Properties of water‐blown rigid polyurethane foams with reactivity of raw materials

Abstract

Rigid polyurethane foams (PUFs) were prepared from polymeric 4,4-diphenylmethane diisocyanate (PMDI; having functionality of 2.9), polyether polyols, silicone surfactant, amine catalysts, and distilled water. The effects of reactivity on the properties such as density, compressive and flexural strength, and glass-transition temperature (T g ) of the PUF samples were studied. The kinetic rate of forming the PUF samples was increased with the catalyst and water content. With increasing OH value and functionality of the polyols, the density and compressive strength of the PUF samples also increased. For the PUF samples synthesized with polyols having high functionality (Ͼ5), the flexural strength of the PUF samples decreased with the functionality of the polyols. With increasing OH value and functionality of the polyols, the T g of the PUF increased because of an increase in the degree of crosslinking of the PUF samples. The T g value and compressive strength of the PUF samples were observed to increase with the NCO index. From this result, it was suggested that the increase in the T g value and compressive strength of the PUF samples may be attributable to the additional crosslinks that arose from allophonate and biuret formation by the supplementary reactions of excess PMDI.

Effects of organoclay on the thermal insulating properties of rigid polyurethane poams blown by environmentally friendly blowing agents

“…After mixing, the reactants were poured into an open mold (250 × 250 × 100 mm) to produce free-rise foams and were cured for 1 week at room temperature. 18,19 In order to investigate the effect of clay on the physical properties and thermal conductivity of PUF, neat PUF was also prepared and compared to PUF/clay composites. The PUF/clay nanocompisites were synthesized with and without ultrasound to study the effect of ultrasonic cavitation on PUF's properties.…”

Effects of silicon surfactant in rigid polyurethane foams

“…Kinetics of the foam formation is followed by the cream time, gel time and tack-free time [4,6,10]. The cream time corresponds to the start of bubble rise and hence color of the mixture becomes creamlike from dark brown due to the introduction of bubbles.…”

“…If the foam is to be dimensionally stable under these conditions, the compression strength must be greater than the pressure rise [2]. The minimum compression strength of 0.1 MPa is generally recommended for closed cell foam [6].…”

“…However, the excessive use of water causes a negative pressure gradient due to the rapid diffusion of CO 2 through the cell wall causing cell deformation [2,3,15,16]. The kinetics of RPUF formation mainly depends on the rates of blowing and gelling reactions, which on the other hand are respectively governed by an amine and a tin catalyst [4,6]. On the other hand, the properties of the foam mainly depend on the type of polyol such as functionality and hydroxyl value, and type and amount of surfactant, and blowing agent.…”

Glass fiber and silica reinforced rigid polyurethane foams

“…The foams were synthesized by one shot method at room temperature [18,19]. Silica particles carrying isocyanate (NCO) group were reacted with the polyol at room temperature for 6 h in a four-necked separable flask equipped with a Figure 1.…”