11] The polymerisation kinetics of the PU foams and the development of the morphology are usually studied by infrared spectroscopy. [33,41,42,195] In the analysis of the infrared spectra of polyurethanes ( The extent of the reaction in PU foams is determined following the isocyanate conversion during the reaction by FT-IR. [195] The isocyanate absorption band appears at approximately 2270 cm -1 and it is normalised to an internal reference band that remains constant during the reaction (CH stretch at 2970 cm -1 ), to compensate for the density change.…”

“…[33,41,42,195] In the analysis of the infrared spectra of polyurethanes ( The extent of the reaction in PU foams is determined following the isocyanate conversion during the reaction by FT-IR. [195] The isocyanate absorption band appears at approximately 2270 cm -1 and it is normalised to an internal reference band that remains constant during the reaction (CH stretch at 2970 cm -1 ), to compensate for the density change. Hence, the conversion is defined by: (4.6) where ANCO is the integrated intensity of the normalised isocyanate absorbance band, and A0 is the normalised isocyanate absorbance band at zero reaction time.…”