Density is an important parameter that influences the properties and performances of rigid polyurethane foam (PUF). Rigid PUF with different densities were prepared by varying the amount of distilled water as blowing agent. This investigation reports the mechanical, morphological, water absorption, thermal conductivity, and thermal behavior of rigid PUF varying with the density, which controls the foam architecture. The density of the PUF decreased from 116 to 42 kg/m 3 with an increase in the amount of water from 0.1 to 3.0 parts per hundred polyol by weight (phr), respectively. It was found that the mechanical properties of the PUFs changed with the foam density. The results of water absorption of the PUFs showed that water absorption increased with decrease in density, due to increase in the cell size and decrease in the cell-wall thickness. The thermal conductivity measurements showed that the thermal conductivity decreased with increase in density. It was due to the decrease in cell size. The thermal analysis of the PUFs shows that the glass transition temperature increases with the decrease in foam density, but the thermal stability decreases with the decrease in foam density.

Water-blown rigid polyurethane foam (PUF) with two different particle sizes (180 and 300 lm) of expandable graphite (EG) as a flame-retardant additive were prepared, and the effects on the mechanical, morphological, water absorption, thermal conductivity, thermal, and flame-retardant properties were studied. In this investigation, EG content was varied from 5 to 50 php by weight. The mechanical properties of PUF decreased with increasing EG loading in both cases. The water absorption of the PUF increased with an increase in the EG loading mainly because of the collapse of foam cells, as evidenced from the scanning electron microscopy pictures. The thermal conductivity of the EG-filled PUF showed that the insulation properties decreased with EG loading. The flame-retardant properties (limiting oxygen index and char yield measurement) of the PUF improved with increasing EG loading. PUF filled with the higher particle size EG showed better mechanical properties and fire-retardant properties than the PUF filled with the lower particle size EG.

Water blown rigid polyurethane foams (PUF) with organoclay/organically modified nanoclay (ONC) were prepared and their properties such as density, mechanical, morphological, insulation, thermal and flame retardant properties were studied. In this investigation, the ONC content was varied from 1 to 10 parts per hundred of polyol (php) by weight. It was observed that the compressive strength of ONC filled PUF increased up to 3 php of ONC loading and then it decreased. Wide angle X-ray diffraction and transmission electron microscopy studies indicated the exfoliated dispersion of ONC in PUF. The thermal conductivity of ONC filled PUF decreases up to 5 php and then increases. The glass transition temperature (Tg) of PUF decreases on loading of ONC. The TGA analysis shows that there is slight increase in degradation temperature with increase in ONC loading. The flame retardant properties (LOI and flame spread rate) are improved slightly on addition (3 php) of ONC filled PUF.

Rigid polyurethane foam (PUF) filled with mixture of alumina trihydrate (ATH) and triphenyl phosphate (TPP) as fire retardant additive was prepared with water as a blowing agent. In this study, the ATH content was varied from 10 to 100 parts per hundred polyol by weight (php), and TPP was used at a higher loading of ATH (75 and 100 php) in a ratio of 1 : 5 to enhance the processing during PUF preparation. The effects of ATH on properties such as density, compressive strength, morphological, thermal conductivity, thermal stability, flame-retardant (FR) behavior, and smoke characteristics were studied. The density and compressive strength of the ATH-filled PUF decreased initially and then increased with further increase in ATH content. There was no significant change in the thermal stability with increasing ATH loading. We determined the FR properties of these foam samples by measuring the limiting oxygen index (LOI), smoke density, rate of burning, and char yield. The addition of ATH with TPP to PUF significantly decreased the flame-spread rate and increased LOI. The addition of TPP resulted in easy processing and also improved FR characteristics of the foam.

Rigid polyurethane foam (PUF) having different fillers such as precipitated silica (SiO2), precipitated calcium carbonate (CaCO3) and glass powder (GP) were prepared by blowing with distilled water. The effect of filler loading on different properties of PUF was studied. In this investigation, the filler content was varied from 5 to 50 parts per hundred of polyol (phr) by weight. The properties such as density, mechanical, morphological, water absorption, thermal conductivity and thermal properties of the filled PUF were compared with the neat PUF. The density of silica filled PUF decreases with an increase in the filler loading. In case of calcium carbonate and glass powder the density initially decreases with filler loading, but after a certain concentration of fillers there is an increase in density with filler content. The mechanical properties such as compressive stress at 10% strain, compressive modulus and hardness of the filled PUF decrease in comparison with the neat PUF, due to the reaction between isocyanate and surface functional group present in filler. In all cases, the water absorption of the PUF increases with the increase in filler loading, due to the decrease in the closed cell content. The thermal conductivity analysis of PUF shows that the insulation properties decrease with the increase in silica as well as CaCO3 loading. This is mainly due to formation of open and damaged cell structure. However, when glass powder is used as filler the thermal conductivity first decreases, but later increases with filler loading.

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