Cellular Polymers

Toughing melamine-formaldehyde (MF) rigid closed-cell foams were prepared by using ethylene glycol (EG) and carbon fiber (CF) as composite toughening agents. The pulverization rate, compressive strength, bending strength, cellular structure, closed-cell ratio, water absorption ratio, thermal conductivity, thermal stability, limiting oxygen index (LOI), and char yield were characterized to study the morphology, mechanical, thermal, and fire-retardant properties of as-prepared toughing MF rigid foams. The pulverization rate result showed that introduction of composite modifier can obviously improve the toughness of MF rigid foams. The cellular structure, closed-cell ratio, and water absorption results showed that the addition of EG/CF can increase the closed-cell ratio and control the cell size of MF rigid foams. The compressive strength and bending strength results showed that the incorporation of composite modifier of MF rigid foams dramatically improved the mechanical properties. The LOI, char yield, and thermal stability results showed that the toughing MF rigid foams remained more intact char skeleton with flame-retardant effect, thus reducing the fire hazards. The as-prepared toughing MF rigid foams showed the best comprehensive performance with pulverization rate of 5.21%, compressive strength of 355.3 kPa, bending strength of 0.44 MPa, closed-cell ratio of 79.1%, water absorption of 9%, thermal conductivity of 0.031 W m⁻¹ K⁻¹, and LOI of 39.6%. Compared with unmodified MF rigid foams, toughing rigid closed-cell MF foams possess excellent pulverization rate, compressive strength, bending strength, cellular structure, thermal insulation, and flame retardancy.

Biopolyols were obtained from liquefaction of sugarcane bagasse and rice husk. Acid and hydroxyl numbers were determined for estimating the polyol value of the liquid products. These prepared biopolyols were mixed with the commercial polyol for the preparation of polyurethane foam (PU). To study the effects of biopolyol on properties of PU foam, various ratios of biopolyol to commercial polyol were used. It was observed that the density and foaming time of the PU foam increases with the increase in biopolyol content. The calculated Isocyanate index showed that sugarcane bagasse polyol can be used to make flexible foam and that rice husk can be used to make rigid foam. Foaming times and full rise times increased with increase in the biopolyol content. The Fourier-transform infrared spectroscopy (FTIR) spectra of prepared foams showed the characteristic peaks related to PU foam. The morphological studies were carried out using scanning electron microscopy (SEM). Thermal conductivity tests proved that the synthesized PU foams can be used as insulating materials. Further, PU foams were also prepared with the incorporation of carbon nanotubes (CNTs) in the polyol. The densities, thermal conductivities and SEM analysis of PU foams with and without carbon nanotubes were compared.

The aim of this work is the fabrication of electrically insulating composite rigid polyurethane foams with improved thermal conductivity. Therefore, this study is focused on the effect of aluminum nitride (AlN) on the thermal and electrical conductivities of rigid polyurethane foams. For this purpose, aluminum nitride/rigid polyurethane composite foams were prepared using a three-step procedure. The electrical and thermal conductivities of the foams were characterized. The thermal transitions, mechanical properties and morphology of the foams were also examined. The results reveal that AlN induces an increase of the thermal conductivity of rigid polyurethane foam of 24% which seems to be a relatively noticeable increase in polymeric foams. The low electrical conductivity of the foams is preserved.