Preparation and characterization of halloysite nanotubes filled palm kernel oil based polyurethane foam

Abstract

A demand for renewable polymer foams has led to the study o f rigid palm oil based polyurethane (PU) filled with halloysite nanotubes (HNTs). Studies on the effects o f hydroxyl:isocyanate (OH:NCO) ratio, amount o f distilled water and surfactant were conducted to obtain the optimum foam formulations. The bio-based rigid polyurethane (PU) nanocomposite foam was prepared by reacting palm kernel oil polyol (POP) with 4, 4-polydiphenylmethane diisocyanate (p-MDI) at 1:1 OH:NCO ratio via direct mixing method. HNTs were incorporated into the designated formulations at 1 to 5 wt% contents. The amount of silicone surfactant and distilled water as blowing agent were fixed at 4 parts per hundred polyol (pphp) and 2 pphp according to the formulations, respectively. The effect of HNTs on the density, surface morphology, mechanical strength and thermal properties o f foams were investigated. Fourier transform infrared spectroscopy spectra confirmed the formation of urethane linkage with the existence of 1714 cm-1, 1518 cm-1 and 1209 cm-1 peaks. All PU/HNTs nanocomposite foams exhibited an average 200 cell sizes of 139 mm, which was larger than the average 200 cell sizes of PU foam (i.e. 126 mm) without HNT. This finding also indicated that there was no extra nucleation process occurring during the cell growth as the average number o f cell per 0.7 mm2 (i.e. 312) was lower than that of PU foam without HNT (i.e. 326). The microimages captured by scanning electron microscopy supported the result. The addition o f HNT in PU foam produced a 14 % decrease in density and 27 % increase in the compressive strength at 4 % HNT loading. Meanwhile, the thermal degradation temperature of PU/HNTs foams increased with the increasing of HNT loading as shown by thermogravimetric analysis plots. At 80 wt% weight loss, T8 0 o f foam containing 5 wt% HNT (551 oC) exhibited 18 % increase compared to PU foam without HNT (466 oC). The presence of HNTs in PU cellular matrix did not significantly affect the flammability of the foams, as measured by limiting oxygen index (LOI) analysis. At the highest HNT loading i.e. 5 wt% the LOI increased about 5.5 % with respect to the PU foam without HNT. This finding suggests that the cellular matrix or foaming texture influences the formation o f the continuous protective layer on the burning surface of the foam. From the obtained results, palm oil based rigid PU nanocomposite foam shows strong potential to be used as thermal insulation materials.