Effect of toluene diisocyanate index on morphology and physical properties of flexible slabstock polyurethane foams

Abstract

ABSTRACT:The effect of toluene diisocyanate (TDI) index on the physical properties, structure, and morphology of flexible slabstock polyurethane foams was investigated. Foams based on a 2700 molecular weight triol, 6 pph water, and varying amounts of an 80/20 mixture of 2,4-and 2,6-TDIs were characterized using a number of physical property and morphological measurements. Extraction experiments using dimethyl formamide (DMF) showed that increasing the index increased the level of covalent crosslinking with perhaps a maximum being reached at an index ca. 100. Viscoelastic measurements also supported the claim of increased crosslinking with TDI index. The initial load in load relaxation experiments at 65% strain systematically increased with increasing TDI while the percent decay in a 3-h period decreased. Temperature and/or humidity ''plasticized'' the load relaxation behavior in all the foams studied, indicating that the hard segment domain physical ''crosslinks'' play a significant role in the properties of these materials. Interestingly, compression set measurements appeared to be independent of the index, likely due to some level of hard segment continuity, but the induced recovery of the compression set at elevated temperatures was indeed sensitive to the index. The amount of recovery systematically increased with increasing TDI index due to the more enhanced ''recoverable'' covalent network. Scanning electron microscopy (SEM) studies of the foams showed that the cellular structure was not significantly affected by the index. However, SEM also showed that the structure of the high index foam was not greatly altered by the extraction process while the lowest index foam's cellular structure was severely disfigured. The fine structure of the foams was found to be influenced by the TDI index. Small angle X-ray scattering, differential scanning calorimetry, and dynamic mechanical analysis all provided evidence that an increase in the TDI index promoted some phase mixing of the soft and hard segments. FTIR showed that the short-range ordering within the hard segment domains displayed a maximum at an index of 100. This was attributed to the concentration of hard segment domains being lower at a lower index and their ordering being disrupted at higher indexes due to more extensive covalent crosslinking prior to completion of phase separation. Wide angle X-ray scattering results also confirmed that for the highest index level, the short-range ordering of the TDI moieties was decreased.

Characterization of flexible polyurethane foams based on soybean‐based polyols

“…The chemical crosslinks arise from the reaction of the hydroxyl groups of the bifunctional or multifunctional polyols and diol higher functionality isocyanate to form urethane linkages that links the urea moieties to the soft segments. Both of these two types of crosslinks play an important role on the final structure, morphology, and mechanical properties of the foams 9–14. Some of the physical and mechanical properties which are particularly important for the application of flexible foams are their compression–strain behavior including set and recovery (analyzed by indentation force deflection tests, IFD), glass transition (analyzed by dynamic mechanical analysis, DMA), cellular morphology, air flow characteristics, etc.…”

“…Both of these two types of crosslinks play an important role on the final structure, morphology, and mechanical properties of the foams. [9][10][11][12][13][14] Some of the physical and mechanical properties which are particularly important for the application of flexible foams are their compression-strain behavior including set and recovery (analyzed by indentation force deflection tests, IFD), glass transition (analyzed by dynamic mechanical analysis, DMA), cellular morphology, air flow characteristics, etc.…”

Sound absorption properties of polyurethane/nano‐silica nanocomposite foams

“…Glass transition temperature ( T g ) decreases and the area of tan δ peak increases with decreasing the isocyanate index value. Crosslinking reactions are favored with more free isocyanates 19. It should be noted, however, that the decrease of isocyanate index decreases the crosslink density, implying that the composite is not fully crosslinked.…”

“…Crosslinking reactions are favored with more free isocyanates. 19 It should be noted, however, that the decrease of isocyanate index decreases the crosslink density, implying that the composite is not fully crosslinked. More detailed studies on this subject using DSC or FTIR spectroscopy are now underway.…”

Flame retardancy of whisker silicon oxide/rigid polyurethane foam composites with expandable graphite

“…To obtain PUF with good mechanical properties, different materials had also been developed 5–7. The ratio of components also affects the mechanical properties of PUF, and higher toluene isocyanate index leads to better compression strength 8. But these means have some defects, for example, the cost increases.…”